M. Hajian

The Decoupled Stator Flux and Torque Sliding-Mode Control of Induction Motor Drive Taking the Iron Losses into Account

This paper presents a novel decoupled sliding-mode (SM) stator flux and torque controller for three-phase induction motor drive which is supplied by a two level SVM voltage source inverter (VSI). The nonlinear controllers are developed in a stationary two axis ( alpha, beta ) IM reference frame with stator fluxes ( phisalpha, phisbeta) and stator currents ( isalpha, isbeta) as state variables. In this model the motor iron losses is modeled by a shunt rotor speed dependent core resistance (Rc) in IM two axis equivalent circuits. Using the proportional integral type SM switching surfaces, the Lyapunov based control efforts are designed so that the errors between stator flux (phis*) and motor reference torque ( Te* ) and the actual values of these signals ( phis,Te ) asymptotically converge to zero in spite of machine parameters mismatching and uncertainty. In this control strategy, since the control of stator flux and torque are decoupled hence, for a given motor load torque and a given motor speed, the drive system efficiency can be easily minimized by adjusting the magnitude of stator reference flux. To do so, both the model based and on-line search methods are adopted. Finally some simulation results are presented to show the capability and validity of the proposed control scheme.

Optimal design of high power MMC-based LCL DC/DC converter

This paper presents an optimal design of the modular multilevel converter (MMC) based LCL DC/DC converter suitable for high voltage direct current (HVDC) systems. The design aims in minimizing the converter total power losses, harmonic pollution, volume and weight. The optimal values for the converter main parameters affecting the above objectives including cell capacitance, operating frequency, and number of cells are determined using in depth analytical and simulation studies. It is shown that a minimum number of cells equal to 40 with an operating frequency of 300Hz/500Hz for onshore/offshore applications gives best trade-off between converter total losses, overall size, and weight. In addition, the harmonics level for AC and DC sides are kept within the acceptable range. A 1GVA, ±250kV/±320kV MMC-based LCL DC/DC converter is designed and modelled in PSCAD and the converter total losses are estimated in the range of 1.61-2.17%.

Maximum torque per ampere control of induction motor drive without mechanical sensor

In this paper, the direct rotor flux field orientation control of speed sensorless induction motor (IM) is presented. In proposed control scheme, the maximum torque per ampere (MTPA) control strategy is achieved using a so-called fast flux search method. Based on this method, for a given load torque and rotor speed, the magnitude of rotor reference flux is adjusted step by step until the effective value (RMS) of stator current becomes minimized finally. In addition, using the IM fifth order model in the stationary reference frame, a nonlinear rotor flux observer is developed which is capable of motor resistances and rotor speed simultaneously estimation. Moreover, a useful method is introduced for DC offset compensation which is a major problem of AC drives especially at low speeds. Simulation and experimental results are presented to confirm the effectiveness of the proposed method.

Equivalent loading of induction motors using a new composite power supply with a linear (V/Hz) characteristic

In this paper, a novel variable voltage magnitude variable frequency (VVMVF) composite voltage source is introduced which has a linear (V/Hz) characteristic and can be used for equivalent loading of ac machines, without any need to apply the mechanical load to the test machines shaft The proposed power supply is composed of a regular constant voltage and frequency source (main source) and an especial PWM inverter (auxiliary source), connected in series using an isolating transformer. As an example, a 1.5 kW single-phase power source of the above type was practically implemented and used for equivalent loading of a single-phase capacitor start induction motor. Simulation and experimental results obtained are in close agreement.

Energy optimized sensorless sliding mode control of IM drive taking core losses into account

This paper presents a novel sensorless discrete sliding-mode (SM) stator flux and torque controller for three-phase Induction motor drive which is supplied by a three level SVM voltage source inverter (VSI). The stator flux is estimated by a sliding-mode observer and is employed in the rotor speed and stator resistance estimation. In the proposed method the motor iron losses is modeled by a rotor speed dependent shunt resistance in IM two axis equivalent circuits. The system efficiency is optimized by adjusting the magnitude of stator flux reference value for a given motor load and motor speed. To do so, two different methods named as Model Based Approach (MBA) and On-line Search Approach (OSA) are adopted. Finally, some simulation results are presented to show the capability and validity of the proposed control scheme.

Automatic synthetic loading of induction motors based on phase modulation using fuzzy PI controllers

This paper describes an automatic equivalent loading method for ac machines based on phase modulation technique. In this scheme , the test motor is supplied by a variable voltage magnitude variable frequency voltage source that is generated by a wound rotor induction machine. A wound rotor induction machine is employed as a three phase synchronous generator with two quadrature rotor field windings. The rotor direct axis excitation winding is fed by a single-phase PWM inverter while the rotor quadrature axis field winding is supplied by a three-phase rectifier. The test motor RMS voltage and current are automatically maintained on their nominal values , using the current and voltage fuzzy PI regulators. The above method can also be applied to a double system test motors so that no power is fed back to the power supply. The proposed control scheme is verified by some simulations. Computer simulation results obtained confirm the feasibility and effectiveness of the automatic synthetic loading method so that the test motor nominal losses can be measured without the need for attaching mechanical load to the shaft. These results also show that the proposed closed loop control system is robust and stable subject to the system parameter uncertainties.

Adaptive backstepping - based controller design for speed sensorless SPMSM using sliding mode observer

In this paper, an adaptive backstepping (ABS) controller is first designed for speed sensorless surface permanent magnet synchronous motor (SPMSM) drives. The ABS controller can secure the system stability and its robustness against the parameter uncertainties an external load torque disturbance. Among the parameters estimate, it is shown that the estimated error in stator inductance, stator resistance and rotor magnetic flux converge asymptotically to zero if the system persistency excitation (PE) of condition is satisfied. The PE condition is satisfied if a low amplitude, low frequency ac signal is superimposed to the d-axes reference current. Then a back EMF sliding mode observer (SMO) is employed in order to detect the rotor speed and position. The proposed control approach is tested by simulation. Computer simulation results obtained, confirm the validity and effectiveness of this control approach.

Robust speed sensorless control of universal field oriented induction motor drive with on-line stator resistance tuning

In this paper, a speed sensorless induction motor drive is introduced which is direct vector controlled in a universal field-oriented (UFO) reference frame. Based on partial feedback linearization theory, a nominal speed control is designed first, regardless of the system parameter uncertainties and external load disturbance. Then, in the perturbed condition, a fuzzy-adaptive sliding mode controller is employed which ensures the sliding motion through the entire drive system state trajectory. Furthermore, a model reference adaptive system (MRAS) estimator is used to estimate the rotor speed and a simple method is also proposed for on-line estimation of the stator resistance. Finally, a digital simulation study is carried out to demonstrate the effectiveness of the proposed speed controller scheme.