High performance disturbance observer based control system design for permanent magnet synchronous AC machine applications

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonAn electrical machine is one of the main workforces in different industries and serves them in various applications. Machine drive control design involves many technical issues for efficient and robust exploitation. Over several decades, Permanent Magnet Synchronous Motor (PMSM) is getting preferred for industrial applications over its counterpart Squirrel Cage Induction Motor (SCIM) drive, because of their higher efficiency, power density, and higher torque to inertia ratio. In the prospective that PMSM drives are considered the drives of the future, there are still technical challenges and issues related to PMSM control. Many studies have been devoted to PMSM control in the past, but there are still some open research areas that bring worldwide researchers’ interests back to PMSM drive control. One of the approaches that may facilitate better performance, higher efficiency, and robust and reliable work of the control system is the disturbance observer-based control (DOBC) with linear and nonlinear output feedback control for PM synchronous machine applications. DOBC is adopted due to its ability to reject external and internal disturbances with improving tracking performance in the variable speed wind energy conversion system (WECS) to maximize power extraction. The high order disturbance observer (HODO) is utilized to estimate the aerodynamic torque-based wind speed without the use of a traditional anemometer, which reduces the overall cost and improves the reliability of the whole system. Also, this method has been designed to improve the angular shaft speed tracking of the PMSM system under load torque disturbance and speed variations. The model-based linear and nonlinear feedback control are used in the proposed control systems. The sliding mode control (SMC) with switching output feedback control law and integral SMC with linear feedback and state-dependent Riccati equation (SDRE) based approaches have been designed for the systems. The SDRE control accounts for the nonlinear multivariable structure of the WECS and is approximated with Taylor series expansion terms. The chattering inherited from SMC is eliminated by the continuous approximation technique. The sliding mode is guaranteed by eliminating the reaching mode in the proposed integral SMC. The model-free cascaded linear feedback control system based on the proportional-integral (PI) controllers use a back-calculation algorithm anti-windup scheme. The proposed speed controllers are synthesized with HODO to compensate for the external disturbance, model uncertainty, noise, and modelling errors. Moreover, servomechanism-based SDRE control, a near-optimal control system is designed to suppress the model uncertainty and noise without the use of disturbance observers. The proposed control systems for PMSM speed regulation have demonstrated a significant improvement in the angular shaft speed-tracking performance at the transients. Their performances have been tested under speed, load torque variations, and model uncertainty. For example, HODO-based SMC with switching output feedback control law (SOFCL) has demonstrated improvement by more than 78% than the PI-PI control system of the PMSM. The performance of the HODOs-based Integral SMC with SDRE nonlinear feedback is improved by 80.5% under external disturbance, model uncertainty, and noise than Integral SMC with linear feedback in the WECS. The HODO-based SDRE control with servomechanism has shown an 80.2% improvement of mean absolute percentage error under disturbances than Integral SMC with linear feedback in the WECS. The PMSM speed tracking performance of the proposed HODO-based discrete-time PI-PI control system with back-calculation algorithm anti-windup scheme is improved by 87.29% and 90.2% in the speed commands and load torque disturbance variations scenarios respectively. The simulations for testing the proposed control system of the PMSM system and WECS have been implemented in Matlab/Simulink environment. The PMSM speed control experimental results have been obtained with Lucas-Nuelle DSP-based rapid control prototyping kit.Center for International Program “Bolashak” of the Ministry of Education and Science Republic of Kazakhsta

Fuzzy logic based online adaptation of current and speed controllers for improved performance of IPMSM drive

Precise torque and speed control of electric motors is a key issue in industries for variable speed drives (VSD). Over the years the induction motors have been widely utilized in industries for VSD applications. However, induction motor has some significant drawbacks like low efficiency, lagging power factor, asynchronous speed, low torque density etc. Nowadays the interior permanent magnet synchronous motor (IPMSM) is becoming popular for high performance variable speed drive (HPVSD) due to its high torque-current ratio, large power-weight ratio, high efficiency, high power factor, low noise and robustness as compared to conventional induction and other ac motors. Smooth torque response, fast and precise speed response, quick recovery of torque and speed from any disturbance and parameter insensitivity, robustness in variable speed domain and maintenance free operations are the main concerns for HPVSD. This work proposes a closed loop vector control of an IPMSM drive incorporating two separate fuzzy logic controllers (FLCs). Among them one FLC is designed. to minimize the developed torque ripple by varying online the hysteresis band of the PWM current controller. Another Sugeno type FLC is used to tune the gains of a proportional-integral (PI) controller where the PI controller actually serves as the primary speed controller. Thus, the limitations of traditional PI controllers will be avoided and the performance of the drive system can be improved. A flux controller is also incorporated in such a way that both torque and flux of the motor can be controlled while maintaining current and voltage constraints. The flux controller is designed based on maximum-torque- per-ampere (MTPA) operation below the rated speed and flux weakening operation above the rated speed. Thus, the proposed drive extends the operating speed limits for the motor and enables the effective use of the reluctance torque. In order to verify the performance of the proposed IPMSM drive, first a simulation model is developed using Matlab/Simulink. Then the complete IPMSM drive has been implemented in real-time using digital signal processor (DSP) controller board DS1104 for a laboratory 5 HP motor. The effectiveness of the proposed drive is verified both in simulation and experiment at different operating conditions. In this regard, a performance comparison of the proposed FLC based tuned PI and adapted hysteresis controllers based drive with the conventional PI and fixed bandwidth hysteresis controllers based drive is provided. These comparison results demonstrate the better dynamic response in torque and speed for the proposed IPMSM drive over a wide speed range

Advances in Rotating Electric Machines

It is difficult to imagine a modern society without rotating electric machines. Their use has been increasing not only in the traditional fields of application but also in more contemporary fields, including renewable energy conversion systems, electric aircraft, aerospace, electric vehicles, unmanned propulsion systems, robotics, etc. This has contributed to advances in the materials, design methodologies, modeling tools, and manufacturing processes of current electric machines, which are characterized by high compactness, low weight, high power density, high torque density, and high reliability. On the other hand, the growing use of electric machines and drives in more critical applications has pushed forward the research in the area of condition monitoring and fault tolerance, leading to the development of more reliable diagnostic techniques and more fault-tolerant machines. This book presents and disseminates the most recent advances related to the theory, design, modeling, application, control, and condition monitoring of all types of rotating electric machines

Fuzzy logic based efficiency optimization of IPM synchronous motor drive

Interior permanent magnet synchronous motor (IPMSM) is highly appreciated by researchers in variable speed drive applications due to some of its advantageous features such as small size, high power density, simple maintenance, high output torque, high power factor, low noise and robustness as compared to the conventional IM and other ac motors. Although these motor drives are well known for their relatively high efficiency, improvement margins still exist in their operating efficiency. Particularly, the reduction of power loss for IPMSM still remains a challenge for researchers. Improvement of motor drives efficiency is important not only from the viewpoints of energy loss and hence cost saving, but also from the perspective of environmental pollution. The thesis presents development of a fuzzy logic based efficiency and speed control system of an IPMSM drive. In order to maximize the efficiency in steady state operation while meeting the speed and load torque demands a search based fuzzy efficiency controller is designed to minimize the drive power losses to achieve higher efficiency by reducing the flux. The air gap flux level can be reduced by controlling the d-axis armature current as it is supplied by rotor permanent magnet. In order for the drive to track the reference speed in transient operation another fuzzy logic based controller is designed to increase the flux depending on the speed error and its derivative. The torque component of stator current (q-axis component of stator current) is generated by fuzzy logic based speed controller for different dynamic operation depending on speed error and its derivative. In this work a torque compensation algorithm is also introduced to reduce the torque and speed fluctuations

Efficiency Optimised Control of Interior Permanent Magnet Machine Drives in Electric Vehicle Applications

The thesis focuses on the losses minimisation of an interior permanent magnet synchronous machine (IPMSM) drive in electric vehicle applications. As drive losses are a combination of the IPMSM losses and the inverter losses, this thesis is mainly divided into two parts: the first part deals with minimising the copper and iron losses of the IPMSM with due account of machine parameters variations and the voltage drop across the stator winding resistance. A new losses minimisation algorithm (LMA) which considers these issues is presented in this research. A comprehensive off-line simulation study based on this LMA is performed in order to evaluate the effect of the parameters variations, resistive voltage drop and iron losses on the IPMSM optimal efficiency operation. It is shown that the parameters variations and resistive voltage drop should be included in the losses minimisation to achieve IPMSM optimal efficiency operation. On the other hand, the minimum losses operation points are not significantly affected by the utilised IPMSM iron losses. The proposed LMA is implemented with non-linear look-up tables (LUTs) using the current commands developed for both constant torque and field weakening operations. Good matching between the simulation and experimental results has been achieved. Reducing the inverter switching losses is the aim of the second part of this PhD research in addition to decrease the common mode voltage (CMV) which may lead to undesirable motor bearing current and electromagnetic interference. A comparative study between up-to-date PWM techniques for CMV reduction with the conventional space vector PWM (SVPWM technique) through simulation studies are presented. Due to its advantages on reducing both the switching losses and CMV of the inverter over all (αβ) voltage hexagon modulation regions, the LuPWM technique is selected for the tested IPMSM drive. Firstly, the scalar implementation of this LuPWM technique using the sine triangle waveform modulation technique on a simulation model of a resistor-inductor (R-L) inductive load is validated with sinusoidal current waveforms. However, implementation of the LuPWM in the closed loop control system of the tested IPMSM drive results in a considerable unexpected distortion in the phase current waveforms especially at low demanded torques. A study on this issue shows that due to the unavoidable ripples on the electrical angle position information leading to the malfunction on determining the (αβ) voltage hexagon sectors, the sector transition point of the LuPWM pulses especially when the state of the LuPWM pulse is changed between On-state and Off-state is strongly affected. Consequently, the current waveforms for a closed-loop drive system under the LuPWM technique during the sectors transition period become seriously distorted. In this thesis, the LuPWM current waveforms distortion problem is proposed to be addressed by modifying the pulse pattern of the traditional LuPWM technique around the (αβ) voltage hexagon sectors transition points associated with significant current waveforms distortion as aforementioned. Under this proposed PWM technique denoted as Mod-LuPWM technique, the switching state of each LuPWM pulse is suggested to be hold for an optimum small period around each transition period. Hence, the adverse effects of the angular ripple and the voltage error will be evened out between the “Turn-On” and “Turn-Off” transitions. Therefore, sinusoidal current waveforms can be obtained for closed-loop drive system under the proposed Mod-LuPWM. In addition, similar to the traditional LuPWM the Mod-LuPWM technique own the ability of on reducing the peak-to-peak common mode voltage value to one sixth of the DC-link voltage compared with the traditional PWMs. On the other hand, due to its switching characteristics, the switching losses of the drive system under the Mod-LuPWM technique are also reduced by one third during the switching period leading to an increase on the switching device life-time. Furthermore, as its implementation does not require any additional hardware, the proposed Mod-LuPWM can be employed for any existing drive system without any increase in the total drive cost. The proposed Mod-LuPWM has been validated with well-matched between simulation and experimental results showing significant current waveform improvements and considerable CMV reduction

Sensorless position estimation in fault-tolerant permanent magnet AC motor drives with redundancy.

Safety critical applications are heavily dependent on fault-tolerant motor drives being capable of continuing to operate satisfactorily under faults. This research utilizes a fault-tolerant PMAC motor drive with redundancy involving dual drives to provide parallel redundancy where each drive has electrically, magnetically, thermally and physically independent phases to improve its fault-tolerant capabilities. PMAC motor drives can offer high power and torque densities which are essential in high performance applications, for example, more-electric airplanes. In this thesis, two sensorless algorithms are proposed to estimate the rotor position in a fault-tolerant three-phase surface-mounted sinusoidal PMAC motor drive with redundancy under normal and faulted operating conditions. The key aims are to improve the reliability by eliminating the use of a position sensor which is one of major sources of failures, as well as by offering fault-tolerant position estimation. The algorithms utilize measurements of the winding currents and phase voltages, to compute flux linkage increments without integration, hence producing the predicted position values. Estimation errors due measurements are compensated for by a modified phase-locked loop technique which forces the predicted positions to track the flux linkage increments, finally generating the rotor position estimate. The fault-tolerant three-phase sensorless position estimation method utilizes the measured data from the three phase windings in each drive, consequently obtaining a total of two position estimates. However, the fault-tolerant two-phase sensorless position estimation method uses measurements from pairs of phases and produces three position estimates for each drive. Therefore, six position estimates are available in the dual drive system. In normal operation, all of these position estimates can be averaged to achieve a final rotor angle estimate in both schemes. Under faulted operating conditions, on the other hand, a final position estimate should be achieved by averaging position estimates obtained with measurements from healthy phases since unacceptable estimation errors can be created by making use of measured values from phases with failures. In order to validate the effectiveness of the proposed fault-tolerant sensorless position estimation schemes, the algorithms were tested using both simulated data and offline measured data from an experimental fault-tolerant PMAC motor drive system. In the healthy condition, both techniques presented good performance with acceptable accuracies under low and high steady-state speeds, starting from standstill and step load changes. In addition, they had robustness against parameter variations and measurement errors, as well as the ability to recover quickly from large incorrect initial position information. Under faulted operating conditions such as sensor failures, however, the two-phase sensorless method was more reliable than the threephase sensorless method since it could operate even with a faulty phase.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201

Novel Flux-weakening Control of Permanent Magnet Synchronous Machines with Particular Reference to Stability Issues

For many applications, such as electric vehicles and washing machines, flux-weakening control is required for permanent magnet synchronous machine (PMSM) drives to extend the operation speed range and maximize the power capability under the voltage and current constraints. Voltage magnitude feedback flux-weakening control is widely employed due to its advantages of simple and standard control structure, robustness against parameter variation, both linear and over modulation flux-weakening operation, and automatic flux-weakening operation. However, stability problems are prone to occur in the flux-weakening region since the PMSM drive will operate on the boundary of the voltage limit. In this thesis, based on a non-salient-pole PMSM, the factors that could cause stability problems in the flux-weakening region with voltage magnitude feedback flux-weakening control are investigated and the corresponding solutions are developed. Firstly, based on a d-axis current voltage feedback controller, an adaptive control parameter method is proposed for the PMSM machine without maximum torque per voltage (MTPV) region, which aims to ensure the stability in a wider speed range. Then, a current reference modifier (CRM) and a voltage limit reference modifier (VRM) are incorporated with the conventional voltage feedback controller in order to improve the stability in the over modulation region. As for the PMSM machine with MTPV region, an extra feedback controller is introduced with an MTPV penalty function. The MTPV penalty function is optimized in terms of its effect on the steady-state performance, the dynamic performance, and the stability in the MTPV region. Afterward, the MTPV controller is properly selected and designed. Furthermore, two flux-weakening control methods accounting for MTPV, i.e. dq-axis current based feedback flux-weakening control, and current amplitude and angle based feedback flux-weakening control, are developed and compared in terms of the stability. It shows that the two methods exhibit complimentary merits and demerits in different regions, and consequently, a hybrid feedback flux-weakening control is proposed to combine their synergies and overcome their demerits. As the feedback voltage ripples that origin from the non-ideal drive system can be amplified by a conventional speed PI controller, the oscillation may even occur if a good speed dynamics is required in the flux-weakening region. An adaptive fuzzy logic speed controller is proposed and implemented to reduce the feedback voltage ripples while maintaining good speed dynamics