DC/DC Step-Up Converters for Automotive Applications: a FPGA Based Approach

Abstract

One emerging application of power electronics is the driving of piezoelectric actuators. These actuators can be used for different kinds of application. They are employed for micro and nano positioning tasks as well as hydraulic or pneumatic valves, where they replace magnetic control elements. Piezoelectric actuators have some specific advantages such as high resolution of the displacement, excellent dynamic properties and energy consumption near to zero for static or quasi static operations. So, high performances, low emissions and less fuel consumption bring car designers to adopt new technologies in automotive systems. The use of piezoelectric actuators (used as injectors) allows less response time with respect to traditional magnetic actuators but requires high driving voltages in order to be driven in a smaller time. This is a big concern in automotive environment, where the battery voltage is still the main power source available. A switching amplifier for reactive loads generally consists of two components. A unidirectional DC/DC converter with a small input power loads and large buffer capacitor and, a second bidirectional DC/DC converter that controls the energy exchanged between the buffer capacitor and the reactive load. The requirements on the unidirectional DC/DC converter are few. It only needs to compensate the power losses of the two stages plus the energy dissipated in the actuator and the connected mechanical system. Second stage presents more problems, because it must be designed for full system power. Conventional DC/DC boost converter is not the best solution in piezoelectric based applications where high step-up ratio and high efficiency power conversion is required. The coupled inductor boost converter meets the demanding requirements of these applications, including high reliability, relative low cost, safe operation, minimal board space and high performance, therefore an excellent choice for interfacing the battery with the high voltage DCBUS used for piezoelectric actuator system. An FPGA based controller allows interleaving two phases reducing both peak primary current and output current ripple. Moreover, a quasi constant frequency hysteretic current control technique reduces EMI interferences and ensures control loop stability. A soft start sequence permits to limit average input current and guarantees start-up phase in a short time.