Constant DC-Capacitor Voltage-Control-Based Reactive Power Control Strategy of Three-Level NPC Inverter-Based STATCOM

This paper proposes a constant de-capacitor voltage-control (CDCVC)-based reactive power control strategy of a static synchronous compensator (STATCOM) with a three-level neutral-point-clamped (NPC) inverter, where the source-side harmonic currents are also compensated simultaneously. The CDCVC-based reactive power control strategy uses only a CDCVC, which is always used in grid-connected inverters, STAT-COMs, etc. Calculation blocks of fundamental active, reactive and harmonic components are not required. Thus, the authors propose a simplified strategy for the source-side reactive power control with the source-side harmonic currents compensations. The instantaneous power flowing into a STATCOM shows that using the CDCVC-based strategy achieves sinusoidal source-currents with controlled source-side reactive power compensating the harmonic currents on the source side. Simulation and experimental results demonstrate that sinusoidal source-currents are obtained with the CDCVC-based strategy controlling the reactive power on the source side.

I. Introduction

Static synchronous compensators (STATCOMs) are now on practical to solve reactive power interferences. A three-level neutral-point-clamped (NPC) inverter, which was originally proposed by Prof. Nabae et al. [1], is widely used in industries [2]–[4]. A three-level NPC inverter based STATCOM can be directly connected to 6,600- Vrms high-voltage distribution feeders. This is a significant advantage of the three-level NPC inverter-based STATCOM. The instantaneous active-reactive power theory originally proposed by Prof. Akagi et al. is widely used for the control strategy of STATCOMs [5]–[7]. This control algorithm is mainly based on instantaneous active-reactive power theory and its extensions for the calculation of reference currents. A synchronous reference frame, decomposition in the time domain of the load currents, and theory of instantaneous symmetrical component are also proposed [8], [9].