Power System Protection and Control Utilizing LCL Filtering DVR Compensation: Transformer Leakage Resistance Determination
By Wu Fuzhuo, Hou Tingting, and Han Liang (Zhongyuan Institute of Technology, Zhengzhou 450007, China)
This paper explores the determination of transformer leakage reactance and impedance drop, focusing on the design of an LCL filter-based Dynamic Voltage Restorer (DVR). The DVR functions by detecting grid supply voltage fluctuations and applying a compensation strategy through a digital signal processing system. This system controls the inverter output to generate a compensation voltage, which is then superimposed onto the load voltage via a series compensation transformer and the LCL filter. This ensures dynamic compensation of voltage drops, maintaining stable load voltage levels.
The equivalent circuit of the compensation transformer shows the secondary side output voltage, the primary side voltage of the series transformer, and the leakage reactance and resistance. The simplified circuit demonstrates how the excitation impedance is negligible, allowing for streamlined calculations.
For the DVR filter, the LCL configuration combines the transformer's leakage inductance with external inductors and capacitors. This setup aims to reduce high-frequency switching ripple in the grid current by providing a low-resistance path for these components.
In designing the LCL filter parameters, considerations include active and reactive power control, harmonic current limitations, and current tracking efficiency. The total inductance must accommodate the inverter’s operational demands under varying grid conditions. Through mathematical modeling, optimal inductance values are determined based on current ripple constraints and harmonic attenuation goals.
Simulations using a 30 kVA DVR model demonstrate effective voltage compensation. Curve analysis reveals that even minor grid voltage drops can be successfully mitigated, ensuring load stability. Results indicate that as grid voltage decreases, the harmonic distortion rates of compensation voltages rise slightly but remain manageable due to their minimal contribution to overall grid power.
The combination of transformer leakage inductance with an LC filter creates an efficient LCL filter circuit. Simulated outcomes validate the approach, showcasing both stability and economic feasibility. These findings confirm the effectiveness of the proposed method in enhancing power system protection and control through advanced filtering techniques.
Further research could explore additional optimization strategies or alternative configurations to enhance performance and reduce costs. This study lays a solid foundation for future advancements in DVR technology and its applications in power systems.
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