Emil Levi

The article introduces for the first time a two-generator system comprising two brushless multiphase doubly fed induction generators, which have control windings (CWs) connected in series. The stator power windings of both machines are standard three-phase ones. However, the CWs of the two generators are of five-phase configuration and are connected in series to a single voltage source inverter, using a special connection, which is described in detail. The connection is such that flux/torque producing currents of one five-phase winding are made nonflux/torque producing currents of the other five-phase winding, and vice versa. The said connection provides means for active and reactive power control of one generator, using a vector control approach, completely independent of the operating state of the other generator. The mathematical model of the generator system with two series-connected five-phase brushless doubly fed induction machines is introduced. Next, a complete generator system model, including the associated vector control scheme, is developed. The performance of the two independently controlled series-connected generators was experimentally investigated using a dedicated test rig developed for this purpose. The experimental results confirm the system’s ability to control two generators independently. Laboratory tests demonstrate that the system achieves voltage regulation within 5%, frequency stability better than 0.1 Hz, and response time below 0.5 s under 20% load and speed variations. Thus, the goal of the article, to provide a proof-of-concept verification, is achieved. Last but not least, various drawbacks of the developed system are qualitatively addressed, and these would have to be weighed against the advantages for any real-world implementation.

Мost grid-forming and grid-following inverters contain an LCL output filter and an internal current controller. The resonant nature of the filter interferes with the injection of high-quality grid currents, degrades disturbance rejection, and compromises stability. Although the subject is quite mature with many innovative control solutions already available, the character of the step response of the grid current and the closed-loop bandwidth obtained with the LCL filters remain far below the performance obtained with the L filter. Most solutions essentially depend on the mutual ratios of resonant frequency, sampling rate, and target bandwidth. In contemporary grids, grid-side inverters should meet conflicting requirements of significantly faster grid-current response with significantly less injection of pulse width modulation (PWM) ripple. To overcome the shortcomings and meet these objectives, a novel control solution is proposed with analytically derived control actions, which ensure internal and external stability, provide a robust and well-damped step response of the grid current with an unprecedented bandwidth, and ensure a stable, resonance-free operation with uncertain grids. The achievement of the stated objectives is confirmed experimentally by carrying out a series of tests in an installation with industrial grid inverters.

Lists the recipients of IES prize paper awards.

Finite-control-set model predictive control (FCS-MPC) of multiphase ( n -phase, n is assumed to be an odd number for simplicity) drives is challenging because of the large number of actual/virtual voltage vectors and the need for current control in ( n –1)/2 subspaces (or planes; multiplane current control). Any suboptimal design (poor or no current control in some of the ( n –1)/2 planes) may result in high individual plane current ripples, due to the low reactance. This work therefore investigates continuous-control-set (CCS) MPC for constant switching frequency multiphase motor drives as another alternative. The high-bandwidth CCS-MPC is designed to accurately account for system nonidealities, namely digital control and pulsewidth modulation delays, inverter dead time, and measurement noise. It will be shown that the CCS-MPC has the advantages of full voltage vector space access, regular switching characteristic, and improved cycle-by-cycle tracking control, while maintaining some of the known advantages of the FCS-MPC, e.g., intuitive cost function design, model-based control, and fast dynamics. The proposed control scheme is benchmarked experimentally against the classical, proportional-integral-based, field-oriented control in conjunction with an asymmetrical six-phase induction motor drive.

This article introduces a novel algorithm for suppression of phase current harmonics in three-phase sinusoidal surface-mounted permanent magnet synchronous machines (SPMSMs) caused by nonideal back EMF waveform and dead time effects. Proposed feedback acquisition chain obtains an exact information on all the relevant harmonics within each period of the fundamental. Design of the harmonic current controller based on the internal model control principle is given. The article outlines the relevant details of implementation and the results of verification performed by both computer simulations and experimentally, using a laboratory prototype machine. Experimental results, obtained in the presence of nonsinusoidal back-EMF and with erroneous dead time compensation, prove the ability of the proposed solution to remove the stator current harmonics quickly, in just two fundamental periods, and thus, eliminate torque ripple.

Presents IES society award recipients and distinguished reviewers for 2021.

Presents a listing of the best papers and distinguished reviewers for this publication in 2020.

The paper develops a method to choose the number of rotor bars in order to eliminate rotor slot harmonics in stator current spectrum and pulsation torques that are their consequence. Mains-fed, three-phase cage induction motors with the most common number of pole pairs and number of stator slots, that result in integer slot winding, are analyzed. The analysis is based on the recently derived general rule for optimal selection of rotor bars, valid for symmetrical multiphase machine with prime number of phases and integer slot stator winding. As a tool for validation of analytically predicted results, parameterized winding function (PWF) model is used. Electromagnetic torque ripple factor is used as a measure of goodness of the number of rotor bar selection. The practical motivation of the study is an attempt to supersede the many existing rules for rotor bar number selection that, depending on the source, may be different, and provide a unified general approach to the problem. One of the main findings derived in the paper is ascertainment that increasing the number of pole pairs increases the degree of freedom in choosing the proper number of rotor bars. The same applies when the number of motor phases increases.