A MOSFET's Driver Applied to High-frequency Switching with Wide Range of Duty Cycles

Zhang, Zhao,Xie, Shaojun The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

A MOSFET's gate driver based on magnetic coupling is investigated. The gate driver can meet the demands in applications for wide range of duty cycles and high frequency. Fully galvanic isolation can be realized, and no auxiliary supply is needed. The driver is insensitive to the leakage inductor of the isolated transformer. No gate resistor is needed to damp the oscillation, and thus the peak output current of the gate driver can be improved. Design of the driving transformer can also be made more flexible, which helps to improve the isolation voltage between the power stage and the control electronics, and aids to enhance the electromagnetic compatibility. The driver's operation principle is analyzed, and the design method for its key parameters is presented. The performance analysis is validated via experiment. The disadvantages of the traditional magnetic coupling and optical coupling have been conquered through the investigated circuit.

A MOSFET’s Driver Applied to High-frequency Switching with Wide Range of Duty Cycles

Zhao Zhang,Shaojun Xie 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

A MOSFET’s gate driver based on magnetic coupling is investigated. The gate driver can meet the demands in applications for wide range of duty cycles and high frequency. Fully galvanic isolation can be realized, and no auxiliary supply is needed. The driver is insensitive to the leakage inductor of the isolated transformer. No gate resistor is needed to damp the oscillation, and thus the peak output current of the gate driver can be improved. Design of the driving transformer can also be made more flexible, which helps to improve the isolation voltage between the power stage and the control electronics, and aids to enhance the electromagnetic compatibility. The driver’s operation principle is analyzed, and the design method for its key parameters is presented. The performance analysis is validated via experiment. The disadvantages of the traditional magnetic coupling and optical coupling have been conquered through the investigated circuit.

Current Harmonics Rejection and Improvement of Inverter-Side Current Control for the LCL Filters in Grid-Connected Applications

Jinming Xu,Shaojun Xie,Binfeng Zhang 전력전자학회 2017 JOURNAL OF POWER ELECTRONICS Vol.17 No.6

For grid-connected LCL-filtered inverters, the inverter-side current can be used as the control object with one current sensor for both LCL resonance damping and over-current protection, while the grid-voltage feedforward or harmonic resonant compensator is used for suppressing low-order grid current harmonics. However, it was found that the grid current harmonics were high and often beyond the standard limitations with this control. The limitations of the inverter-side current control in suppressing low-order grid current harmonics are analyzed through inverter output impedance modeling. No matter which compensator is used, the maximum magnitudes of the inverter output impedance at lower frequencies are closely related to the LCL parameters and are decreased by increasing the control delay. Then, to improve the grid current quality without complicating the control or design, this study proposes designing the filter capacitance considering the current harmonic constraint and using a PWM mode with a short control delay. Test results have confirmed the limitation and verified the performance of the improved approaches.

Modeling and controller optimization for current-fed isolated bidirectional DC-DC converters

Zhang, Zhao,Xie, Shaojun,Shang, Xiaofeng,Qian, Qiang,Xu, Jinming The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.6

Current-fed isolated bidirectional DC-DC converters (CF-IBDCs) play an important role in battery energy storage systems. However, the closed-loop dynamics is rather slow with conventional proportional-integral controllers because a precise mathematic model remains absent for optimization. In this paper, a simple precise mathematical model is presented to describe the large and small-signal behaviors of the CF-IBDC. The full-order continuous model can accurately capture the dynamic behaviors and cover all operation conditions. The small-signal model is derived, and the DC filter inductors and clamp capacitors are found to be the natural causes of instability. Based on this finding, special controllers are proposed to optimize the dynamic response of the full closed-loop control system. The dynamic response time of the CF-IBDC is greatly reduced with the proposed controller. The correctness of the presented model and the dynamic response of the optimized closed-loop control system are verified by simulations.

Soft-switching and low conduction loss current-fed isolated bidirectional DC-DC converter with PWM plus dual phase-shift control

Zhang, Zhao,Xie, Shaojun,Wu, Zhiying,Xu, Jinming The Korean Institute of Power Electronics 2020 JOURNAL OF POWER ELECTRONICS Vol.20 No.3

In battery energy storage systems, the battery and DC bus voltages vary greatly. This makes it difficult for the battery storage converter to maintain high efficiencies under all circumstances. A current-fed isolated bidirectional DC-DC converter is presented in this paper. This converter contains two series transformers, two conventional current-fed half-bridges at the battery side and two half-bridges at the DC bus side. PWM plus dual phase shift modulation with equal duty cycles and voltage-matched control is applied to ensure ZVS of all the switches and low conduction losses. The average and backflow power transmission equations and soft-switching conditions for all of the operation modes in the full operation range are analyzed comprehensively in this paper. Then six recommended modes are addressed based on the above analyses. Moreover, the control scheme and hardware design guidelines are addressed. Finally, the above theoretical analyses and control strategy are verified by experimental results.

Systematic Current Control Strategy with Pole Assignment for Grid-Connected LCL-FilteredInverters

Jinming Xu,Shaojun Xie,Ting Tang 전력전자학회 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.3

For grid-connected LCL-filtered inverters, resonance yields instability and low bandwidth. As a result, careful designs are required. This paper presents a systematic current control structure, where pole assignment consisting of one or more feedbacks is the inner loop, and the outer loop is the direct grid current control. Several other issues are discussed, such as the inner-loop feedback choices, pole-assignment algorithms, robustness and harmonic rejection. Generally, this kind of strategy has three different types according to the inner-loop feedback choices. Among them, a novel pole-assignment algorithm has been proposed, where the inner control maintains four freely-assigned poles which are just two pairs of conjugated poles located at the fundamental and resonance frequencies separately. It has been found that with the different types, the steady-state and dynamic performances are quite different. Finally, simulations and experiments have been provided to verify the control and design of the proposed methods.

Systematic Current Control Strategy with Pole Assignment for Grid-Connected LCL-Filtered Inverters

Xu, Jinming,Xie, Shaojun,Tang, Ting The Korean Institute of Power Electronics 2013 JOURNAL OF POWER ELECTRONICS Vol.13 No.3

For grid-connected LCL-filtered inverters, resonance yields instability and low bandwidth. As a result, careful designs are required. This paper presents a systematic current control structure, where pole assignment consisting of one or more feedbacks is the inner loop, and the outer loop is the direct grid current control. Several other issues are discussed, such as the inner-loop feedback choices, pole-assignment algorithms, robustness and harmonic rejection. Generally, this kind of strategy has three different types according to the inner-loop feedback choices. Among them, a novel pole-assignment algorithm has been proposed, where the inner control maintains four freely-assigned poles which are just two pairs of conjugated poles located at the fundamental and resonance frequencies separately. It has been found that with the different types, the steady-state and dynamic performances are quite different. Finally, simulations and experiments have been provided to verify the control and design of the proposed methods.

Fast Diagnosis Method for Submodule Failures in MMCs Based on Improved Incremental Predictive Model of Arm Current

Kunshan Xu,Shaojun Xie 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.5

The rapid and correct isolation of faulty submodules (SMs) is of great importance for improving the reliability of modular multilevel converters (MMCs). Therefore, a fast diagnosis method containing fault detection and fault location determination was presented in this paper. An improved incremental predictive model of arm current was proposed to detect failures, and the multi-step prediction method was used to eliminate the negative impact of disturbances. Moreover, a control method was proposed to strengthen the fault characteristics to rapidly locate faulty arms and faulty SMs by detecting the variation rate of the SM capacitor voltage. The proposed method can rapidly and easily locate faulty SMs under different load conditions without the need for additional sensors. The experimental results have validated the effectiveness of the proposed method by using a single-phase MMC with four SMs per arm.

Stability Analysis and Improvement of the Capacitor Current Active Damping of the LCL Filters in Grid-Connected Applications

Jinming Xu,Shaojun Xie,Binfeng Zhang 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

For grid-connected LCL-filtered inverters, dual-loop current control with an inner-loop active damping (AD) based on capacitor current feedback is generally used for the sake of current quality. However, existing studies on capacitor current feedback AD with a control delay do not reveal the mathematical relation among the dual-loop stability, capacitor current feedback factor, delay time and LCL parameters. The robustness was not investigated through mathematical derivations. Thus, this paper aims to provide a systematic study of dual-loop current control in a digitally-controlled inverter. At first, the stable region of the inner-loop AD is derived. Then, the dual-loop stability and robustness are analyzed by mathematical derivations when the inner-loop AD is stable and unstable. Robust design principles for the inner-loop AD feedback factor and the outer-loop current controller are derived. Most importantly, ensuring the stability of the inner-loop AD is critical for achieving high robustness against a large grid impedance. Then, several improved approaches are proposed and synthesized. The limitations and benefits of all of the approaches are identified to help engineers apply capacitor current feedback AD in practice.

An Improved Inverter-Side Current Feedback Control for Grid-Connected Inverters with LCL Filters

Jinming Xu,Shaojun Xie,Jiarong Kan,Lin Ji 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

The grid-connected LCL-filtered inverter is widely used in distributed power generation systems based on renewable energies. Single inverter-side current feedback control only needs to sample one current to realize both current control and inverter protection. However, with single inverter-side current feedback control, the closedloop system is under-damped or even unstable due to the digital control delay. In this paper, an active damping control based on only inverter-side current feedback is proposed. With the novel control, the resonance in the digitally-controlled LCL-filtered inverter is successfully solved while only inverter-side current is sampled. Comparisons of the proposed and typical single inverterside current feedback control have verified the improvement of the proposed control. Thus, the proposed control has good application prospect in grid-connected LCL-filtered inverters.