Prevent overcurrent faults in variable frequency speed control systems

The physical experiment was carried out on the two motors by physical experiments, and the experimental results were compared with the results of conventional motor experiments. The voltage type general-purpose inverter is used in the experiment, and the central processing unit has the conversion precision in place. The measuring instrument used in the conventional motor experiment is Yokogawa's power analyzer. In order to make the identification current reach the given value and prevent the overcurrent fault of the variable frequency speed control system, the current closed loop plus regulator method is used to control the current. When the voltage angle is set, the current sampling is started, and a point is sampled in one cycle, and each point is averaged, and the fundamental wave RMS and phase obtained by the Fourier transform are obtained. The value of the fundamental wave is then adjusted to the given value by the value adjusted by the regulator.

The motor parameters are identified by applying high and low frequency current excitation to the induction motor. The larger the frequency difference, the faster the algorithm converges. However, the influence of the dead zone is increased at low frequencies, so the frequency cannot be obtained too low. The low frequency in the experiment is taken as LQV. The current is sampled at one point in one cycle, so the required sampling rate is twice the current frequency, so the frequency at high frequency is also Can not be too high, the detection accuracy of the high frequency taken as the current in the experiment has a crucial influence on the identification accuracy. In order to fully utilize the accuracy, it is always desirable that the larger the current, the better the motor excitation is not saturated. At high frequency, the excitation branch impedance is larger, the current passing through is smaller, the current loop can be given larger, and the rated current of the motor is given in the experiment; at low frequencies, the excitation branch impedance is smaller, and the passing current is larger. Therefore, the current loop cannot be given too much, and the rated current of the motor is given in the experiment.

The induction motor parameters are identified based on the steady state model of the motor. The energization time needs to be longer. However, since the motor cannot be dissipated by the fan in the static state, the internal temperature rises and the resistance value becomes larger, and the temperature rise of the rotor is particularly serious. Therefore, a long power-on time will cause a resistance identification error, and even burn the motor in severe cases. In the experiment, when the absolute value of the error between the effective value of the current fundamental wave detected by the continuous cycle and the current loop reference value is less than, the circuit is considered to be in steady state, and the sum RMS and phase angle at this time are taken as the identification data.