Three-phase unity-power-factor star-connected switch (VIENNA) rectifier with unified constant-frequency integration control

A unified constant-frequency integration (UCI) controller for a three-phase star-connected switch three-level rectifier (VIENNA) with unity-power-factor-correction is proposed. One of advantages of this rectifier is that the switch voltage stress is one half of the total output voltage. The proposed control approach is based on one-cycle control and features great simplicity and reliability: all three phases will be power factor corrected using one or two integrators with reset along with several flips-flops, comparators and logic and linear components. It does not require multipliers to scale the current reference according to the output power level as used in many other control approaches. In addition, the input voltage sensor is eliminated. It employs constant switching frequency modulation that is desirable for industrial applications. The proposed controller can operate by sensing either the inductor currents or the switching currents. If the switching currents are sensed, the cost is further reduced because switching currents are easier to sense comparing with inductor currents. The proposed approach is supported by experimental results.

I. Introduction

Traditional diode rectifiers and thyristor rectifiers draw pulsed current from the ac main, causing significant current harmonics pollution. The international standards presented in IEC 1000-3-2 or EN61000-3-2 imposed harmonic restrictions to modern rectifiers, which stimulated a focused research effort on the topic of unity power factor rectifiers. Among the reported three-phase rectifier topologies, three-phase star-connected switch three-level rectifier (VIENNA rectifier) [1] [2] [3] is an attractive choice because its switch voltage stress is one half of the total output voltage. In this paper, a unified constant-frequency integration (UCI) controller based on one-cycle control [4]–[7] is proposed for this rectifier. The proposed controller employs constant switching frequency modulation that is very simple and desirable for industrial applications. Fig. 1. (a) Three-phase star-connected switch (VIENNA) rectifier and (b) its switching cycle average model.