| Bi-directional DC-DC converter, can realize energy transformation double-quadrant operation. On the occasion of the energy needs bi-directional flow, it can significantly reduce the size and weight as well as cost of the system. So it has a wide application prospects, for instance, electric vehicles, energy storage systems, distributed power generation, power quality regulation, renewable energy power generation and so on. However, in the bi-directional DC-DC converter, due to power devices work in ON-OFF state, which makes the circuit topology is no longer fixed, but changes with the switch state change. Therefore the bi-directional DC-DC converter is a typical hybrid system,switching linear system, which is made up of coupled discrete and continuous subsystems. Because the hybrid characteristic of the converter is neglected, traditional modeling and control methods have fatal limitations.This paper, first analyses the architecture of the bi-directional DC-DC converter, and according to the direction of energy flow, the operation mode of converter is divided into Buck mode and Boost mode. Then the mathematical model of converter is established based on Lagrange and Hamilton equations. After the establishment of model, switching linear system theory is employed to analyse the controllability and observability of the system, which establishes the theoretical basis for the control algorithms.Considering the hybrid characteristics of Bi-directional DC-DC converter, the hybrid automatons representing the Buck mode and Boost mode are obtained based on hybrid automaton theory. Then the process of control algorithm design is equivalent to the guard-selection problem of hybrid automaton. The guard conditions are selected based on a simple circuit therotical approach. The hybrid control algorithm is simulated in MATLAB/Stateflow simulation toolbox, and the results indicate that the proposed hybrid control algorithm has good performances.In the end of this paper, a bi-directional DC-DC converter prototype is built, and the practicality experiments are carried out on the prototype. And the experimental results indicate that the proposed hybrid control algorithm can cover the complete operating range of the converter (CCM and DCM ), and have good disturbance rejection ability for the load and input voltage step changes, besides the control strategy is simple, low computational complexity as well as easy for hardware implementation. |
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