Deadbeat-direct Torque And Flux Control Research Articles

Deadbeat-Direct Torque and Flux Control of a Brushless Axial-Flux Magnetic-Geared Double-Rotor Machine for Power-Splitting HEVs

A deadbeat-direct torque and flux control (DB-DTFC) for brushless axial-flux magnetic-geared double-rotor machines (AMGDRMs) is presented in this paper. The AMGDRM is employed as a power-splitting component in hybrid electric vehicles (HEVs) to enable speed decoupling between the internal combustion engine (ICE) and load. Since the rigid connection between the ICE and the drive train is replaced by the AMGDRM, fast torque control of the AMGDRM is required for the ICE speed regulation. Furthermore, the ICE torque contains abundant harmonics, inevitable sinusoidal components are introduced to the modulating rotor torque for torque balance, and further to the PM rotor torque owing to the magnetic-gear effect. Since both the PM rotor of the AMGDRM and the traction motor contribute to the hybrid electric system total torque output (i.e., torque coupling), the cascaded traction motor should compensate the PM rotor torque ripple actively to guarantee smooth total output torque. However, proportional-integral (PI) regulator suffers from limited bandwidth and thus could not realize accurate torque decoupling. Therefore, DB-DTFC, where torque and flux linkage are decoupled and respectively achieve their reference commands within two sampling periods, i.e., deadbeat responses, is proposed to enable a faster and more robust ICE speed control and accurate torque decoupling. The DB-DTFC law is derived and discrete-time close-loop current and flux linkage observers of the AMGDRM are developed. The proposed scheme and its superiorities are experimentally validated on an AMGDRM prototype test bench.

Improved Deadbeat-Direct Torque and Flux Control for PMSM With Less Computation and Enhanced Robustness

Deadbeat-direct torque and flux control (DB-DTFC) significantly improves the torque response performance compared with the conventional direct torque control. However, the existing DB-DTFC algorithm suffers from a relatively heavy computational burden due to its intricate derivation. Thus, two simplified DB-DTFC algorithms for permanent magnet synchronous machines (PMSMs) are proposed in this article to relieve the burden. The first one is based on the stator flux differential, and the second one is based on the complex power of PMSM. Furthermore, the performance of DB-DTFC highly relies on the accuracy of machine parameters. Thus, modified stator flux observer and electromagnetic torque observer are designed to enhance parameter robustness based on disturbance observer theory. The theoretical derivation of the proposed methods is investigated in-depth. Finally, both simulation and experimental results verify that the proposed deadbeat methods can maintain the deadbeat performances with a reduced computational burden. Meanwhile, the modified observer can help the deadbeat algorithms work well when machine parameters change.

Simulation Research on Deadbeat Direct Torque and Flux Control of Permanent Magnet Synchronous Motor

Direct torque control (DTC) is widely used in a permanent-magnet synchronous motor (PMSM), but it has its own shortcomings caused by high torque ripple. Deadbeat-direct torque and flux control (DB-DTFC) is a new torque and flux method compared with DTC. However, the traditional DB-DTFC is often based on rotor-flux-oriented control. The reference voltage of the stator is computed in a rotor-flux-oriented coordinate system, and the solution involves solving quadratic equations, which will increase the burden of computational processing. To improve the computation of the reference voltages and the control performance, this paper proposes a new DB-DTFC algorithm and introduces its basic principles. First, the proposed DB-DTFC algorithm uses the forward Euler equation to solve the reference voltage in a stator-flux-oriented coordinate system. Second, the discrete mathematical model is used to predict the next control current to achieve deadbeat control. Third, the structural model of the proposed DB-DTFC is constructed. Finally, the simulation model of the proposed DB-DTFC algorithm is built with a MATLAB/Simulink platform. The simulation results prove that the proposed DB-DTFC algorithm can achieve better control performance in torque and flux control compared with the DTC algorithm and SVM-based direct torque and flux control (SVM-DTFC) algorithm. In particular, the torque index of DB-DTFC is reduced about 6% in a limited speed range in comparison with the DTC algorithm.

Model Predictive Torque Control for Dual Three-Phase PMSMs with Simplified Deadbeat Solution and Discrete Space-Vector Modulation

Unprecise voltage vectors applied in conventional model predictive control (MPC) would cause additional ripples in electromagnetic torque. To eliminate the problem, this article proposes an improved model predictive torque control (MPTC) based on deadbeat solution and discrete space-vector modulation (DSVM) for dual three-phase permanent magnet synchronous machines (PMSMs). First, deadbeat-direct torque and flux control (DB-DTFC) algorithm is applied and simplified, so that the computational burden can be reduced. Second, the virtual voltage vectors (VVVs) are adopted in dual three-phase voltage vector space to reduce voltage harmonics. Also, the DSVM is further proposed in this VVVs based vector space to generate more voltage vectors. After that, the simplified DB-DTFC and the DSVM scheme are artfully combined to select suitable voltage vector candidates for the MPTC, and the best one is then chosen to control the dual three-phase PMSMs. Finally, both simulation and experimental results are given to verify the effectiveness of the proposed method.

Accurate Discrete-Time Modeling for Improved Torque Control Accuracy for Induction Machine Drives at Very Low Sampling-to-Fundamental Frequency Ratios

Operations at low sampling-to-fundamental frequency (S2F) ratios of induction machines are required for high-power or high-speed applications. The traditional indirect field-oriented control is open-loop control on torque, which is sensitive to machine parameters and degrades at low S2F ratios. Deadbeat-direct torque and flux control (DB-DTFC) is closed-loop control on torque but also degrades at low S2F ratios with inaccurate discrete-time approximations. This article presents a methodology of accurate discrete-time modeling for the flux and current observer and the deadbeat controller used in DB-DTFC. The current, flux, and torque estimations are improved with the proposed observer model at very low S2F ratios. The torque control is enhanced and insensitive to machine parameters under high-speed low-S2F-ratio conditions. The increased computational time of the proposed model is insignificant for real-time implementations.

Deadbeat Direct Torque and Flux Control for Permanent Magnet Synchronous Motor Based on Stator Flux Oriented

Direct torque control (DTC) has become a widely acceptable alternative to field-oriented control in permanent magnet synchronous motor (PMSM) drives. Deadbeat direct torque and flux control (DB-DTFC) is a significant improvement over the classical DTC. However, there are some aspects that can be improved, such as insufficiently small electromagnetic torque ripple, unsmooth dynamic response, heavy computation burden, and relatively weak robustness to motor parameters variation. To improve the operation performance, an advanced DB-DTFC strategy is proposed in this article. First, the algorithm model based on stator flux oriented coordinate system is deduced. On this basis, the basic principle of proposed DB-DTFC is presented. Second, a novel graphical analysis method is proposed to help illustrate the proposed strategy. Third, a general solution method is proposed to solve the reference stator voltage, which is a key variable for the DB-DTFC. Finally, the stability of system is analyzed. Theoretical and experimental comparisons between the proposed DB-DTFC and the conventional DB-DTFC are done. The results show that the performance in the aspects of electromagnetic torque and stator current ripples reduction, dynamic response, computation burden, and robustness to motor parameters variation are all improved in the proposed DB-DTFC.

Extending High-Speed Operating Range of Induction Machine Drives Using Deadbeat-Direct Torque and Flux Control With Precise Flux Weakening

Flux weakening techniques have been developed for field-oriented control (FOC) drives to achieve the maximum torque capability above the base speed. Deadbeat-direct torque and flux control (DB-DTFC) has the advantages of precise torque and flux control and reduced parameter sensitivity compared to FOC, thus it has the benefit of more consistently achieving the maximum torque capability in the flux weakening region more accurately. This paper introduces a flux weakening strategy for DB-DTFC. Considering voltage and current limits, a simple solution to the optimal trajectory for the stator flux magnitude is derived to achieve the maximum feasible torque over the entire operating range. Results show that the speed control is extended to a significantly higher range beyond the base speed. Torque control is less sensitive to machine parameters and has better dynamics in the flux weakening region compared with the traditional FOC drives. Self-sensing is also investigated in the flux weakening region. Challenges of self-sensing are addressed to significantly extend the high-speed operating range.

Deadbeat-Direct Torque and Flux Control of Wound Field Synchronous Machine at Low Sampling to Fundamental Frequency Ratios

Enhancements to the deadbeat-direct torque and flux control (DB-DTFC) of wound field synchronous machines (WFSMs) are proposed allowing for operation at low sampling frequency to fundamental frequency ratios. Discrete-time current and flux linkage observers, which properly model WFSM d-q and d-f cross-coupling are formed using a Taylor series approximated sampled Laplace approach. The effect of the Taylor series order on the discretization error and model accuracy is examined. The torque curve to determine the inverter voltage commands is derived from the flux linkage model coefficients. Experimental comparison of the WFSM torque response is made between the classical DB-DTFC with current and flux observers formed using a z-transform approach and the torque line derived from a forward Euler method and the newly proposed observers and torque curve.

Enhanced Methodology for Injection-Based Real-Time Parameter Estimation to Improve Back EMF Self-Sensing in Induction Machine Deadbeat-Direct Torque and Flux Control Drives

Back electromotive force (EMF) self-sensing is commonly used in induction machine (IM) drive systems, which can be effectively controlled using deadbeat-direct torque and flux control (DB-DTFC). Accurate machine parameters are needed for back EMF self-sensing DB-DTFC drive systems. In this paper, an injection-based, real-time parameter estimation method for IM DB-DTFC drives, in the back EMF self-sensing mode, is proposed. The methodology for choosing appropriate frequencies for injection signals is introduced. With encoder-based velocity feedback, the proposed DB-DTFC injection method induces no additional torque ripple, compared to traditional d -axis pulsating voltage vector injection used in indirect field oriented control. However, in the self-sensing mode, the injected flux linkage induces an erroneous speed ripple, which causes a real speed ripple. This paper presents two approaches to eliminate the speed ripple. Finally, the injection-based real-time parameter estimation method for the system is experimentally evaluated.

Stability Analysis of Deadbeat-Direct Torque and Flux Control for Permanent Magnet Synchronous Motor Drives with Respect to Parameter Variations

This paper presents a stability analysis and dynamic characteristics investigation of deadbeat-direct torque and flux control (DB-DTFC) of interior permanent magnet synchronous motor (IPMSM) drives with respect to machine parameter variations. Since a DB-DTFC algorithm is developed based on a machine model and parameters, stability with respect to machine parameter variations should be evaluated. Among stability evaluation methods, an eigenvalue (EV) migration is used in this paper because both the stability and dynamic characteristics of a system can be investigated through EV migration. Since an IPMSM drive system is nonlinear, EV migration cannot be directly applied. Therefore, operating point models of DB-DTFC and CVC (current vector control) IPMSM drives are derived to obtain linearized models and to implement EV migration in this paper. Along with DB-DTFC, current vector control (CVC), one of the widely used control algorithms for motor drives, is applied and evaluated at the same operating conditions for performance comparison. For practical analysis, the US06 supplemental federal test procedure (SFTP), one of the dynamic automotive driving cycles, is transformed into torque and speed trajectories and the trajectories are used to investigate the EV migration of DB-DTFC and CVC IPMSM drives. In this paper, the stability and dynamic characteristics of DB-DTFC and CVC IPMSM drives are compared and evaluated through EV migrations with respect to machine parameter variations in simulation and experiment.

Enabling Driving Cycle Loss Reduction in Variable Flux PMSMs Via Closed-Loop Magnetization State Control

Variable flux permanent magnet synchronous machines (VF-PMSMs) have recently been proposed to reduce driving cycle losses in electric vehicle traction motors via magnetization state (MS) manipulation. This paper presents a closed-loop MS control method to enable reliable loss minimization control of VF-PMSMs. The MS is estimated at every sample instant and is used as a feedback for closed-loop control. Under most circumstances, the proposed method maintains precise torque control even during the MS manipulation transient by using a deadbeat-direct torque and flux control (DB-DTFC) framework. The state-of-the-art high-speed flux trajectory generation method for MS manipulation is integrated in the new closed-loop method to allow MS manipulation up to the maximum speed within the inverter voltage limit. The effectiveness of the proposed methods, in terms of driving cycle loss reduction capability and its thermal impact, is evaluated experimentally by emulating the road load using the dynamometer load motor.

Fault-Tolerant Capability of Deadbeat-Direct Torque and Flux Control for Three-Phase PMSM Drives

This paper investigates the performance of a three-phase permanent magnet synchronous motor (PMSM) drive operating under a single fault, adopting a low cost and fault-tolerant control based on deadbeat-direct torque and flux control (DB-DTFC). Under faulty operation, this fault-tolerant DB-DTFC offers an independent regulation of the electromagnetic torque and the stator flux linkage by using the same torque line equation, stator flux linkage, and current observers adopted during healthy conditions, requiring very limited hardware reconfigurations. In particular, it has been demonstrated that in a fault situation, the same drive model equations adopted for the healthy electric drive can be exploited with very limited detrimental effects on the drive performance simply by applying a suitable reference frame transformation set in the torque and flux control structure. The proposed fault-tolerant DB-DTFC has been validated by experimental tests, confirming that the proposed fault-tolerant DB-DTFC ensures satisfactory faulty operations and drive stability, without significant degradation of parameter sensitivity, keeping limited the increment of computational efforts.

Improvement of Back-EMF Self-Sensing For Induction Machines When Using Deadbeat-Direct Torque and Flux Control

Back-electromotive force (back-EMF) self-sensing is commonly used in induction machine (IM) drive systems for its maintenance cost and safety considerations. In recent years, compared with standard indirect field oriented control, deadbeat-direct torque and flux control (DB-DTFC) has been shown to be a highly effective method for IM control with a fixed switching frequency. It has advantages such as fast torque dynamics with one step dynamic response for torque and flux with no current regulator. This paper evaluates the synergy between back-EMF self-sensing technology and DB-DTFC for IM drive systems. In this paper, an observer-based closed-loop back-EMF tracking self-sensing control in an IM DB-DTFC drive system is presented. It includes a back-EMF state filter, back-EMF tracking observer, and cascaded motion observer. Back-EMF harmonic decoupling is explored to improve the low-speed performance. The band-pass filter method (BPF) for back-EMF self-sensing is also presented. Finally, the closed loop system dynamic stiffness at very low speeds, with and without the BPF method, is experimentally evaluated.

Using Volt-Second Sensing to Directly Improve Torque Accuracy and Self-Sensing at Low Speeds

As a result of dead-time, device on-state voltage drop, dc bus voltage measurement error, etc., volt-second errors degrade precise control of torque and flux linkage, particularly at low speeds. This is true for deadbeat-direct torque and flux control (DB-DTFC), which directly manipulates the volt-second vector sourced by inverters as well as for indirect field oriented control (IFOC) drives. This paper introduces a real-time sensing scheme to measure the motor terminal volt-second vectors for each switching period with negligible phase lag. Based on the volt-second sensing, a model reference adaptive system (MRAS)-based approach is developed to decouple the volt-second errors from inverter nonlinearity and dc bus voltage fluctuation and measurement error. By delivering an accurate volt-second vector for each switching period, torque and flux control accuracy, self-sensing performance and parameter estimation accuracy are significantly enhanced.

Real-Time Parameter Identification and Integration on Deadbeat-Direct Torque and Flux Control (DB-DTFC) Without Inducing Additional Torque Ripple

This paper is dedicated to exploring real-time parameter identification approaches and their integration with deadbeat-direct torque and flux control (DB-DTFC) without additional torque ripple. Using the voltage model at medium- and high-speed ranges, DB-DTFC is insensitive to parameters. Performance degrades at low speeds with the rotor time constant errors, because the current model is utilized for flux linkage estimation. Two different real-time parameter estimation approaches are developed, including a flux observer-based model reference adaptive system (MRAS) and a pulsating flux injection-based method. Both are experimentally evaluated for how well they mitigate DB-DTFC performance degradation at low speed. For the MRAS-based method, the fundamental components are used for parameter convergence, which does not induce additional torque ripple. For the injection-based method, traditional d -axis pulsating voltage vector injection used in indirect field-oriented control (IFOC) yields significant torque ripple, particularly at high speed. The proposed pulsating flux injection scheme used in DB-DTFC excites the same magnitude of current harmonics and induces no additional torque ripple over a wide speed range.

Robustness Analysis of Deadbeat-Direct Torque and Flux Control for IPMSM Drives

This paper presents robustness evaluation of deadbeat-direct torque and flux control (DB-DTFC) of interior permanent-magnet synchronous machine (IPMSM) drives with respect to machine parameter variation. For performance comparison, current vector control (CVC), one of the most widely used control methods, is also implemented under identical operating conditions as DB-DTFC. As the metrics to evaluate dynamic performance of DB-DTFC and CVC IPMSM drives, command tracking is used to investigate torque command tracking performance and dynamics stiffness is used to evaluate disturbance rejection performance. In addition, the torque estimation accuracy of DB-DTFC and CVC is investigated with respect to parameter variation. Simulation and experimental results of robustness evaluation of DB-DTFC and CVC are presented in this paper.

A comparative overview of indirect field oriented control (IFOC) and deadbeat-direct torque and flux control (DB-DTFC) for AC Motor Drives

A comparative overview of indirect field oriented control (IFOC) and deadbeat-direct torque and flux control (DB-DTFC) for AC Motor Drives

Loss Manipulation Capabilities of Deadbeat Direct Torque and Flux Control Induction Machine Drives

This paper investigates the loss manipulation capabilities of deadbeat direct torque and flux control (DB-DTFC) induction machine drives. For each switching period, a volt-second-based inverse model provides a range of volt-second solutions to achieve the desired torque at the end of each switching interval, whereas the stator flux magnitude provides another degree of freedom to manipulate machine losses. With a flux-based DB-DTFC loss model proposed, losses can be manipulated each switching period without compromising torque dynamics. For a steady-state operation and typical process trajectories, the minimum loss can be achieved with corresponding energy savings. Alternatively, significant losses can be rapidly induced to dissipate kinetic energy in a machine during braking transients. This loss maximization technique provides significant braking torque without requiring additional hardware to transfer/dissipate energy. DB-DTFC induction machine drives provide an effective and elegant solution for continuous loss manipulation without compromising dynamic performance.

Low-Sampling-Frequency Stator Flux Linkage Observer for Interior Permanent-Magnet Synchronous Machines

Deadbeat-direct torque and flux control (DB-DTFC) is a direct torque control (DTC) method that provides the fastest possible torque response with smooth and continuous operation even at the voltage limits. DB-DTFC achieves the smoothest possible torque and flux trajectory tracking performance by using the machine inverse model to select volt-second solutions that will produce the desired torque and flux by the end of each pulsewidth modulation (PWM) interval. Since the DB-DTFC inverse model requires accurate steady-state and dynamic flux estimates, discrete-time stator current and flux linkage observers are needed to properly implement DB-DTFC. The existing high-sampling-frequency stator current and flux linkage observers are formed based on approximate discrete-time models for IPMSMs by assuming high-sampling-frequency (10-kHz) operation. This paper presents a more exact discrete-time model for IPMSMs, such that, even at low sampling frequencies, proper stator current and flux linkage observers can be formed to achieve accurate current and flux linkage estimation. The proposed low-sampling-frequency stator current and flux observers are developed using discrete-time modeling with an inverter-sourced volt-second input model. The proposed observers are shown to be very feasible for real-time implementation, and their experimental evaluation documents the improvement achieved compared to high-sampling-frequency observers, even under machine parameter variations.

A Low-Switching-Frequency Flux Observer and Torque Model of Deadbeat–Direct Torque and Flux Control on Induction Machine Drives

This paper presents a digital implementation of deadbeat–direct torque and flux control (DB-DTFC) for induction machines at low switching frequencies (SFs). For high SFs, existing discrete-time flux observers and Volt–second-based inverse torque models used for DB-DTFC achieve acceptable flux estimation accuracy and fast torque response. However, the flux estimate is less accurate when the SF is reduced and the DB-DTFC performance degrades. This paper develops a more suitable flux observer and Volt–second-based inverse torque model that minimizes flux estimation error and improves torque control for DB-DTFC. Simulation and experimental results are provided to evaluate the performance of the proposed observer and torque model at very low SFs. Consequently, digital implementation of low-SF DB-DTFC on high-power induction machines is feasible.