Ned Mohan

Design and implementation of an extended Kalman filter for the state estimation of a permanent magnet synchronous motor

Practical considerations for implementing the discrete extended Kalman filter in real time with a digital signal processor are discussed. The system considered is a permanent magnet synchronous motor (PMSM) without a position sensor, and the extended Kalman filter is designed for the online estimation of the speed and rotor position by only using measurements of the motor voltages and currents. The algorithms developed to allow efficient computation of the filter are presented. The computational techniques used to simplify the filter equations and their implementation in fixed-point arithmetic are discussed. Simulation and experimental results are presented to demonstrate the feasibility of this estimation process. >

Control of a Doubly Fed Induction Wind Generator Under Unbalanced Grid Voltage Conditions

Wind energy is often installed in rural, remote areas characterized by weak, unbalanced power transmission grids. In induction wind generators, unbalanced three-phase stator voltages cause a number of problems, such as overcurrent, unbalanced currents, reactive power pulsations, and stress on the mechanical components from torque pulsations. Therefore, beyond a certain amount of unbalance, induction wind generators are switched out of the network. This can further weaken the grid. In doubly fed induction generators (DFIGs), control of the rotor currents allows for adjustable speed operation and reactive power control. This paper presents a DFIG control strategy that enhances the standard speed and reactive power control with controllers that can compensate for the problems caused by an unbalanced grid by balancing the stator currents and eliminating torque and reactive power pulsations

Active input-voltage and load-current sharing in input-series and output-parallel connected modular DC-DC converters using dynamic input-voltage reference scheme

This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.

Asymmetrical duty cycle permits zero switching loss in PWM circuits with no conduction loss penalty

Operating a bridge-type PWM (pulse width modulation) switch mode power converter with asymmetrical duty ratios can eliminate switching losses with no increase in conduction loss. This circuit topology combines the best features of resonant (zero switching loss) and switch mode (low conclusion loss) circuits. Design equations are presented for just such a circuit.<<ETX>>

Common-duty-ratio control of input-series connected modular DC-DC converters with active input voltage and load-current sharing

This paper proposes a simple control method to achieve active sharing of input voltage and load current among modular converters that are connected in series at the input and in parallel at the output. The input-series connection enables a fully modular power-system architecture, where low voltage and low power modules can be connected in any combination at the input and/or at the output, to realize any given specifications. Further, the input-series connection enables the use of low-voltage MOSFETs that are optimized for very low RDSON , thus, resulting in lower conduction losses. In the proposed scheme, the duty ratio to all the converter modules connected in input-series and output-parallel (ISOP) configuration is made common. This scheme does not require a dedicated input-voltage or load-current-share controller. It relies on the inherent self-correcting characteristic of the ISOP connection when the duty ratio of all the converters is the same. The proposed scheme is analyzed using the average model of a forward converter. The stability and performance of the scheme are verified through numerical simulation, both in frequency domain and in time domain. The proposed control method is also validated on an experimental prototype ISOP system comprising of two forward converters

Control strategies for dynamic voltage restorer compensating voltage sags with phase jump

Voltage sags are an important power quality problem and the dynamic voltage restorer is known as an effective device to mitigate voltage sags. In this paper, different control strategies for a dynamic voltage restorer are analyzed with emphasis put on the compensation of voltage sags with phase jump. Voltage sags accompanied by a phase jump are in some cases more likely to trip loads and a satisfactory voltage compensation are more difficult to achieve. Different control methods to compensate voltage sags with phase jump are proposed and compared. Two promising control methods are tested with simulations carried out in Saber and finally tested on a 10 kVA rated dynamic voltage restorer in the laboratory. Both methods can be used to reduce load voltage disturbances caused by voltage sags with phase jump. One method completely compensates the phase jump, which is the best solution for very sensitive loads. The second method does only partly compensate the phase jump, but it is expected to have a better performance in compensating a broader range of voltage sags.

Active filtering of harmonic currents in three-phase, four-wire systems with three-phase and single-phase nonlinear loads

A novel active harmonic-neutralizing filter is proposed which eliminates current harmonic effects, caused by any configuration of nonlinear loads in a three-phase, four-wire systems. The authors present proposed filter topologies and simulation results verifying the concept. Theoretical analysis of the circuit is included to facilitate a detailed converter design. The proposed topology is shown to have distinct advantages over traditional approaches to the problem, particularly over the three single-phase inverter approach.<<ETX>>

Three-Port Series-Resonant DC–DC Converter to Interface Renewable Energy Sources With Bidirectional Load and Energy Storage Ports

In this paper, a three-port converter with three active full bridges, two series-resonant tanks, and a three-winding transformer is proposed. It uses a single power conversion stage with high-frequency link to control power flow between batteries, load, and a renewable source such as fuel cell. The converter has capabilities of bidirectional power flow in the battery and the load port. Use of series-resonance aids in high switching frequency operation with realizable component values when compared to existing three-port converter with only inductors. The converter has high efficiency due to soft-switching operation in all three bridges. Steady-state analysis of the converter is presented to determine the power flow equations, tank currents, and soft-switching region. Dynamic analysis is performed to design a closed-loop controller that will regulate the load-side port voltage and source-side port current. Design procedure for the three-port converter is explained and experimental results of a laboratory prototype are presented.

Novel soft-switching DC-DC converter with full ZVS-range and reduced filter requirement. I. Regulated-output applications

A novel soft-switching topology for DC-DC converters is proposed. It is well suited for applications in the range of a few hundred watts to a few kilowatts. It is essentially a hybrid combination of an uncontrolled half-bridge section and a phase-shift controlled full-bridge section, realized with just four switches. The main features of the proposed topology are zero-voltage-switching down to no-load without serious conduction loss penalty, constant frequency operation and, near-ideal filter waveforms. The improved filter waveforms result in significant savings in the input and output filter requirement, resulting in high power-density. The new topology requires two transformers and two DC-bypass capacitors. The combined VA rating of the two transformers is more than that of the single transformer of conventional full-bridge converters, for variable-input applications. In Part I of the paper, the converter operation is analyzed for typical switch-mode power supply applications, where the input voltage varies widely but the output voltage is fixed and is well regulated. Experimental results obtained from a 100 W/200 kHz proof-of-concept prototype confirm the superior features of the proposed hybrid configuration.

Voltage regulation with STATCOMs: modeling, control and results

This paper presents system modeling and control design for fast load voltage regulation using static compensators (STATCOMs). The modeling strategy gives a clear representation of load voltage magnitude and STATCOM reactive current on an instantaneous basis. The particular coordinate transformation employed here also facilitates extraction of linearized system dynamics in conjunction with circuit simulators. It is rigorously shown that the control problem of load voltage regulation using reactive current is nonminimum phase. Linear and nonlinear controllers for the regulation problem are designed and compared via simulation results. Internal dynamics of the STATCOM are modeled using the same strategy. Lyapunov based adaptive controllers are designed for controlling the STATCOM reactive current while maintaining its dc bus voltage. Simulation results of the controlled STATCOM integrated with the load bus voltage controller are presented to show efficacy of the modeling and control design.