Induction Motor Load

This section presents the experiments performed with the 2.2-kW IM drive described in Section 5.1. The controller parameters are shown in Table 4.3. The results were originally presented in [P7]. The stationary measurement results with nr = 800 rpm and Tload = 22 Nm are presented in Figures 5.11–5.12. Basically, the DMC and the IMC are identical with identical controller parameters. However, the same controller parameters lead to slightly different behaviour because of the different gain of the processes [Esk06], i.e. the converter prototypes have different voltage losses, as presented above with RL load [P7]. As above, the IMC waveforms are slightly more distorted than the DMC waveforms.

Figure 5.11 Experimental results of the DMC-supplied IM drive when n_r = 800 rpm and T_load = 22 Nm:

(a) supply voltage u_a and current i_a, (b) output voltage u_AB, (c) output current i_A, (d) spectrum of i_a, (e) spectrum of u_AB, (f) spectrum of i_A.

Figure 5.12 Experimental results of the IMC-supplied IM drive when n_r = 800 rpm and T_load = 22 Nm:

(a) supply voltage u_a and current i_a, (b) output voltage u_AB, (c) output current i_A, (d) spectrum of i_a, (e) spectrum of u_AB, (f) spectrum of i_A.

The dynamic situations with full load torque Tload of 22 Nm, presented in Figures 5.13–5.18 and originally in [P7], are speed reference step, speed reference ramp and acceleration using the field weakening, respectively. These dynamic results do not show any significant differences between the DMC and IMC. In addition, both prototypes operate as in the ideal simulations presented in Figures 4.19–4.21. Unlike the acceleration using field weakening with the IMC in [P1], the results here show that the field weakening works with both the DMC and the IMC [P7]. The reason for this is that different rotor resistance values are used in the flux model. The value of 1.8 Ω, used in [P1], describes the resistance of the cold rotor, which does not hold true long after start-up in practice. As presented in Table 4.2, the rotor resistance value of 2.16 Ω, used in [P7], describes the value of a warm machine but is too low with a hot

(a) (b) (c)

(a) (b) (c)

(d) (e) (f) (d) (e) (f)

Experimental Setup 73 machine. This shows clearly the importance of parameter tolerance with the flux model, and a more robust and complex model should be applied in commercial applications [Kaz02].

Figure 5.13 Measured speed reference step operation of the DMC when T_load = 22 Nm: (a) rotation speed n_r and its reference n_r,ref, (b) output/stator voltage references u_sx,ref and u_sy,ref, (c) output/stator current component isy and its reference isy,ref.

Figure 5.14 Measured speed reference step operation of the IMC when T_load = 22 Nm: (a) rotation speed n_r and its reference n_r,ref, (b) output/stator voltage references u_sx,ref and u_sy,ref, (c) output/stator current component i_sy and its reference i_sy,ref.

Figure 5.15 Measured speed reference ramp operation of the DMC when T_load = 22 Nm: (a) rotation speed n_r and its reference n_r,ref, (b) output/stator voltage references u_sx,ref and u_sy,ref, (c) output/stator current component i_sy and its reference i_sy,ref.

Figure 5.16 Measured speed reference ramp operation of the IMC when T_load = 22 Nm: (a) rotation speed n_r and its reference n_r,ref, (b) output/stator voltage references u_sx,ref and u_sy,ref, (c) output/stator current component i_sy and its reference i_sy,ref.

Figure 5.17 Measured field-weakening acceleration of the DMC when T_load = 22 Nm: (a) rotation speed n_r and its reference nr,ref, (b) output/stator voltage references usx,ref and usy,ref, (c) output/stator current components i_sx, i_sy and reference i_sy,ref.

Figure 5.18 Measured field-weakening acceleration of the IMC when T_load = 22 Nm: (a) rotation speed n_r and its reference n_r,ref, (b) output/stator voltage references u_sx,ref and u_sy,ref, (c) output/stator current components i_sx, i_sy and reference i_sy,ref.

(a) (b) (c)

(a) (b) (c)

(a) (b) (c)

(a) (b) (c)

(a) (b) (c)

(a) (b) (c)

5.4 Conclusion

The basics of prototype implementations and experimental test setups have been presented in this chapter. Experimental results of both prototypes with passive RL-type load have been presented to show that they operate as assumed. In addition, both prototypes have supplied the IM load in the same conditions as in the simulations presented in Chapter 4.

The main circuit implementations of the DMC and the IMC prototypes have been based on the basics presented in Chapter 2. To assure a reliable comparison, the prototypes have been implemented as identically as possible. Thus, the control software and the first part of the modulator logic are identical in both prototypes. Due to the different main circuits, the second part of the modulator logic implementations and the generation of the safe commutations are different in the prototypes. The structures of the modulator implementations have been based on the structures of the simulation models presented in Chapter 4. As in the simulations in Chapter 4, the modulation method used has been the CSVM with PLL-based synchronisation to the supply voltage, which has been presented in Chapter 3.

The prototypes have been tested in the laboratory and the experimental results show that they both produce sinusoidal supply currents and PWM output voltages, which do not contain significant frequency distortion. The experimental results have also shown that the DMC and the IMC are basically identical in practice but some differences also exist. With RL load, the DMC has had higher input-to-output voltage transfer ratio than the IMC. In addition, the IMC has produced slightly more distorted supply currents than the DMC. These differences have not been found in the simulations with ideal simulation models. Thus, the differences in the voltage transfer ratio and in the supply current distortion are caused by the non-ideal characteristics of real circuits, which are studied in Chapters 6 and 7.

In the experiments with the IM load, the control system in the DMC and the IMC has been the rotor-flux-oriented space vector control presented in Chapter 4. The same IM test bench and the same tachometer system have been used with both converters. In addition, the software implementations and the control parameters have been identical. The measurement results of stationary and dynamic operations of both converters have also been presented. The experimental results are in agreement with the simulation results presented in Chapter 4 and they verify again that the DMC and the IMC operate as assumed. However, the similar differences between the DMC and the IMC as in the experimental test with the RL load have also been found to occur in the experimental tests with the IM load.

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