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Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The AC power system strength exhibits time-varying characteristics during operation, thereby affecting the filtering performance of filters in the system. Failure to account for this variability may result in the harmonic levels exceeding permissible limits under specific power system strength, thereby affecting the normal operation of the power system. Consequently, building upon the existing filtering technique based on parallel-connected fixed capacitors for LCC-HVDC systems, a method for tuning the parameters of parallel-connected capacitors is proposed, thereby the capacitance range meets the filtering requirements under various system strengths. [ABSTRACT FROM AUTHOR]

The AC power system strength exhibits time-varying characteristics during operation, thereby affecting the filtering performance of filters in the system. Failure to account for this variability may result in the harmonic levels exceeding permissible limits under specific power system strength, thereby affecting the normal operation of the power system. Consequently, building upon the existing filtering technique based on parallel-connected fixed capacitors for LCC-HVDC systems, a method for tuning the parameters of parallel-connected capacitors is proposed, thereby the capacitance range meets the filtering requirements under various system strengths.

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Energy storage can effectively alleviate the power fluctuation caused by high permeability distributed new energy in AC/DC system. However, due to the state of charge (SOC) of energy storage, AC/DC system is difficult to give full play to the power complementary. Thus, a coordinated control strategy of AC/DC system considering the state of charge of energy storage is proposed in the paper. Firstly, the power balance between subnets of AC/DC system is analyzed to achieve the balance of supply and demand. Then, according to the power control strategy, the AC/DC coordinated control strategy based on energy storage SOC is studied. In order to improve the stable operation ability of the system, the technology of virtual synchronous generator (VSG) is applied. Finally, the validation model is built based on MATLAB/ Simulink platform. The simulation results show that the strategy can effectively coordinate the power interaction between the subnet power supply and the interconnected converter and improve the system stability.

This paper presents the solution to the security-constrained unit commitment (SCUC) problem for hybrid voltage source converter (VSC) based multi-terminal DC/AC (VSC-MTDC/AC) power systems with high penetration of wind generation. The formulated SCUC model presents a detailed representation of the VSCs with two different VSC control strategies considered, constant DC voltage control (master-slave control) and DC voltage droop control. In addition, Grid Code for wind farm connection is considered. Benders decomposition is used to solve the formulated SCUC problem by decomposing it into a master problem for solving unit commitment (UC) and hourly transmission security check subproblems. The final SCUC solution provides an economic and secure operation and control strategy for the meshed MTDC/AC system. Numerical tests illustrated the efficiency of the proposed SCUC model.

The sequential method is easy to integrate with existing large-scale alternating current (AC) power flow solvers and is therefore a common approach for solving the power flow of AC/direct current (DC) hybrid systems. In this paper, a highperformance graph computing based distributed parallel implementation of the sequential method with an improved initial estimate approach for hybrid AC/DC systems is developed. The proposed approach is capable of speeding up the entire computation process without compromising the accuracy of result. First, the AC/DC network is intuitively represented by a graph and stored in a graph database (GDB) to expedite data processing. Considering the interconnection of AC grids via high-voltage direct current (HVDC) links, the network is subsequently partitioned into independent areas which are naturally fit for distributed power flow analysis. For each area, the fast-decoupled power flow (FDPF) is employed with node-based parallel computing (NPC) and hierarchical parallel computing (HPC) to quickly identify system states. Furthermore, to reduce the alternate iterations in the sequential method, a new decoupled approach is utilized to achieve a good initial estimate for the New-ton-Raphson method. With the improved initial estimate, the sequential method can converge in fewer iterations. Consequently, the proposed approach allows for significant reduction in computing time and is able to meet the requirement of the real-time analysis platform for power system. The performance is verified on standard IEEE 300-bus system, extended large-scale systems, and a practical 11119-bus system in China.

Stochastic nature of some input variables dictates the requisite of probabilistic analysis in power systems operation and planning. Wind generation is considered as a main source of intermittency in power systems due to the uncertain nature of wind speed. The proposed probabilistic optimal power-flow (POPF) method investigates spatial correlation among sources to attain more practical output distributions. The method established reduced-discrete point estimate method (RDPEM) along with the Latin hypercube sampling (LHS) in order to attain the stochastic characteristic of optimization’s outputs. Despite needing less computational effort, highly accurate results can be obtained, while there is no prerequisite for probability distribution of the input random variables. In order to more validate the efficiency of the proposed method, the Gram–Charlier (GC) expansion is used to compare the outputs’ cumulative distribution functions (CDFs) that are obtained from Monte Carlo (MC) with RDPEM methods. The performance and precision of the proposed solution are ascertained by comparison with those of Monte Carlo with discrete LHS (MCDLHS) in a hybrid IEEE 14-bus test system. [ABSTRACT FROM AUTHOR]

Power systems are moving towards hybrid AC/DC grids with the integration of HVDC links, renewable resources and energy storage modules. The load frequency control (LFC) of tomorrow has to consider the complex interactions between these components. Meanwhile, more attention should be paid to cyber security concerns as the LFC loop highly depends on data communications which may be exposed to cyber attacks. In this regard, this article aims to analyze the false data injection (FDI) attacks on the AC/DC interconnected LFC system with inertia emulation and develop advanced diagnosis tools to reveal their occurrence. We build an optimization-based framework for the purpose of vulnerability analysis. Considering the attack impact on frequency stability, it is shown that the multi-area LFC system with parallel AC/DC links and emulated inertia by storage devices is more vulnerable to FDI attacks, compared to the one without inertia emulation and the normal AC system. We then propose a detection approach to detect and isolate each FDI intrusion with a sufficient fast response, and even recover the attack value. In addition to theoretical results, the effectiveness of the proposed method is validated through simulations on the two-area AC/DC interconnected LFC system with inertia emulation capabilities.

In order to coordinate the economy and voltage quality of a meshed AC/VSC-MTDC system, a new corrective security-constrained multi-objective optimal power flow (SC-MOPF) method is presented in this paper. A parallel SC-MOPF model with N -1 security constraints is proposed for corrective control actions of the meshed AC/DC system, in which the minimization of the generation cost and voltage deviation are used as objective functions. To solve this model, a novel parallel bi-criterion evolution indicator based evolutionary algorithm (BCE-IBEA) algorithm is developed to seek multiple well-spread Pareto-optimal solutions through the introduction of parallel computation. In this process, a least absolute shrinkage and selection operator (Lasso)-based N -1 contingency filtering scheme with a composite security index is developed to efficiently screen out the most severe cases from all contingencies. And thereby, the best compromise solutions reflecting the preferences of different decision makers are automatically determined via an integrated decision making technique. Case studies in the modified IEEE 14- and 300-bus systems demonstrate that the presented approach manages to address this SC-MOPF problem with significantly improved computational efficiency.

In order to improve the small-signal stability of AC/DC hybrid systems containing voltage-source converter based high-voltage direct current (VSC-HVDC), this article extends damping torque analysis (DTA) theory to VSC-HVDC supplementary damping controller to analyze its dynamic impacts and inhibit oscillations. Firstly, this article presents the mechanism and procedure of VSC supplementary damping controller and establishes the linearized model of AC/DC system with damping controllers. On this basis, the DTA theory of VSC supplementary damping controller and the equation of damping torque index (DTI) are derived. The theory can be applied to the design of the damping controller including the selection of installation location and channel as well as the parameter tuning. Finally, case studies are carried out in two AC/DC hybrid systems containing VSC-HVDC. The simulation results verify the correctness and feasibility of DTI analysis. VSC damping controllers designed by the proposed method can effectively suppress oscillations and improve the dynamic stability of the AC/DC system.

This article proposes a novel compact dual-permanent magnet (PM) dual-stator generator for hybrid ac/dc generation system. Two sets of windings are installed in the inner and outer stator separately. It has two electric ports, in which one is used to generate ac voltage and the other electric port that also generates ac voltage is rectified to obtain the dc voltage. The key of the generator is that two stators share one rotor with consequent PM structure, and the output power of the machine is much higher than that of the machine with only one stator. Besides, with two separated stator core and armature windings, the reliability of the proposed generator is improved. The advantage of the proposed dual-stator dual-PM generator is illustrated theoretically, and its slot/pole selection guideline is given. Comprehensive sensitivity analysis of the proposed generator is performed and multilevel design optimization method is adopted. The efficiency, torque ripple, and total harmonic distortion of the inner and outer armature windings of the generator after optimization are calculated to verify the effectiveness of the proposed machine design. [ABSTRACT FROM AUTHOR]

With a high proportion of wind power being transmitted through ac and dc lines, a new power grid pattern has gradually emerged. A dc inverter is prone to commutation failure, which may lead to cascading trip of ac lines for overload, resulting in serious consequences. However, existing control methods have problems of over- or under-shedding and are unsuitable for high-proportion wind power transmission systems. Accordingly, a new fault overload control method based on emergency acceleration of doubly fed induction generator (DFIG) is proposed. The fast power control capability of DFIG is fully utilized; the active power of power grid could be rapidly balanced. First, the fault characteristics of a wind power ac/dc transmission system under the fault of dc receiving-end grid are analyzed, and the power flow transfer after self-recovery from the dc commutation failure is derived. Second, by analyzing the power characteristics of DFIG, a fault overload control idea of the wind power transmission system is proposed based on emergency acceleration of DFIG. At last, the maximum controllable capacity of a wind farm is analyzed, and a fault overload control strategy of the wind power transmission system is proposed. The simulation results prove that the proposed method can rapidly reduce the output of wind farms and prevent the overload of ac lines.

Owing to the charging/discharging flexibility, electric storage system (ESS) is widely recognised as a promising technique that can be introduced to enhance transient stability of power systems. Here, a multi-objective ESS allocating and sizing approach is presented to de-risk the loss of stability for the AC/DC power system. The approach contains two major steps. Firstly, transient stability risk (TSR) is assessed based on the severity and probability of contingencies which is simulated according to the good point set sampling considering multiple uncertainties and probabilistic fault. In the second step, an allocating and sizing model is proposed for ESS to minimise the operational cost, while the AC/DC system is subject to the TSR. Additionally, strength Pareto evolutionary algorithm (SPEA2) is employed to solve the model, optimising ESS allocation and size as well as output of regular generators. A modified AC/DC test system is used to validate the presented approach. The results indicate that, with the appropriate planning strategy, ESS is able to significantly contribute to TSR improvement as it can assist in transient power balancing after a severe fault.

In recent years, the low-frequency oscillation (LFO) problem has become increasingly significant with rapid increase in the size of AC/DC interconnected power system containing large-scale wind power. This article aims to conduct the LFO analysis when an offshore wind farm is integrated into the AC power system through module multilevel converter (MMC)-based high-voltage direct current (HVDC). First, the basic mathematical models including the MMC with detailed control strategy and the permanent magnet synchronous generator (PMSG) are described. The eigenvalue analysis is then applied to conduct the LFO study. An interconnected AC/DC test system with a wind farm connected though the MMC-based HVDC transmission line is designed as benchmark. To validate the analysis results, the detailed simulation models built under the PSCAD/EMTDC^TM environment together with the Prony analysis are carried out. Different simulation scenarios involving the changes of point of common coupling (PCC), wind speed, length of transmission line, and wind penetration level are elaborately studied. Some meaningful conclusions are drawn to provide basic foundation for the future design of damping controller to mitigate LFO.

Owing to the charging/discharging flexibility, electric storage system (ESS) is widely recognised as a promising technique that can be introduced to enhance transient stability of power systems. Here, a multi-objective ESS allocating and sizing approach is presented to de-risk the loss of stability for the AC/DC power system. The approach contains two major steps. Firstly, transient stability risk (TSR) is assessed based on the severity and probability of contingencies which is simulated according to the good point set sampling considering multiple uncertainties and probabilistic fault. In the second step, an allocating and sizing model is proposed for ESS to minimise the operational cost, while the AC/DC system is subject to the TSR. Additionally, strength Pareto evolutionary algorithm (SPEA2) is employed to solve the model, optimising ESS allocation and size as well as output of regular generators. A modified AC/DC test system is used to validate the presented approach. The results indicate that, with the appropriate planning strategy, ESS is able to significantly contribute to TSR improvement as it can assist in transient power balancing after a severe fault. [ABSTRACT FROM AUTHOR]

In recent years, the low-frequency oscillation (LFO) problem has become increasingly significant with rapid increase in the size of AC/DC interconnected power system containing large-scale wind power. This article aims to conduct the LFO analysis when an offshore wind farm is integrated into the AC power system through module multilevel converter (MMC)-based high-voltage direct current (HVDC). First, the basic mathematical models including the MMC with detailed control strategy and the permanent magnet synchronous generator (PMSG) are described. The eigenvalue analysis is then applied to conduct the LFO study. An interconnected AC/DC test system with a wind farm connected though the MMC-based HVDC transmission line is designed as benchmark. To validate the analysis results, the detailed simulation models built under the PSCAD/EMTDCTM environment together with the Prony analysis are carried out. Different simulation scenarios involving the changes of point of common coupling (PCC), wind speed, length of transmission line, and wind penetration level are elaborately studied. Some meaningful conclusions are drawn to provide basic foundation for the future design of damping controller to mitigate LFO. [ABSTRACT FROM AUTHOR]

This study introduces a bidirectional power sharing scheme between an ac electric utility and a dc microgrid. These two are connected together through an interlinking converter (IC) and a dual active bridge (DAB). The proposed control scheme allows predefined amount of power to be supplied from the ac to dc side or the other way around. The DAB is connected at the dc side of the IC and it controls the bidirectional power flow. The dc microgrid contains dc–dc converters, where boost converters are used with the sources and buck converters are used to supply loads. These dc–dc converters and the DAB are controlled by state feedback with integral control in a linearised discrete domain. The DAB linearisation and control law are presented in detail. The dc microgrid is controlled by conventional V‐P droop where the power from/to the ac side is considered as negative/positive load. Detailed simulation results are presented to validate the proposal. Also some hardware results are included that support the findings. [ABSTRACT FROM AUTHOR]

The multi-terminal AC/DC system will become one of the important forms of the future power grid. The negative impedance characteristic caused by the constant power load in the DC network will reduce the power transfer capacity between the terminals, especially when a grid fault occurs in AC system at any terminal. Energy storage has played an important role in improving the stability of AC and DC systems. This paper proposes an additional control method based on an energy storage system to improve system power transfer capacity with low cost. The state space model of two-terminal AC/DC system is established, and the feedback laws for additional control are further designed by Lyapunov theory. Furthermore, the additional control strategies based on the energy storage system is built, without changing the existing control system of each control object. Finally, the corresponding system simulation model is established by Matlab/Simulink for analysis and verification. The research results show that the proposed additional control method is effective. The power transfer limitation can be overcome by only adding small damping energy with the stable DC voltages under large disturbances, and the power transfer capacity between the terminals can be significantly improved with low control cost.

This paper presents a new algorithm based on the sequential method for power flow calculation in multiterminal AC/DC systems. The proposed approach differs from other similar studies in the literature by handling two main properties. Firstly, a real equivalent circuit model is considered for the under-load tap changer transformers (ULTCs) of DC converters for the first time in the literature. Hence, new DC equations are obtained. Thus, exact and accurate results can be obtained for practical applications using the proposed algorithm. Tap values adjustment effects of the ULTCs connected to DC converters are included into the Jacobian matrix instead of the bus admittance matrix in the sequential AC power flow algorithm, as well as other ULTCs in the AC system. For this aim, new equations for calculating power and Jacobian matrix elements are obtained. Secondly, more than one independent multiterminal DC subsystem in terms of DC connection is included in the study. DC power ow calculation is performed for each DC subsystem independently in the algorithm. Thus, modularity and exibility are provided for including or removing any DC subsystems without needing to change the proposed algorithm. The proposed approach has been tested on a modified IEEE 20-bus AC/DC test system. The proposed AC/DC power ow algorithm was written and performed in MATLAB. The results show that the proposed approach is accurate and reliable in convergence. [ABSTRACT FROM AUTHOR]

Environmental concerns besides fuel costs are the predominant reasons for unprecedented escalating integration of wind turbine on power systems. Operation and planning of power systems are affected by this type of energy due to the intermittent nature of wind speed inputs with high uncertainty in the optimization output variables. Consequently, in order to model this high inherent uncertainty, a PRPO (probabilistic reactive power optimization) framework should be devised. Although MC (Monte-Carlo) techniques can solve the PRPO with high precision, PEMs (point estimate methods) can preserve the accuracy to attain reasonable results when diminishing the computational effort. Also, this paper introduces a methodology for optimally dispatching the reactive power in the transmission system, while minimizing the active power losses. The optimization problem is formulated as a LFP (linear fuzzy programing). The core of the problem lay on generation of 2m + 1 point estimates for solving PRPO, where n is the number of input stochastic variables. The proposed methodology is investigated using the IEEE-14 bus test system equipped with HVDC (high voltage direct current), UPFC (unified power flow controller) and DFIG (doubly fed induction generator) devices. The accuracy of the method is demonstrated in the case study. [ABSTRACT FROM AUTHOR]

In this paper, an extended optimal power-flow (OPF) model incorporating a detailed model of a voltage-source converter-based–multiterminal high-voltage direct current system (VSC–MTDC) is proposed, hereafter referred to as the mixed ac/dc OPF (M-OPF) model. A cost-benefit analysis approach using the M-OPF model as the calculation engine is proposed to determine the preferred VSC-MTDC alternative to be installed in an existing ac transmission system. In this approach, the operational benefits of VSC–MTDC systems are evaluated against their investment costs to derive the benefit-to-cost ratios (BCR) which reflect the cost-effectiveness of the alternatives. A case study has been carried out using a modified Nordic 32-bus system. The results of the study show that VSC–MTDC systems might lead to a reduction in total operation cost, and the reduction of the total system transmission loss depends to a large extent on the VSC–MTDC configuration. The results from sensitivity analyses show that if the VSC loss could be reduced to a third of the original level, the total benefit from the system would be increased by about 70%. A suggestion for the placement and configuration of a VSC–MTDC system is made based on calculated BCRs. [ABSTRACT FROM PUBLISHER]

Abstract: Reactive power control, which is one of the important issues of power system studies, has encountered some intrinsic changes because of the presence of the hybrid AC/DC systems. The uncertainty in determination of some ill-defined variables and constraints underlines the application of fuzzy set as an uncertainty analysis tool. Herein a fuzzy objective function and some fuzzy constraints have been modeled for the purpose of reactive power optimization then this fuzzy model is dealt with as a linear programming problem to be solved. Contrary to the separate modeling of the conventional AC/DC optimization methods, this study attempts to attain the most optimal solution by the simultaneous employment of the total contributing factors of both AC and DC parts. In this way, the conventional issue of the coordinated control of firing angle and the transformer tap of the DC terminals is resolved, yet the method provides more flexibility to gain the most optimal condition since it uses more control factor for solving the optimization problem. The proposed method is performed on the modified IEEE 14 and 30-bus systems; and it is shown to have less computational burden and further minimized objective function than the conventional method. [Copyright &y& Elsevier]

Abstract: This paper describes a phase-domain frequency domain technique to the harmonic analysis of a three-phase AC/DC system. The methodology is based on the harmonic multi-port network concept, expressed in terms of an ABCD parameter matrix which links voltage and current harmonics of different orders on both sides of the converter. Since the commutation angles are unknown, the harmonic interactions are computed by a sequential solution of the AC/DC system state variables, related by the ABCD matrix, and the updating of the commutation periods. A set of analytical equations has been derived to compute commutation times taking place in the converter. Test results are presented which demonstrate the effectiveness of the proposed methodology to assess harmonic interactions on both balanced and unbalanced operating conditions. The results are validated to those obtained by a time domain simulation. [Copyright &y& Elsevier]

The introduce of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power. To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults. This paper discussed first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC-DC Power System Simulator. Then a stabilization control scheme with an on-line extinction angle estimation; commutation failure preventive control. [ABSTRACT FROM AUTHOR]

• An efficient hybrid method is proposed for the load flow of VSC-HVDC. • The method is based on 1 + 2 Newton and simplified Newton methods. • A dimension reduction treatment for Jacobian matrix of VSC-HVDC is used. • Rule of thumb to select the iteration number of 1 + 2 Newton method is given. • Depth tests are carried out and the efficiency of the method is validated. With the rapid increase of multi-terminal and multi-infeed VSC-HVDC lines, the dimension and scale of AC/DC system equation and Jacobian matrix (JM) increase sharply, which makes the load flow (LF) analysis very complicated. In this paper, a new hybrid method is proposed to address this issue. This hybrid algorithm is composed of a 1 + 2 order Newton-Raphson (NR) method and a simplified Newton (SN) method. Specifically, the 1 + 2 order NR method is executed up to a preset number of iterations first, then the algorithm is switched to the SN until the system accuracy is met. A good compromise between the solution accuracy and computation burden can be achieved once a suitable iteration number is preset. To this end, a unified iterative form suitable for solving the LF of AC/DC systems with VSC-HVDC is derived in detail: a dimension reduction treatment is proposed to solve the problem of increasing dimension of JM; a rule of thumb is provided for the determination of the iteration number of 1 + 2 order NR. Then, the proposed hybrid method is validated on the modified IEEE-14, 30, 57 and 118 test systems. Comparisons and analyses are made for numerous scenarios, including the basic test of LF, different control modes and control objectives, influence of active and reactive powers on VSC parameters, algorithm performance under various initial states and heavy loading, etc. Compared with Newton and 1 + 2 order NR methods, the hybrid method shows a significantly shortened convergence time, 30% of 1 + 2 order NR and 47% of Newton on average. [ABSTRACT FROM AUTHOR]

The multi-terminal AC/DC system will become one of the important forms of the future power grid. The negative impedance characteristic caused by the constant power load in the DC network will reduce the power transfer capacity between the terminals, especially when a grid fault occurs in AC system at any terminal. Energy storage has played an important role in improving the stability of AC and DC systems. This paper proposes an additional control method based on an energy storage system to improve system power transfer capacity with low cost. The state space model of two-terminal AC/DC system is established, and the feedback laws for additional control are further designed by Lyapunov theory. Furthermore, the additional control strategies based on the energy storage system is built, without changing the existing control system of each control object. Finally, the corresponding system simulation model is established by Matlab/Simulink for analysis and verification. The research results show that the proposed additional control method is effective. The power transfer limitation can be overcome by only adding small damping energy with the stable DC voltages under large disturbances, and the power transfer capacity between the terminals can be significantly improved with low control cost. [ABSTRACT FROM AUTHOR]

• The in-depth convergence properties of sequential AC/DC power flow are analyzed. • A modified sequential method using virtual buses and optimal multipliers is proposed. • The decoupled AC grid is augmented with virtual buses to enhance robustness. • Optimal multipliers are applied to the inner loop of NR method to ensure convergence. • It is accurate and efficient for AC/DC system with highly loaded HVDC network. The sequential AC/DC power flow method has been practically employed to solve power flow for systems with HVDC lines, because the sequential method is well aligned with existing Newton–Raphson method for AC systems. However, it is known to be difficult to converge when the HVDC network is highly loaded. In this paper, an in-depth analysis of the divergence of the sequential method under heavy DC power is given. Then, an enhanced approach based on the sequential AC/DC power flow method is proposed to improve power flow convergence under high load cases without compromised accuracy. Two critical techniques, virtual buses and optimal multipliers, are proposed to address the challenge. First, the decoupled AC grid is augmented with virtual buses which enhance the robustness of calculation for inner loops. Then, the inner Newton–Raphson method is combined with optimal multipliers to ensure convergence. Test results with the modified IEEE 14-bus and 300-bus systems demonstrate the effectiveness of the proposed approach and the successful convergence under high load cases which cannot be achieved by conventional sequential AC/DC power flow. [ABSTRACT FROM AUTHOR]