Abstract
The three-phase/switch Y-type two-level rectifier is widely used in the unidirectional power-flowing applications such as LED illumination, communication and uninterruptible power supply. This paper presents the working principle of three-phase/switch Y-type two-level rectifier, and proposes two simple and fast modulation techniques (12-sector SVPWM and simplified equivalent SVPWM) based on the virtual vectors. The reference vectors of the 12-sector SVPWM are synthesized by utilizing real basic vectors and virtual vectors linearly combined from these real vectors in a switching period. So the created virtual vectors can reduce the error of reference voltage synthesis, contributing to better input current performance, this paper proposes a simplified 12-sector equivalent SVPWM, and shows the novel three-phase modulation wave expressions and waveforms. The proposed simplified 12-sector equivalent SVPWM does not need the process of sector determination with reducing computational processing time which is attractive for digital implementation. Finally, performance of the proposed modulation methods for a Y-type two-level rectifier using a 5kW prototype is experimentally verified.
Highlights
When bidirectional power flux is not necessary, the unidirectional three-phase Y-type two-level rectifier presents some advantages as only using three controllable power transistors which is half of the number of switches in traditional PWM rectifier, no short-circuit phenomenon between bridge arms and smaller processing of energy for the active switches in the application of power unidirectional flow such as LED lighting, communication and uninterruptible power supply
In order to improve the voltage utilization and simplify the complex calculation process of traditional SVPWM, the third harmonic component is injected into the sinusoidal modulation wave to form the saddle wave, which is equivalent to the space-vector pulse width modulation
The equivalent SVPWM based on the new three-phase modulation wave is simple, and no sector judgment and vector action time calculation are needed, which can reduce greatly computational processing time which is its simplicity for digital implementation
Summary
When bidirectional power flux is not necessary, the unidirectional three-phase Y-type two-level rectifier presents some advantages as only using three controllable power transistors which is half of the number of switches in traditional PWM rectifier, no short-circuit phenomenon between bridge arms and smaller processing of energy for the active switches in the application of power unidirectional flow such as LED lighting, communication and uninterruptible power supply. The active current path of vector modes, the working states of the circuit are shown in Fig. and they are shown as follows:. During this state, UAB=+Udc, UBC=0, UCA=-Udc, and phase A current decreases, phase B current increases when the line voltage UAB is greater than 0. During this state, UAB=+Udc, UBC=-Udc, UCA=0 , phase A and phase C currents decreases, and ia+ib+ic=0, phase B current increases.
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