Katsumi Nishida

Bio: Katsumi Nishida is an academic researcher from Yamaguchi University. The author has contributed to research in topics: AC power & Induction generator. The author has an hindex of 15, co-authored 83 publications receiving 823 citations.

Advanced control of PWM converter with variable-speed induction generator

Abstract: 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

Advanced current control implementation with robust deadbeat algorithm for shunt single-phase voltage-source type active power filter

Abstract: A deadbeat current control implementation of shunt-type single-phase active power filter (APF) is considered. The deadbeat control technique is often proposed as an advanced current control method of APF, because the superiority of the digital control scheme to the analogue control one can be effectively utilised by adopting the deadbeat-control strategy. Although the one-dimensional deadbeat control method can attain a time-optimal response for APF compensating current, one sampling period is actually required for its settling time. This delay is a serious drawback for this control technique. To cancel such a delay and one more delay caused by DSP execution time, the desired APF compensating current has to be predicted two sampling periods ahead. For the prediction value, the reference value of one source voltage period before is employed as a based value. At the same time, an adaptive line enhancer (ALE) is newly introduced to predict the control error of two sampling periods ahead. By adding the ALE output as an adjustment term to the based value, the settling time is made short in the transient state. On the other hand, in the steady state, the THD (total harmonic distortion) of the utility grid side AC source current can be reduced as much as possible compared to the case when an ideal identification of the controlled system can be made. The experimental results obtained from a DSP-based APF are also illustrated and evaluated. The compensating ability of this APF treated here is extremely high in accuracy and responsiveness.

Static VAR compensator-based voltage control implementation of single-phase self-excited induction generator

Abstract: A single-phase static VAR compensator (SVC) is proposed to regulate smoothly the output voltage of a single-phase self-excited induction generator (single-phase SEIG) driven by a variable-speed prime mover (VSPM) due to inductive load and prime mover speed variations. A PI feedback closed-loop voltage regulation scheme is presented to adjust the equivalent excitation capacitance of the single-phase SVC. The SVC is composed of a fixed excitation capacitor (FC), thyristor switched capacitor (TSC) and thyristor controlled reactor (TCR). The steady-state single-phase SEIG output voltage and the TCR triggering angle responses of the proposed scheme are simply evaluated and discussed. A small-scale single-phase SEIG voltage control prototype is designed in order to verify system viability and assess its performance. System dynamic operation is studied based on experimental results. Simulation and experimental results prove system practical effectiveness in terms of fast response and high performance.

A novel stand-alone induction generator system for AC and DC power applications

Abstract: 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.

A Cost-Effective High-Efficiency Power Conditioner With Simple MPPT Control Algorithm for Wind-Power Grid Integration

Abstract: In this paper, a novel grid integration system for a variable-speed wind turbine using an interior permanent-magnet synchronous generator (IPMSG) is developed. The power conditioner system (PCS) consists of a series-type 12-pulse uncontrolled diode rectifier powered by a phase-shifting transformer and then cascaded to a pulsewidth-modulated (PWM) voltage source inverter. The active current of the grid-side PWM inverter is only controlled to follow the optimal active current reference which is determined by using a simple maximum power point tracking (MPPT) control strategy. The MPPT algorithm requires only three sensors in order to track the maximum power of the wind turbine. The most significant advantage of the proposed system is that the passive filter together with a series-type 12-pulse rectifier provides high efficiency by compensating the power factor angle of the IPMSG and suppresses distortions presented in the IPMSG voltages and currents. The laboratory results indicate that the proposed construction and scheme are simple, cheap, and efficient.

Review of wave energy technologies and the necessary power-equipment

Abstract: The wave energy is having more and more interest and support as a promising renewable resource to replace part of the energy supply, although it is still immature compared to other renewable technologies. This work presents a complete analysis of the wave energy technology, starting with the characterisation of this global resource in which the most suitable places to be exploited are showed, and the classification of the different types of wave energy converters in according to several features. It is also described in detail each of the stages that are part in the energy conversion, that is, from the capture of the energy from the waves to the extraction of a proper electrical signal to be injected to the grid. Likewise, existing offshore energy transmission alternatives and possible layouts are described.

Single-Phase Back-To-Back Converter for Active Power Balancing, Reactive Power Compensation, and Harmonic Filtering in Traction Power System

Abstract: An active power compensator (APC) based on single-phase back-to-back power converter is proposed in this paper to solve problems of power quality of electric railway power supply system. This system adopts a single-phase feeding connection, which is called cophase power supply scheme. In this scheme, APC connects the balance transformer between feeding phase for power supply and another phase for compensation. It has some characteristics, such as active power balancing, reactive power compensating, and harmonics filtering. In order to achieve these characteristics, the control scheme requires seven combination models. In this paper, a multifunctional control algorithm is proposed to realize every conceivable model. A cophase system with APC based on field programmable gate array (FPGA) and YNvd balance transformer is also designed and evaluated. The experimental results obtained from this prototype illustrate that the compensating ability is extremely high in steady-state and dynamic responses, and the power quality of a substation with distorted loads can be improved integrally.

Control techniques for active power filters

Abstract: There have been many variants of the active power filter proposed and these variations cover both the circuit topology and the control system employed. Some of the control variants reflect different control objectives but there are still many variants within similar objectives. The available control techniques are described and contrasted in a structured way to identify their performance strengths. Objectives are classified by the supply current components to be corrected and by the response required to distorted grid voltage. The various signal transformations are described in terms of their impact on the distortion identification problem. Time-domain, frequency-domain, instantaneous power and impedance synthesis methods are examined. Additional control functions such as DC-bus voltage and current reference following are also discussed. It is found that a key difference between control methods is the way in which current distortion is treated in the presence of distorted grid voltage.

DC-link Voltage Control of a Full Power Converter for Wind Generator Operating in Weak-Grid Systems

Abstract: When the wind power accounts for a large portion of the grid power, it may need to help the grid voltage and frequency regulation. This paper investigates a permanent-magnet wind generator with a full power voltage-source converter in weak-grid mode, where the DC-link voltage needs to be controlled from the generator side instead of the grid side. The energy relationship of the wind generator, DC-link energy storage, and load is established. An intrinsic right-half-plane zero, together with the wind power characteristics, the mechanical system inertia, and the DC-link energy storage, is identified as the physical limitations for the control. With the understanding of the system energy relationship and limitations, a hybrid adaptive control algorithm is proposed that searches for the optimal generator acceleration to achieve the maximum wind generator power change rate to match the load power variation. The proposed control scheme is verified through simulation of a 1.5-MW wind system as well as through the experiment of a scaled 1-kW, DSP-/field-programmable-gate-array-controlled, permanent-magnet-generator-based test bed. The results show that it is feasible to regulate DC link by the generator-side converter through the generator speed control. Some important applications issues are also investigated, including the DC-link energy storage requirement, wind speed change impact, and control transition between the weak-grid and strong-grid modes.

Tuning of Phase-Locked Loops for Power Converters Under Distorted Utility Conditions

Abstract: This paper presents a novel approach in the tuning of phase-locked loops (PLLs) for power electronic converters. PLLs are implemented inside a higher level controller to estimate the grid-voltage phase angle and then control the energy transfer between the power converter and the AC mains. The tuning of the PLL is not a trivial task, particularly when considering power-quality phenomena. In a general way, PLLs with a low bandwidth (low-gain PLLs) are required when handling distorted voltages. It is analytically demonstrated in this paper that low-gain PLLs have more tradeoffs than high-gain PLLs (e.g., PLLs for communications); it is not possible to optimize the settling time for a phase jump without making slower the PLL response to frequency variations. Existing tuning methods do not take into account low-gain features, which may result in nonoptimum designs. The proposed PLL tuning methodology is based on inspection of frequency-domain diagrams and, contrary to the other existing tuning methods, takes into account ldquolow-gainrdquo dynamics. It assures an optimized performance in the presence of any kind of disturbances in the grid. From a practical point of view, the proposed tuning procedure is very intuitive for controller designs. Some significant design examples and experimental results, obtained from a discrete implementation (dSpace platform), are provided in order to validate the theoretical approaches.