Higher rotational speeds for micro gas turbines

05. February 2015

High speeds are not only required in applications where a motor is used to drive a compressor, micromachining spindle or a mirror. More and more high-speed generators, with speeds of 300,000 rpm and beyond, are finding their way into gas turbines for stationary or mobile power generation, also called gas turbine generator systems.

Similar to other applications, these high-speed drives face various challenges:

  • The controller has to cope with various operating modes of the overall system, e.g. the generator system first has to be run up to a certain speed before power generation can be initiated, and it has to be shut down in a controlled fashion.
  • Damages due to overspeed or overvoltage have to be avoided by security functions.
  • The current has to be synchronized to the angle and the speed of the common shaft connecting the generator and gas turbine.
  • The drive electronics has to cope with sudden load changes, e.g. when a high power electrical load is connected or disconnected from the gas turbine generator system.

gas turbineFor all of these challenges Celeroton can offer an ideal solution. The different operating modes of the gas turbine can be controlled with our converters, e.g. CC-75-500. During start-up and ignition, both open-loop and closed-loop (sensorless) motor speed control is employed. For normal operation, our converter firmware allows the selection of speed control, torque control or power control modes, or even a combination of them. For shut down, speed control can be employed and the behaviour of the turbine can be monitored by using the measurements from the converter.

The sensorless control algorithm of our converter allows for an easy synchronization of the generator currents to the rotating common shaft which connects the generator and the gas turbine. Even flying starts can be handled, which is where the generator current is synchronized to a running gas turbine.

During the development phase of the gas turbine it is often desired to simulate and test load changes with an external electrical load attached to the generator. For this task, our chopper module CB-120-1500 offers the ideal solution. In combination with a Celeroton converter, the chopper module can be used to simulate and test various application settings such as constant power or constant speed operation. In addition, it can be used to test the generator standalone. When the chopper module is operated in combination with two converters, the system forms an ideal motor-generator test bench.

The chopper module CB-120-1500 is an electronic load with the following key features:

  • Allows the simultaneous connection of two converters for motor-generator test benches.
  • Allows power flow between the input and output as well as between both outputs, and it enables highly-dynamic voltage control for fast transient operation of the motor.
  • Offers a display for the visualization of the main operating parameters such as the input and output power, current, voltage, etc.

More information can be found here.

These technology features and Celeroton products have been applied in a micro gas turbine project that is being carried out by the Korea Institute of Machinery and Materials (KIMM). The researchers at KIMM state that “we are very glad to have Celeroton in our project as the supplier of the generator and electronics that runs the generator in motor mode at start-up of the gas turbine and then after synchronization switches to generator operation. Celeroton also provided us with an electronic load, which allows us to draw power out of the generator during development and testing of the gas turbine in our lab. The cooperation has been very beneficial for all parties involved. We are looking forward to continuing our successful cooperation with Celeroton in the future.”

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