Performance comparison and simulation of permanent magnet AC drives and parameter estimation techniques

This thesis presents research on common PWM switching strategies implemented with permanent magnet AC machine drives. This study also considers online parameter estimation techniques that can be implemented with such drives. Finally a new simulation model of the drive and tools for modelling the specific machine under test are presented. Initially the research focuses on comparisons of the performance parameters which are influenced by the differences in current control strategies. Bang-Bang, PI and SVPWM controllers are the three alternative switching strategies which are discussed and then evaluated. The results highlight the impact the strategy selection has on the phase current quality and hence the power output of the motor under test. PI and SVPWM are both strategies that utilise a fixed switching frequency and as a result exhibit larger power losses in the inverter stage of the drive system. Bang-Bang control is seen to exhibit greater power losses in terms of output power in the motor stage as a direct result of the poor quality phase current waveform generated. The experiments conducted allow for a thorough comparison of each strategy outlined. Techniques used to estimate the average phase voltage commanded under operation are presented in this thesis. Techniques for estimating phase voltage when operating the SVPWM technique on a wye connected machine is described, as are techniques for use with both PI and SVPWM control of a delta connected machine. This is based on published techniques that have been implemented for the PI wye connected case. The voltage estimation techniques are then used to estimate the flux linkage waveforms of the machine under test. Validation for this technique is sought through comparison of measurements with predictions made using commercially available finite element analysis tools; the measurements and predictions are shown to correlate to a significant degree. In search of validating the techniques against measurements made with calibrated measurement equipment – known to be reliable – the validation path results in subsequent techniques to be developed which estimate the average torque output of the machine under test. Torque measurements made using commercially available torque transducer equipment are compared with online estimates allowing for a validation of the voltage estimations. Using a new simulation environment – Portunus from Adapted Solutions – a modern permanent magnetic synchronous machine drive system has been modelled. Making use of a PMSM component developed by Dr Mircea Popescu of Motor Design Ltd, a model of the drive system is constructed by the addition of customised components of the controller technology and other drive system hardware. This includes a custom developed C++ model of the SPEED laboratory FCIV technology which is used to control the drive system used in this research. Use of standard Portunus logic components is also presented which effectively models the interface of the gate drive signals with the voltage inverter components of the drive system. Finally the thesis details the results of simulations modelling the comparison of the control strategies of chapter 2 and also the online estimation techniques of chapter 3. The simulation model’s inclusion of a dedicated machine component allows for effective tailoring of the system model on a per machine basis; this allows for a comparison of the results presented in the initial testing with the simulated equivalents. Such a comparison is also made between the results of the testing of the online torque estimation techniques and the simulated response of the estimation techniques. Strong correlation is shown between the results of the testing carried out in the early stages of the research using the drive system outlined in chapters 2 and 3 with the simulation results obtained using the model outlined in chapters 4 and 5