Stability of Static Power Inverters and Synchronous Reluctance Multimotor Systems

Ten to 100 kVA multimotor variable frequency inverter systems are generally unstable over part of their frequency range. Experimental results from dozens of tests made with single and multimotors, and with several inverters varying in capacity and output impedance, are presented. Aberrations in output shaft angular velocity is the measured variable. Both gain and phase measurements are made while controlled excitation signals are applied to the inverter system. Practical stability criteria for synchronous motors are presented. A system model is presented in block diagram form. Correlation of theory with previously published synchronous reluctance motor analyses is achieved.