Miroslav Chomat

• PhD
• Head of Department at The Czech Academy of Sciences

With the advent of 3D printing, advancements in optimizing structures and innovations to 3D print new materials for electric machines are being developed. Conventional structures are being replaced by lattice structures which provide better properties. From plastics to metals, recent achievements have been made in the 3D printing of soft and hard m...

The paper analyzes a case of the induction motor in which one or more rotor bars in the rotor cage are broken. The method of space vectors and symmetrical components of instantaneous values of currents and voltages is used in the analysis. The solution obtained makes it possible to determine the currents in each of the healthy rotor bars, the stato...

An induction machine with combined star-delta stator winding is analysed by means of numerical simulations based on lump parameter and finite element method (FEM) models. The use of combined star-delta winding may lead to suppressing selected higher spatial harmonics of the magnetic flux density in the air gap and, thus, to lowering the energy loss...

In the case of multi-phase machines and in machines with special winding arrangements, such as combined star-delta winding, the third spatial harmonic of the magnetomotive force can, unlike in three-phase machines, negatively influence the waveforms of stator currents and torque of the machine. The paper shows how permanent magnets give rise to the...

Two basic variants of combined star-delta stator windings of induction machines are analysed. The aim of the use of the combined winding is to suppress a chosen group of higher spatial harmonics of the current layer and magnetic flux density in the air gap and the magnetic flux in the yoke. The suppression of the higher spatial harmonics results in...

The paper deals with the influence of a loss of one phase of a feeding source on the properties of a five-phase induction machine. The attention is paid to the waveforms of the currents in individual stator phases, the increase in torque pulsations and the decrease of speed in emergency operation after the disconnection of a faulty phase of the sou...

The paper introduces the possibility to eliminate certain groups of spatial harmonics of the current layer, magnetic flux density in the air gap and flux in the yoke of the induction machine with the aim to increase the efficiency. The content of higher spatial harmonics is reduced by means of the so-called combined winding. It is shown how this wi...

The paper is aimed at the analysis of the influence of the third spatial harmonic of the MMF on the stator currents and the torque of a five-phase synchronous machine with surface-mounted permanent magnets. The analysis is carried out on the basis of the method of space vectors and symmetrical components of instantaneous values of currents and volt...

The sliding mode control technique applied to the drive control is analyzed in terms of dynamic response and energy saving in a stand-alone network. The drive is equipped with a surface-mounted permanent magnet synchronous motor fed by renewable power through a voltage-source inverter. The design of sliding mode control is presented, and it is show...

The paper is aimed at the analysis of operation of a five-phase induction machine with one phase winding open. It shows different properties of a machine in emergency operation with the stator winding in star, pentagon and pentacle configurations. The currents and torques are determined by means of a developed numerical model. In the paper, the pro...

The influence of the voltage supply method and of the way of connecting a five-phase induction machine to a voltage-source inverter on the torque pulsations and on the harmonic distortion of the stator voltages and currents are investigated. Operation in star, pentagon and pentacle connections is considered. The method of symmetrical components of...

The properties of the induction machine with the combined stator winding are analysed regarding the influence of the angular displacement and the number of turns of the delta and star connected windings on the currents, the torque and the efficiency of the machine. Equations of the machine that are valid for an arbitrary angle of the displacement a...

The paper deals with analysis of the situation in a six-phase induction machine. For this purpose, the method of space vectors is used. It is shown that higher space harmonic waves of current layer, flux density and flux in the stator yoke have to be considered especially when the stator is fed by unbalanced voltages. The equations of a six-phase i...

The paper is aimed at reduction of the content of spatial harmonics of a current layer, air-gap magnetic flux density and flux in yokes of induction machines with the combined stator winding. The reduction of the content of higher spatial harmonics results in improvement of efficiency of induction machines. The analysis is carried out using the the...

A possibility of using the sliding mode technique for elimination of the influence of instability voltage source on the stand-alone drive behavior is discussed. For the AC drive that has an exterior permanent magnet synchronous motor and a classical two-level voltage source inverter the conditions of the sliding mode existing guaranteed elimination...

The mathematical model of a five-phase induction machine derived based on the theory of space vectors and symmetrical components of instantaneous values was verified by means of comparison of simulation and experimental results. A multi-phase voltage source inverter was used to feed an experimental five-phase induction machine by ten-pulse voltage...

The situation when voltage-source inverter is supplied with unbalanced system of voltages is investigated. This can cause problems in operation of an electric drive as voltage pulsations can arise in the DC-bus. Suitable control methods may be applied to eliminate this effect in the active front-end rectifier. The paper particularly focuses on tran...

Voltage pulsations in the DC bus may develop if the voltage-source inverter is fed from an unbalanced voltage supply. Negative effects on the connected electric machine and on the power grid usually result from such operation. It is possible to entirely eliminate or at least minimize such negative effects by suitable control of the active front end...

Analysis of a five-phase induction machine based on the space vector method is carried out. It shows the necessity of considering the spatial harmonic waves of the current layer, magnetic field density and flux in the yoke. A system of equations describing the fivephase induction machine is derived. Based on these equations, a numerical model of th...

The paper deals with analysis of the situation in a six-phase induction machine. The method of space vectors is used for this purpose. The necessity to consider higher space harmonic waves of a current layer, flux density and flux in the stator yoke is shown in the case of feeding by unbalanced stator voltages. Equations of a six-phase machine are...

The experimental verification of the results of the mathematical analysis of a six-phase induction machine is presented in this paper. The verification is based on the measurement of the currents and torques at the feeding of stator winding by voltages which correspond only to a selected symmetrical component. The measured values are compared with...

Voltage-unbalance conditions that can arise in the power network may affect operation of electric drives in a negative way. The cause of the unbalance may be a failure in the network or presence of an unbalanced load in the vicinity of the affected drive. Unsymmetrical system of voltages at the input of a voltage source inverter gives rise to the p...

Non-standard conditions in the power network such as voltage unbalance negatively affect operation of electric drives. The unbalance can be caused by a failure in the network or by an unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source inverter cause pulsations in the DC-link voltage when n...

Electric drives may be negatively affected by non-standard conditions in the power network such as voltage unbalance, which may arise in three-phase power networks. The unbalance can be caused by a failure in the network or by unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source inverter cau...

Operation of electric drives may be negatively affected by non-standard conditions in the power network such as voltage unbalance, which may arise in three-phase power networks. The unbalance can be caused by a failure in the network or by unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source...

The voltage unbalance conditions at the input rectifier stage of the AC-DC-AC rectifier-inverter fed induction motor drive is analysed. This unbalance can cause significant voltage harmonic of twice the line frequency 2 f ₁ in the DC bus. This voltage ripple can have a degrading effect on the induction-machine performance characteristics...

Analytical investigation of the current and electromagnetic torque ripples in the three-phase voltage source inverter fed induction motor drive under DC-link voltage pulsation is presented in this paper. The analytical expressions for the voltage and current space-vectors as a function of the DC-link voltage pulsation are derived. The analytical re...

Operation of the drives may be negatively affected by non-standard conditions in the power network such as voltage unbalance, which may arise in three-phase power networks. The unbalance can be caused by a failure in the network or by unbalanced load in the vicinity of the affected drive. Unsymmetrical voltages at the input of a voltage source inve...

The demands on the robustness and reliability of electrical drives have been steadily rising during the last decade. In some applications, the users require the drive to continue in operation even under certain non-standard conditions. The discusses various types of non-standard conditions and analyzes what impact these non-standard conditions have...

Properties of variable-speed drives utilizing single-phase induction machines are investigated and discussed in the paper. Such drives may find its way into applications where single-phase induction machines were traditionally used. Introduction of variable-speed operation would improve their energy efficiency substantially. Two different topologie...

Operation of voltage-source inverter with fully controlled front-end stage supplied from an unbalanced power grid has been investigated and analyzed. A method of finding optimal switching functions based on various optimizing criteria has been investigated that generates the demanded output DC-link current. The overall power factor and current unba...

Properties of the control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC bus of a voltage source inverter are analyzed. These pulsations can have negative effects on operating properties of the drive as well as on the quality of power supply in the electrical vicinity of the inverter. The impact...

The work deals with emergency feeding of induction motor by injected currents after a failure of one converter leg and subsequent reconfiguration of the converter. In terms of theoretical analysis optimum phase shift of stator currents is determined from the viewpoint of minimization of stray losses and parasitic torques in the emergency feeding. E...

The paper deals with emergency feeding of a three-phase induction motor by injected currents after disconnection of the faulty leg of the feeding converter and subsequent reconfiguration of the converter. At reconfiguration, the winding fed by the damaged leg is disconnected and the stator winding neutral is connected to the midpoint of the capacit...

A control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC bus of a voltage source inverter is investigated and analysed. Such a pulsating current can have detrimental effects on operating properties of the drive as well as on the quality of power supply in the electrical vicinity of the inverter....

This paper analyses the operation of a power unit with a doubly fed machine. A novel vector control method is presented which enables independent control of both positive- and negative-sequence components of stator currents. Also, operation of the system under the condition of unbalanced voltage supply applied to the stator is discussed. Copyright...

Changes and pulsations in the active and reactive powers generated by wind turbines due to wind speed variations and tower shadow effect may cause serious problems in operation of isolated or distant areas of power grids. Particularly resulting flicker effect may deteriorate power quality in connected power networks. Use of doubly fed machines with...

The rise of the third space harmonic waves of stator current layer and flux in stator yoke in connection with zero-sequence component in stator currents is discussed. It is proved that the flux wave can give rise to additional rotor currents in dependence of rotor winding configuration and, consequently, to additional torque and losses. The possibi...

A control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC bus of a voltage source inverter is investigated. Such a pulsating current can have detrimental effects on operating properties of the drive as well as on the quality of power supply in the electrical vicinity of the inverter. The impact o...

Changes and pulsations in the active and reactive powers generated by wind turbines due to wind speed variations and tower shadow effect may cause serious problems in operation of isolated or distant areas of power grids. Particularly resulting flicker effect may deteriorate power quality in connected power networks. Use of doubly fed machines with...

The stator and rotor currents of a doubly fed machine (DFM) with a 12-pulse cycloconverter in the rotor circuit for different operating states are analyzed. It is shown that the stator as well as the rotor currents contain harmonic spectra dependent on the machine operating state, especially on the mutual relation of fundamental component frequenci...

The paper focuses on dependences of individual stator winding inductances on magnetic saturation in the induction machine. Magnetizing currents with a range of magnitudes and phase angles were considered to cause saturation of magnetic paths in the machine. Mutual inductances between stator phases for superimposed small signals that do not contribu...

The power factor correction achieved with a control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC link of a voltage source inverter is investigated and analyzed. A feasible range of control parameters is determined based on the required level of immunity against unbalanced voltage supply and on...

A novel low-cost single-phase induction machine drive containing only two controlled solid-state switches is presented. The drive is intended for heating, ventilation, and air conditioning or a similar type of application requiring variable-speed operation with a fan-type load characteristic. An experimental drive based on the proposed setup has be...

T he presented paper deals with doubly fed machines (DFM) operating in units that convert mechanical to electric power and vice versa. We concentrate especially on their usage in pumped storage plants which, used in the power system, can increase its stability and operating efficiency. A mathematical model of the power unit with a doubly fed machin...

A control method for the compensation of unbalanced voltage supply that eliminates pulsating current in the DC link of a voltage source inverter is investigated. Such a pulsating current can have detrimental effects on operating properties of the drive as well as on the quality of power supply in the electrical vicinity of the inverter. A feasible...

The present paper analyses operation of a power unit with a doubly fed machine under the condition of unbalanced voltage supply applied to the stator. An extended vector control method is proposed to increase the immunity to a negative-sequence voltage component and to improve the controllability of such a power unit.

Improved reliability and fault tolerant operations of converter system are extremely important for industrial AC drives. In this paper an induction motor drive with fault tolerance capability is investigated through an analytical model. After the faulted leg in six-step voltage source inverter operation has been detected, the motor is driven by the...

The paper concerns with an induction machine that operates with one stator phase open and with the stator winding neutral connected to the centre of a bank of DC-link capacitors after the converter reconfiguration due to a failure in the supplying inverter. This reconfiguration allows the drive to continue in operation and prevents the driven equip...

A numerical model of an adjustable-speed power unit utilizing a doubly fed machine with a 12-pulse cycloconverter in the rotor circuit was developed. The synchronous frame vector control scheme with impressed rotor voltages was employed to control the produced active and reactive powers of the unit. Both steady-state and transient operation of the...

An adjustable-speed unit with a doubly-fed machine running both in generator and pump modes is dealt with. Operation of a power unit with a doubly fed machine driven by a Francis turbine regulated at the optimal speed is analyzed and compared to the cases when the speed is kept constant. The response of the system to changes in demanded active powe...

A novel low-cost drive with a single-phase induction machine for HVAC applications that require adjustable-speed operation is proposed. An experimental drive based on the proposed setup has been developed and built to verify its practical viability and properties. The paper presents results of investigation obtained by means of numerical simulation...

A novel low-cost single-phase induction machine drive containing only two controlled solid-state switches is presented. The drive is intended for an HVAC type of application requiring variable-speed operation. An experimental drive based on the proposed setup has been developed and built to verify its practical viability and properties. The paper p...

A numerical model of a power unit with a doubly fed machine is developed. The model contains all the components of the considered system including the vector controller of the rotor voltage and the turbine control. The interaction of vector control of the electrical machine with a cycloconverter in the rotor circuit and control of the turbine at op...

A semi-analytical method has been developed for quick determination of the distribution of selected field quantities (magnetic flux density, permeance) along the air gap of a synchronous reluctance machine (SRM) in different operation regimes. The aim of this effort was to find the parameters necessary for building up dynamic equations of the machi...

A mathematical model of a synchronous reluctance machine based on the space phasor theory was developed. The third spatial harmonic of the magnetic flux density along the air gap of the machine due to the rotor magnetic saliency is considered. The distribution of the magnetic field in the machine is computed using an FEM model in 2D. The results ob...

The working regions of an adjustable-speed generation unit with a doubly fed machine connected to the power grid are determined. The analytical relations for the control range of the rotor voltage phasor due to the maximal permissible values of currents and voltages of the machine and supply cycloconverter are presented. Simulation results are show...

First Page of the Article

Not Available

Heating, ventilating, air conditioning & refrigeration (HVAC&R) systems represent one of the largest potential applications for Adjustable Speed Drives (ASD's). The focus of this work is to sudy the switching performance of a new alternative circuit topology. The drive is specifically aimed at applications that do not require continuous speed contr...

A novel low-cost drive with a single-phase induction machine for HVAC applications that can operate at either full or reduced speed is proposed. An experimental drive based on the presented setup has been developed and built to verify its practical viability and properties. The paper presents results of investigation obtained by means of numerical...