Abstract
This thesis presents a high power bi-directional three-phase four-wire half bridge converter for charger/discharger systems, including grid-connection mode, rectification mode and dc-bus voltage regulation mode. In grid-connection mode, power is transferred from DC to AC and injected into the utility grid. In rectification mode, the utility power is transformed to DC with power factor correction. In dc-bus voltage regulation mode, the converter can inject power into the utility grid or supply DC loads when the bus voltage is higher than the setpoint. On the contrary, it will regulate the voltage by operating at rectification mode. A single-chip microcontroller Renesas RX62T is adopted to realize the control algorithm. In the thesis, component selection, including IGBT modules and design of inductors is first presented. Next, control law and operation principle of the converter with division-summation (D- ) digital control are addressed. Additionally, the converter in grid-connection mode and rectification mode with the D- digital control is simulated. Due to the DC bus constructed with capacitors in series, capacitor voltage balancing algorithm is also proposed. Finally, the converter has been implemented and tested so as simulated and measured results can verify the control scheme and feasibility. The major contributions of this research can be summarized as follows: First, the derived control law can accommodate grid voltage and inductance variations. The microcontroller RX62T is adopted to calculate the duty ratio exactly which can avoid output current distortion when inductance varies over a wide range. Secondly, the proposed operation does not yield high frequency common mode voltage so as it can be applied to PV inverter system. Thirdly, the converter has a property of multi-functions which can not only reduce production cost and volume, but can execute different operation modes according to load demands.