Research On Control Strategy Of Piezoelectric Ceramic Transformerin High Voltage Stabilized Power Supply

As the piezoelectric ceramic transformer is flat, small and easy to be integrated, so it can help to reduce the overall size of the converter. Moreover, because it is highly-insulated and has no electromagnetic interference, and there are some other advantages which the wounded-rotor electromagnetic transformer does not have, so the research and application of piezoelectric ceramic transformer is getting more and more attention. However, due to the lack of simple and effective control method, the application of the piezoelectric ceramic transformer meets a lot of limitations. In this paper, a method based on two-stage cascade structure is proposed, and also a high voltage power supply is designed using this method.Here, a control method using fixed frequency and constant duty cycle combined with PWM control is applied, and it drives the piezoelectric transformer to work properly with fixed frequency and constant duty cycle and makes sure that the output voltage of the power supply is stable through PWM control loop. The control method which works with constant frequency and constant duty ratio makes the circuit easier to optimize. For this approach, a network composed of three switches working in the invert er mode is necessary at the input terminal of the piezoelectric ceramic transformer. Though it can steady the output voltage successfully, the circuit is working in a discontinuous state instead and the output voltage ripple is very large. Then the circuit is rectified in this paper, with a Buck circuit to adjust the output voltage, which fulfill the required value of output voltage ripple.Furthermore, a comparison is made among three kinds of common topologies including push-pull type topology, half bridge topology and E topology. And half bridge topology is chosen as the driv e circuit of the piezoelectric ceramic transformer. Then, the resonant process of the half bridge circuit and LC filter circuit is analyzed theoretically in detail, whose results are in agreement with the experiment’s. A deduction of requirements needed to achieve ZVS condition is carried out. Based on the results, dead time of the switches of half bridge topology is designed. Because the switching loss is reduced by soft switch, so the overall efficiency can be improved.According to the main topology proposed, a small signal model is built, and the system stability is met by the addition of the compensation network. In order to make the circuit work safely and reliably, the hardware circ uit is designed, including synchronous circuit, isolation circuit, reverse voltage sampling circuit, auxiliary power supply and over current protection. The synchronization of the front and rear circuits is realized through the synchronous circuit, and the interaction between the two stages is avoided.In this paper, the analysis in principle and the process of parameter design of high-voltage power supply using the piezoelectric ceramic transformer are given, and a power supply prototype of-3000 V is built. The result of the experiment above shows that the control method has stable output, linear regulated output voltage, zero-voltage switching and low output ripple. It meets all the requirements of the power index, and it has a very fabulous practical value.