Yaguang Liu

Multilevel selective harmonic elimination PWM technique in series-connected voltage inverters

The selective harmonic elimination PWM (SHEPWM) method is systematically applied for the first time to multilevel series-connected voltage source PWM inverters. The method is implemented based on optimization techniques. The optimization starting point is obtained using a phase-shift harmonic suppression approach. Another less computationally demanding harmonic suppression technique, called a mirror surplus harmonic method, is proposed for five-level (double-cell) inverters. Theoretical results of both methods are verified by experiments and simulations for a double-cell inverter. Simulation results for a five-cell (11-level) inverter are also presented for the multilevel SHEPWM method.

Multilevel space vector PWM technique based on phase-shift harmonic suppression

A new multilevel space vector PWM technique is proposed for high power applications. The technique is developed for H-bridge series-connected multilevel inverters. A phase-shift between space vectors produced by power cells is used for harmonic suppression. As a result, hardware and software implementation is greatly simplified. The phase-shift concept has been verified by simulations and experiments with a two-cell (five-level) series-connected voltage inverter with a space vector PWM. The proposed technique can be easily extended to higher level inverters.

Multiphase operation of switched reluctance motor drives

Previous work on switched reluctance motors (SRMs) have dealt largely with singly excited phases. Where doubly excited phases have been used, either for torque production or position detection, the mutual coupling and effects of mutual saturation have been neglected. This paper demonstrates that these effects can produce erroneous results. Some fundamental relationships for torque production during multiphase operation are determined, and applied to an 8-6 SRM.

A startup control algorithm for the split-link converter for a switched reluctance motor drive

This letter analyzes and presents the motor startup problem when a split-link converter is used for switched reluctance motor drives. A new control algorithm to solve this problem is presented in this paper, as well as the calculation of the split-link capacitance required during normal operation.

Improved torque performance of switched reluctance Machines by reducing the mutual saturation effect

Switched reluctance machines (SRMs) are normally designed to operate in the saturated region, and phase currents have some overlap to achieve better output torque performance. This results in mutual saturation effects. These effects are analyzed in detail in this paper. The experimental results show the influence of both the magnitude and direction of the leading phase current and the influence of the trailing phase current on the flux linkage of the working phase. In addition, the effect of the mutual saturation on the output torque is also demonstrated. It shows that a change of the phase winding connections can increase the output torque.

Optimal surplus harmonic distribution in selected harmonic elimination PWM technique for multilevel inverters

A concept of optimal surplus harmonics distribution in the selective harmonic elimination PWM technique for multilevel inverters is introduced in this paper. There are several performance indexes that can be optimized in PWM inverters, e.g., distortion factor, current or voltage total harmonic distortion or efficiency. Minimization of magnetic noise is selected as an example here. Several methods of alleviating the magnetic noise problems in PWM inverters, like harmonic decentralization and random PWM modulation, have been given in literature but only for three-level (single-cell) inverters. Numerical difficulties associated with a solution of PWM harmonic elimination equations for multilevel systems are overcome by using a nonconstrained optimization. Simulation and experimental results are presented for a double-cell series-connected voltage source PWM inverter. The theoretical and experimental results are in a very good agreement.

A novel switched reluctance motor drive with optical graphical programming technology

Due to its magnetic nonlinearities, SRM drive control is complicated and normally requires a microprocessor or a DSP. This paper presents a simple and reliable SRM drive using an innovative encoder based on optical graphical programming technology. There is no microprocessor in the drive, no A/D or D/A circuitry, with a drive system that matches the simplicity of the motor construction. It features a simple and effective control capability. Current waveform optimization for the encoder is carried out offline, for high efficiency and programmed directly into the encoder. Experimental results validate the concept.