A Segmented Magnet Interior Permanent Magnet Machine with Wide Constant Power Range for Traction Application in Hybrid Vehicles

A Segmented Magnet Interior Permanent Magnet Machine with Wide Constant Power Range for Traction Application in Hybrid Vehicles
　　I. INTRODUCTION
　　The wide constant-power speed range of the propulsion system in a hybrid/electrical vehicle is crucial to meet the harsh operating constraints with minimum Neodymium Magnets power. Recent studies reveal that a highly efficient electric motor with a constant power speed ratio of 1:4 will be ideal choice for the propulsion system of hybrid and electric vehicles .
　　In recent years,the Permanent Magnet machine has been adopted for many high performance automotive applications because of its higher efficiency and torque per size ratio. The Interior Permanent Magnet (IPM) machine has the advantage of inverse saliency (q-axis inductance is greater than d-axis inductance) and performs better in constant power region than its counter part surface permanent magnet machine. However, most of the commercially available IPM machines offer only a limited speed range of constant power. The segmented magnet pole IPM rotor presented in offers a very wide constant power range. In this paper an investigation has been made for the suitability of such IPM machine for traction application. Its performance is compared with a prototype IPM machine of the University of New South Wales (UNSW) and a commercially available Kollmorgen IPM machine.
　　II. SELECTION OF TRACTION MOTOR
　　In traction operation of hybrid or electric vehicle, the electric motor plays a very important part. The ideal torque and power-speed characteristics of the electrical machine as shown in Fig.1 have two distinctive regions. In the first region, the torque remains constant up to the base speed and known as constant torque region and in the adjoining part, output power remains constant, hence the name constant power region. In the constant power region, the air-gap flux of the electric machine is weakened so that the terminal voltage can be kept constant at rated value. Consequently, it is also known as flux-weakening region of the electric machine. The flux-weakening range of a practical electric motor is limited to a maximum speed at which the output power ultimately becomes zero.
　　Recent study is showing that power requirement for acceleration in a vehicle reduces with an electric motor that has wider constant power speed range. Reduced power rating means a more cost effective system. Along with constant power range, efficiency of the traction motor is equally important. The over all energy efficiency of the vehicle ultimately determines its fuel economy. Hence, the traction motor needs to be highly efficient in its all operating conditions.
　　The Induction Motor (IM), Switch Reluctance Motor (SRM) and Interior Permanent Magnet (IPM) motors are the three main contenders of automotive traction applications. All three machines have their own benefits and shortcomings as traction motor of vehicle. The major arguments against use of PM machines are expensive high power magnet material, affect of temperature rise on the performance and severe consequences with short circuit faults. However, it is seen that with better technology, cost of rare earth magnet is in decline and expected to reduce farther in near future. Better protection against Curietemperature-limit and short-circuit fault is feasible with careful designing approach. Weighing these shortcomings against many advantages of IPM machines such as zero rotor copper loss, almost negligible rotor iron loss, higher torque per size and inherent higher efficiency at constant torque region, makes it a very appealing candidate for traction applications.
　　Study on electroless plating Ni-Co-P alloy protection deposit of sintered NdFeB permanent magnet material
　　In this paper,N45-type sintered NdFeB permanent magnet materials were protected by the electroless plating Ni-Co-P to improve its corrosion resistance.In first period,carton steel was used as substrate,in which the pre-treatment technology and electroless plating bath and plating technology parameters were optimized.Based on this basis,the Ni-P/Ni-Co-P alloy deposits were prepared on the NdFeB permanent magnet,in which the deposits combined with the porous magnets substrate closely.And the structures and properties of Ni-Co-P deposits were studied.
　　The optimization steps of the pre-treatment processes on sintered NdFeB permanent magnet material are:electrolytic degreasing，weak acid activation and pre-plating alkaline Ni-P alloy,in which the plating temperature is 85℃and plating time is 20min.The optimization results of electroless plating bath and plating technology parameters are:the complexing agent is sodium citrate,stabilizer is a trace thiourea,metal ion concentration ratio is within 0.3~0.6,pH value is 9~10 and plating temperature is 85℃.The results of Ni-P/Ni-Co-P deposits structure show that,the bonding interface between the deposit and substrate presents the form of interdigitate,the surface of Ni-Co-P deposit is flat and silver-white metallic luster,the porosity of deposit is almost zero,and the Ni-Co-P deposit http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets on the Ni-P deposit is combined closely.As the pH value increases,the Ni-Co-P deposits structure transforms from amorphous to crystalline.The deposit structure are amorphous structure when the metal ion concentration ratio is in the range of 0.2~0.6,but the structure of the Ni-Co-P deposits changes from amorphous structure to microcrystalline as the metal ion concentration ratio increased continuously to 0.8.The Ni-Co-P deposits consist of cellular with different dimensions,and the cellular size of the deposit surface decreases gradually with the metal ion concentration ratio increase.When the metal ion concentration ratio increases up to 0.6,the cellular size of the deposit surface coarsens.EDS analysis shows that with the metal ion concentration ratio increase,the Co content is increasing and the Ni and P content are decreasing in plating.And P elements tend to segregate in the junction of one cell connected with another cell.The experiment results on corrosion resistance of deposits show that the metal ion concentration ratio of 0.3 has the best acid-corrosion resistance,while the metal ion concentration ratio of 0.6 is best on alkali salt corrosion resistance.In the electrochemical environment(corrosive medium of 3.5%NaCl solution),the metal ion concentration ratio of 0.3 has the best corrosion resistance.
　　The heat treatment results of Ni-Co-P deposits show that,as the heat treatment temperaturerises,the hardness increases.When the temperature reaches 400℃,Ni-Co-P plating starts to occur crystallization transformation,Ni12P5 phase is precipitated and the hardness is at peak;when the temperature reaches 500℃,metastable phase Ni12P5 is transformed http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets into Ni3P phase,and crystallization transformation is completed and the hardness decreases.With the heat treatment temperature continuous rise,Ni3P phase aggregates and coarsens,and the hardness continuously decreases,and the cellular morphology of Ni-Co-P deposit surface changes into a worm-like morphology.