Robust Control of Low-Cost Direct Drives Based on Interior Permanent Magnet Synchronous Motors (original) (raw)
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Journal of Vibroengineering, 2013
The Direct Torque Control (DTC) technique of Permanent Magnet Synchronous Motor (PMSM) receives increasing attention due to its simplicity and robust dynamic response compared with other control techniques. The classical switching table based DTC presents large flux, torque ripples and more mechanical vibrations in the motor. Several studies have been reported in the literature on classical DTC. However, only limited studies that actually discuss or evaluate the classical DTC. This paper proposes a simple DTC method / Switching table for PMSM, to reduce flux and torque ripples as well as mechanical vibrations. In this paper two DTC schemes are proposed. The six sector and twelve sector methodology is considered in DTC scheme I and DTC scheme II, respectively. In both DTC schemes a simple modification is made in the classical DTC structure that is by eliminating two level inverter available in the classical DTC is replaced by three level Neutral Point Clamped (NPC) inverter. To furth...
A Modified Direct Torque Control Scheme for Permanent Magnet Synchronous Motor Drives
This paper presents a Direct Torque Control (DTC) scheme for permanent magnet synchronous motor (PMSM) drive. The proposed scheme was designed to overcome the main disadvantage of the conventional DTC – the high torque ripple generated in steady state operation. For this purpose, the voltage level at the inverter output is modified according to the instant values of the torque error and the stator flux angle. Every sample time, a reference voltage vector is calculated, in terms of magnitude and phase, and applied to the inverter using the Space Vector Modulation technique. The reference voltage vector is calculated using a simple algorithm, which preserves the principle of the conventional DTC regarding the decoupled torque and flux control. Numerical simulations have been made to test the proposed method and results are presented for a set of operating points.
Nonlinear Direct Torque Control of Interior Permanent Magnet Synchronous Motor Drive
Tanzania Journal of Engineering and Technology, 2019
This paper presents a nonlinear direct torque control (NDTC) strategy of interior permanent magnet synchronous motors (IPMSMs) for electric vehicle (EV) propulsion. The proposed NDTC scheme applies a nonlinear model of IPMSM to dynamically determine the optimal switching states that optimize the EV drivers’ decision to reduce the workload. Moreover, the proposed NDTC method has a simple control structure and can explicitly handle system constraints and nonlinearities. The performance evaluation is conducted via a prototype IPMSM test-bed with a TMS320F28335 DSP. Comparative experimental results provide the evidence of improvements of the proposed NDTC strategy over the conventional DTC strategy by indicating a fast torque response and an accurate speed tracking even under rapid speed change conditions.
Improvised direct torque control of a permanent magnet synchronous motor
International Journal of Power Electronics and Drive Systems (IJPEDS), 2023
Permanent magnet synchronous motor (PMSM) is widely used in different applications because of their different key operation features. But despite having important key features, PMSM suffers from torque ripple when simple control techniques like direct torque control (DTC) are employed. Several approaches have been raised by many researchers to lessen the ripple when DTC is used for controlling the PMSM drive. In this work, duty ratio-optimized DTC control, which has the same simplicity as conventional DTC (CDTC), and delay compensation for input signal prediction are proposed. In the proposed system, to determine the duty ratio, slope manipulation was made by considering the minimization of torque error and forcing the developed torque to be equal to the reference torque at the end of the span. An online slope determination approach was employed to compute the duty ratio. MATLAB 2021b is used for simulation purposes. The dynamics and steady-state performance of the proposed scheme were tested for both variable-load and variable-speed operations. In addition, the harmonic performance and ratio of harmonic power loss to total active power loss of the motor were evaluated. In general, the proposed scheme performs effectively in reducing steady-state ripple and harmonic.
DIRECT TORQUE CONTROL OF PERMANENT MAGNET SYNCHRONOUS MOTORS (DTC-PMSM
Direct torque control (DTC) of AC drives is considered one of the most interesting high performance control techniques nowadays. Permanent magnet synchronous motors (PMSM) are now replacing induction motors (IM) in a variety of applications due to their valuable characteristics especially the increased efficiency and compact size. The combination of DTC and PMSM in one drive system leads to high dynamic response drive system that seems to be an interesting topic to gain the increased research in the literature. DTC offers high dynamic torque, flux, and speed responses better than that of Field Oriented Control (FOC) technique with simple controller architecture that utilizes two hysteresis controllers and a switching table to select the most suitable voltage vector to meet the torque and flux requirements. No machine parameter dependences, no axes transformation required, no voltage modulation techniques, and no current controllers are the advantages of DTC over FOC. Comparisons between DTC and FOC of PMSM are made through MATLAB simulations to show their characteristics with respect to the other. It is found that DTC gives excellent dynamic responses in both torque and flux but the ripple content is high. DTC requires the estimation for both flux and torque. A lot of methods are found in the literature to estimate the flux and the most powerful methods are compared via simulations. Pure integration method of flux estimation is the basic method that has a lot of demerits like offset, resistance variation dependence, initial value problem, and low performance at low speeds. Low Pass Filter (LPF) is intended to solve the pure integration problems but its performance at transient period is not good and there is some drift in the flux beyond the actual flux. Modified integrator is also one of the interesting flux estimation methods that gives better performance at both transient and steady state conditions than that of LPF estimator but it contains PI controller and low pass filters so that several tunings are required and complexity is increased. A flux estimator uses tunable-cutoff-frequency-LPF is simple and accurate. It is used for IM and never be used for PMSM. It is also compared and shows excellent results in both transient and steady state periods which implies the effectiveness of it for PMSM as well as IM. Switching Look-up Table is a unique characteristic in a DTC drive and it has a lot of schemes based on the number of hysteresis levels of the torque and flux comparators and the inclusion / exclusion of the zero voltage vectors. Various switching tables appeared in the literature are compared to judge the merits and demerits of each one and to show their effect on the drive performance. A relatively new switching table using modified definition of the flux sectors is used for PMSM for the first time and its results are excellent because it avoids a fatal problem appeared in the table proposed by Takahashi, the inventor of the DTC system. Selection of the amplitude of the flux and torque hysteresis bands is a very important issue in implementing the DTC drive system as they affect torque ripples, flux distortion, switching losses, and current harmonics. Simulations are made to show these effects. Trade off should be made to correctly choosing of the hysteresis band amplitudes according to the performance requirements. Torque / flux ripples and variable switching frequency are the main disadvantages of DTC system. Solutions to these problems are an interesting researching aspect nowadays. Increased number of voltage vectors and/or sectors, Space Vector Modulation (SVM), Duty Ratio control, and Model Predictive Control (MPC) techniques are the most common solutions to the problems of high ripple content and variable switching frequency. The loss of the DTC simplicity is something that makes these solutions inconvenient so that compromise studies should be done to select the most suitable control technique that meets the application needs without increasing the complexity of the system. Digital Signal Processors (DSPs) are now considered the basic controllers used in the motor control area. DSP programming is often done using hand written code by C or Assembly languages which is very time consuming and very prone to errors. Computer Aided Control System Design (CACSD) is some sort of block programming can be implemented using Matlab/Simulink. The Simulink model itself can be downloaded to the DSP which makes the real time control system design easier. The complete description of the DTC-PMSM drive system is discussed showing the power, control, measurement, and signal conditioning circuits used in the system. Six step operation of the inverter as well as open loop V/F control of PMSM are implemented in order to verify the effectiveness of the CACSD using Matlab/Simulink.