Performance Improvement for PMSM Driven by DTC Based on Discrete Duty Ratio Determination Method
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applied sciences Article Performance Improvement for PMSM Driven by DTC Based on Discrete Duty Ratio Determination Method Dazhi Wang 1, Tianqing Yuan 1,* , Xingyu Wang 1, Xinghua Wang 2, Sihan Wang 1 and Yongliang Ni 3 1 School of Information Science and Engineering, Northeastern University, Shenyang 110819, China 2 Physical Education Department, School of Humanities and Law, Northeastern University, Shenyang 110819, China 3 China North Vehicle Research Institute, Beijing 100072, China * Correspondence: [email protected] Received: 27 May 2019; Accepted: 17 July 2019; Published: 22 July 2019 Abstract: In order to improve the performance of the servo control system, which is composed ofthe permanent magnet synchronous motor (PMSM) driven by novel direct torque control based on the fixed sector division criterion (FS-DTC) utilizing the composite active vectors, a discrete duty ratio determination method (FS-DDTC) is proposed in this paper. The determination of the accurate duty ratio is the key to obtain the desired error compensational results for PMSM, which is related to the performance of the servo system directly. As the applied master vector and slave vector during each control period are the adjacent vectors, therefore, the direction of the synthetic vector is between the directions of the two applied active vectors. Additionally, the analytical relationship between the sector angle of the synthetic vector and the error rate, which can realize the determination of the discrete duty ratio value without complicated calculations is deduced first. Furthermore, the duty ratio values of the two applied active vectors in FS-DTC are obtained through the selections of the duty ratio scale in the novel discrete duty ratio determination method directly, which can simplify the calculation process of the accurate duty ratio values effectively. The effectiveness of the proposed discrete duty ratio determination method is verified through the experimental results on a 100-W PMSM drive system. Keywords: direct torque control (DTC); permanent magnet synchronous motor (PMSM); synthetic vector; discrete duty ratio 1. Introduction The performances of the servo motor and the motor control strategy determine the quality of the servo system. Permanent magnet synchronous motor (PMSM) has lots of merits, including high reliability and good control performance. Additionally, it has been applied in industrial robot application widely [1–7]. Field-oriented control (FOC) and direct torque control (DTC) are the two widely applied high-performance control strategies for the PMSM [8–13]. Torque is the variable in DTC that is controlled directly, so the quickest dynamic response can be obtained in the PMSM driven by DTC [14–16]. Therefore, the servo system that is composed by the permanent magnet synchronous motor (PMSM) driven by direct torque control owns many merits than other servo systems. The torque error and the flux error are compensated by a single active vector comprehensively in single vector error compensational strategy (SV-DTC). Therefore, the PMSM driven by SV-DTC suffers from some drawbacks, such as large torque and flux linkage ripples as the errors of flux linkage and torque in conventional DTC (CDTC) are compensated by only one active vector [17–20]. On the other hand, in order to improve the steady-state performance of the PMSM, the novel direct torque control Appl. Sci. 2019, 9, 2924; doi:10.3390/app9142924 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, x FOR PEER REVIEW 2 of 11 linkage and torque in conventional DTC (CDTC) are compensated by only one active vector [17–20]. Appl. Sci. 2019, 9, 2924 2 of 11 On the other hand, in order to improve the steady-state performance of the PMSM, the novel direct torque control (NDTC) utilizing composite active vectors has been proposed in [2]. Despite the (NDTC)better steady-state utilizing composite and dynamic-state active vectors performanc has beene proposed of the PMSM in [2]. Despitesystem thecan better be obtained, steady-state the andcomputation dynamic-state burden performance is inevitably of increased the PMSM with system the using can beof the obtained, adaptive the sector computation division burdencriterion, is inevitablytherefore, the increased fixed sector with thedivision using criterion of the adaptive is proposed sector for division the control criterion, system therefore, (FS-DTC) the in fixed [3]. sector divisionIn order criterion to simplify is proposed the forcomplexity the control of systemthe control (FS-DTC) system, in [ 3the]. determination method of the duty Inratio order value to simplify is studied the in complexity this paper.The of the analyt controlical system, relationship the determination between the methodsector angle of the of duty the ratiosynthetic value vector is studied and the in this error paper.The rate is deduced analytical first. relationship It should betweenbe noted the that sector the applied angle of master the synthetic vector vectorand slave and thevector error during rate is each deduced control first. period It should in FS-DTC be noted are that the the adjacent applied mastervectors, vector therefore, and slave the vectordirection during of the each equivalentsynthetic control period in vector FS-DTC is between are the adjacent from the vectors, directions therefore, of the thetwo direction active vectors. of the equivalentsyntheticThe precondition of vector the accurate is between duty from ratio the valu directionse determination of the two activeis the vectors.selection The of preconditionthe suitable ofdiscrete the accurate duty ratio duty value. ratio valueThe complexity determination of the is thecontrol selection system of thewill suitable be increased discrete while duty the ratio discrete value. Theduty complexity ratio value of is the much control accurate, system on will the be othe increasedr hand, while the therequired discrete error duty compensation ratio value is results much accurate,cannot be on obtained the other while hand, the the discrete required duty error ratio compensation value is inaccurate. results cannot The proposed be obtained discrete while duty the discreteratio determination duty ratio value method is inaccurate. can solve the The ex proposedisting problems discrete in dutyFS-DTC ratio effectively. determination method can solveThe the rest existing of this problems paper comprises in FS-DTC the effectively. following sections. The calculations of the accurate active factorsThe are rest described of this paper in Section comprises 2. The the scheme following diagram sections. of Thethe discrete calculations duty of ratio the accuratedetermination active factorsmethod are is describedillustrated in in Section Section2. 3. The The scheme calculation diagram for of the the synthetic discrete dutyvector, ratio the determination discrete sector method angle, isthe illustrated discrete error in Section angle,3. Theand calculation the duty ratio for the scale synthetic are also vector, described the discrete in this sector Section, angle, which the discrete are the errorindispensable angle, and integral the duty parts ratio of scalethe discrete are also duty described ratio indetermination this Section, whichmethod. are The the description indispensable of integralexperimental parts setup of the and discrete discussions duty ratio on determinationexperimental results method. are The given description in Section of 4. experimental The conclusion setup is andanalyzed discussions in Section on experimental 5. results are given in Section4. The conclusion is analyzed in Section5. 2. Calculating the Accurate Active Factors In thethe proposedproposed novel novel direct direct torque torque control control (NDTC) (NDTC) scheme scheme in [2 ],in two [2], active two vectorsactive vectors are applied are inapplied one control in one period, control which period, can improvewhich can the steady-stateimprove the performance steady-state of performance the control system of the eff ectively.control Additionally,system effectively. the fixed Additionally, sector division the fixed criterion sector is division proposed criterion for NDTC is proposed (FS-DTC), for which NDTC can (FS-DTC), classify thewhich complexity can classify of thethe controlcomplexity system of the [3], control as shown system in Figure [3], as1 .shown It is also in Figure shown 1. in It Figure is also1 shownthat the in proposedFigure 1 that discrete the proposed duty ratio discrete determination duty ratio method determination in this paper method is used in to this replace paper the is traditionalused to replace duty ratiothe traditional determination duty methodratio dete inrmination FS-DTC. method in FS-DTC. Figure 1. Schematic diagram of the discrete duty ratio determinationdetermination method for novel direct torque control based on the fixedfixed sector division criterioncriterion (FS-DDTC) for a permanent magnet synchronous motor (PMSM). Appl. Sci. 2019, 9, 2924 3 of 11 Appl. Sci. 2019, 9, x FOR PEER REVIEW 3 of 11 As the main errors can be compensated by the applied active vector in SV-DTC [2], the applied As the main errors can be compensated by the applied active vector in SV-DTC [2], the applied two active vectors in FS-DTC are classified as master vector and slave vector [3]. Consequently, the two active vectors in FS-DTC are classified as master vector and slave vector [3]. Consequently, the active angle of the master vector and the slave active vector in FS-DTC are defined as θsm and θss, active angle of the master vector and the slave