Bhaskar Sen

A High-Fidelity and Computationally Efficient Model for Interior Permanent-Magnet Machines Considering the Magnetic Saturation, Spatial Harmonics, and Iron Loss Effect

Interior permanent-magnet (IPM) machines exhibit relatively large spatial harmonics in phase voltages and high nonlinearity in torque production due to both the presence of reluctance torque and the magnetic saturation in stator and rotor cores. To simulate the real electromagnetic behavior of IPM machines, this paper proposes a high-fidelity and computationally efficient machine model considering the magnetic saturation, the spatial harmonics, and the iron loss effect based on the inverse solution of the flux linkages extracted via finite-element analysis (FEA). Neither FEA nor a derivative computation is involved in the time-stepping simulation; thereby, the proposed model is computationally efficient and numerically robust. The high fidelity of the proposed machine model is validated by both the FEA and the experimental results.

Stator Interturn Fault Detection in Permanent-Magnet Machines Using PWM Ripple Current Measurement

This paper proposes a novel method of interturn fault detection based on measurement of pulsewidth modulation (PWM) ripple current. The method uses the ripple current generated by the switching inverter as a means to detect interturn fault. High-frequency (HF) impedance behavior of healthy and faulted windings is analyzed and modeled, and ripple current signature due to interturn faults is quantified. A simple analog circuit is designed to extract the PWM ripple current via a bandpass (BP) filter and a root-mean-square (RMS) detector for fault detection. In addition, this method can also identify the faulted phase, which can be used for fault mitigation strategies. The method is tested experimentally on a five-phase permanent-magnet (PM) machine drive.

Stationary Frame Fault-Tolerant Current Control of Polyphase Permanent-Magnet Machines Under Open-Circuit and Short-Circuit Faults

The paper presents a stationary frame control strategy to achieve optimal current control for star-connected polyphase permanent-magnet machine under asymmetric phase faults, namely, phase open circuit (OC) and phase short-circuit (SC) condition. Current regulation under these faults is particularly challenging because optimal torque control strategy generates nonsinusoidal current references with unbalance in both fundamental and higher order working harmonics, to achieve minimal copper losses and torque ripple under fault condition. Under field-weakening operation, voltage limit introduces additional control problems. The paper describes a solution for these control issues by employing a novel controller in stationary frame. This control strategy allows minimal reconfiguration of the control structure from healthy to postfault operation. Extensive simulation and experimental results are presented as validation for the proposed strategy.

Real-Time Hardware-in-the-Loop Simulation of Permanent-Magnet Synchronous Motor Drives Under Stator Faults

Hardware-in-the-loop (HIL) testing methods can facilitate the development of control strategies in a safe and inexpensive environment particularly when extreme operating conditions such as faults are considered. HIL methods rely on accurate real-time emulation of the equipment under investigation. However, no validated tools for real-time emulation of electrical drives under fault conditions are available. This paper describes the implementation of a high-fidelity real-time emulator of a permanent-magnet synchronous motor drive in a platform suitable for HIL tests. The emulator is capable of representing the drive operation under both healthy conditions and during interturn stator winding faults. Nonlinearities due to saturation, higher order harmonics, slotting effects, etc., are accounted for using four-dimensional look-up tables (LUTs) obtained by finite element analysis. The proposed model is computationally efficient and capable of running in real time in a field programmable gate array platform and is validated against simulations and experimental results in a wide range of operating conditions. Potential applications of the proposed emulation environment to the development of drive control, fault detection, and diagnostic algorithms are proposed.

A High-Fidelity Computationally Efficient Transient Model of Interior Permanent-Magnet Machine With Stator Turn Fault

An accurate transient model of interior permanent-magnet (IPM) machine with stator turn fault with due account of magnetic saturation is essential to develop robust and sensitive interturn fault detection algorithms and to evaluate drive controller performance and stability under fault conditions. This paper proposes a general method of modeling stator turn fault using flux linkage map of IPM machine under fault extracted from finite-element (FE) analysis. Simulation results from the proposed fault model are compared against FE and experimental results. The results show that the proposed model matches well with experimental data.

Current ripple reduction in 4kW LLC resonant converter based battery charger for electric vehicles

Electric vehicles rely on efficient charging techniques to maximize battery performance, efficiency and lifetime. Most EV on-board chargers are supplied from single phase AC mains, and contain 2nd order mains frequency harmonic in the battery current. This harmonic current incurs extra loss in the battery, increases battery temperature, and hence reduces charging efficiency and battery lifetime. Conventional battery charger controllers are unable to reject this harmonic current completely. This paper describes a resonant controller employed to suppress the low-frequency current ripple in an LLC resonant converter for EV battery chargers. A small-signal model of the LLC resonant converter based battery charging system has been established from time-domain simulations by injecting a small perturbation signal into the converter switching frequency. A resonant controller is subsequently designed and the closed-loop charger system performance is analyzed. The effectiveness of the proposed resonant controller on suppressing the harmonic current is assessed by extensive simulations and experimental tests.

A detailed transient model of Interior Permanent Magnet motor accounting for saturation under stator turn fault

The development of an accurate transient model of Interior Permanent Magnet (IPM) motor with stator turn fault with due account of magnetic saturation is essential to evaluate drive controller performance and stability under fault conditions, and to develop robust and sensitive inter-turn fault detection algorithms. The paper proposes a new semi-analytical model of IPM motor under stator winding inter-turn fault conditions. The model uses dq flux-linkage map of the healthy IPM motor derived from Finite Element (FE) model, and combines it with analytical equations of turn fault motor in the dq frame, to derive transient model for the motor with stator turn fault. Simulation results derived from the proposed fault model are compared against FE results of the turn faulted IPM motor. It is shown that the proposed model predicts with much better accuracy the peak currents and current wave shape when compared to the current state-of-art transient models.

PWM Ripple Currents Based Turn Fault Detection for Multiphase Permanent Magnet Machines

Most permanent magnet (PM) machines are driven by inverters with pulse-width modulation (PWM) voltages. The currents contain high-frequency (HF) components which are inversely proportional to machine inductance. The HF PWM ripple currents can be used to detect a turn fault that gives rise to changes in inductance. The features of these HF components under turn fault conditions are analyzed. A bandpass filter is designed to extract the selected sideband components, and their root-mean-square (rms) values are measured. The rms values in all phases are compared. It is shown that the rms ripple current ratios between two adjacent phases provide a very good means of detecting turn fault with high signal-to-noise ratio. The detection method can identify the faulted phase and tolerate inherent imbalance of the machine, and is hardly affected by transient states. The method is assessed by simulations and experiments on a five-phase PM machine.

Experimental Assessments of a Triple Redundant Nine-Phase Fault-Tolerant PMA SynRM Drive

Fault-tolerant machine drives are key enabling technologies in safety critical applications. The machine drives are expected to exhibit high performance in healthy conditions and accommodate as many faults as possible, namely open circuit or short circuit in the machine and inverter or even an interturn short circuit. This paper aims to assess a triple redundant nine-phase (3 × 3-phase) permanent magnet assisted synchronous reluctance machine (PMASynRM) drive by comprehensive experimental tests under both healthy and fault conditions on a 35 kW machine drive prototype. The healthy performance, fault behavior, fault detection, and mitigation strategy are presented and assessed by extensive tests which demonstrate that the machine drive exhibits high performance and excellent fault tolerance with simple and cost-effective implementation. Therefore, the proposed machine drive has proven to be a practical candidate for safety critical applications.

Active thermal management for Interior Permanent Magnet Synchronous Machine (IPMSM) drives

This paper proposes an active temperature management scheme for Interior Permanent Magnet Synchronous Machine (IPMSM) drives based on the model predictive control concept. The proposed control scheme can adaptively set torque limit based on thermal state of the machine in order to limit the machine winding and end-winding temperatures. A temperature feedback loop is also adopted to compensate the error in the machine thermal model. The proposed control scheme is assessed by experiments on a laboratory machine drive system and simulated for traction drives over World-wide harmonized Light duty Test Cycle (WLTC) cycles. Compared with conventional traction control scheme, the proposed scheme can effectively reduce peak temperature and hence thermal stress of the machine.