直流チョッパを用いたディジタル制御一軸吸引形磁気浮上装置の安定性

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The effects of chopping frequencies and sampling periods on the stability of a digitally-controlled magnetic suspension device using a DC chopper have been studied. The use of a DC chopper for controlling the magnetic coil current gives low loss and high-current control capability in comparison with the use of a conventional linear amplifier. Digital control enables the system to be more flexible and advanced than analog control. However, the DC chopper causes current ripple and control dead time, and the digital control system causes control delays due to computation time. These factors will affect the stability of the suspension device.First, we neglect the chopping operation and deduce a linearized state equation around the neighborhood of an equilibrium position, and then design an optimal regulator. Next, we consider the control delay and calculate the eigen values of the system. Further we take the ON/OFF operation of the chopper into consideration and neglect the control delay and then calculate the eigen values. The both calculations show that the two factors have relatively small effect on the stability when the sampling period is less than 7 ms. The experiment revealed that the major factor which makes the device unstable was the noise of the current feedback signal produced by the asynchronous operation of chopping and sampling. When the ripple is filtered out, the lower stable operation limit of the PWM frequencies is close to the theoretical values. As a result, the device is unstable regardless the chopping frequencies when the sampling period is very long. When the sampling period become shorter than 7 ms and at high PWM frequencies we can use a simplified model neglecting the control delay and the chopping operation. At lower PWM frequencies a model considering the control delay is effective when using a current filter.
社団法人電気学会の論文

直流チョッパを用いたディジタル制御一軸吸引形磁気浮上装置の安定性

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