Direct Torque Control with Full Order Stator Flux Observer for Dual-Three Phase Induction Motor Drives

Abstract

Keywords: DTC, dual-three phase induction motor, stator flux observer, constant inverter switching frequency SummaryThe main advantage of multi-phase drives is the possibility to divide the controlled power on more inverter legs. That will reduce the current stress of each switch, compared with a three-phase converter. For this reason, multi-phase drives are convenient in highpower and/or high-current applications, such as ship propulsion, aerospace applications, and electric/hybrid vehicles.A very interesting and discussed multi-phase solution is the dual three-phase induction machine having two sets of three-phase windings spatially shifted by 30 electrical degrees with isolated neutral points (Fig. 1).Traction drives require an accurate control of the machine flux and torque. For this reason, Rotor Field Oriented Control (RFOC) solutions have been proposed in order to get decoupled control of the flux and torque.These schemes must use current control loops to impose the flux and torque producing stator current components resulting in a quite complicated control scheme. An alternative solution is the use of Direct Torque Control (DTC) strategies.For these reasons, the proposed paper deals with a DTC solution for dual-three phase induction motor drives. The proposed solution uses simple PI regulators implemented in the stator flux synchronous reference frame to get a robust control scheme against parameters detuning. The flux estimator scheme employs an Adaptive Stator Flux Observer (ASFO) combined with a current-speed (I-ω) based stator flux estimator. The (I-ω) estimator is used to get the stator flux only at low speed, while the ASFO provides the flux Fig. 1. Dual-three phase induction machine estimation for the remaining speed range. Doing so, besides getting an accurate flux estimation, it is possible to use the observed currents to compensate the inverter dead-time effects at low speed. This is particularly important for low voltage/high current applications, as the drive considered in this paper.The advantages of the discussed control strategy are: constant inverter switching frequency, good transient and steady-state performance and less distorted machine currents in contrast to DTC schemes with variable switching frequency.Experimental results are presented for a 10 kW dual three-phase induction motor drive prototype. The motor is supplied by a battery fed six-phase IGBT inverter whilst the control algorithm has been implemented on the dSPACE DS1103 PPC Controller Board. A start-up of the drive to 6500 rpm followed by a speed reversal is shown in Fig. 2 where are illustrated the rotor reference and actual speed, the pull-out and estimated electromagnetic torque and the estimated stator flux. The field-weakening strategy computes the stator flux reference according to the available DC-link voltage and limits the reference torque in order to get a safe and stable drive operation up to the maximum speed.The obtained results show good control performance for the whole drive speed range. The proposed DTC al...

Multiphase induction motor drives – a technology status review

“…The algorithm has been implemented in stator flux oriented reference frame. Another PWM-DTC scheme, based once more on the VSD theory, is presented in [102]. The reference voltage vector is obtained through simple PI regulators implemented in the stator flux oriented reference frame.…”

“…The stator flux is estimated by means of a full-order Luenberger observer, which provides also stator current estimation. The estimated currents (that are less noisy than the real ones) are used to successfully compensate the inverter dead-time effects, improving significantly the drive performance at very low speed [102].…”

Dual-Three Phase Induction Machine Drives Control—A Survey

“…To get a robust control scheme against motor parameters detuning, a PWM-DTC scheme, based on the VSD theory, is presented in (51) . The reference voltage vector is obtained through simple PI regulators implemented in stator flux synchronous reference frame.…”

“…The reference voltage vector is obtained through simple PI regulators implemented in stator flux synchronous reference frame. The stator flux is estimated by means of a full-order observer, which provides also stator current estimation; the estimated currents are used to compensate the inverter dead-time effects (51) .…”

“…The literature reports different multi-phase solutions from the point of view of the phase number and the machine type; the more interesting and addressed ones are the five-phase and six-phase ones, employing induction and synchronous permanent magnet or synchronous reluctance motors (3) . The paper deals with a review on the most relevant research results published in the literature (1)- (51) , regarding the VSI fed dual-three phase induction motor drives. The machine has two sets of windings spatially shifted by 30 electrical degrees with isolated neutral points (Fig.…”