Abstract
This article proposes a distribution static compensator (DSTATCOM) with interface LCL (inductor-capacitor-inductor) filter for load compensation in three-phase four-wire distribution system. DSTATCOM, consisting of voltage source inverter (VSI), is connected in parallel to the load and injects currents corresponding to load reactive, harmonic powers. But this injected current consists of unnecessary high-frequency switching ripple generated by VSI. This LCL filter has superior switching ripple attenuation capability compared to L filter. Moreover, this can be achieved with small value of overall LCL filter inductance than L filter. Thus providing high slew rate for output current to track the desired reference current closely, reducing voltage drop across it, as well as cost and size of filter. However, one major concern with LCL filter is its resonating frequency (determined from its L, C, L values), which can create high-resonance oscillating currents and results in improper load compensation. Therefore, in this study, proper design of LCL filter with high switching ripple attenuation and a current controller with proportional integral (PI) plus harmonic compensation (HC) regulators along with active damping feature of LCL filter in synchronous rotating reference (dq0) frame are presented. HC regulator minimizes the steady-state error in the non-sinusoidal filter currents (fundamental and harmonic) which are tracked by the VSI. Active damping feature (obtained by capacitor current feedback control of LCL filter) is used to overcome resonance oscillations and provides proper control, operation of DSTATCOM under steady-state and dynamic load conditions. Stability studies for designed LCL filter and current controller using Bode and root locus plots are also performed and presented. Extensive simulation study, to understand the compensation performance of LCL filter DSTATCOM with two types of current controllers (PI and PI plus HC) under steady-state and dynamic load conditions, is carried out in PSCAD simulator and the corresponding results along with THDs of various parameters are presented.
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