Showing papers on "Voltage regulation published in 2010"

Dynamic Performance of a Modular Multilevel Back-to-Back HVDC System

Abstract: The modular multilevel converter (MMC) is a newly introduced switch-mode converter topology with the potential for high-voltage direct current (HVDC) transmission applications. This paper focuses on the dynamic performance of an MMC-based, back-to-back HVDC system. A phase-disposition (PD) sinusoidal pulsewidth modulation (SPWM) strategy, including a voltage balancing method, for the operation of an MMC is presented in this paper. Based on the proposed PD-SPWM switching strategy, a mathematical model for the MMC-HVDC system, under both balanced and unbalanced grid operation modes, is developed. Dynamic performance of the MMC-based back-to-back HVDC converter system, based on time-domain simulation studies in the PSCAD/EMTDC environment, is then evaluated. The reported time-domain simulation results show that based on the adopted PD-SPWM switching strategy, the MMC-HVDC station can respond satisfactorily to the system dynamics and control commands under balanced and unbalanced conditions while maintaining voltage balance of the dc capacitors.

A Battery-Less Thermoelectric Energy Harvesting Interface Circuit With 35 mV Startup Voltage

Abstract: Energy harvesting is an emerging technology with applications to handheld, portable and implantable electronics. Harvesting ambient heat energy using thermoelectric generators (TEG's) [1] is a convenient means to supply power to body-worn electronics and industrial sensors. Using TEG's for body-wearable applications limits the output voltage to 50mV for temperature differences of 1–2K usually found between the body and ambience. Several existing systems [2, 3] use a battery or an initial high voltage energy input to kick-start operation of the system from this low voltage. Further, changing external conditions cause the voltage and power generated by the TEG to vary, necessitating efficient control circuits that can adapt and extract the maximum possible power out of these systems. In this paper, a battery-less thermoelectric energy harvesting interface circuit which uses a mechanically assisted startup circuit to operate from 35mV input is presented. An efficient control circuit that performs maximal end-to-end transfer of the extracted energy to a storage capacitor and regulates the output voltage at 1.8V is demonstrated.

Design and Analysis of a Grid-Connected Photovoltaic Power System

Abstract: A grid-connected photovoltaic (PV) power system with high voltage gain is proposed, and the steady-state model analysis and the control strategy of the system are presented in this paper. For a typical PV array, the output voltage is relatively low, and a high voltage gain is obligatory to realize the grid-connected function. The proposed PV system employs a ZVT-interleaved boost converter with winding-coupled inductors and active-clamp circuits as the first power-processing stage, which can boost a low voltage of the PV array up to a high dc-bus voltage. Accordingly, an accurate steady-state model is obtained and verified by the simulation and experimental results, and a full-bridge inverter with bidirectional power flow is used as the second power-processing stage, which can stabilize the dc-bus voltage and shape the output current. Two compensation units are added to perform in the system control loops to achieve the low total harmonic distortion and fast dynamic response of the output current. Furthermore, a simple maximum-power-point-tracking method based on power balance is applied in the PV system to reduce the system complexity and cost with a high performance. At last, a 2-kW prototype has been built and tested to verify the theoretical analysis of the paper.

Options for Control of Reactive Power by Distributed Photovoltaic Generators

Abstract: High penetration levels of distributed photovoltaic(PV) generation on an electrical distribution circuit present several challenges and opportunities for distribution utilities. Rapidly varying irradiance conditions may cause voltage sags and swells that cannot be compensated by slowly responding utility equipment resulting in a degradation of power quality. Although not permitted under current standards for interconnection of distributed generation, fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions. As side benefit, the control of reactive power injection at each PV inverter provides an opportunity and a new tool for distribution utilities to optimize the performance of distribution circuits, e.g. by minimizing thermal losses. We discuss and compare via simulation various design options for control systems to manage the reactive power generated by these inverters. An important design decision that weighs on the speed and quality of communication required is whether the control should be centralized or distributed (i.e. local). In general, we find that local control schemes are capable for maintaining voltage within acceptable bounds. We consider the benefits of choosing different local variables on which to control and how the control system can be continuously tuned between robust voltage control, suitable for daytime operation when circuit conditions can change rapidly, and loss minimization better suited for nighttime operation.

Novel High Step-Up DC–DC Converter for Fuel Cell Energy Conversion System

Abstract: A novel high step-up dc-dc converter for fuel cell energy conversion is presented in this paper. The proposed converter utilizes a multiwinding coupled inductor and a voltage doubler to achieve high step-up voltage gain. The voltage on the active switch is clamped, and the energy stored in the leakage inductor is recycled. Therefore, the voltage stress on the active switch is reduced, and the conversion efficiency is improved. Finally, a 750-W laboratory prototype converter supplied by a proton exchange membrane fuel cell power source and an output voltage of 400 V is implemented. The experimental results verify the performances, including high voltage gain, high conversion efficiency, and the effective suppression of the voltage stress on power devices. The proposed high step-up converter can feasibly be used for low-input-voltage fuel cell power conversion applications.

Decentralized Parallel Operation of Inverters Sharing Unbalanced and Nonlinear Loads

Abstract: In this paper, a wireless control strategy for parallel operation of three-phase four-wire inverters is proposed. A generalized situation is considered where the inverters are of unequal power ratings and the loads are nonlinear and unbalanced in nature. The proposed control algorithm exploits the potential of sinusoidal domain proportional+multiresonant controller (in the inner voltage regulation loop) to make the system suitable for nonlinear and unbalanced loads with a simple and generalized structure of virtual output-impedance loop. The decentralized operation is achieved by using three-phase P/Q droop characteristics. The overall control algorithm helps to limit the harmonic contents and the degree of unbalance in the output-voltage waveform and to achieve excellent power-sharing accuracy in spite of mismatch in the inverter output impedances. Moreover, a synchronized turn on with consequent change over to the droop mode is applied for the new incoming unit in order to limit the circulating current completely. The simulation and experimental results from -1 kVA and -0.5 kVA paralleled units validate the effectiveness of the scheme.

Examination of a PHEV bidirectional charger system for V2G reactive power compensation

Abstract: Plug-in hybrid electric vehicles (PHEVs) potentially have the capability to fulfill the energy storage needs of the electric grid by supplying ancillary services such as reactive power compensation, voltage regulation, and peak shaving. However, in order to allow bidirectional power transfer, the PHEV battery charger should be designed to manage such capability. While many different battery chargers have been available since the inception of the first electric vehicles (EVs), on-board, conductive chargers with bidirectional power transfer capability have recently drawn attention due to their inherent advantages in charging accessibility, ease of use, and efficiency. In this paper, a reactive power compensation case study using just the inverter dc-link capacitor is evaluated when a PHEV battery is under charging operation. Finally, the impact of providing these services on the batteries is also explained.

Topology comparison for Solid State Transformer implementation

Abstract: In this paper, a comparison of six representative topologies for the implementation of Solid State Transformers (SST) is performed. The objective is to help identify the most suitable topology capable of supporting additional functionalities as compared to a regular transformer, e.g. on-demand reactive power support to grid, voltage regulation, and current limiting. The comparison is based on switch loss, switch count, control characteristics and supported functionalities. It has been concluded that a three-stage configuration comprising distinct AC-DC, DC-DC and DC-AC stages results in the most suitable implementation. A Simulink model corresponding to this three-stage configuration is developed to demonstrate the desired characteristics and functionalities of the SST.

A Steady-State Voltage Stability Analysis of Power Systems With High Penetrations of Wind

Abstract: As wind generation begins to contribute significantly to power systems, the need arises to assess the impact of this new source of variable generation on the stability of the system. This work provides a detailed methodology to assess the impact of wind generation on the voltage stability of a power system. It will also demonstrate the value of using time-series ac power flow analysis techniques in assessing the behavior of a power system. Traditional methods are insufficient in describing the nature of wind for steady-state analyses, and as such, a new methodology is presented to address this issue. Using this methodology, this paper will show how the voltage stability margin of the power system can be increased through the proper implementation of voltage control strategies in wind turbines.

Distributed control of reactive power flow in a radial distribution circuit with high photovoltaic penetration

Abstract: We show how distributed control of reactive power can serve to regulate voltage and minimize resistive losses in a distribution circuit that includes a significant level of photovoltaic (PV) generation. To demonstrate the technique, we consider a radial distribution circuit with a single branch consisting of sequentially-arranged residential-scale loads that consume both real and reactive power. In parallel, some loads also have PV generation capability. We postulate that the inverters associated with each PV system are also capable of limited reactive power generation or consumption, and we seek to find the optimal dispatch of each inverter's reactive power to both maintain the voltage within an acceptable range and minimize the resistive losses over the entire circuit. We assume the complex impedance of the distribution circuit links and the instantaneous load and PV generation at each load are known. We compare the results of the optimal dispatch with a suboptimal local scheme that does not require any communication. On our model distribution circuit, we illustrate the feasibility of high levels of PV penetration and a significant (20% or higher) reduction in losses.

Scheduling of Droop Coefficients for Frequency and Voltage Regulation in Isolated Microgrids

Abstract: This paper details a procedure based on bifurcation theory to evaluate the impact that droops and primary reserve scheduling have on the microgrid stability. The methodology is based on finding the worst primary reserve share-that is, the share closest to instability-that can be found after rescheduling the droops of selected generating units that support frequency (and voltage) regulation. The solution-which consists of a measure of the distance to instability in a given direction-is found in a multi-parameter space endowed with coordinates corresponding to the droop coefficients. Two stages are proposed to achieve the solution. First, an investigation of the distance to bifurcation is computed in a one-dimensional parameter space in a defined search direction. Then the direction of this search is updated by calculating the normal vector at the found bifurcation point. The procedure is iteratively repeated until the closest bifurcation is found. The proposed approach is analyzed in a 69-bus and 11-generation unit isolated microgrid. It is shown through the analysis of some scenarios how the distances and normal vectors provide valuable insight on the correct scheduling from the stability point of view, giving advice on how the primary reserve should be more reliably scheduled.

Local Control of Reactive Power by Distributed Photovoltaic Generators

Abstract: High penetration levels of distributed photovoltaic (PV) generation on an electrical distribution circuit may degrade power quality due to voltage sags and swells caused by rapidly varying PV generation during cloud transients coupled with the slow response of existing utility compensation and regulation equipment Fast-reacting, VAR-capable PV inverters may provide the necessary reactive power injection or consumption to maintain voltage regulation under difficult transient conditions As side benefit, the control of reactive power injection at each PV inverter provides a new tool for distribution utilities to minimize the thermal losses in circuit We suggest a local control scheme that dispatches reactive power from each PV inverter based on local instantaneous measurements of the real and reactive components of the consumed power and the real power generated by the PVs Using one adjustable parameter per circuit, we balance the requirements on power quality and desire to minimize thermal losses The performance of the proposed control scheme is evaluated via numerical simulations of realistic rural lines in several generation/consumption scenarios Simultaneous improvement of both the power quality and the magnitude of losses is observed for all the scenarios, even when the renewable generation in excess of the circuit own load

Voltage regulation of photovoltaic arrays: small-signal analysis and control design

Abstract: This study deals with the regulation of the output voltage of photovoltaic (PV) arrays. As a case study, the DC-DC buck converter is used as an interface between the PV array and the load, but other types of converters can be used for the same purpose. The input voltage of the converter is controlled in order to regulate the operating point of the array. Besides reducing losses and stress because of the bandwidth-limited regulation of the converter duty cycle, controlling the converter input voltage reduces the settling time and avoids oscillation and overshoot, making easier the functioning of maximum power point tracking (MPPT) methods. The voltage regulation problem is addressed with a detailed analysis that starts with the modelling of the PV array and the converter. This analysis is followed by study, design, simulation and practical experiments of three closed-loop control strategies for the buck converter. Control stability and implementation considerations are presented.

Feedback Linearization Control of Three-Phase UPS Inverter Systems

Abstract: In this paper, a feedback linearization technique is proposed to control the output voltage control of three-phase uninterruptible power supply systems. First, a nonlinear model including the output LC filters is derived from the power balance condition between the inverter output terminal and the load side. Then, input-output feedback linearization is applied to the nonlinear model to make it linear. The controller of the linearized model is designed by linear control theory. The tracking control law is obtained with a pole placement technique. It is shown experimentally that the proposed control scheme gives high dynamic responses in response to load variation as well as a zero steady-state error.

Adaptive voltage droop scheme for voltage source converters in an islanded multibus microgrid

Abstract: In this study, a novel voltage droop scheme for the parallel operation of voltage source converters (VSCs) in an islanded multibus microgrid is proposed. In this scheme, the voltage droop coefficient is defined as a function of respective VSC active and reactive power outputs. Thus, each VSCs voltage reference is adaptively drooped as a non-linear function of its active and reactive power outputs. This approach leads to reduction in the reactive power sharing dependence on real power control and system parameters such as mismatched connecting and line impedances. A multiobjective index is introduced for evaluating the scheme performance. The index is used as an objective function in an optimisation problem that is employed to obtain optimal parameters of the scheme. The detailed analysis shows that this scheme has a superior behaviour compared to the conventional voltage droop method, in view of the reactive power sharing and loads voltage control under all loading conditions. Simulation and experimental results show the good performance of the method for three paralleled VSCs in a multibus microgrid system.

Method for determining the maximum allowable penetration level of distributed generation without steady-state voltage violations

Abstract: One of the main factors that may limit the penetration level of distributed generation (DG) in typical distribution systems is the steady-state voltage rise. The maximum amount of active power supplied by distributed generators into each system bus without causing voltage violations can be determined by using repetitive power flow studies. However, this task is laborious and usually time-consuming, since different loading level and generation operation modes have to be evaluated. Therefore this article presents a method that, based on only one power flow solution and one matrix operation, can directly determine the maximum power that can be injected by distributed generators into each system bus without leading to steady-state voltage violations. This method is based on the determination of voltage sensitivities from a linearised power system model. In addition, this article proposes a numerical index to quantify the responsibility of each generator for the voltage level rise in a multi-DG system. Based on this index, utility managers can decide which generators, and in which degree, should be penalised by the voltage rise or rewarded by not depreciating the voltage profile. The method is applied to a 70-bus distribution network. The results are compared with those obtained by repetitive power flow solutions in order to validate the proposed method.

Increasing distributed generation penetration using soft normally-open points

Abstract: This paper considers the effects of various voltage control solutions on facilitating an increase in allowable levels of distributed generation installation before voltage violations occur. In particular, the voltage control solution that is focused on is the implementation of ‘soft’ normally-open points (SNOPs), a term which refers to power electronic devices installed in place of a normally-open point in a medium-voltage distribution network which allows for control of real and reactive power flows between each end point of its installation sites. While other benefits of SNOP installation are discussed, the intent of this paper is to determine whether SNOPs are a viable alternative to other voltage control strategies for this particular application. As such, the SNOPs ability to affect the voltage profile along feeders within a distribution system is focused on with other voltage control options used for comparative purposes. Results from studies on multiple network models with varying topologies are presented and a case study which considers economic benefits of increasing feasible DG penetration is also given.

A Transformerless Hybrid Active Filter Using a Three-Level Pulsewidth Modulation (PWM) Converter for a Medium-Voltage Motor Drive

Abstract: This paper presents a transformerless hybrid active filter integrated into a medium-voltage motor drive for energy savings. This hybrid filter is intended for line harmonic-current mitigation of the three-phase diode rectifier used as the front end of the motor drive. It is based on direct connection of a passive filter tuned to the seventh-harmonic frequency in series with an active filter using a three-level pulsewidth modulated (PWM) converter. This paper provides a theoretical discussion on voltage-balancing control of two split dc capacitors of the active filter. The 400-V 15-kW motor drive system is designed, constructed, and tested, which can be considered as a downscaled model from a medium-voltage motor drive without regenerative braking. Experimental results verify that the hybrid filter has the capability of satisfactory harmonic filtering and stable voltage balancing in all the load conditions.

Interleaved-Boost Converter With High Voltage Gain

Abstract: This paper presents an interleaved-boost converter, magnetically coupled to a voltage-doubler circuit, which provides a voltage gain far higher than that of the conventional boost topology. Besides, this converter has low-voltage stress across the switches, natural-voltage balancing between output capacitors, low-input current ripple, and magnetic components operating with the double of switching frequency. These features make this converter suitable to applications where a large voltage step-up is demanded, such as grid-connected systems based on battery storage, renewable energies, and uninterruptible power system applications. Operation principle, main equations, theoretical waveforms, control strategy, dynamic modeling, and digital implementation are provided. Experimental results are also presented validating the proposed topology.

Hybrid PWM Strategy of SVPWM and VSVPWM for NPC Three-Level Voltage-Source Inverter

Abstract: Neutral-point (NP) voltage drift is the main technical drawback of NP-clamped (NPC) three-level inverters. Traditional space vector pulsewidth modulation (SVPWM) is incapable of controlling the NP voltage for high modulation indexes and low power factors. Virtual SVPWM (VSVPWM) is capable of controlling the NP voltage under full modulation indexes and full power factors. However, this modulation strategy is more complex than SVPWM, increases the switching frequency, and deteriorates the output waveforms of the inverter. A novel PWM concept that includes NP voltage-balancing conditions is proposed. Based on this concept, a hybrid modulation scheme that uses both SVPWM and VSVPWM is presented for complete control of the NP voltage in NPC three-level inverters. The performance of this new modulation approach and its benefits over SVPWM and VSVPWM are verified by simulation and experiments.

Control Scheme of Cascaded H-Bridge STATCOM Using Zero-Sequence Voltage and Negative-Sequence Current

Abstract: This paper presents a control scheme of cascaded H-bridge STATCOM in three-phase power systems. Cascaded H-bridge STATCOM has merits in point of switching losses, output harmonics, and the number of circuit components. But every H-bridge cell has isolated dc capacitors. So the balancing problem of capacitor voltages exists. Since STATCOM is often requested to operate under asymmetrical condition by power system faults, capacitor voltage balancing between phase clusters is particularly important. Solving this problem, a technique using zero-sequence voltage and negative-sequence current is proposed. By this scheme, the STATCOM is allowed to operate under asymmetrical conditions by power system faults. The validity is examined by digital simulation under one line and two-lines fault circuit condition.

Adaptive PI Stabilization of Switched Power Converters

Abstract: Linear proportional-integral (PI) controllers are widely used in power converter applications. In a recent paper, a methodology to design such controllers ensuring asymptotic stability was proposed. The technique relied on the basic fact that if an affine system can be rendered passive with a constant control, then it is stabilizable with a PI. A structural condition was imposed then on the power converter to satisfy the former property with a passive output generated as a linear combination of the states. This condition is technical and has no clear physical interpretation. In this brief this result is extended in three directions: first, the aforementioned condition is removed; second, a larger class of converters (with switching external sources) is considered; third, the load resistance is assumed unknown and an adaptive PI controller (with three different estimators) is proposed. Instrumental to establish the result is the proof that the nonlinear incremental model of power converters defines a passive map-a property first observed by Sanders and Verghese in the early 1990's. The methodology is applied to the problem of power factor compensation of a 3-phase voltage source rectifier, already considered in our previous paper, which is revisited from the incremental passivity perspective yielding simpler proofs. Also, a stable adaptive PI is designed for the output voltage regulation of a quadratic boost converter. Simulations complete the brief.

Digital Average Current-Mode Control of PWM DC–DC Converters Without Current Sensors

Abstract: This paper introduces a digital average current-mode control technique for pulsewidth modulation dc-dc converters which only rely on voltage sampling. The proposed approach is to estimate inductor current using first-order discrete-time low-pass filter; therefore, the controller can calculate average inductor current in every switching cycle. As a novel technique of predictive average current control, it has been investigated by choosing an appropriate duty ratio to regulate valley inductor current first and then eliminating error between the estimated average inductor current and a reference current in succedent switching cycle. The algorithm is based on a two-loop control structure to achieve an accurate voltage regulation and is derived for three basic converters: buck, boost, and buck-boost. The validity of the proposed approach has been demonstrated by simulation and experimental results on a dc-dc boost converter.

Developing DC Transmission Networks Using DC Transformers

Abstract: This paper studies principles of developing dc transmission grids based on high power dc/dc converters. There has been much research on dc/dc converters and it is likely that some megawatt size units will achieve commercialisation stage soon. In this study, we assume that electronic dc transformers can achieve three functions: 1) voltage stepping, 2) voltage (or power) regulation, and 3) fault isolation. The location, sizing, and control of dc transformers is first analyzed using a simple 4-terminal, 1.8 GW dc grid. It is postulated that this grid would be a better alternative to a point-to-point HVDC. Detailed simulations on PSCAD/EMTDC demonstrate the capability to independently regulate power flow in each dc branch. The simulations of worst case faults on dc lines and ac grids show that dc transformers can isolate the faulted segments enabling the remaining part of the grid to operate normally. The generic principles of developing more complex dc grids with meshed power flows, are also presented. It is concluded that there are no significant technical barriers in developing dc transmission grids but the cost and losses of dc transformers remain as the primary challenges.

Adaptive Voltage Control With Distributed Energy Resources: Algorithm, Theoretical Analysis, Simulation, and Field Test Verification

Abstract: Distributed energy resources (DE) or distributed generators (DG) with power electronics interfaces and logic control using local measurements are capable of providing reactive power related ancillary system services. In particular, local voltage regulation has drawn much attention in regards to power system reliability and voltage stability, especially from past major cascading outages. This paper addresses the challenges of controlling DEs to regulate local voltage in distribution systems. An adaptive voltage control method has been proposed to dynamically modify control parameters to respond to system changes. Theoretical analysis shows that there exists a corresponding formulation of the dynamic control parameters; hence the adaptive control method is theoretically solid. Both simulation and field experiment test results at the Distributed Energy Communications and Controls (DECC) Laboratory confirm that this method is capable of satisfying the fast response requirement for operational use without causing oscillation, inefficiency, or system equipment interference. Since this method has a high tolerance to real-time data shortage and is widely adaptive to variable power system operational situations, it is quite suitable for broad utility application.

Interphase AC–AC Topology for Voltage Sag Supporter

Abstract: A new topology is proposed in this paper to compensate voltage sags in power distribution systems. Voltage sag is one of the major power quality problems encountered by industries. The traditional voltage sag compensator, which is a dynamic voltage restorer based on energy storage device with a series-connected voltage-source inverter, is not adequate for compensating deep and long-duration voltage sags. As per the sensitive load concern, deep and long-duration sags are more vulnerable than shallow and short-duration sags. To compensate the voltage sag, a new interphase ac-ac topology is proposed that needs no storage device. The compensator of each phase is connected on the other two phases and the power is tapped from them. A single-phase compensator is realized with two ac chopper circuits and two transformers. By controlling the duty cycle of each ac chopper, the required voltage is realized to compensate the voltage sag. Analysis, simulation, and experimental results are presented to demonstrate the proposed concept.

Voltage-sharing converter to supply single-phase asymmetrical four-level diode-clamped inverter with high power factor loads

Abstract: The output voltage quality of some of the single-phase multilevel inverters can be improved when their dc-link voltages are regulated asymmetrically. Symmetrical and asymmetrical multilevel diode-clamped inverters have the problem of dc-link capacitor voltage balancing, especially when power factor of the load is close to unity. In this paper, a new single-inductor multi-output dc/dc converter is proposed that can control the dc-link voltages of a single-phase diode-clamped inverter asymmetrically to achieve voltage quality enhancement. The circuit of the presented converter is explained and the main equations are developed. A control strategy is proposed and explained in details. To validate the versatility of the proposed combination of the suggested dc-dc converter and the asymmetrical four-level diode-clamped inverter (ADCI), simulations and experiments have been directed. It is concluded that the proposed combination of introduced multioutput dc-dc converter and single-phase ADCI is a good candidate for power conversion in residential photovoltaic (PV) utilization.

Monitoring power-related parameters in a power distribution unit

Abstract: A power distribution unit (PDU) disposable in an electrical equipment rack. The PDU has a housing, a power input penetrating the housing, outlets in the housing, a processor disposed in the housing, voltage and current sensors, and a voltage calculation procedure communicable with the processor. The processor samples voltage and current waveforms and calculates RMS values and other power parameters. A method of managing electrical loads each drawing electrical power from a PDU includes repeatedly sampling voltage across and current flowing through each of the loads, calculating raw RMS values of voltage and current, and scaling the raw RMS values to obtain corrected RMS voltage and current values and other power parameters.

Decentralised control of voltage in distribution systems by distributed generators

Abstract: Recently, renewable energy such as wind turbine generators and photovoltaic systems are introduced as distributed generators (DGs). Connection of a large amount of DG causes voltage deviation beyond the statutory range in distribution systems. Reactive power control of inverters interfaced with DGs is one of the solutions against this problem. Additionally, reactive power control has a possibility to contribute to the reduction of distribution loss. In this study, the authors propose a voltage control method in distribution systems by reactive power control of inverters interfaced with DGs. The proposed method has been developed in order to reduce distribution loss and voltage regulation into statutory range without any telecommunication. In the proposed method, each interfaced inverter controls reactive power based on voltage control reference, which is calculated from self-information. The calculation rule of control reference has been developed using optimal data which consist of relations between randomly given inputs and corresponding optimal outputs, which are calculated by an optimisation technique. Simulations are conducted to show the effectiveness of the proposed method.