A novel fuzzy direct torque control system for three-level inverter-fed induction machine

Abstract

Diode clamped multi-level inverter (DCMLI) has a wide application prospect in high-voltage and adjustable speed drive systems due to its low stress on switching devices, low harmonic output, and simple structure. However, the problem of complexity of selecting vectors and capacitor voltage unbalance needs to be solved when the algorithm of direct torque control (DTC) is implemented on DCMLI. In this paper, a fuzzy DTC system of an induction machine fed by a three-level neutral-point-clamped (NPC) inverter is proposed. After introducing fuzzy logic, optimal selecting switching state is realized by applying various strategies which can distinguish the grade of the errors of stator flux linkage, torque, the neutral-point potential, and the position of stator flux linkage. Consequently, the neutral-point potential unbalance, the dv/dt of output voltage and the switching loss are restrained effectively, and desirable dynamic and steady-state performances of induction machines can be obtained for the DTC scheme. A design method of the fuzzy controller is introduced in detail, and the relevant simulation and experimental results have verified the feasibility of the proposed control algorithm.

Review of recent advancements of direct torque control in induction motor drives – a decade of progress

“…Based on the flux and torque errors of both motors, optimised voltage vector is chosen from a common switching table. Soft computing techniques [48,111,118] and sensorless control algorithms [94][95][96] were implemented as in conventional two-level inverter based DTC.…”

“…To overcome this, techniques to synthesise intermediate voltage vectors in two‐level inverter [47, 48, 69] and DTC using special converters are introduced. Special converters like matrix converters [44, 94–96, 109–111] and multilevel inverters [49–52, 97, 98, 112–119] provided more voltage vectors for better control options. This allowed to design modified switching table, increased torque hysteresis levels [47, 69] and selecting optimised voltage vector to provide maximum torque rate under dynamic conditions [48] for better controllability and reliability.…”

Constant Frequency Torque Controller for DTC with Multilevel Inverter of Induction Machines

“…Figure 6 shows a system torque loop. After the averaging process of (15) and (16), a simplified and averaged torque equation can be written as in (19). By introducing a small perturbation in T e , d and ω slip for linearization in (22) and transformed it to the frequency domain, the small-signal transfer function and steady state equation can be extracted as follows:…”

“…As a result, more precise control can be obtained. Several control method have been proposed for DTC scheme using multilevel inverter (DTC-MLI); hysteresis-based and non-hysteresis-based such as predictive control strategy [11,15,17,18,20,22,26,27,30], space vector modulation strategy [2, 4, 8-10, 14, 21, 28, 29, 33] and fuzzy logic control strategy [3,5,7,19,31,[34][35][36].The employment of hysteresis-based control strategy in discrete implementation has led to high torque ripple even with a small hysteresis band. This is due to the delay in sampling time.…”

Impact of the control constraint on a buck converter design based on multi-objective optimization procedure

“…As a result, more precise control can be obtained. Several control method have been proposed for DTC scheme using multilevel inverter (DTC-MLI); hysteresis-based and non-hysteresis-based such as predictive control strategy [11,15,17,18,20,22,26,27,30], space vector modulation strategy [2, 4, 8-10, 14, 21, 28, 29, 33] and fuzzy logic control strategy [3,5,7,19,31,[34][35][36].…”