基于两相三桥臂开关功放的电磁悬浮系统差动位移估计

Differential Displacement Estimation of Electromagnetic Levitation System Based on Two-Phase-Three-Arm Switching Power Amplifier

自传感电磁悬浮系统利用线圈电感电流与定、动子间气隙的函数关系估计动子位移信息,减少位移传感器的使用,具有成本低、可靠性好和集成度高的优点。该文针对传统单线圈电流纹波变化率检测法估计误差大、易受干扰的问题,基于两相三桥臂开关功率放大器的差动电流控制,建立了两相线圈电流纹波变化率检测的差动位移估计方法,提高了自传感控制精度。首先,阐述了两相三桥臂拓扑的工作原理和电流纹波的特性,明确了差动控制下电流纹波变化率与动子位移的函数关系,给出自传感差动位移估计的实现方法。然后,结合实验分析了线路电阻、偏置电流和母线电压等参数对电流纹波变化率的影响。最后,在单自由度电磁悬浮平衡梁实验平台上开展了自传感动态悬浮控制实验,验证了所提方法的有效性。

Electromagnetic levitation technology has been widely concerned and studied in recent years because of its excellent characteristics such as no friction,less maintenance,and adjustable dynamic characteristics.However,the integration,reliability,and cost of its system restrict the application and development of electromagnetic levitation technology.The appearance of displacement self-sensing has effectively solved the above problems.Because the traditional displacement self-sensing estimation method uses a single coil to estimate the displacement of the suspension according to the change rate of the current ripple,there are many problems,such as large displacement estimation error and easy to be disturbed by the external environment.Therefore,this paper proposes a displacement self-sensing detection method of an electromagnetic suspension system driven by a two-phase,three-leg switching power amplifier.The displacement of the suspension body is estimated by detecting the ripple change rate of the two-phase differential current.Compared with detecting single-phase current,it can effectively reduce the impacts of switching transients and noise on the accuracy of displacement estimation.The self-induced electromagnetic levitation of the mover is realized on a single degree of freedom rigid electromagnetic levitation experimental platform,which verifies the effectiveness of the proposed method.Firstly,the structure of the differential control system of a single degree for freedom electromagnetic suspension is introduced.Then,the topology of the two-phase,three-leg switching power amplifier is analyzed.Compared with the traditional full bridge switching power amplifier,the two-phase,three-leg switching power amplifier can reduce 1/4 switching devices while its basic functions and current ripple characteristics remain unchanged.It not only improves the integration of the circuit,but also reduces the number of PWM signals output by the controller and the number of driving circuits,which is conducive to the improvement of the overall integration of the system.Accordingly,the working principle and the modulation mode of the two-phase,three-leg switching power amplifier are introduced.This paper analyzes the self-sensing principle of the differential electromagnetic levitation system by modeling the single degree of freedom suspension.Through theoretical analysis and derivation,it is proved that the magnitude of the coil inductance is approximately linear with the mover displacement,and the relationship between the differential displacement and the current ripple change rate is obtained.Then,the current ripple characteristics of the two-phase,three-leg switching power amplifier are analyzed theoretically.It is verified that the amplitude of the current ripple is only related to the inductance of the coil under the condition that the bus voltage and the switching frequency are determined.Moreover,the method for measuring the change rate of the current ripple is feasible to realize the self-sensing of the mover displacement.The change rate of the two-phase current ripple is obtained by sampling the rising edge and the falling edge of the current ripple and using the least square method.In the derivation of differential displacement self-sensing theory,the influence of device and line internal resistance is neglected.The actual power device and the internal resistance of the line are affected by temperature and other factors,which will affect the detection results of the current ripple change rate.Therefore,the influence of loop internal resistance on the current ripple change rate under different bus voltage and current average values is analyzed.The linear relationship between the air gap size and the current ripple change rate is also analyzed.It can be seen from the analysis that the influence of the loop internal resistance change on the displacement estimation accuracy can be ignored in the actual application of the electromagnetic suspension system.The self-sensing dynamic suspension experiment was carried out on a single degree of freedom rigid electromagnetic suspension balance beam experimental platform.Experimental results show that the differential displacement estimation method based on detecting the current ripple changing rate of two-phase coils can significantly improve the accuracy of displacement estimation compared with the traditional displacement estimation method based on detecting the current ripple changing rate of a single coil.