Katsumi Nishida

Advanced control of PWM converter with variable-speed induction generator

This paper describes simple control structures for the vector-controlled stand-alone induction generator (IG) used to operate under variable speeds. Different control principles, indirect vector control and deadbeat current control, are developed for a voltage source pulsewidth-modulation (PWM) converter and the three-phase variable-speed squirrel-cage IG to regulate dc link and generator voltages with the newly designed phase-locked loop circuit. The required reactive power for the variable-speed IG is supplied by means of the PWM converter and a capacitor bank to buildup the voltage of the IG without the need for a battery, to reduce the rating of the PWM converter with the need for only three sensors, and to eliminate the harmonics generated by the PWM converter. These proposed schemes can be used efficiently for variable-speed wind energy conversion systems. The measurements of the IG systems at various speeds and loads are given and show that these systems are capable of good ac and dc voltage regulations

A Novel Stand-Alone Induction Generator System for AC and DC Power Applications

This paper presents a novel dynamic model in the stationary reference frame for a diode bridge rectifier with a dc-link filter directly connected to an induction generator (IG). Moreover, a hybrid excitation system consisting of a capacitor bank with a small-scale active power filter (APF) regulates the stand-alone IG systems output voltages by controlling its reactive current component and cancels the harmonic currents generated by a nonlinear diode rectifier load. A deadbeat current control strategy for the small-scale APF is used to enhance the operating performances of the stand-alone IG. This power generating system can be used for small hydro and wind energy applications, where its generated electrical power is supplied to different load types, i.e., dc and ac loads. The measurement results validate the proposed power generating system with the deadbeat current controller as a good application for the IG to reduce the total system cost and the required number of sensors.

Robust deadbeat current control with adaptive predictor for three-phase voltage-source active power filter

This paper is concerned with a deadbeat current control implementation of shunt-type three-phase active power filter (APF), and the method for improving the control accuracy in both a steady and a transient states is presented. To cancel a delay of settling and one more delay caused by DSP execution time, the desired APF compensating current is to be predicted two sampling periods ahead. In the prediction process, an adaptive predictor is newly applied to predict the control error of two sampling periods ahead, and the reference is modified by the predictor output, so that robustness about parameter uncertainties can be brought to the deadbeat control system.

Grid power integration technologies for offshore ocean wave energy

In this paper, the advanced electric technologies for grid power integration of different offshore wave energy conversion devices are presented. The electrical connection configurations for integrating the electric power of the multi wave energy conversion devices such as the Oscillating Water Column, Pelamis, the Wave Point Absorbers and the Wave Dragon are developed by employing the most efficient low cost grid interface electrical technologies based on the advanced power electronics. The bi-directional power converter is employed for wide-range variable speed operation of wave energy conversion device to reduce the power output fluctuations and improve the whole power generation efficiency.

Cost-Effective Deadbeat Current Control for Wind-Energy Inverter Application With

This paper proposes analytical expressions of a deadbeat control system for the output LCL filter in a grid-connected inverter with a settling time of three sampling periods. Unlike the conventional analysis, the proposed control algorithm is derived in the descritised time-domain instead of the s-domain. Furthermore, not only integrated active power but also reactive power can be controlled independently. Experimental results of the proposed deadbeat control system indicate that the feedback of both grid and converter currents have the same highest capabilities of attenuating switching frequency components and damping resonance. This is due to the undetected two remained control variables are possible to be estimated in the DSP.

LCL

In this paper, the steady-state operating performances of single-phase squirrel-cage self-excited induction generator (SEIG) are evaluated by using the per-unit frequency in addition to a simple steady-state analysis based on the per-unit slip frequency. The single-phase SEIG operating performances, estimated by the per-unit slip frequency steady-state analysis at the prime move speed and the inductive load power variations, are discussed with those obtained by using the per-unit frequency. The results provide close agreements with a simple analysis and an efficient computation processing procedures. Moreover, the single-phase static VAr compensator (SVC) composed of the thyristor controlled reactor, the thyristor switched capacitor and the fixed excitation capacitor is applied to regulate smoothly the generated output voltage of the stand-alone single-phase induction generator with a variable inductive load. The fixed gain PI controller is employed to adjust the equivalent capacitance of the single-phase SVC. The experimental and simulation results are illustrated the practical effectiveness of the additional SVC with the PI controller-based feedback loop to regulate smoothly the output voltage of the single-phase SEIG.

Filter

For an active power filter (APF), a three-phase current source PWM converter using IGBTs is not always used in place of a three-phase voltage source PWM converter with a voltage regulated DC capacitor. This is due to the difficulty of current control implementation for three-phase current source PWM converter. In this paper, the effective method to apply three-phase current-source PWM converter with a deadbeat controller to APF is presented. In this APF, the compensation of current harmonics is attained by setting the control purpose compensating the instantaneous reactive current component in load current and reducing the ripple in the instantaneous actual current component. In three-phase current source PWM converter, the time-optimal response for utility AC grid side input current is two-dimensional finite time settling response, in which two sampling periods are required for a settling time. To cancel this delay and one more delay caused by DSP control strategy, the reference value of three sampling periods ahead has to be predicted. For this prediction, the adaptive filter is introduced. Finally, it is proven from an experimental point of view that the compensating ability of this APF is very accurate though the PWM frequency is rather low.

Static VAr compensator-based voltage regulation implementation of single-phase self-excited induction generator

In this paper, a 1.5 kW Interior Permanent Magnet Synchronous Generator (IPMSG) with a power conditioner for the grid integration of a variable-speed wind turbine is developed. The power-conditioning system consists of a series-type 12-pulse diode rectifier powered by a phase shifting transformer and then cascaded to a PWM voltage source inverter. The PWM inverter is utilized to supply sinusoidal currents to the utility line by controlling the active and reactive current components in the q-d rotating reference frame. While the q-axis active current of the PWM inverter is regulated to follow an optimized active current reference so as to track the maximum power of the wind turbine. The d-axis reactive current can be adjusted to control the reactive power and voltage. In order to track the maximum power of the wind turbine, the optimal active current reference is determined by using a simple MPPT algorithm which requires only three sensors. Moreover, the phase angle of the utility voltage is detected using a simple electronic circuit consisting of both a zero-crossing voltage detecting circuit and a counter circuit employed with a crystal oscillator. At the generator terminals, a passive filter is designed not only to decrease the harmonic voltages and currents observed at the terminals of the IPMSG but also to improve the generator efficiency. The laboratory results indicate that the losses in the IPMSG can be effectively reduced by setting a passive filter at the generator terminals.

Novel current control scheme with deadbeat algorithm and adaptive line enhancer for three-phase current-source active power filter

This paper presents the work carried out to develop the Wave Hub project off the coast of southwest of the UK, which represents the worlds first large-scale wave-energy farm. Four companies have been chosen to deploy their own particular wave-energy converters. These include the Pelamis, the Overtopping Device, the Multiple Point Absorber System, and the Oscillating Water Column. The work focuses on integrating offshore wave energy plant into the UK electrical grid and finds the optimum configuration for grid — integration of multiple WEC devices. It discusses how to mitigate the grid integration challenges associated with 16MW commercial implementation of offshore wave energy technologies in terms of voltage and reactive power control and investigates their impact on electrical networks.

Wind Power Grid Integration of an IPMSG using a Diode Rectifier and a Simple MPPT Control for Grid-Side Inverters

In this paper, an effective deadbeat current control scheme for a third-order inductor-capacitor-inductor(LCL) filter in voltage source inverter applications of wind energy is developed. The novel scheme is not only used to damp the LCL resonance but also to achieve time-optimal responses of the grid-side currents. Based on the theoretical analysis of the LCL-filter with the deadbeat current control algorithm in the α-βstationary reference frame, the settling time is set to three times of the sampling period. In addition, the state identification algorithm is only adopted in order to achieve the detection of the inverter currents via two current sensors. The effectiveness of the proposed deadbeat current algorithm is substantially confirmed by the simulation and experimental results.