Control Approach Research For Inductive Coupled Boost / Buck Bidirectional DC-DC Converter

Bi-directional DC-DC converter can realize energy transformation double-quadrant operation, namely, the input and output voltage polarity doesn’t change, but the direction of the input and the output current can be changed according to the requirement of loads. On the occasion of requiring bi-directional energy flowing, it can significantly reduce the size and weight as well as cost of the system. So it has a wide application prospects, for instance, energy storage systems, communication stations, electric vehicles, distributed power generation, power quality regulation, renewable energy power generation and so on. Currently, domestic and foreign scholars have studied the bi-directional DC / DC converter topology and its control strategy.For the bi-directional DC-DC converter, due to power devices work at ON-OFF state, which makes the circuit topology change with the switch state. Bidirectional DC / DC converter is a kind of typical nonlinear system. The purpose(such as contradiction between dynamic performance and steady-state performance) of control can’t reach when applying linear control strategy to the converter and may result in deteriorated output signal or unstable behavior under the presence of large disturbance. So some nonlinear control methods are applied to DC-DC converter, such as optimal control、sliding mode control、fuzzy control. Sliding mode control, which have some advantages, such as fast dynamic response, robustness against uncertainties and simplicity of implementation, and is one of the most powerful robust control strategiesThe research object of this paper is bi-directional DC-DC converter. Firstly, several bidirectional DC-DC converter topologies are analyzed and compared. Combined with the application of small and medium power requirements(communication station, Electric vehicle with dual-power supplying), a novel inductive coupled Boost/buck bidirectional DC-DC converter is selected as the main circuit topology.Based on learned and studied the novel inductive coupled Boost/buck bidirectional DC-DC converter and the operation principle at step-up and step-down of this bidirectional DC-DC converter, verifying the feasibility of using the equivalent inductance to replace coupling inductance. The voltage gain, switch voltage, current stress and some related important performances parameters have been gotten, and this paper designs the related parameters of converter in control system. Establishing small-signal model and reducing order of this converter system, then giving a detailed description of the steady-state performance and dynamic performance for the system.For the shortcomings of the novel inductive coupled Boost/buck bidirectional DC-DC converter without robustness when operated at open loop, sliding mode control is presented which based on fixed-frequency equivalent control theory. This theory can complete closed-loop control of the output voltage. When the inductive coupled Boost/buck bidirectional DC-DC converter working at buck and boost state, analysis method and Rolls criterion are used to designed the controller coefficients, finally the controller which meets the design requirement is completedFinally, based on the theoretical research, simulations of the closed-loop control system of this novel inductive coupled Boost/buck bidirectional DC-DC converter are carried out through Matlab and results of simulations are given. And the traditional PID control method is compared with sliding mode. The simulation results show that the theoretical analysis is correct and the superiority of the designed controllers.