Transformer Control Experiment Results and Analysis

The experimental principle of voltage transformer control is shown in Figure 1.

By changing the power supply voltage of the inverter bridge, the current added to the motor winding is adjusted to achieve the purpose of controlling the motor current and speed. Because the power supply voltage range of the core chip MC33035 of the motor control is 10~30V, if the power supply voltage is adjusted to below 10V in the experiment (because the voltage of the original DC power supply is +28V, so the voltage transformation experiment will not exceed the upper limit of 30V), it is very likely to cause the low-voltage protection action of MC33035 or incorrect logic control, so that the experiment cannot be carried out normally, and even cause motor failure. Therefore, when conducting the voltage transformation control experiment, it is very necessary to power the MC33035 (including other control chips and devices) and the inverter bridge separately, use the original +28V DC power supply to power the MC33035, and the 0~30V voltage transformer to power the inverter bridge.
At the same time, in order to make the original current protection circuit still work, the two power supplies must be grounded.

After verifying that all functions of the control system are normal and the protection is effective, a high-speed voltage transformation experiment of 11000r/min was carried out on the magnetic suspension control moment gyro. The results are shown in Table 1.

The above experimental results are inconsistent with the conclusion of theoretical analysis that voltage conversion power supply can reduce losses. The reason drawn from the analysis is that the inverter bridge (MPM3003) and the controller (MC33035) are used to supply power separately, which may cause the driving signal voltage value of the P-channel MOSFET gate on the upper side of the inverter bridge to be higher than the supply voltage of its source, resulting in an increase in power consumption caused by the switching circuit. This increase in power consumption includes the increase in power consumption of the inverter itself and the commutation lag caused by it, which puts the motor in a non-optimal commutation state and increases the power consumption of the motor itself.

Based on the above analysis, an experimental scheme of jointly transforming the inverter bridge (MPM3003) and the controller (MC33035) is adopted to verify the correctness of the above analysis and the voltage matching problem of the control chip and the inverter chip. The principle is shown in Figure 2.

This solution only needs to change the power supply of the original analog control circuit to a 0-30V transformer power supply, and still use the phase-locked loop to automatically control the speed. In the experiment, it should be noted that the transformer range should be kept above the minimum operating voltage of the control chip (>10V). The waveforms of the phase voltage and phase current collected in the transformer experiment are shown in Figure 413, and the experimental data are shown in Table 2.

Figure 3 Motor phase voltage and phase current waveforms under different bus voltages

From the above waveforms and data, it can be seen that with the reduction of the supply voltage, the current pulsation amplitude in the motor winding is significantly reduced, and the power consumption of the motor at the same speed is significantly reduced (the power consumption is reduced by more than 40%), which is completely consistent with the previous theoretical analysis results, indicating that the loss caused by the PWM component in the motor body cannot be ignored, confirming the correctness of reducing the power consumption by reducing the current pulsation amplitude, and also verifying that the experimental results are indeed caused by the voltage matching problem of the control chip and the inverter chip.

Although the power consumption of the motor can be significantly reduced by the voltage control method, it also has very obvious defects in engineering applications: the engineering implementation of the voltage-controlled transformer is difficult (although the voltage-controlled transformer is feasible in engineering, in the special context of aerospace applications, this solution will inevitably increase the complexity of the system, reduce reliability and increase weight); reducing the supply voltage reduces the maximum speed of the motor while reducing the power consumption (although reducing the system supply voltage can reduce power consumption, as the supply voltage decreases, the maximum speed of the motor will also decrease, so it is not suitable for high-speed applications).