Abstract:Compared with the three-phase, two-split-capacitor active power filter (3P2C-APF), the three-phase, four-leg active power filter (3P4L-APF) has been widely used in three-phase, four-wire grid utility for power quality control due to its numerous advantages, such as higher current output capability, particularly in phase N, lower current and easier voltage control on the DC-side. However, designing the grid-connecting interface, which is between the voltage source converter (VSC) and grid utility, is rather difficult due to the higher requirement for current ripple filtering in phase N, cross-coupling in four phases and lack of relevant design methodology and specification. In this paper, a four-branch LCL-type (4B-LCL) grid-connecting interface is proposed for 3P4L-APF, which features better current ripple filtering performance without decreasing the current output capability in all phases. First, this paper describes the mathematical models of 4B-LCL in the fully-complex-vector form from the zero and non-zero sequence perspective, resulting in two independent and uniform equivalent circuits without cross coupling terms. Then, the 4B-LCL parameter design method based on the most comprehensive performance index is proposed, including three main stages as the specification: performance index requirement determination, fulfillment of that requirement, and verification. Finally, the validity and effectiveness of the proposed design are proven by the simulated and experimental results of a 3P4L-APF with 4B-LCL.

A large number of distributed photovoltaic grid connected to the grid is the main reason for voltage overrun of low-voltage distribution network. Therefore, this paper proposes a voltage control method using electric vehicle (EV) and photovoltaic inverter. Firstly, the distributed control of photovoltaic inverter is adopted. The voltage is regulated by controlling the active power output and reactive power output of the photovoltaic inverter, and the utilization rate of each photovoltaic inverter is the same. If the voltage is not within the safety threshold or the spare capacity of the PV inverter is insufficient, the charging and discharging power control of the electric vehicle will be carried out, and the charging and discharging rate will be controlled according to the consistency target of the electric vehicle power utilization and the SOC local information. The low-voltage distribution system is built in Matlab/Simulink. The simulation results show that the proposed control method is feasible and effective, and the voltage overrun problem in this area is effectively solved.

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