Junggi Lee

Sensorless Control of Surface-Mount Permanent-Magnet Synchronous Motors Based on a Nonlinear Observer

A nonlinear observer for surface-mount permanent-magnet synchronous motors (SPMSMs) was recently proposed by Ortega et al.(LSS, Gif-sur-Yvette Cedex, France, LSS Internal Rep., Jan. 2009). The nonlinear observer generates the position estimate ¿¿ via the estimates of sin ¿ and cos ¿. In contrast to Luenberger-type observers, it does not require speed information, thus eliminating the complexity associated with speed estimation errors. Further, it is simple to implement. In this study, the nonlinear observer performance is verified experimentally. To obtain speed estimates from the position information, a proportional-integral (PI) tracking controller speed estimator was utilized. The results are good with and without loads, above 10 r/min.

Estimation of Rotor Position and Speed of Permanent Magnet Synchronous Motors With Guaranteed Stability

The control algorithms used in high performance ac drives require the knowledge of rotor position and, in the case of speed regulation, also of speed. Since in many applications rotational transducers cannot be installed, their reconstruction is needed. The use of observers is stymied by the fact that the dynamics of electrical machines are highly nonlinear and does not belong to the class studied by the nonlinear control community. In this paper solutions to both problems, which are particularly tailored for the widely popular permanent magnet synchronous motors, are provided. A key step for the design of both observers is the choice of a suitable set of coordinates. The position observer is a standard gradient search whose detailed analysis reveals outstanding (global asymptotic) stability properties. Furthermore, the analysis clearly exhibits the interplay between rotor speed and the gain of the gradient search-that (essentially) determines its convergence rate. The position observer is a simple two-dimensional nonlinear system, hence is easily implementable. The speed observer is designed following the immersion and invariance technique and is also shown to be globally convergent. Simulation and experimental results of the position observer, used together with a classical field-oriented control algorithm, are presented.

Inverter-Based Local AC Bus Voltage Control Utilizing Two DOF Control

Small- and medium-sized distributed generation (DG) systems in a microgrid normally have inverters, and the inverter outputs are connected to the grid through an LCL filter. In this paper, we are interested in designing a DG inverter that behaves like a uninterruptible power supply (UPS) for its dedicated loads, while enabling power flow control with the microgrid. If the grid power is lost, then the DG system can be transferred smoothly to the island (stand-alone) operation. This islanding capability provides a higher reliability of the local ac bus than the conventional power system. In order to have such a UPS functionality, the inverter is desired to have a high control bandwidth, which is required for regulating the ac bus voltage at the presence of nonlinearities and unpredictable behaviors of the loads. As for a fast controller, a two-degree-of-freedom (DOF) controller is applied to the LC filter plant with the inverse dynamic model. The voltage command levels are selected considering the amount of power share with the grid. The effectiveness of the proposed control scheme is shown by experimental results.

A Lookup Table Based Loss Minimizing Control for FCEV Permanent Magnet Synchronous Motors

A loss minimizing control law is developed for a fuel cell electric vehicle (FCEV) permanent magnet synchronous motor (PMSM) which reflects the effects of field saturation and cross coupling. Inductances are modelled as functions of q-axis current based on the flux data obtained experimentally. For a given torque and a given speed, the loss minimizing current sets are searched from the experimental power loss data which are obtained for various d-axis current. The loss minimizing current sets are made into a lookup table, and it is utilized in the torque control loop. This controller guarantees high efficiency in every possible torque-speed operating point.

Compensation of Current Measurement Error for Current-Controlled PMSM Drives

Accurate measurement of phase current is crucial in a current-controlled PMSM drive system. Current measurement error directly deteriorates torque control performance. This paper analyzes effects of the current measurement error on the phase current and the output voltage of the current controller. Based on the analysis, a compensation method is proposed. It compensates the offset error and the scaling error separately without any additional hardware but using the output voltage reference of the current controller. The proposed method can be applied to general current-controlled PMSM drives in whole operation range. Experimental results verify the effectiveness of the proposed compensation method.

Loss Minimizing Control of PMSM with the Use of Polynomial Approximations

Normally, look-up table based methods are being utilized for loss minimizing control of permanent magnet synchronous motors (PMSMs). But, numerous repetitive experiments are required to make a look-up table, and the program size becomes bulky. In this work, analytic methods of finding the loss minimizing solution are studied. Since the solution lies either in the interior, or on the voltage limit boundary, two different cases are dealt separately. In both cases, fourth order polynomials are derived. To obtain approximate solutions, methods of order reduction and linear approximation are utilized. The accuracies are good enough for practical use. These approximate solutions are fused into a proposed loss minimizing algorithm (LMA), and implemented in an inverter DSP. Experiments were done with the real PMSM developed for a sport-utility fuel cell electric vehicle (FCEV). The analytically derived minima were justified by experimental evidences, and the dynamic performances over wide speed range were shown to be satisfactory.

An Optimal Selection of Induction-Heater Capacitance Considering Dissipation Loss Caused by ESR

In the design of a parallel resonant induction-heating system, choosing a proper capacitance for the resonant circuit is quite important since both output-power maximization and capacitor heat loading should be considered. The temperature rise often blows up the water-cooled capacitors in high-power induction heaters or reduces the lifetime of capacitors significantly. This paper, therefore, presents a method of finding an optimal capacitance that maximizes the output power while considering the capacitor loss at the same time. To count the effect of the capacitor heatup, an equivalent series resistance is included in the model. Based on the equivalent circuit model, the output power and the capacitor loss are obtained as the functions of capacitance, and an optimization technique is applied treating the capacitance as a control variable. The effectiveness of the proposed method is verified by simulations and experiments. Equivalent series resistance (ESR), induction heater, optimal selection, parallel resonant circuit.

An optimal selection of induction heater capacitance considering dissipation loss caused by ESR

In the design of a parallel resonant induction heating system, choosing a proper capacitance for the resonant circuit is quite important. The capacitance affects the resonant frequency, output power, Q-factor, heating efficiency and power factor. In this paper, the role of equivalent series resistance (ESR) in the choice of capacitance is significantly recognized. Without the effort of reducing temperature rise of the capacitor, the life time of capacitor tends to decrease rapidly. This paper, therefore, presents a method of finding an optimal value of the capacitor under voltage constraint for maximizing the output power of an induction heater, while minimizing the power loss of the capacitor at the same time. Based on the equivalent circuit model of an induction heating system, the output power, and the capacitor losses are calculated. The voltage constraint comes from the voltage ratings of the capacitor bank and the switching devices of the inverter. The effectiveness of the proposed method is verified by simulations and experiments.

Generation of low-energy neutral beam for Si etching

As the feature size shrinks toward the nanoscale, charge-up damage from ion-induced etching becomes a very serious problem. Neutral beam etching is one of the most popular techniques used to reduce charge-up damage. We have performed a neutral beam simulation to optimize the neutral beam, which is generated by collisions between ions produced by a plasma source with an ion gun and low angle reflectors. An ion gun is simulated using the two-dimensional Xgrafic object oriented particle-in-cell (XOOPIC) code to obtain a higher ion flux and to improve the directionality of ions. For neutral beam simulation, we use the modified XOOPIC code to which reflection data obtained by the transport of ions in matter (TRIM) code are appended. Neutral flux, energy and angle distributions, which have an influence upon the etch rate, are calculated in the neutral beam simulation. A low-energy neutral beam from an ion gun with two grids has a low neutral flux and a broad angle distribution. Therefore, we propose a three-gri...

A stator turn-fault detection method for inverter-fed IPMSM with high-frequency current injection

This paper presents a turn-fault detection method for inverter-fed Interior Permanent Magnet Synchronous Machines(IPMSMs) using high-frequency current injection when the motor is at standstill. When the motor is stopped, the fault current which flows in the faulty turns and the phase currents can be expressed with the injected phase current and the mutual inductance between each phase winding and the faulty turns. Because of the turn-fault, the injected high frequency currents cause different losses according to the direction of the injection. The proposed detection method exploits the difference of the losses of each case to diagnose the turn-fault. Experimental results are provided to verify the proposed detection method. The resultant loss pattern agrees well with that of the electrical model and shows reasonable sensitivity to the turn-fault. Two-turn fault among 27 turns of a phase winding of the motor under test has been detected easily with existing hardware of the drive system.