Aligned Position Estimation Based Fault-Tolerant Sensorless Control Strategy for SRM Drives

Factors such as machining precision and electrical failures may lead to phase inductance unbalance in a switched reluctance motor (SRM). Under unbalanced inductance conditions, most of the traditional sensorless schemes would be invalid if no modification is applied. To prove the existence of this problem, an inductance partition based rotor position estimation scheme under balanced and unbalanced inductance conditions are investigated and compared for identifying the position estimation error characteristics. The theoretical analysis shows that the position estimation error is highly dependent on the degree of the inductance unbalance. To maintain stable sensorless operation under unbalanced condition, a modified full-cycle inductance partition based rotor position estimation scheme with unbalanced inductance adaptive capability is proposed in this paper. In this method, the linear region of each phase full-cycle inductance is relocated with the predetermined inductance thresholds. By locating the linear inductance regions, the rotor position can be estimated from a simple partition linear model between the rotor position and the phase inductance. This method is easy for implementation without additional hardware and complex calculation. Experiments are performed on a 12/8 structure SRM and the results verify the effectiveness of the proposed method.

Phase inductance is a key parameter in switched reluctance motor (SRM) design because torque and the dynamics of phase voltages and currents are directly related to inductance. Therefore, accurate calculation of the inductance at arbitrary rotor positions is important in determining the SRM behavior. Contrary to the popular but time-consuming approach to determine the flux linkage and inductance of a SRM with finite element analysis (FEA), this paper proposes a novel analytical solution based on the partial differential equations of magnetic potentials to calculate the inductance profile of a 4/2 SRM with respect to rotor position, which makes the inductance prediction more time-efficient. The accuracy of this method is validated by comparing its estimated inductance profile to the inductance obtained by FEA.

An efficient and reliable operation of the Switched Reluctance Motor (SRM) can be achieved only by proper estimation of the rotor position. The rotor position information in switched reluctance motor (SRM) drives is essential for generating the proper firing sequence and for controlling the speed of the drive. Also SRM drives in recent days are more expensive than their conventional AC and DC drives. This is to a great extent caused by the lack of a standardized power electronic converter for SRM drives. This paper describes a new and simple method for determining the rotor position of a switched reluctance motor (SRM) based on motor design structure and a design of low cost converter for low and high speed operations. The scheme is successfully implemented with minimum number of switching devices and position sensors to control the speed of the switched reluctance motors in both the direction. This controller executes controller algorithms via micro-controller to generate SRM driving signal.

An accurate rotor position signal is quite necessary for high-performance control of switched reluctance motor (SRM). In general, the position signal faults may lead to abnormal operation, which deteriorates the reliability of the switched reluctance drive system. Thus, it is quite vital but still a challenge to develop a control strategy that can diagnose and control the position signal faults in an autonomous way. In this paper, a square-wave position signal edge prediction-based control strategy is proposed for position signal faults diagnosis and position faults recovery. Integrated with the rotor position fault-tolerant control method, the SRM drive system can maintain reliable operation under different position signal fault conditions. In addition, a phase inductance slope-based sensorless control method is proposed for position fault-tolerant control under the extreme case with failure of all position signals. To verify the validation of the proposed methods, the experiments have been implemented in a 12/8 structure SRM prototype. The results show that the proposed control methods can further improve the fault-tolerant capability of the SRM system.

Problem statement: The Switched Reluctance Motor (SRM) is an old member of the Electric Machines Family. It’s simple structure, ruggedness and inexpensive manufacturing capability make it more attractive for Industrial applications. Now, the applications of switched reluctance motors in various industrial fields are tried by many engineers. However, switched reluctance motors are not used so far in submersible underwater motor for agriculture purposee. The torque developed by an SRM is dependent on the change of flux-linkage and rotor position. The flux linkage characteristic of the motor is required to make the control circuit. Since the SRM is non-linear in nature, estimation and calculation of the flux linkage characteristics is very difficult. Approach: With the flux tube method concept a simple algorithm is being developed in a MATLAB. ANSYS Software is used to determine the flux distribution at various rotor positions. Results: The aligned and unaligned flux linkage values for theoretical calculation at a current of 7 A is 72.7 mwb and 13.79 mwb respectively. With FEA simulation the obtained value is 92.73 mwb and 19.175. Conclusion: In this and, a simplified method for the determination of flux linkage characteristics of submersible SRM using MATLAB has been presented. The obtained value has been validated with the ANSYS FEM method. the calculated unaligned and aligned inductance values of a 4- phase, 3 hp, 220 V Submersible SRM using simplified MATLAB method very much matches with the ANSYS FEM Method.

Accurate modeling of flux-linkage characteristics is the basis of design and control of switched reluctance motor(SRM). The flux-linkage characteristic of SRM is a function of both the excitation current and rotor position. But due to the highly nonlinear characteristics of SRM, modeling is cumbersome. In this paper, three effective algorithms for modeling of SRM are investigated, which are based on subregional mathematical model, neural network and adaptive neural fuzzy inference systems(ANFIS) respectively. The performance of each method is validated and compared via matlab tools. Simulation results show that all these models can accurately and successfully modeling of SRM, while RBF neural network is the best. Moreover, a new SRM dynamic simulation model based on RBF is developed for verification. Simulation and experimental results validated the accuracy of RBF modeling algorithm.

Abstract-Due to nonlinear electromagnetic characteristics of Switched Reluctance Motor (SRM), as well as complexity of voltage and current waveforms, it is of great difficulty to control SRM optimally and compute power losses. A novel optimal control strategy of Non-Energy Returnable Current Chop (NERCC) was proposed, which is suitable for high power SRM drive. This method can obtain current waveform in accordance with driving mode by reasonably choosing zero-voltage status. And then power losses of SRM drive system was analyzed under Chopped Current Control (CCC) method, it is concluded that NERCC control strategy is suitable for high power SRM application. In the end, the high power SRM drive system has been on trial in coal mine, experimental results of the system confirmed that current ripple is less than 5% and good performance of the proposed strategy proved its feasibility and applicability.

A sensorless control strategy of a high-speed 315 kW brushless dc (BLDC) motor based on a speed-independent flux linkage function is proposed in this paper. It addresses the two key challenges on the sensorless control of high-speed BLDC motor: proposing a speed-independent flux linkage function to ensure reliable operation in the low-speed range, and presenting correction strategy to provide accurate commutation points in the high-speed range. First, the sensorless detection circuit model of a 315 kW BLDC motor is discussed. The analysis shows that the speed-independent flux linkage function is really suitable for BLDC motor sensorless control strategy in the low-speed range. Then, an improved closed-loop system based on the change of current in the full speed range is proposed. The experimental results show that the proposed control strategy can provide a highly accurate and robust sensorless operation from near zero to 20 000 r/min.

In this paper, two kinds of control strategies applied to a switched reluctance motor (SRM) with 12/8 teeth configuration have been analyzed based on a three-phase bridge converter. The first strategy is that the three phase SRM windings have to be connected in delta, with a separate diode connected in series with each phase, which is possible to control the voltage and current of each phase independently. The second strategy is that the three-phase windings of SRM are star-connected, and two-phase excitation strategy is applied. Field-circuit coupled finite-element models of SRM are set up in case of two kinds of control strategies respectively. The dynamic performance of SRM is investigated with two different strategies. Compared with the traditional SRM drive based on the asymmetric half-bridge converter, the SRM drive systems proposed in this paper can achieve the similar performance with low cost.

This paper studies the speed control strategy of a switched reluctance motor based on angle-position control (APC). The switched reluctance motor has three control parameters: turn-on angle, turn-off angle and voltage PWM duty cycle. This paper studies the function of the three parameters and designs the control algorithms of the parameters, respectively, which can reduce the coupling degree, simplify the control process, and realize the optimal control of the switched reluctance motor. By studying the nonlinear characteristics of the switched reluctance motor, the optimal current waveform in the effective working range of the inductor is obtained, and then a control strategy of the turn-on angle is designed to realize the ideal winding current waveform. According to the torque characteristics of the motor, taking the coincidence of the freewheeling zero point and the position angle at the end of the maximum inductance interval as the control target, a control strategy for the turn-off angle that makes full use of the effective inductance working interval is proposed, which improves the efficiency of the system. For the nonlinear and time-variant switched reluctance motor running process, a data-driven model-free adaptive control algorithm is introduced, and a switched reluctance motor speed control algorithm based on voltage PWM duty cycle is designed. The main contribution of this paper is to propose a control strategy that is generally applicable to switched reluctance motors, which does not depend on the precise mathematical model of the motor. The control algorithms are designed separately for the three control parameters according to the characteristics of the motor, which reduces the degree of coupling among them. A switched reluctance motor drive system based on angle-position control is designed. This strategy is especially suitable for driving the load with sudden large torque pulsation.

The torque developed by a switched reluctance motor (SRM) is dependent on the change of flux-linkage and rotor position. The flux-linkage is a function of both the excitation and the rotor position. Due to the nonlinear nature of this motor, estimation of the flux-linkage characteristics is cumbersome. In this paper, a simple analytical method to estimate the flux-linkage characteristics of SRM is presented. Here, equations for the calculation of inductance and the flux-linkage for three identified regions based on the rotor position; a) fully unaligned to starting of pole overlap, b) starting of pole overlap to full pole overlap, and c) full pole overlap to fully aligned conditions, are derived in terms of motor dimensions, the magnetic properties of the materials used, and the stator excitation. The validation of the results obtained from this new analytical method is carried out using the finite element analysis of the motors.

This paper presents a new and novel method which is designed to detect the rotor position at standstill and also low speeds in switched reluctance motor. In this method a small capacitor is connected in series with the motor winding for sampling the voltage rise during the detection period. The supply voltage in conjunction with the drive transistor produces short pulses for this series connection. Since the motor phase inductance varies according to the rotor position, therefore the rise-time for the voltage produced on the capacitor is different. Now this voltage is compared with a pre-set value and a voltage pulse with proper width is then generated. The width of created pulse is proportional to the rotor position. Now, a digital pulse width modulation decoder (DPWM Decoder) employed to convert the produced pulse width to a digital value. This technique is applied to all the phases at stand still to select the proper phase. In the running mode, the same procedure is applied but only to the un- energized phases winding. Finally, experimental results derived from an FPGA based drive are also presented for the motor to confirm the feasibility and practicability of the method.

Two novel indirect switched reluctance motor (SRM) rotor position (RP) sensing schemes based on winding current amplitude and phase modulation are presented. An off phase is supplied with a stiff sinusoidal carrier voltage from the sensing circuit to be modulated by an RP dependent phase inductance function. The modulated signal is decoded to obtain the information signal and is calibrated to obtain the RP angle continuously. A combination of phase modulation and amplitude modulation encoder techniques was designed and tested on a 5 hp three-phased 6-4 SRM over a wide range of speed. The position detection scheme kept excellent track of the rotor angle continuously under both load and no-load conditions. This scheme is extremely robust to switching noise present in the sensing phase due to mutually induced voltages.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper presents a new speed control strategy for interior permanent magnet motor at full speed range. The key is to apply the appropriate control strategies according to the operation region of the motor. In constant torque region, the maximum torque per ampere control is employed to acquire high pull torque. On the other hand, the weakening-flux control is applied to keep the output power unchanged when the motor operates in constant power region. Both the simulation and experimental results are given to verify the proposed control strategy.

Inductance profile has an important bearing on the performance of a switched reluctance motor (SRM). This paper presents the results of a frequency response method to estimate the inductance profile of SRMs. The stator winding is energized by a variable voltage variable frequency supply. An approximate equivalent circuit incorporating stator resistance, winding inductance and loss component has been used to estimate the inductance at different rotor positions. The inductance value is obtained over a band of rotor positions spanning one rotor pole pitch. Supply frequency is varied from 10 Hz to 55 Hz. The method is found to be simpler to the one using DC switching and processing of transient response. Interestingly, inductance at any given rotor position is not found to be sensitive to excitation frequency. However, as could be expected, core loss under test condition is very sensitive to supply frequency. Typical test results on a 4 kW, 8/6 pole, 4 phase SRM are presented and discussed.