Research On The Topology And Modulation Of High-frequency Link Auxiliary Power Supply Inverter

With the rapid development of urban rail transit and the improvement of living level, the loads on the city rail vehicle tend to be diversified and complicated, which leads to a more important role for auxiliary converter, requiring the auxiliary converter on the basis of high reliability to be more lightweight and densification. So it is imperative to explore new topology and modulation method. This paper mainly focuses on the exploration and analysis of the topological form and modulation method of auxiliary converter, and has obtained certain research results.Firstly, this paper points out the deficiency and development trend of the main auxiliary inverter topology on the urban rail vehicles, and makes exploration and analysis for high frequency chain topology. Combining with the requirements of burdening unbalanced load, withstanding high pressure and providing high power for auxiliary converter on city rail vehicle, this paper put forward a new three line four line full bridge high frequency inverter with pulse DC link. This new inverter adopts a intermediate tap type of high frequency isolation transformer, which avoids the adverse effects of traditional power frequency transformer and meets the demand of single phase load. And due to the use of less power switching devices and the removal of the intermediate DC link filter, the service life of the converter is prolonged, and the reliability and power density are increased. On the basis of theory mentioned before, this paper proposes two modulation methods:single-reference six-pulse width modulation(SRSPWM) method and compensated sinusoidal pulse width modulation (CSPWM) method.Before analyzing and verifying the performance of the two modulation methods, this paper explores a more fair and reliable mothed of analysising the modulation strategy, pointing out that the simulation can be used to analyze the switching sequence of the modulated phase voltage when the carrier frequency is less than 5kHz. And it also notes two kinds of design of output LC filter:based on the ripple voltage current method and the characteristic impedance method. In view of no intermediate DC filter in the topology, it chooses the latter. At last, through comparative analysis of advantages of simulation tools of MATLAB and PSIM, a joint simulation method is proposed. And the two sampling methods based on digital system(symmetric regular sampling and asymmetric regular sampling) are compared through theoretical analysis on Double Fourier analysis, and then the sampling method with smaller harmonic is adopted.Aiming at two kinds of modulation methods, this paper carries out a comprehensive analysis and simulation verification under different carrier ratio and modulation ratio. Output voltage under SRSPWM modulation method is compared adopting three-phase three wires system and three-phase four wires system with different carrier ratio and modulation ratio. It is concluded that when carrier frequencies of DC/HFDC and HFDC/LFAC are same, output voltage contains much low order harmonic, and the shape of output voltage is not sinusoidal waveform but saddle shaped waveform under three-phase four wires system. However, when compensated SPWM modulation method is adopted, DC/HFDC uses phase shift PWM control mode, leading to intermediate DC voltage containing some fixed zero portions. So it can put forward the corresponding compensation measures through comparing the mean value of phase voltage in a carrier cycle. Quality of output voltage without compensation and compensated is analyzed and verified under different carrier ratio and modulation ratio. Through Fourier analysis of zero zone, it is pointed that the size and position of zero zone have great influence on the phase voltage amplitude and harmonic spectrum. A modulation method rear carrier shift is extended, making the zero zone is distributed in the positive and negative parts of the phase voltage. By comparing with the compensated voltage quality, it proves its superiority.In order to verify the proposed topology and two modulation methods, a prototype platform of 30kVA is built. The experimental results show that the theory is correct.