A new approach to an individual‐phase reactive power compensator for nonsinusoidal and unbalanced three‐phase systems

Many researchers have attempted to clarify the definitions of active power, reactive power, active current, reactive current, etc. for unbalanced and nonsinusoidal three‐phase situations. The so‐called pq theory has given a new definition of instantaneous reactive power, and it has been discussed and developed by many authors. In this paper, the merits and demerits of the instantaneous reactive power compensator are discussed. It is shown theoretically that applying instantaneous reactive power compensation to unbalanced three‐phase systems has a serious disadvantage in that it causes third‐order harmonic currents on the source side, which problem cannot be avoided. To overcome this problem the authors propose a new approach, and name it the “quasi‐instantaneous” reactive power compensator. It compensates individual‐phase reactive currents. The basic principles of the quasi‐instantaneous reactive current compensator are discussed in detail, and its validity is confirmed using digital simulation. In particular the authors show that the power factor of each phase becomes unity on the source side, but the source currents remain unbalanced when the proposed method is applied. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 139(3): 73–81, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.1162     

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     

A three‐phase,active power filter with a predictive‐instantaneous‐current PWM controller

One of the most emphasized problems to be solved in power systems in recent years is the line‐current harmonics problem. This is due to the use of diode rectifiers, PWM converters, nonlinear loads, and so on. To reduce or eliminate such current harmonics, an active power filter (APF), which is a sophisticated power electronic converter, has been studied and used in some practical applications. In this paper, we propose and discuss two new control methods for three‐phase shunt APFs: the sinusoidal line‐current control method and the instantaneous‐reactive‐power compensation control method. They are based on pulsewidth prediction control, or a predictive‐instantaneous‐current PWM control. Neither any instantaneous power information nor coordinate transformation is necessary for control. In the sinusoidal line‐current control scheme, the controller governs the switching devices of the APF by using the pulse width that is optimally predetermined at the beginning of every switching period with the sinusoidal current reference. The line currents flow sinusoidally and are in phase with the voltage accordingly. In the instantaneous‐reactive‐power compensation control, the control is performed so that the resultant circuit of the load and the APF is regarded as a time‐variant conductance circuit model. The APF with this control scheme can cancel effectively the instantaneous reactive component produced by the load though the controller is simple. This paper discusses the performance characteristics of the APFs when a three‐phase diode rectifier and an unbalanced load are connected to the line. The practicability of the proposed methods is verified by experiment. © 1999 Scripta Technica, Electr Eng Jpn, 130(3): 68–76, 2000     

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     

Analysis of the current distortion factor of a three‐phase,three‐wire system

In a balanced three‐phase system, the three‐phase current distortion factor of three‐phase ac power sources has been expressed by applying the conventional single‐phase current distortion factor, which is defined for a single‐phase system. However, in an unbalanced three‐phase system, it is difficult to express the three‐phase current distortion factor for distorted three‐phase ac currents by means of the conventional single‐phase current distortion factor. For instance, the conventional current distortion factors for three‐phase ac currents are usually different from each other in the unbalanced three‐phase system. To solve the above problem, this paper proposes a novel definition of the three‐phase current distortion factor. The proposed three‐phase current distortion factor is quite effective for the unbalanced three‐phase system as well as the balanced three‐phase system. © 2000 Scripta Technica, Electr Eng Jpn, 131(4): 1–10, 2000     

A new three‐input/output characteristic‐varying filter in the D‐module for direct processing of three‐phase signals

This paper proposes a new three‐input and three‐output characteristic‐varying filter in the D‐module for direct processing of three‐phase signals, which are becoming indispensable for effective active compensation of three‐phase power such as harmonics current, negative phase current, reactive power, and varying voltage compensations. The filter in the D‐module can show different filtering characteristics to positive, negative, and zero phase components of three‐phase signals and can allow direct processing of the signals based on frequency polarities. The filter in the D‐module can also change dynamically its filtering characteristics by simply injecting a shift‐signal to itself. These filtering effects are obtained in a very simple manner using the D‐module. A new unified analysis of attractive general characteristics of the proposed filter in the D‐module is given for its easy designs and realizations as well. Effectiveness of the analysis and usefulness of the filter in the D‐module are newly examined and confirmed through experiments. The newly proposed filter in the D‐module has potential regarding a variety of three‐phase signal filtering applications. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 145(1): 28–38, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10170     

A novel three‐phase soft‐switched converter with high power factor using a lossless snubber

Recently, three‐phase converters with high power factor, especially using the discontinuous current mode (DCM), have been studied as novel rectifier circuits instead of conventional converters. In this circuit, the current of reactor is zero at turn on because of operating on DCM. Then ZCS (Zero Current Switching) is achieved. However it is necessary to turn off the switch at the maximum current. Then the switching losses increase at higher switching frequency. Therefore, soft‐switching method using the lossless snubber is proposed. In this method, ZVS (Zero Voltage Switching) at the turn off can be achieved by a lossless snubber and ZCS at the turn on can be obtained by operating under the DCM. In this paper, the theoretical analysis, numerical analysis using PSPICE, and results of the experiments show the verification of the proposed converter. © 1999 Scripta Technica. Electr Eng Jpn, 129(3): 69–76, 1999     

A novel robust current control approach using adaptive line enhancer for three‐phase current‐source active power filter

An effective system control method is presented for applying a three‐phase current‐source PWM converter with a deadbeat controller to active power filters (APFs). In the shunt‐type configuration, the APF is controlled such that the current drawn by the APF from the utility is equal to the current harmonics and reactive current required for the load. To attain the time‐optimal response of the APF supply current, a two‐dimensional deadbeat control scheme is applied to APF current control. Furthermore, in order to cancel both the delay in the two‐dimensional deadbeat control scheme and the delay in DSP control strategy, an Adaptive Line Enhancer (ALE) is introduced in order to predict the desired value three sampling periods ahead. ALE has another function of bringing robustness to the deadbeat control system. Due to the ALE, settling time is made short in a transient state. On the other hand, total harmonic distortion (THD) of source currents can be minimized compared to the case where ideal identification of the controlled system can be made. The experimental results obtained from the DSP‐based APF are also reported. The compensating ability of this APF is very high in accuracy and responsiveness although the modulation frequency is rather low. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 50–61, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20014     

A three‐vector‐based direct power control strategy for three‐phase voltage source PWM converters

For traditional direct power control strategy, there exist high steady‐state power ripples and large current harmonics. To solve this problem, this work proposes a novel three‐vector‐based direct power control strategy for three‐phase voltage source pulse‐width‐modulated (PWM) converters. Different from traditional predictive direct power control strategy, an improved vector table is presented and three voltage vectors are selected, which considers the impact of voltage vectors on the active and reactive power simultaneously. The performance of the three‐phase voltage source PWM converters with the proposed control strategy is investigated and compared with the predictive deadbeat direct power control strategy. Furthermore, the three‐phase voltage source PWM converters have also been tested in the condition of different loads and when voltage unbalance occurs. Simulation and experimental work are conducted. The results conclude that the proposed strategy is of simple structure and fast dynamic response. Besides, it can effectively reduce steady‐state power ripples and current harmonics, improving the performance of the three‐phase PWM converters. Copyright © 2016 John Wiley & Sons, Ltd.     

A three‐phase constant‐current source using an immittance converter

The term immittance converter refers to an impedance–admittance converter. The immittance converter has an input impedance that is proportional to the admittance of the load connected across output terminals. In this converter, the output current is proportional to the input voltage and the input current is proportional to the output voltage. Consequently, it converts a constant‐voltage source into a constant‐current source and a constant‐current source into a constant‐voltage source. It is well known that the quarter wavelength transmission line shows immittance conversion characteristics. However, it has a very long line length for the switching frequency, and is not suitable for power electronics applications. We thus proposed immittance converters that consist of lumped elements L, C and show improved immittance conversion characteristics at a resonant frequency. A three‐phase constant‐current source is proposed in this paper. It is possible to realize this by a simple circuit using an immittance converter. In this paper, circuit operation, characteristic equations, and results of simulation are described. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 47–54, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20078     

Development of equipment models for fast distribution three‐phase unbalanced load flow calculation

This paper presents distribution system equipment models for fast distribution three‐phase unbalanced load flow calculation. Recently, the number of distributed generators introduced into distribution systems has been increasing and detailed system analysis using load flow calculation has been eagerly awaited. Moreover, since many distribution system loads are composed of single phase loads, three‐phase unbalanced load flow calculation is required for the distribution system analysis. Although the fast distribution three‐phase unbalanced load flow calculation has been developed, equipment models considering interconnection of distributed generators have not as yet been developed in Japan. This paper develops practical equipment models such as various distributed generators, voltage control equipment, and loads for fast three‐phase unbalanced load flow calculation in distribution systems. The feasibility of the developed models is verified and demonstrated on practical distribution system models with promising results. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 142(3): 8–19, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10106     

Investigating the frequency for load‐independent output voltage in three‐coil inductive power transfer system

Using circuit theory, this letter investigates the output voltage characteristics of three‐coil inductive power transfer (IPT) system against load variations and determines the operating frequency to achieve a constant output voltage. First, a three‐coil IPT system is modeled, and the analytical expression of the root‐mean‐square of the output voltage is derived. By substituting the coupling coefficient, the quality factor, and the resonant frequency, we propose an intuitive method of calculating the frequency for load‐independent output voltage for the first time. When the coupling coefficient is relatively small, there are three frequencies that achieve load‐independent output voltage. If the coupling coefficient increases and is greater than , only two frequencies can achieve load‐independent output voltage. Experiments are conducted to confirm these conclusions. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling of unbalanced three‐phase driving‐point impedance with application to control of grid‐connected power converters

The dq transformation is widely used in the analysis and control of three‐phase symmetrical and balanced systems. The transformation is the real counterpart of the complex transformations derived from the symmetrical component theory. The widespread distributed generation and dynamically connected unbalanced loads in a three‐phase system inherently create unbalanced voltages to the point of common coupling. The unbalanced voltages will always be transformed as coupled positive‐sequence and negative‐sequence components with double‐frequency ripples that can be removed by some filtering algorithms in the dq frame. However, a technique for modeling unbalanced three‐phase impedance between voltages and currents of same sequences or of opposite sequences is still missing. We propose an effective method for modeling unbalanced three‐phase impedance using a decoupled zero‐sequence impedance and two interacting positive‐sequence and negative‐sequence balanced impedances in the dq frame. The proposed method can decompose a system with unbalanced resistance, inductance, or capacitance into a combination of independent reciprocal bases (IRB). Each IRB basis belongs to one of the positive‐sequence, negative‐sequence, or zero‐sequence system components to facilitate further analysis. The effectiveness of this approach is verified with a case study of an unbalanced load and another case study of an unbalanced voltage compensator in a microgrid application. Copyright © 2015 John Wiley & Sons, Ltd.     

Fuzzy logic controller for three‐level shunt active filter compensating harmonics and reactive power

In this paper, the use of a three‐level inverter as a shunt active power filter is carried out, taking advantage of the benefits of multi‐level inverter, namely, the reduction both in the overall switching losses and in total harmonic distortion. The main focus of this article is to investigate the potentialities of the inverter employed as shunt active power filter on the compensation of the reactive power and the mitigation of harmonics drawn from a nonlinear load and unbalanced sources. The most previously reported three‐level inverter‐based shunt active power filters have been controlled and monitored through conventional controllers, which require a complicated mathematical model. In order to overcome this problem, an extended intelligent controller is proposed for a three‐level shunt active power filter. The aim of the proposed fuzzy logic control algorithm is to improve the behavior of voltage across the floating capacitors in steady/dynamic states and to minimize the switches commutations by taking into account the references of the harmonic currents injected in the network. The proposed control strategy has been simulated, and the obtained results prove that it is very successful. Copyright © 2015 John Wiley & Sons, Ltd.     

An improved three‐phase reactive power measurement algorithm using walsh functions transform

This paper proposes an improved algorithm for three‐phase power component measurement using the Walsh function (WF), which takes into account the advantages offered by the algorithm in the analysis of nonlinear load problems to improve the accuracy and reliability of measurement. In the pricing of electricity based on the value of the integral of the load active power measured using a kilowatt‐hour meter, the electric utility loses some revenue for the energy delivered to current harmonic generating customers and customers whose load causes current asymmetry. An improved algorithm based on the WF for measuring the active and reactive power of a network with linear and or nonlinear and sinusoidal or nonsinusoidal network is developed and tested, and the result compared with IEEE standard 1459–2000 which is based on fast Fourier transformation. The method does not require phase shifting of the phase current signals by π/2 with respect to the voltage signals. The proposed algorithm enables reactive power measurement for proper electricity billing to the consumer with nonlinear loads. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Input power factor control of three‐phase to three‐phase matrix converters

This paper presents input power factor control of three‐phase to three‐phase matrix converters. The authors propose three kinds of switching patterns for the matrix converters that can realize an arbitrary input‐power‐factor angle between 0 and 2π and reduce the number of commutations in all three phases to four during the control period. Also, the control range of the output voltage reference in the proposed control scheme is derived. The improvement of the input power factor by using the proposed control algorithm has been verified by experiments. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 178(3): 42–52, 2012; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21199     

A damping of rotor natural vibration in three‐phase hybrid stepping motors

This paper proposes a damping method of rotor natural vibration in three‐phase hybrid stepping motors, in which optimal commutation signals are calculated from the period of the natural vibration measured by detecting the motor voltages. Moreover, an acceleration and deceleration pattern is derived from a simple model of the rotor vibration, to suppress undesirable transient oscillation in acceleration, deceleration, and positioning operations. An experimental drive system has been implemented and tested to confirm the effectiveness and versatility of the proposed method. Some experimental results show that the experimental system can damp the rotor natural vibration even if the rotor inertia varies. Compared with the conventional pattern, it is confirmed that the proposed pattern makes a great contribution to damping the undesirable transient oscillations. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 144(3): 69–77, 2003; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10153     

Study of phase current measurement by the whole conductors clamping method for three‐phase cable

This paper describes a new measuring method for the phase current in a high‐voltage three‐phase cable. Twenty‐four pieces of independent coils wound around the coreless bobbins are used to make a CT sensor. The primary phase current may be calculated based on the output voltage of each coil. The certain correlation between the output voltage and primary phase current is observed by the experimental data. This new CT sensor enables the measurement of the phase current using the whole conductors clamping method for a three‐phase cable. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 165(2): 9–20, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20753     

三相矩形母线相电感的计算

以三相母线平均相电感的计算公式为基础,推导了三相矩形母线相电感的计算公式。该公式能计算具有分裂导线的三相矩形母线的平均相电感,计算实例说明了该公式的有效性和准确性,对解决各种类型母线的相电感工程计算问题具有参考价值。     

A three‐phase hybrid stepping motor drive system combined with position‐sensorless closed‐loop control

This paper proposes a drive system for a three‐phase hybrid stepping motor, combining sensorless closed‐loop control with conventional open‐loop control. It is characterized by sophisticated control providing both prevention of pulling out from synchronism and suppression of natural rotor oscillation, without any position sensor attached to the motor shaft. A switching technique in chopper control which can enlarge the speed range controllable in the sensorless closed‐loop control is described. Starting and stopping sequences are developed to reduce mechanical natural oscillation produced in the transient state. Finally, the proposed drive system is compared experimentally with a conventional constant‐current open‐loop drive system. It is shown that the proposed drive system can perform the switchover from starting to sensorless closed‐loop operation within 20 ms, and can reduce the natural oscillation caused just after positioning. © 2000 Scripta Technica, Electr Eng Jpn, 131(3): 80–90, 2000