Fast Power Control Research Articles

Suppression strategy of coupled oscillation and power anti‐regulation of variable speed pumped storage unit with full size converter

AbstractThe ultra‐low frequency oscillation and poor speed regulation performance caused by the fast power control decrease the stability and efficiency of the variable speed pumped storage unit with a full size converter (FSC‐VSPSU). This paper presents a fast frequency control strategy to solve this problem. The small‐signal model of the FSC‐VSPSU in fast frequency mode is established, and the key parameters for the system stability are studied by the eigenvalue method. Aiming at the coupling oscillation mode caused by the governor and generator side converter (GSC), the corresponding control parameters optimisation method is proposed. In order to solve the power anti‐regulation problem, the strategy of combining rotor kinetic energy release, power slope adjustment, and delay acceleration control is proposed. PSCAD and RTDS simulation results show that the proposed strategy can effectively avoid the ultra‐low frequency oscillation caused by the fast power control and significantly improves the frequency and power control performance.

Dynamic modeling and favorable speed command of variable-speed pumped-storage unit during power regulation

Variable-speed pumped-storage unit (VSPSU) has advantages in flexibility, efficiency, and reliability. It has become a state-of-the-art technology in pumped-storage industry. However, there is little research about the transient process of VSPSU working at a favorable speed command during power regulation. To study the issue, a refined model considering hydraulic–mechanical and electrical subsystems is built in this work. All submodels are created by the authors as individual modules on Simulink platform, and these modules can be easily combined to model different VSPSUs. For the VSPSU that uses a doubly fed induction machine and adopts the fast power control strategy, there are several speed constraints. To satisfy the speed constraints during transient process, the speed command is adjusted to avoid exceeding the allowable speed variation range and eliminate the oscillation caused by the S-shaped region, while being guided by the optimal speed to achieve higher efficiency. The faster the speed command changes, the more rapid the power regulation could be. But fast-changing speed command also leads to larger pressure fluctuations in penstocks. Hence, different schemes of the speed command are compared, and suitable schemes are proposed by comprehensively considering the balance between rapidity and safety. The dynamic model and analysis of favorable speed command can provide support and advice for engineering practice.

Active power fluctuations and control in hydraulic disturbance of variable speed pumped storage plants

Variable-speed pumped-storage unit (VSPSU) is state-of-the-art technology and has appeared as a new orientation of the world pumped-storage industry in recent years, but the dynamic performance of VSPSU under hydraulic disturbance has yet to be developed. The hydraulic disturbance means that normally operating pumped-storage units are inevitably affected by sudden operation changes of other units in the same waterway system. It is an important working condition in transient simulations of pumped-storage plants. In this study, a nonlinear model of a VSPSP containing multiple units is established based in MATLAB/Simulink, integrating hydraulic, mechanical, and electrical subsystems. The model is validated through comparison with on-site experiments. The fast power control strategy is adopted, enabling the unit to follow the power command rapidly and stably. The simulations show that VSPSU outperforms fixed-speed pumped-storage unit (FSPSU) in mitigating active power fluctuations under hydraulic disturbance. But VSPSU still faces active power fluctuations. This phenomenon is induced by the effect of the speed pulling-back control, which is used to keep the unit speed within the allowable speed variation range. Factors that influence the active power fluctuations are analyzed, and a useful countermeasure is proposed to solve active power fluctuations. The findings in this paper could provide understanding and guidance for the practical operation of VSPSUs.

Optimal Operation for Hybrid AC and DC Systems Considering Branch Switching and VSC Control

This article presents an optimal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">N</i> −1 security constrained operation model for hybrid ac and dc power systems with voltage source converters (VSC). In the proposed model, the fast VSC power control and the branch switching-based topology optimization are utilized together to achieve a more economic and secure operation. Also, the postcontingency short-term operation security and the wind power uncertainty are considered in the proposed optimal operation model. The proposed model is formulated as a mixed integer convex optimization model. To efficiently solve this model, a two-stage optimization approach is proposed to improve the computational speed by finding the effective branch switches. Results of two hybrid ac and dc power systems validate that the economy and security level can be enhanced by simultaneously considering the topology optimization and the grid-coupling VSC control. Also, the results demonstrate that the proposed two-stage optimization method is much faster than the direct optimization in solving the proposed model.

A fast power control method based on high-speed communication for the continuous co-phase traction power system

Continuous co-phase traction power system is an effective method to eliminate neutral sections and provide high quality power for both the public grid and the catenary. The substations have the ability to provide cooperative support to each other to reduce capacity and improve system reliability. A fast power control method for substations is needed due to rapid load changes and low overload capability of the system. This paper proposes a fast power control method based on high-speed communication between substations, with additional transient power control to significantly improve the dynamic response of the system.

Anti-interference characteristics of variable speed pumped storage units for load cases of hydraulic disturbances

Variable speed pumped storage unit (VSPSU) is an innovative technology, and investigations regarding operating characteristics of VSPSU are significant. However, there are relatively few studies towards hydraulic disturbances of VSPSUs. The hydraulic disturbance means that pumped-storage units, which were originally in steady operation, are inevitably affected by suddenly operating changes of other units in the same waterway system. Normally, it will cause the power output of fixed-speed units to oscillate, and adversely affect the safety of generators and stability of power systems. Hence, investigations of VSPSUs’ characteristics under hydraulic disturbances are necessary. In this paper, VSPSU using doubly fed induction machine (DFIM) is adopted as a study case, and fast power control strategy is used in the controlling of VSPSU. The simulation result shows that VSPSU has good anti-interference performance, and normally operating VSPSU can still maintain stable power output and stator current even under disturbance from other units. However, despite the good anti-interference performance of VSPSU, the mechanical power of VSPSU lags far behind the electromagnetic power, and the hydraulic-mechanical transient processes of VSPSU are similar to that of a fixed-speed unit. The findings in this paper could provide understanding and guidance for practical operation of VSPSUs.

A Model Predictive Controller for the Core Power Control System of a Lead-Cooled Fast Reactor

To study the model predictive control (MPC) for a lead-cooled fast reactor's core power control system (LFR), firstly, the LFR core is established with the state space model. Then, to establish an LFR core power control system, a predictive model controller is used. Finally, the conditions of 20pcm step reactivity and 5% step down of coolant inlet temperature are introduced to study the control characteristic. The maximum overshot (MO) and the transient time are calculated in the time domain, and the stability of the core power control system is analyzed using the Nyquist and Bode diagrams in frequency domains. The result shows that the MPC controller and PID controller are feasible in core power control, and the core power control systems are closed-loop stable systems.

Coordinated Reactive Power Control with a Variable Shunt Reactor and an Inverter-Based Wind Power Plant

Underground or submarine cables have a higher capacitance component than overhead lines, and they inject a large amount of capacitive reactive power into the system. A separate reactive power compensation device is required in order for a wind power plant (WPP) connected to the public network with a cable to meet the reactive power requirements required by the grid code. In this paper, a reactive power control using a variable shunt reactor (VSR) was proposed to satisfy the reactive power requirement required by the grid code for a WPP connected to the grid through a cable. The proposed reactive power control method compensates for the capacitive reactive power of the cable by using a VSR, and it follows the reactive power command through the reactive power control of a WPP. In the section where it is difficult to follow the WPP reactive power command only with the reactive power capacity of a WPP due to cable losses or a cable reactive power compensation error of the VSR, the reactive power control is additionally supported through the hysteresis control of the VSR. The proposed method satisfies the grid codes, and it enables fast and accurate reactive power control. The performance of the proposed method was verified through simulation using MATLAB/Simulink.

Distributed Secondary Control in Microgrids Using Synchronous Condenser for Voltage and Frequency Support

A high share of distributed energy resources (DERs) in power distribution grids has posed many challenges for system operation and control. Microgrid (MG) application with different distributed control approaches for DERs has been drawn a lot of attention from the research community to provide more flexibility, reliability and resilience for the system. This paper develops a distributed secondary control for DERs in MGs and on top of that using synchronous condenser (SC) participating in the secondary control for voltage support. The proposed distributed secondary control framework of MGs is designed to obtain four objectives as follows: (i) frequency restoration, (ii) average voltage restoration, (iii) arbitrary active power sharing among SGs and BESSs and (iv) arbitrary reactive power sharing among all SGs, BESSs and SCs. The comparison results under different scenarios show that with SC participating in the distributed secondary control in MGs, the system frequency and voltage response are much improved and quickly recovered to the nominal values thanks to the natural inertia response and fast reactive power control of SC sharing with other DERs in the MGs. Additionally, a multi-agent system is implemented to realize the proposed control method in hardware environment.

Research on super-capacitor fast power control system

In the context of carbon peak and carbon neutrality targets, high-proportion new energy power systems exhibit low inertia and weak damping characteristics. The frequency stability of the new power system has become a major problem for the safe and stable operation of the power grid. The traditional primary frequency modulation technology based on thermal power units or hydropower units has the defects of slow response speed and long frequency detection delay time. Therefore, we propose a multi-functional multiplexing super capacitor fast power control system, which has the functions of frequency stability control and voltage sag management. In the meantime, we proposed a fast frequency detection algorithm for cascaded signal delay, and the frequency detection delay is less than 10 ms. The system uses a high-speed communication ring network, and the communication delay is less than two milliseconds. Finally, we built a super capacitor energy storage system with a capacity of 50kW to verify that the super-capacitor has the ability to quickly and actively support the power system under frequency disturbances.

Variable Speed Hydropower for Provision of Fast Frequency Reserves in the Nordic Grid

The main purpose of this article is to demonstrate the grid support capability of variable speed hydropower (VSHP). The hypothesis is that active power control of VSHP plants can improve both the frequency stability and the transient rotor angle stability by contributing to virtual inertia (VI), fast frequency reserves and power oscillation damping. Fast active power control is made possible by power electronic converters obtaining the energy from the rotating masses of the turbine and generator while the rotational speed is restored by control of the guide vane opening of the hydro turbine. A detailed dynamic simulation model is developed to simulate the VSHP within the Nordic 44-bus grid model. The VSHP controller includes a moving horizon estimator (MHE), model predictive control (MPC) with inertia emulation realised by the frequency converter of the VSHP plant. The results show that VSHP can contribute significantly to reduce the maximum frequency deviation following a sudden loss of generation. In addition, the amplitudes of power oscillations are reduced and the critical fault clearing times are generally improved. The VSHP should, therefore, be regarded as one of the technically viable options for provision of fast balancing system services.

Investigation on GaN HEMTs Based Three-Phase STATCOM with Hybrid Control Scheme.

The modern trend of decarbonization has encouraged intensive research on renewable energy (RE)-based distributed power generation (DG) and smart grid, where advanced electronic power interfaces are necessary for connecting the generator with power grids and various electrical systems. On the other hand, modern technologies such as Industry 4.0 and electrical vehicles (EV) have higher requirements for power converters than that of conventional applications. Consequently, the enhancement of power interfaces will play an important role in the future power generation and distribution systems as well as various industrial applications. It has been discovered that wide-bandgap (WBG) switching devices such as gallium nitride (GaN) high electron mobility transistors (HEMTs) and silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) offer considerable potential for outperforming conventional silicon (Si) switching devices in terms of breakdown voltage, high temperature capability, switching speed, and conduction losses. This paper investigates the performance of a 2kVA three-phase static synchronous compensator (STATCOM) based on a GaN HEMTs-based voltage-source inverter (VSI) and a neural network-based hybrid control scheme. The proportional-integral (PI) controllers along with a radial basis function neural network (RBFNN) controller for fast reactive power control are designed in synchronous reference frame (SRF). Both simulation and hardware implementation are conducted. Results confirm that the proposed RBFNN assisted hybrid control scheme yields excellent dynamic performance in terms of various reactive power tracking control of the GaN HEMTs-based three-phase STATCOM system.

Differential Flatness-Based, Full-Order Nonlinear Control of a Modular Multilevel Converter (MMC)

Modular multilevel converter (MMC) is an attractive topology in industrial applications such as high-voltage direct current (HVdc) transmission system where fast power control is required. The most conventional control method for MMC uses cascaded structures, where the power transmission and internal energy dynamic (outer loops) is limited by the “frequency separation” constraints since the dynamic choice of the currents (inner loops) must consider the tradeoff between rapidity and robustness. In this article, we present a new control method based on a differential flatness theory. The main interest of the proposed control is the possibility to obtain a very high dynamic performance of the MMC power flow, even under noisy measurements and parametric disturbances. Using the well-known average model of the MMC, a flat output is proposed, proving the differential flatness property of the MMC. Trajectory tracking controllers of ac grid active and reactive power are proposed using input-state full-order linearization. Simulation results, including losses corresponding to a realistic case of on-shore, point-to-point HVdc interconnection, are presented to show the performance of the proposed control scheme even with strong measurement noise.

Coordination control method for multi-wind farm systems to prevent sub/super-synchronous oscillations

In recent years, the sub/super-synchronous oscillations occur frequently in the large-scale wind power bases of China. Since the oscillation frequencies are close to the fundamental frequency, the current components can spread over a large area, and may destroy the shafting of rotating devices in the power grid. Improving the control strategy and parameters of wind turbines can prevent this problem to some extent, however, due to the complex operation conditions and continuous development of wind power, the off-line improvement measure on wind turbines cannot eliminate the potential oscillations risks. This paper is to propose an oscillation risk screening and stability assessment method, and develop a coordination control method for the large-scale wind farm systems to prevent the sub/super-synchronous oscillations. The Nyquist criterion and the modal analysis method are combined to generate quantitative factors for the stability assessment and the control strategy design. The coordination control method consists of minute-level power coordinated allocation and second-level fast power control to prevent and eliminate the oscillations. Detailed simulation model of a multiple wind farms system originated from the actual wind power base in China is presented to verify the effectiveness of the proposed method.

A Comprehensive Inverter-BESS Primary Control for AC Microgrids

This paper proposes the design of a comprehensive inverter-BESS primary control capable of providing satisfactory performances both in grid-connected and islanded configurations as required by international standards and grid codes, such as IEEE Std. 1547. Such control guarantees smooth and fast dynamic behavior of the converter in islanded configuration as well as fast power control and voltage-frequency support in grid-connected mode. The performances of the proposed primary control are assessed by means of EMT (ElectroMagnetic Transients) simulations in the dedicated software DIgSILENT PowerFactory® (Germany, Gomaringen) . The simulation results show that the proposed BESS (Battery Energy Storage System) primary control is able to regulate frequency and voltage in Grid-Forming mode independently of the number of paralleled generators. This is achieved adopting a virtual generator technique which presents several advantages compared to the conventional one. Moreover, the proposed control can be switched to Grid-Support mode in order to provide fast control actions to allow frequency and voltage support as well as power control following the reference signals from the secondary level.

Determination of Local Voltage Control Strategy of Distributed Generators in Active Distribution Networks Based on Kriging Metamodel

The increasing penetration of uncontrollable distributed generators (NDGs) exacerbates the risk of voltage violations in active distribution networks (ADNs). It is difficult for a centralized control strategy to meet the requirements of fast voltage and reactive power control because of the heavy computational and communication burdens. Local voltage control based on real-time measurements can respond quickly to the frequent fluctuations of distributed generators (DGs). In this paper, a local voltage control strategy of DGs with reactive power optimization based on a kriging metamodel is proposed. First, to build the metamodel for local voltage control, the steps for determining the input variables are presented in detail, and the effects of different variables on the accuracy of the metamodel are analyzed. Then, taking minimum network losses and voltage deviations as the objective function, we construct the metamodel for local voltage control based on kriging methods. Finally, operation strategies for DGs are developed by calculating the optimally weighted vector based on real-time measurements, and the operation strategies for DGs will be added into the original sample set to improve the accuracy of the metamodel. The proposed local voltage control strategy based on only the local measurements can quickly respond to the frequent DG fluctuations, reduce the communication burden for large networks and improve the adaptability of local voltage control in ADNs. Case studies under different scenarios on the IEEE 33-node system and the IEEE 123-node system are conducted to verify the effectiveness of the proposed method, and the results show that the proposed method can effectively solve the problems of voltage deviation and voltage fluctuation caused by the high penetration of DGs.

Fault Overload Control Method for High-Proportion Wind Power Transmission Systems Based on Emergency Acceleration of Doubly-Fed Induction Generator

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.

A Novel Dynamic Switching Table Based Direct Power Control Strategy for Grid Connected Converters

Direct power control (DPC) has gained much attention for medium-voltage applications due to its fast power control capability. However, a conventional static switching table based DPC can lead to unsatisfactory response when the converter is connected to an electric grid because it is commonly designed assuming ideal and constant voltages of the grid and the dc link. Therefore, the actual grid voltage and the actual converter dc-link voltage should be considered while designing the switching table. This paper proposes a novel dynamic switching table for the DPC, considering actual grid and dc-link voltages variation. The proposed dynamic switching table incorporates a new definition of power influence crossover angles of each converter space vector. The proposed scheme dynamically adapts the switching table by feeding forward the actual grid and dc-link voltages, and hence the converter's power is precisely controlled. The proposed technique is verified for the three-level neutral point clamped converters connected to a standard IEEE 9-bus test system. Moreover, the real-time simulations are performed in a real-time digital simulator, OPAL-RT. The obtained results verified the effectiveness of the proposed DPC strategy under different grid fault scenarios.

Fast quasi-static time-series analysis and reactive power control of unbalanced distribution systems

Fast quasi-static time-series analysis and reactive power control of unbalanced distribution systems

Multi crowd fast power control algorithm based on neighborhood opportunistic learning

For improving the energy-saving power generation scheduling in the electric power industry energy saving and emission reduction capability and enhance the safety and economy of power energy structure, we based on neighborhood opportunity learning multi intelligent power quickly swarm intelligent control algorithm is presented in this paper. Firstly, the proposed algorithm is based on the characteristic value of each neighborhood characteristic value which is obtained by chance mining. The system can obtain the real-time sensing data of each neighborhood power station. This algorithm establishes a neighborhood modular architecture. The algorithm in the opportunity to automate the operation of the module information on the opportunity to learn. Secondly, based on the opportunity to learn and fast variation of the power vector, the algorithm is derived to control the power generation fast group. The algorithm of the multiple power generation control system through the opportunity to control and quickly set the mapping link. Finally, the experimental results show that the proposed algorithm has a significant advantage in real-time, reliability and cost of intelligent management and fast control of power generation to adapt to a variety of power generation devices.