Comparison of zero-power controllers in double parallel magnetic suspension system with parallel connected coils

A basic single-degree-of-freedom magnetic suspension system consists of one floator, one electromagnet and one amplifier. For multi-degrees-of-freedom control, multiple electromagnets and multiple amplifiers are necessary, which increases the cost of total system. As a means of overcoming this problem, parallel magnetic suspension has been proposed where multiple floators are controlled with a single power amplifier. Parallel magnetic suspension systems are classified into two types according to the output of the power amplifier: current-controlled and voltage-controlled. Voltage-controlled parallel magnetic suspension systems are classified into two types: series connected and parallel connected. The feasibilities of these systems have been already demonstrated in the previous work. This paper focuses on the voltage-controlled parallel magnetic suspension system with parallel-connected coils. Three approaches to zero-power control are applicable in such a system. This paper compares these approaches in a viewpoint of pole assignment. In addition, a relationship in the feedback gains between the three approaches are presented numerically.