Research On Interleaved Converters With Switched Capacitors And Inverter Parallel Control Strategy

Power electronics technology is one of the most widely used technologies in the 21st century. With the rapid development of modern science and technology, the performance and reliability requirements of the power electronics system increase. High-frequency and modularized power products has become the current trend because of the small size, less pollution, as well as easy maintenance and volume extension. Parallel and interleaving control technology have resulted in the replacement of the single converter of low-frequency and high-power with the high-frequency, low-power, modularized converter.Power electronics technology is also one of essential technologies to help solve the energy shortage and environmental pollution problems which are increasingly concerned about by the human beings. Because of its green, safe, renewable characteristics, the new renewable energy sources have received more and more concern. In order to realize and promote the application of the new renewable energy with low output voltage, high step-up DC/DC converter and inverter as the application of the high voltage DC bus have become the research focus. Interleaved DC/DC converter and inverter parallel control technology have become one of the most popular topic in the world because of their easy volume extension characteristic.Based on the analysis and the conclusion of the conventional interleaved flyback and forward converters, this paper put forward the thought that adding a series connected duty cycle controlled DC voltage source to the secondary side of the flyback transformer, which provide a new method to extend the voltage gain and auto-balance the input current of the converter. On the basis of this thought, an isolated and interleaved flyback-forward converter with the combination of flyback transformer and switched-capacitor is proposed. The converter makes full use of the forward characteristics of the transformer which reduces the magnetizing current and improves the utilization of the magnetizing core. The current auto-balancing characteristic is also realized because of the charge balance of the switched capacitor. In order to absorb the energy stored in the leakage inductance and restrain the turn-off voltage spike of the switches, active clamp strategy is adopted. The reverse recovery currents of the diodes are limited by the leakage inductances, so the efficiency of the converter is promoted. In order to improve the power density of the converter further, single switch clamping technique is also examined. The simulation and experiment results show that the isolated and interleaved flyback-forward Boost converter has high efficiency and good performance. The concept of flyback-forward based on switched capacitor provide a new practicable thought of the interleave DC/DC converter.As for the non-isolated application, based on the analysis of the traditional interleaved boost converter and boost converter with coupled inductors, this paper presents a non-isolated and interleaved combination boost converter with switched capacitor implemented by the duty cycle controlled DC voltage source concept. Due to the existence of the coupled inductors and the switched capacitors, the voltage gain of this converter is extended further and the voltage stress of the switch is alleviated. With the help of the switched capacitor, the transformer can not only be operated in coupled inductor mode, but also in forward mode. Therefore, the power level of the converter is improved. The charge balance of the switched capacitor realizes the current auto-balance characteristic of the converter, so the designing and the realization of the converter are simplified. In order to realize the close loop control of the proposed non-isolated and interleaved combination boost converter with switched capacitor, the small signal model is deduced with basic modeling method. Voltage-current-dual loop control strategy is used to implement the close loop control of the proposed converter. The simulation and the experiment results validate the model.In order to improve the reliability of the circuit, passive lossless clamp strategy is investigated. Based on the analysis of the high step-up lossless interleaved boost converter, this paper proposes a high step-up interleaved boost converter with passive lossless clamp circuit using the foregoing duty cycle controlled DC voltage source concept. With the structurally crossed diodes, this converter can not only realize the passive lossless clamp of the switches, but also has the current auto-sharing characteristic. In order to extend the voltage gain further, the clamp capacitor is replaced by switched capacitor. As a result, the passive lossless clamping interleaved boost converter with switched capacitor is proposed. With the replacement of the clamp capacitor with the switched capacitor, the voltage gain of this topology in increased and the voltage stress of the switch is alleviated. By adding additional two diodes into the passive lossless clamping interleaved boost converter with switched capacitor, the forward current route for the coupled inductor is obtained. Consequently, a new topology named passive lossless clamping interleaved combination boost converter is presented. Because of the forward mode, this converter achieves high power density and increased voltage gain.The purpose of the flyback-forward conception is to lift the low output voltage of the new renewable energy to the standard high voltage DC bus. As its application, the realization and the optimization of the parallel inverters technology is discussed in the fifth section of this paper. Based on the average current sharing strategy, the modeling, simulation and experiment of the parallel inverters are implemented. Subsequently, a new parallel control strategy named auto-master-slaver strategy is proposed. By encoding the on-line inverters, this strategy realizes the auto master/slave assignment and exchange of the on-line inverters. Therefore, the reliability of the parallel system is improved. In order to restrain the flux imbalance of the output transformer, the close loop compensation using primary voltage and current strategies are discussed. Based on this comparison, a new DC voltage feedback compensation circuit is proposed. This circuit can achieve the primary DC voltage component sampling and compensating with no additional auxiliary power and control circuit.