512 Methods for Improving Efficiency of Linear Induction Motor for Urban Transit∗ Nobuo FUJII∗∗, Toshiyuki HOSHI∗∗ and Yuichi TANABE∗∗ To improve the efficiency of the linear induction motors (LIMs) for transportation, the compensation of end effect for LIM with the restriction of length and the long LIM with small end effect essentially are discussed respectively. Based on the proposed concept, the com- pensation method of the magnet rotator type and AC coil type of compensators are developed respectively. The utility is not yet confirmed. As for the long LIM with length of 10 m, the analysis shows that the efficiencies are about 85% at 40 km/h and above 90% at 360 km/h respectively. Key Words: Linear Motor, Linear Induction Motor, LIM, Linear Drives, Transportation, Traction, Subway, Electromagnetic Analysis, End Effect, Compensator length of LIM, the compensation of end effect is the only 1. Introduction method for remarkable improve of the characteristics. The In a part of new type transit, linear induction motors compensating winding method was proposed previous- (1) ff (LIMs) have been used as a direct electromagnetic drive ly , but it was not e ective. The authors have proposed ff (2) device without adhesion. In Japan, the LIM-driven train the new type of end e ect compensator . The proposed ff has been used in the subway in some large cities, as the method is based on the new concept that the end e ect can LIM reduces the construction cost of tunnel because the be compensated only by supplying the eddy current syn- thin shape makes the sectional area of tunnel small and the chronizing with the LIM frequency in front of LIM, which large gradability enables the minimum length of the route. was derived from the previous study. In another case, the LIMs are used in magnetic levitation In the paper, as examples of the way to realize the vehicle called HSST which will be used for the urban or theory of compensation, the magnet rotator with perma- intercity transit, and in an air suspended vehicle with low nent magnets as a mechanical rotating type and the AC floor which aims to be used for a personal rapid transit. coil type with concentrated winding as a static compen- On these LIM-driven trains, there is the problem of sator are discussed. large power consumption. That is, the efficiency is not On the other hand, the long LIM is basic to the small ff satisfactory. In the induction type motor, the efficiency de- end e ect in case we can use the space along the vehi- pends on the operating slip and the small slip is required cle length. In the paper, the use of an onboard primary- fundamentally for the high efficiency. On the other hand, member type LIM with long armature core of 10 m is stud- the LIM has its own end effect which decreases the ef- ied analytically. ficiency and power factor in the small slip region. The 2. LIM with End Effect Compensator influence of end effect becomes serious as the speed in- ff creases. That is, the essential measure for high efficiency The end e ect compensator is attached in front of the is to overcome the end effect, which is a long-pending ob- entry end of primary of LIM to compensate the dynamic ff ject. entry end e ect. Under the condition that there is restriction on the 2. 1 Magnet rotator type of compensator Figure 1 shows the magnet rotator type of end effect ∗ Received 13th January, 2004 (No. 04-4019) compensator installed at the front of armature of LIM. The ∗∗ Department of Electrical and Electronic Systems Engi- magnet rotator has the poles of permanent magnets, and neering, Faculty of Information Science and Electrical En- the rotating speed ns (rps) is synchronized with the fre- gineering, Kyushu University, 6–10–1 Hakozaki, Higashi- quency of LIM. That is, ku, Fukuoka 812–8581, Japan. E-mail: [email protected] ns = 2 f1/p (1) Series C, Vol. 47, No. 2, 2004 JSME International Journal 513 Table 2 Numerals of magnet rotator type of compensator Fig. 1 Magnet rotator type of compensator Table 1 Example of LIM parameters (a) Thrust where, f1 (Hz) is the frequency of current in the primary winding of LIM and p the number of poles of the magnet rotator. The rotating speed is constant for the slip of LIM. This type of compensator has the merit that there is little (b) Efficiency power consumption except the joule loss by the eddy cur- Fig. 2 Characteristics of LIM with the magnet rotator type of rent in the secondary conducting plate, and it is a compact compensator size with large magnetomotive force and without ohmic loss. The phase adjustment between the compensator and the LIM can be done by controlling the inverter of LIM in Figure 2 shows the analytical characteristics of LIM the practical use. when the optimal phase of current for compensation is As it is very difficult to analyze of LIM with the supplied. The thrust and efficiency of LIM increase by magnet rotator type compensator exactly, the rotator is means of the compensator respectively. It is very difficult replaced by the equivalent static winding with rotating to analyze the overall efficiency at the current stage. We field (2). In the procedure, the 3-D dynamic electromag- are preparing for the experimental study using the test fa- netic analysis (Package ELF/MAGIC) for the real model cility shown in Fig. 3. of magnet rotator, and the 2-D finite element method 2. 2 Single-phase AC coil type of compensator (FEM: Package ANSYS) for the equivalent model were Figure 4 shows the compensator using AC coils to used. The quasi-3D analysis is done by using the 2-D avoid the mechanical rotation and to enable the adjustment FEM for the model of LIM with the compensator, con- of magnetomotive force (MMF) of compensator, although sidering with the effect of transverse direction by using it has the problem of poor power factor in the compensator Russell-Norsworthy coefficient. due to its own end effect. The frequency of compensator The characteristics of LIM with the magnet rotator current is equal to that of LIM. type of compensator are studied on the parameters as In this model, it is not difficult to analyze the over- shown in Tables 1 and 2. The parameter of LIM is sim- all characteristics of LIM with the compensator, compared ilar to that of the subway vehicle in Tokyo. with the magnet rotator type. The quasi-3D analysis using JSME International Journal Series C, Vol. 47, No. 2, 2004 514 (a) Thrust Fig. 3 Test facility of LIM (rotating secondary type) with the magnet rotator type of compensator (b) Efficiency Fig. 5 Characteristics of LIM with the coil type of compensator Fig. 4 AC Coil Type of Compensator elements for this model. Table 3 Design example of two-coil type compensator 2. 3 Consideration of overall efficiency The overall characteristics of the LIM and compen- sator must be studied for the net improvement by the com- pensator. The overall efficiency is expressed as: ηt = v2(FLIM + FC)/(PLIM + PC)(2) where, FLIM is the thrust in LIM region and it is not the thrust at LIM alone, v2 the speed of LIM, FC the thrust in the compensator region, PLIM the input power of LIM, PC the input power of compensator. For the magnet rotator type of compensator, PC is: 2-D FEM is done to analyze the model. As a numerical P = ω T + P = 2πn T + P (3) example, the LIM of Table 1 and the compensator shown C C C dl s C dl in Table 3 are used. where, the TC is the torque and Pdl the loss in driving The single-phase AC coil type of compensator gener- mechanism of the compensator. At the current stage, we ally generates the negative thrust in the region due to its don’t yet get the analytical technique to estimate TC in this own end effect. Figure 5 is the characteristics of LIM with model. ffi the coil type of compensator, in which the pole-pitch and We discuss about the e ciency on the condition ne- ffi pole-length of the compensator are selected optimally for glecting the iron loss. The e ciency in case of LIM alone the minimum braking thrust of compensator respectively. is defined by: The thrust characteristics of Fig. 5 (a) shows that the η0 = Fxv2/(Fxv2 + PL1 + PL2)(4) coil type has the ability to compensate the end effect and where, Fx is the thrust of LIM, PL1 the copper loss of the the MMF of compensator increases the overall thrust lin- primary winding of LIM and PL2 the copper loss in the eally. Figure 5 (b) shows the overall efficiency consider- secondary member (reaction rail). The overall efficiency ing both LIM and compensator. The overall efficiency de- of the LIM and compensator is expressed: creases when the MMF of compensator is large, because η = k F v /(k F v + P +k P + P + P )(5) the copper loss in the winding becomes large. The maxi- t t x 2 t x 2 L1 L L2 C1 C2 = + mum value of overall efficiency is large attractively. The ktFx FLIM FC (6) accuracy of computation is not yet confirmed because the where, kt is the thrust ratio to that of LIM alone, kL the numerical solution of FEM needs a very large number of ratio of secondary copper loss in the LIM region to that of Series C, Vol.