Impact of the motor magnetic model on direct flux vector control of interior PM motors

The stator-field-oriented, direct-flux vector control has been proven to be effective in terms of linear torque control and model independent performance at limited voltage and current (i.e. in flux weakening) for AC drives of various types. The performance of the direct-flux vector control relies on the accuracy of the flux estimation, as for any field oriented control. The knowledge of the motor magnetic model is critical for flux estimation when the operating at low speed. This paper addresses the effects of a limited knowledge of the motor model on the performance of the control at low speed, for an Interior Permanent Magnet motor drive. Experimental results are give

Unified Direct-Flux Vector Control for AC Motor Drives

The paper introduces a Unified Direct-Flux Vector Control scheme suitable for sinusoidal AC motor drives. The AC drives considered here are Induction Motor, Synchronous Reluctance and synchronous Permanent Magnet motor drives, including Interior and Surface-mounted Permanent Magnet types. The proposed controller operates in stator flux coordinates: the stator flux amplitude is directly controlled by the direct voltage component, while the torque is controlled by regulating the quadrature current component. The unified direct-flux control is particularly convenient when flux-weakening is required, since it easily guarantees maximum torque production under current and voltage limitations. The hardware for control is standard and the control firmware is the same for all the motors under test with the only exception of the magnetic model used for flux estimation at low speed. Experimental results on four different drives are provided, showing the validity of the proposed unified control approac

Accurate Inverter Error Compensation and Related Self-Commissioning Scheme in Sensorless Induction Motor Drives

This paper presents a technique for accurately identifying and compensating the inverter nonlinear voltage errors that deteriorate the performance of sensorless field-oriented controlled drives at low speed. The inverter model is more accurate than the standard signum-based models that are common in the literature, and the self-identification method is based on the feedback signal of the closed-loop flux observer in dc current steady-state conditions. The inverter model can be identified directly by the digital controller at the drive startup with no extra measures other than the motor phase currents and dc-link voltage. After the commissioning session, the compensation does not require to be tuned furthermore and is robust against temperature detuning. The experimental results, presented here for a rotor-flux-oriented SFOC IM drive for home appliances, demonstrate the feasibility of the proposed solution

Direct torque control for dual three-phase induction motor drives

A direct torque control (DTC) strategy for dual three-phase induction motor drives is discussed in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The DTC strategy is based on a predictive algorithm and is implemented in a synchronous reference frame aligned with the machine stator flux vector. The advantages of the discussed control strategy are constant inverter switching frequency, good transient and steady-state performance, and low distortion of machine currents with respect to direct self-control (DSC) and other DTC schemes with variable switching frequency. Experimental results are presented for a 10-kW DTC dual three-phase induction motor drive prototype

Self-Commissioning of Inverter Nonlinear Effects in AC Drives

The paper presents a novel technique for an accurate identification of the inverter nonlinear effects, such as the dead-time and on-state voltage drops. The proposed technique is very simple and it is based only on a current control scheme. If the inverter load is an AC motor, the inverter effects can be identified at drive startup using as measured quantities the motor currents and the inverter DC link voltage. The identified inverter error is stored in a Look-Up Table (LUT) that can be subsequently used by the vector control algorithm. The proposed method has been tested on a 1 kVA inverter prototype and the obtained results demonstrate the feasibility of the proposed solutio

Multiphase induction motor drives - a technology status review

The area of multiphase variable-speed motor drives in general and multiphase induction motor drives in particular has experienced a substantial growth since the beginning of this century. Research has been conducted worldwide and numerous interesting developments have been reported in the literature. An attempt is made to provide a detailed overview of the current state-of-the-art in this area. The elaborated aspects include advantages of multiphase induction machines, modelling of multiphase induction machines, basic vector control and direct torque control schemes and PWM control of multiphase voltage source inverters. The authors also provide a detailed survey of the control strategies for five-phase and asymmetrical six-phase induction motor drives, as well as an overview of the approaches to the design of fault tolerant strategies for post-fault drive operation, and a discussion of multiphase multi-motor drives with single inverter supply. Experimental results, collected from various multiphase induction motor drive laboratory rigs, are also included to facilitate the understanding of the drive operatio

Admittance Model Identification of Inverters using Voltage Injection

The advancements in power electronics are leading to a growing number of electronic converters connected to the electric grid. Even though this enables a more efficient transformation and use of energy, the harmonic interaction between converters can cause instabilities in the network. Therefore, it is important to model the individual converters and their interconnection in an efficient way, in order to study the global stability of the system. A promising modelling strategy analytically derives the equivalent admittance of the converters. However, due to industrial secrecy issues, experimental identification methods are also necessary to obtain the converter equivalent admittance with a black-box approach. This paper analyses the experimental characterization of inverters using the voltage injection method. A detailed explanation of the theoretical background of this method and its practical implementation are provided

Vector Control of Multiple Three-Phase Permanent Magnet Motor Drives

With the rapid development of power electronics, multiphase electrical solutions are becoming a competitive alternative to the conventional three-phase drives. Nowadays, the multiphase drives represent a robust and consolidated technology in both safety-critical and high-power applications. In addition, soon they will most likely be employed in the transportation electrification process. In this context, the multiple three-phase structures are undergoing an impressive development since they use the well consolidated three-phase technology reducing cost and design time. In this paper, a highperformance vector control for multiple three-phase permanent magnet motor drives is proposed. The developed solution employees a modular approach for the independent control of each three-phase unit. To show the feasibility of the developed control scheme, experimental results are provided for a ninephase permanent magnet machine employing a triple threephase configuration

Model predictive Direct Flux Vector Control of multi three-phase induction motor drives

A model predictive control scheme for multiphase induction machines, configured as multi three-phase structures, is proposed in this paper. The predictive algorithm uses a Direct Flux Vector Control scheme based on a multi three-phase approach, where each three-phase winding set is independently controlled. In this way, the fault tolerant behavior of the drive system is improved. The proposed solution has been tested with a multi-modular power converter feeding a six-phase asymmetrical induction machine (10kW, 6000 rpm). Complete details about the predictive control scheme and adopted flux observer are included. The experimental validation in both generation and motoring mode is reported, including post open-winding fault operations. The experimental results demonstrate the feasibility of the proposed drive solution

Electric vehicle ultra-fast battery chargers: A boost for power system stability?

As a consequence of the exponential growth of the electric vehicle (EV) market, DC fast-charging infrastructure is being rapidly deployed all around the world. Ultra-fast charging (UFC) stations are starting to pose serious challenges to the electric power system operation, mostly due to their high peak power demand and unregulated discontinuous operation. To address these issues, local energy storage can be installed, ensuring a smoother grid power absorption profile and allowing to provide grid-supporting features. In this work, a control solution for the grid-side AC/DC converter of next-generation EV UFC stations is proposed. A virtual synchronous compensator (VSC) control algorithm is implemented, in order to lessen the impact of the charging station on the utility and to provide the full spectrum of grid ancillary services (i.e., frequency regulation, reactive power compensation, harmonic reduction, short circuit current generation, etc.). The proposed control strategy is verified experimentally on a downscaled 15 kVA three-phase inverter, emulating the grid front-end of the charging station