MEASUREMENT OF LOSSES IN DIRECT TORQUE CONTROLLED PERMANENT MAGNET SYNCHRONOUS MOTOR BY ANALYSIS AND EXPERIMENTAL SETUP

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1 IJRET: International Journal of Research in Engineering an Technology eissn: pissn: MEASUREMENT OF LOSSES IN DIRECT TORQUE CONTROLLED PERMANENT MAGNET SYNCHRONOUS MOTOR BY ANALYSIS AND EXPERIMENTAL SETUP A N Gokulprakash 1, A Sivaprakasam 2, T Maniganan 3 1 P.G Scholar, Department of EEE, Kongu Engineering College, TamilNau, Inia 2 Assistant Professor (Selection Grae), Department of EEE, Kongu Engineering College, TamilNau, Inia 3 Principal, P.A. College of Engineering an Technology, Tamil Nau, Inia Abstract Direct Torque Control (DTC) appears as an effective an practical control scheme for AC motor rives. The DTC of Permanent Magnet Synchronous Motors (PMSM) Drives attracte great attention, ue to many features like high efficiency, quick ynamic performance an provie excellent steay state response. The ajustable spee rives are rapily introuce in the area of electric vehicle an motion control evices an these evices are often powere by a battery source. Due to the restriction in energy supply, the improvement of motor efficiency is the most important priority, an hence the DTC technique is use to measure the losses in PMSM. In orer to measure the losses, the offline an online calculation methos are propose. In this work, the mechanical losses is epens on rotor spee an friction torque, an it is often uncontrollable but the electrical losses are controllable an hence the electrical losses can be measure certainly. The Offline control metho is use for optimizing the steay-state efficiency of PMSM uner DTC. In this propose work, the losses are calculate by offline metho for simulation an experimental setup in orer to obtain the better steay state efficiency, an also comparatively investigate with analysis an experimental results. Keywors: Permanent Magnet Synchronous Motors, Direct Torque Control an Electrical Losses *** INTRODUCTION The technology has been evelope in many inustrial riving systems. The evelopment of the switching spees of the equipment has enable the control techniques which have high switching frequency an feasibility of high efficiency riving systems. However, the inuction motor s efficiency changes with slip value from its esire reactive current, an it not able to prouce high torque / weight ratio which neee for high performance applications such as robotics. The Switche reluctance motor (SRM) [5], has high reliability ue to its simple an robust rotor structure. However, the core loss in the soli rotor is very large at super high-spee. Lamination of the rotor can reuce the core loss in the rotor. However, it is not recommene at super high-spees since it will reuce critical spees. Therefore, the ifferent solutions are being stuie an issimilar motor esigns have been evelope. One of these recently urbanize motors is the permanent magnet synchronous motor. In this, the applications where high concert is emane, some properties of the permanent magnet synchronous motor such as high power, high torque, high efficiency an low noise have mae it more popular compare to other alternating current motors. Especially, because of the high power ensity the permanent magnet synchronous motor is relate for areas such as automation, robotics, an aeronautics technologies. Since the excitation flux is abouning by the magnets an ue to the magnet characteristics an position the permanent magnet synchronous motors have both synchronous machine an a irect current machine characteristics Spee Estimator Volume: 3 Special Issue: 7 May-214, 72 ω m-com T L value ω m-est PI Controller Look-up Table T com ψ s-opt. Fig -1: Propose DTC V, V q, i, i q,... Conventional DTC Control System The Fig -1 shows the propose DTC [6] [18] block iagram, for getting the optimize efficiency for a PMS motor rive. The machine terminal voltage an current can be estimate T ψs

2 IJRET: International Journal of Research in Engineering an Technology eissn: pissn: from the rive an it given to the input of a spee estimator for estimating the spee of a machine. By comparing, the estimate spee an reference spee which has been given to the controller of PI. The output of PI is given to the DTC block for controlling the rive. The PMSM offers the avantage of high efficiency compare to other types of motors since there is no excitation power loss in the rotor, an low ey current loss in the stator an rotor [17]. Therefore, there is an increasing interest to consier PMSM for super high-spee applications. For unloae conitions, the velocity is irectly proportional to voltage an it is inversely proportional to the flux an, for loae conitions it is proportional to the flux an current. The Synchronous motors have three phase winings in their stators, just like the inuction motors [3]. Though, the rotor structure is ifferent. The permanent magnet synchronous motor (PMSM) [14], becoming more an more attractive ue to its high efficiency an high torque to current ratio For a PMSM rive system mechanical sensors are often require for correct commutation of the inverters [2]. The use of mechanical sensors however reuces the reliability an increases the cost of the system. To overcome this isavantage sensor less control scheme is much esirable. Recently the Direct Torque Control (DTC) [9] [1], scheme is increasingly use in PMSM rive systems because of its fast torque response an possibility of eliminating the mechanical sensors if the initial rotor position is known. 2. MACHINE MODEL The minimization of electrical loss [5] [7], in PMS motor rive necessitates consieration of copper an iron losses in the machine moel. An equivalent circuit moel of a PMS machine in synchronously rotating reference frame is use through following equations. The - an the q-axis stator flux linkage components are: In the steay state we have, ω = (ω ) m m com. (5) T = T = T + B ( ω ) com. e ss m L (6) Mechanical loss epens on rotor spee an friction torque an often is un-controllable, W = T ω m M mech (7) Electrical loss consists of iron loss an copper loss, therefore, the following equations are, W = W + W cu E fe (8) W E = R S (i + i ) + R c(i c + i c ) (9) W LOSS = W M + W E (1) The machine efficiency is a function of output power an loss terms, as: p out η= p + w out LOSS (11) 3. PROBLEM FORMULATION The electrical loss relation has been simplifie an appropriate formulation of the loss minimization problem, has been introuce. Fig -2 shows the equivalent circuit for PMSM, we have i R s i o L q = L q ioq (1) ψ = ψ m + L i (2) o V R c i c ωel q i oq The electro-magnetic torque in terms of the torque proucing currents, i o an i oq is given as: i q R s i oq L q T e = P i oq [ψ m + (L - L q ) i o ] (3) i cq ωel i o The motor rive system ynamics is also signifie by: V q R c ωeψ m ω T = T + B ( ω ) + J m e L m t (4) Fig -2: Equivalent circuit for PMSM Volume: 3 Special Issue: 7 May-214, 73

3 IJRET: International Journal of Research in Engineering an Technology eissn: pissn: i = c V - Rsi o R s + Rc an i = V + Rci o R s + Rc (12) 2T 1 ss 1 1 = ψ m + - ψ 3pψ L L L q q (2) Vq Rsioq i cq Rs Rc an i = q V q + Rsioq 2 Vs RsRc 2 2 W = + E i + i oq R s + Rc R s + R o c i = oq q q - m i = L o q L Substituting the i oq an i o into equation, R s + Rc (13) Vs RsRc ψ - ψ ψ m q W E = + + R s + Rc R s + R c L L q Where, V s = V + Vq (17) (15) (14) (16) V s, is the magnitue of the stator voltage. In DTC metho the magnitue of the stator voltage is always constant. The first term in the above equation is always constant. This term represents the unavoiable electrical loss in irect torque control of PMSM. Therefore, secon term is ecrease. The variable part as Performance Inex has been consiere. Therefore, the optimization problem becomes Minimize 2 2 ψ - ψ ψ m q J = + L L q (18) This optimization problem is subject to steay state torque generation constraint T ss = pψq ψ m + - ψ 2 L L L q (19) For ifferent values of T ss obtaine from (6), this equation characterizes ifferent hyperbolic trajectories in (ψ, ψ q ) plane. ψ = q 2T ss p ψ m + - ψ L L L q Substitute the ψ q into equation number (18) (21) 2 2T ss p ψ m + - ψ L L L ψ - ψm q J= + 2 L (22) -3 J ψ - ψm 4Tss = 2-2 ψ m + - ψ - ψ (23) L 9p L L L 4. OPTIMUM STATOR FLUX LINKAGE DETERMINATION Obtaining the ψ q component from (19) an substitution in (18), yiels the performance inex as a function ψ of only. Now, it is possible to ifferentiate J with respect to ψ to fin the optimum ψ J (24) -3 ψ - ψ 2 m 4T ss = ψ m + - ψ L 9p L L L ψ - ψ 2 m 4T L ss = * L 9p L q ψ m + - ψ L L L q (25) (26) Volume: 3 Special Issue: 7 May-214, 74

4 ψq(wb) ψ(wb) IJRET: International Journal of Research in Engineering an Technology eissn: pissn: The following equation is obtaining, for the optimum ψ aψ + bψ + cψ + ψ + e = Where - L 3 q a = L b=ψm 4 - L - 9L L q + 6L c=ψm9l - 6-3L =ψm4-3l 2 4 4TssL 4 3 e = L - ψml 2 q 9P (27) hanle the many algorithms for getting the better efficiency. In this propose scheme, the conventional DTC has been use to the control system for efficiency optimization of PMS machine. For esire set point an existing loa torque, fin an optimum stator flux linkage from look-up table. Use the optimize stator flux linkage as an optimal stator flux comman in DTC proceure. In this online calculation, the esire efficiency has been obtaine from the offline calculation. From, the offline calculation the optimize stator flux linkage ha obtaine from the PMS machine moel. 6. SIMULATION RESULTS The Simulation Results for ψ an ψ q is shown in Fig -3 an Fig -4. It is possible to erive the close-form solution of (27) for salient-pole PMS machine where L = L q. In this case, the solution is as follows: Steay state torque 2TssL ψ = q (28) opt. 3Pψ m Fig -3: D-Axis Stator Flux Linkage Component From this, optimum stator flux linkage can be calculate, for the optimize efficiency; ψ = ψ 2 + ψ 2 s opt. opt. q opt., ψ = ψ opt. m (29) 5. ONLINE CALCULATION In this online calculation, to fin the optimum stator flux linkage for obtaining the better efficiency. An important point in DTC is that the magnitue of the stator flux linkage is controlle an there is no control on the components of the stator current or stator flux in or q axis [18]. That the optimization problem can be solve more easily in terms of ψ an ψ q rather than ψ s an δ (angle of flux vector in the ψ - ψ q plane). Loss minimization of PMS machines has been ealt with in the vector control framework. As shown before, some parts of electrical loss of DTC strategy are unavoiable an loss minimization proceure eals with another part. Therefore, the optimization here is substantially ifferent from that performe in vector control. The reference spee an the loa torque can be given to the input to the lookup table for calculating the optimize stator flux linkage. The obtaine stator flux linkage an output of PI controller can be given to the conventional DTC control system. Normally, for obtaining the optimize solution, they Fig -4: Q-Axis Stator Flux Linkage Component The stator flux components an electrical losses are epicte in Fig -3 through Fig -4 in aition, flux components an electrical loss are epicte for a typical non optimum ψ s value (ψ s = 1.25 Wb). Note that although the flux control system only controls the magnitue of stator flux, the ψ an ψ q converges to their optimal values. ψ values settles at 1.25 Wb from peak value of 2.75 Wb an ψ q values settles at 1.25 Wb from 3.25 Wb by online control metho. Fig -5 shows the simulation results for the electrical losses, a esirable torque response shows that the propose efficiency optimization system oes not eteriorate the effectiveness of torque control. The stator flux components an electrical loss are epicte in Fig -1. The electrical loss value is (W). Volume: 3 Special Issue: 7 May-214, 75

5 Te(Nm) wm(ra/sec) Efficiency (%) We(W) IJRET: International Journal of Research in Engineering an Technology eissn: pissn: Fig -5: Electrical Loss The simulation results for PMSM efficiency is shown in the Fig -6. Desirable torque response shows that the propose efficiency optimization system oes not eteriorate the effectiveness of torque control. In aition, flux components an electrical loss are epicte for a typical non-optimum value. Fig -6: PMSM Efficiency The efficiency value is 8(%). The loa torque is equal to the rate torque of the PMS machine i.e. 3. Nm. The esire spee is as before. With these values T ss = 3. (N.m.) an optimization proceure results (ψ ) opt. = 1.25 (Wb) an (ψ q )opt.= 1.25(Wb) an consequently. In aition, to verify the robustness of close loop system to loa isturbances, the loa torque increase to 3Nm in.1 sec at 1 sec perio. Fig -8 shows Simulation Result for Electro-Magnetic Torque, Hysteresis Bans an Actual Spee. The motor spee control can perform isturbance compensation task an esire spee is obtaine after a short transient time. The electro-magnetic torque value is 3 (Nm) an Actual motor spee value is 17 (ra / sec). In this loss measurement of DTC PMSM use offline control metho an online control metho to enhance the efficiency of traitional control of the motor. The offline values can be calculate from the machine moel. By using the values of offline, for simulate the online control metho values of using optimize stator flux linkage ψ s. This can be achieve from - axis stator flux linkage ψ an q axis stator flux linkage ψ q. Table -1: Quantitative comparative stuy for optimize efficiency Propose PMSM Spee = 1 rpm Torque = No loa Spee = 1 rpm Torque = 1 Nm Spee = 1 rpm Torque = 1.5 Nm Spee = 1 rpm Torque = 2 Nm Spee = 1 rpm Torque = 2.5 Nm Spee = 1 rpm Torque = 3 Nm Electrical Losses(W) Efficiency (%) Although the flux control system only controls the magnitue of stator flux, the ψ an ψ q converges to their optimal value foun ue to torque generation constraints. The electrical loss can be epicte through the optimize stator flux ψ s. The electrical loss can be simulate using the optimize stator flux linkage ψ s. The flux components an electrical losses can be inferre from the non optimal values. The resulte PMSM efficiency graph shows the motor spee control can perform the isturbance compensation task an esire spee is obtaine after a short time. The efficiency enotes the motor spee an motor torque. By varying the loa from to 4Nm at a constant spee of 1rpm has achieve a optimize efficiency. At a spee of 1rpm an a motor torque of 1Nm has 87.35% of electrical loss is watts an no loa of 89.3% of electrical loss is 12.53watts achieve a better efficiency. Fig -7: Electro-Magnetic Torque an Hysteresis Bans, Actual Motor Spee 7. EXPERIMENTAL RESULTS Energy efficient pulse with moulation inverters are wiely use to control electrical machine accurately for process nees. The pulse with moulation has averse effect an prouce aitional losses in the motor. These losses increases Volume: 3 Special Issue: 7 May-214, 76

6 EFFICIENCY(%) Efficiency(%) EFFICIENCY(%) IJRET: International Journal of Research in Engineering an Technology eissn: pissn: the motor temperature an egraing of the machine power in converter use. For the performance preiction of the variable spee rives a reliable an reasonably accurate loss moel of a PMSM rive system is important. Measurement were taken uner no loa an loa conition for PWM supplies. 7.1 No Loa Conition The motor has been teste uner the no loa conition as per the motor nameplate ata, together with parameter erive from the test are presente in Table -2. Table -2: No loa conition operating at a spee of 5Hz Operating conition Without usage of DTC Voltage(V) 154 Current(A).3 Input power(w) Synchronous spee(rpm) 15 Spee (RPM) 1498 Output power(w) Loa Conition The motor was teste uner the range of loa conition, for PWM supply conitions an also the various losses was calculate for rate spee as well as the better efficiency has been achieve for PWM inverter. Table -3 inicates the losses are calculate at 5Hz operating point. Table -3: Inicates the loa conition operating at a frequency of 5Hz Operating conition Without usage of DTC Voltage (V) 151 Current (A) 1.25 Input power (W) Synchronous spee 15 (RPM) Spee (RPM) 138 Output power (W) Efficiency (%) 75 Copper loss (W) Iron loss (W) Friction an winage 2.7 loss(w) Core loss (W) 17 Total loss Comparative Analysis of Various Losses with Efficiency Comparative analysis of various losses like(copper loss, iron or core loss calle electrical loss an friction an winage loss also calle as mechanical loss) with efficiency operating at a frequency of 5Hz Fig -9: Efficiency Vs Copper Loss Fig -9 shows that the, Copper losses increase as the value of electrical current passing through the conuctors increases. An rise in the temperature of the wire or conuctor causes the resistance of the wire to increase causing the copper losses to also increase. Copper losses result from Joule heating stating that the energy lost increases as the square of the current through the wire an is in proportion of the electrical resistance of the conuctors. Copper Loss = I 2 R Fig -1: Efficiency Vs Core Loss Fig -1 shows that the lamination of core area increases the resistance value has to be ecreases at a time the iron loss to be more. Since the ecreases of core area the efficiency is achieve high COPPER LOSS(W) Core loss(w) FRICTION AND WINDAGE LOSSES(W Fig -11: Efficiency Vs Friction an winage Loss Volume: 3 Special Issue: 7 May-214, 77

7 Efficiency(%) EFFICIENCY(%) EFFICIENCY(%) IJRET: International Journal of Research in Engineering an Technology eissn: pissn: Fig -11 shows that the mechanical losses occur at the bearing an brush friction loss occurs in woun rotor inuction motor. These losses happens with the variation in spee. The spee usually remains constant at three phase inuction motor. Hence these losses nearly remains constant. 1 Fig -12: Efficiency Vs Total Loss Fig -12 shows that the total loss can be calculate by the summation of all above losses Fig -13: Efficiency Vs Line voltage In line voltage increases at that time the efficiency gets increase because the efficiency an voltage are irectly proportional to each other Fig -14: Efficiency Vs Torque In this fig -14 the torque increases at that time efficiency gets ecrease because the torque an efficiency is inversely proportional to each other. 8. COMPARATIVE STUDY The quantitative comparative stuy for optimize efficiency of PMSM for both simulation an measure result was compare in Table TOTAL LOSSES(W) LINE VOLTAGE(V) Torque(Nm) Table -4: Shows the comparison of efficiency for Simulation an Experimental setup Torque Efficiency of Efficiency of (Nm) measure result (%) simulation result (%) CONCLUSIONS In this metho the optimization of steay state efficiency in irect torque control of permanent magnet synchronous machines is propose. The optimum stator flux comman is foun out at any operating point by an off-line proceure such that the minimum electrical loss is obtaine. The On-line computations are limite to fin the optimum stator flux linkage comman from a calculate offline control metho. For PMSM machine, the close form solution of optimum stator flux has been erive. Although, the flux control system only controls the magnitue of stator flux converge to their optimal values ue to torque generation constraint. Lower steay state electrical losses are obtaine by efficiency optimization approach. In the outcome, the effectiveness of the optimal flux etermination proceure has been verifie, an the resulte motor spee, the motor torque an efficiency are epicte an motor spee control can perform isturbance compensation task an esire spee is obtaine after a short transient time. The result which has been obtaine from the online calculation was one by MATLAB environment an experimentally. The Simulation results also confirm the machine efficiency over a loa changes at constant spee. In the measure value of electrical losses the optimize efficiency has been achieve at a loa torque of 1Nm has 87.35% an no-loa of 89.3% an as compare to simulation the experimental result efficiency has been ecrease by 23% at rate torque. REFERENCES [1] B. Asghari, V. Dinavahi, M. Rioual, J. A. Martinez, an R. Iravani(29), Interfacing techniques for electromagnetic fiel an circuit simulation programs IEEE Task Force on Interfacing Techniques for Simulation Tools, IEEE Trans. Power Del., vol. 24, no. 2, pp [2] A. Boglietti, A. Cavagnino, an M. Lazzari(21), Fast metho for the iron loss preiction in inverter-fe inuction motors, IEEE Trans. In. Appl., vol. 46, no. 2, pp [3] A. Boglietti, A. Cavagnino, D. M. Ionel, M. Popescu, D. A. Staton, an S. Vaschetto(21), A general moel to preict the iron losses in PWM inverter-fe Volume: 3 Special Issue: 7 May-214, 78

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