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In this paper, the new closed-loop current harmonics compensation strategy is introduced in the switching-table-based direct torque control (ST-DTC) of dual three-phase permanent magnet synchronous machines (dual 3-ph PMSMs). The harmonic current distortion is the major problem of ST-DTC of multiphase machines and is typically caused by the lack of control in the auxiliary x-y subspace under the vector space decomposition model. The synthetic vectors to obtain average zero voltage in the x-y subspace can be a solution. However, this cannot compensate for current harmonics, for example, due to dead-time and backelectromotive force distortion, which are also mapped into the x-y subspace. Therefore, in this work the x-y voltage references are obtained by the closed control loop that controls x-y currents to zero. To modulate the non-zero x-y voltage reference, the new modulation approach employing voltage vector groups in x-y subspace together with the new switching table is developed and incorporated into ST-DTC. Meanwhile, the analysis of the two available sets of twelve voltage vector groups illustrates a trade-off between linear range in x-y subspace and the DC link voltage utilization rate. Finally, the effectiveness of the proposed ST-DTC strategy is verified through experiments and simulation.

A new rotor initial position estimation method for surface-mounted permanent magnet synchronous machines (SPMSM) is presented in this paper. The proposed method is based on the magnetic saturation effect and is suitable to prevent starting failure and reverse rotation. Compared with conventional methods, the proposed method shows better effective estimation performance. New strategies for utilizing current responses and voltage pulse injection process are developed. As a result, only three pulses are needed in total at no cost of extra sensors, while maintaining at least 30-degree estimation resolution at the same time. Moreover, a boundary detection strategy (BDS) is proposed to enhance the estimation performance regarding the impact of current measurement noises. Further, based on the BDS, a concept of ‘boundary width’ is proposed. By properly selecting the boundary width, the estimation resolution can be improved from 30 degrees to 15 degrees. Experimental results are given to verify the effectiveness of the proposed method.

This study proposes a generic mathematical modelling and decoupling fault‐tolerant vector control for dual three‐phase permanent magnet synchronous machine (PMSM) with one phase open based on the conventional dual three‐phase voltage source inverters, accounting for the mutual coupling between two sets of three‐phase windings and the second harmonic inductance. When the dual three‐phase PMSM has one phase open, the permanent flux‐linkages are asymmetric and there are second harmonic components in the conventional synchronous reference frame (dq‐frame). Based on the proposed mathematical modelling, both permanent magnet flux‐linkages and currents become DC values in the dq‐frame, and therefore, the conventional proportional integral (PI) controller can be used to regulate the dq‐axis currents. Then, a decoupling fault‐tolerant vector control with/without a dedicated feed‐forward compensation is proposed to validate the correctness of the proposed mathematical modelling. Experimental results on a prototype dual three‐phase PMSM with one phase open show that the second harmonic dq‐axis currents can be well suppressed simply by the conventional PI controller and dedicated feed‐forward compensation. It also shows that the decoupling fault‐tolerant control based on the proposed modelling and control method has excellent dynamic performance, which is equivalent to the vector space decomposition control for the healthy machine.

This article first proposes a generalized decomposition model for dual three-phase (3-ph) permanent magnet synchronous machines (PMSMs) with 0°, 30°, and 60° angle displacements between two sets of windings, allowing machines controlled in two-dimensional orthogonal αβ and xy subspaces. This model can decouple mutual inductances coupling phases from two sets, respectively. However, there often exist asymmetric impedances, due to inherent asymmetric machine parameters, cables with unequal lengths, manufacture tolerances, etc., in dual 3-ph PMSMs inevitably causing unbalanced phase currents and deteriorating the decoupling performance of the generalized machine model. Therefore, the generalized decomposition model incorporating asymmetric impedances is further developed, in which additional terms incurred by asymmetric impedances lead to the cross-coupling of αβ subspace and xy subspace. Through this model, the compensation capability of asymmetries is derived at a given dc link voltage. Then, a compensation strategy is illustrated to suppress unbalanced phase currents together with current harmonics caused by nonlinearities. Finally, experimental results testify the current balancing performance and simulation results further validate the machine model and the compensation capability.

In this article, a simple position error correction method is proposed to minimize the influence of parameter deviation on the model-based rotor position estimation, with the help of two sets of windings in a dual 3-phase permanent magnet synchronous machine (PMSM). In the proposed method, when each set of 3-phase windings is individually used for sensorless rotor position estimation, the nominal parameters that are set in each observer are identical but inaccurate, which leads to errors in the estimated rotor position from both observers. Since the error is varied according to the current level, small current pulses are injected respectively into d - or q -axis of one set (or both set) of 3-phase windings, which causes the difference between the rotor position estimation errors from two sets of 3-phase windings. This difference is subsequently used as the input of an updated controller to minimize the parameter deviation and the corresponding rotor position error. The proposed method is experimentally validated on a dual 3-phase PMSM system.

To eliminate the influence of parameter mismatch for fundamental model based sensorless methods, an effective online position error correction method is proposed for permanent magnet synchronous machines in this paper. Based on the derived position error mechanism, i.e. the error varies proportionally to the dq -axis currents, the proposed method injects a sinusoidal current signal with a small amplitude and low frequency into the $d$ - or $q$ -axis current for a short period. During injection, the corresponding sinusoidal response for current injection can be acquired from the estimated speed of the sensorless position observer. It is found that the amplitude of the response in the estimated speed decreases as the parameter mismatch reduces, and eventually reaches a minimum if there is no parameter mismatch. Thus, by applying the least mean square (LMS) algorithm, the amplitude of the response in the estimated speed can be minimised as the parameters are adaptively adjusted to the actual values, and then the position error can be corrected. The proposed method is validated through experiments on a permanent magnet generator drive system.

A new simple rotor initial position detection method for permanent magnet machines is proposed in this article. It is based on the magnetic saturation effect, which is commonly used by existing methods. Different from the conventional methods utilizing phase current or phase voltage sensors, the dc-link voltage sensor is used to estimate the rotor initial position. In the proposed method, a specific excitation approach is used to enhance the performance and a so-called “equivalent injection position” is developed to simplify the estimation process. The proposed method can achieve a 30° estimation resolution. Besides, practical considerations, including the dc-link voltage measurement errors, dc-link resistance, dc-link capacitance, and dc-link voltage ripples, are discussed in this article. A guideline of voltage pulse selection is presented to minimize the impact of these practical issues. Moreover, it is found that as the dc-link resistance increases, the proposed method shows a better estimation performance than the conventional methods. Besides, the proposed method is insensitive to sensor measurement errors. The experimental results are given to verify the effectiveness of the proposed method.

In the past, various fundamental model based sensorless control methods have been proposed. However, most of them are developed under a healthy condition. Hence, in this article, fundamental model based sensorless control of permanent magnet synchronous machines (PMSM) under rotor eccentricity (RE) is investigated which is a common issue in many drive systems. It is known that under RE, three-phase back-EMFs, flux-linkages, inductances, and torque will be influenced. Mathematical derivation reveals that these effects will cause undesired harmonics in the position estimation. Since the frequencies of these low-order harmonics are much smaller than the bandwidth of position observer such as phase-locked loop, it is difficult to effectively eliminate them. Hence, the conventional back-EMF method is modified by adding an adaptive notch filter to suppress these undesired harmonics. Furthermore, the RE effects on PMSM characteristics are examined by measurements. The modified position estimator is implemented on a dSPACE platform and is verified by experiment results.

Generalised predictive control (GPC) is known for its good dynamic performance and long prediction horizon, but the performance can be severely deteriorated when measurement noises exist due to the wide control bandwidth of GPC. Meanwhile, the unmodelled periodic disturbances can cause ripples to the output variables. In this study, a practical permanent magnet synchronous motor (PMSM) drive system with speed measurement noise and periodic disturbances is considered, for which a novel multivariable GPC method is proposed to achieve both good dynamic performance and speed ripple mitigation. The proposed method has a simple structure, since the traditional cascaded speed and current control loops are replaced by a non-cascaded one. To reject the measurement noise without jeopardising the system stability, an internal low-pass filter is embedded in the GPC. Meanwhile, external resonant loops are added to the GPC to mitigate the low-order speed ripples caused by the periodic disturbances. Furthermore, a deadbeat-based current constraint method is proposed to avoid overcurrent during transient processes. Theoretical stability analysis of the proposed method is presented. Experimental results show that the proposed method has good steady-state and dynamic performances, including measurement noise rejection and speed ripple mitigation.

For dual three-phase machines, vector space decomposition allows the control of fundamental and main harmonic components in αβ and xy subspaces, respectively. However, the modulation of voltage references in the two subspaces using the space vector pulsewidth modulation (SVPWM) is not independent but coupled. In that, voltage references of two subspaces cannot be modulated simultaneously beyond the modulation restraints, thereby distorting the voltage regulation and causing harmonics or even system misbehavior. Meanwhile, the fundamental voltage in αβ subspace responsible for electromagnetic torque generation should be prioritized and secured. Thus, this article proposes a systematic analysis of modulation restraints of three representative SVPWM techniques, i.e., the linear modulation range of xy subspace under an assured modulation index of the fundamental voltage. Voltage references of xy subspace within this range can be modulated successfully without affecting the assured modulation index and the margin left for harmonic control in xy subspace is then acknowledged. This can be used to limit the output of current controllers not to exceed the voltage modulation restraint, thereby avoiding the modulation failure. Finally, the experimental results validate the linear modulation range and demonstrate the modulation behaviors within and out of the linear modulation range.

Majority of sensorless control techniques is developed based on the healthy condition of permanent magnet synchronous machines (PMSMs). Therefore, the effect of static rotor eccentricity, one of the common issues, on saliency tracking based sensorless control of PMSM is analyzed in this paper. The static rotor eccentricity effect is studied based on two PMSMs with different slot/pole number combinations using finite element analysis (FEA). FEA results show that static rotor eccentricity can introduce three-phase inductance unbalance and change the inductance saliency. In this paper, a conventional pulsating signal injection sensorless control method is used for analysis. Mathematic derivation illustrates static rotor eccentricity can cause 2nd order harmonics in the position error due to three-phase inductance unbalance and influence the signal-to-noise ratio (SNR) of the position dependent signal due to saliency variation. These effects are examined by FEA based simulation model.

In this paper, an online rotor position error correction method is proposed to eliminate the impact of parameter mismatch in sensorless control of dual three-phase (DTP) permanent magnet synchronous machines (PMSMs). The position error production mechanism is firstly derived, i.e., the error changes with the trend of current variation when there is a parameter mismatch. Based on this mechanism, by injecting sinusoidal current signals into both sets of three-phase windings, the presence of parameter mismatch and its level can be revealed through the corresponding sinusoidal responses from the estimated speed of sensorless observers. Since the amplitudes of rotor position error responses decrease as the parameter mismatch level reduces, with the help of the least mean square (LMS) algorithm, the parameters can be adaptively adjusted to the actual values, and the position error can be thus corrected. Moreover, through a simple technique and with the extra freedom of DTP machines, the detrimental effects because of current signal injection can be eliminated. The proposed method has been validated through simulation and experimental results.

For sensorless control of surface‐mounted permanent magnet synchronous machines (SPMSMs), the major issue is in zero‐ and low‐speed ranges. Since back‐electromotive force (EMF) is proportional to speed, back‐EMF based methods fail at zero and low speed. A solution considering the starting process and low speed sensorless control is presented. A simplified fundamental model‐based method is proposed. Based on the simplified model, the measured stator currents in the stationary reference frame can be directly utilised for position estimation so that the sensorless control performance at low speed and starting is improved. Moreover, with the knowledge of rotor initial position sector information, a stable and reliable starting performance is achieved with the proposed method. The effectiveness of the proposed method is verified through experimental results.

Transverse flux permanent magnet (TFPM) machines are a potential candidate for direct-drive wind power application due to high torque and power densities. The operating principle of TFPM machines is firstly described with various topologies available in literature, with the placement of magnets as a criterion for the classification of TFPM machine topologies. This review includes characteristics, power factor improvement, cogging torque minimization, material consideration, modelling techniques, and scalability. Different wind turbine concepts with direct-drive machines, control techniques and power converter topologies are also considered in this paper.

This paper aims to improve the sensorless control performance for permanent-magnet synchronous machines (PMSMs) under resistance asymmetry. The improved sensorless method can eliminate the undesired 2nd order fluctuation in position and speed estimation with the help of sequence component extractor (SCE) while the DC offset position error caused by asymmetric resistance and temperature variation can be compensated by applying a novel pulse injection method. Experimental and simulation results are provided to validate the proposed methods.

For modular permanent magnet (PM) machines with overlapping (OLP) windings widely employed in wind power generation, the large torque ripple and long end winding are major issues. In order to solve these problems, PM machines with non-overlapping (NOLP) windings and redundant teeth for easy modularity are proposed in this paper. The comparative study between modular machines with these two kinds of windings is necessary and is the major focus of this paper. For the sake of clarity, two modular dual 3-phase machines with 42-slots/32-poles (42S/32P) and 192S/32P combinations are chosen as examples to show the differences in terms of machine performance. The proposed 42S/32P modular machine adopts NOLP winding, while the conventional 192S/32P one uses the OLP type. Based on the results, it is found that the modular machine with NOLP winding has comparable average torque and efficiency. In the meantime, much lower torque ripple exists for the proposed modular machine regardless of the current value. The shorter and simpler end windings are beneficial to manufacturability. Moreover, the proposed modular machine with NOLP winding will be more fault tolerant due to smaller mutual inductances between phases and larger d -axis inductance. Finally, the proposed 42S/32P modular machine is prototyped and the experiments validate the correctness of the analyses in this paper. Despite two specific examples being used, the conclusion should be generic and can be employed to modular machines with other slot and pole number combinations.

Dual three phase permanent magnet synchronous generators (dual 3-ph PMSGs) have been used as wind power generators increasingly. Lifetime is one of main concerns in wind power applications, especially in offshore farms due to their high maintenance cost. In particular, generator insulation plays a key role in determining lifetime of the overall system. Therefore, reduction of common mode voltage (CMV) through advanced switching pattern generation strategies will have a positive impact on the lifetime. In this paper, a vector selection strategy based on synthetic vector theory is proposed to reduce CMV of a dual 3-ph PMSGs drive system. This strategy is based on finite-set model predictive control (MPC) providing a modified finite voltage vector set which can maintain CMV at a low level. Meanwhile, it can significantly reduce harmonics and maintain a low switching frequency as well. After detailed explanation of this strategy, experimental results validate the performance.

Two modular dual 3-phase PM machines with 42-slots/32-poles (42S/32P) and 192S/32P combinations are compared to show the influence of winding configurations on modular machine performance. The proposed 42S/32P modular machine with redundant teeth for easy modularity adopts non-overlapping (NOLP) winding, while the conventional 192S/32P one uses overlapping (OLP) type. Based on the comparative study with two sets of winding operation, it can be found that two modular machines show similar torque performance with rated currents fed into windings. However, the slightly larger average torque is expected for the proposed modular machine with higher current. Moreover, the torque ripple of the proposed modular machine will not significantly vary with the current. The experiments validate the correctness of the analyses in this paper.

This paper proposes a phase correction strategy for the zero sequence back EMF based sensorless drive under current regulation control (viz., I/f control). The straightforward phase correction process based on the nearest principle might lead to false correction under different load conditions. The proposed strategy can achieve robust phase correction by injecting transitory high frequency (HF) signal into the stator winding to track the secondary saliency information without polarity identification. Then the estimation position angle, which can be inphase or π rad shifted to the real position angle, is used in tandem with the estimation position angle from zero sequence back EMF based sensorless method to deduce the required phase correction values which can be 0, 2/3π or 4/3π. The proposed strategy is suitable for zero sequence back EMF based sensorless drive with I/f startup. The transitory HF injection imposed during the transient switching process from I/f control to sensorless mode induces negligible audible noise due to the short injection duration. Hence, the proposed strategy keeps the merits of the conventional method and provides robust phase correction as well.

The performance evaluation of an adjustable space-vector (SV) PWM (SVPWM) strategy for open-winding (OW) permanent magnet synchronous machine (PMSM) (OW-PMSM) drives with common DC bus is presented. Different from modifying the conventional SVPWM algorithm, the proposed method is realized by reconstructing the voltage references for individual SVPWM module. No need of modification on a conventional SVPWM means that it can be easily implemented on the OW voltage source inverter based drive systems. It can be easily adjusted to generate matching common mode voltage (CMV) to compensate other zero sequence disturbances including zero sequence back EMF, zero sequence cross coupling voltages and inverter nonlinearities within OW-PMSM drive and consequently to achieve zero sequence current suppression capability. In the experimental evaluation, for the tested 3kW OW-PMSM containing 13% zero sequence back EMF, the proposed method typically achieves 8.51% higher DC bus voltage utilization and reduces 58.9% of the peak-to-peak value of the zero sequence circulating current when compared to the conventional phase shift based method.

Kinetic energy storage systems have considerable potential for use as peak power buffers in drive-trains for electric and hybrid vehicles, as a means of enhancing their performance and improving efficiency. The paper describes a flywheel system based around a cylindrical fibre composite rim, which is supported on magnetic bearings and incorporates an integral motor/generator. Particular consideration is given to minimising power losses, by appropriate choice of magnetic circuit design and magnetic materials, so as to obtain a high 'round-trip' efficiency and limit the temperature rise of the rim.

The robust control of active magnetic bearings, based on a linearised interval model, is considered. Through robust stability analysis, all the first-order robust stabilizing dynamical compensators for the interval system are obtained. Disturbance attenuation and minimum control effort are also addressed. The approach is applied to a high-speed flywheel supported by two active and two passive magnetic bearings. Simulation and experimental results both show that it is simple, effective, and robust.

The paper describes a design methodology for robust current-tracking control of active power filters using quantitative feedback theory (QFT). The design aim is to address system issues of power quality and power factor correction in a double-sided converter (rectifier/inverter combination) subject to parametric uncertainty, nonlinear dynamic behavior and exogenous disturbances. The paper includes simulation results to demonstrate the dynamic performance attributes afforded to the resulting closed-loop control system, and to verify the design procedure.