Research On Spread Spectrum Modulation Techniques For Indirect Matrix Power Converters

The traditional modulation technique for an indirect matrix power converter (called indirect matrix converter) using regular PWM suffers from discrete and high harmonics at multiplies of the switching frequency in the power spectra of output voltages. These high harmonics can result in electromagnetic interference. The spread spectrum modulation technique of power converter is proposed to spread harmonics to a wider sideband, attenuate harmonic peaks by changing instants of switchings. This paper makes a presentation of spread spectrum schemes, methods and implementations for an indirect matrix converter.The basic schemes and implementation processes of spread spectrum modulation are explained. Using simulatuion, spectral characteristics of periodic and chaotic modulation signals and their hybrid modulation signals are analized. An experimental platform is established to measure and compare line voltage spectrum between periodic, chaotic and hybrid modulation where the triangular waves whose frequency is changed by logistic chaotic sequences is taken as hybrid modulation signals. The experimental results as the same as theoretical analyses verify that hybrid modulation singals not only to gain the ability to restrict spread-spectrum like periodic modulation signals, but also to obtain the advantage of reducing harmonic peaks like chaotic modulation signals.The indirect matrix converter with fixed carrier frequency has discrete and high peaks in the spectra of output line voltages. In this paper, a chaotic carrier frequency modulation technique is applied in indirect matrix converter to spread sideband range and suppress harmonic peaks. The spectra of output voltages are analyzed and ripples of input and output currents are also studied. However, the proposed technique will increase the difficulty of commutation. Thus, the rectifier in indirect matrix converter uses the PWM modulation containing zero vectors to extent zero current commutation time, and carrier and modulation waveforms are also properly chosen to simplify commutation processes. An experimental platform is designed and experimental results show that harmonics of line voltages are efficiently suppressed.In order to maintain carrier frequency, three carrier-based randomized pulse position modulation techniques are proposed for an indirect matrix converter. In the first scheme, to avoid commutation of rectifier stage at instants of carrier transition, one of four different pulse positions of rectifier stage is selected randomly based on Markov chain with a limited degree of freedom and poor spread spectrum but low commutation frequency. The second scheme randomly places the center of the pulse position with a larger degree of freedom, which has a lower harmonic spectrum but higher commutation frequency. The maximum degree of freedom is achieved in the third scheme, which randomly varies the pulse position by delaying its edge along entire carrier cycle, resulting in a continuous and flat harmonic spectrum, but the maximum commutation frequency in three proposed schemes. Effectiveness of the proposed techniques is validated through comparison with traditional carrier based modulation technique.To solve the problems that spread spectrum modulation techniques simply spread harmonic spectrum but are unable to change spectrum distribution with any purpose, a spectra distribution indirect manipulation technique is proposed on the basis of the predictive current control technique and is applied to manipulate output voltage spectrum for an indirect matrix converter. In this technique, the current errors weighted by a filter are taken as performance object to keep currents follow their references and to indirectly manipulate output voltage spectrum by selecting different filters. Comparing with predictive current control technique, the current waveform and voltage spectrum are improved by reducing low-frequency harmonics and eliminating periodic switching-frequency-related high harmonics. An experimental platform based on FPGA and DSP controllers is established to verify practical feasibility of the spectra distribution indirect manipulation technique.