Design and Hybrid Analytical Model for Interior Permanent Magnet Generator in an Electric Vehicle Auxiliary Power Unit Application

This paper presents a comparison of different design choices in small wind power systems design. A vertical axis wind turbine is considered,to take advantage of the fact that it is omni-directional, i.e. it can accept wind from any direction. The vertical axis turbine that has been used is a type of straight-bladed Darrieus turbine coupled with a Savonius turbine, in order to built a self starting turbine. To chose the electric generator with its drive, an economic analysis is carried out on the basis of generator, power converter and mechanical system costs. The optimal ratings are found on the basis of the maximum profit over payback time. An Interior Permanent Magnet (IPM) generator and a Surface Permanent Magnet (SPM) generator are compared. The IPM generator can be driven in the flux weakening region, exploiting higher turbine rotation speeds. The paper shows that economic advantages are obtained using an IPM generator, optimized together with the power converter.

In order to solve the problem that no-load magnetic flux leakage coefficient is not accurate when it is calculated by the method of magnetic circuit, a model of interior permanent magnet(IPM) generator with 36 slots for vehicle was built through the finite element method of the ANSYS, and then a means of calculating the IPM generator’s magnetic flux was put forward after analyzing the magnetic flux leakage conditions of different rotor structures under the circumstance of not changing stator structure. The ralationships among the pairs of poles, the magnet width, the thickness of non-magnetic sleeve, the length of air-gap and the magnetic flux leakage coefficient were obtained, and they provided forceful guidance for the structural design of IPM generator.

A new switched reluctance (SR) generator was designed for possible application in hybrid electric vehicles. The proposed generator was designed to be mostly competitive with the target interior permanent-magnet (IPM) generator currently used in mass-produced hybrid vehicles. The energy efficiencies of the SR and IPM generators were compared in typical driving cycles, such as US06, HWFET, and UDDS modes. We found that the energy efficiency of the SR generator was close to the IPM generator in high-speed driving cycles because the SR generator has no iron loss during the generator idling period due to the fact that it has no PM.

To address the limitations of flux regulation in traditional permanent magnet synchronous generators and the low power density of electrically excited generators, an interior double-radial asymmetric permanent magnet (PM) and salient-pole electromagnetic hybrid excitation generator are introduced in this study. Equations for the no-load induced electromotive force, the voltage adjustment range, and the total harmonic distortion (THD) are derived theoretically through the analysis of generator parameter relationships. The optimization parameters include the offset angles of the double-layer asymmetric PMs and the structural parameters of the salient-pole rotor. A multi-objective optimization model is established with the no-load induced electromotive force amplitude, the voltage adjustment range, and the THD as the objectives. Samples are generated by Latin Hypercube Sampling, followed by sensitivity analysis of the optimization parameters. The optimization parameters are then screened using Pareto front analysis and a defined parameter matching coefficient. The optimal magnet pole parameters are determined. As a result of optimization, the no-load induced electromotive force amplitude increases by 18.7%, the voltage adjustment range expands by 17.6%, and the THD decreases by 38.2%. Finally, a prototype is fabricated and tested, and the results confirm both the accuracy of the theoretical analysis and the effectiveness of the optimization method. The output characteristics of the designed generator are thereby significantly improved.

Control reliability of interior permanent magnet generator (IPMG) depends on accurate knowledge of the generator outputs (torque, currents etc.) and model parameters (resistance, inductances etc.). These outputs and parameters can be obtained by measurements or can be estimated. Reducing measurement equipment, cost of the control system is reduced as well. On the other hand, if control system contains accurate estimation algorithms, control reliability tends to increase. In this paper, comparison of the three torque estimation methods is done. First method considers the IPMG torque estimation using cross product of the IPMG flux and current vectors in the αβ reference frame. Second one estimates the IPMG torque also as a cross product of the IPMG flux and current vectors, but in the dq reference frame. Third method is based on generator electrical power and shaft speed. All of the mentioned methods are experimentally compared to the measured IPMG torque.

Flying start of a wind generator is a common requirement in wind turbine applications. This paper proposes a novel method for allowing the flying start of a permanent magnet generator (PMG). The proposed method is based on the discontinuous mode of operation of the converter and the phase-locked loop (PLL). During the discontinuous mode of operation, a series of zero-voltage pulses is applied to the generator, causing the occurrence of the short-circuit current, and thereby employing the PLL structure to estimate the rotor speed and angle. Also, a short-circuit current control structure with automatic adjustment of the reference value is proposed. The input signal to a PLL structure is adequately selected in order to enable a continuous mode of operation of the PMG. Simulation results demonstrate the applicability of the proposed method on the surface and interior PMGs, as well as on low- and high-power PMGs. The estimation accuracy does not depend on changes in the PMG parameters. The proposed method was implemented in a digital control system and experimentally verified on a 375 kW interior PMG. Experimental responses referring to the flying start of the PMG demonstrate the effectiveness of the proposed method.

Recently, there has been a lot of researches on various methods for a sensorless control of permanent magnet generators (PMG) in wind turbines. The sensorless control of the PMG considers estimations of a rotor angle and speed which are based on the PMG parameters estimation. The parameters that have been estimated are stator resistance, rotor flux, d-axis and q-axis inductance. For more precise rotor angle and speed estimation, it is essential to determinate values of the PMG parameters in every operating point as accurately as possible. A change of the operating point (different rotor speed, shaft torque etc.) causes the change of the PMG parameters due to stator currents and temperature variation. Accordingly, the PMG parameters could be measured during a PMG commissioning. In this work, the stator resistance is measured while taking into considering a dead time compensation and voltage drop on a power switching devices. A determination of the d-axis and q-axis inductances is based on PMG voltage equations in a dq synchronous reference frame. Thus, the measurements of the rotor speed, stator currents and voltages are required. The experimental measurements are carried out on a 375 kW interior permanent magnet generator. Finally, the measured values could be saved on a digital signal processor (DSP) as look-up tables and used for the sensorless control of the PMG.

Interior Permanent Magnet (IPM) synchronous generators can achieve high-efficiency and wide voltage range with field strengthening and weakening. The purpose of this paper is to drive a high speed Surface Permanent Magnet (SPM) motor powered by the IPM generator with the field strengthening at a low rotational speed. The control systems of both the IPM generator and the high speed motor are proposed. The experimental results demonstrate the effectiveness of the control system.

Traditional electric machine design requiring the balancing of the phases both in phase voltage magnitudes and the angles between adjacent phases informs that the number of stator slots per phase must be an integer. There are situations however, where it is cheaper to use existing laminations for designs with non-integer number of slots per phase to build generators for specialized applications especially for DC power. In such cases a multi-phase design ensures a measure of fault tolerance and the unbalances in the phase angles between the winding phases have little effect on the quality of the output DC voltage. The methodology for the design of a five phase, 4-pole interior permanent magnet (IPM) generator using 36 slots as a source of DC power is outlined. Experimental results for the operation under healthy and faulty conditions (one and two phase windings open) are presented for verification of fault tolerance of multi-phase machines.

This paper presents an analytical model for predicting the magnetic field performance of permanent magnet synchronous motor with permanent magnet cutting. In order to satisfy the boundary conditions, the defective permanent magnet is equivalent to a double-layer sector permanent magnet, and the size of the sector-shaped permanent magnet is determined, this process is obtained by an equivalent magnetic circuit model. Then, the motor is divided into four sub-domains: inner sector permanent magnet sub-domain, outer sector permanent magnet sub-domain, air gap sub-domain and stator slot sub-domain. Under the boundary conditions, the analytical solution and harmonic decomposition of the air gap magnetic flux density and cogging torque for several different permanent magnet cutting sizes under no-load condition are obtained by solving the Poisson equation and Laplace equation with the method of separating variables. The analytical model is verified by the finite element method. The results show that the error between the analytical method and the finite element method is less than 6%, and the solution time of the analytical method is only 0.59% of the finite element method, the chamfered structure proposed in the paper reduces the cogging torque amplitude 35%. Therefore, this method can provide powerful help for the initial design of permanent magnet motors.

Flying start and sensorless control of permanent magnet wind power generator using induced voltage measurement and phase-locked loop

The availability of high-energy permanent magnet materials has brought about renewed interest in the use of permanent magnets to provide field excitation in electric generators for use in industrial and utility applications. This paper sets forth the analysis and computer simulation of such an interior permanent magnet generator feeding an impedance load, a rectifier load and a rectifier-PWM inverter connected to an impedance load. The analysis accounts for the changing saturation and armature reaction dependent axes inductances and magnet flux linkage. Experimental results from a 2 HP interior permanent magnet generator system corroborate the analysis and computer simulations.

This study presents a systematic approach for modelling, analysing and evaluating steady-state performances of directly driven interior permanent magnet generators (IPMG) for wind energy conversion systems. The proposed approach for modelling and analysing the performance of PMGs is based on relating the harmonic components present in the stator currents to the harmonic components present in the terminal voltages. Three laboratory IPMG of 1, 5 and 50 kW are tested at different shaft speeds for supplying a resistive load, a rectifier and a resistive load and rectifier inverter with a resistive load. Experimental performances of the tested IPMGs demonstrate direct relationships between terminal voltage harmonic components and harmonic components present in stator currents. Also, investigated experimental performances show significant impacts of stator currents harmonic components on the IPMG efficiency.

This paper introduces the design and performance analysis of an interior permanent magnet generator (IPMG) for applications in low speed wind turbine systems. The developed design is based on optimizing the geometry of double-layered permanent magnets (PMs), which are buried in the rotor body of an IPMG. The geometry of the double-layered permanent magnets is optimized and simulated using the 2-D finite element analysis method (FEA). The optimization of the PMs is established based on the induced electromotive force (EMF), harmonic contents of the stator current and torque ripples at low speeds. The optimization shows that the π-shape double-layered permanent magnets geometry is capable of inducing an EMF with the high magnitude and low harmonic contents, along with producing stator currents with the low harmonic contents and minimum torque ripples.

Overhang is a useful structure for increasing the torque and power densities of permanent-magnet (PM) machines without expansion of the machine space. A 3-D finite-element method (FEM) is needed to evaluate the performances of PM machines with an overhang structure because the overhang structure results in non-uniform magnetic flux distributions in the axial direction. However, it is computationally expensive, especially in the early design stage. In this paper, we propose a magnetic equivalent circuit (MEC) model considering the overhang effects of interior PM (IPM) machines. With the proposed MEC, the performances of IPM machines with an overhang structure were precisely calculated and the computational time was significantly reduced. The proposed MEC was verified by the 3-D FEM.