Modified Cross Feedback Control for a Magnetically Suspended Flywheel Rotor with Significant Gyroscopic Effects

For magnetically suspended rigid rotors (MSRs) with significant gyroscopic effects, phase lag of the control channel is the main factor influencing the system nutation stability and decoupling performance. At first, this paper proves that the phase lag of the cross channel instead of the decentralized channel is often the main factor influencing the system nutation stability at high speeds. Then a modified cross feedback control strategy based on the phase compensation of cross channel is proposed to improve the stability and decoupling performances. The common issues associated with the traditional control methods have been successfully resolved by this method. Analysis, simulation, and experimental results are presented to demonstrate the feasibility and superiority of the proposed control method. 1. Introduction High speed flywheel systems are being widely employed in power industry, aerospace, transportation, military applications, and so on, which show promise as an alternative to energy storage and attitude control for spacecraft, such as storage energy flywheels, reaction wheels, and momentum flywheels in control moment gyroscopes [1–3]. With the advance of high performance magnetic bearings, a magnetically suspended flywheel (MSFW) is becoming an exciting alternative to the traditional mechanical flywheel due to its inherent superior features such as contact-free operation, small noise, and adjustable damping and stiffness as well as the potential for low vibration and super high rotational speeds [4–7]. To maximize the energy storage capacity, the magnetically suspended rotor (MSR) is often designed as a plot structure [8]. In this case, the gyroscopic effects are especially significant, which puts a challenging issue on the high-stability and high-precision control of the system. Recently the demand for higher power density and efficiency has led to more significant gyroscopic effects and higher operating speed, making the stability control more difficult [9, 10]. Over the years, considerable research has been conducted to resolve the gyroscopic effects, and various approaches have been proposed. Ahrens et al. [11] proposed decentralized PID plus speed cross feedback control approach to attain this goal. Although this method is relatively simple to implement, it inevitably introduces noise amplification due to derivative operation. Brown et al. [12] further presented the filtered cross-axis proportional gains method, which not only can greatly improve the stability of the gyroscopic modes, but also can effectively avoid excessive noise