Showing papers by "Pragasen Pillay published in 2020"

Mathematical Model of an Interior PMSM With Aligned Magnet and Reluctance Torques

Abstract: Mathematical modeling of a machine allows a better understanding, and it gives insight on the effect of each variable on the machine dynamics. This article develops the mathematical model of a novel shifted interior permanent magnet synchronous machine (IPMSM) with aligned magnet and reluctance torques. It is a new class of IPMSM where the flux barrier is modified in such a way that the relative positions of the magnet and reluctance axes shift from their regular positions. The angle of shift between the axes is designed such that the magnet and reluctance torques in the machine have their maximum values at the same torque angle. In order to validate the developed mathematical model, a prototype motor is built. This article also presents experimental tests to obtain the parameters of the prototype machine in the developed model, and the model is verified by comparing the torque–angle and torque–speed characteristics obtained using the model with the experimental results obtained on the prototype machine.

Space Vector Based Capacitor Voltage Balancing for a Three-Level NPC Traction Inverter Drive

Abstract: A dc-link capacitor voltage balancing topology based on virtual space vector is proposed for traction drive application in the field-weakening region. Four different strategies are implemented and their duty ratios are individually derived. The system is then connected to an interior permanent magnet synchronous machine (IPMSM) generally used for traction applications. A comprehensive investigation on the capacitor voltage variation in the field-weakening region is studied and the main contributing vectors are identified. All the required duty cycles of the vectors are analytically calculated based on the three nearest available voltage vectors. All the four proposed strategies helped to minimize the neutral point potential fluctuation (NPPF) considerably in comparison to the earlier proposed schemes. The proposed scheme is then supported by the simulation and experimental verification with a 6.0-kW IPMSM.

Fault-Tolerant Cooperative Control in a Wind Farm Using Adaptive Control Reconfiguration and Control Reallocation

Abstract: High reliability and availability are crucial for cost-effective operation of any wind farm. In this regard, effective schemes for fault detection, diagnosis and accommodation need to be developed to improve the reliability and availability of wind turbines and consequently wind farms (groups of wind turbines). Addressing this issue in a wind farm, this paper proposes a novel fault-tolerant cooperative control scheme based on an adaptive control reconfiguration approach that is augmented with an innovative control reallocation mechanism in a cooperative framework. Applied to a wind farm, this scheme tackles the effects of power loss faults in wind turbines, whether mild (due to mild icing or debris build-up on rotor blades) or severe (due to heavy icing). Different simulations on a wind farm benchmark model indicate the high effectiveness of the proposed scheme.

Induction Machine Parameters Determination and the Impact of Stator/Rotor Leakage Split Ratio on Its Performance

Abstract: The relationship between the stator and rotor leakage reactance of the induction machine (IM) according to IEEE Std 112 is assumed to be constant under all operating conditions. However, this is not substantially accurate during severe transients such as the direct online startup and loading conditions of a three-phase induction motor. The leakage reactance of the machine can vary widely during severe conditions. Hence, using constant parameters in the machine model will result in an inaccurate dynamic performance prediction. Moreover, considering a constant ratio between the stator and rotor leakage reactance is no longer valid for all current levels. In this article, a direct and precise method is proposed to estimate and separate the stator and rotor leakage reactance parameters under normal operating conditions and when the core is deeply saturated. The method exploits the two-dimensional time-stepping finite-element method (FEM) with a coupled circuit. The obtained current-dependent reactance functions in both leakage flux paths are included in the dq -model of the IM. Other machine parameters are determined by implementing the standard tests in FEM. To verify the effectiveness of the proposed method, the predicted results are compared to the dynamic responses obtained experimentally from a three-phase, 5-hp squirrel cage IM.

Automated Current Control Method for Flux-Linkage Measurement of Synchronous Reluctance Machines

Abstract: This article presents a novel approach to the dc standstill measurement of flux linkage and inductance of a synchronous reluctance machine. In the existing standstill test to measure the flux linkage of a machine, a pulsed voltage is applied to the machine in open loop. The flux-linkage characteristics are computed using the measured response. This article discusses the limitations of the voltage pulse-based method, and a current control based method is proposed to overcome these limitations. In the proposed method, a pulsed current in closed loop is applied to the machine at standstill (shaft locked). The major benefit is that the time response of the machine can be modified by properly tuning the controller parameters such that the number of measurement samples available during the transient is improved. Thus, the measurement process can be programmed in a real-time processor to automate the measurement process. The automation leads to bypassing the recording and offline processing of huge datasets. This article also proposes a method to automatically tune the current controllers required in the measurement process. The proposed method is verified by an experiment performed on a 7.5-hp machine.

Induction Machine Emulation under Asymmetric Grid Faults

Abstract: Machine emulation is the concept of developing a virtual machine in real time with power-hardware-in-the-loop (PHIL) technology. This process of emulation allows testing the variable speed drive or drive inverter or the performance of grid without using a real machine. In this paper, the machine emulated is a three-phase induction motor (IM) fed from the grid. The common asymmetric-grid faults namely unbalanced voltages, line-to-line (L-L) and line-to-neutral (L-N) faults are applied at the input terminals of a virtual induction machine. The main contribution of this paper is a detailed analysis of machine’s asymmetric fault behavior and its cause by mathematical derivations and simulations for the process of imitation by a virtual machine. This is being done by corresponding step by step improvement in emulator controller design. The experimental results with the emulator are validated with a real machine and also with Matlab simulation to prove the dynamic performance and accuracy of the proposed novel emulator.

Effect of Skewing in a Variable Flux Interior Permanent Magnet Synchronous Machine

Abstract: The motivation of this article is to minimize the cogging torque and the torque ripple in a 6-pole 27-slot variable flux interior permanent magnet synchronous machine (VF IPMSM) by skewing the permanent magnets (PMs) in several steps. AlNiCo9 is used as the PM material in the rotor as the magnetization level of the AlNiCo9 PM can be changed and controlled by proper current control. The optimum skewing angles to minimize the cogging torque are found analytically and verified by using the finite-element analysis (FEA). The effect of these skewing angles on the back electromotive force and the torque ripple is also studied at different magnetization levels of the AlNiCo9 magnets. An FEA shows that a step skewed PM pole significantly minimizes the cogging torque and the torque ripple in the VF IPMSM. A current pulse in the d -axis is applied to magnetize or demagnetize each step in the step skewed PM pole. The minimum optimum skewing angle is chosen such that each step of the step skewed PM pole is magnetized or demagnetized with minimum nonuniformity.

Design of an Iron loss Tester for the Evaluation of Assembled Stator Cores of Electric Machines

Abstract: The iron loss in the steel core of electric machines is influenced by the manufacturing processes, such as punching, stacking and shrink fit. This causes a considerable deviation from the estimated iron loss using standard measurement methods, e.g. Epstein frame test. This paper presents a rotational loss tester that can measure the iron loss in assembled stator cores of electrical machines. The proposed tester is designed with a flexible winding configuration that can emulate the rotating magnetic fields in different types of AC electric machines with various design variations. A prototype of the proposed tester is fabricated and the experimental results of an industrial motor stator show 38% higher loss compared to the FEA calculated loss using the Epstein frame data.

Emulation of an Isolated Induction Generator Under Unbalanced Conditions

Abstract: The induction generator is an essential element of many renewable energy systems, such as wind power plants. The advantages of using induction machines (IMs) compared to other types of machines are well-known and discussed extensively in the literature. In isolated power systems, the self-excited induction generator (SEIG) is commonly used to feed power in remote areas. In this paper, a power electronic converter based SEIG emulator is developed using dSPACE to investigate the SEIG operation under unbalanced conditions. The induction generator (IG) model considering the saturation effect and variable stator/rotor leakage split ratio is established, and used in the SEIG emulator. The SEIG system under unbalanced condition is then simulated based on Matlab/Simulink. Furthermore, experimental results based on a real SEIG are presented to verify the developed machine emulator.

Power Hardware-in-the-Loop based Emulation of an Open-Winding Permanent Magnet Machine

Abstract: Open-winding permanent magnet (PM) motors are increasingly being used in electric drive systems due to several advantages over traditional PM motors such as a wider speed range of operation, and improved fault tolerance. Novel testing techniques such as power hardware-in-the loop (PHIL) based machine emulation can be used to expedite the testing of new motor topologies such as the open-winding PM motor. This paper investigates the emulation of an open-winding PM machine. In order to control or suppress lower order harmonics resulting due to the emulated machine back-emf, current controllers are proposed in this paper. These proposed controllers, used for the driving inverter and the machine emulator, use multiple resonant controllers in combination with proportional-integral (PI) controllers to achieve control over emulated current harmonics of interest. Experimental results are presented to validate the performance of the proposed current controller and also highlight the utility of the developed machine emulator system to emulate various operating conditions of the open-winding PM machine.

A Novel Multipurpose V2G & G2V Power Electronics Interface for Electric Vehicles

Abstract: This paper proposes and analyses a novel multipurpose power electronic interface (MPEI) designed for the new generation plug-in electric vehicles (PEVs), and plug-in hybrid electric vehicles (PHEVs). The proposed topology allows vehicle to grid (V2G) and grid to vehicle (G2V) operation to support the grid in times of high load or stress. The operation principles of the MPEI in its different modes are explained and practical results obtained using a real-time controller are discussed and validated in this paper.

Sinusoidal Shaped Surface Permanent Magnet Motor Using Cold Spray Additive Manufacturing

Abstract: With the global trend towards electrification of transport, the interest in various configurations of electric motors is growing. Several applications require low torque pulsations as it can lead to mechanical vibrations and acoustic noise. Optimization of the shape of the rotor permanent magnet (PM) has been the most effective technique for reducing torque pulsations. Unfortunately, the low versatility of the motor magnet fabrication technologies limits the development of new motor geometries. Cold spray additive manufacturing is used for shaping PMs for the direct fabrication of electric motor parts without the need for additional assembly steps. This fabrication technique allows an increase in the design flexibility of electrical machine geometries targeting improved performance. This paper presents rotor PM shaping design for radial flux inner rotor surface permanent magnet synchronous machines (SPMSM). PMs being shaped according to a sinusoid along the axial direction while the thickness of the magnet is kept uniform along the radial direction. The performance of the machine with sinusoidal shaped rotor PM (Model-B) is compared against a conventional rectangular shaped rotor PM (Model-A) design. The effect of sinusoidal shaped rotor PM shape on flux linkage, load torque, cogging torque and back EMF is analyzed and simulated using the 3-D finite-element method for both models. Also, the magnetization current magnitude required to completely magnetize the rotor PM fabricated using cold spray additive manufacturing is calculated.

Co-simulation Based Electric Vehicle Drive for a Variable Flux Machine

Abstract: This paper presents a co-simulation platform for an electric vehicle motor drive system for a Variable Flux Permanent Magnet Synchronous Machine (VF-PMSM). A pair of software tools: JMAG, which allows computing the electromagnetic behavior and MATLAB, which allows the dynamic simulation of the control circuit and power converters are coupled to develop a VF-PMSM drive. Then, the co-simulation results are compared with conventional simulation (dq-mathematical model) and experimental results. The co-simulation gives higher fidelity results since it includes magnetic saturation (inductance nonlinearities) and machine geometry (torque ripple) effects, unlike conventional simulation approach.

Parameter Measurements and Modeling of a Novel Hybrid Variable Flux Machine with Series Rare-Earth and AlNiCo Magnets

Abstract: High accuracy machine emulations require a highly accurate behavioral model of an electric machine. This paper present the parameter measurements of a novel hybrid variable flux Machine (VFM) with series rare-earth and AlNiCo magnets. A current control based method is used to measure the machine flux linkages and inductances including cross-saturation at different magnetization states. The same current controller is used to obtain the magnetization and demagnetization characteristics of the test VFM. Based on the experimentally measured magnetization curves and flux linkages, a look-up table based model of the prototyped VFM is built in MATLAB Simulink considering the conditions that affect the magnetization state, which is useful for machine emulation applications. The developed model is validated with the experimental test results for steady state and transient operations.

An Improved Method to Estimate Turn-on Switching Loss of 650V GaN HEMTs in Hard-switching Topology

Abstract: As new-generation semiconductors, gallium nitride high electron mobility transistors (GaN HEMTs) are featured as high efficiency and high power density being utilized in various power conversion application. Compared with conventional silicon devices, GaN HEMTs have faster switching speed, but lower losses which include conduction loss and switching losses. Due to the high switching frequency and compact size of GaN HEMTs, it is of importance to assess their switching losses as precisely as possible. In this paper, an improved method to estimate the turn-on switching loss of GaN HEMTs in hard-switching topology is proposed and verified. The calculation results are compared with the double pulse test simulation results from LTspice and the experimental results.