Full Decoupling Control of Two-Connected Motor Drives with Matrix Converter Supply

Multi-phase (more than three-phase) converters are required mainly for feeding variable speed multi-phase drive systems. This paper presents one such solution by using a direct AC-AC converter that can be used to supply a quasi-six-phase drive system. Carrier-based pulse-width modulation technique is developed for the proposed matrix converter configuration. The developed modulation technique is based on the comparison of high frequency carrier signals with the modulating signals to produce duty-ratios. Although carrier-based schemes are widely employed for control of voltage source inverters, they have only recently been used for controlling a three-phase to three-phase matrix converter. A similar concept is extended in this paper for controlling a three-phase to quasi- six-phase matrix converter. Two techniques are proposed: one outputs 0.75 of the input magnitude, and the second outputs up to 0.7764 of the input. This is the maximum value of the output voltage in the linear range that can be achieved in this configuration of the matrix converter. The viability of the proposed control technique is proved using analytical, simulation and experimental approaches.

In the vector control of a linear induction motor (LIM), it is difficult to calculate air gap field vector exactly because of end effects of LIM. So, this paper shows the longitudinal end effect and the transverse edge effect of LIM by experiment and determines the position of the sensor for detecting the air gap field vector. The direct vector control scheme is utilized to control the speed of LIM. As a result, simulation values by finite element analysis and experimental values of direct vector control using DSP are compared, and investigated.

Large hydro-electric generators are individually designed for the specific hydraulic and system conditions of a particular site. The paper reviews the various mechanical features of such a machine, in particular the bearings and how they are disposed relatively to the rotor, the stator frame core and windings with particular reference to the problems of transport to site, and the rotor design which is influenced by the high overspeed and high inertia requirements as well as transport limitations. In common with other electrical machines, the maximum output of a hydro-generator is limited by the temperature at which the insulated parts may be operated to give an acceptable life and attention is drawn to the use of direct water cooled machines. The special requirements of machines for pumped storage application are indicated, in particular those resulting from the need to operate in both directions of rotation, the effect of cyclic operation and the means of starting in the pumping direction. Axial flow turbines require specially designed generators and the more usual types are illustrated. For small hydro-generators, adaptation of the designs from the manufacturer's existing ranges of industrial machines is the usual approach but, irrespective of the size of the machine and its application, simplicity of construction with maximum reliability is the aim.

The modification of magnetic structures for an E-core switched reluctance machine (SRM) comprising two segmented stator cores or a monolithic stator core is presented for ease of assembly, good manufacturability, mechanical robustness, and electromagnetic performance improvement. The E-core stator has four small poles with phase windings and two or four large poles (hereafter referred to as common poles), in between. The common poles are shared by both phases for positive torque generation during the entire operation. The E-core SRMs are compared to a conventional two-phase SRM. The comparison includes cost savings, torque, copper and core losses, and efficiency in order to validate the distinct features of the E-core SRMs. Magnetic equivalent circuit (MEC) technique is employed for proving the benefits of the E-core common-pole structure.

The six-phase induction machine (SPIM) has two sets of three-phase stator windings spatially shifted by 30 electrical degrees. It has many advantages, such as reducing the torque pulsations, enhancing the power handling capability. The matrix converter (MC) is a very promising converter, which has the following characteristics: operation with unity power factor, bidirectional power flow. In this paper, six-phase induction motor driven by the six-phase matrix converter has been proposed. It can combine the advantage of the SPIM and the MC. A direct modulation algorithm is presented. The control system can realize bidirectional power flow and the unity power factor. Simulation results have tested the performances of the proposed method.

Some key parameters of a single-sided hybrid linear stepping motor(HLSM) were analyzed for optimization by finite element method(FEM).The influence of the winding current on the normal force and the tangential force was studied by FEM with a certain machine volume,as well as that of the distance of the air-gap between mover and stator,and the relationship curves were given respectively.The characteristics of force-displacement with different tooth width/tooth pitch ratios were calculated to find out the optimum ratio for the maximum thrust and a lower normal force.The harmonic waves of the tangential thrust were analyzed by FFT in different ratios of tooth width/tooth pitch,which were conducted when the ratio of the forcer and that of the stator were equal and unequal respectively.The result shows that the range between 0.33 and 0.38 is preferable for the ratio of tooth width/tooth pitch to increase the thrust and its fundamental part while suppress the normal force,the favorable ratio of tooth width/tooth pitch is about 0.36 to obtain the maximum static thrust.

This paper presents a review of the researches done on fault tolerant control types, methods, main objectives of the fault tolerant control and fault diagnosis of induction motor faults that used the wavelet transform. Wavelet transform from the fault diagnosis point of view, is a summary of the wavelet types (continuous and discrete), machine faults, diagnosis methods and their validation, respectively. Types of software, generality of codes, one dimensional and two dimensional DWT and frequency characteristics components of healthy and faulty induction motor are given. Finally, stator short winding and open winding are taken as a case study to show the effectiveness of the wavelet techniques for fault diagnosis. Key words: Wavelet, induction motor, fault diagnosis, fast Fourier transform, fault indicator, fault tolerant control.

Two series-connected two-motor drive systems with a single inverter supply have been proposed recently. The first one consists of two five-phase machines supplied from a single five-phase inverter, whereas the second one comprises one symmetrical six-phase machine, a three-phase machine, and a single six-phase inverter. It has been verified experimentally that, by introducing an appropriate phase transposition in the series connection, completely independent dynamic control of the two machines can be realized using principles of vector control. Detailed dynamic models in the stationary common reference frame have also been reported for the two drive systems. These are taken here as the starting point, and equivalent circuit steady-state representation of the series-connected two-motor drive systems is developed. The equivalent circuits can then be used to evaluate steady-state characteristics of the drives in the same manner as it is done for three-phase induction machines, as well as for the inverter design. The dc-link voltage required for operation of the two series-connected machines is investigated next. It is shown that the specific winding connections lead to a dc voltage requirement that is smaller than it would have been had the windings of the two machines been connected directly in series. Experimental results, obtained during steady-state operation of the series-connected five-phase and six-phase two-motor drives, are presented. Developed equivalent circuit representation is finally verified by comparing calculated and experimentally obtained values for various voltages of the two-motor drives.

This paper proposes the space vector pulse width modulation technique of a matrix converter topology with three phase fixed grid input and seven phase variable voltage variable frequency output. Voltage source inverter is generally used for feeding multi-phase drives. Multi-phase matrix converter is proposed in this paper as a new solution for feeding multi phase system. The paper develops the complete space vector algorithm of the proposed multi-phase matrix converter topology. The developed space vector model suggests 221 possible switching combination vectors. After imposing mathematical constraints the number of switching combinations reduce to 2184 active and three zero vectors. The complete space vector PWM algorithm is developed in the paper. The feasibility of the proposed algorithm is proved using analytical, simulation and real-time approach.

The matrix converter (MC) is an array of controlled bidirectional semi-conductor switches that allows direct ac-ac conversion without an intermediate dc link. To extend its future application, multilevel matrix converter can be a proposed solution due to its merits in multilevel output, high voltage application, high power conversion, improved harmonics issue and less voltage step, etc. This paper presents an improved voltage balancing control using utility function on a capacitor-clamped multilevel matrix converter; the improved modulation strategy based on amplitude coefficient is employed to improve the performance in terms of modulation precision. Simulations and experimental results from a small-scale experimental prototype are presented to validate the theoretical findings.

This paper aims at obtaining fixed output voltage of frequency 50 Hz to the load by a Self Excited Induction Generator (SEIG) employed in Wind Energy Conversion System (WECS). The output voltage of a SEIG is a function of wind turbine’s speed, which varies with wind velocity. Due to the variation in shaft speed of the wind turbine, the output voltage and frequency of Doubly Fed Induction Generator (DFIG) will vary. In this paper, a new WECS is proposed in which the conventional PWM AC/ DC/ AC converter is replaced by a Matrix Converter (MC) topology and the DFIG machine is replaced by a low cost Squirrel Cage Induction Generator. MC eliminates bulky DC link capacitor, provides bi-directional power flow capability, independent control on the output voltage magnitude, frequency and phase angle as well as the input power factor. Space Vector Pulse Width Modulation (SVPWM) technique is used for controlling MC in such a way that output load voltage and frequency is kept constant for all wind velocities. The SVPWM technique provides higher voltage transfer ratio without lower order harmonics. SVPWM is digitally implemented using DSP processor (TMS320 F2407A). Switching times are pre-calculated offline. Semi soft commutation procedure for safe switching control of MC switches is also presented.

Matrix converter technology have so far been mainly limited to low power applications. Multi-level voltage source converters are often used for high power applications. In order to combine the good characteristics of both topologies this paper presents the principle of operation of multi-modular matrix converters. Among all the proposed control techniques, predictive control has become a viable and highly versatile option due to its ability to cope with different operating requirements. Therefore this paper also proposes a predictive control technique with a fixed switching frequency applied to the multi-modular matrix converter as well as a comparison of the performance between the proposed control and a variable switching frequency counterpart, showing the advantages and disadvantages between the two strategies.

Doubly-fed induction generator (DFIG) is currently the choice for many wind turbines. These generators, when connected to the grid through a converter, is subjected to varied power system conditions like voltage variation, frequency variation, short circuit fault conditions, etc. Further, many countries like Canada, Germany, UK, Scotland, etc. have distinct grid codes relating to wind turbines. Accordingly, following the network faults, wind turbines have to supply a definite reactive current. To satisfy the requirements including reactive current capability, an optimum electrical design becomes a mandate for DFIG to function. This paper intends to optimize the equivalent circuit parameters of an electrical design for satisfactory DFIG performance. Direct search method has been used for optimization of the parameters. The variables selected include electromagnetic core dimensions (diameters and stack length), slot dimensions, radial air gap between stator and rotor and winding copper cross section area. Optimization for 2 MW DFIG has been executed separately for three objective functions - maximum reactive power capability (Case I), maximum efficiency (Case II) and minimum weight (Case III). In the optimization analysis program, voltage variations (10%), power factor- leading and lagging (0.95), speeds for corresponding to slips (-0.3 to +0.3) have been considered. The optimum designs obtained for objective functions were compared. It can be concluded that direct search method of optimization helps in determining an optimum electrical design for each objective function like efficiency or reactive power capability or weight minimization.

In this paper, decoupled control of rotor torque and rotor electric power in a reluctance wound rotor brushless doubly fed machine, (BDFM), is presented. The machine stator windings are fed from two separate voltage source inverters. The proposed control technique is applied to the inverters such that the BDFM is capable of producing mechanical torque at any desired synchronous speed and simultaneously delivers n-phase rotor electric power through the rotor terminals independent of the mechanical loading. This technique can eliminate the need for slip-rings and can be used in applications such as rotational antennas and turret systems. An existing slip-ring induction motor is modified to build up the proposed prototype BDFM. Simulation and experimental results validate the proposed control technique.

Rotating machine insulation ageing has been the subject of intensive research over the years. In this paper, model stator bars are investigated with the aid a Partial Discharge (PD) detector. The maximum PD magnitude is recorded as the applied voltage increases and as it decreases. The resulting “hysteresis curve” indicates whether the stator bar is in a “good” or “bad” condition, i.e. it indicates its “state of health”. The proposed method has certain advantages over other methods since it requires only one parameter, i.e. the maximum PD magnitude. It is suggested that the proposed method can be used as a diagnostic tool for assessing the quality and controlling the state of ageing of model stator bars.