Z-source inverter control for traction drive of fuel cell-battery hybrid vehicles

This paper presents a Fuel Cell Vehicle (FCV) control strategy using the Z-source inverter to control power from the fuel cell, power to the traction motor, and State of Charge (SOC) of the battery. The recently presented Z-source inverter is well suited for many applications, including FCVs. The Z-source inverter utilizes an exclusive Z-source (LC) network to link the main inverter circuit to the fuel cell (or any do power source). A new concept is revealed that substitutes a high voltage battery for one (or both) of the capacitors from the Z-source network. By controlling the shoot-through duty cycle we can control the battery voltage (thus controlling SOC) therefore there is no need for a separate dc-dc converter. By controlling the shoot-through duty cycle and modulation index we can produce any desired output ac voltage (thus there is no need for a dc-dc boost converter), regulate battery SOC, and control FC output power (or voltage) simultaneously. The Z-source inverter has the benefit of enhanced reliability due to the fact that momentary shoot-through can no longer destroy the inverter (i.e. both devices of a phase leg can be on for a significant period of time). These facts make the Z-source inverter highly desirable for use in hybrid electric vehicles, as the cost and complexity is greatly reduced when compared to traditional inverters. Although the Z-source inverter could be utilized in any HEV, this paper presents the control strategy and demonstrates these features for use in a FCV. These new concepts will be demonstrated by simulation and experimental results.