Study of distribution system surge and harmonic characteristics. Final report

Harmonic interference problems generated by bulk semiconductor power converters become more serious in power systems as they are widely used in industrial applications. Shunt passive filters consisting of LC tuned filters or shunt active filters using PWM inverters have been used to suppress harmonic currents in distribution systems. In order to install the passive or active filters, it is necessary to exactly find a dominant harmonic source in distribution feeders. A harmonic power on each phase and order at a receiving terminal has been investigated by using a digital power meter including an FFT analyzer. However, the conventional detection method has such a problem that it is difficult to exactly discuss harmonic power flow because the detected harmonic power is much smaller compared with a fundamental active power at the receiving terminal. In this paper, the harmonic power in three phases, which can be detected on real time, is defined by applying the pq theory. Next, it is verified by a digital simulation that the proposed method can discuss harmonic flows more easily than the conventional method. As a result, it is more simple and precise to find the harmonic source. Moreover, measurement errors of the harmonic power is revealed quantitatively, and the validity of the proposed method is demonstrated by digital simulation.

Power Line Communication is becoming more common each passing day. Narrowband Power Line Communication systems use a frequency range from 3 kHz to 500 kHz. Nonlinear loads are common in residences and unfortunately they produce harmonics. It is possible that some harmonics produced by the nonlinear loads may interact with the power line communication system. AC dimmers produce impulse noise. In this study, Fourier series of an AC chopper is computed and its current harmonics magnitudes which is in Narrowband Power Line Communication frequencies are examined with and without a smoothing inductor. Their harmonic magnitudes in the power line communication frequencies are compared. It has been found that the smoothing inductor performs well to decrease the AC chopper harmonics within the Narrowband power line frequencies.

This paper proposes a multi-objective benefit function for operation of active distribution systems considering demand response program (DRP) and energy storage system (ESS). In the active distribution system, active network management (ANM) is applied so that the distribution system equipment is controlled in real-time status based on the real-time measurements of system parameters (voltages and currents). The multi-objective optimization problem is solved using ε-constraint method, and a fuzzy satisfying approach has been employed to select the best compromise solution. Two different objective functions are considered as follows: benefit maximization of distribution company (DisCo); benefit maximization of distributed generation owner (DGO). To increase the benefits and efficient implementation of distributed generation (DG), DGO has installed battery as energy storage system (ESS) in parallel with DG unit. Consequently, DGO decides for the battery charging/discharging. DisCo has the ability to exchange energy with the upstream network and DGO. Also, DisCo focuses to study the effect of demand response program (DRP) on total benefit function and consequently its influence on the load profile has been discussed. This model is successfully applied to a 33-bus radial distribution network.

Loss minimization of distribution systems with hybrid AC and DC multi-microgrids is one of the main tasks in operation of active distribution systems. This paper presents a coordinated loss minimization scheme for distribution system including multiple AC/DC microgrids with high penetration of distributed energy resources (DERs). The coordination is conducted using a non-cooperative coordination framework in which the agents i.e. distribution system operator (DSO) and micro-grids managers (MGOs), selfishly minimize power losses of their sub-systems. However, they interact with each other to modify their solutions until an equilibrium is obtained in which each agent reach a satisfactory value for the power loss of its relevant network. The proposed scheme is modeled as a decentralized optimization problem which decomposes the whole problem into DSO and MGOs sub-problems which are coordinated through exchanging only boundary information. Thus, the computational and communicational burdens are reduced and data privacy of agents is preserved while matching all boundary variables. The exchanged boundary variables between DSO and each AC microgrid are active and reactive powers and voltage magnitude and angle whereas DC micro-grids exchange active power and voltage with DSO. The effectiveness and high computational performance of the proposed decentralized non-cooperative scheme is verified by various simulations on a modified 69-bus distribution system consisting of some AC and DC micro-grids.

Due to the increased use of power electronic converters, power system harmonics are becoming one of the major problems facing the electric utility industry. These serious problems have led to the development of many techniques for their analysis and evaluation. There are many computer programs for calculating harmonic propagation in a power system when the harmonic source is known. These computer techniques are completely ineffective when the source of the harmonics is not known. This paper presents a reverse power flow procedure to identify the sources of harmonic signals in electric power systems. A computer program called HARMFIND has been developed. This program helps the user to identify the source and type of harmonics in a given power system without performing much measurement. The results indicate that this program can be used to identify the type and location of harmonic sources in distribution systems. The accuracy of the program has been demonstrated and compared with harmonic power flow programs.

This article deals with experience gained on vacuum switchgear for use in distribution systems. Part of that experience is based on a very wide range of tests carried out in test laboratories and confirmed by experience in various types of service

Uncoordinated charging of EVs may result in overloading, increased losses and voltage deviations in distribution system. In this context, coordinated charging of EVs by parking lot operator (PLO) is a potential solution these problems. PLO coordinates charging of EVs during low electricity prices to avail monitory benefits. However, charging of EVs during low electricity prices results in unusual peaks which may adversely affect the operation of distribution system. Therefore, coordinated scheduling of EVs by PLO considering operational constraints of distribution system is essential. To this end, this study proposes a hierarchical framework of coordination between PLO and distribution system operator (DSO) for scheduling of EVs. In the hierarchy, PLO coordinates the charging demand of EVs to minimizing the charging cost. Thereafter, optimal operation of distribution system is considered at DSO level with EVs load demand obtained from PLO. If the operational constraints of distribution system are violated, DSO determines the load boundaries for EVs load and communicates to PLO. Finally, PLO allocates the charging demand to EVs considering the load boundaries suggested by DSO. The proposed methodology is validated on 33-bus radial distribution system. Simulation results indicate that proposed approach results in efficient operation of distribution system while minimizing charging cost to PLO.

This novel automated fault isolation system has been developed and integrated into a new customer side distribution system of 415/240V. The distribution system is based on the Tenaga Nasional Berhad (TNB), the Malaysia's power utility company especially the distribution system. Supervisory Control and Data Acquisition (SCADA), Remote Terminal Unit (RTUs) and power line communication (PLC) system have been used and developed for detecting, fault locating, fault isolating, fault segregating and power restoration in terms of hardware and software. Open loop distribution system is the distribution configuration system used as TNB distribution system. It is the first distribution automation system (DAS) based on fault management research work on customer side substation for operating and controlling betweenthe consumer side system and the substation.

A competitive decentralized framework for Volt-VAr optimization of transmission and distribution systems with high penetration of distributed energy resources

The paper presents a methodology proposal for testing and evaluation of communication systems in Smart Grids, especially for Power Line Communication (PLC) systems. The PLC technology is widely used in power grid as a part of Advanced Metering Infrastructure (AMI) allowing mainly data transfers between a management system at utility and customer-premises smart meters. However, the PLC technology on medium voltage (MV) lines is often used for remote control and monitoring of distribution transformers as well. Since power grid and consequently power lines have different transmission parameters affected by their placement and potentially burdened by interferences, the PLC systems have to be evaluated on site before placed to production. In this paper, authors propose a methodology for long-term benchmarking of the PLC systems using newly developed testing tools. The methodology is subsequently tested on real power grid and a selection of results is presented.

Recently, non-linear loads have diversified and increased. It results in deterioration of power quality on a distribution system, since the equipment, which includes the non-linear loads, generates harmonics. The harmonics cause not only deterioration of power quality but also further various problems. Nowadays, the state of harmonics is becoming evident by the recent researches. However, since the harmonic analysis by using a detailed model of distribution system is too difficult, the analysis is carried out by a simplified model. In this paper, the authors construct an analytical distribution system model in consideration of the non-linear loads with the harmonic sources based on the practical data. Moreover, the influence analyses of harmonics are carried out by using this model. In addition, the authors estimate the harmonic sources in the simplified distribution system.

Most of the electric equipment used in low voltage distribution systems have a single phase rectifier at the front end of their internal circuits to convert the alternating current (ac) supply into direct current (dc). If these equipment can directly be powered by a suitable dc supply, overall efficiency can be improved and harmonics can be reduced. In this paper the performance of a hybrid distribution system which accommodates both ac and dc loads is analyzed. A harmonic power recovery scheme is incorporated into the network to recover the harmonic power which is usually wasted in the primary delta winding of distribution transformer. The effectiveness of the system is validated by simulation on SIMULINK/MATLAB platform.

The importance of probabilistic assessment in distribution systems is very high due to the increasing penetration of renewable energy sources (RESs) with their fluctuating behavior. Also, there are some other uncertain variables in distribution systems such as loads fluctuations. More awareness of the system state by considering many uncertainties provides more certainty in decision making and causes better risk management. Moreover, the distribution static compensator (DSTATCOM) has been recently implemented due to its efficient abilities in the distribution systems operation especially when RESs are integrated into them. This article investigates the probabilistic assessment of DSTATCOM operation in a distribution system using the k-means-based data clustering method (DCM). The uncertainty of load demands, wind speed, and solar radiation are considered in this study. The performance of DCM is compared to the Monte Carlo simulation (MCS) and Latin Hypercube sampling (LHS) methods in terms of accuracy and computational burden. The efficiency of k-means-based DCM is investigated in the IEEE 69-node test system.

Harmonic voltages and currents are created by nonlinear loads in power systems. These harmonics can cause serious problems to the energy suppliers (utility companies) and energy users (consumers). This dissertation presents new techniques for harmonic measurement and the accompanying problem, harmonic reduction. To reduce harmonics, the location and magnitude of harmonic sources must be known a priori. However, to measure and monitor harmonic sources requires specialized instrumentation that is not generally permanently installed at most buses. In this study, a method is developed to use neural networks in conjunction with state estimation for monitoring and estimating harmonic sources with only a few permanent instruments. The method can also identify and monitor a "suspected" harmonic source that has not previously been measured. Once harmonic sources are known, the objective from an energy supplier's point of view is to minimize the combined total harmonic distortion of all buses on a distribution system. A procedure is developed for designing optimum filters on distribution feeders that have distributed and balanced or unbalanced harmonic sources and variable compensating capacitors. The design includes finding optimum filter admittances and the corresponding locations. Symmetrical components are used for the unbalanced harmonic source case. Filter realization with the lowest cost including sensitivity analysis is also discussed. The optimum filters chosen and placed in this manner may produce results superior to the conventional filter design procedures. The problem of harmonic reduction is alternatively approached as an energy user's problem. The user's objective is to eliminate his voltage harmonic distortion problem locally without considering the effects of voltage distortion at neighboring buses. The remedy is insertion of a reactor in series with the local compensating capacitor. A method is presented for finding the optimum fixed LC combination to minimize voltage harmonic distortion at a load bus while holding the displacement factor (fundamental power factor) at a desired value and constraining the total cost of the compensating equipment. Source harmonics and impedances are represented as randomly time-varying quantities.

The AGGREGATE project team successfully developed and validated various modules for outage management. Brief summaries of each module are provided to showcase their strength for outage management and restoration for a distribution system with a high penetration of connected distribution energy resources (DERs).In recent years, inverter-based DERs have been widely deployed in distribution system. A most of behind-the-meter (BTM) solar power generation is not visible to the utility. The data-driven DER and load estimation modules are using machine learning (ML) and artificial intelligence (AI) to manage this issue, which provides an opportunity for distribution system operators (DSOs) to operate systems and make decisions in real-time for a distribution system with a high penetration of DERs deployed. Also, the estimated DER and true load can be further leveraged in network aggregation and cold-load pick up estimation for reducing the computing complexity and providing for fast restoration. After load demand and DER power generations have been estimated, the information will support topology and state estimation(SE). The topology estimation module demonstrated the viability of mixed integer linear programming (MILP) formulation to estimate the most likely operational radial topology and outage sections using power flow measurements, historical/estimated load and DERs data and smart meter ping measurements. Formulation includes continuous (power flow, load and DERs data) and binary measurements (smart meter ping measurements) in a single formulation. Errors in continuous data and binary data are modeled as normal distribution and Bernoulli distribution, respectively. In the future distribution grid, the power injection from controllable DERs will be essential for efficient and resilient grid operation. However, determining the optimal DER injections and restoration actions is dependent on knowledge of the system states. State estimation (SE), already the cornerstone of transmission energy management systems, will become commonplace in distribution management systems as more measurements become available from deployment of automated metering infrastructure (AMI). Observability analysis is the first step in SE, as it determines the sufficiency of the available measurements for accurately estimating the current system states. A new type of pseudo-measurement called a Correlational Measurement (CM) is introduced in this module, to enhance the observability of the system to enable more accurate SE. CMs encapsulate knowledge of correlation between demand patterns for similar classes of loads as well as injection patterns for same-technology renewable DERs. During grid contingency scenarios, DERs have been traditionally disconnected, without any fault ride-through capabilities. However, with new regulations and better technology, it is feasible for these resources to contribute to the grid’s restoration after an adverse event and hence enhance resilience. The controllability module proposes a two-step restoration scheme for the power system restoration process by leveraging additional degrees of freedom in power electronics interfaced DERs for mitigating voltage problems. In a resilience mode without the utility system, the distribution grid relies on DERs to serve critical load. In such a severe event with multiple faults on the distribution feeders, actuation of various protective devices (PDs) divides the distribution system into electrical islands. The undetected actuated PDs due to fault current contributions from DERs can delay the restoration process, thereby reducing the system resilience. The Advanced Outage Management (AOM) and the Advanced Feeder Restoration (AFR) modules developed in this project provide improved system resilience with multiple DERs. AOM identifies the faulted sections and actuated PDs in a distribution system with DERs by incorporating smart meter data. The most credible outage scenario including fault locations, PD actuations, and fault indicator (FI) failures is identified by a set of binary integer linear programming incorporating hypotheses. The AFR module serves to restore a distribution system with available energy resources taking into consideration the availability of utility sources and DERs. By partitioning the system into islands, critical load will be served with the available generation resources within islands based on the solution of a MILP. When the utility systems become available, the optimal path will be determined by a spanning tree search algorithm that reconnects these islands back to substations and restores the remaining load. The transmission and distribution (T&D) co-simulation module was used to validate the effect of a control action performed on the distribution side assets as it propagates to the transmission side. This ensures that the control action performed results in a feasible operating point on both the transmission and the distribution system. In addition to validation, the team used the T&D co-simulation module to demonstrate how distribution system assets can be used to mitigate issues on the transmission system. Specifically, the team demonstrated that appropriate switching operations on the distribution side can alleviate the line overload condition on the transmission side without causing new operational constraint violations.