This paper presents a comprehensive evaluation of several direct torque control (DTC) strategies for permanent magnet synchronous machines (PMSMs), namely DTC, model predictive DTC, and duty ratio modulated DTC. Moreover, field-oriented control is also included in this study. The aforementioned control strategies are reviewed and their control performances are analyzed and compared. The comparison is carried out through simulation, finite-element analysis, and experimental results of a PMSM fed by a two-level voltage source inverter. With the intent to fully reveal the advantages and disadvantages of each control strategy, critical evaluation has been conducted on the basis of several criteria: Torque ripple, stator flux ripple, switching frequency of inverter, steady-state control performance, dynamic response, machine losses, parameter sensitivity, algorithm complexity, and stator current total harmonic distortion.

Comparative Evaluation of Direct Torque Control Strategies for Permanent Magnet Synchronous Machines

The four-switch three-phase (B4) inverter, having a lower number of switches, was first presented for the possibility of reducing the inverter cost, and it became very attractive as it can be utilized in fault-tolerant control to solve the open/short-circuit fault of the six-switch three-phase (B6) inverter. However, the balance among the phase currents collapses due to the fluctuation of the two dc-link capacitor voltages; therefore, its application is limited. This paper proposes a predictive torque control (PTC) scheme for the B4 inverter-fed induction motor (IM) with the dc-link voltage offset suppression. The voltage vectors of the B4 inverter under the fluctuation of the two dc-link capacitor voltages are derived for precise prediction and control of the torque and stator flux. The three-phase currents are forced to stay balance by directly controlling the stator flux. The voltage offset of the two dc-link capacitors is modeled and controlled in the predictive point of view. A lot of simulation and experimental results are presented to validate the proposed control scheme.

Predictive Torque Control Scheme for Three-Phase Four-Switch Inverter-Fed Induction Motor Drives With DC-Link Voltages Offset Suppression

This paper proposes a novel duty ratio modulated direct torque control (DDTC) to concurrently reduce torque ripple and stator flux ripple that are typically associated with conventional direct torque control (DTC). Three different methods of duty ratio determination are presented to achieve various control objectives, namely DDTC-final, DDTC-mean and DDTC-rms. Additionally, adjustable error weight coefficients are introduced to balance the torque ripple reduction and stator flux ripple reduction. Experimental results are presented to validate the effectiveness of proposed DDTC. Furthermore, the comparative evaluation of proposed DDTC, conventional DDTC and DTC is conducted on the basis of several criteria to verify the superiority of proposed DDTC.

Direct Torque Control for Permanent-Magnet Synchronous Machines Based on Duty Ratio Modulation

This paper presents a sensorless flux adaption-direct torque control (FADTC) for a new flux-modulated permanent-magnet (FMPM) wheel motor, in which space-vector pulsewidth modulation (SVPWM) and a wide-speed sliding mode observer (SMO) are adopted. SVPWM-FADTC has several advantages over conventional hysteresis direct torque control, such as low torque/flux ripples in motor drive and reduced direct axis current when the motor is operated at a light or a sudden increased load. To achieve the sensorless control of SVPWM-FADTC system, a wide-speed SMO is proposed. Compared with conventional SMO, system chattering is improved, the low-pass filter and the phase compensation are eliminated, and the estimation accuracy of the rotor position at low speed is enhanced. Numerical simulations and experiments with a 2-kW FMPM wheel motor are carried out. The results verify the feasibility and effectiveness of the proposed sensorless SVPWM-FADTC method adopted by the FMPM wheel motor.

Sensorless SVPWM-FADTC of a New Flux-Modulated Permanent-Magnet Wheel Motor Based on a Wide-Speed Sliding Mode Observer

This paper designs a feedback linearization direct torque control (FL-DTC) based on the space vector modulation (SVM) which can noticeably reduce the electromagnetic torque and stator flux ripples that affect the system efficiency on interior permanent magnet synchronous motor (IPMSM) drives. First, a decoupled linear IPMSM model with two state variables (i.e., the stator flux and electromagnetic torque) is derived to implement the proposed FL-DTC strategy that preserves some advantages such as fast torque control, high torque at low speed, and fast speed response. Also, the proposed technique greatly alleviates the torque and stator flux ripples which are the major concerns of the classical hysteresis-based DTC scheme and have an effect on the stator current distortion. The system stability with the designed FL-DTC method is mathematically analyzed using the Lyapunov stability theory. Finally, the effectiveness of the proposed control law is validated through simulation results with MATLAB/Simulink and experimental results obtained from a prototype 1-HP IPMSM drive with TI TMS320F28335 digital signal processor (DSP). The verification results demonstrate that the proposed FL-DTC scheme achieves faster torque response, smaller torque ripple, and lower stator flux ripple than the conventional SVM-based PI-DTC approach under parameter uncertainties and external disturbances.

Feedback Linearization Direct Torque Control With Reduced Torque and Flux Ripples for IPMSM Drives

This paper proposes a novel direct torque control (DTC) strategy for induction motor (IM) drives fed by a four-switch three-phase inverter (FSTPI). The introduced strategy is based on the emulation of the operation of the conventional six-switch three-phase inverter (SSTPI). This has been achieved thanks to a suitable combination of the four unbalanced voltage vectors intrinsically generated by the FSTPI, leading to the synthesis of the six balanced voltage vectors of the SSTPI. This approach has been adopted in the design of the vector selection table of the proposed DTC strategy which considers a subdivision of the Clarke plane into six sectors. Simulation results have revealed that, thanks to the proposed DTC strategy, FSTPI-fed IM drives exhibit interesting performance. These have been experimentally validated and compared to the ones yielded by the Takahashi and the basic DTC strategies dedicated to the SSTPI and to the FSTPI, respectively.

DTC Scheme for a Four-Switch Inverter-Fed Induction Motor Emulating the Six-Switch Inverter Operation

This paper deals with a new direct torque control (DTC) strategy based on the bus-clamping technique dedicated to induction motor drives. The proposed strategy consists in the synthesis of two vector selection tables suitably arranged considering the bus-clamping technique. Such synthesis depends on the rotation direction of the stator flux vector. The resulting DTC strategy leads to clamp each motor phase during 60° interval in every half cycle of the reference stator flux vector. Therefore, a reduction of the inverter switching losses is gained. Furthermore, it has been found that the proposed DTC strategy offers a lower harmonic distortion of the motor phase currents and a higher capability to operate at low levels of the dc-bus voltage, which could be of interest for electric vehicle (EV) and hybrid electric vehicle (HEV) applications. These performances are confirmed by simulation and validated by experiments.

Bus-Clamping-Based DTC: An Attempt to Reduce Harmonic Distortion and Switching Losses

Currently, road vehicles are more and more equipped by PM synchronous motors. Of particular interest are brushless DC (BLDC) motors with their low resolution encoder make it feasible their integration in a large scale industry such as the automotive one. Within this trend, the paper deals with the synthesis and implementation of a new DTC strategy dedicated to the control of BLDC motor drives. Compared to the most recent and high-performance DTC strategy, the proposed one offers an improved reliability thanks to the achievement of a balanced switching frequencies of the inverter upper and lower IGBTs, on one hand, and the reduction of the average value of the motor common mode voltage, on the other hand. Furthermore, the torque ripple is significantly damped during sequence-to-sequence commutations using a three-level hysteresis torque controller. An experimentally-based comparative study between the most recent and high-performance DTC strategy and the introduced one clearly highlights the potentialities exhibited by the latter.

Direct torque control of brushless DC motor drives with improved reliability

The paper is aimed at hybrid propulsion systems upgrade and their capability to be competitive with the thermal propulsion systems. This could be achieved through the improvement of their cost-effectiveness, compactness and reliability thanks to the substitution of the conventional three-leg inverters by reduced structure ones. Of particular interest are four-switch and three-switch-delta inverters. These could be suitably associated to brushless DC and induction motors. This paper develops this idea.

On the potentialities of reduced structure inverters integrated in automotive electric motor drives

This paper investigates a novel direct torque control (DTC) strategy for induction motor (IM) drives fed by NPC three-level-three-phase inverter. The proposed strategy is based on the basic DTC operation implemented for the IM control using six-switch three-phase inverter (SSTPI). This proposed strategy consists in the synthesis of two vector selection tables suitably arranged considering the bus-clamping technique. Such synthesis depends on the rotation direction of the stator flux vector. The resulting DTC strategy leads to clamp each motor phase during 60° interval in every half cycle of the reference stator flux vector. Simulation results have proven that the bus-clamping-DTC (BCDTC) strategy exhibits high dynamic performance during both transient and steady-state operations. Therefore, a reduction of the inverter switching losses is gained Through the minimization of the switching frequency.

B. El Badsi

Papers

DTC Scheme for a Four-Switch Inverter-Fed Induction Motor Emulating the Six-Switch Inverter Operation

Bus-Clamping-Based DTC: An Attempt to Reduce Harmonic Distortion and Switching Losses

Direct torque control of brushless DC motor drives with improved reliability

On the potentialities of reduced structure inverters integrated in automotive electric motor drives

Bus-clamping-DTC strategy of a three-level-iverter fed induction motor drive with reduced switching frequency and torque ripple