Research on DSP-based Permanent Magnet Synchronous Motor Direct Torque Control System

Because PMSM has the characteristics of high power density, high efficiency, and high power factor, it has become more and more widely used in industrial, civilian, military, and other fields. The DTC abandons the decoupling control concept in vector control, removes the PWM control and current feedback links, and uses a specific stator flux orientation and space vector concept to observe the stator flux and current directly to observe the motor flux linkage in the stator coordinate system. The torque is compared with the given flux linkage and torque. The difference is adjusted by the hysteresis controller to obtain the corresponding control signal. Then the current flux linkage state is integrated to select the corresponding voltage space vector and the motor stator is directly controlled. Flux and torque for fast torque response and excellent control performance. For the permanent magnet synchronous motor direct torque control strategy, the theoretical basis is clarified, and the existing asynchronous motor DTC research results are used to select the table from the theory and the space voltage vector.

Table 1 When the counterclockwise operation of the inverter switching table flux chain 7 torque T flux chain vector area ~ VI represents the current flux area (), U said the selected voltage vector, which is the PMSMDTC control law.

In an actual digital control system, the flux linkage will often be in a small sector at the partition boundary, causing uncertainty in the choice of voltage vector. For this purpose, the voltage vector perpendicular to the partition boundary is selected on the partition boundary, and the correction table shown in Table 2 is obtained.

Table 2 The original switch correction table The torque of the stator flux linkage at the boundary of the flux chain is wide or 1 If the stator flux amplitude variation is 0.5% at the area boundary, the output electromagnetic torque variation can reach 10%. If you do not use Table 2 to correct the original switch table 1, the motor often does not start normally.

The input signal processing is to observe the stator flux and torque and detect the motor voltage and current. For PMSMDTC, starter motor needs to know the exact position of the rotor pole to determine the stator flux initial vector, and also need to use photoelectric encoding signal to calculate the motor speed to achieve speed closed-loop control. For this purpose, a processing circuit for input signals such as voltage, current, and photoelectric encoding is provided.

System protection circuit Because the PMSMDTC system has no current loop, the switch state of the inverter is directly controlled by means of discrete two-point adjustment (Ban-Bang control), and current shock may occur. Therefore, the overcurrent protection of the system must be perfected.

The over-current protection measures are implemented in three layers, followed by software, hardware, and IPM self protection, and their current protection values increase sequentially. Hardware over-current measurement and latch circuit as shown.

There are three fault signal sources in the protection system: three-phase motor over-current, DC bus over-current, and IPM fault signal. The three fault signals are processed to obtain a total alarm signal, which is respectively input to the DSP and the hardware protection circuit. To ensure that the protection function is achieved, after the zone boundary is corrected, good starting and starting characteristics are obtained.

The rotational speed (top) and torque (bottom) waveforms of the no-load starting of the motor show the stator flux vector locus during stable operation at 2000r/min, and have a circular characteristic. The torque response waveform obtained when the motor is switched between rotation speeds of 000r/min. 0 is the torque waveform obtained when the torque is between -5Nm and 5N*m, and the switching speed is open-loop.

It can be seen that the change time of the output torque of the motor from -5Nm to 5Nm is only 1ms, which shows that the rapid torque dynamic response effect can be obtained by adopting the PMSMDTC strategy.

6 Conclusions The differences between PMSMDTC and DTC are analyzed. For the errors in the selection of voltage vector on the stator flux linkage zone boundary, the PMSMDTC switch table is supplemented and optimized. Based on this, a set of control schemes and realizations are proposed. technology. Experimental results show that the proposed PMSMDTC scheme is practical and has good torque dynamic response performance.

... Factory 0 Torque Given Switching Speed (Top), Torque (Down) Waveform

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