Babak Nahid-Mobarakeh

Modeling and Control of Six-Phase Symmetrical Induction Machine Under Fault Condition Due to Open Phases

This paper introduces a new fault-tolerant operation method for a symmetrical six-phase induction machine (6PIM) when one or several phases are lost. A general decoupled model of the induction machine with up to three open phases is given. This model illustrates the existence of a pulsating torque when phases are opened. Then, a new control method reducing the pulsating torque and the motor losses is proposed in order to improve the drive performances. The proposed method is compared to two other existing techniques. The simulation and experimental results obtained on a dedicated test-rig confirm the validity and the efficiency of the proposed method for a fault-tolerant symmetrical 6PIM drive.

Linear Stabilization of a DC Bus Supplying a Constant Power Load: A General Design Approach

In this paper, an oscillation compensation technique is proposed to improve the stability margin of an electrical system constituted by a dc power supply, an LC filter, and a constant power load. This is realized here by an actuator (inverter-permanent-magnet synchronous motor). To design the compensator, input impedance of the constant power load and output impedance of the filter are required and derived in this paper. To develop the load input impedance expression, small signal approximation is employed and all dynamics are taken into account except by the inverter ones only, which can often be neglected in practical applications. Then, the control structure of the whole system is slightly modified to implement the oscillation compensation block that increases the stability margin, and thus, permits to reduce the dc-link capacitance value. In this paper, the proposed method is applied to an actuator designed for aerospace applications. The influence of the actuator control parameters and the input filter parameters on the stability of the dc-link voltage is discussed. Simulations and experimentations confirm the validity of the proposed approach.

Large Signal Stability Analysis Tools in DC Power Systems With Constant Power Loads and Variable Power Loads—A Review

Electric motor drives and power electronic converters have become increasingly common in advanced power systems. Passive LC filters are used in these systems to reduce the power ripples. These filters are usually poorly damped for reducing the losses as well as the size/weight and the cost of the system. This leads to instability phenomena if the load power exceeds a power limit depending on the filter parameters. The purpose of this paper is to present tools allowing large signal stability analysis of a dc power system. These tools allow estimation of the domain of attraction of the system operating point. It will be shown that this large signal stability analysis gives useful hints on the design of the system to optimize the stability criteria for constant and variable power loads. The impact of the load dynamics on stability is also studied. An electric drive connected to a dc power supply through a poorly damped LC filter is used as a case study. The simulations and the experimentations confirm the analytical results.

Back-EMF estimation based sensorless control of PMSM: robustness with respect to measurement errors and inverter irregularities

In this paper, the influence of measurement errors and inverter irregularities on performances of sensorless control is studied. The control algorithm is based on the back-EMF estimation whose robustness with respect to the machine parameter uncertainties was already studied Mobarakeh, BN et al., (2001) by supposing that current measurements and the power stage are ideal. Here, these hypotheses are canceled and we show analytically and experimentally that the control performances at low speed are highly affected by the imperfection of the electronic components. We also present the interest of on-line stator resistance estimation improving the sensorless control performances in spite of the presence of above disturbances.

Fault Tolerant and Minimum Loss Control of Double-Star Synchronous Machines Under Open Phase Conditions

In this paper, a new method for filtering the torque pulsations is proposed for double-star permanent magnet synchronous machines under fault conditions. The machine is supplied by two independent electric sources via two voltage source inverters. The proposed method deals with the case where an open-circuit fault occurs. To reduce the torque pulsations, the usual solution consists in supplying only the healthy star winding. Here, we propose to supply not only the healthy winding, but also the two remaining phases of the other star winding by the healthy legs of the faulty inverter. The stator current waveforms can be easily determined to minimize the copper losses while reducing the torque pulsations. Simulation and experimental results confirm the efficiency of the proposed method.

Large-Signal Stabilization of a DC-Link Supplying a Constant Power Load Using a Virtual Capacitor: Impact on the Domain of Attraction

It is known that the interaction between poorly damped LC input filters and constant power loads (CPLs) leads to degradation of dynamic performance or system instability. This paper addresses a large-signal stability study and stabilization of an electrical system containing a dc power supply, an LC filter, and a CPL. This latter is realized here by a voltage source inverter supplying a motor drive. To stabilize the system, the control structure is slightly modified to implement a nonlinear stabilization block that virtually increases the dc-link capacitance and, hence, the damping of the system. The main idea consists in adding a capacitive power component to the CPL power reference. This allows reducing the real dc-link capacitance value and volume, which is, for weight and size reasons, an important issue in aerospace applications. The impact on the large-signal stability will be analyzed by estimating the domain of attraction of the operating point. An illustrative example consisted of an LC input filter connected to an inverter-permanent-magnet synchronous motor designed for aircraft applications treated by simulations and experimentation, which confirm the validity of the proposed approach.

General Active Global Stabilization of Multiloads DC-Power Networks

Implantation of complex dc-power network is one of the main research topics in more electric aircraft (MEA). In such applications, small and light systems are required and so optimization of passive elements, such as dc-bus capacitance and filtering inductance, is an important issue. It is known that the reduction of dc-bus capacitance may lead to instability of an MVdc network. So, if no stabilizer is used, the risk of instability must be considered, while designing the system passive elements. In this paper, we will first study the small signal stability of an MVdc network composed of three loads: an inverter supplying a permanent magnet synchronous motor, a dc/dc converter feeding a resistive load, and a supercapacitor controlled by a bidirectional dc/dc converter. Then, we will propose a large-signal-stabilizing system to ensure global stability by generating proper stabilizing power references for the whole system. The contribution of the loads to network stability is adjustable. The validity of the proposed method will be confirmed by experimentations.

Online Identification of PMSM Parameters: Parameter Identifiability and Estimator Comparative Study

In this paper, a model-reference-based online identification method is proposed to estimate permanent-magnet synchronous machine (PMSM) parameters during transients and in steady state. It is shown that all parameters are not identifiable in steady state and a selection has to be made according to the users objectives. Then, large signal convergence of the estimated parameters is analyzed using the second method of Lyapunov and the singular perturbations theory. It is illustrated that this method may be applied with a decoupling control technique that improves convergence dynamics and overall system stability. This method is compared with an extended Kalman filter (EKF)-based online identification approach, and it is shown that, in spite of its implementation complexity with respect to the proposed method, EKF does not give better results than the proposed method. It is also shown that the use of a simple PMSM model makes estimated parameters sensitive to those supposed to be known whatever the estimator is (both the proposed method and EKF). The simulation results as well as the experimental ones, implemented on a nonsalient pole PMSM, illustrate the validity of the analytic approach and confirm the same conclusions.

Active Stabilization of DC Microgrids Without Remote Sensors for More Electric Aircraft

DC microgrids are increasingly used in transportation systems such as more electric aircraft. Such applications require small and light systems, and thus, the optimization of passive elements like dc-bus capacitor and filtering inductor is an important issue. It is known that the reduction of dc-bus capacitance may lead to instability of the dc microgrid when tightly controlled loads are employed. To overcome this risk, a seductive solution is to implement a centralized stabilization system in the dc microgrid. Nevertheless, a centralized stabilizer requires a lot of sensors and particularly those providing the load input voltages. The latter is often far from the stabilizer, and fast data transmission lines must be provided. In this paper, an observer is developed for estimating the load input voltages, thus removing the required voltage sensors. Its convergence as well as the stability of the whole system is proved. The validity of the proposed method is confirmed by simulations and experimentations.

Experimentally Validated Dynamic Fault Model for PMSM with Stator Winding Inter-Turn Fault

In this paper a simple dynamic model for a PMSM with inter-turn winding fault is derived. FEM is used for parameter determination of the machine with inter-turn fault. This fault model is used to study the behavior of the machine with inter-turn fault. The experimental test is conducted to validate the fault model for different levels of fault severity. The comparison of the results obtained by the model simulation and experimental tests allowed verifying the precision of the proposed dynamic model. This fault model is used to study of the PMSM under various fault conditions and severity and seems to be well adapted for PM motors health monitoring and inter-turn fault diagnosis.