Design and control of a bidirectional Z-Source inverter

Z-Source inverter is a single-stage power converter capable of either stepping down or stepping up the input dc voltage while converting it to ac form. However, due to the presence of a diode in series with the input source, the power flow is limited to one direction, i.e. from the dc source to the ac side. However, for some energy storage applications such as ultracapacitor banks, battery banks etc., bidirectional power flow is essential for the operation. This can be achieved by connecting a transistor in parallel with the dc link diode for reverse conduction of current. This paper describes how such a bidirectional Z-Source inverter can be designed and controlled to facilitate power flow in both directions. The switching signal of this additional transistor is derived so that its presence would not affect the voltage buck/boost ratio. Design guidelines are presented in sizing the components and logic circuit used in generating switching signal of transistor is described. Computer simulations results are presented to verify the proper operation of the converter.