Hybrid Wind Power Plant on Tonaki Island | Power Systems Headquarters

November, 2001

Hybrid Wind Power Plant on Tonaki Island

Developing a hybrid wind turbine generator system:
Isolated isles with their own small-scale independent power systems are mainly supplied with power by small-sized, diesel-engine generators. However, many of these isles are blessed with favorable wind conditions. It is significantly advantageous, therefore, for such an isolated isle to implement a wind power plant as compared to another on the mainland. The electric power generated from a wind power plant, however, varies greatly with wind fluctuation. As such, if a wind power plant should be implemented directly into a small-scale independent power system, the power will vary significantly in both line voltage and frequency. For this situation, a hybrid wind turbine generator system has been developed by combining a wind turbine power plant (hereinafter referred to as "wind plant") with batteries, so that power generated in a wind power plant may be controlled in coordination with a diesel-engine generator as much as possible to maintain electric power quality. Outlined below is the equipment delivered to Tonakishima Power Station in Okinawa.

A system block diagram of the hybrid power plant is shown in Fig. 1. In the power station equipped with a diesel-engine generator, a hybrid controller is installed to remotely monitor and operate the equipment, and to control it in coordination with the diesel-engine generator. The wind turbine generator equipment is provided with a battery and a DC link unit, which is used to control both wind plant and battery power.

The Hydroid DC Link Unit is used to covert the wind plant output to DC once in a PWM control type variable-speed converter employing the IGBT, with wind plant output taken for a switching element. And, it is further converted to an alternating current in a grid inverter. The DC link unit is provided with a battery charger and a discharger resistor.

Operation result
As shown in Fig. 2, the vane pitch control feature will release wind or will discharge the battery if the wind plant output should exceed a certain range. Thus, the diesel-engine generator is controlled from exceeding its operating range.

Tonaki Island (with an area of 3.46 square kilometers, a population of approximately 600 and a total power demand of approximately 120 thru 600 kW) has started running the system from around April 2001. Thus far, it has operated in good working service condition without causing any power failure. Fig. 3 shows the results of operating the hybrid equipment in a mode where the system output could be kept completely constant. The equipment delivered displayed a system input ratio (a ratio of wind plant output to power demand) of more than 50% on a short-time basis at a high wind velocity. It exceeded far more than 10%, which has been conventionally considered a wind plant’s limit.

Kyushu and Okinawa districts have many isolated islands with their own independent power supply systems. A hybrid wind plant system to stabilize line power is indispensable for the implementation of a wind plant in such isolated isles. From now forward, we would like to tackle the development of a system capable of supplying quality power at low cost, while incorporating state of the art technology such as various power storage units and so on.