Aimed at the problem that DC-DC converters with coreless transformers must operate at high frequen-cies, a DC-DC converter with a coreless transformer based on free decay oscillation is proposed. First, a circuit model in series-series topology with no excitation sources is established, the evolution of the eigenvalue is discussed, and the free decay oscillation behavior of the system is analyzed. Second, the DC-DC converter with a coreless transformer based on free decay oscillation is designed. The switching frequency of this converter can be significantly lower than the operating frequency of the coreless transformer, and the output power from the converter and the operating frequency of the core-less transformer can be described by the eigenvalue of the free decay oscillation system. Finally, an experimental proto-type was constructed, which was under constant duty control. The switching frequency of the converter was reduced to one half(103 kHz) and one third(69 kHz) of the operating frequency of the coreless transformer(206 kHz), respective-ly. The converter efficiency achieved 91.2%, and the transformer efficiency was always higher than 96%.
Based on the fact that inductance and capacitance are of fractional-order, the nonlinear dynamic characteristics of a fractional-order Boost converter are studied. The predictor-corrector model of the Boost converter is established using the predictor-corrector algorithm of fractional-order calculus. On this basis, the bifurcation diagrams with the reference current, input voltage and orders of capacitance and inductance as bifurcation parameters are obtained. The period doubling bifurcation and chaotic behaviors of the fractional-order Boost converter are studied, and its nonlinear dynamic behavior is compared with that of an integer-order Boost converter at the same time. Results show that under certain operating conditions, some nonlinear phenomena such as bifurcation and chaos will appear in the fractional-order Boost converter with changes in some circuit parameters. Under the condition of the same circuit parameters, the parameter stability domains of integer- and fractional-order converters are different. Compared with that of the integer-order converter, the parameter stability region of the fractional-order converter is smaller, which more truly reflects the nonlinear dynamic characteristics of the Boost converter.
In this paper, a Boost converter model in the pseudo-continuous conduction mode(PCCM) of inductive cur-rent based on the definition of R-L fractional-order is studied. On this basis, the state-space averaging model of the con-verter is derived. Then, the expressions for the step-up ratio, DC static operating point, inductive current ripple, and out-put voltage ripple are derived. Results show that compared with the corresponding expressions derived on the basis of the definition of Caputo fractional-order, the derived expressions for DC static operating point and step-up ratio under the definition of R-L fractional-order are related to both the duty cycle and the orders of the capacitor and inductor. The ex-pression for output voltage ripple is not only related to the order α of fractional-order inductor, but also related to the or-der β of fractional-order capacitor. Therefore, the orders of inductor and capacitor obviously affect the DC component of state variables and the stable-state characteristics of factional-order PCCM Boost converter. Finally, a mathematical mod-el and a circuit model of the R-L fractional-order PCCM Boost converter are built in MATLAB/SIMULINK, and simula-tion results show that the analysis result of the R-L fractional-order PCCM Boost converter model is more stable than that of the other PCCM Boost model, and the corresponding error is smaller.
Due to the duty cycle constraint on the traditional Boost converter, its applications to high-voltage-gain power supply are limited to certain degree. In this paper, a DC-DC converter with high voltage gain based on an isolated Boost converter and Cockcroft-Walton voltage multiplier cell(VMC) is studied, and its working principle and characteristics are analyzed. This converter achieves a conversion with an ultra-high step-up ratio by integrating the isolated Boost converter with the VMC. Compared with the traditional Boost converter, this topology has a high voltage gain in a low duty cycle, a low voltage stress of active switching device, and a simple control circuit with one single switch. Finally, a 35 W prototype with an efficiency of 89.5% was built to achieve a high step-up conversion from 24 V to 1 000 V, and the theoretical analysis results was verified by experimental results.
A soft-switching DC-DC converter with low current ripple and high gain is proposed, which can be applied to new energy generation systems. Based on the conventional interleaved Boost converter, the proposed converter can achieve high gain by introducing a coupled inductor, diodes and a capacitor Boost unit. The coupled inductor transmits energy during the entire switching cycle, thus improving the utilization rate of magnetic core. The input Boost stage works in an interleaved mode, and the current ripple of the two-phase inductor can cancel each other, so as to obtain a lower input current ripple. Due to the existence of leakage inductance of the coupled inductor, the reverse recovery problem of rectifier diodes are alleviated. Meanwhile, an active clamp circuit is adopted to absorb the leakage inductance energy, thereby achieving the zero-voltage soft-switching of all switches, restraining the turn-off voltage spike of switches, and improving the converter’s conversion efficiency. The working principle, circuit characteristics and soft-switching realization method of the converter are analyzed in detail. Finally, a 200 W experimental prototype was built to verify the theoretical analysis.
The two-switch Buck-Boost converter has been widely applied in step-up and step-down scenarios. However, it usually operates under hard switching conditions in the existing various control and modulation modes. In addition, its interleaved control circuit is usually complicated. A three-switch interleaved Buck-Boost circuit with co-directional coupling inductor and its control method are given based on the characteristics of co-directional coupling inductor. First, the coupling process of the coupling inductor during the switching process is analyzed under a large coupling coefficient, based on which the circuit’s fundamental operating principle is given in detail. Then, it is concluded that the extended duty cycle and soft switching of Boost-side power switches can be achieved in the discontinuous self-induction current mode, so as to avoid the synchronous and current-sharing circuits in the two-phase interleaved control circuit, thus obviously simplifying the control circuit. Finally, simulation and experimental results verified the analysis results.
Aimed at the poor voltage regulation performance and large circulating current of the traditional frequency-controlled LLC resonant converter in wide voltage applications, a six-switch dual-resonant LLC converter is designed, which is a hybrid combination of two full-bridge LLC resonant converters sharing one bridge arm. Compared with the traditional frequency control, fixed-frequency phase-shift control is employed in this converter to adjust the output voltage and reduce the switching frequency range. According to different connection modes of two transformers, the converter has two topological forms. When the two transformers are connected in series in the forward polarity, the converter’s gain range is 0-1, which can achieve an ultra-wide output voltage range. When the two transformers are connected in series in the reverse polarity, the gain range is 1-2, and the circulating current loss during the working process is small. Under the two topological forms, the ZVS turn-ON of the primary switch tube and ZCS turn-OFF of the secondary diodes can be achieved, respectively. Finally, the validity of the research in this paper was verified by Simulink simulations and experimental results.
Aimed at the problem of low efficiency of a dual active bridge(DAB) converter in the wide voltage range of single phase shift modulation strategy, a one-sided asymmetric duty modulation strategy is proposed in this paper, which significantly improves the efficiency of DAB converter, especially in the case of light load. First, the principle of one-sided asymmetric duty modulation scheme is described, and two operation modes are obtained according to the relationship of control degrees of freedom. Second, based on the time-domain analysis, the steady-state characteristics in the two operation modes are derived, including inductance current and transmission power. Third, in order to find the optimal combination of control degrees of freedom, the peak-to-peak value of inductance current is selected as the optimization objective, and the optimal one-sided asymmetric duty modulation strategy is obtained by applying the KKT condition. Finally, an experimental platform for DAB converter based on SiC device was built, and experimental results verified the effectiveness of the proposed one-sided asymmetric duty modulation strategy.
Multi-level converters are widely applied in DC microgrids because of their capability to reduce the voltage stress on switches and the volumes of filtering inductors and filtering capacitors. Since the flying-capacitance voltage and output voltage of a three-level Buck converter are coupled, the converter is a nonlinear system with strong coupling of multi-input and multi-output. To solve this problem, a decoupled backstepping sliding mode control method for inverse system is proposed in this paper. The inverse system method is used to decouple the output voltage control and flying-capacitance voltage control, and the backstepping sliding mode control method is used to ensure the stability and robustness of output voltage. The flying-capacitance voltage is balanced at 1/2 of the input voltage by the state feedback control. Simulation and experimental results show that the proposed control strategy can achieve satisfying steady-state and dynamic characteristics of flying-capacitance voltage and output voltage.
A design method for small- and medium-power DC/DC converters suitable for low-orbit commercial aerospace is given in this paper. A synchronous rectifier flyback topology and surface mounted devices are adopted, which can meet the demands for common single- and multi-output DC/DC converters applied in aerospace, with advantages of low cost, high performance, high reliability, and mass production. To further improve the conversion efficiency and power density, gallium nitride(GaN) FETs are also used. In addition, the losses of main power devices in the topology under different operating conditions are calculated and compared. Finally, a DC/DC converter with a wide range of input voltage(23-47 V) and output of 5 V and 30 W was built for verification.
Aimed at the problem of DC voltage fluctuations caused by load switching, power fluctuations and dou-ble-frequency injection in DC microgrids, a dynamic compensation control strategy for a Buck-type bidirectional DC-DC converter based on model predictive control(MPC) is proposed. First, the corresponding discrete state space matrix is es-tablished, and the input current is used as the disturbance. Second, the model-based inner-loop current predictive control and outer-loop voltage control of the Buck-type bidirectional DC-DC converter is designed. Third, a dynamic compensa-tion control structure based on a residual generator is designed for the current disturbance, and the dynamic compensa-tion controller Q(z) is solved. At the same time, the recursive least squares algorithm is used for parameter identification to reduce the influence of model uncertainty on the dynamic compensation control strategy. Finally, a comparative ex-periment was designed on the PSCAD/EMTDC simulation platform to verify the effectiveness of the proposed control strategy. Experimental results show that the compensation control structure can effectively solve the problem of DC bus voltage fluctuations and enhance the robustness of the entire system without changing the original predictive control.
Aimed at the low conversion efficiency and all the load power that needs to be processed by converters at different stages in the two-stage architecture of a DC transformer cascaded PWM converter, a quasi single-stage DC-DC conversion method with partial power active regulation based on a split-sigma structure is proposed. By splitting the output port of the DC transformer into two ports, the power of one port is directly transmitted to load without being pro-cessed by the back-stage PWM converter, thus realizing the quasi single-stage power conversion equivalently. In addi-tion, the power capacity and loss of the PWM converter are effectively reduced, and the system efficiency is improved. The principle and circuit implementation method for the split-sigma structure are analyzed in detail, and the principle and characteristics of system output voltage regulation are also studied. One of the circuits is taken as an example, and its working principle, voltage regulation characteristics and design method for key parameters are analyzed. Finally, experimental results verified the effectiveness and correctness of the proposed scheme.
The three-port converter studied in this paper includes three ports, i.e., power supply, energy storage and load, in which the load can directly obtain electric energy from the power supply or the energy storage port. First, a mathematical model of Euler-Lagrange form is established, a passivity-based controller is designed, and the simulation of passivity-based control(PBC) is carried out. The PBC strategy has advantages of strong global stability and strong robustness to system parameter deviation and external disturbance in the nonlinear system. Based on the PBC theory, the passivity of the three-port converter system is demonstrated. Through the PBC and single-phase-shift control of dual-active-bridge(DAB), the energy transfer between the three ports is realized. Finally, simulation results in Matlab/Simulink are given, which proves that the load in the device can directly obtain electric energy from the energy storage port and run safely, stably and reliably.
Aimed at the problems of complex topologies, high total standing voltage of switches, and unbalanced series capacitor voltages in the existing multilevel inverters, a novel seven-level inverter based on switched-capacitor is proposed. By adopting the phase disposition pulse width modulation strategy, three capacitors are reasonably controlled in series/parallel with the DC source, so that the seven-level output with a triple boost gain is realized. The proposed inverter uses only one single DC source, so it has advantages such as a simple structure, fewer components, high boost gain and self-balanced capacitor voltage. In addition, it does not use the H-bridge to change the polarities of output levels, thus reducing the total standing voltage of switching devices. The topology, working principle, capacitor voltage self-balance, modulation strategy, capacitor parameter and current stress are analyzed, and five aspects including the numbers of switches, diodes and capacitors, the total standing voltage and the boost gain are compared with those of the existing topologies, which fully proves the practicality of the proposed topology. Finally, the feasibility of this topology was verified by experimental results.
Aimed at the problems of current spikes and voltage fluctuations in the charging process of existing multi-level inverters, a novel quasi-resonant five-level inverter is proposed in this paper. A carrier-stacked pulse width modulation scheme is adopted, and the switched capacitor technology is combined with the traditional five-level inverter, which reduces the accumulated level at the previous stage and realizes the output of five-level voltage. In addition, the capacitor charging process and the series inductance resonate to eliminate current spikes and voltage fluctuations, while reducing the heating problem of the capacitor and prolonging the service life of the circuit. Finally, simulation verification is carried out, and results prove the correctness and feasibility of the scheme for the proposed inverter structure.
A single⁃phase transformerless inverter for photovoltaic power generation is proposed, which has a com⁃mon ground between its input and output and thus eliminates the common⁃mode current in the photovoltaic system. Meanwhile, its voltage gain is higher than that of the traditional single⁃phase quasi⁃Z⁃source inverter. In addition, the use of thin film capacitor makes the inverter more reliable and prolongs its service life. The working principle of this inverter is also analyzed in detail. Finally, a 140 W prototype was built, and results verified the correctness of the proposed in⁃verter topology and the effectiveness of the control strategy in islanding and grid⁃connected operation modes.
The advantages of a Boost-APFC circuit operating in critical conduction mode are introduced. Aimed at the disadvantages of the traditional single-phase CRM-Boost APFC voltage mode control method, such as a long PI parameter debugging time, a poor adjustment effect and increasing unstable factors, a single-phase CRM-Boost APFC voltage mode control method with a static operating point is proposed, and the advantages of this method are verified by PSIM simulations. Considering the shortcomings of the novel interleaved control method, such as a long PI parameter debugging time, increasing unstable factors and the need to use an additional voltage-controlled current source, an improved two-phase interleaved parallel CRM-Boost APFC voltage mode control method is put forward, and the PSIM simulations are completed, with a power factor as high as 99.96%. A 4 kW two-phase interleaved parallel CRM-Boost APFC experimental prototype was made, and it was experimentally debugged, with a power factor of 99.66% and an efficiency of 98.02%.
A virtual synchronous generator(VSG) can provide inertia and damping for the grid connection of new en-ergy by simulating the characteristics of a synchronous generator. However, a circuit breaking fault may occur in the process of high-frequency switching of power electronic switching devices, which will lead to a serious distortion of out-put current waveform and affect the safe and stable operation of power grid. In this paper, a VSG fault-tolerant model predictive control strategy based on neutral point voltage equalization is proposed to solve the fault problem of neutral point clamped(NPC) three-level VSG bridge arm. The operation mechanism of NPC three-level VSG single-phase bridge arm after fault is analyzed. The DC-side capacitor forms a virtual bridge arm after the switching device fault, which is reconstructed as a VSG bridge arm fault-tolerant structure. Under fault conditions, a current predictive model is estab-lished, and the space voltage vector in a fault state is reconstructed. The neutral point capacitor voltage on the DC-side is introduced into the cost function of fault-tolerant model to reduce capacitor voltage fluctuations and realize the fault-tolerant operation of VSG bridge arm. Experimental results show that the NPC three-level VSG can operate continuously after the switching device fault, which verifies the effectiveness of the proposed model predictive fault-tolerant control strategy and improves the operation reliability of VSG.
The large grid inductance in weak grid may cause a grid-connected converter to be unstable. Therefore, an impedance model of grid-connected converter is built at first, and the influence of grid inductance on the stability of grid-connected converter is analyzed according to the impedance ratio criterion. Then, aimed at the problem of low adaptability of the grid-connected converter to inductive grid impedance, a virtual impedance control strategy based on band-pass filter is proposed, and the influence of virtual resistance value on the adaptability of grid-connected converter to weak grid is studied. Furthermore, a selection principle for the virtual resistance value is also given. Finally, a system simulation model is built, and simulation results verify the correctness of theoretical analysis and the effectiveness of the proposed control strategy.
In a weak grid, due to the existence of grid impedance, the natural resonant frequency of a new energy grid-connected LCL filter will shift, and the traditional active damping control strategy cannot guarantee the system stability. Moreover, as the proportion of new energy power generation in the power system continues to grow, how to reduce the operating costs is a hot topic for research. Therefore, a novel control strategy based on grid-connected current and common coupling voltage feedback is proposed in this paper, which not only provides active damping to suppress LCL resonance, but also reduces the use of sensors. In addition, it has a strong adaptability under wide-ranging changes in grid impedance. Simulation and experimental results show that, compared with that under the traditional control strategy, the practical range of weak grid under the improved strategy increases, the system stability is enhanced, and the capability to suppress harmonics is raised, indicating that the quality of grid-connected current is well improved.
The influence of ash deposition on the output characteristics of photovoltaic(PV) modules and the deposition rule of pollution particles on the modules’ surface are studied, which are helpful for formulating an ash removal scheme and improving the efficiency of photoelectric conversion. The PV array on the roof of a fan hall in North China Electric Power University is taken as the research object, and an artificial ash distribution experiment was carried out to explore the influence of different ash deposition amounts on the output power, current and voltage of modules. To determine the influence of one single factor on the deposition of pollution particles, a numerical model of particle deposition is established using COMSOL under the same conditions as those in the natural deposition test of PV modules, and the influences of wind speed, humidity, particle size and pollution concentration on the deposition of pollution particles on the surface of PV modules are simulated and analyzed. Test results show that ash deposition has little influence on the working voltage, but a great influence on the output power and working current. When the ash deposition density is 5.07 g/m2, the changing rates of output power, current and voltage are 8.71%, 6.48% and 0.40%, respectively. Simulation results show that when other conditions are the same, the deposition amount of particles decreases first and then increases with the growing wind speed and particle size, and the minimum value is reached at the wind speed of 3 m/s and particle size of 15 μm. Under the same conditions, the particle deposition amount increases with the growing humidity and pollution concentration.
As power lithium-ion batteries play a key role in the electric vehicle industry, ensuring their working reliability has become a research hotspot at present. In this paper, the materials and manufacturing processes of lithium-ion batteries are reviewed. The battery state estimation and remaining useful life prediction methods are summarized in detail, and the advantages and disadvantages of these methods are discussed. From the perspective of battery management system, the relevant knowledges of equalization management system and thermal management system are sorted out in turn. From the perspective of electric vehicle hybrid energy storage system, the performance degradation mechanism under actual working conditions and the relevant technologies are elaborated upon. Finally, the status quo of key technologies related to the reliability of power lithium-ion batteries used in electric vehicles is summarized from four aspects, and the development possibilities in the future are forecasted.
To ensure the safety of new energy vehicles during the entire period of use, it is necessary to conduct health monitoring for the full life cycle of lithium-ion batteries. Aimed at the low learning rate due to the small capacity of training data set for the remaining useful life(RUL) prediction model based on neural network and the duplicate collinearity of the extreme learning machine(ELM) method, a method for augmenting the training data set is proposed. In addition, based on the improved ELM, an RUL prediction model for the full life cycle of lithium-ion battery is built. First, the early operation data of battery is extracted to formulate health factors, and the Akima interpolation method is used to augment the amount of training data. Then, the salp swarm algorithm is used to improve the ELM network, and the RUL prediction model for the full life cycle of lithium battery is established. Finally, the NASA battery data set is used to validate the model. Experimental results show that the proposed method for augmenting the training data capacity is effective, the capacity tracking capability of the RUL prediction model in full life cycle is strong, and the prediction error is small.
To effectively reduce the inconsistency of series lithium-ion batteries in use, a novel equalization topology with the combination of a Cuk equalizer and a double-layer selector switch is proposed, which can quickly realize the energy transfer between any single cells and improve the equalization speed. According to the characteristics of the open circuit voltage(OCV)-state-of-charge(SOC) curve, piecewise equalization is adopted with voltage and SOC as equalization variables, and a fuzzy logic control(FLC) algorithm is designed to dynamically adjust the equalization current to reduce the equalization time and energy loss. Matlab/Simulink software is used to build a model and conduct simulations. Experimental results show that the energy transfer topology proposed in this paper saves of the equalization time by 22.17% compared with the traditional topology of energy transfer between adjacent cells of Cuk circuit. In addition, compared with the mean difference algorithm, the FLC algorithm improves the time efficiency by more than 30% and the energy efficiency by about 11% under static and charge-discharge conditions. Therefore, the feasibility of the proposed equalization scheme is verified.
The state-of-charge(SOC) balance control of series-connected lithium batteries is of significance to the improvement of battery life. In this paper, a hybrid SOC equalization scheme based on active-passive equalization is proposed against the SOC discreteness of a lithium battery cell, in which the topology of the active equalizer is realized by a multi-winding flyback converter, and the passive equalizer consists of a resistor and a switch connected in parallel at both ends of the cell. The operating principle for the hybrid SOC equalizer is analyzed in detail, and the effect of SOC discreteness on equalization speed is discussed in terms of control strategy. The standard deviation representing the degree of discreteness and the coefficient representing the reasons of discreteness are introduced to realize the fast equalization of SOC under different discrete conditions. The topology of the proposed hybrid equalizer and the corresponding control scheme can optimize energy consumption and balancing speed, and experimental results verify the feasibility of theoretical analysis.
The hybrid energy storage system can effectively alleviate the frequency instability caused by the strong fluctuation and randomness of wind power output. In this paper, a hybrid energy storage system composed of batteries and super capacitors is taken as the research object, and a hybrid energy storage capacity allocation method is proposed. First, adaptive wavelet transform is adopted to perform a primary distribution of the wind power output, and the grid-connected power and energy storage power satisfying the requirements are obtained. Second, HHT transform is used to decompose the energy storage power, and a series of fluctuating power components and the instantaneous frequency of each component are obtained. Third, the cutoff frequency is determined according to the instantaneous frequency, the power components with a frequency higher than the cutoff frequency are allocated to super capacitors, and the rest are allocated to batteries. Finally, the rated capacity and rated power of the energy storage system are configured according to the energy storage power of batteries and super capacitors, respectively. Simulation results show that adaptive wavelet transform and HHT transform can effectively decompose the wind power output, thus realizing the stabilization of wind power output, as well as the capacity and power allocation of hybrid energy storage system.
Aimed at the voltage distortion and current distortion of power grid with pulse load, a three-level unified power quality conditioner(UPQC) with supercapacitor energy storage is designed. A method based on artificial neural network is proposed to control the series and shunt compensation units, and a method based on double closed-loop PI control is used to control the supercapacitor energy storage unit. The series compensation unit compensates voltage to maintain the stability of load voltage and ensure the power demand of load, while the shunt compensation unit compensates current to maintain the stability of supply current and avoid the continuous and large impact on power grid. The supercapacitor energy storage unit charges and discharges on the DC side to maintain a constant voltage on the DC side and ensure the normal operation on the series and shunt sides. The proposed method eliminates the complicated coordinate transformation process and avoids the phase lag caused by multiple filters. Simulation experiment results show that the proposed topology and control strategy are helpful for improving the power quality of power grid with pulse load.
The grid-connected operation of an energy storage system is realized by a converter. Due to the low switching frequency of the conventional converter, there exists time delay in sampling and calculation, which will lead to poor transient characteristics of the energy storage system and even instability of the whole power grid. In this paper, model predictive control(MPC) is used to achieve a fast power response of energy storage system and avoid the influence of time delay. A power weight value function is introduced to calculate the optimal output voltage of energy storage converter in the MPC control of active and reactive power. To solve the problem of inaccurate MPC model caused by the parameter deviation of filter inductor, inductance error compensation control is used to improve the model accuracy. Through Matlab/Simulink simulations and experimental results, it is verified that the proposed scheme can improve the transient characteristics of energy storage system and effectively eliminate the influence of error on the MPC control performance.
The converter with constant-power control in a flexible DC distribution system has characteristics of constant-power load, which will reduce the system damping and adversely affect the system stability. To address this problem, a superconducting magnetic energy storage(SMES) device is introduced to improve the system stability. A feedback control model of the flexible DC distribution system is derived, and the effect of constant-power load characteristics of the converter on system stability is investigated by frequency-domain analysis. Combined with a mathematical model and frequency-domain analysis, it is also pointed out that the SMES device can improve the system stability by introducing positive damping to grid and increasing the phase margin of the system’s open-loop transfer function at the shear frequency. To prevent over-high voltage at both ends of the superconducting magnet, the DC/DC converter which connects the SMES device with the DC distribution network needs to have certain voltage regulation performance. Therefore, the SMES device with a modular multilevel DC/DC converter(DC-MMC) is studied, which can adjust the number of sub-modules flexibly to set the voltage ratio of the converter. Moreover, the DC-MMC can control the voltage at both ends of the superconducting magnet while realizing a bidirectional flow of energy in the converter, thus protecting storage device. The feasibility and effectiveness of the SMES device with DC-MMC in improving the stability of flexible DC distribution system is verified by time-domain simulation waveforms.
A shutdown strategy for a low-cost hybrid DC converter based on diode rectifier is studied. The shutdown process of the auxiliary converter is divided into an energy feedback stage and an energy dissipation stage. At the energy feedback stage, part of the energy stored in the capacitors of sub-modules is fed back to grid through the DC transmission line under the active control. At the energy dissipation stage, the resonant capacitor and the capacitors of sub-modules are discharged in sequence through a discharging resistor. The calculation methods for the discharging current, capacitance voltage, and discharging time are derived, and the design method for the discharging resistor is also given. The capacitors of the auxiliary converter can be discharged quickly and efficiently under the proposed shutdown strategy without a high-voltage and large-capacity discharging resistor, which is conducive to the realization in engineering projects. Finally, a simulation model is constructed in Matlab/Simulink, and the validity of the shutdown strategy is verified by simulation results.
Aimed at the problem that the existing incentive pricing compensation mechanism cannot meet the differentiated needs of multiple types of load, a compensation method for interruptible load is proposed in the form of sectional compensatory price. Meanwhile, a two-dimensional alternating function of load transferable time and load transferable power is introduced to establish a transferable load compensation model to quantify the cost of load transfer. A model of multi-type demand response participating in the optimal operation of distribution network considering uncertainties in interruptible load is established. Aimed at the non-convex nonlinearity constraint of the model, it is transformed into a mixed integer second-order cone programming model by the second-order cone relaxation method, which is further solved by the CPLEX solver. In addition, the contribution degree and confidence degree are introduced to evaluate the user responsiveness. Simulation results show that the novel compensation mechanism can more reasonably guide users to adjust the power load, smooth the load curve, and improve the operating economy of distribution network.
In view of the high fluctuation and randomness of wind turbine output, which affects the safe and stable operation of power system as well as the accuracy of wind power prediction, a wind power prediction method based on the fluctuation characteristics of wind power is proposed. First, the fluctuation characteristics of wind power are analyzed in terms of time scale and unit scale, and the appropriate wind power data is selected for wind power prediction. Then, a wind turbine short-term power prediction model based on least squares-support vector machine(LS-SVM) is established. The adaptive variational mode decomposition(AVMD) is used to decompose the wind power data to achieve frequency division, and the improved particle swarm optimization(IPSO) is used to optimize the model parameters affecting the regression prediction in the LS-SVM model. Experimental results show that the prediction model has strong adaptability, and the effectiveness of the prediction method can be proved by prediction error evaluation indexes.
The optimal configuration of source-storage in micro energy grid(MEG) is a primary challenge at the early stage of its construction since there exist complicated energy flows. In addition, the uncertainties(especially the stochastic fluctuations of wind, solar, and multi-energy load power) in MEG are difficult to describe and overcome. To address these problems, the uncertainties of renewable energy and load demand are described as intervals, the minimization of annual converted investment cost is taken as the objective, and a linear AC power flow model is coupled. The constraints of cool/heat/electric power balance, node voltage static security, line capacity and heat pipe transmission power are taken into account, and the indeterministic constraints are transformed into deterministic ones based on the interval linear programming theory, thereby constructing an interval-based optimal planning model of MEG with the consideration of source-load uncertainties. The feasibility and superiority of this model are verified by case studies and analyses, indicating that the planning scheme can adapt to different uncertain scenarios and ensure the system’s stable operation.
The development of the flexible DC fault line selection technology plays an important role for DC distribution network. In this paper, a novel algorithm is proposed to solve the problem that there is less available fault information about the existing flexible DC fault, which makes full use of the advantages of ensemble empirical mode decomposition(EEMD), principal component analysis(PCA) and the correlation coefficient algorithm. First, the transient current sample signal is extracted, and the data matrix represented by the orthogonal basis function is obtained by EEMD. Then, the feature vector of the matrix element is transformed into the principal component based on PCA, and the sample signal is projected into the principal component space to realize coordinate transformation, so as to obtain the clustering and identification results of the sample data. Finally, fault line identification is performed based on the correlation coefficient. The EEMD of the proposed algorithm reveals the internal variation law of the original historical data, while PCA can effectively select the effective fault features. A large number of experiments show that the novel algorithm is accurate and effective. Compared with other existing methods, it has advantages in the cases of unclear fault information and different transition resistances.
Compared with 4G communication, 5G communication uses key technologies such as large-scale anten-nas, ultra-dense networking, and high-frequency communication to greatly improve its performance, resulting in increased power consumption of single 5G base stations and multiple sites. As a result, the power supply requirements are also changed. At present, there are two kinds of power supply forms which can meet the new power supply requirements, i.e., near supply and HVDC remote supply. Aimed at the HVDC remote supply, the power supply architecture and key tech-nology are sorted out, and a feasible operation mode is proposed by comprehensively considering the operating invest-ment cost in the economic mode of peak-shaving and valley-filling, the busy and idle periods of 5G base station service load, and the peak-valley time-of-use electricity price. On the basis of the construction which has already been invested under the HVDC remote supply scheme, the investment cost is small, and the economic benefit is obtained by using the time-of-use electricity price difference between peak and valley periods, thus reducing the power consumption cost of base stations to a certain degree. Finally, the development of 5G base station power supply is forecasted, providing refer-ence for the research or design of its power supply.
As a commonly used islanding detection method, the active detection method can reduce the non-detection zone by increasing the disturbance intensity, but it will also increase the degree of harmonic pollution to the grid at the same time. Aimed at this problem, a hybrid fuzzy low-harmonic islanding detection method without non-detection zone is proposed in this paper. First, the non-detection zone is judged, and the passive islanding detection method which has no harmonic pollution to the grid is used preferentially. If this zone is within the non-detection zone of the passive detection method, then a fuzzy low-harmonic islanding detection method with fuzzy disturbance control is used to disturb the output current in its second and fourth quarter periods. Finally, the corresponding simulation model is built to verify the effectiveness of the proposed method.
Aimed at the problem that the power quality control equipment in distribution network is lack of collaborative allocation, an optimal allocation strategy for the control equipment of harmonics, reactive power and three-phase imbalance is proposed, which is based on the multi-objective particle swarm optimization(MOPSO) algorithm. The active power filter(APF) is used to suppress harmonics, the intelligent capacitor is used to compensate reactive power, and the phase-change switch is used to reduce three-phase imbalance. The control effect and operating cost about each power quality issue are taken as optimization objects, and the relevant power quality standards are considered as constraints. Through the MOPSO algorithm, an optimal allocation scheme for the allocation nodes and relevant access capacity of control equipment can be obtained. Furthermore, a power quality assessment model is built, and a simulation model based on an improved IEEE 18-node distribution system is also constructed. The harmonics, reactive power and three-phase imbalance loads are separately connected to simulate power quality issues, and simulation results verify the feasibility of the proposed strategy and its advantages compared with the traditional scheme for power quality control equipment.
Monitoring the power quality of power supply system is an effective method for ensuring the safe operation of power system and user-side equipment. To ensure the power quality of power supply system, a monitoring method for its power quality stability is studied. Based on the Hilbert-Huang transform(HHT) algorithm, the harmonic frequency and amplitude of the power quality signal frame of power supply system are monitored, and the disturbance time amplitude and frequency of the power quality disturbance signal are detected, so as to realize the power quality stability of monitoring system. The frame loss rate, accuracy and transmission delay of the monitored power quality signals under different pressures(with different numbers of power quality signal frames) were tested by experiments, and results show that the proposed method can realize the monitoring of power quality.
Aimed at problems such as the setup of an additional excitation source required by active magnetic shielding and the expensive magnetic shielding materials used in passive magnetic shielding, a wireless power transmission(WPT) coupling mechanism with magnetic shielding based on Halbach effect is proposed on the basis of the traditional DD coil structure. First, the topology of WPT coupling mechanism with magnetic shielding effect is proposed, and the principle for the magnetic shielding effect is analyzed theoretically based on the corresponding equivalent magnetic circuit model. Second, the expression for the magnetic field intensity of the coupling mechanism on any plane in the space is derived using the micro-element method. Finally, an experimental platform was built to verify the WPT performance and magnetic shielding effect of the proposed coupling mechanism. Results show that the Halbach effect coil can effectively weaken the magnetic field intensity outside the coupling mechanism and improve the magnetic shielding effect while ensuring that the power transmission efficiency is basically the same as that of the DD coil.
To improve the degree of intelligence of a substation and cut down the cost of inspection, substation inspection robots instead of the human labor are employed to perform daily inspections. However, the battery life greatly limits the work of inspection robots, so the full-time inspection cannot be realized. To solve this problem, a dynamic wireless charging method is used to charge the robots, so that the robots can perform inspections while charging and realize full-time inspection. In this paper, the relationship between coil mutual inductance and system efficiency is analyzed at first. Then, aimed at the segmented primary coil rails used in the dynamic wireless charging system, a soft-switching method for rails is put forward to reduce the inrush current during the switching process, thus protecting the circuit components. Finally, the influence of coil mutual inductance on the system efficiency was verified by experimental results, and the feasibility and effectiveness of the soft-switching method for rails was also proved.
For a traditional Boost power factor correction(PFC) converter, its output voltage must be greater than its input voltage, which limits its applications in light emitting diode(LED) drivers to a certain degree. Meanwhile, due to the existence of a rectifier bridge at the input end of the traditional LED driver, the improvement of its efficiency is also confined. In this paper, a bridgeless Boost LED driver based on passive current balancing is proposed, which is based on the topology of a resonant Boost PFC converter. With the introduction of a resonant capacitive current-balancing network, the output current of each LED string can be balanced. In addition, the elimination of the rectifier bridge further improves the system efficiency. Finally, a 140 W prototype with a peak efficiency of 93.64% was built, and experimental results verified the correctness and feasibility of theoretical analysis.
A flux-weakening control method for permanent magnet synchronous motor(PMSM) used in electric vehicles is put forward on the basis of current prediction to improve the dynamic performance in the flux-weakening region of PMSM. The voltage boundary problem in the flux-weakening region is analyzed in detail, and the stability problem under different voltage selection criteria is also introduced. On this basis, a dynamic overmodulation strategy considering the stability and dynamic characteristics is proposed. Furthermore, a model-based predictive current control algorithm is investigated, in which the advantages of fast dynamic response and manageable constraints help to improve the dynamic performance in the flux-weakening region while guaranteeing the stability. Finally, the effectiveness of the proposed algorithm was verified on a simulation platform and an experimental platform, respectively.
The silicon carbide(SiC) device is considered as a semiconductor device with high temperature resistance, and a careful study on its loss and heat dissipation is required when it is applied to high-power-density and high-tem-perature scenarios. The maximum current conduction capability of SiC MOSFET power module at high temperature is stud-ied, and the relationship between electrical performance and heat dissipation is taken into account. Based on an electro-thermal coupling model of SiC MOSFET device and a heat dissipation model of the cooling system, the mechanism of thermal runaway process is analyzed. A co-simulation is conducted to determine the current conduction capability of one SiC power module at high temperature, and the simulation error with respect to the experimental result is about 4%, which verifies the effectiveness of the proposed method.
Building a complete spacecraft electrical power and distribution standard system is an important tool for improving the design of spacecraft electrical power and distribution system and ensuring the safety and reliability of satellite energy. In this paper, the electrical power and distribution standard systems published by European Cooperation for Space Standardization(ECSS), National Aeronautics and Space Administration(NASA), Japan Aerospace Exploration Agency(JAXA), International Standard Organization(ISO) and American Institute of Aeronautics and Astronautics(AIAA) were investigated. The focuses of their respective standard specialties were analyzed, the corresponding content was discussed, and the standard systems of various organizations were summarized. Combined with the actual situation in China, the suggestion and reference for the spacecraft electrical power and distribution standard system are put forward.
Aimed at the problem that the performance of dielectric barrier discharge(DBD) load cannot be fully utilized by the common load resonant-type power supply with continuous waveform and the deficiency that the topologies of existing pulsed power supplies are complicated, a power supply with unipolar forward pulse is proposed in this paper, which consists of one power switch, two diodes and one coupled inductor. Through the analysis of its working modes, it is shown that this power supply can provide a fast-rising pulse voltage for DBD load. In addition, the power switch operates in a soft-switching state. Simulation and experimental results verified the feasibility of the proposed power supply, indicating that it can provide certain reference for the upgrade of the existing power supplies for DBD load.
In response to the high-voltage steep pulse application demands such as those in the biomedical industry, a series and parallel high-voltage steep pulse generator circuit based on solid-state switches is designed, and a novel pulse steepening method is proposed by combining the timing control technology. The key to pulse steepening, the system’s working process and the main points of design are analyzed theoretically. This method can better reduce the influences of stray parameters, wiring inductance and wire inductance on the switching speed after adding the switching tubes. An experiment was carried out with a 2 kV high-voltage DC power supply and a load resistance of 110 Ω, and experimental results show that the rising edge of load pulse signal was 50 ns approximately, the falling edge was 70 ns approximately, and the output current amplitude was 18 A approximately. The half-height width of the minimum pulse width signal was 100 ns, and the system’s minimum resolution was 5 ns, which can realize a flexible adjustment of 5 ns pulse width step by step. The maximum pulse width was related to the energy storage capacitor.
The existing power amplifier cannot strike a balance among aspects such as its output efficiency, output power and linearity. To solve this problem, on the basis of a three-level cascade amplification method, a kind of AB class RF power amplifier based on a power synthesizer and a power splitter is proposed. Aimed at the problems of linearity and gain, the band-pass matching and T-network matching techniques are used to optimize the design of the pre-driver circuit. The problem that the output power of the final amplifier is too large is solved by using the power synthesis technique, and the stability and efficiency of the power amplifier are guaranteed. To prevent the temperature of the power amplifier from being too high, the thermal characteristics of the power amplifier cavity are analyzed. The highest temperature is 81℃, which can make the power amplifier get a good cooling. At room temperature, the RF power amplifier has an output power of 47 dBm, an amplification gain of 42 dB and a maximum power added efficiency of more than 45% at a central frequency point of 2.45 GHz. The test results were close to simulation results, indicating that the research in this paper can provide some guidance for the subsequent research and design of amplifiers.
Silicon carbide(SiC) switching devices are widely applied in DC/DC converters owing to their faster switch-ing speed and higher operating frequency. However, the high working frequency of SiC devices will result in strong elec-tromagnetic radiation interference. To optimize the internal structure of DC/DC converter and achieve a higher power density, an optimization method for the electromagnetic radiation interference of SiC DC/DC converter is proposed. First, the characteristics of the converter’s electromagnetic radiation interference source are analyzed, and a space electromag-netic radiation model is established according to the topology of DC/DC circuit. Then, based on the electromagnetic radi-ation model and simulated annealing algorithm, the low electromagnetic radiation optimization is carried out for the layout of components within the DC/DC converter. The optimized layout scheme reduces the length of high-frequency wire by 60.2%. Finally, the three-dimensional finite element simulation is carried out, and it is verified that the proposed method can optimize the circuit layout of SiC DC/DC converter and reduce the electric field intensity produced on the sensitive circuit by two orders of magnitude.
The fast on-off switching signal is the main cause of electromagnetic interference(EMI). At present, the research on EMI suppression by chaos mainly focuses on the suppression of conducted EMI by integer-order chaos. On this basis, the suppression by fractional-order chaos on radiated EMI and the selection of optimal order are studied in this paper. First, through the analysis of spectrum characteristics of fractional-order Lorenz and Lyapunov exponent spectrum, 1.8-order Lorenz signal is selected as the best spread spectrum series. Second, based on the principle of EMI suppression technology with variable switching frequency, Lorenz chaotic spread spectrum PWM signals with fixed frequency, integer-order, 2.7-order and 1.8-order are implemented in an STM32 single chip microcomputer. A near-field radiation experiment was carried out on a 5 W flyback converter, which proved that the 1.8-order Lorenz signal had the strongest suppression effect on the near-field magnetic field radiation. Finally, experimental results showed that the prototype’s overall efficiency was about 2% different when it was under the fractional-order Lorenz Chaos PWM control and constant-frequency PWM control, respectively, which verified the superiority of the fractional-order chaotic PWM in radiated EMI suppression performance.
The magnetic leakage from an indoor air-core reactor leads to problems such as serious nearby electromagnetic pollution and heat generation by metal equipment. To solve these problems, based on the ANSYS finite element simulation platform, the indoor air-core reactor and its surrounding ancillary facilities and building structure of a 500 kV substation are modeled in three dimensions, and the building roof is equipped with a shielding plate. Through the optimization analysis of shielding materials, thickness and gap width, a scheme is formulated to improve the electromagnetic environment surrounding the indoor reactor. Simulation results show that the magnetic induction intensity of the steel structure can be effectively reduced by adding a shielding plate which is overlapped by 3 mm thick aluminum plates above the steel beam. The temperature change of the reactor during its operation meets the insulation heat resistance requirement for the air-core reactor. The edge section temperature of the shielding device is higher, with a peak of 53.26 ℃. The average temperature of surrounding buildings and facilities increases by about 5-10 ℃, which meets the requirements of safe operation.
Sponsored by: China Power Supply Society Edited by: Editorial Department of JOURNAL OF POWER SUPPLY Distribution in China: Local Post Offices or Online subscription Editor-in-Chief: Jiaxin Han Acting Editor-in-Chief: Xinbo Ruan Co-Editor-in-Chief: Xiong Du and Wu Chen Editorial Manager: Guozhen Chen CN: 12-1420/TM ISSN: 2095-2805 Postal Code in China: 6-273 International Postal Code: BM8665