Digital Current-Control Schemes

The paper is about comparing the performance of digital signal processor-based current controllers for three-phase active power filters. The wide use of nonlinear loads, such as front-end rectifiers connected to the power distribution systems for dc supply or inverter-based applications, causes significant power quality degradation in power distribution networks in terms of current/voltage harmonics, power factor, and resonance problems. Passive LC filters (together with capacitor banks for reactive power compensation) are simple, low-cost, and high-efficiency solution

Self-Commissioning Algorithm for Inverter Non-Linearity Compensation in Sensorless Induction Motor Drives

In many sensorless field-oriented control schemes for induction motor (IM) drives, flux is estimated by means of measured motor currents and control reference voltages. In most cases, flux estimation is based on the integral of back-electromotive-force (EMF) voltages. Inverter nonlinear errors (dead-time and on-state voltage drops) introduce a distortion in the estimated voltage that reduces the accuracy of the flux estimation, particularly at low speed. In the literature, most of the compensation techniques of such errors require the offline identification of the inverter model and offline postprocessing. This paper presents a simple and accurate method for the identification of inverter parameters at the drive startup. The method is integrated into the control code of the IM drive, and it is based on the information contained in the feedback signal of the flux observer. The procedure applies, more in general, to all those sensorless ac drives where the flux is estimated using the back-EMF integration, not only for IM drives but also for permanent-magnet synchronous motor drives (surface-mounted permanent magnet and interior permanent magnet). A self-commissioning algorithm is presented and tested for the sensorless control of an IM drive, implemented on a fixed-point DSP. The feasibility and effectiveness of the method are demonstrated by experimental result

Experimental Identification of the Magnetic Model of Synchronous Machines

This paper proposes and formalizes a comprehensive experimental approach for the identification of the magnetic model of synchronous electricalmachines of all kinds. The identification procedure is based on controlling the current of the machine under test while this is driven at constant speed by another regenerative electric drive. Compensation of stator resistance and inverter voltage drops, iron loss, and operating temperature issues are all taken into account. A road map for implementation is given, on different types of hardware setups. Experimental results are presented, referring to two testmotors of small size, and references of larger motors identified with the same technique are given from the literature

Sensorless self-commissioning of synchronous reluctance motors at standstill without rotor locking

This paper proposes a standstill method for identification of the magnetic model of synchronous reluctance motors (SyRMs). The saturation and cross-saturation effects are properly taken into account. The motor is fed by an inverter with a short sequence of bipolar voltage pulses that are first applied on the rotor d- and q-axes separately and then simultaneously on both the axes. The stator flux linkages are computed by integrating the induced voltages. Using the current and flux samples, the parameters of an algebraic magnetic model are estimated by means of linear least squares. The proposed method is robust against errors in the stator resistance and inverter voltage, due to the high test voltages (of the order of the rated voltage). The fitted model matches very well with the reference saturation characteristics, measured using a constant-speed method, and enables extrapolation outside the sample range. The method was tested with a 2.2-kW SyRM, whose shaft was uncoupled from any mechanical load, which is the most demanding condition for this method. The proposed method can be used for automatic self-commissioning of sensorless SyRM drives at standstill

A Phase Variable Model of Aircraft Brushless Exciter Based on Finite Element Analysis and Its Coupling with the Rotating Rectifier Circuit

This paper presents the phase variable model of brushless exciter employed by aircraft integrated starter/generators. The model uses current-flux linkage functions obtained by finite element analysis. Since the developed model contains the exciter machine and its connected rotating rectifier, a particular attention is paid to adequately considering coupling effects between the exciter and the rotating rectifier which govern operation of the rectifier. One important parameter of this coupling is the inductance which contributes in commutation process of the rectifier (commutation inductance). In this regard, a simple finite element analysis technique is proposed to identify the commutation inductance. Finally, the developed model is validated by comparing its results with finite element analysis

A control strategy for an induction motor used for vehicular traction and/or positioning systems with variable speeds

The paper presents a control strategy employed to control an induction motor (IM) used in vehicular traction applications with variable speed. This strategy is based on the Direct-Flux Vector Control (DFVC) method. In such applications, deep flux weakening is required, and the maximum torque production must be obtained under current and voltage constraints. Information on the mathematical model and control scheme for DFVC is provided. The reference frame is given by the stator flux, all the calculations being made with respect to this frame. The proposed control scheme is also implementing a limitation of the maximum values of current and voltage, according to specific control laws - MTPV (Maximum Torque per Volt) and MTPA (Maximum Torque per Ampere). Experimental results are presented for a small power IM, accelerating in idle running, with an inertial load and for the steady state respectively. They are showing the efficiency of the proposed solution and a robust operation in flux-weakening conditions. The controller is belonging to the dSPACE family, being able to provide very fast floating point results. The proposed strategy can be used for controlling other types of motors, as the Interior Permanent-Magnet (IPM), Synchronous Reluctance (SyR) and wound rotor synchronous motors, considering the modifications imposed by the magnetic model (load angle, flux orientation a.s.o.)

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Advanced DC-DC converter for power conditioning in hydrogen fuel cell systems

The fuel cell (FC) generators can produce electric energy directly from hydrogen and oxygen. The DC voltage generated by FC is generally low amplitude and it is not constant, depending on the operating conditions. Furthermore, FC systems have dynamic response that is slower than the transient responses typically requested by the load. For this reason, in many applications the FC generators must be interfaced with other energy/power sources by means of an electronic power converter. An advanced full-bridge (FB) DC-DC converter, which effectively achieves zero-voltage switching and zero-current switching (ZVS-ZCS), is proposed for power-conditioning (PC) in hydrogen FC applications. The operation and features of the converter are analyzed and verified by simulations results. The ZVS-ZCS operation is obtained by means of a simple auxiliary circuit. Introduction of the soft-switching operation in PC unit brings improvements not only from the converter efficiency point of view, but also in terms of increased converter power density. Quantitative analysis of hard and soft-switching operating of the proposed converter is also made, bringing in evidence the benefits of soft-switching operation mode. The proposed converter can be a suitable solution for PC in hydrogen FC systems, especially for the medium to high-power application