Showing papers on "Total harmonic distortion published in 2008"

High-Performance Stand-Alone Photovoltaic Generation System

Abstract: This study develops a high-performance stand-alone photovoltaic (PV) generation system. To make the PV generation system more flexible and expandable, the backstage power circuit is composed of a high step-up converter and a pulsewidth-modulation (PWM) inverter. In the dc-dc power conversion, the high step-up converter is introduced to improve the conversion efficiency in conventional boost converters to allow the parallel operation of low-voltage PV arrays, and to decouple and simplify the control design of the PWM inverter. Moreover, an adaptive total sliding-mode control system is designed for the voltage control of the PWM inverter to maintain a sinusoidal output voltage with lower total harmonic distortion and less variation under various output loads. In addition, an active sun tracking scheme without any light sensors is investigated to make the PV modules face the sun directly for capturing the maximum irradiation and promoting system efficiency. Experimental results are given to verify the validity and reliability of the high step-up converter, the PWM inverter control, and the active sun tracker for the high-performance stand-alone PV generation system.

An Improved Control Strategy for Grid-Connected Voltage Source Inverters With an LCL Filter

Abstract: A novel current control strategy based on a new current feedback for grid-connected voltage source inverters with an LCL-filter is proposed in this paper. By splitting the capacitor of the LCL-filter into two parts, each with the proportional division of the capacitance, the current flowing between these two parts is measured and used as the feedback to a current regulator to stabilize and improve the system performances. Consequently, the V-1 transfer function of the grid-connected inverter system with the LCL-filter is degraded from a third-order function to a first-order one, therefore the closed-loop current feedback control system can be optimized easily for minimum steady-state error and current harmonic distortion, as well as the system stability. The characteristics of the inverter system with the proposed controller are investigated and compared with those using traditional control strategies. Experimental results are provided, and the new current control strategy has been verified on a 5 kW fuel cell inverter.

Long-Lifetime Power Inverter for Photovoltaic AC Modules

Abstract: This paper presents a power inverter tailored for low-power photovoltaic (PV) systems. The inverter features high reliability, thanks to a circuit topology that obviates aluminum electrolytic capacitors from the circuit. Moreover, all components, including logic and control, have been designed to exhibit high reliability at high temperatures. Three conversion stages form the power topology. First, a full bridge connected to a high-frequency transformer and a full-bridge rectifier amplifies the voltage of the PV panel to approximately 475 V. This stage is controlled by using a phase-shift pulsewidth-modulation controller that permits zero-voltage switching, thereby minimizing losses. Second, a buck converter is connected in series with the rectifier and is controlled by using current mode in order to shape the current injection into a rectified sine wave. Last, a full bridge is operated at line frequency to unfold the current injection. The amplification stage has a proportional compensator that maintains the voltage at the PV terminals constant. The current injection stage has a proportional-derivative compensator that controls the amplitude of the grid current so that the dc-link average voltage is maintained constant. Experimental results show that the peak efficiency of the system is 89%, and the total current harmonic distortion is below 5%. Finally, analyses show a designed lifetime of approximately ten years.

Dead-Time Elimination for Voltage Source Inverters

Abstract: A novel dead-time elimination method is presented in this paper for voltage source inverters. This method is based on decomposing of a generic phase-leg into two basic switching cells, which are configured with a controllable switch in series with an uncontrollable diode. Therefore, dead-time is not needed. In comparison to using expensive current sensors, this method precisely determines the load current direction by detecting which anti-parallel diode conducts in a phase-leg. A low-cost diode-conduction detector is developed to measure the operating state of the anti-parallel diode. In comparison with complicated compensators, this method features simple logic and flexible implementation. This method significantly reduces the output distortion and regains the output RMS value. The principle of the proposed dead-time elimination method is described in detail. Simulation and experimental results are given to demonstrate the validity and features of this new method.

Virtual-Flux-Based Predictive Direct Power Control of AC/DC Converters With Online Inductance Estimation

Abstract: This paper presents an improved predictive direct power control (P-DPC) algorithm for grid-connected three-phase voltage source converters without AC-side voltage sensors. The new algorithm is based on virtual-flux (VF) estimation and operates with constant switching frequency. Predictive controller selects in every sampling period appropriate voltage vector sequence and calculates duty cycles in order to minimize instantaneous active and reactive power errors. The theoretical principles of this algorithm are discussed, and selected experimental measurements and scope graphs that illustrate the operation and performance of the system are presented. It is shown that VF-P-DPC algorithm exhibits several advantages, particularly sinusoidal-grid-current low harmonic distortion even when grid voltage is distorted. In addition, the algorithm provides high dynamics at low switching frequency of 2 kHz.

Triple-Hop Distance as a Valid Predictor of Lower Limb Strength and Power

Abstract: Context: Hop tests are functional tests that reportedly require strength, power, and postural stability to perform. The extent to which a triple-hop distance (THD) test measures each of th...

Space Vector Based Hybrid PWM Techniques for Reduced Current Ripple

Abstract: This paper investigates certain novel switching sequences involving division of active vector time for space vector based pulsewidth modulation (PWM) generation for a voltage source inverter. This paper proposes two new sequences, and identifies all possible sequences, which result in the same average switching frequency as conventional space vector PWM (CSVPWM) at a given sampling frequency. This paper brings out a method for designing hybrid PWM techniques involving multiple sequences to reduce line current ripple. The three proposed hybrid PWM techniques (three-zone PWM, five-zone PWM and seven zone PWM) employ three, five and seven different sequences, respectively, in every sector. Each sequence is employed in a spatial region within the sector where it results in the lowest rms current ripple over the given sampling period. The proposed techniques lead to a significant reduction in THD over CSVPWM at high line voltages. The five-zone technique results in the lowest THD among real-time techniques with uniform sampling, while the seven-zone technique is the best among real-time techniques with twin sampling rates. The superior harmonic performance of the proposed techniques over CSVPWM and existing bus-clamping PWM techniques is established theoretically as well as experimentally.

Predictive control of an indirect matrix converter

Abstract: This paper presents the implementation of a predictive control scheme for an indirect matrix converter. The control scheme selects the switching state that minimizes the reactive power and the error in the output currents according to their reference values. This is accomplished by using a prediction horizon of one sample time and a very intuitive control law. Experimental results with a 6.8-kVA indirect matrix converter prototype are provided in order to validate the proposed control scheme. The converter uses standard digital signal processor operating at a sampling frequency of 20 mus. It is shown that the idea of controlling this converter topology with a predictive approach can be implemented simply and input currents with unity power factor and a total harmonic distortion lower than 5% can be obtained.

Analysis of Harmonics in Power Systems Using the Wavelet-Packet Transform

Abstract: This paper proposes a new algorithm based on the wavelet-packet transform for the analysis of harmonics in power systems. The proposed algorithm decomposes the voltage/current waveforms into the uniform frequency bands corresponding to the odd-harmonic components of the signal and uses a method to reduce the spectral leakage due to the imperfect frequency response of the used wavelet filter bank. This paper studies the selection of the mother wavelet, the sampling frequency, and the frequency characteristics of the wavelet filter bank for the two most common wavelet functions used for harmonic analysis and compares the performance of the proposed method with the results obtained using the discrete Fourier transform (DFT) analysis and the harmonic-group concept introduced by the International Electrotechnical Commission (IEC) under different measurement conditions.

Optimal Predictive Control of Three-Phase NPC Multilevel Converter for Power Quality Applications

Abstract: This paper presents the optimal control of the AC currents, the DC voltage regulation, and the DC capacitor voltage balancing in a three-level three-phase neutral point clamped multilevel converter for use in power quality applications as an active power filter. The AC output currents and the DC capacitor voltages are sampled and predicted for the next sampling time using linearized models and considering all the 27 output voltage vectors. A suitable quadratic weighed cost function is used to choose the voltage vector that minimizes the AC current tracking errors, the DC voltage steady-state error, and the input DC capacitor voltage unbalancing. The obtained experimental results show that the output AC currents track their references showing small ripple, a total harmonic distortion (THD) of less than 1%, harmonic contents that are 46 dB below the fundamental, and almost no steady-state error (0.3%). The capacitor voltages are balanced within 0.05%, and the balancing is assured even when redundant vectors are not chosen. Near-perfect capacitor DC voltage balancing is obtained while reducing current harmonic distortion. Some experimental evidence of robustness concerning a parameter variation was also found, with the optimum controller withstanding parameter deviations from +100% to -50%. Compared to a robust sliding mode controller, the optimal controller can reduce the THD of the AC currents or reduce the switching frequency at the same THD, being a suitable controller for power quality in medium-voltage applications.

Optical Millimeter-Wave Signal Generation Using Frequency Quadrupling Technique and No Optical Filtering

Abstract: This letter demonstrates a novel method to generate high-purity optical millimeter-wave signals with carrier suppression by using a frequency quadrupling technique. To the authors' knowledge, this is the first time that a frequency quadrupling system requires only a single integrated Mach-Zehnder modulator without a narrowband optical filter to remove undesired optical sidebands. Since no optical filter is needed, fast frequency tuning is straightforward and this approach will be particularly attractive for optical up-conversion in wavelength-division-multiplexing radio-over-fiber systems. This letter provides both theoretical analysis and experimental demonstration. The generated optical millimeter-wave signals have very high quality with an optical carrier and harmonic distortion suppression ratio of more than 38 and 36 dB at 40 and 72 GHz, respectively.

Power Flow Control of a Single Distributed Generation Unit

Abstract: This research addresses power flow control problem of a grid-connected inverter in distributed generation applications. A real and reactive power control solution is proposed on the basis of an existing voltage control strategy developed for island operations. The power control solution takes advantage of a newly designed system parameter identification method and a nonlinear feedforward algorithm, both of which are based on Newton-Raphson iteration method and implemented in real time. The proposed power control solution also performs grid-line current conditioning and yields harmonic free grid-line current. A phase locked loop based algorithm is developed as a part of the solution to handle possible harmonic distorted grid-line voltage and maintain harmonic free line current. The effectiveness of the proposed techniques is demonstrated by both simulation and experimental results.

Comparison of the FPGA Implementation of Two Multilevel Space Vector PWM Algorithms

Abstract: Multilevel converters can meet the increasing demand of power ratings and power quality associated with reduced harmonic distortion and lower electromagnetic interference. When the number of levels increases, it is necessary to control more and more switches in parallel. Field programmable gate arrays (FPGAs), with their concurrent processing capability, are suitable for the implementation of multilevel modulation algorithms. Among them, space vector pulsewidth modulation algorithms offer great flexibility to optimize switching waveforms and are well suited for digital implementation. In this paper, two algorithms, 2-D and 3-D, are analyzed and implemented in an FPGA. In order to carry out the implementation, both algorithms have been described in very high speed integrated circuit hardware description language, partly hand coded, and partly automatically generated using the system generator tool. Both implementations are compared in terms of implementation complexity and logic resources required. Finally, test results with a neutral-point-clamped inverter are presented.

A Carrier-Based PWM Method With Optimal Switching Sequence for a Multilevel Four-Leg Voltage-Source Inverter

Abstract: In a three-phase four-wire utility system, three-phase unbalanced loads and many single-phase nonlinear loads result in a neutral line current that is zero-sequence current. To deal with unbalanced and nonlinear loads in a high power system, this paper suggests a multilevel four-leg pulsewidth modulation (PWM) voltage-source inverter (VSI) as a topology for the high power applications where a function is required to control the zero-sequence component as well as dq components. This paper proposes a carrier-based PWM method for a multilevel four-leg PWM VSI along with introducing a novel offset voltage. The proposed offset voltage makes it possible for the switching sequence of all the legs to be optimized for minimizing the harmonic distortion of the output voltage irrespective of the number of inverter levels. The proposed PWM method based on digital signal processors is implemented and tested by using a prototype three-level four-leg VSI. The feasibility of the proposed PWM method is verified by the spectral analysis, simulation, and experimental results.

Comparison of state of the art multilevel inverters

Abstract: In this paper, a comparison between existing state of the art multilevel inverter topologies is performed. The topologies examined are the neutral point clamp multilevel inverter (NPCMLI) or diode-clamped multilevel inverter (DCMLI), the flying capacitor multilevel inverter (FCMLI) and the cascaded cell multilevel inverter (CCMLI). The comparison of these inverters is based on the criteria of output voltage quality (Peak value of the fundamental and dominant harmonic components and THD), power circuitry complexity, and implementation cost. The comparison results are based on theoretical results verified by detailed simulation results.

On Attaining the Multiple Solutions of Selective Harmonic Elimination PWM Three-Level Waveforms Through Function Minimization

Abstract: Selective harmonic elimination pulsewidth modulation techniques are some of the control methods used in voltage/current source converters. However, challenges such as the task of finding all the multiple sets of solutions of the switching angles for a given problem may be difficult to deal with. In this paper, a direct minimization of the nonlinear transcendental trigonometric Fourier functions in combination with a random search is discussed. The unipolar (three-level) waveform is used to illustrate the proposed method confirming its ability to find multiple sets of solutions, including a case where 51 angles are sought for single- and three-phase applications. A simple harmonic distortion factor is studied for each set of solutions to assess their performance against the noneliminated harmonics. The results presented both at theoretical and experimental level are in close agreement and confirm the robustness of the proposed approach.

Five-Level Diode-Clamped PWM Converters Connected Back-to-Back for Motor Drives

Abstract: This paper addresses a transformerless medium-voltage adjustable-speed motor drive consisting of two five-level diode-clamped PWM converters connected back-to-back. It is followed by designing, constructing, and testing a 200-V downscaled model to verify the validity and effectiveness of the medium-voltage motor drive. This downscaled model has four split DC capacitors equipped with a voltage-balancing circuit using two bidirectional buck-boost choppers. The two five-level converters are based on sinusoidal pulsewidth modulation with a carrier frequency of 3 kHz. The motor tested in this paper is a three-phase four-pole induction motor rated at 200 V, 5.5 kW, and 60 Hz. Experimental waveforms show that the four split dc-capacitor voltages are well balanced in any operating conditions and that the total harmonic distortion values of the input line current and the output motor current are 3.9% and 3.5%, respectively.

Space Vector Sequence Investigation and Synchronization Methods for Active Front-End Rectifiers in High-Power Current-Source Drives

Abstract: Space vector pulsewidth modulation (PWM) schemes for the active front end of a high-power drive normally produce low-order and suborder harmonics due to the low switching frequency and the drifting of synchronization between the PWM waveform and the rectifier input frequency. To provide a synchronized PWM and achieve the best harmonic performance, different space vector sequences suitable for a current-source converter are investigated in this paper. Details on how to achieve the waveform symmetries with a minimum switching frequency for each sequence are discussed. A thorough comparison of the harmonic performance of different space vector sequences is carried out. An optimum space vector modulation method by switching between two best sequences is proposed to achieve the best line-current total harmonic distortion with reduced switching losses. In addition, two synchronization methods, namely a PWM frame regulation method and a direct digital phase-locked loop synchronization method, are proposed. Both methods are equally effective in providing tight synchronization of the PWM waveform with the rectifier input frequency. The work has been verified in simulation and experiment.

Control Strategies for Load Compensation Using Instantaneous Symmetrical Component Theory Under Different Supply Voltages

Abstract: In this paper, the theory of instantaneous symmetrical components is applied to explore various control strategies of load compensation, under different supply voltages. When the supply voltages are balanced and sinusoidal, all of these strategies converge to the same compensation characteristics. However, when the supply voltages are not balanced sinusoids, these control strategies result in different degrees of compensation in harmonics, power factor, neutral current, and compensator ratings. These control strategies are discussed in detail and a comparative study of their performance in terms of the rms value, total harmonic distortion, power factor of source currents, and compensator ratings is presented. Based on this study, it is possible to select the best strategy to meet the required load compensation characteristics for available supply voltages. A three-phase four-wire distribution system supplying an unbalanced and nonlinear load is considered for simulation study. The detailed simulation results using MATLAB are presented to support the proposed compensation strategies.

A Three-Phase Four-Wire Inverter Control Technique for a Single Distributed Generation Unit in Island Mode

Abstract: A control technique is developed for a three-phase four-wire split DC bus inverter of a single distributed generation unit working in island mode. The control technique combines an inner discrete-time sliding mode controlled (DSMC) current loop and an outer robust servomechanism controlled voltage loop. The control algorithms are developed under stationary alphabeta0 (Clarke's) reference frame and a modified space vector pulsewidth modulation (MSVPWM) is proposed to implement the algorithm under Clarke's reference frame. The proposed technique achieves voltage regulation with low steady state error and low total harmonic distortion and fast transient response under various load disturbances. Meanwhile the usage of MSVPWM in a stationary alphabeta0 reference frame yields better transient performance under limited DC bus voltage compared to conventional uniformly sampled sine wave modulation in ABC reference frame. In this paper, besides the development and description of the algorithms, a series of discussions, analysis and studies are performed on the proposed control technique, including the L-C filter design issue, frequency domain closed-current-loop and closed-voltage-loop responses, and time domain simulations and experiments under various load conditions. All the analysis, simulations, and experiments demonstrate the effectiveness of the proposed control solution.

Identification of RF Harmonic Distortion on Si Substrates and its Reduction Using a Trap-Rich Layer

Abstract: Harmonic distortion (HD) is measured arising from coplanar waveguide structures on various substrates at 900 MHz, and significant distortion for silicon substrates is demonstrated for the first time. For an input power of +35 dBm, 2nd harmonic power of -47 dBm and 3rd of -57 dBm are measured for a thru calibration structure on oxidized high-resistivity silicon (HRS) substrates, and 2nd harmonic of -23 and 3rd of -20 dBm for a longer line on a thinner oxide. These levels are high compared to a full cellular transmit switch product specification of -45 and -40 dBm for 2nd and 3rd harmonics, respectively, at similar power levels. The contribution of the silicon substrate to high harmonic levels is investigated experimentally, and an efficient technological solution based on the introduction of a trap-rich layer is demonstrated.

Reduced Switching-Frequency Active Harmonic Elimination for Multilevel Converters

Abstract: This paper presents a reduced switching-frequency active-harmonic-elimination method (RAHEM) to eliminate any number of specific order harmonics of multilevel converters. First, resultant theory is applied to transcendental equations to eliminate low-order harmonics and to determine switching angles for a fundamental frequency-switching scheme. Next, based on the number of harmonics to be eliminated, Newton climbing method is applied to transcendental equations to eliminate high-order harmonics and to determine switching angles for the fundamental frequency-switching scheme. Third, the magnitudes and phases of the residual lower order harmonics are computed, generated, and subtracted from the original voltage waveform to eliminate these low-order harmonics. Compared to the active-harmonic-elimination method (AHEM), which generates square waves to cancel high-order harmonics, RAHEM has lower switching frequency. The simulation results show that the method can effectively eliminate all the specific harmonics, and a low total harmonic distortion (THD) near sine wave is produced. An experimental 11-level H-bridge multilevel converter with a field-programmable gate-array controller is employed to experimentally validate the method. The experimental results show that RAHEM does effectively eliminate any number of specific harmonics, and the output voltage waveform has low switching frequency and low THD.

Recurrent Neural Networks Trained With Backpropagation Through Time Algorithm to Estimate Nonlinear Load Harmonic Currents

Abstract: Generation of harmonics and the existence of waveform pollution in power system networks are important problems facing the power utilities. The determination of harmonic currents injected into a power network by a nonlinear load is complicated when the supply voltage waveform to the load is distorted by other loads and not a pure sinusoid. This paper proposes a neural network solution to this problem. A recurrent neural network trained with the backpropagation through time training algorithm is used to find a way of distinguishing between the so-called load harmonics and supply harmonics, without disconnecting the load from the network. The advantage of this method is that only waveforms of voltages and currents have to be measured. This method is applicable for both single and three phase loads and could be fabricated into a commercial instrument that could be installed in substations of large customer loads, or used as a hand-held clip on instrument. This paper is particularly useful in determining whether the utility or the customer side has a higher contribution to harmonic pollution in a network. Hence, this method would be helpful in settling utility-customer disputes over who is responsible for harmonic pollution.

A Repetitive-Based Controller for the Compensation of $6\ell\pm 1$ Harmonic Components

Abstract: In this paper, a repetitive-based controller for the compensation of 6 lscr plusmn 1 harmonic components is proposed. This control scheme is more appropriate for processes that involve the use of six-pulse converters or other converters that mainly produce harmonic components at those frequencies. The control scheme is based on the feedback array of two delay lines plus a feedforward path that compensates only the 6 lscr plusmn 1 multiples of the fundamental frequency, thereby reducing the possibility of reinjecting unnecessary distortion into the system. The proposed scheme is, then, plugged into a generic feedback control system where a stability analysis is carried out. In addition, the passivity properties of the proposed scheme are presented, which open the possibility of control design following the passivity-based approach. Experiments that are based on a simple digital implementation are provided to illustrate the merits of our solution. These results include the open-loop responses of the proposed scheme and the responses in a practical example to validate its effectiveness in an application. For this latter result, the proposed scheme has been used in the controller of a 2-kVA shunt active filter to compensate the current harmonic distortion.

Fast Dynamic Control of Medium Voltage Drives Operating at Very Low Switching Frequency—An Overview

Abstract: Medium voltage AC machines fed by high-power inverters operate at a low switching frequency to restrain the switching losses of power semiconductor devices. Particular care is thus required in the design of the drive control system. The signal delay caused by low switching frequency operation increases undesired cross-coupling effects in vector-controlled schemes. These are not sufficiently compensated by established methods like feedforward control. Improvements are achieved by a more accurate modeling of the machine and the inverter. An adequate controller is introduced, having a transfer function with complex coefficients. The high harmonic distortion due to the low switching frequency is a tradeoff. Using synchronous optimal pulsewidth as an alternative permits reducing the switching frequency without increasing the harmonics. The detrimental effects of conventional control methods are eliminated by forcing the harmonic components on an optimal spatial trajectory. Deadbeat behavior and complete decoupling are thus achieved. The performance of the aforementioned schemes is compared based on mathematical analyses and experimental results.

Kalman filter based synchronisation methods

Abstract: Single- and three-phase synchronisation methods based on optimum filtering theory are proposed. These methods are based mainly on the Kalman filter and are therefore termed Kalman filter-phase locked loop. They explicitly include in the problem formulation the presence of harmonics, voltage unbalance, measurement noise, transients and frequency deviation. Such perturbations degrade the performance of many synchronisation structures presented in literature. The formulation presented here makes the synchronisation signals less sensitive to these perturbations. It is also shown that the proposed methods can be helpful by also providing the amplitude, instantaneous phase and frequency of grid voltages that can be useful for the analysis of power quality. Furthermore, the Kalman filter provides a way of obtaining the best compromise between transient response and measurement noise rejection for the synchronisation signals. The paper sets out the development of the proposed methods together with the choice of tuning parameters and their physical meaning. Simulations and experimental results using a DSP TMS320F2812 are presented to show the effectiveness of the proposed schemes.

Analysis of Control-Delay Reduction for the Improvement of UPS Voltage-Loop Bandwidth

Abstract: This paper investigates the effects of control-delay minimization in the dynamic performance of the output stage of uninterruptible power supplies (UPSs) by shifting the sampling time of inductor current and output voltage toward the duty-cycle update instant. This paper shows how a small shift of the output-voltage sampling can significantly increase the UPS voltage-loop bandwidth while keeping the same stability margin. Instead, less contribution comes from the delay minimization of the inductor-current sampling, so that current-ripple cancellation techniques are not needed. A detailed model based on the modified Z-transform, which accounts for different time delays in multiloop control, is proposed. The effectiveness of the proposed analysis is demonstrated by simulation and experimental results on a typical industrial three-phase/three-phase 8-kHz 30-kVA UPS prototype. By using two control designs based on the same phase margin, the output-voltage total harmonic distortion with the normalized distorting load is reduced from 6.8% to 5.7%, using a delay of the output voltage sampling equal to 25 mus.

Control Design of a Three-Phase Matrix-Converter-Based AC–AC Mobile Utility Power Supply

Abstract: This paper describes the control analysis and design of an ac-to-ac three-phase mobile utility power supply using a matrix converter capable of high-quality 50-, 60-, and 400-Hz output voltage and reduced input harmonic distortion. Instead of the traditional structure employing a diode bridge rectifier, a dc link and a pulsewidth-modulated inverter, a three-phase-to-three-phase direct ac-ac (matrix) converter has been used as the power-conditioning core of the system, working in conjunction with input and output LC low-pass filters. An optimizing control design method using a genetic algorithm approach has been used, which yields designs to minimize a cost function, taking into account transient and steady-state output voltage performance targets, together with robustness to different operative conditions and system parameters drift. Simulation and experimental tests have demonstrated that the system meets the power-quality requirements of the application.

Current Waveform Construction to Generate AC Power with Low Harmonic Distortion from Localized Energy Sources

Abstract: Methods and apparatus to provide low harmonic distortion AC power for distribution by converting energy from natural or renewable sources into electrical form, and constructing a current waveform on a primary winding of a transformer by recapturing inductive energy previously stored in the transformer so as to transform the converted electrical energy into substantially sinusoidal AC voltage at a secondary winding of the transformer. For example, AC power may be supplied to a utility power grid from raw electrical energy from renewable energy sources (e.g., solar cells). An inverter may construct the primary winding current waveform using two unidirectional switches. On each half cycle, one of the switches first applies energy previously recaptured from primary winding inductance, and then applies the raw energy to the transformer primary winding at the utility power grid frequency. Accordingly, the constructed primary winding current may exhibit substantially improved total harmonic distortion.

A particle swarm optimization for sitting and sizing of Distributed Generation in distribution network to improve voltage profile and reduce THD and losses

Abstract: This paper presents a method for optimal sitting and sizing of distributed generation (DG) in distribution systems. In this paper, our aim would be optimal distributed generation allocation and sizing for voltage profile improvement, loss reduction, and THD (total harmonic distortion) reduction in distribution networks. Particle swarm optimization (PSO) is used as the solving tool, which referring determined aim, the problem is defined and the objective function is introduced. Considering the fitness values sensitivity in PSO algorithm process, it is needed to apply load flow and harmonic calculations for decision-making. Finally, the feasibility of the proposed method is demonstrated for typical distribution network, and it is compared with the GA method in terms of the solution quality and computation efficiency. The experimental results show that the proposed PSO method is indeed capable of obtaining higher quality solutions efficiently.