Parallel Operation of Microgrid Inverters Based on Adaptive Sliding-Mode and Wireless Load-Sharing Controls

Zhang, Qinjin,Liu, Yancheng,Wang, Chuan,Wang, Ning The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3

This study proposes a new solution for the parallel operation of microgrid inverters in terms of circuit topology and control structure. A combined three-phase four-wire inverter composed of three single-phase full-bridge circuits is adopted. Moreover, the control structure is based on adaptive three-order sliding-mode control and wireless load-sharing control. The significant contributions are as follows. 1) Adaptive sliding-mode control performance in inner voltage loop can effectively reject both voltage and load disturbances. 2) Virtual resistive-output-impedance loop is applied in intermediate loop to achieve excellent power-sharing accuracy, and load power can be shared proportionally to the power rating of the inverter when loads are unbalanced or nonlinear. 3) Transient droop terms are added to the conventional power outer loop to improve dynamic response and disturbance rejection performance. Finally, theoretical analysis and test results are presented to validate the effectiveness of the proposed control scheme.

Parallel Operation of Microgrid Inverters Based on Adaptive Sliding-Mode and Wireless Load-Sharing Controls

Qinjin Zhang,Yancheng Liu,Chuan Wang,Ning Wang 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.3

This study proposes a new solution for the parallel operation of microgrid inverters in terms of circuit topology and control structure. A combined three-phase four-wire inverter composed of three single-phase full-bridge circuits is adopted. Moreover, the control structure is based on adaptive three-order sliding-mode control and wireless load-sharing control. The significant contributions are as follows. 1) Adaptive sliding-mode control performance in inner voltage loop can effectively reject both voltage and load disturbances. 2) Virtual resistive-output-impedance loop is applied in intermediate loop to achieve excellent power-sharing accuracy, and load power can be shared proportionally to the power rating of the inverter when loads are unbalanced or nonlinear. 3) Transient droop terms are added to the conventional power outer loop to improve dynamic response and disturbance rejection performance. Finally, theoretical analysis and test results are presented to validate the effectiveness of the proposed control scheme.

A novel smooth switching control strategy for multiple photovoltaic converters in DC microgrids

Qinjin Zhang,Wangbao Hu,Yancheng Liu,Hanwen Zhang,Honglai Wang 전력전자학회 2022 JOURNAL OF POWER ELECTRONICS Vol.22 No.2

With the photovoltaic (PV) penetration rate increasing in PV-storage-based DC microgrids, the conventional PV controller with only the maximum power point tracking (MPPT) control function can hardly meet the needs of the coordinated operation. The PV converter should operate at the MPPT or the constant voltage droop (CVD) mode according to the load demand. Two sets of relatively independent control loops are used to control the two modes. Inevitably, bus voltage and PV output power fluctuations are caused in the process of mode switching. This paper proposes a novel smooth switching control strategy for the smooth transition of multiple PV converters between MPPT and CVD modes. When combined with the PV array output characteristic curve, the value of dp/di is selected as the control variable. By tracking different dp/di command values, the PV converter can realize the control of the MPPT mode, the CVD mode, and smooth switching between the two modes. The MPPT and CVD modes are unified in the sense of using the same control loop, which avoids control loop switching during the PV mode switching. Finally, the effectiveness of the novel smooth switching control strategy is verified by the simulation and hardware in loop (HIL) experimental tests.

An Improved SoC Balancing Strategy for Battery Energy Storage System in All-Electric Propulsion Ships Current Sharing Effect

Zhang Qinjin,Qu Tengda,Liu Yancheng,Zeng Yuji,Hu Wangbao,Zhang Hanwen 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3

A dynamic state of charge (SoC) balancing strategy for parallel battery energy storage units (BESUs) based on dynamic adjustment factor is proposed under the hierarchical control framework of all-electric propulsion ships, which can achieve accurate power distribution, bus voltage recovery, and SoC balance accuracy. In the primary control layer, the arccot function is introduced into the improved balancing strategy, and the bus voltage drop is effectively limited while the SoC balancing speed is quickly achieved by adjusting the SoC convergence factors. In the secondary control layer, power and voltage compensation controllers are designed individually to improve the SoC balance accuracy and compensate the bus voltage. Furthermore, neighbor-to-neighbor communication network is constructed by using dynamic consensus algorithm to reduce the communication burden as well as its error rate. Finally, the simulation and StarSim HIL experimental results show that the proposed control strategy can achieve accurate power distribution, bus voltage recovery, and has a faster SoC convergence speed than advanced methods.

Autonomous Load Current Sharing Control Strategy for Distributed DC Micro-sources Based on Active Frequency Injection and Line Impedance Compensation Control

Zhuang Xuzhou,Zhang Qinjin,Zeng Yuji,Liu Yancheng,Liu Siyuan,Yu Heyang 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.4

Traditional droop control methods are diffi cult to achieve accurate and autonomous current sharing between micro-source converters in DC microgrid, due to the mismatch of line impedance and the existence of low-speed communication. In this paper, an autonomous current sharing control strategy based on active frequency injection and line impedance compensation is proposed. Firstly, an active frequency injection method is used for all supported voltage-source converters. Under the feedback mechanism of the reactive power and voltage, the accurate current sharing can be achieved, and the total equivalent droop coeffi cient of each converter would be approximately equal. On the basis, the line impedance compensation information of each converter can be obtained accurately. Then, the original droop control method, in which the droop coeffi cient is the obtained compensation value, is utilized to replace the injection method. Without introducing any communication, this method not only can ensure the accuracy of load current sharing, but also can eff ectively improve the large ripple problem caused by frequency injection method, and avoid the secondary bus voltage drop. The design process and stability of the controller are analyzed in detail. Finally, the feasibility and eff ectiveness of the proposed control strategy are verifi ed by using the corresponding simulation model and HIL experimental platform.

Power distribution strategy based on state of charge balance for hybrid energy storage systems in all-electric ships

Liu, Yancheng,Wang, Honglai,Zhang, Qinjin,Wen, Yuanquan,Hu, Wangbao,Zhang, Hanwen The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.8

During the navigation of all-electric ships, a hybrid energy storage system (HESS) is required to compensate power imbalance and maintain bus voltage stability. For a HESS composed of multiple energy storage (ES) devices, an unreasonable power distribution causes the ES devices with a low state of charge (SoC) to draw from power supply early, which deepens the operating pressure of the other ES devices. This in turn, affects the stable operation of the entire system. To achieve power distribution based on the SoC of different ES devices, a novel power distribution strategy for use in all-electric ships was proposed. In the proposed strategy, the virtual impedance of an ES device is connected with the SoC through exponential functions. As a result, the output power can be dynamically changed according to changes of the SoC. On the premise of obtaining a proper dynamic power distribution among ES devices with complementary characteristics, the SoC balance among ES devices with the same characteristics can be realized. Meanwhile, the bus voltage deviation induced by the virtual resistor is eliminated via an added compensation voltage. The effectiveness of proposed method is verified by both simulations and a StarSim hardware in loop (HIL) experimental platform.