Very simple converters may employ analogue electronics to provide the transistor gate or base control signals. In all other cases, the internal control of a modern converter is provided by a dedicated microprocessor or digital signal processor (DSP). By controlling the exact timing of transistor gate or base control signals, the microprocessor has control over the currents, voltages and power flow through the converter. The microprocessor will often be used to provide a number of other functions. In a grid – connected PV inverter, for example, the microprocessor will typically perform the maximum power point tracking (MPPT), anti-islanding protection and perhaps some diagnostics and communications.
Depending on the application, the microprocessor based control system in a modern converter may have a variety of control objectives. For example, in a standalone inverter, the objectives would be to keep the output at constant voltage and constant frequency; in a grid – connected PV inverter, the objective would be to achieve maximum power extraction as the solar radiation varies, a task that would require control of the inverter output current; and in a motor drive inverter, the objective might be to control the torque. The power electronic circuits used in all three of these examples could be very similar, but the implemented control systems make them behave very differently.
