Influence of Control Strategy on Measured Actuator Power Consumption in an Energy Storage Flywheel with Magnetic Bearings

Minimizing power consumption is a key requirement in the system design of an energy storage flywheel. For magnetic bearing supported flywheels, synchronous power losses can be reduced by proper use of well-established control approaches. Analysis and test results of amplifier and actuator power consumption are presented for several different control schemes: 1) a baseline gain scheduled compensator, 2) an improved compensator with reduced stiffness in the operating range, and 3) the baseline compensator with adaptive open loop control set up to minimize the synchronous currents. To compare the impact of the control changes, power usage and rotor displacement measurements were made on an operating 2.0 kWh flywheel in 2,000 rpm increments from rest to 40,000 rpm. Power consumption was derived from direct measurement of coil currents, coil voltages, and amplifier supply currents using a high-speed digitizer (2 MHz sample rate).