Improved Residential Distribution System Harmonic Compensation Scheme Using Power Electronics Interfaced DGs

The reliability and cost of any electrical system depends greatly on the quality of the power supplied to and consumed by the system. The electrical utilities are very much concerned about the power quality due to the presence of nonlinear loads in their power distribution systems. The Non linear residential loads cause harmonics in the residential distribution systems. To mitigate the harmonics, active or passive filters are normally used. In the recent years there is an increase in the installation of the Distributed Generation (DG) systems in the residential areas. Especially renewable energy based DG's such as Photovoltaic (PV), Wind, Biomass etc. are getting considerable interest and are installed in residential areas. These DG systems have DG-Grid interfacing converters and with the increased implementation of DG systems the use of interfacing converters to reduce the harmonics was proposed. In this paper, the use of PV interfacing inverters was considered. The concept of virtual harmonic damping impedance for the control of PV interfacing inverters was proposed for improving the power quality of the residential distribution system. The residential load and DG systems were modeled and compensation of the current harmonics in the system by using the virtual harmonic damping impedance concept was carried out. These were analyzed and verified using simulations.

To manage the microgrid effectively, it is important to get the power information among multiple distributed generation (DG) units. However, when the droop control method is adopted, as the corresponding DG units cannot be simply modeled as VF or PQ buses, the conventional power flow algorithm may become inapplicable. To solve this issue, a time domain iteration (TDI) based power flow algorithm is hereby proposed. Firstly, a microgrid model is prepared, containing a network model and several DG unit models. Then, the proposed TDI is executed for power flow calculation, which mimics the real-time operation of microgrids. In each iteration, the DG unit models input voltages and currents to the network model; then the network model changes its state accordingly and feeds related parameters back to those DG unit models. As the DG unit models simulate the behavior of actual DG units, the proposed algorithm is not limited to the droop control governed microgrids. Moreover, as the TDI has definite physical meaning, convergence problems can be avoided. Finally, the validity of the proposed power flow algorithm is verified through the Matlab simulation results from an 8-bus microgrid system.

In electrical systems the most critical disturbance is the interruption of the power service. However, the main concern for many commercial and industrial users is the mal-operation produced by voltage sags. This paper presents a study about performance of a distribution system in presence of voltage sags using a distribution generation (DG) unit and a distribution static compensator (DSTATCOM). The analysis is performed by using a stochastic generation of disturbances method and ATP/EMTP software tool. Several case studies in the IEEE-13 bus test feeder taking to account different DG locations and penetration levels for DG unit are presented. In addition, the relation between the injected DSTATCOM reactive power, the type of sag and the location of affected nodes is considered. Simulations show that for IEEE-13 system the DSTATCOM is the best alternative for sags mitigation. However, the DG unit is an alternative that can be considered in larger distribution systems to reduce the effects of voltage sags.

This paper discusses harmonic compensation schemes using distributed generation (DG) units. As most DG units are connected to the grid with interfacing converters, the harmonic compensation functions can be realized through flexible control of these converters. Both current controlled and voltage controlled DG systems are considered in this paper. Details on how to implement the harmonic compensation function on those systems are presented. Additionally, the recently proposed hybrid control method (HCM) is also discussed. It shows that the HCM has better performance and is more flexible. Selective simulated and experimental results are provided to verify the feasibility of the HCM approach.

Recent deployment of distributed generation has led to a revolution in distribution systems and the emergence of “smart grid” concepts. The smart grid mainly intends to facilitate integration of renewable energy sources and to achieve higher system reliability and efficiency. Different distributed generation types found in modern distribution systems can be classified into two main categories: intermittent- and dispatchable-based distributed generation; the latter has a unique capability of enabling successful islanding operation, thus improving system reliability. This article proposes a methodology for allocating dispatchable distributed generation units in distribution systems to economically improve system reliability. Distributed generation installation and operation costs are to be optimized against the reliability value, expressed as customers’ “willingness to pay” (WTP) to avoid power interruptions. Therefore, the main goal of this research work is to determine the optimal combination between distributed generation units to be installed and loads to be shed during all possible contingencies. A probabilistic load model is adopted to determine the optimal size of allocated distributed generation units.

A large petrochemical company installed nearly 50 000 hp of electrical submersible pumps (ESPs) at an existing midwest U.S. oil field. Being equipped with adjustable-speed drives (ASDs), these ESPs introduced high levels of current harmonic distortion, which resulted in 14%-19% voltage harmonic distortion at the electrical utility supply. Initially, the utility noticed the low power factor (PF) and had the oil company pay for the installation of power factor correction (PFC) capacitors on their medium-voltage supply. Once installed, the utility began to have problems with these capacitors and continued to receive complaints from other customers adjacent to the oil field; thus, they enforced harmonic limits, as defined by IEEE Std 519, at all points of common coupling. Measurements were made with a harmonic analyzer at several locations throughout the electrical system to quantify harmonics and determine the effect the ESPs were having on the utility distribution system. Computer simulations were performed to analyze different methods of harmonic mitigation. Ultimately, passive harmonic filters were installed on all ESPs in phases. In addition, the PFC capacitors were permanently disconnected after determining that a power system resonance condition existed. Once all phases of the project were complete, the voltage distortion level decreased to below 5%, and PF improved to near unity without the PFC capacitors. This paper will describe the effect of harmonics on the electrical distribution system caused by ASDs, practical solutions to excessive voltage harmonic distortion, resonance issues with PFC capacitors, and the challenges associated with different methods of harmonic mitigation.

A large Petrochemical company installed nearly 50,000 HP of electrical submersible pumps (ESP's) at an existing midwest USA oil field. Being equipped with Adjustable Speed Drives (ASD's) these ESP's introduced high levels of current harmonic distortion which resulted in 14%-19% voltage harmonic distortion at the Electrical Utility supply. Initially, the Utility noticed the low power factor (PF) and had the Oil company pay for the installation of power factor correction (PFC) capacitors on their medium voltage (MV) supply. Once installed, the Utility began to have problems with these capacitors and continued to receive complaints from other customers adjacent to the oil field so they enforced harmonic limits, as defined by IEEE Std 519, at all points of common coupling. Measurements were made with a harmonic analyzer at several locations throughout the electrical system to quantify harmonics and determine the effect the ESP's were having on the Utility distribution system. Computer simulations were performed to analyze different methods of harmonic mitigation. Ultimately, passive harmonic filters were installed on all ESP's in phases. In addition, the PFC capacitors were permanently disconnected after determining that a power system resonance condition existed. Once all phases of the project were complete, the voltage distortion level decreased to below 5% and power factor improved to near unity without the PFC capacitors. This article will describe the effect of harmonics on the electrical distribution system caused by ASD's, practical solutions to excessive voltage harmonic distortion, resonance issues with PFC capacitors and the challenges associated with different methods of harmonic mitigation.

Renewable Energy Resources (RES) can supply a clean and a smart solution to satisfy the rapidly growing load demand. The Photovoltaic (PV) and wind turbines are considered as resources of Distributed Generation (DG). The integration of PV - DG units into distribution systems has a significant effect on reducing the system active power losses. In this paper, a new technique based on the Moth Flame Optimization (MFO) algorithm, is used to optimally allocate the PV -DG units in Radial Distribution Systems (RDSs) and determine the optimal size of each unit. The objective of the technique is to minimize the total active power losses of the system, while satisfying several operating constraints. The proposed optimization algorithm is tested using three different IEEE standard RDSs of various sizes, which are 33, 69 and 118-bus systems. In order to demonstrate the applicability and the performance of the MFO algorithm, numerical simulations are obtained when applying the MFO algorithm, and compared with different existing optimization techniques. This comparison shows the validity of the proposed MFO algorithm.

Reliability assessment is of primary importance in designing and planning distribution systems that operate in an economical manner with minimal interruption of customer loads. Distributed generation (DG) is expected to play an increasing role in emerging power systems because they use different type of resources and technologies to serve energy to power systems. DG is expected to improve the system reliability as its backup generation. Since DG units are subject to failures as all other generation units, the random behavior of these units must be taken into account in the analysis. Existence of DG units in a distribution system will effect on restoration time of load points. In this paper, an algorithm for assessing restoration time of load points for a radial distribution system with back up DG units is presented. The Impacts of DG units, their location, number of DG units in each location and their availability, on distribution system reliability are investigated using a real distribution network in Tehran utility/Iran.

Purpose This paper aims to propose, the multi-objective method for optimal planning and operation of distributed generators (DGs) on distribution system (DS) using hybrid technique is proposed. Design/methodology/approach The proposed hybrid technique denotes hybrid wrapper of black widow optimization algorithm (BWOA) and bear smell search algorithm (BSSA). BWOA accelerates the convergence speed with combination of the search strategy of BSSA; hence, it is named as improved black widow-bear smell search algorithm (IBWBSA) technique. Findings The multiple-objective operation denotes reducing generation cost, power loss, voltage deviation with optimally planning and operating the DS. For setting up the DG units on DS, IBWBSA technique is equipped to simultaneously reconfigure and find the optimal areas. Originality/value In this planning model, the constraints are power balance, obvious power flow limit, bus voltage, distribution substation’s capacity and cost. Then, proposed multiple-objective hybrid method to plan electrical distribution scheme is executed in the MATLAB/Simulink work site.

The use of Distributed Generators (DGs) in distribution system has increased at fast pace in recent times. These DGs can work both as grid connected or standalone mode. Thus when it comes to DG placement, getting the optimal location for its placement and the optimal sizing becomes very important. In this paper, finding the optimal location and optimal size of DGs is dealt keeping active power loss as the objective, considering different load models. A novel method called Backtracking Search Optimization Algorithm is used to find the most significant positions for DG placement. DGs supplying both active and reactive power have been studied. Case studies have been done about the effect of 1, 2 or 3 DGs on the IEEE 69 bus test system for DGs operating at 0.85 pf. on different load models.

This paper presents a new framework to analyze the penetration of distributed generation (DG) in distribution systems (DS) based on modified Monte Carlo simulation. The placement and capacity of DG are generated as random variables with probability density functions following the optimality principle of the system. The method of power flows analysis is employed to evaluate the economic and technical aspect of the network both with and without DG sources inside. The results in different scenarios are combined with weighted factors to form the performance indices. The proposed framework is testified in a practical 15 MVA, 22 kV, 48-bus DS in Thai Nguyen, Vietnam. The simulation result shows that many advantages can be achieved with DG such as lower power losses, smaller voltage deviation, over-load reduction, etc. The proposed framework can serve as a platform for DS planning with DG sources in practice.

Voltage regulation in the distribution networks becomes more challenging when the distribution generation (DG) units are introduced. The reasons behind that are: the reverse power flow which is introduced by the DG units, in addition to the probabilistic nature of the generated power due to renewable-based DG units. In this paper, a fuzzy algorithm is proposed to provide an adaptive reference of the OLTC controller, such that the OLTC, which feeds a multiple feeders, can mitigate the effect of the high penetration of the DG units. The motivations behind using the fuzzy logic are: 1) it can map nonlinear relations behind its inputs and output; and 2) it can provide a smooth transition, which lead to a more relaxed tap operation compared to the conventional logic control. The proposed fuzzy algorithm is tested using a radial structure distribution network which is modeled using SIMULINK/MATLAB.

Control strategies of a microgrid which includes both synchronous generators and converter-based distribution generation (DG) units must be designed such that effective operation of the microgrid is achieved. The main objective of this paper is to develop a high performance control strategy for an islanded medium voltage (MV) microgrid consisting of inverter and non-inverter interfaced DG units. A new control method for the synchronous generator in an islanded microgrid is proposed based on a virtual droop scheme. The proposed strategy can effectively manage the real and reactive powers of the microgrid among the inverter and non-inverter based DG units. The steady state and dynamic responses of the MV microgrid is significantly improved by using the proposed power management scheme. The performance of the proposed control strategy is verified by using digital time-domain simulation study in the PSCAD/EMTDC software environment.

With high penetration of power electronics-based distributed generation (DG) units, the decentralized control strategy based on droop control with virtual impedance has been widely studied in recent years. But the conventional virtual impedance cannot properly deal with the massively increasing of nonlinear loads. Therefore, an improved virtual impedance method based on second-order general-integrator (SOGI) is presented. Besides, a further value correction of reactive power in droop control is also proposed in this paper. The proposed approaches have been applied and verified in a parallel system formed by two DG units connected with nonlinear loads. The form of SOGI and derivative formula of corresponding virtual impedance in the system has been analyzed in detail. The obtained experimental results show the proposed approaches can achieve less output voltage and current distortion of DG units with nonlinear loads, and also realize good performance of power sharing.