Optimal vector control of pumping and ventilation induction motor drives

An original speed control for centrifugal pump and fan drives with squirrel-cage induction motors that seeks the maximum energy saving is proposed. The strategy is based on minimizing the motor and converter losses at the steady state and minimizing the transient time that the motor employs in passing from one steady stage to another. The shortest transient time is achieved by applying the Pontriagin's maximum principle taking into account the parabolic load torque-speed dependence of these types of drives. Short-time transients, which take the motor from one point of maximum efficiency to another, contribute to reduce losses and to extend the application of the energy-saving concept to the drives with frequent changes of load torque and speed.     

Speed sensorless vector control of induction motor usingKalman-filter-assisted adaptive observer

This letter presents a new method of estimating rotor speed of an induction motor. The new method is based on an adaptive flux observer. A second-order Kalman filter is then employed to modify the estimated rotor flux. Experimental results show that the new method has better accuracy in following the speed command under heavy loads     

Decoupling control of induction motor drives

The decoupling control of induction machines is investigated. Three different schemes for decoupling-control methods based on stator flux, airgap flux, and rotor flux field regulation are developed. The control dynamics of each scheme are outlined and studied. Simulation results are presented to verify that these schemes provide decoupling control with excellent dynamic behavior. The transient and steady-state relationships between slip frequency and torque, under constant stator flux, airgap flux, and rotor flux operations, are simulated and compared. The sensitivity characteristics of the three methods of flux-control, machine fed by impressed currents and voltages, are also compared and studied. A prototype torque-drive system is implemented to demonstrate the decoupling control of a squirrel-cage induction machine     

Variable structure current control for induction motor drives byspace voltage vector PWM

In this paper, a variable structure current controller based on a space voltage vector PWM scheme is presented for induction motor drives. In this current controller design, only the current sensors are employed and we attempt to force the stator currents to be exactly equal to the reference currents rapidly. This proposed current controller, which is based on the space voltage vector PWM drive, exhibits several advantages in terms of reduced switching frequency, robustness to parameter variations, elimination of current/torque ripple, and improved performance in induction motor drive. It shows that the current control laws can be demonstrated in theory. Finally, simulation and experimentation results verify the proposed control scheme     

Adaptive decoupling control of induction motor drives

A novel control approach for a robust induction motor drive system with a voltage source inverter has been developed. In the scheme, the induction motor and its corresponding inverter gating signal are controlled using the decoupling control theory. In addition, an adaptive optimal speed regulator employing the model reference adaptive control (MRAC) is incorporated into the drive system to compensate for unfavorable errors. The principles and special features of the control scheme are discussed, and the configuration of the drive system is presented. Comparison is made between conventional proportional plus integral (PI) control and the MRAC. Test results show the robustness and superior dynamic performance of the proposed control system     

Five-phase induction motor drives with DSP-based control system

This paper introduces two kinds of control schemes: vector control and direct torque control (DTC). These control schemes can be extensively applied to the operation of a five-phase induction motor using a fully digital implementation. Vector control of the five-phase induction motor not only achieves high drive performance, but also generates the desired nearly rectangular current waveforms and flux profile in the air-gap resulting in an improvement in air gap flux density and an increase of 10% in output torque. The DTC method has additional advantages when applied to multiphase, in this case a five-phase, induction motor. The five-phase inverter provides 32 space voltage vectors in comparison to 8 space voltage vectors provided by the three-phase inverter. Therefore, a more elaborate flux and torque control algorithm for the five-phase induction motor can be employed. Direct torque control of the five-phase induction motor reduces the amplitude of the ripples of both the stator flux and the torque, resulting in a more precise flux and torque control. A 32-b floating-point TMS320C32 digital signal processor (DSP) enables these two sophisticated control techniques to be conveniently implemented with high control precision. Experimental results show that an ideal control capability is obtained for both control methods when applied to the five-phase induction motor and further validates theoretical analysis     

Sensorless vector and speed control of brushless motor drives

In the present paper an approach is presented to the speed control of permanent magnet synchronous motors without mechanical transducers. The rotor position, which is an essential component of any vector control scheme, is calculated through the instantaneous stator flux position and an estimated value of the load angle. A closed-loop state observer is implemented to compute the speed feedback signal. Experimental results on a laboratory tested motor drive are presented to validate the proposed procedure     

A MRAS-based adaptive pseudoreduced-order flux observer for sensorless induction motor drives

The performance of vector-controlled sensorless induction motor drives is generally poor at very low speeds, especially at zero speed due to offset and drift components in the acquired feedback signals, and the increased sensitivity of dynamic performance to model parameter mismatch resulting especially from stator resistance variations. The speed estimation is adversely affected by stator resistance variations due to temperature and frequency changes. This is particularly significant at very low speeds where the calculated flux deviates from its set values. Therefore, it is necessary to compensate for the parameter variation in sensorless induction motor drives, particularly at very low speeds. This paper presents a novel method of estimating both the shaft speed and stator resistance of an induction motor. In this novel scheme, an adaptive pseudoreduced-order flux observer (APFO) is developed. In comparison to the adaptive full-order flux observer (AFFO), the proposed method consumes less computational time, and provides a better stator resistance estimation dynamic performance. Both simulation and experimental results confirm the superiority of the proposed APFO scheme for a wide range of resistance variations from 0 to 100%.     

Current control for induction motor drives using random PWM

Current control in voltage-source inverters with random pulsewidth modulation (RPWM) is investigated. The random modulation is introduced to alleviate the undesirable acoustic, vibration, and EMI effects in inverter-fed AC drive systems. A novel RPWM digital technique with dithering of the switching frequency and compensation of the processing time is described. Design of the current control loop is discussed. Results of investigation of an experimental drive system are presented, proving the feasibility of the proposed solutions     

Adaptive speed control for induction motor drives using neuralnetworks

In this paper, the adaptive speed control of induction motor drives using neural networks is presented. To obtain good tracking and regulating control characteristics, a digital two-degree-of-freedom (2DOF) controller is adopted and a design procedure is developed for systematically finding its parameters according to prescribed specifications. The parameters of the controller corresponding to various drive parameter sets are found off-line and used as the training patterns to estimate the connection weights of neural networks, Under normal operation, the true drive parameters are real-time identified and they are converted into the controller parameters through multilayer forward computation by neural networks. The parameters of the 2DOF controller can be adapted to match the desired specifications under various operating conditions     

A digital current control technique for voltage-fed induction motor drives

Precise control of stator current is essential to high performance field orientation controlled induction motor drives. Any current error degrades the performance of the drive in the same way as incorrect tuning of field orientation. Previous research has shown that accurate current control can be achieved with intelligent but complex control algorithms. This paper presents a new current control scheme which can achieve high accuracy and fast dynamic response but which is very simple for microprocessor implementation. The scheme was derived using the discrete state space modelling of the induction motor. The control law does not require knowledge of rotor flux and was independent of the field orientation control tuning. Good static and dynamic performances were obtained in both the simulation and experimental verifications. The results also show that the leakage inductance model error might cause a current ripple. However, this parameter can be tuned to its correct value easily by inspecting the current response.     

Quick response and low-distortion current control for multipleinverter-fed induction motor drives

This paper describes a PWM control method to balance two unit inverter currents and to reduce the distortion of motor currents in a multiple GTO inverter for large capacity AC variable-speed drive systems. For an 11 kW induction motor driven by a 15 kVA multiple inverter, the imbalance current can be reduced to less than 5% of the rated motor current, and the motor current waveform can be made very close to sinusoidal. The GTO switching frequency in the multiple inverter can be lowered to one-quarter of that in the single inverter. In a 2750 kVA GTO inverter drive system which was developed based on the 15 kVA multiple inverter, excellent performance is obtained including unity power factor operation at an AC power source, smooth 4-quadrant operation, and quick speed response of 85 rad/s. The quick response is realized by field-oriented control with decoupling control between torque and exciting currents, and direct control of three-phase AC currents. In the future, the multiple GTO inverter is expected to be applied to rolling mill drives instead of cycloconverters     

A fault-tolerant control architecture for induction motor drives in automotive applications

This paper describes a fault-tolerant control system for a high-performance induction motor drive that propels an electrical vehicle (EV) or hybrid electric vehicle (HEV). In the proposed control scheme, the developed system takes into account the controller transition smoothness in the event of sensor failure. Moreover, due to the EV or HEV requirements for sensorless operations, a practical sensorless control scheme is developed and used within the proposed fault-tolerant control system. This requires the presence of an adaptive flux observer. The speed estimator is based on the approximation of the magnetic characteristic slope of the induction motor to the mutual inductance value. Simulation results, in terms of speed and torque responses, show the effectiveness of the proposed approach.     

New hybrid fuzzy controller for direct torque control induction motor drives

A new hybrid fuzzy controller for direct torque control (DTC) induction motor drives is presented in this paper. The newly developed hybrid fuzzy control law consists of proportional-integral (PI) control at steady state, PI-type fuzzy logic control at transient state, and a simple switching mechanism between steady and transient states, to achieve satisfied performance under steady and transient conditions. The features of the presented new hybrid fuzzy controller are highlighted by comparing the performance of various control approaches, including PI control, PI-type fuzzy logic control (FLC), proportional-derivative (PD) type FLC, and combination of PD-type FLC and I control, for DTC-based induction motor drives. The pros and cons of these controllers are demonstrated by intensive experimental results. It is shown that the presented induction motor drive is with fast tracking capability, less steady state error, and robust to load disturbance while not resorting to complicated control method or adaptive tuning mechanism. Experimental results derived from a test system are presented confirming the above-mentioned claims.     

Direct torque control induction motor drives withself-commissioning based on Taguchi methodology

This paper presents the analysis and design of direct torque control (DTC) induction motor drives with self-commissioning. Neither motor parameters nor controller parameters are known a priori. The self-commissioning process consists of the calculation of motor parameters, including stator resistor, inertia and friction coefficient, as well as the design of the controller. The effects of several factors, including test conditions for deriving motor mechanical parameters and natural frequency for controller design, on the performance of speed response are investigated using Taguchi's method which is widely used in quality engineering to significantly reduce the number of experiments. Therefore, the presented drive system cannot only provide self-commissioning but also dramatically improve the performance of speed response, which is evaluated using the performance index of root-mean-squared error (RMSE) of speed. Experimental results derived from a PC-based experimental system are presented to fully support the theoretical development and analysis     

Improved direct torque and flux vector control of PWM inverter-fedinduction motor drives

In this paper, a direct torque and stator flux vector control system is presented. The principle of this method was proposed by Takahashi and Noguchi in 1985. In contrast to the field oriented control, no coordinate transformation and current control loop is required. In practical application, however, problems occur with starting and operation in the zero speed region. This paper shows how, by introducing an additional carrier signal to the torque controller input, a robust start and improved operation in the low speed region can be achieved. The simulation and experimental results which illustrate the performances of the proposed system are presented. Also, nomograms for controller design are given     

Thermal and slip effects on rotor time constant in vector controlled induction motor drives

In this paper, the fast variation of rotor resistance due to winding temperature is shown. Thus, the rotor time constant in the vector controlled induction motor drives, in contrary to common belief, changes fast via temperature. Moreover, it depends on the motor slip. The slip dependency of rotor time constant is due to motor loss that is usually ignored. The iron and stray loss is introduced in the induction machine dynamic and static models and a new expression of the rotor time constant is derived, that contains the motor slip. Thus, the rotor time constant rapidly varies at load torque changes. A novel slip frequency calculation procedure is proposed that ensures the accurate and fast estimation of the valid machine rotor time constant. The above aspects have been verified by extensive simulation and experimental tests in a wide speed-torque range.     

Fuzzy adaptive speed control of a permanent magnet synchronous motor

A fuzzy adaptive speed controller is proposed for a permanent magnet synchronous motor (PMSM). The proposed fuzzy adaptive speed regulator is insensitive to model parameter and load torque variations because it does not need any accurate knowledge about the motor parameter and load torque values. The stability of the proposed control system is also proven. The proposed adaptive speed regulator system is implemented by using a TMS320F28335 floating point DSP. Simulation and experimental results are presented to verify the effectiveness of the proposed fuzzy adaptive speed controller under uncertainties such as motor parameter and load torque variations using a prototype PMSM drive system.     

Quick-response torque-controlled induction motor drives usingphase-locked loop speed control with disturbance compensation

This paper presents an excellent speed control scheme for induction motor drives. Phase-locked loop (PLL) techniques based on proportional-integral derivative (PID) feedback of the phase difference is employed to provide extremely accurate speed regulation. The quick-response torque control of an induction motor is used to provide better torque characteristics. In addition, a disturbance is estimated by a disturbance observer and the estimated value is fed back to eliminate the disturbance effect on the motor speed. The proposed system combines the precise speed regulation of PLL technique and the advantage of the quick-response torque control, with the insensitivity to disturbance by the disturbance compensation. A phase-plane analysis is used to evaluate the effects of gain coefficients of PID feedback of phase difference. Experimental results are presented to verify the characteristics of the proposed system