Research on Oscillation Suppression Methods in Shunt Active Power Filter System

Abstract

The shunt active power filter (SAPF) system oscillation is a massive threat to the security and stability of the power grid. This study classifies SAPF oscillation into two categories according to the difference in mechanisms. The SAPF oscillation in one category is caused by the resonant characteristics of a switching noise filter and is called external loop amplification. The SAPF oscillation in the other category is induced by the presence of a capacitor in the load current for SAPF and is called self-excited oscillation. Unlike previous studies, this study tried to reveal the internal relationship between the two kinds of SAPF oscillation, present a general shunt virtual-damping-based SAPF oscillation suppression strategy covering the previous resonant damping method, and provide the discrete domain stability criterion of the control system. The sampling frequency was at least six times the resonant frequency. The stability region was enlarged with an increase in the sampling frequency and narrowed with a rise in the resonant frequency. As to the harmful self-excited oscillation problem, this study proposes a composite control strategy combining selective harmonic compensation and grid-side current feedback. Moreover, this study considers the more general resistance–inductance–capacitance load situations and analyzes the stability of the SAPF–Thyristor Switched Capacitor (TSC) hybrid compensation system. Simulations and experiments demonstrated that the proposed compound control method can reduce the primary harmonics of the system by more than 90% and has a better oscillation suppression performance than previous suppression methods. In particular, if we selected the TSC series reactance rate following more than 6%, self-excited oscillation could usually be avoided.

Research on an Adaptive Compound Control Strategy of a Hybrid Compensation System

“…It then achieves precise reactive power compensation between layers using the APF, while also suppressing harmonics. This combination of TSC's economy and reliability with APF's accuracy and flexibility has made it widely used in power supply systems [16]. However, in practical applications, it has been observed that under specific operating conditions, harmonic currents at the load side may affect the distribution system, resulting in more severe harmonic resonance phenomena that seriously impact power quality and normal system operation.…”

“…The TSC enables graded reactive power compensation [13], while the APF compensates for harmonics and provides stepless continuous compensation of reactive power between TSC stages [14]. This system achieves simultaneous reactive power compensation and harmonic current suppression, resulting in excellent compensation effects and better economy [15,16]. As a result, this hybrid system has been widely adopted.…”

Integral Power Theory and Active Filtering Using the α-β Reference Frame

“…The increasing number of non-linear powerful consumers asymmetrically connected to the power supply system leads to a deterioration in the power quality and increasing power losses. The most effective hardware for improving power quality in points of common coupling is shunt active filters (SAFs), which improve the harmonic content of the consumed currents and compensate for inactive power components, minimizing power losses in the transmission line [1][2][3]. These works also aim to assess the most advanced SAFs by reducing the number of power switches and focusing on reducing grid-connected inverters' cost, size, and weight.…”