The integration of the various types of distributed generators in low-voltage (LV) distribution networks becomes a great concern, especially the rooftop photovoltaic (PV) systems. The negative impacts of the rooftop PVs on the distribution feeder buses’ voltage include voltage rise and voltage unbalance (VU). Such a voltage-violation condition depends mainly on the PVs ratings and the network unbalance percentage. This study presents a review for different techniques used to mitigate the voltage violation resulting from PVs integration in a typical three-phase four-wire LV distribution network case study. The voltage-violation mitigation techniques studied in this study are enhancement of the feeder, on-load tap changer, demand-side management, active power curtailment, a reactive power control, static transfer switch, energy storage systems and hybrid strategies. The LV distribution network case study was modelled based on constant power model method using MATLAB software environment. The simulation results demonstrate both voltage regulation and alleviating VU capabilities of each technique.

With the increase in a number of online high-voltage direct current (HVDC) systems in China, a big question for their use as black-start and restoration of power system outages arises. Line-commutated converters (LCC)–HVDC systems can significantly reduce recovery time. The black-start-up and recovery conditions for LCC–HVDC systems and the connected AC systems are discussed in this study. The appropriate start-up and recovery modes are identified and the results of the control characteristics of LCC–HVDC systems are analysed in detail. The stability requirements of AC systems in terms of LCC–HVDC system effects are evaluated. Furthermore, the restoration using LCC–HVDC systems, including the priority sequence index of the multi-HVDC links and the optimisation model of the mentioned problem, is discussed in detail. Compared to the conventional black-start strategy, the applicability and effectiveness of the proposed method are illustrated using a part of the actual Guangzhou power system as a test system.

An optimal power routing (OPR) scheme between and within interlinking converters (ICs) in unbalanced hybrid AC–DC microgrids to minimise the power imbalance factor at the point of common coupling, active power losses, and voltage deviation indices for microgrids in grid-connected operating mode is proposed in this study. These goals are achieved through a multi-objective optimisation model by optimal distributing of mobile loads between available charging stations and at the same time, OPR within three phases of three-phase four-lag AC/DC converters. Numerical results obtained from implementing the proposed method on the modified IEEE 13-bus system, as an unbalanced hybrid microgrid, and IEEE 34-bus test system, as an unbalanced distribution system, demonstrate that proposed OPR algorithm is successful to satisfy the optimisation goals. For this purpose, four case studies are defined and studied to demonstrate the unique features of the proposed OPR comparing with other power routing schemes. In addition to simulation results, the OPR scheme between ICs is realistically implemented at Florida International University smart grid testbed to show the effect of the power routing on energy losses reduction.

Synchronous reference frame (SRF) control strategy for solar photovoltaic (SPV) sources is widely used to deliver maximum power to the grid. However, poor inertia support just after a disturbance and improper phase angle tracking in presence of the harmonics and system unbalance are noticed when the conventional phase-locked loop (PLL) based SRF control structure is used. In this study, an inertia enhancement method for inverter interfaced SPV sources is proposed, which adjusts only the PLL parameters with a notch filter (NF) in the SRF controller. NF in PLL is used due to its disturbance rejection potential and accurate phase angle tracking, even during system unbalance. The dynamic equation of pseudo induced voltage (PIV) vector with respect to the point of common coupling is derived. The kinematic equation of the PIV angle vector correlates inertia contribution and inverter terminal voltage. The impact of the change in PLL parameters on inertia enhancement is analyzed by validating the proposed technique on a test system in the real-time digital simulator. The frequency response by the proposed method has been compared with two state-of-art methods to prove the superiority of the proposed approach in enhancing the inertia of the SPV source in a microgrid.

Plug-in electric vehicles (PEVs) are gaining popularity as a solution to reduce greenhouse gas production. On the other hand, uncoordinated charging of PEVs is a reason for grid stress and increasing congestion, total power consumption (TPC) and distribution lines and transformers losses. Moreover, single-phase connection of electric vehicles in residential buildings causes line current imbalance and it has more negative effects on TPC and power losses. Thus, they are characterised as unbalanced loads with random locations, plug-in times, charging rates, and durations. Hence, a charging coordination algorithm is proposed to utilise the integration of PEVs in both operational modes (grid-to-vehicle, vehicle-to-grid) to guarantee power loss reduction, voltage profile maintaining and load current balancing. The introduced algorithm can perform an optimal calculation to determine proper phase for PEVs in distribution feeders and decline the unbalancing by deploying a new device called phase switcher which is in series with chargers in residential buildings. The phase switcher is connected to the smart load management centre which uses the proposed algorithm to determine the proper phase for connection or disconnection of PEVs and finding the appropriate numbers of PEVs. To show the effectiveness of the proposed algorithm, simulation results are provided.

Reliability evaluation of bulk power systems (BPSs) has inherent computational complexity due to the numerous system states and the time-consuming system state analysis, including power flow calculation, load curtailment, recognition of split power systems and network reconfiguration. In this study, a novel uniform-design based method is proposed to improve the computational efficiency of power system reliability evaluation. The main idea is that the uniform-design technique is used to generate the system states in reliability evaluation, which makes the sampled states more uniform and representative in the overall state space compared to the enumerated system states in an analytical method or the random-generated system states in Monte Carlo simulation. As a result, the sample size and the computational time can be significantly reduced. In addition, the confidence intervals of the reliability indices, such as LOLP, FLOL and EENS, are given. And the estimation errors of reliability indices are discussed. The proposed method is tested on several BPSs, including the IEEE-RTS79, IEEE-RTS96 and a real BPS in China. All the case studies indicate that the proposed technique can significantly improve the computational efficiency of BPS reliability evaluation.

As an islanded multi-microgrid (IMMG) receives little support from the main network, it is necessary to develop new dispatch frameworks to fulfil its real-time dispatch requirement. Hence, a decentralised collaborative dispatch framework of IMMG based on multi-agent consensus algorithm is proposed. In the framework, the ttal power command of IMMG can be optimally allocated among all the microgrids (MGs) based on consensus algorithm. Then the power command of each MG can be efficiently allocated among all the dispatchable units based on the proposed priority-based collaborative dispatch strategy. Based on the decentralised collaborative dispatch framework, in order to optimise the planning and operation of dispatchable active power resources (DAPRs), on one hand, a bi-level model that couples the planning and operation problems of an IMMG is established to optimise the configuration of DAPR; on the other hand, more detailed models are proposed for the regulation costs of various dispatchable units, which is an improvement over the existing regulation cost model. By considering the two aspects, the consensus algorithm is embedded in multiple population genetic algorithm to solve the bi-level model. Case studies are conducted on an IMMG consisting of three MGs to examine the effectiveness of the proposed planning and dispatch model.

This paper proposes a layered stochastic optimization approach for residential demand response (DR) under real-time pricing (RTP) and an incentive-based mechanism, which contains three steps. In the first layer, an independent system operator (ISO) announces day-ahead RTP to a residential load aggregator (RLA). The RLA predicts individual household loads (step 1) and aggregates the loads to minimize electrical cost (step 2). In the second layer, the RLA announces incentives to homes, and home energy management systems (EMS) control the loads to maximize the reward in real-time (step 3). In Step 1, probability based individual load prediction models are developed. In Step 2, a stochastic optimization model is developed to aggregate controllable loads of residential consumers. In Step 3, an incentive-based mechanism is proposed, based on which, a real-time load control model for individual homes is developed to benefit the RLA and homeowners. A highly efficient real-time control algorithm for home EMS is developed. The case studies show that, with 10% controllable energy integration, the peak demand is reduced by 17.5% and the energy cost of the controllable loads is reduced by 28%. The proposed mechanism can effectively aggregate many individual residential controllable loads to participate in an electricity market.

This study proposes a novel fault tolerant voltage control method considering actuator faults and disturbances by using the backstepping control augmented by a new differentiator for islanded microgrids (MGs). Existing voltage control methods are designed based on the ideal condition that the distributed generations' actuators work healthily with the assumption of the absence of faults and disturbances, whereas MGs are exposed to the actuator faults including partial loss of effectiveness and biased faults. The proposed controller robustly regulates the MG voltages irrespective of the actuator faults. In contrast to existing methods, the controller has considered both actuator faults and loads with harmonic/interharmonic currents, which does not need to know the exact model of faults and frequency of harmonic and interharmonic of MG loads. This feature enables the MG to work properly, even at the lowest level, instead of the system completely collapsing. Therefore, it improves the reliability of the MG system. The MATLAB/SimPowerSystems toolbox has verified the validity of the proposed fault tolerant control method. Compared with effective methods, both the theoretical and simulation results show that the proposed method has better, robust, resilient, acceptable, and desirable performance, with respect to the unknown faults, actuator faults, non-linear loads, and disturbances.

Ultra high voltage direct current (UHVDC) transmission under hierarchical infeed mode (HIM) embedded into AC networks with diverse voltage levels (500 and 1000 kV) has been used by energy utilities for bulk power transfer. It has some dynamic characteristics challenges such as commutation failures under certain faults at inverter station. The installation of reactive power compensators (RPCs) such as synchronous condenser and static synchronous compensator at inverter's end can support the AC grid to mitigate commutation failures, which can ultimately result in the improved dynamic characteristics of UHVDC-HIM system. There is a need for analytical index that can accurately indicate the AC system's strength of UHVDC-HIM system with consideration of impact from RPCs and the interaction between AC networks. In this study, the resulting improvement in dynamic characteristics is quantified by proposed ‘equivalent hierarchical mode short circuit ratio’ (EHMSCR) index. An equivalent model of UHVDC-HIM system with AC system's strength modified via EHMSCR is established in PSCAD/EMTDC in order to assess the application of proposed index. Then, three different cases are carried out to further validate the accuracy of EHMSCR index. The results indicate that EHMSCR can accurately evaluate the AC system's strength of UHVDC-HIM system with RPCs.

Voltage source converter (VSC)-based high-voltage dc (HVDC) transmission is widely utilised nowadays. However, a VSC-HVDC connected to a weak ac system still faces the problem of phase-locked loop (PLL) synchronisation. To tackle this problem, this study proposes a dc voltage synchronisation control (DCSC) based on the power synchronisation control and the power balance equation of the virtual synchronous generator. To analyse the dynamic stability of DCSC, voltage sensitivity indicator (VSI) is used to reflect the voltage fluctuations. Considering the deviations of dc voltage and converter losses, a closed-loop transfer function of dc voltage is designed. Three important parameters including VSI, virtual damping coefficient and inertia time constant are investigated. The dynamic stability analysis shows DCSC has strong controllability. Then, a three terminals VSC-MTDC model is simulated in PSCAD/EMTDC. Herein, DCSC is used in one inverter and PLL is used in another inverter. The waveforms obtained by using DCSC are compared with that by using PLL. Simulation results clearly depict that the inverter with DCSC has a normal steady state and a better transient response than using PLL when connected to a strong ac system, also provides better power transfer capability when connected to a weak ac system.

In recent years, sub-synchronous oscillations have occurred frequently. Torsional interactions may cause oscillations in turbo-generator rotor shafts and thus huge losses. Conventional studies focus on the damping of system oscillation modes, but little on the damping of components, which could aid in finding out the source of a poorly damped or undamped oscillation. This study aims at a quantitative evaluation method of the damping characteristics of each component in torsional interaction. The transient energy flow method successfully applied in component damping evaluation and source location of low-frequency and ultra-low-frequency oscillations is further developed for that of sub-synchronous oscillation. The transient energy flow method evaluates the damping of a component by its dissipation rate of transient energy. A method of computing the transient energy flow in sub-synchronous oscillation is proposed. It is found that the rate of energy flow is relevant to the difference between the super-synchronous and sub-synchronous powers. The relation between the transient energy dissipation and the damping of a component is validated by both mathematical deduction and simulation results. The transient energy flow method can evaluate component damping and therefore locate oscillation sources effectively in sub-synchronous oscillation.

Accurate renewable energy generation and electricity demand forecasting tools constitute an essential part of the energy management system functions in microgrids. This study proposes a hybrid approach for short-term load forecasting in microgrids, which integrates empirical mode decomposition (EMD), particle swarm optimisation (PSO) and adaptive network-based fuzzy inference systems (ANFISs). The proposed technique first employs EMD to decompose the complicated load data series into a set of several intrinsic mode functions (IMFs) and a residue, and PSO algorithm is then used to optimise an ANFIS model for each IMF component and the residue. The final short-term electric load forecast value could be obtained by summing up the prediction results from each component model. The performance of the proposed model is examined using load demand dataset of a case study microgrid in Beijing and is compared with four other forecasting methods using the same dataset. The results show that the proposed approach yielded superior performance for short-term forecasting of microgrid load demand compared with the other methods.

This paper is intended to give an effective coordination method between high penetration of plug in electric vehicles (PEVs) and optimal operation management (OOM) of distribution network problem. An effective fuzzy logic controller (FLC) is proposed which focuses on coordinated smart charge/discharge control of high penetration of PEVs with OOM in an iterative optimization process. In each iteration, the proposed FLC receives the voltage of the connection node of the PEVs, the remaining time to the peak load and the available energy of the PEVs while appropriately specifies the amount of absorbed or injected active power of the PEVs. This coordination leads to the minimization of the electric network losses, voltage flattening and reducing the produced pollutant. A modified version of Sine-Cosine Algorithm (MSCA) is used to minimize the objective functions while the problem constraints are satisfied. An appropriate 33-bus distribution network with 1000 PEVs in 100 groups is considered in order to show the authenticity and efficiency of this work. The results show that the proposed FLC-based coordination procedure could effectively adjust the exchange power of the PEVs with the OOM decision variables in an acceptable time duration.

Voltage magnitude and sag duration are known as acknowledged basic voltage sag characteristics in the last decades. However, these values cannot meet the demands of waveform analysis in the modern smart grid. Therefore, voltage sag multi-dimension characterisation is required to extract more essential information from measured waveforms. This study focuses on the unsolved issue that how to obtain required characteristics from voltage sag waveforms effectively. Overall, multi-dimension characterisation method contains several parts: voltage sag detection, segmentation and characteristics calculation. Fundamental voltage magnitude and phase angle, obtained by the proposed adaptive generalised morphology filter, are segmented in several parts. Then, a set of characteristics are calculated to characterise the voltage sag waveform in a multi-dimensional way. Performance of the proposed method is validated by synthetic and measured waveforms. Results show that both detection and segmentation methods have better performance than existing typical methods, and multi-dimension characteristics can be extracted from waveforms accurately. Moreover, the proposed method can be implemented in power quality monitoring system to support further sag studies.

The rapid growth in load demand results in higher line loses in distribution systems and also demands distribution system augmentation. Apart from this, due to fluctuating loads, it becomes a challenge for the utility sectors to maintain voltage stability of the system under healthy condition. For addressing such problems, simultaneous optimal placement of distributed generations (DGs) and capacitors in radial distribution systems employing multi-objective optimisation technique based approach is explored in this work. In line with this, the present work uses a simple and powerful multi-objective strength Pareto evolutionary algorithm 2 (SPEA2) for solving distributed generator and capacitor placement problem considering load uncertainty. The uncertainty characteristics of load are designed by probabilistic approach and the same is utilised during the optimisation process. Thereafter, a set of non-dominated Pareto optimal solution is obtained according to the objective function value. A compromised solution is selected from the set of Pareto optimal solutions by using fuzzy set theory. Along with the above, the impact of reverse power flow is studied by taking different test cases. The studied algorithm has been tested on different standard IEEE 33-bus and 69-bus radial distribution test systems.

Accurate transmission line parameters values are of high importance in setting protection relays and rigorous locating faults that may occur along the transmission network. For this purpose, the work reported in this study presents a new technique for the delicate determination of transmission lines parameters that are uniformly distributed along the line length. The developed technique is able to approximate the steady-state profiles for the transmission line voltage and current as a function of time and line length by given sets of polynomials that, in turn, are substituted in model equations. Synchronised time-domain data, recorded from both line terminals, are utilised as boundary conditions for the distributed-parameter transmission line model. The well-known Galerkin method is adopted to transform the line model into a system of non-linear algebraic equations to be solved. This system of algebraic equations is converted to residuals that are consequently regrouped in a cost function to be optimised. Thereby, the series resistance, series inductance and the shunt capacitance per line length are the parameters minimising the cost function. Both simulations and calculation are performed with MATLAB software. The obtained results show the effectiveness and accuracy of the new approach.

In this study, the design and implementation of a new hybrid soft computing control technique called Levenberg–Marquardt backpropagation (LMBP)-based icosϕ is proposed. Two different compensation techniques are evaluated for the performance analysis of three-phase three-wire (3P3W) voltage source converter (VSC)-based DSTATCOM. The first one is the conventional icosϕ control technique whereas the other one is called the LMBP-based icosϕ control technique. The better power quality of the system is obtained using the proposed control algorithm by maintaining a less voltage across the capacitor as compared to the conventional one. So, the reduction in the size of the DSTATCOM is realised by the LMBP-based control algorithm. Furthermore, the performance parameters such as load balancing, harmonics elimination, power factor improvement, and voltage regulation are evaluated under both balanced and unbalanced loading conditions as per the IEEE guidelines. The effectiveness of the proposed controller is studied in the MATLAB/Simulink environment and also validated with a low power rated prototype experimental results.