【正文】 anent magnet synchronous motor (PMSM) such as 200kW or 300kW, to obtain the good cooling effect, there are radius channels and axis holes inside the motors. At present, the influences of radius channels and core length on noload leakage coefficient are hard to be obtained with existing calculation method. This made the blind choice of noload leakage coefficient while designing the motors. It prolonged the course of research and development (Ramp。D), increased the cost of Ramp。D, and lacked of scientific basis in design optimization and performance simulation. This influences the application of PMSM. So as for the medium capacity the exact noload leakage coefficient of PMSM is more essential to the optimal design of motor than small motor.Due to the effect of permanent magnet material, the reactance parameters calculating method is different form other AC machines. For PMSM there are no open circuit and short circuit states like the electrical excited motor. The excitation of permanent magnet material is effected at all time. At the same time, different magnetic motive force and field saturation the reactance parameters are different. The parameters calculating method must take the influence of PM material into account. Based on the above reasons, the traditional circuit calculating method is not fit for the PMSM. So the finite element method is applied to calculate the parameters , and . is the noload leakage flux coefficient. In this paper the 3D electromagnetic field is used to get the exact parameters of U form medium capacity PMSM[46]. Through analyzing the electromagnetic parameter changing with the structure, the detailed experience data and curve can be obtained. Finally selecting rules of three main electromagnetic parameters are integrated with the self piled electromagnetic design program to optimize the prototype motor and a good foundation will make for designing and applying of PMSM..II. NO LOAD LEAKAGE FLUX COEFFICIENTIn this part, Ansoft is used to calculate the noload leakage coefficient of U form interior PMSM, On the basis of the calculations of many PMSM’s, the change law and influence factor of the noload leakage coefficient with motor structure parameters are analyzed, and the curve of different structure dimension is given. is the Cross section of Multisegment U form rotor structure. is the U form magnetic circuit structure separate magnetic bridge diagram. is the solved magnetic density of PMSM.A. Motor modelingDuring the calculating process of electromagnetic parameter only based on exact analysis model of motor analysis model we can get valid simulation result. Therefore, a 3D FEA model is established as following: 1) According to the motor structure dimensions, the motor simulation model is established. 2) Confirm the material attribute。 3) Ensure the boundary condition and outside source parameter。 4) Mesh。 5) Setting the resolve parameter, calculate.B. FEM analysis results of leakage flux coefficient is the curve. is the air gap lengthen, and is the length of the permanent magnet material. is the noload leakage coefficient change with magnetic bridge length w of proposed U form motor. is the noload leakage coefficient change with magnetic bridge width b.III. INFLUENCE OF STRUCTURE DIMENSION ON REACTANCE PARAMETERSAs for the Xad, the air gap fundamental flux and the effective air gap fundamental flux were gotten when the direct axis armature current is equal to the . (2)As for the reactance , directly give the winding current , and resolve the air gap flux .(3)Where, Kdpis the waveform coefficient of flux. From the above 3D FEA results, the dq axes reactance parameters are calculated by self piled program in matlab software. A．Influence of air gap length and the magnetism length on reactance This section presents the dq axes reactance Xad,Xaq curves variation with the air gap length and permanent magnet magnetism length. and are the curve of dq axes reactance parameter Xad , Xaq variation with the air gap length δ and the permanent magnet magnetism length of U form rotor. From can see with the increase of hm, Xad bees more and more smaller。 with the increase of hm influence of hm and on Xaq has a little difference pared with the Xad. It is because that a few flux passing through the PM. The influence of air gap length on Xad is higher than Xaq . As for the q axis reactance Xaq, it is mainly influenced by the air gap. and indicate that with the increase of δ, Xaq and Xad decreased very obvious. It shows that rational selection δ is very important.B. Influence of magnetic bridge on reactance. shows reactance parameters Xaq and Xad variation with the separate magnetic bridge dimension in the proposed U form rotor structureFrom above figures we can see that the of U form decre. ase by % when the bridge length change from 2 mm to 12mm. of U form decreases about % when the bridge length changes from 2 mm to 12mm. The influence of bridge length on reactance parameter is gotten. At the same time when the bridge width bchanges from 1mm to 2mm, the Xad of U form is increase %. The Xaq of U form changes %. C．Comparison between simulation and measured of reactance For validating the veracity of the FEA results, the voltage integral method [79] is adopted to measure the reactance parameters of different type PMSM. From the pared results in table I between FEA and measured data of different type PMSM, it can be seen that the calculated values agree with the measured values very well. It is proved that the proposed method is feasible.IV. FIELD CIRCUIT COUPLING OPTIMIZATION DESIGN AND PROTOTYPE MOTOR MANUFACTUREThrough the 3D electromagnetic field analysis of U form rotor magnetic circuit structure, the noload leakage coefficient and dq axes reactance variation rules with rotor dimensions are obtained. Several kinds of electromagnetic design strategies are p