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The hybrid LCC/VSC cascaded HVDC (HC-HVDC) scheme, in which the LCC is adopted as rectifier, and one LCC in series with multiple paralleled VSC based MMCs is adopted as inverter, combines the advantages of both LCC and VSC-MMC technologies. Presently, a HC-HVDC project is planned to deliver the hydro power from Baihetan to Jiangsu in China. One of the major challenges is to suppress the DC overcurrent issue of VSC-MMCs especially under commutation failure condition of LCC at inverter side. Based on Baihetan-Jiangsu project under construction, the model of HC-HVDC system is developed in PSCAD/EMTDC. In the system, the rectifier employs a dual 12-pulse LCC, while the inverter adopts a hybrid scheme, i.e., one LCC converter in series with three paralleled VSC-MMC converters. This paper addresses the main cause and feature of the DC overcurrent, then proposes an overcurrent suppression control method for HC-HVDC system based on fuzzy clustering and identification approach. And the system transient performances with the proposed control approach are evaluated under AC fault conditions. The results show that the proposed approach can not only suppress the DC overcurrent following the commutation failure to a certain extent, but also improve the post-fault recovery performance of the overall system. [ABSTRACT FROM AUTHOR]

There are a large number of plug-and-play loads in an active distribution network, such as EVs(Electric Vehicles), energy storage, solar power, etc. Due to the lack of security control methods for each terminal node and the lack of distributed power voltage control methods, the large number of loads brings a huge challenge to the security of the distribution network. At present, some regional distribution networks dominated by new energy in China have long-standing problems, such as high voltage impact and frequency flickering, which are extremely harmful to electric equipment, and the resulting load-side accidents have brought huge economic losses. Therefore, research on an optimization model of the source–grid–load interaction in the active distribution network considering the safety characteristics, especially the voltage of the system, will help to improve the quality of the grid dispatch. In this paper, the safety limits of the independent operation of a source network loaded on three sides are used as the operating constraints of the system, and the social welfare of the interaction is maximized as the goal. A joint optimization modeling after the independent solution of the three sides is used as the core means, a heuristic algorithm is used to solve the overall optimization of the whole system, a scheduling optimization model that meets the system security goals is constructed, and this model is used to guide the operation strategy of each node in the system. The Lagrangian relaxation factor is introduced for structural optimization, and finally, the simplified 36-node model of the actual power grid is used for verification. The results show that under the goal of ensuring the economy of the system, the system voltage is controlled within the specified range of the safe operation of the system, which can meet the safety needs of the interaction. [ABSTRACT FROM AUTHOR]

The uncertain nature of renewable energy resources (RERs) and fast demand response lead to recurring voltage violations in the power systems, which causes frequent transformer tap shifting and capacitor switching. Therefore, this paper resorts to the static var compensators (SVCs) to manage the bus voltages based on the multi-agent deep reinforcement learning (MA-DRL) algorithm. The proposed scheme includes several system agents and SVC agents to collaboratively adjust the injected reactive power to restrict the bus voltages within the normal range. All the agents are trained centrally and executed separately, which requires minimum communication cost. The IEEE 14-bus system, IEEE 300-bus system, and China 157-node urban power grid are used to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

In practical power systems, it is still very challenging to figure out a cost-effective undervoltage load shedding (UVLS) scheme that can reliably and adaptively react to the short-term voltage stability (SVS) problem. Faced with this challenge, this paper develops an intelligent data-driven predictive UVLS scheme for online SVS enhancement. Inspired by valuable ideas in model predictive control and supplementary excitation control in power systems, a novel deep feedback learning machine (DFLM) is designed to precisely predict future voltage violations after UVLS execution. With the help of the DFLM, the UVLS scheme is aware of potential effects of various candidate UVLS actions. Owing to this desirable nature, it can adaptively respond to diverse SVS conditions and optimize UVLS decisions in a non-iterative way. Further, two well-designed strategies, i.e., stepwise constraint relaxation and incremental DFLM adaptation, are introduced to enhance the scheme's reliability and adaptability during online application. Numerical test results on the Nordic test system and the realistic North GZ Power Grid in China showcase the excellent performances of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, a special control solution called virtual voltage source (VVS) is developed for no-load tests of induction machines. This concept is applied to a 2 × 27 MVA high-power machine test bench where the test bench is requested to precisely characterize, e.g., 3 MW machines at no-load currents. The developed VVS thoroughly solves the stability issue of induction machines at low-speed ranges. A set of optimizations is presented here that systematically improves the voltage precision of the test bench. Experimental results prove that the proposed concept achieves 0.08–0.12% voltage unbalance, less than 3% current unbalance, with less than 0.3% harmonic-voltage-factor, and verified by more than 100 induction machines. [ABSTRACT FROM AUTHOR]

With the rapid development of China high-speed railway, the low frequency oscillation (LFO) of electrical quantities appears more often recently and leads to some severe problems of train operation. To improve the traction line-side converter control and suppress the phenomenon economically and effectively, a model-based predictive direct power control (MPDPC) approach is proposed in this paper. The approach adopts a discrete-time model of traction line-side converter in d–q reference frame to predict the future values of the input active and reactive power. The optimal switching state is selected by minimizing a cost function of power to evaluate the power errors at the next sampling time. Through the theoretical analysis and simulations, the performance of MPDPC is compared with traditional transient direct current control (TDCC) that is widely adopted in China Railway High-Speed 3 electric-multiple-unit. The real-time online simulations based on Real-Time Laboratory (RT-LAB) are also realized to further validate the results. Moreover, two vehicle-grid cascade simulation systems are constructed, and the LFO suppressing capability of MPDPC and TDCC is compared. Finally, the steady-state characteristic, dynamic characteristic, and LFO suppressing capability of MPDPC are demonstrated through the analysis of key performance indexes. [ABSTRACT FROM AUTHOR]

• This paper is the first attempt of Deep Neural Network in China ADS injector II. • Explore the relationship the beam position and quadrupole magnet under noise. • Analyse the applicability of BPNN to the quadrupole magnet control model. • This paper provide a new method for beam debugging of the system. In the beam debugging of China ADS Injector II, the mathematical matrix operation, software simulation or physical derivation methods are mainly used. These methods do not take into account noise conditions, so it is difficult to accurately control the deflection position of the beam. For this reason, this paper takes MEBT as an example to establish a function model of quadrupole magnet control parameter and beam position, and based on the BPNN to fit the function model to reduce the influence of noise on the control process, and then realizes control prediction model in beam debugging. The experiments results show that the prediction accuracy of the quadrupole magnet control voltages Q2 and Q3 are 0.9072 and 0.9352, respectively, and the MSE is 0.0064. This paper is the first attempt of deep neural network in China ADS injector II, which provides a new method for beam debugging of the system. [ABSTRACT FROM AUTHOR]

To make better use of local generators' dynamic var reserve to improve short-term voltage stability (STVS), this paper proposes an integrated high side var-voltage control (IHSV^2C) for power plants in receiving-end power systems. The IHSV^2C consists of a plant-level multi-machine var coordinator (MMVC) and several unit-level high side voltage controllers (HSVCs). MMVC coordinates the reactive power output among generators and provides control parameters for HSVCs, while HSVCs can maintain the voltage of a pre-defined voltage control point (VCP) by regulating the voltage reference of the excitation control of each generator. Therefore, when the system suffers a serious fault, IHSV^2C can drive the generators to provide stronger var support. Consequently, the voltage stability can be improved. A conceptual model of the receiving-end power system in China Southern Power Grid (CSG) is established, and the IHSV^2C has been validated through a simulation analysis on the system. Both time-domain simulation results and the voltage sag severity index (VSSI) have fully demonstrated its performance. Therefore IHSV^2C offers a new and effective approach to improve STVS of receiving-end power systems. [ABSTRACT FROM AUTHOR]

Due to the uneven geographical distribution between load and wind power, currently it is difficult to integrate the large-scale wind power into the State Grid in China. There are significant wind curtailments for wind farms due to system restrictions. This paper proposes a new way of utilizing wind power, i.e., in-situ consumption, as an alternative to the costly development of long-distance transmission of large-scale wind power. Electrolytic aluminum load, which is one of the most typical high energy consuming loads, is employed to absorb the excess wind power in western China. An actual isolated industrial power system for aluminum production driven by wind power and coal-fired power is described. The penetration level of wind power in the isolated power system is up to 48.8%. The power imbalance between generation and load demand caused by wind power fluctuation or the tripping of coal-fired generators can dramatically impact the frequency stability of the isolated power system, which is of small inertia. An online identification method of power imbalance based on Wide Area Measurement System (WAMS) is presented. According to the characteristics of the electrolytic aluminum load, a system frequency control method by regulating the bus voltages of aluminum loads to eliminate the power imbalance is introduced. The simulation is done in Real Time Digital Simulator (RTDS) and the results verify the validity of the proposed frequency control method. [ABSTRACT FROM PUBLISHER]

In order to solve the frequently occurring lightning flashover problems on ±500 kV dc transmission lines in China, the authors have conducted the research on the dc line arrester since 2011. In this paper, the structure and installation, technical parameters, and protection performances, as well as their deterministic processes of the arrester are presented and analyzed in detail. In 2013, the authors successfully developed the arrester products, and the type tests show that they have excellent performance parameters and can act effectively against the lightning impulse and cutoff the dc follow current. By now more than 500 dc line arresters have been installed and used on seven ±500 kV dc transmission lines in eight provinces of China. About four years of operating experience shows that the arresters work safely and reliably over a long period of time, and have been effectively reducing the lightning flashover rate of the ±500 kV dc lines. [ABSTRACT FROM PUBLISHER]

The power industry in China has grown significantly over the past decade, spurring the adoption of system-wide automatic voltage control (AVC) technology to meet stricter requirements for security and economical power system operation. To cope with the rapidly developing and frequently changing Chinese power grid, an AVC scheme based on adaptive zone division is introduced in this paper. Logically, this type of system has a three-level hierarchical structure, but, here, both secondary voltage control (SVC) and tertiary voltage control (TVC) are implemented via software at the same control center. The control zones are no longer fixed but are reconfigured online and updated in accordance with variations in the grid structure. The technical details of these procedures are presented here. The implementation of TVC (which is based on an online reactive optimal power flow) and SVC are also discussed, together with some technical details on improvements to their reliability and robustness. Some results obtained from field-site applications based on similar-days testing rather than simulations are employed to evaluate the performance and improvements of the AVC system. This system has been installed at over 20 control centers in China. [ABSTRACT FROM PUBLISHER]

With the rapid development of high-speed and high-power railway system in China, power quality such as the negative sequence current and harmonic current caused by electric locomotives becomes more and more critical. This paper proposes a half-bridge-converter-based railway static power conditioner (RPC) (HBRPC) which consists of two half-bridge converters connected by two capacitors in series. Compared with the traditional RPC, the HBRPC requires only a pair of power switch legs and two capacitors. Under the premise of accomplishing the same function of RPC, the proposed conditioner can reduce half of the power switches, which can make it with lower cost and hardware complexity. A double-loop control is proposed for HBRPC to keep the dc-link voltage stable and achieve the dynamic tracking of the current reference signals, while a balanced voltage control is proposed to eliminate the error of two capacitor voltages and maintain the normal operation of HBRPC. Finally, simulation and experiment results have verified the proposed structure and its control method effectively. [ABSTRACT FROM PUBLISHER]

To solve the problems of voltage violation and fast voltage fluctuation caused by photovoltaic (PV) grid connections in distribution networks, a two‐stage coordinated voltage control strategy for PV inverters with multimode coordinated operation in distribution networks (DNs) is proposed. It is based on the characteristics of PV inverters that can be regulated rapidly and continuously. First, the voltage control process is divided into two control stages according to the voltage change rate, and the corresponding voltage control models are established. Then, the operating modes of PV inverters are classified into three modes: economic prevention, economic control, and efficient control. Different operating modes are used to adapt to the two‐stage voltage control. Finally, a voltage fast control solution algorithm is proposed, which considers adaptive time delays and combines local measurement, prediction, and communication information to update control commands. The effectiveness and feasibility of the proposed voltage control strategy were demonstrated through simulation tests on a real 10‐kV line with a high PV penetration rate in the Anhui province of China. The results show that the proposed strategy can prevent voltage violation and sudden changes and can smooth out voltage fluctuation. [ABSTRACT FROM AUTHOR]

The hybrid HVDC with cascaded multi-infeed MMC inverters will be put into reality soon in China, but its MMC inverter in constant DC voltage control would become a rectifier when disturbance happens. Thus, to solve such problem and enhance the stabilities, the adaptive droop control is proposed for MMC inverters and a hierarchical coordinated adaptive strategy is designed, which are realized through three parts. The first coordinated strategy is to maintain the inverter side DC voltage in constant by shifting the MMC inverters’ droop curves, such that the operation variation will not change the DC voltage in droop control, where the power transferred by the hybrid HVDC would be varied if voltage deviation occurs; the second part is to realize MMC inverters’ accurate power control considering the practical project and power dispatch, which is achieved through the droop control reference adjustment. Based on the above coordinated strategies, the third strategy is designed to make MMC inverters and LCC rectifiers coordinate with each other for the power fluctuates and fault situations, which is used to avoid inverters’ overload operation. The simulation results validate the effectiveness of the proposed strategy finally. [ABSTRACT FROM AUTHOR]