Donald S. Zinger

A variable speed wind turbine power control

To optimize the power in a wind turbine, the speed of the turbine should be able to vary with the wind speed. A simple control scheme is proposed that will allow an induction motor to run a turbine at its maximum power coefficient. The control uses a standard V/Hz converter and controls the frequency to achieve the desired power at a given turbine speed.

The Influence of Motor Parameter Deviations in Feedforward Field Orientation Drive Systems

If the value of the time constant used in the slip calculator of a feedforward field orientation drive system deviates from the correct value, the decoupling of flux and torque is lost, and both steady-state and transient response is degraded. An analysis of detuned operation shows that the amount of performance degradation is strongly dependent on machine parameters. The large magnetizing inductance and low rotor resistance typically associated with larger, more efficient machines is shown to tend to amplify the effects of detuning compared to the relative insensitivity of small low-efficiency machines. It is also shown that for many applications the transient response effects of detuning can be handled by the outer control loops and that the major problem is maintaining the steady-state operating flux and current at reasonable levels.

PI and fuzzy estimators for tuning the stator resistance in direct torque control of induction machines

Direct torque control (DTC) of induction machines uses the stator resistance of the machine for estimation of the stator flux. Variations of stator resistance due to changes in temperature or frequency make the operation of DTC difficult at low speeds. A method for the estimation of changes in stator resistance during the operation of the machine is presented. The estimation method is implemented using proportional-integral (PI) control and fuzzy logic control schemes. The estimators observe the machine stator current vector to detect the changes in stator resistance. The performance of the two methods are compared using simulation and experimental results. Results obtained have shown improvement in DTC at low speeds.

Fuzzy controller for inverter fed induction machines

A fuzzy logic controller for direct self-control of an induction machine is presented. A response faster than that of the conventional direct self-controller during startup and during a step change in torque is achieved. To improve the system performance at low speeds a fuzzy resistance estimator is proposed to eliminate the error due to the change in stator resistance. At constant flux and torque commands any change in stator resistance of the induction machines causes an error in stator current. This error is utilized by the fuzzy resistance estimator to correct the stato resistance used by the controller to match the machine resistance. Both fuzzy controller and fuzzy resistance estimator are simulated for a 3 hp induction motor. The simulation results demonstrate good performance.<<ETX>>

Annualized wind energy improvement using variable speeds

To optimize the operation of a wind turbine, variable turbine speeds are desirable. To determine the advantages of a variable-speed turbine, the annualized energy production of the turbine needs to be considered. This is done by using a Rayleigh probability distribution to determine the number of hours of a particular wind speed which occur in a given year. This distribution is used with the aerodynamic power generated at a given average wind speed to determine the total energy generated during the year. The total energy for fixed- and variable-speed turbine control are compared. The variable-speed turbines show improved energy production over constant-speed systems.

Parallel connected LEDs operated at high to improve current sharing

Light emitting diodes (LEDs) are have many features that make them attractive for use in an increasing number of applications. For many of these applications it is desirable to have LEDs in parallel. Because forward conduction characteristics vary considerably in for one device to another there is a problem with current sharing in parallel connected LEDs. This paper proposes a new circuit to regulate current in parallel LEDs. The circuit uses a capacitor in series with sets of antiparallel connected LEDs to control the current flow in each of the branches. The circuit is driven with a high frequency voltage generated by a resonant converter. Experimental results show large reductions in current differences between parallel connected LEDs.

An effective LED dimming approach

As light emitting diodes (LEDs) have become increasingly accepted as a light source in many applications, the demand for dimming LEDs has also increased. Typically LEDs are supplied with voltage source. Dimming is accomplished by adjusting the average current in the LEDs through pulse width modulation of a switch in series with the load. This paper proposes a technique that uses a current source as the base supply. The average current is adjusted with a switch in parallel to the load. This circuit is shown to be effective in increasing the dimming range of the LEDs.

Fuzzy implementation of direct self-control of induction machines

A system with fast torque response is very beneficial in applications where direct torque control is highly desirable. The response of direct self control is slower during start-up and during change in command torque. Fuzzy control is used for the implementation of direct self control to improve its slow response. Experimental implementation of the fuzzy logic controller was carried out to verify the behavior of the controller. The controller was implemented with a single board computer that uses a TMS320C14 DSP. The experimental results with fuzzy control are compared with those of the conventional direct self controller. The starting flux and torque response and the responses to step changes in command torque with fuzzy implementation showed a considerable improvement over the conventional control. The steady state response for both controllers are the same. >

A direct field oriented controller for induction motor drives using tapped stator windings

A direct method of field orientation has been implemented that requires little knowledge of machine parameters and requires only readily measurable quantities. The system uses tapped stator windings to measure the air gap flux. The signals from the tapped windings are also used in a flux regulation loop. The ripples created in the tapped windings by the motion of the rotor slots through the flux provide speed information to the speed controller.<<ETX>>

Learning techniques to train neural networks as a state selector for inverter-fed induction machines using direct torque control

Neural networks are receiving attention as controllers for many industrial applications. Although these networks eliminate the need for mathematical models, they require a lot of training to understand the model of a plant or a process. Issues such as learning speed, stability, and weight convergence remain as areas of research and comparison of many training algorithms. This paper discusses the application of neural networks to control induction machines using direct torque control (DTC). A neural network is used to emulate the state selector of the DTC. The training algorithms used in this paper are the backpropagation, adaptive neuron model, extended Kalman filter, and the parallel recursive prediction error. Computer simulations of the motor and neural-network system using the four approaches are presented and compared. Discussions about the parallel recursive prediction error and the extended Kalman filter algorithms as the most promising training techniques is presented, giving their advantages and disadvantages.