Deployed Setup and Experimental Validation

MTPA LUT T^*

Current Controller

PWM Modulator

Three-phase Inverter idq*

iabc

θ_el

dSPACE system FPGA

PMASR Motor Encoder

Motor

Figure 6.2: Torque control system block scheme.

Secondly, due to this introduction, the integrators inside the current controller need to be provided with a dedicated reset signal which need to be produced after the modulation is enabled. This aspect is achieved by the RST_CTR_INT signal, which is provided by the dSPACE system: when it is activated, the integrators states are set to 0. Furthermore, the computed sine and cosine values and the dq-frame voltages are added to the control system outputs since they are transmitted to the dSPACE system.

Thirdly, the encoder block, which implements the previously described counter based on the A, B, Z signals, is deployed. Its output, namely the electrical angle 𝜃𝑒𝑙, is given to the control system besides the dSPACE slaves manager.

Finally, the dSPACE slaves manager is accordingly modified: in particular, refer-ring to the implementation presented in Chapter 5, the FPGA modules receives the RST_CTR_INT signal on the third channel and transmits the dq-frame voltages to the dSPACE system. Moreover, the fourth channel is exploited to transmit the offset value for the encoder to the FPGA, whilst the sine and cosine values, the electrical angle computed by the encoder and the A, B, Z signals are provided to the dSPACE system.

With respect to the block scheme depicted in Figure 6.2, an important additional comment regards the motor mechanical load. In the following experiments, the setup depicted in Figure 6.4 is exploited. It is composed of the PMASR motor, namely the Motor Under Test (MUT), which is connected to a Driving Machine (DM), hence another electric motor, by means of a shaft on which a torque meter is placed. The two electric motors are driven by two different three-phase inverters. The actual electric motors setup is reported in Figure 6.5.

DC AC

DC AC Three-phase

Inverter

Motor Under Test

Driving Machine

MUT DM

T,ω

Three-phase Inverter Torque

Meter

Figure 6.4: Motor Under Test and Driving Machine block scheme.

The DM can be set to impose either a certain rotational speed or a specific load torque.

In a first experiment, the DM is exploited to impose a 500 rpm rotational speed. After that, the control system and the modulation are activated, the MTPA look-up table is used to provide the dq-frame reference currents values from the dSPACE system, the integral operations inside the current controller are enabled and the torque is measured by means of the torque meter. The performed test, whose result is depicted in Figure 6.6, consists of requesting a 10 Nm reference torque to the MUT and checking the correct regulation

MOTOR UNDER TEST

DRIVING MACHINE

TORQUE METER

Figure 6.5: Motor Under Test and Driving Machine setup.

by looking at the torque meter measurement on the oscilloscope. Since this is strongly affected by noisy oscillations, as can be seen from the instantaneous signal plot, the torque average value is computed considering the analyzed time interval. As reported, the average torque value is approximately equal to the wanted one. Then, the system response due to a torque variation is highlighted in Figure 6.7, by applying a reference torque step from 0 Nm to 5 Nm. Since also in this case the measurement is affected by noisy oscillations, a moving average filter is applied and the resulting waveform is plotted.

As can be seen, after the transient has elapsed, the wanted torque value is obtained.

Figure 6.6: Torque regulation oscilloscope waveforms.

Figure 6.7: Torque regulation after a reference step plot.

After that, an external speed control loop is added, as shown in Figure 6.8: the speed of the motor is compared with a reference value and the error between them is fed to a PI regulator which produces the reference torque value. Thus, through the dSPACE system, the user provides the wanted reference speed in this case instead of the reference torque, which is regulated accordingly depending on the speed error. Since the inertia of the tested PMASR motor is not known, the K_P and K_I gains values are manually tuned in order to achieve the wanted regulation [3]. The speed of the motor, in the implemented case, is obtained by exploiting the mechanical angle.

MTPA LUT T^* PI Regulator ω^*

ω

MTPA LUT

i_dq^* dSPACE system

Current Controller

PWM Modulator

Three-phase Inverter i_abc

θ_el

FPGA

PMASR Motor Encoder

Motor

Figure 6.8: Torque control system with external speed loop block scheme.

A second experiment is then performed by configuring the DM to impose a load torque independently of the shaft rotational speed: starting from a null value, the reference speed is set to 500 rpm and then back to 0 rpm. The result of this test is reported in Figure 6.9:

as shown, the motor speed is well regulated. After that, the reference speed is set to 500 rpm and the load torque is varied: this produces a change in the motor speed value. The

speed control reacts to this variation adjusting the reference torque value and the wanted speed is recovered. An example of this behavior is reported in Figure 6.10 where the response of the control system due to load torque variations is depicted.

0 1 2 3 4 5

0 100 200 300 400 500 600

Figure 6.9: Speed regulation plot.

0 1 2 3 4 5

0 100 200 300 400 500 600

Figure 6.10: Speed regulation after a load torque variation plot.