Design tips for a general purpose application PWM inverter based on a low cost microcontroller

PWM inverters for motor drive applications are quite complex due to the fact that both the amplitude and the frequency of the output voltage should be controlled. Furthermore, the control system is a key issue to achieve a good performance. However, inverters for general purpose applications can be much simpler because the frequency is constant (50 Hz / 60 Hz) and the amplitude can even have some voltage tolerance. It should be noted that most loads can perfectly deal with a 10% voltage swing. This paper presents a 1kW PWM inverter for general purpose applications which input is the automotive 12 V battery. The power system is based on a two stage scheme: the first stage is a dc-to-dc converter that boosts the voltage up to 325 V and provides galvanic isolation; the second stage is a full-bridge inverter driven by a very simple microcontroller operating in an open loop basis. Although there is only one analog control loop that regulates the DC link voltage, the performance of the system is very good and the sinusoidal output voltage can be used to power any general purpose application.