Three-level Direct Torque Control Research Articles

Speed regulator and hysteresis based on artificial intelligence techniques of three-level DTC with 24 sectors for induction machine

Direct torque control (DTC) of induction motor (IM) is important in many applications. In this paper presents a three-level direct torque control with 24 sectors is applied for IM using PI-flou controller and hysteresis regulators based in artificial intelligence techniques. The DTC system is known to offer fast decoupled control between torque and flux via a simple control structure. Nevertheless, DTC system has two major drawbacks, with are the variable inverter switching frequency and high torque output ripple. The validity of the proposed control scheme is verified by simulation tests. The stator flux, torque, and current are determined and compared to the above technique.

Modified LUT-based DTC of NPC 3-Level Inverter fed Sensorless IPMSM Drive with DC Link Voltage Balance

In the proposed work, a modified look-up table-based direct torque control (DTC) scheme is reported for a neutral point-clamped three-level inverter-fed interior permanent magnet synchronous motor drive. In the classical DTC scheme, there are significant torque and flux ripples in the drive due to low number of available switching states. To reduce the oscillations in torque and flux, a three-level inverter-operated IPMSM drive is discussed. In a three-level inverter, the increased count of active voltage vectors is results in more sinusoidal output waveforms. Moreover, stator flux plane has 12 sectors in the proposed work unlike classical DTC. Besides, the higher level of flux and torque hysteresis comparators is implemented. DC link capacitor voltage balancing scheme is also instigated to minimize voltage stress on semiconductor devices, improve stator current THD and increased capacitor life. Based on the sector information, flux and torque hysteresis output and capacitor voltage balance logic, an improved LUT is established and explained for a three-level DTC scheme. Consequently, improved stator current (THD) and decrement in torque and flux ripples are observed. To make the system robust, model reference adaptive control (MRAC) based sensorless speed estimation algorithm is realized. The proposed DTC scheme is compared with a two-level inverter-fed and a three-level-inverter-fed DTC scheme without DC link voltage balance strategy. To carry out the analysis, MATLAB/Simulink environment is utilized. Moreover, to validate the simulation results, experimental analysis of the proposed technique is carried out using dSPACE1104.

Torque Ripple Reduction in PMSG for Standalone Wind Energy System Using Three Level DTC with A Dither Signal

In this paper, focused on direct torque control (DTC) for permanent magnet synchronous generator direct driven standalone variable speed wind turbine. The machine side converter (MSC) employed three-level DTC with dither signal strategy proposed for minimizes the torque & flux ripple. The triangular signal used as a dither signal & injected in a hysteresis band controller of torque & flux comparator. The optimum magnitude of the triangular wave is 3% of its rated torque & flux used in order to reduce acoustic noise. The proposed strategy minimizes torque & flux ripple as compared to conventional two-level DTC technique. Three-level SVPWM strategy employed for a load-side converter (LSC) in order to reduce harmonic distortion.

Seven-level NPC Inverter-based Neuronal Direct Torque Control of the PMSM Drives with Regulation Speed Using Neural PI Controller

In the scope of this work, a new structure of the direct torque control (DTC) technique scheme of permanent magnet synchronous motors (PMSMs) is proposed using a seven-level neutral point clamped (NPC) inverter and artificial neural networks (ANNs) controllers. This intelligent strategy was used to replace, on the one hand the integral proportional (PI) speed controller, on the other hand and the traditional switching table in order to reduce total harmonic distortion (THD) of voltage/current, stator flux ripple and electromagnetic torque ripples. The modeling and simulation of the proposed control scheme were carried out in Matlab/Simulink environment. The simulation results show that the proposed strategy scheme reduced harmonic distortion of stator voltage/current, stator flux and electromagnetic torque ripples compared to traditional DTC control scheme, DTC control scheme with space vector pulse width modulation (SVPWM) and three-level DTC control scheme. It was found that the stator current waveform becomes purely sinusoidal with a reduction in the harmonic distortion rate to 11.77%.

Three-Level Inverter-Fed Direct Torque Control of IPMSM With Constant Switching Frequency and Torque Ripple Reduction

The major drawbacks of classical direct torque control (DTC) are large torque ripples and variable switching frequency. Torque ripples in DTC drives can be attenuated if a three-level inverter is employed instead of a two-level inverter. Nevertheless, torque ripples can still be large if low switching frequencies are used. To alleviate these problems, a constant-switching-frequency-based three-level DTC (3L-DTC) algorithm is presented in this paper. Operating at low, constant switching frequency, the proposed algorithm is effective in reducing torque ripples under all operating conditions. Detailed analysis and design guidelines for the proposed 3L-DTC algorithm are presented. In addition, typical issues associated with the three-level inverter, such as neutral-point voltage fluctuations and smooth voltage vector switching, are addressed. Experimental results are presented to validate the effectiveness of the proposed method.

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

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.

An Improved Direct Torque Control for Three-Level Inverter-Fed Induction Motor Sensorless Drive

A sensorless three-level neutral-point-clamped inverter-fed induction motor drive is proposed in this paper. The conventional direct torque control (DTC) switching table fails to consider the circuit limitations, such as neutral-point-balance and smooth vector switching, caused by the topology of a three-level inverter. Two kinds of modified schemes for three-level DTC are proposed to solve these problems. They also provide performance enhancement while maintaining robustness and simplicity. Fuzzy logic control and the speed-adaptive flux observer (with novel gain and load toque observation) are introduced to enhance the performance of the system. The issue of large starting current is investigated and solved by introducing the technique of preexcitation. A 32-bit fixed-point DSP-based motor drive is developed to achieve high-performance sensorless control over a wide speed range. The effectiveness of the proposed schemes is confirmed by simulation implementation and experimental validation.