Design of charging circuit for battery of wind turbine generator

(1) Circuit using a diode

The simplest circuit is to insert a diode between the wind turbine and the battery to achieve charging. The following figure a is the basic principle circuit, and the following figure b is the actual circuit using a three-phase wind turbine. When the wind speed increases, the windmill speed increases so that the generator output voltage is higher than the battery voltage, and the charging current flows into the battery. With this simple charging circuit, the output voltage is low when the wind speed is low, and the wind speed needs to increase to be able to charge. However, even if the wind speed reaches the requirement, the output voltage of the generator is clamped by the battery voltage, the load torque of the generator becomes larger, and the windmill speed is suppressed to a certain value, so it cannot work at the optimal load point and the efficiency is not high.

(2) Control circuit using DC-DC converter

The circuit is shown in the figure below. Inserting a DC-DC converter between the wind turbine and the battery can effectively cope with changes in wind speed and make the wind turbine work at the highest efficiency point.

(3) Obtaining maximum output from wind turbines

In the circuit shown above, the input characteristics of the load side from the generator side are shown in the figure below a. When the wind speed increases and the generator output voltage rises, and reaches the battery voltage (12V or 24V) and starts charging, the generator output voltage will be clamped to the battery voltage. At this time, the generator load torque increases sharply, and even if the wind is strong, the windmill speed is fixed at a certain value.

This just turns the generator into a current source and the battery works as a load.

Usually, when the wind speed is constant, the speed of the windmill can make the windmill produce the maximum torque, that is, the optimal speed. For example, the optimal load of a windmill with a diameter of 1.3m and an optimal speed ratio of 55 is shown in Figure b below. When the circuit shown in the figure above is not designed, the input characteristics of the generator side should meet the characteristics of Figure b below, so that the maximum output can be obtained at any wind speed.