Closed Loop Controlled Hybrid Boost Three Level DC-DC Converter with High Voltage Gain for PV Systems

To overcome the problem of mismatched voltage levels between parallel-connected low voltage photovoltaic (PV) arrays and the higher grid voltage, a hybrid boost three level dc-dc converter is developed based on three level inverter with the traditional single phase diode clamping. Only one inductor, two capacitors in series, and those power switches and diodes, which are easy to be integrated, are used for establish the topology with transformerless high voltage gain. The operation principle of the topology is analyzed, and then the pulse width modulation (PWM) control method is obtained according to the switching functions about the output pulse voltages of both half-bridges. Therefore, the converter can not only operate with high voltage gain, but also make the duty cycles of power switches closer to 0.5. A feedforward closed loop control operation is proposed such that even in varying input the converter is capable of giving a constant output. Finally an experimental is set up in the laboratory for open loop control operation. All experimental results verify the feasibility of the circuit and validity of the PWM control method.