Electromechanical aspects of a uCHP system

Involved People
Marko Merdzan, M.Sc.PhD student
dr. A. BorisavljevicCo-promotor
Prof. dr. E.A. Lomonova, M.Sc.First promotor

In a Combined Heat and Power (CHP) system a heat engine is coupled with electrical generator with the goal of producing both electricity and useful heat. The micro-CHP system developed at Micro Turbine Technology BV combines a gas turbine with a very-high-speed generator so as to provide 3 kW of electrical power for homes and small enterprises. In order to make the CHP system cost-effective at such a low power, the efficiency of the thermal-to-electrical conversion needs to be raised beyond the state-of-the-art level.

The project is focused on performance of the electrical components of the system, particularly the high-speed generator and high-frequency converter. Analysis, modeling, improvements and tests of those components will be performed in order to maximize total efficiency of the electromechanical conversion within the micro-CHP system.

In order to make the CHP system cost-effective at such a low power (3 kW), the efficiency of the thermal-to-electrical conversion needs to be raised beyond the state-of-the-art level. This requires a very efficient generator and power electronics to convert the turbine mechanical power and feed it to the electricity grid. At the same time, the electromechanical design may not compromise the final investment cost of the system (low bill of material).

This research will focus on:

  • evaluation and enhancement of the component specifications, particularly with respect to the (PM) generator-inverter interaction;
  • loss and thermal modeling of electrical components;
  • tests - performance verification;
  • design improvements: new concepts for the high-efficiency energy conversion at high frequencies targeted for low-cost micro CHP applications;
  • inclusion of the electrical components in a functional prototype system.

Solutions for the generator and inverter of the micro CHP system are not readily available on the market. Efficient operation of the gas turbine imposes the demand for very high rotational speed of the generator – 240,000 rpm. The generator is required to produce more than 3 kW electric power in a reasonably small volume which would not compromise robustness, stability and efficiency of the system. A high-frequency power converter is required to enable bi-directional power flow between the generator and grid; the demand for sinusoidal currents brings about requirement for very high switching frequency in the converter (≥60 kHz).

The permanent magnet machine has been chosen as the generator type since this technology is the most promising for high-speed machines: it offers high efficiency and very high power density at low volumes. Further development work is needed to tailor the generator and converter to the micro CHP application. Particular attention is given to interaction between the generator and converter and their combined performance. To make the micro CHP system cost-effective, the overall efficiency is the major criterion for the system design however, the design may not compromise the final cost price of the system.