MICROTURBINES FOR POWER GENERATION

Microturbines For Power Generation

Microturbines for power generation

Introduction

This paper is performing a technology review to assess the market for commercially available power electronic generations that can be used to connect microturbines to either the electric grid or local loads. The intent of the review is to facilitate an assessment of the present status of marketed power conversion technology to determine how versatile the designs are for potentially providing different services to the grid based on changes in market direction, new industry standards, and the critical needs of the local service provider. The project includes data gathering efforts and documentation of the state-of-the-art design approaches that are being used by microturbine manufacturers in their power conversion electronics development and refinement.

This project task entails a review of power generations used in microturbines sized between 20 kW and 1 MW. The power generations permit microturbine generators, with their non-synchronous, high frequency output, to interface with the grid or local loads. The power generations produce 50- to 60-Hz power that can be used for local loads or, using interface electronics, synchronized for connection to the local feeder and/or microgrid. The power electronics enable operation in a stand-alone mode as a voltage source or in gridconnect mode as a current source. Some microturbines are designed to automatically switch between the two modes. The information obtained in this data gathering effort will provide a basis for determining how close the microturbine industry is to providing services such as voltage regulation, combined control of both voltage and current, fast/seamless mode transfers, enhanced reliability, reduced cost generations, reactive power supply, power quality, and other ancillary services. Some power quality improvements will require the addition of storage devices; therefore, the task should also determine what must be done to enable the power conversion circuits to accept a varying dc voltage source. The study will also look at technical issues pertaining to the interconnection and coordinated/compatible operation of multiple microturbines.

It is important to know today if modifications to provide improved operation and additional services will entail complete redesign, selected component changes, software modifications, or the addition of power storage devices. This project is designed to provide a strong technical foundation for determining present technical needs and identifying recommendations for future work.

Power Conversion Designs

This section considers the high-speed generator designs that are used in microturbine systems and the power electronics (i.e., power converter) that generally interface with the generators to develop the necessary 3-phase, line-frequency voltages.

Microturbine Generators

The highest efficiency operating speeds of microturbines tend to be quite high, often exceeding 100,000 rpm. The speeds are generally variable over a wide range (i.e., from 50,000 rpm to 120,000 rpm) to accommodate varying loads while maintaining both high efficiency and optimum long-term reliability. The microturbine drives a high-frequency generator that may be either synchronous or asynchronous (or non-synchronous). The caged rotor design in asynchronous (or induction) generators tends to make it a less-costly alternative to synchronous generators. Synchronous generators contain a magnetic rotor that is designed to use either ...