Rotation angle detection device, electric power steering device and method of controlling electric power steering device

A rotation angle detection device of a motor comprising:

• a sensor configured to output a sensor signal including a sine-wave signal and a cosine-wave signal in accordance with a directly measured amount of rotation of a motor rotation shaft of a motor;
• a sensor power supply unit configured to supply power to the sensor;
• a power control unit configured to control the sensor power supply unit to supply power to the sensor continually when a power switch is on and supply power to the sensor intermittently when the power switch is off;
• a sensor signal detection unit configured to detect a change in the sine-wave signal and a change in the cosine-wave signal;
• wherein
• the power control unit sets a drive interval for driving the sensor by providing power intermittently to the sensor to a first time interval when no change is detected in the sine-wave signal and the cosine-wave signal, sets to a second time interval that is shorter than the first time interval when a change in only one of the sine-wave signal and the cosine-wave signal is detected, and sets to a third time interval that is shorter than the second time interval when a change in one of the sine-wave signal and the cosine-wave signal is detected and then a change in the other is detected.