Direct Power Control of a Pulse Width Modulation Rectifier Using Space Vector Modulation Under Unbalanced Grid Voltages

Compared with conventional table-based direct power control (DPC), DPC using space vector modulation (DPC-SVM) exhibits several specific features, such as a constant switching frequency and small ripples in both active power and reactive power. However, conventional DPC-SVM exhibits highly distorted grid currents when the grid voltages are unbalanced. In this study, we propose a novel and simple DPC-SVM that is effective under both ideal and unbalanced grid voltage conditions by using an extension of original instantaneous power theory. After deducing the power slopes of both active power and reactive power, the suitable converter voltage reference to nullify the errors of active power and reactive power is analytically derived, which is subsequently synthesized by SVM. The proposed DPC-SVM does not require the extraction of complex positive/negative sequence from the grid voltage/current or power compensation. Compared to prior DPC-SVM using original imaginary power, the proposed method exhibits much better performance by obtaining highly sinusoidal line currents and eliminating twice grid-frequency ripples in both active power and the reactive power under unbalanced conditions. Simulations and experimental results supported the theoretical study and confirmed the effectiveness of the proposed method.

I. Introduction

Pulse width modulation (PWM) rectifiers have attracted widespread attention because of their advantages in terms of bidirectional power flow, sinusoidal line current, controllable input power factor, good dc-link voltage regulation ability [1], [2], and other features. Currently, the most popular high-performance control methods for PWM rectifiers are voltage-oriented control (VOC) [3] and direct power control (DPC) [4] –[6]. VOC decomposes the grid currents into active power component and reactive power component in synchronous frame, which are regulated by inner current loops using PI controllers. The obtained converter voltage vector references are subsequently synthesized by space vector modulation (SVM). Good steady-state performance and quick response can be obtained in VOC, but it requires fine tuning work and accurate system parameters.