Gilbert Foo

A Sensor Fault Detection and Isolation Method in Interior Permanent-Magnet Synchronous Motor Drives Based on an Extended Kalman Filter

Interior permanent-magnet synchronous motors (IPMSMs) become attractive candidates in modern hybrid electric vehicles and industrial applications. Usually, to obtain good control performance, the electric drives of this kind of motor require one position, one dc link, and at least two current sensors. Failure of any of these sensors might lead to degraded system performance or even instability. As such, sensor fault resilient control becomes a very important issue in modern drive systems. This paper proposes a novel sensor fault detection and isolation algorithm based on an extended Kalman filter. It is robust to system random noise and efficient in real-time implementation. Moreover, the proposed algorithm is compact and can detect and isolate all the sensor faults for IPMSM drives. Thorough theoretical analysis is provided, and the effectiveness of the proposed approach is proven by extensive experimental results.

An Efficiency Optimization Scheme for Bidirectional Inductive Power Transfer Systems

Unidirectional inductive power transfer systems allow loads to consume power, while bidirectional inductive power transfer (BIPT) systems are more suitable for loads requiring two-way power flow such as vehicle to grid applications with electric vehicles. Many attempts have been made to improve the performance of BIPT systems. In a typical BIPT system, the output power is controlled using the pickup converter phase shift angle, while the primary converter regulates the input current. This paper proposes an optimized phase-shift modulation strategy to minimize the coil losses of a series-series compensated BIPT system. In addition, a comprehensive study on the impact of power converters on the overall efficiency of the system is also presented. A closed-loop controller is proposed to optimize the overall efficiency of the BIPT system. Theoretical results are presented in comparison to both simulations and measurements of a 0.5 kW prototype to show the benefits of the proposed concept. Results convincingly demonstrate the applicability of the proposed system offering high efficiency over a wide range of output power.

An Improved Robust Field-Weakeaning Algorithm for Direct-Torque-Controlled Synchronous-Reluctance-Motor Drives

This paper presents an improved field weakening (FW) algorithm for synchronous-reluctance-motor drives. The proposed algorithm is robust to the variations in the machine d- and q-axis inductances. The transition between the maximum torque per ampere, current and voltage limits, and the maximum torque per flux trajectories is smooth. The proposed technique is combined with the direct-torque-control method to attain a high performance drive in the FW region. Simulation and experimental results are supplemented to verify the effectiveness of the proposed approach.

Modeling and Sensorless Direct Torque and Flux Control of a Dual-Airgap Axial Flux Permanent-Magnet Machine With Field-Weakening Operation

This paper presents the modeling and motion-sensorless direct torque and flux control of a novel dual-airgap axial-flux permanent-magnet machine optimized for use in flywheel energy storage system (FESS) applications. Independent closed-loop torque and stator flux regulation are performed in the stator flux ( x-y) reference frame via two PI controllers. This facilitates fast torque dynamics, which is critical as far as energy charging/discharging in the FESS is concerned. As FESS applications demand high-speed operation, a new field-weakening algorithm is proposed in this paper. Flux weakening is achieved autonomously once the y-axis voltage exceeds the available inverter voltage. An inherently speed sensorless stator flux observer immune to stator resistance variations and dc-offset effects is also proposed for accurate flux and speed estimation. The proposed observer eliminates the rotary encoder, which in turn reduces the overall weight and cost of the system while improving its reliability. The effectiveness of the proposed control scheme has been verified by simulations and experiments on a machine prototype.

A Switching Control Strategy for Single- and Dual-Inductor Current-Fed Push–Pull Converters

A switching control strategy is proposed for single- and dual-inductor current-fed push-pull converters. The proposed switching control strategy can be used with both current-fed push-pull converters with an active voltage doubler rectifier, or active rectifier, in the secondary-side of the isolation transformer. The proposed switching control strategy makes turn-on and turn-off processes of the primary-side power switches zero-voltage switching and zero-current switching, respectively. The soft-switching operation of the single- and dual-inductor push-pull converters, with both types of active rectifier, is explained. Simulation and experimental results are provided to validate soft-switching operation of the current-fed push-pull converters with the proposed switching control strategy.

Cascaded multilevel converter based bidirectional inductive power transfer (BIPT) system

A typical low power IPT system employs an H-Bridge converter with a simple control strategy to generate a high frequency current from DC power supply. This paper proposes a cascaded multilevel converter for bidirectional IPT (BIPT) systems, which is suitable for low to medium power applications as well as for situations such as PV cells where several individual DC sources are to be utilized. A novel modulation strategy is proposed for the multilevel converter with the aim of minimizing switching losses. Series - Series (SS) compensation circuit is adopted for the IPT system and a mathematical model is presented to minimize the coil losses of the system under varying output power. Theoretical results presented in comparison to the simulations to demonstrate the applicability of the proposed concept and the validity of the developed model. The experimental results show the feasibility of the proposed phase shift modulation.

Constant Switching Frequency Based Direct Torque Control of Interior Permanent Magnet Synchronous Motors With Reduced Ripples and Fast Torque Dynamics

The conventional direct torque control (DTC) features control structure simplicity, fast dynamic response, and parameter robustness. Nevertheless, it suffers from the problems of variable switching frequency and large torque ripples. This paper presents a modified DTC algorithm for interior permanent magnet synchronous motor drives with fast torque dynamics and constant switching frequency. The aforementioned problems are alleviated by adding a PI torque regulator to autonomously alter the effective duty cycle of the applied voltage vector. As a result, a constant switching frequency and also reduced torque ripples are obtained while retaining the benefits of the classical DTC. In addition, the torque dynamic response is further improved by introducing a modified switching table during transient conditions. By incorporating the modified switching table, the torque dynamic response is superior to that of the classical DTC. Simulation and experiment results included confirm the effectiveness of the proposed method.

A Simple Duty Cycle Control Strategy to Reduce Torque Ripples and Improve Low-Speed Performance of a Three-Level Inverter Fed DTC IPMSM Drive

This paper presents a novel duty cycle-based direct torque control (DDTC) strategy for a three-level neutral point clamped inverter fed interior permanent magnet synchronous motor. DDTC methods proposed in the literature for three-level inverter fed DTC (3L-DTC) are complicated, parameter dependent, and pay little attention to inverter inherent switching constraints. In this paper, a simple yet robust duty ratio calculation method, which respects the inverter switching constraints, is proposed. Additionally, a novel switching strategy is adopted to minimize the effects of flux drooping phenomena seen in 3L-DTC drives during low-speed operations. The proposed 3L-DTC method is efficient in reducing both torque and flux ripples while operating at low switching frequencies. Therefore, it is suitable for medium-high power ac drives. Experimental results on a scaled down test rig and comparative analysis are provided to validate the effectiveness of the proposed strategy.

Evaluation of velocity servo performance of IMPSM drive under high-performance sensorless operation

This paper examines the accuracy and suitability of sensorless velocity estimation for application in a velocity servo system. Because of the magnetic saliency, the interior permanent magnet (TPM) motors have advantages of acting as their own position and velocity sensors, of course via estimators, over other more conventional AC machines with uniform airgap. The elimination of the position/speed sensor is also desirable as it reduces the overall cost while increasing its reliability. Instead, the rotor speed and position are estimated from the measured stator currents and voltages. Existing solutions can be broadly classified into open and closed-loop estimators and signal injection methods, exploiting the saliency property of the IPM motor. This paper provides an overview of these methods and highlights their strengths and weaknesses. Simulation and experimental results are included to supplement the discussion of this topic.

A Constant Switching Frequency-Based Direct Torque Control Method for Interior Permanent-Magnet Synchronous Motor Drives

Direct torque control (DTC) is known to be a promising candidate for interior permanent-magnet synchronous motor drives. It provides fast dynamic response and good immunity to parameter variations. However, except for its merits, DTC also suffers from two major problems of variable switching frequency and large torque ripples. Research proposals have been published to solve these problems. Nonetheless, most of the proposals present very complex control algorithms. This paper proposes a constant switching frequency-based DTC algorithm for IPMSM drives. It consists of only one PI regulator and one triangular-wave carrier. The proposed algorithm reduces the torque ripples to a noticeable extent. In-depth analysis and design guidelines of the proposed controller are given. Simulation and experiment results are provided to verify the effectiveness of the proposed method.