ELC

Advanced Electronic Load Controller with voltage and frequency Droop for parallel operation of micro-hydro generators

scheme

In rural places which don’t have access to grid electricity micro and pico hydropower plants are popular. In order to save cost such plants use Electronic Load Controllers (ELC) instead of conventional speed governor. Unlike conventional governors which reduce input water flow when consumer loads are decreased (to achieve power and frequency balance); ELCs function by dumping the excess electrical power into a dummy ballast load without changing input mechanical power. As the consumer load changes, it tends to change the generator frequency. ELC detects this change and then switches on dummy loads so as to make the net electrical load constant and equal to the constant mechanical power input. This results in constant power (and hence frequency) operation at all loading condition.

scheme

Traditional design of ELCs were isochronous (constant frequency) because they were operated in isolated mode. But recently, due to increased number of micro-hydro power plants in the rural areas of Nepal, possibility of parallel operation of two micro-hydro power plants have been arised. Parallel operation would be beneficial from the point of reliability and security. So, a new form of ELC that has provision for Voltage and frequency droop (in order to proportionally share reactive and active load power) needs to be designed to enable the parallel operation. This project aims to design such ELC with additional enhancement of using 2 dummy loads per phase instead of one dummy load per phase as in the traditional design. The benefits of using 2 dummy loads instead of one is the reduced harmonics during partial load condition. Since, the dummy load power is controlled by chaning firing angle of the thyrister, during partial load condition firing the thyrister near 90 degree introduces considerable harmonics. By employing two dummy loads, the problem can be reduced since, one of the dummy loads could be completely switched on/off and would be harmonics free. Since the dummy load power rating would be halfed when using two instead of one, the harmonics produced by the other thyrister switched dummy load would be only half as much as that would be produced when using single dummy load.

I am working on both the simulation/modelling of this new form of ELC and also on the hardware design side. I will keep posting more as we progress in the project.

Objectives:

Ø  To design an advanced electronic load controller with frequency droop

Ø  To operate two synchronous generator in parallel by using the advanced electronic load controller

Ø  To ensure proportional load sharing during the parallel operation

What’s new?
Conventional ELCs are run in isochronous mode, i.e. frequency is maintained constant for all loading condition. This made it impossible for two plants to operate in parallel. This project aims to implement frequency droop so that parallel operation would be possible. Also, this project aims to use two sets of dummy loads for each phase, thereby reducing harmonics and improving voltage quality.

A preliminary simulation was carried out to test whether employing frequency droop will result in successful parallel operation of generators.

layoutThe simulation was carried out with the following condition

conditionThe following graphs shows power transaction on the generator 1 side

result1The following graphs shows power transaction on the generator 2 side

result2The following plot of speed shows the droop characteristics, with the frequency changing with each change of the generator loading.

result3

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