Abdul Rehman Tariq

Iron and Magnet Losses and Torque Calculation of Interior Permanent Magnet Synchronous Machines Using Magnetic Equivalent Circuit

We present a faster and simpler approach for the calculation of iron and magnet losses and torque of an interior permanent-magnet synchronous machine (IPMSM) than finite-element methods (FEM). It uses a magnetic equivalent circuit (MEC) based on large elements and takes into account magnetic saturation and magnet eddy currents. The machine is represented by nonlinear and constant reluctance elements and flux sources. Solution of the nonlinear magnetic circuit is obtained by an iterative method. The results allow the calculation of losses and torque of the machine. Due to the approximations used in the formulation of the MEC, this method is less accurate but faster than nonlinear transient magnetic FEM, and is more useful for the comparison of different machine designs during design optimization.

Thermal Analysis of Permanent Magnet Motor for the Electric Vehicle Application Considering Driving Duty Cycle

A lumped parameter thermal analysis of permanent magnet motor by considering real driving duty cycle is presented. As driving motors of electric vehicle, permanent magnet motors exhibit high efficiency and high power density. However, they are susceptible to suffer irreversible demagnetization and insulation failure of coils under severe thermal condition. Therefore, it is essential to accurately evaluate heat losses and precisely predict temperature distribution in driving motors under the real driving duty cycle. In this paper, an improved core loss model is employed and implemented by using finite element method. The thermal behavior of the driving motor is analyzed by means of lumped thermal parameter method. A test bench has been set up to measure the temperature distribution in the driving motor. The calculation and experiment results are compared and discussed.

Trajectory Optimization for the Engine–Generator Operation of a Series Hybrid Electric Vehicle

This paper presents a methodology of calculating the optimal torque and speed commands for the engine-generator system of a series hybrid electric vehicle (HEV). In series HEVs, the engine-generator subsystem provides electrical energy to the dc link. This paper proposes an optimal control strategy of the engine-generator subsystem to generate a desired amount of energy within a given period of time. The optimization algorithm, based on trajectory optimization, determines the torque and speed reference signals for the engine-generator subsystem that achieve maximum efficiency. A simplified version of the controller is also presented for online implementation. The proposed control strategy is compared with nonoptimized control techniques, and simulation results show the improvements in energy efficiency.

Overload Considerations for Design and Operation of IPMSMs

Although interior permanent magnet synchronous machines and their cooling are designed to match the rated power, power demands other than rated may arise. One may keep the same machine dimensions and basic electromagnetic design, but increase the cooling for different operating conditions. Modifications of the cooling system can compensate for the increase in machine losses in the windings, magnets, or iron. Increasing the allowed stator current affects the machine performance in other ways as well. These include demagnetization of the magnets, and hence, shrinking of the speed range to avoid this. In this paper, these effects are studied for a baseline machine, as well as for machines with the same stator but modified rotor design. A cross-saturated model is developed and shown to be more accurate than the classic one. To account for higher stator current with higher temperatures, the effects on efficiency, torque, and speed range by changing the magnet material from the more commonly used NdFeB to SmCo are also studied and discussed.

Consideration of magnet materials in the design of PMSMs for HEVs application

This paper discusses two vital issues regarding design and performance of high power Permanent Magnet Synchronous Machines (PMSMs) using different magnet materials; high temperature applications and machine design without using rare earth permanent magnets. In the first part, designs were developed using NdFeB and SmCo magnets for hybrid bus application. They were evaluated at different temperatures taking into account the fact that remanent flux density of NdFeB magnets reduces with increase in temperature at faster rate than that of SmCo magnets. Based upon the torque-speed and efficiency plots of the machines, feasibility of the designs are suggested for specific temperature range. Ferrite magnets can also work at higher temperature than NdFeB but they provide significantly less flux density. Four variants of PMSMs using ferrite magnets are designed and discussed here. Comparison of their torque speed and efficiency characteristics is made with that of the NdFeB machine having the same volume. The results lead to design consequences of PMSMs in the absence of rare earth magnet materials.

Optimal speed control of an Interior Permanent Magnet Synchronous Motor including cross saturation

This paper presents the methodology to design an optimal speed controller (total losses minimization) of an IPMSM for traction applications. IPMSMs have high efficiency, however to exploit that efficiency it is required to design an optimal control, with the capability to accurately calculate and command the current components for the whole range. The speed controller is optimized by calculating the optimal trajectory between two points, defined by their torque and speed. The trajectory calculation is made in two stages: current space vector calculation based on the concept of maximum torque per ampere and optimal trajectory calculation. The first stage corresponds to the calculation of the optimal magnitude and angle of the current space vector for any given torque and speed point, maximum torque per ampere is the control technique selected for the IPMSM model inversion. The second stage involves calculating the currents that define the trajectory from one point to another, with minimal copper losses. The proposed optimization is numerical, constrained, based on the steepest descent method. Simulation and experimental results are presented to validate the proposed methodology.

Design and analysis of PMSMs for HEVs based upon average driving cycle efficiency

Permanent magnet synchronous machines (PMSMs) are widely used as traction machines in the hybrid and electrical vehicles (HEVs) due to their high power density, wide field weakening range and high efficiency. An optimized and efficient design of PMSMs depends upon the driving cycle requirements and consideration of losses of every subsystem in the traction drive. Efficiency of a traction drive over a driving cycle is more important than the efficiency of the traction machine at one operating point. This paper presents an approach for the design of PMSMs based upon the average driving cycle efficiency (ADCE) of traction drive for an urban series hybrid bus for a specific driving cycle. It includes the efficiency of machine, inverter as well as the energy utilized by their cooling systems. The proposed approach was applied to two different machines to demonstrate its validity.

Effect of cooling conditions on the design and operation of IPMSM

High power Interior Permanent Magnet Synchronous Machines (IPMSM) are used extensively in hybrid vehicle applications due to their high power density, wide speed range and better efficiency. In general, a high power IPMSM and its cooling is designed according to its rated power. Depending upon the application, specific power demand (other than rated) may arise to run the same machine at less or more than rated current. One may like to keep the same machine but change its cooling. Modification in machine cooling can compensate for the increase in machine losses due to its current change. The design of such a machine needs special attention because every machine designed for rated current may not be used continuously at current greater than that. In this paper, the operational range of a baseline machine design is presented and analyzed at less as well as more than rated current, using a cross saturated dq model. It is imperative to consider the demagnetization limit of permanent magnets in the analysis of machine operation. Different machine designs are presented and compared for torque-speed profile and efficiency at different current conditions with increased machine cooling. Machine design with increased width of permanent magnets provides more wider operating region at the cost of reduction in its efficiency for higher speeds.

A novel numerical method for the calculation of iron and magnet losses of IPMSMs

This paper presents a faster and simpler approach for the calculation of iron and magnet losses of an IPMSM than Finite Element Analysis. It uses large elements and takes into account the magnetic saturation and magnet eddy currents. The machine is represented by its magnetic equivalent circuit, consisting of non-linear and constant reluctance elements and flux sources. Solution of non-linear magnetic circuit is obtained by an iterative method. The results allow the calculation of losses and efficiency of the machine. Owing to the approximations used in the formulation of the magnetic equivalent circuit, this method is less accurate but faster than non-linear transient magnetic FEM, and is more useful for the comparison of different machine designs during design optimization process.

Design and thermal analysis of traction motor for electric vehicle based on driving duty cycle

To reduce cost and improve efficiency, a novel design concept of a traction motor for electric vehicle based on a driving cycle is proposed. In comparison with conventional design method of electric motors, the proposed design concept considers the real load condition and highlights special requirements of electric vehicle. Based on the proposed approach, an interior permanent magnet traction motor is designed with high average efficiency overall operation region. The thermal behavior of the designed traction motor is investigated and the temperature distribution in key parts under the driving cycle is obtained. To verify validity and generality of the proposed designed concept, a surface mount permanent magnet traction motor is designed and evaluated by experiment.