Research For Control Method Of Brush-less DC Motor Using Bi-directional Quasi-Z-Source Converter In EV

In recent years, with the problem of environmental pollution and gradual depletion of fossil fuels, the application of traditional fuel vehicles is becoming more and more restricted. Pure electric vehicles(EV), with its cleanness, zero-emission and low noise advantages, have become an important study object in the transformation and upgrading of automobile industry. And brushless DC motor(BLDCM) which has the advantages of high power density, convenient control method, low price and so on, is more suitable for driving micro-electric car at this stage. However, just with single and simple function, the traditional brushless DC motor controller is unable to meet the complex driving demands in climbing, acceleration and speed above operation, because low battery voltage limits the motor speed and torque performance. The Z-source inverter, as a new single-stage and high efficiency power converter, with its unique buck-boost feature, has become one of the main research directions in pure electric power converter. In this paper, based on the Z-source inverter, square-wave and sine-wave control system of brushless DC motor are respectively studied. And on this basis, the flexible and smooth switching of operating mode is achieved,which effectively broadens the applications of the electric vehicle driving cycles.First, this paper analyses the quasi-Z-source inverter working principle and the BLDCM control methods. In view of single-way energy flow of Z-source inverter, it can not recycle the braking energy back to the voltage sources. This paper makes the quasi-Z-source inverter bi-directional by referring to bi-directional Z-source inverter, which makes it more suitable for electric vehicle applications.Then, based on the BLDCM traditional control method, a bi-directional quasi-Z-source square wave and a bi-directional quasi-Z-source sine wave BLDCM control method are proposed in this paper, which make the BLDCM control system have four working modes and six working states through the flexible switching of these two control methods. A way that switching to appropriate working mode according the advantages, disadvantages and its suitable applications has proposed in this paper to improve the performance of EV, which broadens EV applications effectively. Research associate with Z-source inverter are respectivly analysizd detailly, such as their work principle and conditions. Quasi-Z-source network parameter design methods are given in this paper respectively according to square-wave and sine-wave driving characteristic. Motor rotor angle estimation method of sine-wave driving is also given in this paper. The feasibility and superiority of using bi-directional quasi-Z-source inverter is verified through theoretical analysis and simulation experiments.Finally, a low power prototype has been built in this paper to verify the feasibility of the proposed control systems. With the practical requirements of electric vehicles, bi-directional Z-source square and sine wave experimental research are respectively tested on the test platform, realizing a flexible switch operating mode under different working conditions. Test results prove the effectiveness and the accuracy of the proposed system.