Current Compensation Control of Converter Under Distortion Current and Exponentially Decaying DC Conditions

In order to improve the reliability of flexible DC transmission. This paper proposes current offset control (COC) strategy of active power filter (APF) under harmonically distorted current and decaying dc (DDC) conditions. The proposed COC method is realized in a rotating coordinate system, so that the harmonic current and DDC caused by nonlinear loads can be effectively eliminated. First, a mathematical model of the fault current is established, and the DDC is extracted using the property that the integral of the periodic function is zero. Secondly, the fundamental wave component of the fault current signal is separated in the rotating coordinate system to obtain the current command value for APF compensation. Finally, compared with the conventional APF harmonic current compensation strategy under the experimental platform, the results show that the strategy takes into account the influence of the DDC component, so that the APF has the ability of transient current compensation.

I. Introduction

With the increase of non-linear loads and impulsive loads in the power grid. For example, large-capacity diodes or thyristor rectifiers, motor variable-speed drive devices, etc [1–3]. Power conditioning is becoming more and more important in high-efficiency and high-reliability power systems. In many cases, harmonic pollution and decaying dc (DDC) components with uncertain amplitude and attenuation rate are not tolerated [4]. The diffusion of nonlinear loads in the power system leads to the generation of p-q theory, which is not only valid in the steady state, but also in the transient process [5]. The p-q theory has been widely used in the design of active power filters (APF) for reactive power and harmonic compensation, but there are few studies on the compensation of DDC components in the transient process.