Analysis of PWM Method for TFC (3L-NPC)

In modern power industry, one of the important stages of development is the development and implementation of decentralized gas turbine power plants with electrical equipment based on electric machine-valve complexes. One of the enterprises engaged in this activity is JSC «GT Energo», where the link between the generator with 6000 rpm and the power system is a thyristor frequency converter. Improvement of pulse width modulation (PWM) methods for controlling power converters is one of the most important tasks for power electronics. The purpose of this article is to analyze the existing PWM methods and to choose the most effective one based on the analysis performed. There are many methods that differ in the implementation and resulting power quality. Sinusoidal PWM as well as the method of 3 harmonics addition PWM (THIPWM) are used in the article. However, the total harmonic distortion (THD) is high when using these methods. The most effective methods are space vector PWM (SVPWM) and optimal pulse width modulation (OPM). Compared with carrier-based methods, the control strategy for selective elimination and mitigation of harmonics (SHEPWM and SHMPWM) leads to a significant improvement in the performance of converters.

I. Introduction

Manufacturing and implementation of distributed gas turbine electric power plants (GTPP) based on valve-engine complex is one of the most important stages of the development in modern electrical power industry. JTC «GT Energo» is one of the companies engaged in this activity. The company has an operating GTPP «Yekaterinburgskaya» (18 MW), which is a part of Sverdlovsk power system. GTPP is connected to the substation «Kalininskaya» 220/110/10 kV by the overhead line 110 kV. There are two electrical power units at the GTPP, namely GTE-009M and substation «UETM» 110/10/6 kV. The main subject of this research is thyristor frequency converter (TFC) which is the connecting link of the generation equipment. In this article different methods of PWM for grid-connected TFC are considered. TFC has a three-level Neutral Point Clamped (3L-NPC) topology which was first proposed in [1].