Constant Flux Linkage Research Articles

Стійкість систем векторного керування напругою асинхронного генератора

The paper presents an analysis of the stability properties of typical structures of induction generators-based vector control systems with linear proportional-integral currents and DC-link voltage controllers. The study is based on the mathematical model of an induction machine taking into account the magnetization curve. It provides the modification of the typical voltage-flux vector control algorithm by considering the saturation of the magnetic system. The stability proof problem of an induction generator-based generation system is that its model is nonlinear and nonminimal-phase, and that the dynamics of the DC-link voltage is nonlinear even for a constant flux linkage and speed due to the presence of nonlinear components which are proportional to active losses. The conditions which provide consideration of the reduced-order system dynamics are formulated and properties of local asymptotic stability of the generation system with typical vector control algorithms are proven based on the singular perturbation theory. It is shown that the local asymptotic stability is ensured when the regulation processes of the DC-link voltage and the torque-forming stator current component are decoupled, which is achieved due to the proposed special adjustment of the voltage and current controllers. A modified vector control algorithm of induction generator is studied in simulation and experimentally. At the first stage, the system dynamics is investigated when the flux subsystem is in equilibrium point. As a result, the possibility of the reduced-order system consideration for the design and analysis of the voltage regulation subsystem was confirmed. At the second stage, the dynamic behavior of the voltage control loop for different settings of the controllers was experimentally investigated. It is shown that the configuration of the voltage control algorithm proposed in the work provides the timescale separation of the current and DC-link voltage regulation processes, as well as their quasi-decoupling.

Performance Analysis of a Modular E-Shaped Stator Hybrid Excited Flux Switching Motor With Flux Gaps

This paper proposes a new modular hybrid excited flux switching motor (MHEFSM) with flux gaps, adding the fault-tolerant capability to the proposed motor. The proposed motor uses an E-Shaped stator, as the middle teeth of E-core produce fault-tolerant capability, and in C-core, this capability is eradicated. The no-load flux linkage is calculated by the magnetic network model (MNM) to reduce time and disk storage. The drawback of the constant flux linkage of PM motors is overcome by employing field excitation (FE). The FE helps in regulation flux at higher speeds. The motor leading geometry variables are optimized by using Genetic Global Optimization (GGO). The GGO helped in refining the structure of the motor and has improved the flux linkage by 68.18%, average torque and torque density by 62.35% each, reduced torque ripples by 20.62%, and cogging torque by 18.52%. The volume of permanent magnet (PM) in the proposed MHEFSM is reduced by 36.24%, and 48.49% higher average torque and torque density is obtained compared to the state of art motor proposed in the literature. Furthermore, a 3D analysis of the proposed MHEFSM is done to further evaluate the electromagnetic performance.

MINIMIZATION OF ELECTRICAL CONSUMPTION OF A FREQUENCY-REGULATION INDUCTION MOTOR WITH A FAN LOAD IN START-BRAKING REGIMES

Purpuse. To minimize the total power consumption in start-braking regimes by a three-phase squirrel-cage frequency-regulated induction motor, loaded a centrifugal fan (or smoke exhauster), and also to obtain analytical dependencies for calculating the optimal durations of acceleration and deceleration times, corresponding to minimizing the total energy consumption of this motor in start-braking regimes with the indicated type of load. Metodology. Based on the methods of calculus of variations and numerical solution of non-linear differential equations, the quasi-optimal type of trajectories of speed change (tachograms) of the motor with the considered load in start-braking regimes is determined. Using the methods of mathematical analysis and similarity, the acceleration and deceleration times of an induction motor with a fan load were optimized for different (linear, parabolic and quasi-optimal) types of tachograms. Using the method of computer simulation, the energy consumption in the start-braking regimes of an induction motor with the indicated load for these types of tachograms was quantified. Results. Refined analytical dependencies are obtained for calculating the consumed active power and energy in start-braking regimes by a frequency-regulated induction motor with a fan load for the mentioned various types of tachograms. Analytical optimization of the consumption of active energy of this motor in start-braking regimes has been carried out. The change at the optimal durations for the starting-braking regimes and the corresponding it’s total energy consumption of the motor with varying the maximum value of the motor speed in these regimes has been researched. A quantitative assessment of transient electromechanical and energy processes in the considered motor with a fan load has been carried out. For this motor, as applied to the non-regenerative version of the static frequency converter, a scalar automatic control system is proposed, by means of which the motor accelerates with a constant rotor flux linkage with a given (linear, parabolic or quasi-optimal) speed trajectory and brakes on freewheel. The expected annual saving of active energy by an induction motor, loaded with a smoke exhauster, in starting and braking regimes, achieved by optimizing the form of the tachograms and the duration of the acceleration and deceleration times, is determined. Originality. Analytical dependencies are obtained for calculating the optimal durations of the acceleration and deceleration times of an induction motor with a fan load, corresponding to minimizing the energy consumption of this motor in start-braking regimes. The "U"-shaped form of dependences of the total energy, consumed during acceleration (or the total generated energy during braking) of the induction motor in function the duration of the deceleration (or braking) times is established. An analytical dependence is obtained for changing the speed of a motor loaded by a fan or a smoke exhauster during the freewheel braking regime, and an analytical expression is proposed for determining the duration of the indicated braking time. Practical value. On the example of an induction motor loaded by a smoke exhauster, the possibility of saving the total energy consumption in start-braking regimes was identified: from 77 to 90 % – due to the use of the proposed quasi-optimal tachogram and the use of practically realizable optimal acceleration and deceleration times, and also in the amount of 10 % – through the transition from freewheel braking to regenerative braking. Figures 6, tables 6, references 22.

SPEED OBSERVER FOR SENSORLESS ENERGY GENERATION SYSTEMS BASED ON FIELD ORIENTED INDUCTION GENERATOR

The paper presents a novel adaptive speed – rotor flux linkage observer for sensorless field oriented control of induction generators. The proposed solution is based on Matsuse observer structure to- gether with specially designed correction terms and utilize current measurement and calculated stator volt- ages for real-time flux and speed reconstruction. A special coordinate transformation is used to avoid non- linear parametrization in the right side of flux linkages differential equations. Adaptive observer is designed in two steps: at the first step nonadaptive flux linkage observer is designed under condition of speed meas- urement; at the second step adaptive to rotor speed version of the flux linkage observer is designed. Infor- mation about rotor speed for adaptive flux observer is calculated by developed speed observer. A second Lyapunov’s method together with adaptive control theory are utilized for observer’s correction terms synthe- sis and stability proof. Designed adaptive observer under persistence of excitation conditions guarantees local exponential estimation of constant rotor speed and flux linkage vector components of induction ma- chine. From the practical point of view persistency excitation conditions are met if rotor flux linkages are nonzero. Proposed solution investigated by simulations. It is shown, that developed adaptive speed observer provides asymptotic estimation of induction motor currents, speed and flux linkage components under con- stant speed conditions. For varying speed proposed observer provides estimation of required variables with a small dynamic error. Proposed observer can be used in energy generation systems based on induction generators as well as in sensorless induction motor-based drive systems with constant or slowly varying ro- tor speed.

Concurrent unity power factor and constant mutual flux control for PMSG-WT MPPT

In this paper, a new concurrent unity power factor and constant stator flux linkage (UPF-CFL) control is presented. The main goal of this technique is to introduce the Permanent Magnet Synchronous Generator (PMSG) as an optimal wind energy transducer. The handled generator load angle and back EMF control achieve the optimum requirements for wind applications namely Maximum Power Point Tracking (MPPT). To do this, both UPF and CFL are integrated into one control methodology to obtain the advantages of each one. While the first well utilizes the apparent power increasing the generator side converter capability, the second protects the generator against magnetic saturation to enable higher speed operation. Mathematical model based on constant current fed equivalent circuit is presented taking the constraints of each individual control algorithm into account. The concurrent performance characteristics are presented and compared with each of concurrent separated algorithm characteristics for assessments. The control technique is implemented and finally, simulation testing is provided for evaluation.

Novel Empirical Model for Calculation of Core Losses in Permanent Magnet Machines

This article presents a simple model for the calculation of core losses in permanent magnet machines based on the total flux linkage of the stator winding. In reality, the total core losses will vary as a function of permanent magnet field and the combination of $d-q$ current components even in the case when different $d-q$ currents produce the same amount of stator winding flux linkage at a given speed. The classical model with constant equivalent core loss resistance predicts constant core losses for constant flux linkage which leads to incorrect results. The model presented in this paper expands the classical core loss resistance based model with a novel additional term which corrects the classical model and calculates an additional core loss component as a function of $d$ axis current, total flux linkage of the stator winding, and two constant parameters. The accuracy of the model is confirmed by finite element simulations and core loss measurements for the cases of an interior permanent magnet traction motor and an industrial surface permanent magnet motor (only simulations).

Оценка эффективности классических законов управления частотно-регулируемых асинхронных двигателей

Adjustable-frequency induction motor-based drives occupy the dominating place among adjustable electric drives. Therefore, it is important to consider rational methods for controlling induction motors (IMs) from the viewpoint of decreasing their energy consumption. There are two such control methods: using the proportional law of controlling the motor power supply frequency and voltage and using the law that maintains constant stator and rotor flux linkages and the main flux linkage in the air gap. A procedure for calculating the power performance indicators of an adjustable-frequency IM for these control laws is proposed, using which they can be calculated and compared in a relatively simple manner without iterations. The calculation formulas used in the procedure are based on the system of vector equations for a steady-state operation mode and on the equivalent circuit drawn from these equations. An example of calculating the indicators of induction motors with the capacity P2 = 15 kW during their operation with a constant torque in the specified range of rotation frequencies is given. The results from calculating the motor power performance indicators during motor operation with a constant torque and with decreasing the power supply voltage have shown that the control law maintaining a constant rotor flux linkage yields higher values of the efficiency and power factor. It is exactly this law that is more preferable for use in the adjustable-frequency drive control systems.

Efficient operation of deadbeat direct torque and flux control for IPMSM drives by minimizing copper losses

This paper presents copper loss minimization of an interior permanent magnet synchronous machine (IPMSM) drive using deadbeat direct torque and flux controller (DB-DTFC). With its constant switching frequency of DB-DTFC, the desired air-gap torque and stator flux can be achieved at the end of PWM sampling period. In this paper, a copper loss minimization DB-DTFC algorithm for an IPMSM is derived and demonstrated experimentally. Applying the presented DB-DTFC, the magnitude of stator flux linkage can be controlled while developing the commanded torque, such that copper losses of an IPMSM drive can be manipulated. The stator flux linkage that achieves minimum copper losses in an IPMSM over the given torque and speed operating space is presented. The effect of the proposed DB-DTFC algorithm is verified by analysing the efficiency maps of an IPMSM drive applying the copper loss minimizing stator flux linkage and a constant stator flux linkage.

Influence of magnetic circuit saturation and skin effects on the adjustable induction motor characteristics

The aims of this work are to show the influence of saturation and the rotor skin effect current on the characteristics of an adjustable induction motor (AIM). The coefficient of the voltage increase is determined in order to realize the frequency control laws with constant flux. The regulation characteristics of the induction motor are obtained for developed control laws. Great advantages of a first proposed law of frequency control were revealed. The determination of the equivalent scheme parameters taking account the saturation of the magnetic circuit and the skin effect of the rotor current guarantee the accuracy of calculation of the adjustable induction motor energy indices.As a result of frequency control of the AIM research in a dynamic mode it is established, that while taking into account magnetic conductor saturation and skin effect current in a rotor winding faults while calculating current throws for a control mode U/f = const decreased about 6 compared with 13% without taking into account and, till 3 compared with 17% in a regulation law with a rotor constant flux linkage Ψ2 = const. Results of mathematical modeling in the course of which power indicators (efficiency and power factor) of the adjustable induction motor defined in transitional regimes at various laws of frequency regulation are experimentally confirmed.

Steady-State Analysis and Comparison of Control Strategies for PMSM

Permanent Magnet Synchronous Motor (PMSM) has been considered as the best choice for numerous applications. To make PMSM a high performance drive, effective control system is required. Vector control is accepted widely due to its decoupling effect but it is not the only performance requirement. Additional control methods such as constant torque angle control (CTAC), optimum torque per ampere control (OTPAC), unity power factor control (UPFC), constant mutual flux linkages control (CMFLC), and angle control of air gap flux and current phasor (ACAGF) can also be implemented. This paper therefore presents some important control strategies for PMSM along with merits and limitations which provide a wide variety of control choices in many applications. The performance characteristics for each strategy under steady state are modelled and simulated in MATLAB environment. Based on the simulation results, a conclusion is drawn that OTPAC is superior in normalized torque per unit normalized stator current (Ten/isn) ratio whereas UPFC yields very lowTen/isnratio. In addition, performances of these control strategies are compared, which is a key to select optimum strategy depending on requirements. Based on the comparative study, it can be concluded that CMFLC is superior to CTAC, ACAGF, OTPAC, and UPFC. Hence, it can be a good control strategy to consider.

Modular Stator High Temperature Superconducting Flux-Switching Machines

Flux-switching permanent magnet (FSPM) machines have advantages of robust rotor, strong permanent magnet (PM) dissipation ability, etc, but its flux-weakening capability is poor for its constant PM flux linkage. High temperature superconducting (HTS) excitation windings can produce higher flux density than PM excitation and modify the airgap flux density easily. But if the HTS coils are placed adjacent to the armature winding in the same slot, the heat produced by the armature winding is difficult to cool down. In this paper, a modular stator HTS flux-switching (HTS-FS) machine is first proposed, and the operation principle is described in details. Second, mathematical equations are proposed and detailed electromagnetic design has been done. Then, the optimization of width of flux barrier, rotor pole arc and split ratio have been made to get higher back-EMF, higher output torque capability, and lower torque ripple. Moreover, the comparisons of key performance indexes between HTS-FS machine and conventional FSPM machines have been made. The results show that the HTS-FS machine can produce higher back-EMF than FSPM machine, and at small armature current, it can produce higher torque with little electromagnetic saturation.

Electric drive based on double-inverter-fed induction machine with minimization of power losses

An electric drive based on a double-inverter-fed induction machine is presented. The control system of the electric drive minimizes the electromagnetic losses both at constant flux linkage in the gap and during its regulation at the optimal level. The considered variant of control permits one to significantly increase the acceptable electromagnetic torque during two-region rate regulation and to improve the energy characteristics.

Test Signal Based Speed Estimation for Induction Motor Drives

In the first part of the paper an estimation method for sensorless control employing a test signal based reference model is presented. The method estimates the slip frequency by a comparison of the measured test signal impedance curves while the machine is in operation with curves from a test signal based reference model. The reference model which describes the test signal behaviour of the machine is measured during DC magnetisation of a cold machine at steady state and constant rotor flux linkage. During normal machine operation the machine temperature and the stator frequency differ from these conditions and, thus, have a negative influence on quality of the estimation. In the second part of the paper the impact of these disturbances is investigated and two compensation strategies are presented. Measurements on two different standard induction machines which are not especially designed for sensorless control show that the estimation method allows safe operation at standstill and even at zero frequency.

A sensorless, stable v/f control method for permanent-magnet synchronous motor drives

When permanent-magnet synchronous motors (PMSMs) are used for pump and fan applications, V/f control methods can be used to control them. The problem with open-loop V/f control of PMSMs without having damper windings in the rotor is the inherent instability after exceeding a certain applied frequency. In this paper, a new V/f control method is proposed for motor drives for stable operation in a wide frequency range. The magnitude of the voltage is controlled in order to maintain a constant stator flux linkage in the PMSM. The applied frequency is modulated proportional to the input power perturbations to stabilize the drive for a wide frequency range. No position sensor is required to implement this stabilizing technique. The small-signal analysis and the experimental results confirm the effectiveness of this stabilizing technique. The experimental results also indicate the satisfactory performance of the drive for pump and fan applications.

Control and dynamics of constant-power-loss-based operation of permanent-magnet synchronous motor drive system

The operational envelope of electrical machines is limited by the maximum permissible power loss of the machine at any given speed. The control and dynamics of the permanent-magnet synchronous motor (PMSM) drive operating with a maximum power loss versus speed profile is proposed in this paper. The proposed operational strategy is modeled and analyzed. Its comparison to the conventional strategy of limiting current and power to rated values demonstrates the superiority of the proposed scheme. The implementation of the proposed strategy is developed. It is achieved with an outer power loss feedback control loop. This has the advantage of retrofitting the present PMSM drives with the least amount of software/hardware effort. The PMSM drives in this case then can use the existing controllers to implement any torque control criteria, such as constant torque angle, unity power factor, constant air-gap flux linkages, maximum torque per unit current, or maximum-efficiency operation. Experimental verification of the new operational strategy is provided. The concepts presented in this paper can be applied to all other types of motor drives.

Stator resistance voltage-drop compensation for open-loop AC drives

The paper presents two simple stator resistance voltage-drop compensation methods that maintain the stator flux linkage constant in the steady state and achieve approximately constant flux linkage during transient conditions. These methods are based on an induction motor model in a rotating reference frame. A mathematical analysis of the two possible alternatives is shown, indicating the stability limits for each. Practical results are then compared with the traditional volts/hertz (V/f) configuration and the stabilily limits verified.

Transient Analysis of the Rectified Superconducting Alternator

A set of five differential equations is derived to describe the transient electrical behavior of a three-phase superconducting alternator connected to a full-wave thyristor bridge. The approximation of constant flux linkages for the rotor circuits is utilized to reduce the number of numerical integrations from five to two. This produces a very efficient algorithm that is quite useful for studies requiring a large number of simulations. Numerical results based on the parameters of a 10-MVA superconducting machine are included.

An Approximate Incorporation of Field Flux Decay into Transient Stability Analyses of Multimachine Power Systems by the Second Method of Lyapunov

This paper presents a new approach to incorporate in an approximate manner field flux decay into transient stability analysis of multimachine power systems by the second method of Lyapunov; this has not been successful so far in other investigations. In this approach, changes in field flux linkages are not dealt with as other state variables, but treated as parameter variations, because of their small changes, in the conventional stability analysis under the assumption of constant field flux linkages. Therefore, the approach can utilize any Lyapunov function which has been proved to be effective for multimachine power systems, and hence never requires the laborious and very difficult process of constructing an effective Lyapunov function with inclusion of field flux decay. Simulation results have demonstrated the proposed method's practicability and its clear advantage over the exact treatment of the field flux decay attempted by other authors for a simple one machine connected to an infinite bus system.

Interaction between Converter, Signal-Processing and Control for a Converter-Fed Squirrel-Cage Motor

A 4-quadrant induction motor drive, its converter and its control are described. The features of the investigated system are the following: A converter with intermediate constant d.c. voltage, forced commutation with the possibility of controlling the instantaneous values of the phase currents at the machine side, superimposed speed control, measurement of the rotor position angle as a basis for deriving the appropiate current reference values ensuring constant rotor flux linkage. The system is designed for high quality dynamic response. The behaviour of the converter and its interaction with the drive is also considered. The used signal processing avoids a measurement of the air-gap field, which has been used by other authors. This simplification has as a consequence a dependency on the rotor resistance which is discussed in this paper.

Electromechanical stiffness and damping coefficients in the repulsive magnetic levitation system

The electromechanical stiffness and damping coefficient matrices for three translational degrees of freedom are derived for the repulsive levitation system consisting of a single superconducting magnet interacting with a finite width sheet guideway. The persistent node (constant flux linkage) is assumed. The results of this study provide the data for stability and ride quality analysis. The methodology can be extended to multi-magnet systems including active damping coils.