Transactions of China Electrotechnical Society 2024 No. 8 Item and Abstract

Transactions of China Electrotechnical Society is a comprehensive academic journal in the field of electrical engineering sponsored by the China Electrotechnical Society, reporting international and domestic leading academic and scientific research achievements in basic theoretical research and engineering application. Ma Weiming, academician of the Chinese Academy of Engineering, is the director of the editorial board of the Journal and the editor-in-chief of the journal.

"Research on Microgrid Stability Analysis and Optimal Control".

Message from the special editor-in-chief

Contributing Editor-in-Chief: Prof. Bo Zhang and Prof. Hong Li

Sub/hypersynchronous oscillation analysis of grid-connected converter in low inertia AC system

Authors: Hu Guang, Zhuang Kehao, Gao Huisheng, Xin Huanhai, Wang Haijiao, etc

Abstract:The grid-based converter in the low-inertia power system may interact with the rotor dynamics of the synchronous machine, which introduces new problems to the system stability analysis, and it is no longer accurate to measure the strength of the AC system only by the dynamics and short-circuit ratio of the grid-based equipment. Therefore, this paper comprehensively analyzes the influence of system inertia and short-circuit ratio on the synchronous stability of grid-connected converters with small interference, and proposes a method suitable for analyzing the stability of grid-connected converters in low-inertia systems.

Firstly, the closed-loop model of the hybrid system of converter and synchronous machine is derived, and the interaction coefficient matrix that can characterize the low inertia dynamics is extracted, and the interaction relationship between the two types of equipment is qualitatively analyzed. Secondly, based on the modal perturbation theory, the original multi-machine system is decoupled into a subsystem with equivalent stability. Then, a phase-dominant loop suitable for analyzing the synchronous stability problem of small interference is selected, and a stability analysis method considering inertia and short-circuit ratio is proposed according to the loop. Finally, based on simulation examples, the effectiveness of the proposed synchronous stability analysis method for grid-connected converters with small interference in low inertia systems is verified.

Improved Gershgorin circle stability criterion and multi-dimensional resonance characteristic analysis of heterogeneous inverter parallel system

Authors: Lin Hongbin, Ge Pingjuan, Xu Hailiang, Wu Han, Zhang Weijie

Abstract:The new power system with new energy as the main body is gradually showing the characteristics of heterogeneous inverter parallel system, that is, it is presented in the form of coexistence of two types of inverters: grid-based and grid-constructed. In order to comprehensively and accurately analyze the stability of the heterogeneous inverter parallel system, and fully consider the interaction between inverters and between inverters and power grids, a multi-inverter interaction admittance matrix model is established.

At the same time, a multi-machine stability criterion based on Gershgorin's circle theorem is proposed, and the analysis process is simplified by introducing the distance vector function. Then, based on the improved stability criterion, a parameter sensitivity calculation method was proposed, and the influence of key factors on the stability of heterogeneous systems was quantitatively analyzed. Finally, the validity of the theoretical analysis and the effectiveness of the stability criterion are verified by time-domain simulation examples and experiments.

Stability Detection of DC Microgrid System with Passive Damping Based on Machine Learning

Authors: Liu Xiao, Yang Jian, Li Li, Dong Mi, Song Dongran

Abstract:The constant power load (CPL) in DC microgrid has a negative damping characteristic, which will reduce the stability of the system. To this end, the stability of the DC microgrid system is enhanced by adding passive damping to the filter, and a machine learning-based method is proposed to detect the stability of the DC microgrid system with passive damping.

Firstly, a small signal model of the DC microgrid system with passive damping is established to determine the parameters affecting the stability of the system. Secondly, the simulation scenario was established with the selected system parameters as variables to obtain the dataset for machine learning algorithm training. Thirdly, a stability detection model of DC microgrid based on Lightweight Gradient Elevator (LGBM) was proposed, and the influence of selected parameters on the LGBM prediction results and the stability of DC microgrid system was analyzed by Shapliga Interpretation Method (SHAP). Finally, simulations and hardware-in-the-loop experiments are used to verify the effectiveness and superiority of the proposed method.

Research on AC and DC microgrid oscillation problem based on frequency domain impedance network modeling and analysis

Authors: Wu Xiangyu, Zhang Xiaohong, Shang Zixuan, Zhao Yigang, Wu Xiaoyu

Abstract:AC and DC microgrids are prone to cause broadband oscillation in the system under the action of different bandwidth control links of different types of power electronic converters. The existing microgrid oscillation analysis is mainly based on impedance analysis and characteristic analysis, but these two methods have certain limitations. To solve this problem, the modeling and analysis method of AC and DC microgrid oscillation based on frequency domain impedance network model is studied.

Firstly, the equivalent impedance network model of AC/DC microgrid in the frequency domain is established, and the admittance matrix of node frequency domain and loop frequency domain impedance matrix are calculated. Secondly, based on the frequency domain mode analysis method, the node/loop oscillation participation degree index and the sensitivity index of equipment and control parameters of AC/DC microgrid are established, and the analysis method of AC/DC propagation characteristics of oscillation is given, which is convenient to clarify the oscillation mechanism and key influencing factors of the system. Finally, the effectiveness of the above frequency-domain impedance network modeling and oscillation stability analysis methods is verified by Matlab/Simulink time-domain simulation and case analysis.

Power hierarchical coordination control strategy of AC/DC hybrid microgrid based on hybrid energy storage

Authors: Wang Li, Hu Jiacheng, Zeng Xiangjun, Zhao Bin, Zhang Zhiguo

Abstract:In order to solve the problem that the power coordination between the grids cannot effectively alleviate the system frequency and voltage fluctuations by interconnected converters alone, and it is difficult to apply the power demand of multiple scenarios for single battery energy storage, a power coordination control strategy of AC/DC hybrid microgrid using supercapacitors and battery hybrid energy storage is proposed. The hybrid energy storage is connected to the DC bus as an energy storage subnet, and the supercapacitor is preferentially used to smooth out the power fluctuation in the AC and DC subgrids, and an improved hybrid energy storage control strategy is proposed to divide five working modes according to the state of charge of the energy storage.

Taking into account the fast response characteristics of supercapacitors and the reduction of frequent start-up of interconnected converters, a two-level hierarchical coordinated control strategy of power autonomy and power mutual assistance is proposed according to the fluctuation degree of DC subgrid voltage and AC subnetwork frequency. By designing the inter-grid power mutual aid scenarios of hybrid energy storage in different working modes, the simulation proves that the proposed coordinated control strategy of hybrid energy storage and interconnected converter can stabilize the load power fluctuation of each subgrid.

Instability analysis and stability control of grid-connected inverter based on circuit equivalence

Authors: Gao Lei, Lv Jing, Ma Junchao, Liu Jianing, Cai Xu

Abstract:The new energy power generation system with grid-connected inverter as the power interface is prone to oscillation instability under the condition of weak power grid. In this paper, the control loop of the grid-connected inverter is visualized as the virtual impedance composed of circuit elements, and the mechanism of the oscillation instability of the grid-connected inverter caused by the interaction between the current inner loop and the phase-locked loop under the condition of weak power grid is analyzed based on the circuit model.

The results show that the impedance-high-pass filter active damping control strategy has a better stability improvement ability to solve the oscillation instability problem caused by the introduction of negative resistance into the phase-locked loop. Finally, the oscillation suppression effect of different active damping control strategies is compared by PSCAD/EMTDC simulation and hardware-in-the-loop experiments of Yuanwide StarSim controller, and the dynamic performance of impedance-high-pass filter active damping control is verified. The results show that the designed stability control can effectively suppress the system oscillation within 200 ms, and can achieve stable operation under the condition of extremely weak power grid with a short-circuit ratio of 1.

Carbon Emission Determination Operation Domain of Microgrid: Theory, Construction and Observation

Authors: Zhang Jiyue, Ren Zhouyang, Jiang Yunpeng, Feng Jianbing, Sun Yan

Abstract:It is an important development direction to realize the green and low-carbon transformation of the energy system by building a low-carbon microgrid with a high proportion of renewable energy as the main body and fully tapping the low-carbon regulation and control potential of the microgrid. In order to clarify the low-carbon operation space of microgrids under the carbon emission target, this paper proposes the theory and characterization method of microgrid Defined Carbon Emission Operation Domain (CCEOR) considering the low-carbon regulation characteristics of microgrids, and intuitively quantifies the low-carbon regulation and control capabilities of microgrids based on the geometric characteristics under CCEOR projection observation, which provides an effective tool for the dispatching center to monitor and perceive the operation status of microgrids. In order to ensure that CCEOR has observable theoretical conditions.

Firstly, starting from the concept of CCEOR, a CCEOR transformation model considering second-order cone relaxation is established for the non-convex properties, and the mathematical properties of the CCEOR boundary are revealed. Furthermore, according to the complex characteristics of CCEOR's high-dimensional coupling, the CCEOR dimensionality reduction observation model is constructed based on the carbon emission flow theory, and the low-carbon operation space of the microgrid is projected to the load space of key nodes. Then, a geometric characteristic index that can describe the low-carbon operation capacity and variable coupling relationship of the microgrid is established to realize the quantitative evaluation of the low-carbon regulation potential of the microgrid.

Finally, combined with typical microgrid examples, the observation and evaluation of CCEOR dimensionality reduction are carried out, and the effectiveness of the proposed model and method is verified. Based on the visual analysis, the potential applications of CCEOR in guiding the optimization of low-carbon resources in microgrid collaborative distribution network and electricity carbon market trading are deeply explored.

A DC fault ranging method based on active injection of solid-state circuit breaker

Authors: Wang Wei, Shuai Zhikang, Li Yang, He Lili, Fang Chenchen

Abstract:With the rapid development and deepening application of DC distribution network, accurate and reliable fault location technology is very important for DC fault repair and recovery. In this paper, a DC fault ranging method based on Solid State Circuit Breaker (SSCB) active injection is proposed. Firstly, SSCB interrupting is used to actively inject signals with different pulse widths, and the time difference between the first end of the injected pulse and the first end of the reflected wave is detected as the propagation time interval of the injected waveform, which can reduce the error caused by the sampling frequency. Then, the linear modulus of the cable line voltage is extracted as the detection quantity, and the coupling effect between the positive and negative lines is weakened to obtain a stable wave velocity. Finally, based on the wavelet transform principle, an improved adaptive mode maximum method is proposed to detect the first and last moments of the pulse, and reduce the influence of noise and transition resistance on the ranging accuracy. The simulation results show that the SSCB active injection ranging method can achieve accurate and fast positioning in the case of single-pole grounding and inter-pole short-circuit faults in the DC distribution network.

Electrotechnical theory

Design and optimization of multi-array Lamb wave electromagnetic ultrasonic transducer for steel plate based on Barker code pulse compression technology

Authors: Shi Wenze, Li Qixin, Lu Chao, Hu Bo, Liu Yuan

Abstract:In order to solve the problems of the traditional Marker code pulse compression technology due to the limitation of the rated parameters (duty cycle, maximum pulse width, etc.) of the pulse power amplifier, a multi-array element Lamb wave electromagnetic ultrasonic transducer (EMAT) based on Barker code pulse compression technology is proposed. The finite element model of the multi-array Lamb wave EMAT detection process based on tone-burst signal excitation-Walker code pulse compression technology was established, and the effects of the configuration of the permanent magnet, the length of the array element sequence, the number of excitation signal periods, and the number of zigzag coil turns on the main sidelobe ratio and the width of the main lobe after pulse compression were analyzed, and the experimental verification was carried out.

The results show that the signal-to-noise ratio (SNR) of the multi-array EMAT with 4 turns and 13 bits of Barker sequence length can be increased by 9.8 dB after configuring 3 external permanent magnets. Considering the spatial resolution and SNR of the detection echo, the optimal parameters of the multi-array Lamb wave EMAT are as follows: the number of turns of the zigzag coil is 10, the number of excitation signal periods is 11, the Barker sequence is 13 bits, and 3 external permanent magnets are configured.

Anti-offset method of LCC-S compensated inductive energy transmission system based on clamping circuit

Authors: Zhang Binshan, Zhang Zeheng, Yang Bin, Mai Ruikun, Chen Yang

Abstract:In the induction power transfer (IPT) system, coil misalignment is unavoidable, and the resulting coupling change will lead to the instability of the transmission power of the system. In order to ensure the power supply flexibility of the IPT system, the system needs to be able to tolerate a wide range of coil deviations. Therefore, drawing on the idea of modal switching, an LCC-S compensated IPT system based on clamping circuit is proposed to enhance the system anti-offset. Compared with the traditional multi-modal switching IPT system, the clamping circuit in this system can adaptively turn on or off according to the coupling change to adjust the operating mode, so as to achieve a nearly constant power output, and this method does not require auxiliary means such as coupling identification, output detection and feedback communication.

In this paper, the power transmission characteristics of different operating modes of the system are deduced and analyzed, and a set of parametric design methods are provided based on the constraints related to the system design. Finally, a set of 500 W experimental equipment was designed and built to verify the correctness and feasibility of the theoretical analysis. The experimental results show that the output power of the proposed method is stable between 470~505W and the efficiency is 83.29%~90.21% when the coupling degree is 0.205~0.42.

Motors and their systems

Electromagnetic transient equivalent modeling method for permanent magnet synchronous generator for offshore wind power simulation

Authors: Liu Yifan, Zou Ming, Wang Yan, Feng Moke, Xu Jianzhong, etc

Abstract:Modeling and simulation of offshore wind power is a key supporting technology for the construction of a new power system with new energy as the main body. As the core component of the direct drive or semi-direct drive model, the existing model of permanent magnet synchronous generator (PMSG) has certain limitations: the gray box model provided by commercial software cannot know the modeling principle, and the degree of openness is not enough, which restricts the application of efficient electromagnetic transient modeling algorithm and parallel acceleration algorithm for wind turbines; the commonly used PMSG modeling method cannot generate an interface to connect with the external circuit; PMSG is a kind of synchronous generator, and the synchronous generator has a mathematical model of different orders, and the existing model is inconvenient to change.

In order to solve the above problems, an order-selectable equivalent modeling method for PMSG electromagnetic transients is proposed. Firstly, the generator voltage and flux equations are discretized, then the PMSG model is reconstructed by eliminating the algebraic loop by single-step delay, the Norton equivalent circuit is derived, and the overall simulation framework of the model is constructed. The results show that the fourth-order and second-order models have applicability in station-level simulation, while the sixth-order model realizes the multi-condition height fitting of the benchmark model, with an average relative error of less than 4%, which can meet the simulation requirements of both the station level and the unit.

Permanent magnet servo system speed tracking control and data-driven parameter design method

Authors: Lian Chuanqiang, Guo Liyuan, Xu Guanda, Xiao Fei, Zhang Weiwei

Abstract:In the permanent magnet servo control system, the traditional speed control strategy has the problems of amplitude and phase deviation in the low frequency band, which reduces the accuracy of speed tracking control. In order to solve this problem, a high-precision speed tracking control strategy and data-driven parameter design method are proposed. The main idea is to connect a hysteresis-lead compensator in series in the speed control link to correct the amplitude and phase of the low frequency band, and to minimize the amplitude and phase error of the compensation in the low frequency band as the optimization goal, and at the same time constrain the maximum amplitude gain and phase shift of the compensator in the full frequency range, a data-driven compensator parameter optimization method is designed, and the performance of the compensation control system is analyzed and evaluated.

The experimental results show that the speed tracking error of the compensator designed based on the experimental data is less than 2 r/min in the low-band interval where the speed command frequency is less than 1 rad/s, which is significantly improved compared with the traditional method.

An IPMSM model prediction current control method based on a novel virtual vector modulation method

Authors: Wang Yizhe, Huang Sheng, Liao Wu, Zhang Ji, Huang Shoudao

Abstract:The model predictive control method has been widely used in the control of built-in permanent magnet synchronous motor (IPMSM), and the traditional model predictive control method will produce large current and torque harmonics during the operation of the motor due to the limited number of candidate voltage vectors. In order to increase the number of candidate voltage vectors, a method for constructing virtual voltage vectors is proposed. However, when the virtual vector modulation method is applied, the computational burden of the system will increase with the increase of the number of virtual vectors, so the control effect will be limited by the computational power of the system.

In order to solve this problem, a new virtual voltage vector modulation method is proposed, in which the voltage sector is subdivided to increase the number of virtual voltage vectors, then the angles are obtained by standardizing the command voltage vector coordinates, and finally the optimal voltage vectors are selected from the angle search between the basic and virtual voltage vectors. In this method, the computational size of the system is independent of the number of virtual voltage vectors, so the control performance of the system can be improved without increasing the computational burden of the system.

Experimental results show that compared with the virtual vector predictive control method with limited number of virtual vectors, the proposed method effectively reduces the harmonic content of three-phase current and reduces the execution time of the control algorithm.

Second-order terminal sliding mode current control of permanent magnet synchronous motor with low jitter and high noise immunity based on enhanced extended state observer

Authors: Higashino Yalan, Yang Shuying, Wang Qishuai, Xie Zhen, Zhang Xing

Abstract:The current sliding mode control of permanent magnet synchronous motor has good parameter robustness, but the control accuracy is affected by the sliding mode jitter, and there is a contradiction between the jitter suppression and the noise immunity. Therefore, a second-order terminal sliding mode current control scheme based on an enhanced extended state observer is proposed, which can effectively improve the current control performance.

Through the design of the second-order terminal sliding mode controller, the first-order integral fast terminal sliding mode is nested in the second-order non-singular terminal sliding mode surface, so that the sliding mode jitter is well suppressed, and the rapid convergence of the current without steady-state error is realized. By introducing the lumped estimation and compensation of the disturbance signal by the extended state observer, the contradiction between jitter and noise immunity is alleviated, and the current accuracy is further improved. Aiming at the delay effect of digital control, a Smith estimator was designed to improve the accuracy of disturbance compensation. Finally, the current control scheme designed in this paper is verified by experiments, and the effectiveness of the scheme is demonstrated by comparison.

A thrust fluctuation suppression strategy for PMLSM based on a proportional resonant internal mode expansion state observer

Authors: Zhang Guoqiang, Zhao Xinru, Zhang Heng, Wang Gaolin, Xu Dianguo

Abstract:Positioning force is the main reason for thrust fluctuation of permanent magnet synchronous linear motor (PMLSM), which leads to vibration and noise, and deteriorates the operation performance of the drive system. In order to solve this problem, a PMLSM thrust fluctuation suppression strategy based on Proportional Resonant Internal Mode Expansion State Observer (PR-IMESO) is proposed to improve the control accuracy and operation performance of the system.

Firstly, the thrust fluctuation of PMLSM is modeled and analyzed, and the internal mode expansion state observer (IMESO) considering the positioning force model is studied according to the principle of internal mode, and the resonant term is introduced into the observer to strengthen the suppression of the secondary pulsating positioning force. The proposed suppression strategy has good observation and compensation ability for PMLSM positioning force, and can also suppress the thrust fluctuations of other complex movers that are not modeled, and has a good overall thrust fluctuation suppression effect. Finally, the effectiveness of the proposed inhibition strategy was verified on a 750 W PMLSM experimental platform.

Hybrid stepper motor speed oscillation suppression control based on active damping

Authors: Shi Yu, Wu Zhitao, Su Xiaoying, Tong Wenming

Abstract:Due to its special mechanical structure, the hybrid stepper motor has very little damping, and the problem of excessive oscillation or even out-of-step will occur in the actual operation process. In order to improve the control quality of hybrid stepper motor, a stepper motor speed oscillation suppression method based on active damping was proposed.

Firstly, the motor model is transformed into a synchronous rotation DQ coordinate system, the current ID is controlled to the rated current, and the position error and speed error are used to adjust the current IQ to generate instantaneous torque, so as to suppress the oscillation phenomenon during the operation of the motor. Secondly, in order to realize the closed-loop feedback control of the motor, a sensorless control method combining the synchronous frequency extraction filter (SFF) and the third-order phase-locked loop (PLL3rd) was proposed. SFF can filter out the higher harmonics in the back EMF signal, and PLL3rd can eliminate the steady-state error during the speed change. Experiments show that this method can effectively suppress the oscillation phenomenon during the operation of the stepper motor and improve the operation quality of the motor.

Parallel control of variable parameter displacement velocity of permanent magnet synchronous linear motor based on composite neural network reconstruction object

Author: Bao Mingkun, Zhou Yangzhong

Abstract:In order to solve the problem of insufficient control accuracy caused by the fixed coefficient of the controller in the traditional displacement control algorithm of permanent magnet synchronous linear servo motor (PMSLM), a PMSLM variable-parameter displacement velocity parallel control strategy based on composite neural network reconstruction object is proposed. Firstly, using the mover displacement, Secondly, a composite radial basis neural network with multi-dimensional information of the control object is established to observe the mover displacement and obtain the partial derivation information of the control object。

Power electronics

The influence of the heat sink on the power cycle aging life of IGBT modules

Authors: Chang Guiqin, Luo Haihui, Fang Chao, Chen Jie, Huang Yongzhang

Abstract:Power semiconductor modules usually reduce the thermal resistance of the crust to reduce the operating junction temperature, and the integrated Pin-Fin substrate is an effective choice to replace the flat plate substrate. The thermal impedance characteristics of the two package structures are different, which may affect their failure mechanism and application life. The power cycling test under the same thermal test conditions (junction temperature difference of 100 K, maximum junction temperature of 150°C) was carried out for two common automotive-grade IGBT modules of flat panel substrate and integrated Pin-Fin substrate, and the results showed that the power cycle life of Pin-Fin module with stronger heat dissipation was lower than that of flat panel module.

The failure analysis shows that the failure mode of both is bond line desorption, but the bond failure point of the Pin-Fin module is concentrated in the center area of the chip, while the bond failure point of the flat panel module is more scattered. Based on the electrical-thermal-mechanical coupling analysis method, the finite element simulation model of the power cycling test is established, and the results show that the chip temperature gradient of the Pin-Fin module is larger, and the temperature of the bonding point in the center area of the chip is higher, which makes the plastic deformation of the bonding point in the center of the chip greater, resulting in a shorter lifetime than that of the flat module, which is consistent with the test results.

A hybrid three-level active mid-point clamp zero-voltage conversion soft-switching converter of silicon carbide and silicon device

Authors: Li Jin, Dang Enshuai, Fan Yushun, Dong Hangfei, Liu Jinjun

Abstract:In this paper, a hybrid three-level active mid-point clamp zero-voltage conversion (3L-ANPC ZVT) converter topology for silicon carbide and silicon (SiC&Si) devices is proposed. In this topology, two SiC MOSFET devices are used in each phase of the main circuit to work at high frequency, and the rest of the main circuit switches to Si devices at low frequency, and the SiC devices are operated under ZVT soft switching conditions through auxiliary circuits, which further reduces the high-frequency switching loss and switching stress of SiC MOSFETs. In the topology, the auxiliary circuit switch adopts Si devices and only works in the commutation process of the main device, which has the characteristics of small rated current and no switching loss.

In this paper, the circuit topology and working principle of the soft-switching converter are introduced, and the optimal design process of auxiliary circuit parameters is given. Then, based on the double-pulse test data, the loss modeling of the converter is carried out, and the loss distribution and efficiency changes of the hard-switching and soft-switching active mid-point clamp three-level converters under different switching frequencies are analyzed and compared, and it is revealed that the proposed soft-switching converter topology can effectively improve the efficiency of the converter at high switching frequencies. Finally, the correctness of the above analysis conclusions is verified by the single-phase converter experimental platform built.

Frequency conversion double-shift phase-shift modulation strategy for wide-gain and high-efficiency CLLLC converter

Authors: Zhou Guohua, Wang Qi, Deng Lunbo

Abstract:When the input voltage changes in a wide range, the variable frequency modulated CLLLC converter has the problem of wide switching frequency variation, while the phase shift modulated CLLLC converter is difficult to achieve wide range zero voltage turn-on (ZVS). In order to achieve the high efficiency of CLLLC converter with wide input voltage, a frequency-conversion double-phase shift modulation method is proposed. By simultaneously adjusting the switching frequency and the phase-shifting angle between the primary-side full-bridge and the secondary-side full-bridge, the gain and efficiency of the CLLLC converter are broadened. The time-domain analysis method is used to solve the voltage gain and resonant inductor current rms of frequency conversion double-phase shift modulation CLLLC converter, and the influence of frequency and phase shift angle on voltage gain and resonant inductor current rms is analyzed. Finally, an experimental prototype with 100~300 V input and 48 V/400 W output was built to verify the correctness of the theoretical analysis.

Discrete domain current control strategy for high-power grid-connected converter

Authors: Wang Xu, Yang Shuying, Li Dian, Zhang Xing

Abstract:The switching frequency of megawatt high-power grid-connected converter is low, and the delay and discretization error have a great impact on the control performance, resulting in problems such as slow dynamic response and large influence of power grid background harmonics. Therefore, the design of a direct discrete domain control system becomes necessary. In this paper, a discrete-domain mathematical model is established for the LCL filtered grid-connected converter, and a discrete-domain current controller based on the fusion of bridge-arm current and grid-side current is proposed. At the same time, in order to obtain the grid-connected current information without adding additional current sensors and detection circuits, a capacitance-voltage differential is designed to realize the estimation of grid-side current, reducing hardware complexity and control cost.

The results show that the discrete domain current controller designed in this paper has good dynamic performance and grid background harmonic suppression ability. Finally, the proposed design is experimentally verified by the hardware-in-the-loop hardware-in-the-loop simulation system.

An asymmetric modulation strategy for three-phase Buck rectifier with low input current total harmonic distortion

Authors: Cao Haibin, Xu Jianping, Xie Fei, Zhou Chenli, Chen Xin

Abstract:The traditional Space Vector Pulse Width Modulation (SVPWM) three-phase Buck rectifier does not consider the influence of DC chain current ripple on the input current, and the input current is seriously distorted at the sector switching point, resulting in the increase of the total harmonic distortion rate (THD) of the input current. In this paper, the influence of DC chain current ripple on the input current of the three-phase Buck rectifier is analyzed, and the cause of the distortion of the switching point of the input current sector is analyzed, and a new asymmetric SVPWM strategy is proposed, which significantly reduces the input current THD of the three-phase Buck rectifier. Finally, simulations and a 1 kW experimental prototype verify the correctness of the theoretical analysis and the effectiveness of the proposed modulation strategy.

Impedance remodeling control strategy of grid-connected inverter based on grid voltage feedforward under weak grid

Authors: Yang Ming, Yang Zhuo, Li Yulong, Zhu Jun

Abstract:Under weak power grid, the negative resistance characteristic introduced by the phase-locked loop in the frequency band above the fundamental wave will reduce the phase of the system output impedance and seriously affect the stability of the system. In view of this, the grid voltage feedforward function that can eliminate the negative resistance characteristic of the phase-locked loop is derived through the equivalent transformation of the system control block diagram, and then a grid-connected inverter impedance remodeling control strategy based on grid voltage feedforward control is proposed.

At the same time, in order to improve the universality of the strategy, this paper provides two design methods for the optimization of the grid voltage feedforward function by using function approximation and multi-objective constraints, and analyzes the error from the aspects of system fundamental current tracking performance and grid-connected power factor, so as to prove the feasibility of the function optimization design method. The theoretical analysis shows that the optimized grid voltage feedforward control strategy can effectively reshape the phase characteristics of the output impedance of the system, and greatly broaden the adaptability range of the system to the grid impedance. Finally, the effectiveness of the proposed control strategy is verified by simulation and experiments.

High voltage and discharge

A recursive quantitative analysis and identification method of circuit breaker vibration signal traceable to the spring deformation process

Authors: Liu Huilan, Chang Gengyao, Zhao Shutao, Fu Lei, Liu Jiaomin

Abstract:From the truncation of the locking mechanism to the energy release of the energy storage spring, and then to the stationary movement of the moving contact driven by the components, each action has strict stage characteristics, and the mechanical vibration accompanying the action of the circuit breaker shows the energy transfer and the health state of the equipment. In this paper, a recursive quantitative analysis method of circuit breaker vibration signal tracing the deformation process of spring is proposed.

Firstly, the high-speed camera captures the action image of the energy storage spring when the circuit breaker is operated, dynamically extracts the feature frame reflecting the spring deformation through computer vision tracking, and then divides the operation process according to the time sequence of the feature frames。 The proposed method has a broad application prospect in the state identification of circuit breaker operating mechanism.

A short-circuit cumulative mechanical damage evaluation method for power transformer

Authors: Ou Qiang, Luo Longfu, Li Yong, Yang Xian, Zhou Lawu

Abstract:Multiple short circuits will gradually accumulate mechanical damage to the winding, and eventually lead to damage to the power transformer. However, there is currently a lack of a quantitative assessment method to assess such damages, which poses a threat to the safe operation of the power grid. Therefore, this paper proposes a method to evaluate the cumulative mechanical damage of power transformer winding short-circuit considering the nonlinear characteristics of windings and the accumulation process, which provides a new way to evaluate the impact of winding short-circuit on power transformers. In this method, the damping ratio and reliability loss coefficient are used as characteristic quantities, and the mechanical weakening process of winding is simulated by exponential curves. At the same time, considering the influencing factors such as the initial ability of the transformer to withstand short circuit, the amplitude of the short circuit current and the number of faults, the relationship between the short circuit damage and the dynamic mechanical life of the winding is quantified.

In addition, the correctness of the evaluation method is verified by multiple short-circuit destructive tests of a 110 kV power transformer. Finally, the proposed evaluation method is applied to different check control methods, and the positive effect of controlling the damping ratio in reducing the cumulative damage is emphasized.