This brief describes the two unique Fractional Order (FO) speed controllers' FOPI and FOPI design and validation for the induction motor drive. The detuning of the conventional PI controller issues ...under machine parameter variations and low speed operating regions are overcome by the proposed two types of FO speed controllers. This brief presents the novel FO controller design procedure for the Voltage Source Inverter (VSI) fed IM. The actual FO VSI fed IM transfer function model is identified using the chirp signal injection method with the Hardware-In-Loop (HIL) system for the laboratory prototype. The parameter variation is subjected to different stator winding resistance machines of the same rating. The rotor inertia change of up to eight times the no-load value is incorporated to investigate the robust performance of these speed controllers under dynamic operating conditions. The performance of the designed <inline-formula> <tex-math notation="LaTeX">FOPI </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">FOPI </tex-math></inline-formula> controllers are analyzed at low speeds. The results show the supremacy of the <inline-formula> <tex-math notation="LaTeX">FOPI </tex-math></inline-formula> controller over the <inline-formula> <tex-math notation="LaTeX">FOPI </tex-math></inline-formula> and PI under the same stability boundary limits. The experimental validation of these controllers is provided.
This paper presents an improved direct torque control (DTC) method for an asymmetrical six-phase induction motor using a two-level six-phase inverter. As is well known, a simple extension of ...three-phase DTC technique to an asymmetrical six-phase motor, using large vectors only, introduces significant current harmonics of the order 6 n±1 (n = 1, 3, 5,...), which are mapped into the nonflux/torque producing (xy) plane. These harmonics cause only losses in the motor winding as they do not take part in torque production. Hence, a number of different improved DTC techniques have been developed in the past for multiphase motor drives. The paper takes one such DTC method as the starting point and improves it further by using the concept of virtual voltage vectors. Developed vector selection algorithm, based on two virtual voltage vectors, requires the information on position of the flux in the auxiliary (xy) subspace and provides stator current quality commensurate with the currently available best DTC algorithm for six-phase drives. However, use of two virtual voltage vectors enables a substantial reduction of the torque ripple, which is achieved by means of a five-level torque comparator. Extensive experimentation is performed and it is shown that the reduction of the current harmonics is in essence almost the same as in another recently developed DTC scheme, based on the use of a single virtual voltage vector. However, the achieved torque ripple reduction, which is verified experimentally, makes the scheme superior when compared to the existing approaches. At the same time, developed scheme retains qualities of conventional DTC schemes, such as simple structure and fast response. Its additional beneficial feature is the easiness of implementation.
Summary
This paper presents the fractional‐order voltage‐source‐inverter‐controlled induction machine (FO‐VSI‐IM) model extraction and integration to improve the closed‐loop speed control performance ...of variable speed drives. In the operating range of variable speed drive, it is susceptible to load disturbance and speed tracking error. This paper provides the practical approach to obtain the fractional‐order model of VSI‐fed induction motor (IM) drive by using PWM signal injection technique. The injected PWM signals and speed encoder response signals are recorded using the dSPACE 1104 platform. This model is used in constructing the closed‐loop speed control of VSI‐IM with designed integer‐order PI speed controller. The comparative performance is evaluated for FO‐VSI‐IM and integer‐order voltage‐source‐inverter‐controlled induction machine (IO‐VSI‐IM) with feed‐forward gain variations and load disturbances. It is observed that the robust speed tracking capability with the controller designed using the FO‐VSI‐IM model over the controller with IO‐VSI‐IM model under load disturbances. The improvement in speed tracking with less control effort in the FO‐VSI‐IM model is advantageous in field‐oriented control (FOC) drives.
This work has addressed the inherent fractionality present in the induction motor inductance while working with a non‐sinusoidal (PWM) voltage source and its effect on closed‐loop speed control performance. In this work, the authors have demonstrated to identify the time constants by proposing the novel FO model identification method. A detailed speed controller design procedure is proposed for the closed‐loop FOC using the FO and IO VSI‐fed IM models.
In a switching-table-based direct torque control method (ST-DTC), the torque ripple reduces with increasing number of levels of the torque comparator. The number of levels is decided by the ...availability of the number of voltage vectors according to the topology of the inverter. This paper proposes the seven-level torque comparator to reduce the torque ripple in the DTC-controlled five-phase induction motor fed by the three-level five-phase inverter. In the five-phase induction motor, an elimination of x - y stator flux is inevitable otherwise the stator phase current will be distorted. In order to eliminate the x - y stator flux, the virtual voltage vectors are formed. Experimental results are presented to validate the proposed DTC method.
Summary
This paper presents the digital realization of the fractional‐order PI (FOPI) controller fractional integrator element using the improved constant phase approximation method. A new pole‐zero ...rationalization approach is proposed within the bandwidth of the Bode phase plot. The voltage source inverter fed induction motor fractional‐order model has been identified. A novel mathematical FOPI controller design procedure for the identified FO plant model has been proposed. The designed FOPI controller fractional integrator element is implemented using the constant phase approximation method. A detailed comparative performance study of the proposed approximation method with the existing Charef, Oustaloup, and refined Oustaloup methods has been carried out using the Bode, Nyquist, and Nichols plots. The proposed FOPI controller is placed in the speed feedback loop of the rotor field‐oriented control algorithm of IM. To confirm the proposed FOPI controller approximation method's robustness, a hardware study is carried out on the laboratory hardware‐in‐loop (HIL) platform. In addition, variation in the number of pole‐zero pair's effect on the speed tracking performance, robustness against parameter and load variations are also analyzed.
An improved constant phase FO approximation method is proposed, with an additional design parameter μ. This gives an optimized values of pole‐zero pairs to fit better with in the designed phase, which reflects into the dynamics. A generalized design methodology with frequency domain approach for FOPI controller parameters calculation and a detailed FO integrator approximation algorithm is presented clearly. A comparative frequency domain analysis of the Charef, Oustaloup, refined Oustaloup, and proposed approximation methods is given along with their integer‐order approximations.
The conventional PI-based speed controllers are susceptible to speed tracking error and limited load rejection capability. This paper presents the high-performance fractional-order PI speed ...controller (FOPI) for field oriented control of induction motor (FOC-IM) drives with enhanced disturbance rejection capability. The design of FOPI involves third-order voltage source inverter fed induction motor (VSI-IM) model identification, fitting it into the required phase margin and gain margin constraints and Oustaloups fractional element approximation. The identification algorithm using the hardware-in-loop system is provided. The non-linear integer order VSI-IM model improves the tracking and dynamic performance of the drive. The designed FOPI speed controller performance is compared with the literature’s existing FOPI controller design methods. The experimental analysis found that, in terms of speed tracking, parameter variations, inertia variations, and disturbance rejection capabilities, the suggested controller is more effective and resilient than existing tuning approaches.
•A novel identification method based on a chirp signal is proposed to obtain an accurate integer order plant model for VSI-fed IM. Compared to existing identification techniques, the proposed method is more practical and yields comparable accuracy.•A robust FOPI controller is developed to address various operating conditions such as load disturbances, inertia changes, and parameter variations. The proposed controller’s speed control performance is evaluated in realistic field situations and found to be more robust than existng PI ZN-method, FOPI (John etal, 2020), and FOPI (Sudheer and Aware, 2022) controllers.•The classical Oustaloup’s approximation method suitable for practical hardware implementation. A design procedure is presented to implement the FOPI controller for the identified nonlinear VSI-fed IM IO plant model. This makes the proposed controller more feasible for real-world induction motor applications.•A comparative study has been carried out on the Hardware-In-Loop (HIL) system with existing tuning rules of the FOPI controller and Ziegler and Nicholas (ZN) PI controller tuning method to evaluate the proposed design method advantages. The proposed controller’s error and control signals performance analysis, load disturbance rejection analysis, robustness against parameter and inertia variations are also demonstrated on the laboratory HIL prototype.
This paper proposes two direct torque control (DTC) strategies to reduce the common-mode voltage (CMV) in the fivephase induction motor driven by three-level five-phase inverter. In each technique, ...31 voltage vectors consisting of 30 nonzero voltage vectors, and a zero voltage vector are selected out of available 243 voltage vectors. The selection of these voltage vectors are based on their capabilities of reducing the CMV, eliminating the x-y stator flux and maintaining the torque ripple under control. The ten large, ten small, and a zero voltage vector are same in both schemes, however only difference in designing the control strategy for the two schemes is the utilization of different ten medium voltage vectors. First proposal (DTC-I) reduces the CMV to 3V dc /10 and second proposal (DTC-II) reduces to V dc /10. These schemes are compared with DTC technique of five-phase induction motor fed by two-level five-phase inverter in order to judge the capabilities of proposed schemes in context of reducing the CMV. The simulation and experimental results validate the proposed DTC techniques.
This article presents the reduction in common mode voltage (CMV) in a three-phase to six-phase indirect matrix converter feeding power to a six-phase load using space vector modulation technique ...based on virtual vector synthesization. From the total available 64 vectors, 6 virtual vectors are derived to develop a switching algorithm giving an effective reduction in CMV for symmetrical ( 60° ) six-phase system. The voltage transformation ratio is maintained maximum possible from the presented switching algorithm. This three-phase to six-phase conversion system maintains unity power factor across the three-phase supply side, hence no reactive power is drawn from the supply. This complex control is implemented using two conjunct processors controlled in a master and slave manner. Simulation, as well as hardware, results are presented to validate the proposed control technique.
A classical symmetrical carrier‐based digital Average Current Mode (ACM) control has two sampling choices, peak point and valley point, to control the average inductor current. If it is employed to ...regulate the DC‐DC boost converter, there will be a difference in the dynamic performance at peak and valley point sampling instants because of discontinuous output voltage ripple due to Equivalent Series Resistance (ESR) of the output capacitor. Therefore, this paper investigates the effect of sampling instant on the dynamic performance of the PWM DC‐DC boost converter in consideration of capacitor ESR. The small‐signal transfer functions of a boost converter for both sampling positions are prominent to analyze each sampling impact on its dynamics. They are derived by using discrete‐time modeling. Further, the choices of sampling instant are investigated related to the RHP zero elimination, voltage stability, and peak‐to‐peak ripple current of the DC‐DC boost converter. The boost converter has improved stability performance by synchronizing the ADC sampling at starting position (valley point) of the symmetrical carrier signal, as evident by the analytical and hardware results of both sampling techniques working from 25% to 100% load working conditions.
In the proposed work, detailed analysis with an application‐oriented approach has been provided in both frequency‐ and time‐domain approaches to effectively understand the effect of sampling position on a digitally controlled DC‐DC boost converter. It is proven that the sampling location of the control variable must be precisely synchronized with the starting position of the carrier signal to ensure the proper functioning of a digitally controlled boost converter.
The predictive torque control (PTC) is researched extensively for control of electrical drives because of its fast-dynamic response and robust control. In multiphase motors, it is mandatory to design ...a multiobjective cost function with more than two terms for controlling <inline-formula> <tex-math notation="LaTeX">x\!y </tex-math></inline-formula>-subspace current and common-mode voltage (CMV). However, selecting the weighting factor for multiple control variables is time penalizing and increases the computational burden. Using a noisy speed input from the speed sensor in the prediction model reduces the steady-state performance in terms of higher torque ripple, flux ripple, and phase current total harmonic distortion (THD), especially during low speeds. In this article, PTC for a five-phase induction motor (IM) drive without speed sensor sensorless PTC (PTC-S) is presented. The adaptive full observer is incorporated to estimate the stator flux, stator resistance, and rotor speed. The proposed algorithm is capable to eliminate CMV and <inline-formula> <tex-math notation="LaTeX">x\!y </tex-math></inline-formula>-current harmonics having advantages over the conventional PTC (PTC-C) algorithm. The elimination of CMV is achieved by the selection of set of voltage vectors from available 243 voltage vectors. The proposed speed sensor-less control is implemented with a three-level neutral-point clamped (NPC) inverter using synthetic voltage vectors. The use of a synthetic voltage vector eliminates the <inline-formula> <tex-math notation="LaTeX">x\!y </tex-math></inline-formula>-subspace current and reduces the computational burden. The PTC-S is implemented with a seven-level hysteresis torque comparator, which reduces the torque ripple significantly. To further improve the effectiveness of the control algorithm, two-step delay compensation is implemented. The discussed algorithms are tested on a laboratory prototype for experimental evaluation. The proposed study also highlights the effect of torque ripple reduction on the speed adaptive flux observer for sensor-less operation. The experimental results show the effectiveness and applicability by comparing the steady-state and dynamic performances of PTC.
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