Yogesh N. Tatte

Torque ripple reduction in five-phase direct torque controlled induction motor

This paper presents the torque ripple reduction in the direct torque controlled (DTC) five phase induction motor (IM). The ripples are directly related to the hysteresis band of the controller in torque and flux loops within the operating switching frequency limits. It is proposed to increase the switching frequency by dither signal injection into the torque and flux control loops. A conventional DTC control of five phase model is modified by superimposing a high frequency and small amplitude triangular waveform into torque and flux error. The operation of five phase induction motor within the operating speed range indicates the reduction in the torque ripple and improves its performance in the low speed region. It is observed that the torque ripple is reduced by 30% and improvement in the total harmonic distortions (THD) of current. The overall dynamic performance improvement is indicated through MATLAB/SIMULINK simulation.

Torque ripple minimization in five-phase three-level inverter fed direct torque control induction motor drive

This paper presents the torque ripple minimization in direct torque control (DTC) five-phase induction motor drive fed with three-level five-phase inverter. Selective space vector utilization in three-level five-phase inverter is investigated and compared with its two-level counterparts. In order to minimize the torque ripple, five-level torque comparator is presented which allows the utilization of full, half and zero voltage vectors. These voltage vectors utilization in three-level DTC not only minimizes the torque ripple but also the x-y stator flux distortion. Performance is evaluated through simulation and validated through experimental results.

Torque Ripple and Harmonic Current Reduction in a Three-Level Inverter-Fed Direct-Torque-Controlled Five-Phase Induction Motor

In a switching-table-based direct torque control method (ST-DTC), the torque ripple reduces with increasing number of levels of the torque comparator. The number of levels is decided by the availability of the number of voltage vectors according to the topology of the inverter. This paper proposes the seven-level torque comparator to reduce the torque ripple in the DTC-controlled five-phase induction motor fed by the three-level five-phase inverter. In the five-phase induction motor, an elimination of x − y stator flux is inevitable otherwise the stator phase current will be distorted. In order to eliminate the x − y stator flux, the virtual voltage vectors are formed. Experimental results are presented to validate the proposed DTC method.

Selection of Voltage Vectors in Three-Level Five-Phase Direct Torque Control for Performance Improvement

This paper presents a Direct Torque Control (DTC) strategy for the five-phase induction motor driven by a three-level five-phase inverter in order to improve the performance of the five-phase induction motor. In the proposed DTC technique, only 22 voltage vectors out of 243 available voltage vectors in a three-level five-phase inverter are selected and are divided in 10 sectors each with a width of 36˚. The four different DTC combinations (DTC-I, II, III and IV) for a three-level five-phase induction motor drive are investigated for improving the performance of five-phase induction motor. All four of the DTC strategies utilize a combination of the same large and zero voltage vectors, but with different medium voltage vectors. Out of these four techniques, DTC-II gives the best performance when compared to the others. This DTC-II technique is analyzed in detail for improvements in the performance of five-phase induction motor in terms of torque ripple, x-y stator flux and Total Harmonics Distortion (THD) of the stator phase current when compared to its two-level counterparts. To verify the effectiveness of the proposed three-level five-phase DTC control strategy, a DSP based experimental system is build. Simulation and experimental results are provided in order to validate the proposed DTC technique.

A split three phase induction motor for battery charging application

This paper presents an integrated high power battery charging topology by incorporating a split three phase induction motor for electric vehicle. In charging/vehicle to grid mode, stator winding is used as an inductive filter between grid and converter. During this operation, the rotor of machine is kept in stationary position as rotating magnetic field is cancelled out due to built-in nature of split phase stator winding. Therefore, mechanical locking is not required. Proposed configuration works under unity power factor operation. Through the reconfiguration of stator winding, same motor is used as three phase induction motor for traction purpose. Simulation results for proposed concept are provided for both charging and vehicle to grid mode.

Performance improvement of three-level five-phase inverter fed DTC controlled five-phase induction motor during low-speed operation

In this paper, the Direct Torque Control (DTC) for three-level five-phase inverter fed five-phase induction motor is proposed to improve the low speed performance. The classic DTC method initiates flux demagnetization effect when the five-phase induction motor runs at low speed, especially below 5Hz. This classic DTC scheme is modified in order to minimize the demagnetization effect during low speed operation. According to modification, the voltage vector space plane is divided into twenty sectors, each of width 18°. For odd number of sectors, ±36° displaced intermediate voltage vectors and for even number of sectors, ±36° displaced main voltage vectors are selected instead of ±72° displaced voltage vectors. Simulation results are presented in order to validate the proposed DTC scheme.

Direct torque control of asymmetric six-phase induction motor with reduction in current harmonics

In this paper direct torque control of asymmetric six-phase induction motor is presented. 5th and 7th order current harmonics are observed in the phase currents if conventional Direct Torque Control (DTC) scheme is extended for asymmetric six phase machine. These harmonic components are not responsible for torque production, thus cause losses in motor winding. Synthetic vectors are used in this paper for reduction of current harmonics. Average voltage in xy-subspace is maintained to zero by synthetic vectors leading to reduction of currents in xy-subspace. Experimental results are presented in paper to verify the proposed scheme.

Direct Torque Control of Induction Motor with Common-Mode Voltage Elimination

Abstract If the common-mode voltage in the induction motor drive is not eliminated, it may cause failure of motor bearings and malfunctioning of the electrical equipment associated with the drive. This article proposes the modified direct torque control technique to control the induction motor fed by three-level inverter, commonly called a neutral-point-clamped inverter. The selective voltage vectors in three-level inverter determine elimination of the common-mode voltage. The classic three-level direct torque control based on selection of 6-full, 6-half, and 2-zero voltage vectors out of available 27 is modified so that the 6-intermediate voltage vectors and a zero voltage vector are employed. A comparative investigation with another three-level direct torque control method which reduces both common-mode voltage and torque ripple is also carried out. These methods are compared with classic two-level direct torque control method in context of common-mode voltage, torque ripple, current total harmonic distortion (THD) and DC-link utilization. The simulation and experimental results validate the proposed common-mode voltage elimination and common-mode voltage reduction direct torque control techniques.