Search

Stator and rotor cores of interior permanent magnet (IPM) motors are usually saturated, and the saturation distribution and saturation depth vary with the stator current. Also, their rotor structures are complex; hence, the saturation cannot be accurately reflected by a saturation factor. These considerations lead to the existing equivalent air-gap length models of induction motors and inset permanent magnet (PM) motors no longer suitable for IPM motors. Therefore, based on the consideration of stator and rotor saturation, this article proposes the equivalent air-gap length model of IPM motors expressed by magnetic potentials on the stator inner surface and the rotor outer surface. The proposed equivalent air-gap length model can accurately reflect the influences of complex structure and severe saturation of IPM motors. Compared with the existing models, the proposed one is no longer uniquely determined by motor structure parameters; it is also a function of stator current and rotor position. Furthermore, the obtained equivalent air-gap length model is combined with the winding function and the modified winding function to solve the inductances under different stator currents and different rotor eccentricity states. Finally, the proposed method is verified by both finite element analysis (FEA) and experiments. [ABSTRACT FROM AUTHOR]

In this article, the rotor magnetic potential (RMP) model of spoke-type machines is proposed, which can accurately describe rotor surface magnetic potential distribution. No-load and load magnetic fields are calculated by using the proposed RMP model. In order to accurately establish and solve the RMP model, the magnetic field in the machine is divided into the $d$ -axis magnetic field and the $q$ -axis magnetic field. Then, corresponding $d$ - and $q$ -axis RMP models are proposed, which can consider the saturation of the bridge region and the dq-axis cross-coupling. The unknown parameters in $d$ - and $q$ -axis RMP models are then obtained using simple lumped magnetic circuit (LMC) models. Furthermore, the total RMP model can be obtained by superimposing the above $d$ - and $q$ -axis RMP models. The modeling process proposed in this article is intuitive and straightforward, and it has fewer variables to be solved. Moreover, the proposed method does not need to consider the change of the relative position between the stator and rotor caused by rotor rotation. Finally, the FEA is used to validate the validity of the proposed method. [ABSTRACT FROM AUTHOR]

Finite-control-set model predictive control is a promising candidate in torque control of permanent magnet synchronous machines due to its straightforward control structure and multiobjective optimization. In order to suppress torque ripples, the zero- or the nonzero-voltage vector is inserted within one sampling period. However, the total control period of two voltage vectors is restricted to the constant sampling period, which restricts the further improvement of reference tracking performance. To solve this problem, an enhanced two-vector-based model predictive flux control of permanent magnet synchronous machines is developed. In this method, the total control period of the active voltage vector and the zero-voltage vector is no more restricted. The control periods of both voltage vectors are flexibly modulated on the basis of the cost function minimization. Minimum torque ripples can be obtained without increasing switching losses. The simulation and experimental results verify that the proposed control strategy achieves enhanced steady-state performances while maintaining fast dynamic responses. [ABSTRACT FROM AUTHOR]

Fault-tolerant control is normally required to achieve continuous operation under postfault modes in some critical fields. Regarding the remedial strategy for open-end-winding permanent magnet synchronous machines (OW-PMSMs) in the case of open-phase fault, the typical way is to reconfigure the controller after the fault is detected. Different from those mainstream control strategies, which account for the postfault situations by reconfiguring controllers or modulators, the fault-tolerant predictive control strategy proposed in this article handles the asymmetry produced by open-phase fault in a different manner. By combining the predictive control strategy with an embedded vector-resonant control scheme, the proposed strategy can achieve effective regulation of OW-PMSMs in both pre- and postfault operations. Controller reconfiguration and switching between pre- and postfault control modes based on fault detections are thus avoided. Besides, with the rotor flux harmonics taken into account and benefiting from the proposed zero-sequence controller, the triple-frequency component in the zero-sequence current is successfully suppressed to reduce torque ripples while the fundamental-frequency component in the zero-sequence current is properly retained under postfault operations, which is required in order to obtain an uninterrupted rotating magnetic field after one phase is open circuited. Experimental validations are conducted to verify the effectiveness of the proposed strategy and its superiority over conventional voltage compensation methods. [ABSTRACT FROM AUTHOR]

Open-winding permanent magnet synchronous machines (OW-PMSMs) with a common dc bus have gained increasing research focus in recent years due to its advantages including multilevel modulation and flexible control capability. However, a low impedance zero-sequence electrical path exists in this type of configuration. Significant uncontrolled zero-sequence current will result in unexpected power losses, reduced efficiency, and undesired high-frequency torque ripples. The linear proportional resonant controller has been previously proved to be an effective solution to suppress the zero-sequence current. However, the zero-sequence current regulation performances will be degraded, even become unstable, when the switching to operating frequency ratio is reduced, i.e., when the switching frequency is decreased or the machine operating frequency is increased. This article addresses this issue using a discrete-time controller, which is designed based on virtual three-phase expansion. The exact closed-form hold-equivalent discrete model, including the zero-order hold characteristic and the control delay, of OW-PMSMs is derived. The zero-sequence components are expanded to virtual three phases and, then, converted to direct signals by means of reference frame transformation. A synchronous-frame state-space framework for OW-PMSMs is designed directly in the discrete-time domain, which can obtain improved control performances with decreased switching frequency and increased operating frequency. Relevant experimental validations and performance comparisons based on a 2.3-kW OW-PMSM setup is presented to confirm the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

This article introduces a method to achieve the variable action period (VAP) of voltage vector in the finite control set model predictive control (FCS-MPC). In the conventional FCS-MPC, the control behavior is limited since the action period of a voltage vector is normally fixed to the sampling period. This article aims to enhance the control performances by means of regulating the action period of selected voltage vectors, together with the selection of an optimal control action. A VAP-based predictive flux control strategy is thus proposed. The optimal voltage vector and its optimal action period are both obtained by means of a two-step cost function minimization. In this manner, the future states of the control objectives are taken into account in the construction of cost function. The action period for the selected voltage vectors is no longer fixed to the sampling period, which provides an additional control freedom to obtain improved reference tracking behaviors. Experimental validations and comparison studies demonstrate that enhanced steady-state performances as well as excellent dynamic behaviors can both be obtained with the proposed strategy adopted. [ABSTRACT FROM AUTHOR]

Open-end winding permanent magnet synchronous machines (OW-PMSMs) supplied by dual inverters have gained increasing research focus due to its advantages in multilevel modulation, flexible control capability, and enhanced fault-tolerant performance. Zero-sequence current is one of the most concerned issues when the common dc bus configuration is adopted. Feedback control of zero-sequence current has been previously proved to be an effective solution to suppress zero-sequence current. However, due to the existence of current measurement errors, dc disturbance and periodic disturbances will inevitably occur in zero-sequence current, which may result in obvious deteriorations of the suppression performance of zero-sequence current. Zero-sequence current circulates in the OW-PMSM, which will lead to unexpected power losses and reduced efficiency. In addition, current measurement errors also cause increased periodic disturbances in the torque and the rotor speed, resulting in torque ripples and speed fluctuations. To address these problems, the exact closed-form hold-equivalent model of OW-PMSMs is derived, and the specific periodic disturbances introduced by current measurement errors are analyzed. Subsequently, zero-sequence current controller and speed controller are designed with enhanced mitigation capability of periodic disturbances resulting from current measurement errors. Its effectiveness under different operation conditions is confirmed experimentally on a 2.3-kW OW-PMSM setup. [ABSTRACT FROM AUTHOR]

In the control of permanent magnet synchronous machines (PMSMs), predictive controllers have received considerable attention due to the enhanced dynamic responses. However, periodic disturbances caused by dead-time effects and sampling errors deteriorate the performances of PMSMs. In order to suppress periodic disturbances, one typical control structure is to adopt several corresponding resonant controllers connected in parallel with the main controller. Even though excellent steady-state performances can be obtained, coupling effects between reference tracking and periodic disturbance attenuation can be observed, leading to significant transient oscillations under the situation of a reference step change. In order to realize decoupling between reference tracking and disturbance attenuation, this paper proposes a dual-loop predictive control structure, in which the reference tracking is only determined by the primary predictive controller. Periodic disturbance attenuation is achieved through an embedded disturbance rejection loop. By applying the proposed controller, periodic disturbances are strongly attenuated while smooth and fast transient performances are simultaneously guaranteed. Furthermore, a wide range of low frequency harmonics can be successfully suppressed, including but not limited to the main periodic harmonics. The steady-state performance, dynamic responses, and robustness against parameter variations of the proposed controller are verified through experiments based on a 2.3-kW PMSM. [ABSTRACT FROM AUTHOR]

In this paper, an observer-based predictive vector-resonant current control strategy for permanent magnet synchronous machines is proposed, which can effectively improve system performance in case of disturbances caused by converter dead-time effect and model mismatch. Taking the external periodic, nonperiodic disturbances, and system delay into consideration, the system model in discrete-time domain is built. This model is then embedded with vector-resonant scheme with the aim of suppressing periodic disturbances resulting from converter dead-time effect and rotor flux harmonics. An extended-state observer is constructed in order to predict system behavior and to estimate the nonperiodic disturbances caused by parameter variations. The overall control law is then derived on basis of cost function minimization. With the proposed method adopted, the undesired anomalous peak around the resonant frequency in the frequency responses can be avoided. Moreover, enhanced transient performances and wider stability margin can also be obtained. The effectiveness and advantages of the proposed strategy are verified by frequency-domain analysis and comparative experimental studies. [ABSTRACT FROM AUTHOR]