Overmodulation

Abstract: The power output and the dynamic performance of pulse width modulation (PWM)-controlled AC motor drives can be improved by increasing the inverter output voltage through overmodulation. Two different solutions are proposed to increase the output voltage in a continuously controllable fashion up to the maximum possible value, which is reached in the six-step mode. The solutions differ in their approach. A space vector strategy is used for high dynamics performance high switching frequency drives, while a field-oriented PWM method is used for low switching frequency high power inverters. The methods are described and analyzed, and experimental results are presented. >

Abstract: In this paper, the overmodulation region voltage-gain characteristics and waveform quality of carrier-based pulsewidth-modulated (PWM) methods are investigated. Through detailed analytical study, voltage-gain characteristics are extracted independent of carrier frequency. The influence of blanking time and minimum pulsewidth (MPW) control on the inverter gain characteristics are studied and shown to be significant. A comparative evaluation of the modulator characteristics reveals the advantageous high-modulation-range characteristics of discontinuous PWM methods and, in particular, the superior overmodulation performance of a discontinuous PWM method. The modulation methods under consideration are tested on a PWM voltage-source inverter (VSI)-fed induction motor drive in the laboratory, and the theoretical results are verified by experiments. Also, a gain linearization technique is presented and experimentally verified. The results of this study are useful in the design, performance prediction and development of high-performance overmodulation strategies for PWM-VSI drives.

Abstract: This paper investigates the inherent damping characteristic of LCL- filters for three-phase grid-connected voltage source inverters. Specifically, it is found that when the converter-side current is used for implementing the feedback control, there will be an inherent damping term embedded in the control loop, which can neutralize the resonance introduced by LCL- filters. Theoretical analysis is then presented to suggest a general design guideline for choosing values of grid- and converter-side inductors, so that optimum damping can be naturally achieved by solely using converter current control, doing away with active damping, passive damping, or complex state observer. In cases where the design criterion is not fulfilled, the damping information contained in the converter current is extracted by a second-order notch filter, and then processed by a compensation gain to tune the system damping factor. The proposed compensation strategy requires no additional hardware and it will not cause an overmodulation problem due to its free of fundamental component. Both simulation and experimental results are finally provided to validate the theoretical findings developed in this paper.

Abstract: The power output and the dynamic performance of PWM (pulse width modulated) controlled AC motor drives can be improved by increasing the inverter output voltage through overmodulation. Two different solutions are proposed to increase the output voltage in a continuously controllable fashion up to maximum possible value, which is reached in the six-step mode. The solutions differ in their approaches. A space vector strategy is used for high dynamic performance, high switching frequency drives, while a field-oriented PWM method is used for low switching frequency, high power inverters. Experimental results are presented. >