Development of a maximum‐power‐point‐limiting control system for a direct methanol fuel cell

A new maximum‐power‐point limiting (MPPL) control method for a direct methanol fuel cell (DMFC) was proposed. In regard to achieving MPPL, it was affirmed by experiment that it is possible to control the DMFC by simply ensuring that its voltage does not fall below a certain level regardless of its state. An MPPL control system that accomplishes the DMFC voltage limitation required for MPPL control by using a ‘soft‐start function’ fitted in a ready‐made DC/DC converter was developed. It was confirmed by experimental tests that the circuit board of the developed MPPL control system can perform DMFC voltage limitation control. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

A High‐Frequency Cycloconverter Based on a Phase‐Shift Control Method

This paper proposes a new control method for a high‐frequency cycloconverter consisting of two half‐bridge inverters and a series–resonant circuit. This cycloconverter acts as an ac‐to‐ac direct power conversion circuit without any dc stage. This circuit does not require a diode bridge rectifier, and thus, can be used to reduce forward voltage drops and power losses in the diodes. A new phase‐shift control method is proposed to regulate the capacitor voltage in each half‐bridge inverter and to achieve zero‐voltage switching. The proposed phase‐shift control is theoretically discussed and is also verified by an experimental circuit consisting of superjunction power MOSFETs. As a result, the proposed high‐frequency cycloconverter exhibits a good power conversion efficiency as high as 97.7% at the rated power of 1.3 kW.     

Design and implementation of a high‐efficiency bidirectional DC‐DC Converter for DC micro‐grid system applications

This paper studies the design and implementation of a non‐isolated dual‐half‐bridge bidirectional DC‐DC converter for DC micro‐grid system applications. High efficiency can be achieved under wide‐range load variations by the zero‐voltage‐switching features and an adaptive phase‐shift control method. A three‐stage charging scheme is designed to meet the fast‐charging demand and prolong the lifetime of LiFePO₄ batteries. A digital‐signal‐processing control IC is used to realize the power flow control, DC‐bus voltage regulation, and battery charging/ discharging of the studied bidirectional DC‐DC converter. Finally, a 10 kW prototype converter with Enhanced Controller Area Network communication function is built and tested for micro‐grid system applications. A light‐load efficiency over 96% and a rated‐load efficiency over 98% can be achieved. Copyright © 2013 John Wiley & Sons, Ltd.     

A New Control Method of Suppressing the DC‐Capacitor Voltage Ripple Caused by Third‐Order Harmonic Compensation in Three‐Phase Active Power Filters

This paper proposes a new control method suitable for active power filters, which can reduce the dc capacitor voltage ripple associated with the third‐order harmonic current compensation. The proposed method superimposes a negative‐sequence fundamental current on the compensating current to cancel out the active power ripple caused by the third‐order harmonic current. As a result, the proposed method has the capability to eliminate the dc capacitor voltage ripple oscillating at double the source frequency. Experimental results obtained by a 10‐kW three‐phase diode rectifier load verify the validity of the proposed method. The proposed method exhibits a small dc capacitor voltage ripple reduced to 43% of that using the conventional method.     

The theory of instantaneous power in three‐phase four‐wire systems and its applications

This paper discusses “the p–q theory” and “the cross‐vector theory” in three‐phase four‐wire systems, with the focus on similarities and differences between the two theories. They are perfectly identical if no zero‐sequence voltage is included in a three‐phase three‐wire system. However, they are different in definition of the instantaneous active power and instantaneous reactive power in each phase if a zero‐sequence voltage or current is included in a three‐phase four‐wire system. Based on both theory and computer simulation, this paper leads to the following conclusions: An instantaneous reactive‐power compensator without energy storage components can fully compensate for the neutral current even in a three‐phase four‐wire system including a zero‐sequence voltage or current, when a proposed control strategy based on the p–q theory is applied: However, the compensator cannot compensate for the neutral current fully, when a conventional control strategy based on the cross‐vector theory is applied. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 74–86, 2001     

PDM Control Method for a Matrix Converter Converting Several‐Hundred‐kHz Single‐Phase Input to Commercial Frequency Three‐Phase Output

This paper discusses pulse density modulation (PDM) control methods for a single‐phase to three‐phase matrix converter (MC) in high‐frequency applications. The proposed circuit is used as an interface converter for a wireless power transfer system. This converter can input a frequency of several hundred kilohertz and output a low frequency, that is, 50 Hz or 60 Hz, for a commercial power grid. The proposed circuit implements zero voltage switching (ZVS) operation by using PDM control methods and obtains high efficiency. In this paper, two PDM control strategies are compared: delta–sigma conversion and the PDM pattern generation method based on space vector modulation (SVM), which is proposed here. Also, the experimental results obtained with the proposed system will be presented and discussed. The total harmonic distortions (THDs) of the output voltage with delta–sigma conversion and the PDM pattern generation method based on SVM are found to be 5.96% and 2.15%, respectively. In addition, the maximum efficiencies with delta–sigma conversion and the PDM control based on SVM are 93.4% and 97.3%, respectively. From the results, the validity of the PDM control based on SVM has been confirmed for improvement of the output waveforms and reduction of the switching loss.     

Fast‐scale instability in a PFC boost converter under average current‐mode control

This paper investigates the fast‐scale instability in a power‐factor‐correction (PFC) boost converter under a conventional average current‐mode control. The converter is operated in continuous mode. Computer simulations and theoretical analysis are performed to study the effects of the time‐varying input voltage under the variation of some chosen parameters on the qualitative behaviour of the system. It is found that fast‐scale instability may occur during a line cycle, which can cause distortion to the line current and degrade the practical power factor. The results provide useful information for the design of PFC boost converters to avoid distortion due to fast‐scale bifurcation. Copyright © 2003 John Wiley & Sons, Ltd.     

Maximum‐power‐point tracking method of photovoltaic power system using a single transducer

This paper describes a novel strategy of maximum‐power‐point tracking for photovoltaic power generation systems. A unique feature of this method is the capacity to see the maximum power point using only a single transducer, that is, a Hall‐effect CT or an isolation amplifier. Output power of the photovoltaic can be estimated with an average value and ripple amplitude of the detected reactor current or the capacitor voltage. A conventional hill‐climbing method is employed to seek the maximum power point, using the output power estimated with only the current or voltage transducer. In this paper, not only a theoretical aspect of the proposed method is discussed, but also experimental results are presented to prove the feasibility of the method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 79– 86, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20275     

Low‐Voltage‐Ride‐Through Performance of an HVDC Transmission System Using Two Modular Multilevel Double‐Star Chopper‐Cells Converters

This paper presents an intensive discussion on a long‐distance high‐voltage direct‐current (HVDC) transmission system that combines two modular multilevel cascade converters based on double‐star chopper cells (MMCC‐DSCC) with DC power cables. Hereinafter, a single MMCC‐DSCC is referred to as a DSCC converter or just as a DSCC for the sake of simplicity. The HVDC transmission system is required to provide low‐voltage‐ride‐through (LVRT) capability to enhance transmission system availability. This paper proposes a new LVRT method without any direct information exchange between the two DSCC converters. The validity of the method is verified, using simulated waveforms from the software package of “PSCAD/EMTDC” and experimental waveforms from a three‐phase 200‐V, 400‐Vdc, 10‐kW, 50‐Hz downscaled HVDC system with a set of 300‐meter‐long DC power cables.     

A novel three‐phase converter using a three‐phase series chopper

This paper proposes a novel three‐phase converter using a three‐phase series chopper. The proposed circuit is composed of three switching devices, three‐phase diode bridge, input reactors, and LC low‐pass filter. In the conventional circuit, which combines three‐phase diode bridge and boost voltage chopper, to obtain sinusoidal input current the output voltage must be two or three times larger than the maximum input line voltage. However, in the proposed circuit, the input current can be controlled to be sinusoidal also when the output voltage is the same as the maximum input line voltage. This can be achieved because in the proposed circuit the discharging current of the reactors does not flow through the voltage source. The control method of the proposed circuit is as simple as that of the conventional circuit since all three switching devices are simultaneously turned on and off. This paper discusses the theoretical analysis and the design of the proposed circuit. In addition, simulation and experimental results are reported. The proposed circuit has obtained a 93% efficiency, and 99.7% at 1.3kW load as the input power factor. © 2000 Scripta Technica, Electr Eng Jpn, 132(4): 79–88, 2000     

Steady‐state stability of shaft torsional oscillation in an ac‐dc interconnected system with self‐commutated converters

Recent progress in power electronics technology makes it possible to consider applying self‐commutated converters using gate turn‐off thyristors (GTOs) to HVDC transmission systems. Since the self‐commutated converter can be operated stably without depending on ac‐side voltage, the magnitude and the phase angle of the converter output voltage can be controlled independently. Therefore, this type of converter will improve voltage stability at its ac side. On the other hand, shaft torsional oscillation of a thermal power plant caused by the interaction between the shaft‐generator system and the control system of the self‐commutated converter is still an open problem. In this paper, a linearized model for eigenvalue analysis of a power system, including HVDC interconnection with self‐commutated converters, is described to analyze the effect of the self‐commutated converter on the shaft torsional oscillation of a thermal power plant. Then, numerical results from the eigenvalue analysis of the shaft torsional oscillation are presented. Results obtained by the frequency response method are also reported. The numerical results make it clear that parameter regions of DC‐AVR and ACR control systems of self‐commutated converters exist where the shaft torsional oscillation may be caused. © 1999 Scripta Technica, Electr Eng Jpn, 128(4): 25–37, 1999     

Voltage stability preventive and emergency‐preventive control using VIPI sensitivity

Recently, power systems have become larger and more complicated, and the rate of occurrence of constant power loads has increased. Under a situation like this, concerns about voltage instability phenomena have been raised. Therefore, in addition to the conventional local voltage control, the necessity of a global on‐line voltage control scheme has risen. In this paper, we propose a method of on‐line voltage stability control including preventive and emergency‐preventive controls to retain voltage stability even if a severe fault occurs. According to the result of contingency analysis for severe faults, we consider operation of control equipment as preventive control. And in the case that the fault seems severe still after preventive control, we consider load curtailment as emergency‐preventive control. When we select the control equipment and loads to curtail, we use voltage stability index VIPI sensitivity. And we determine the amount of control and load curtailment using Optimal Power Flow calculation. The effectiveness of the proposed method is verified by simulations using a 28‐bus system. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 143(4): 22–30, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10128     

A control method for small‐scale DC power systems including distributed generators

This paper describes a DC micro‐grid system interconnecting distributed power generators. The system consists of five generation and control units: a solar‐cell generation unit, a wind‐turbine generation unit, a battery energy‐storage unit, a flywheel power‐leveling unit, and an AC grid‐interconnecting power control unit. The control method is proposed for suppressing the circulating current by detecting only the DC grid voltage. This method brings high reliability, high flexibility, and maintenance‐free operation to the system. The method pays attention to DC output voltage performance of each unit. Each of the power control units and the energy‐storage unit is controlled to act as a voltage source with imaginary impedance. On the other hand, each of the two generation units is controlled to act as a current source. The power‐leveling unit is controlled to act as a current source having the function of frequency selectivity like a high‐pass filter. A 10‐kW prototype system verifies experimentally the validity and effectiveness of the proposed control method for the DC‐grid system. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(2): 86–93, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20603     

A 0.1 to 2.7‐GHz SOI SP8T antenna switch adopting body self‐adapting bias technique for low‐loss high‐power applications

A low‐loss high‐power single‐pole 8‐throw antenna switch adopting body self‐adapting bias technique in a 0.18‐μm thick‐film partially depleted silicon‐on‐insulator complementary metal‐oxide‐semiconductor process is implemented for multimode multiband cellular applications. A topology with symmetric port design is developed. We employ the body‐contacted field‐effect transistor to handle high power level and obtain low harmonic distortion. However, the conventional bias method for body‐contacted field‐effect transistor leads to poor insertion loss (IL), serious imbalanced voltage division, and large die size. Therefore, a new body self‐adapting bias scheme is adopted to improve the IL and power handling capability with die area reward by removing the employment of extra biasing resistor and voltage supply at the body. The presented silicon‐on‐insulator antenna switch utilizing the new body bias strategy reveals similar harmonic performance as a conventional switch version, thanks to the analogous DC bias to the gate and body, while it exhibits effectively lower IL, imbalanced voltage division, and die area. The measured IL and 0.1‐dB compression point (P_?0.1dB), at 1.9/2.7 GHz, are roughly 0.52/0.82 dB and 39.2/36.9 dBm, respectively. The overall IL and P_?0.1dB are apparently improved by approximately 0.05 to 0.13 dB and 0.5 to 0.8 dBm compared with the conventional version.     

Autonomous decentralized voltage profile control of super‐distributed energy system using multi‐agent technology

A super‐distributed energy system is a future energy system in which a large part of its demand is fed by a huge number of distributed generators. At one time some nodes in the super‐distributed energy system behave as load, whereas at other times they behave as generator—the characteristic of each node depends on the customers' decision. In such situation, it is very difficult to regulate the voltage profile over the system due to the complexity of power flows. This paper proposes a novel control method of distributed generators that can achieve autonomous decentralized voltage profile regulation by using multi‐agent technology. The proposed multi‐agent system employs two types of agent: a control agent and a mobile agent. Control agents generate or consume reactive power to regulate the voltage profile of neighboring nodes and mobile agents transmit the information necessary for VQ‐control among the control agents. The proposed control method is tested through numerical simulations. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 43–52, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20484     

Dynamic modeling of a dual active bridge DC to DC converter with average current control and load‐current feed‐forward

Bidirectional power flow is needed in many power conversion systems like energy storage systems, regeneration systems, power converters for improvement of the power quality and some DC‐DC applications where bidirectional high power conversion and galvanic isolation are required. The dual active bridge (DAB) is an isolated, high voltage ratio DC‐DC converter suitable for high power density and high power applications, being a key interface between renewable energy sources and energy storage devices. This paper is focused on the modeling and control design of a DC‐DC system with battery storage based on a DAB converter with average current mode control of the output current and output voltage control. The dynamic response of the output voltage to load steps is improved by means of an additional load‐current feed‐forward control loop. An analytical study of the load‐current feed‐forward is presented and validated by means of both simulations and experimental results. Copyright © 2014 John Wiley & Sons, Ltd.     

Phase‐Locked Loop Using Complex‐Coefficient Filters for Grid‐Connected Inverter

Recently, photovoltaic (PV) power systems have attracted considerable attention in attempts to mitigate global warming. In a PV power system, it is necessary to synchronize the grid voltage when a PV inverter is interconnected with a grid. This paper proposes a high‐speed and high‐precision phase‐locked loop (PLL) using complex‐coefficient filters for a single‐phase grid‐connected inverter. The proposed PLL can detect the phase of grid voltage that has superimposed harmonic components for grid fault. Moreover, numerical results show the effectiveness of the proposed method.     

Performance of Dead‐Time Compensation Methods in Three‐Phase Grid‐Connection Converters

This paper discusses the performance of compensation methods for dead‐time voltage error in voltage‐source grid‐connection pulse‐width modulation converters. The theoretical analysis in this paper reveals the relationship between the voltage error and the current ripples through the converter. The analytical results imply that the voltage error is strongly affected by the amplitude of the current ripples as well as the source power factor. This paper proposes a new compensation method which makes it possible to use two lookup tables to reduce the calculation time in the controller. The compensation characteristics are compared by using a 200‐V 5‐kW three‐phase grid‐connection converter. As a result, conventional approximation‐based compensation methods exhibit an acceptable performance in a restricted power‐factor operation range. In contrast, the turn‐off transition‐based compensation method and the proposed method have a good compensation performance all over the power factor.     

Power factor improvement of single‐phase diode rectifier circuit by field‐weakening of inverter‐driven IPM motor

This paper proposes a novel inverter drive system to improve the input power factor of single‐phase diode rectifier. Conventional rectifiers need a high‐frequency switching device and a reactor to improve the input power factor. However, the proposed power converter does not need the switching device, electrolytic capacitor, or reactor. By making many ripples across the DC‐bus voltage, the input power factor can be improved. The proposed system consists of only a single‐phase diode rectifier, small film capacitor, three‐phase inverter, and motor. The proposed system adopts an interior permanent magnet (IPM) synchronous motor. The IPM motor is well known as a high‐efficiency motor and can realize field weakening. The basic ideas of the inverter control method are based on the following operations: the inverter's controlled synchronous with the DC‐bus ripple voltage by field‐weakening method, and direct active power feeding from the source side to the motor without smoothing the DC‐bus voltage. This paper describes that the proposed method can obtain an input power factor of 97.3% by experimental tests, and realizes the goals of small size and long life of the system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 152(2): 66–73, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20047