Impact on power system transient stability of AC-line-emulation controllers of VSC-HVDC links (original) (raw)
Related papers
Iet Generation Transmission & Distribution, 2020
This paper investigates the impact of embedded Voltage Source Converter-based High Voltage Direct Current (VSC-HVDC) links on AC grids transient stability. Firstly, using Transient Energy Functions (TEF), it is demonstrated that VSC-HVDC links controlled to track constant power references, do not inherently improve transient stability of the surrounding AC grid as an AC line naturally does. Then, a control law using the feedback linearization technique on a simple but representative power system is derived. The control law highlights and combines the three main actions the VSC-HVDC link can offer to enhance rotor angle stability: fast power reallocation, injection of synchronising power and injection of damping power. The control law is implemented and validated in EMT simulation. It is then shown that an HVDC link can assure the synchronisation of different AC areas even if no AC transmission lines interconnect them. Through another case study, it is shown how the HVDC link can help to share dynamic frequency reserves in order to not jeopardise the stability of the system. A last example investigates the effect of a DC fault on AC transient stability and how the control can help improving the system response.
HVDC control strategies to improve transient stability in interconnected power systems
2009
This paper presents three HVDC modulation strategies to improve transient stability in an interconnected power system. AC variables such as rotor speeds, voltage phasors, and tieline power flows are used as input to the controller that modifies the power flow settings through the HVDC-links. The proposed techniques are tested on the IEEE 24-Bus reliability test system and critical clearing times obtained for several contingencies are analyzed. The paper shows that HVDC modulation can lead to substantial improvement in transient stability.
Study of supplementary controls for embedded HVDC links in a AC power system
2008
This document reports a comprehensive study of supplementary control schemes for HVDC inter-ties parallel to AC transmission lines in order to reduce electromechanical inter-area oscillations employing a suitable two-area power system. The study includes design procedure and an extensive analysis based upon time domain detailed simulations, developed using PSCAD/EMTDC. Results obtained from two-area power system show how the control over the HVDC inter-tie effectively reduces the electromechanical inter-are oscillations. The supplementary outer control loop of the HVDC link, suitably designed, permits to increase the damping ratio of the system to a safe value, which can not be attained solely using power system stabilizers. Power modulation through the HVDC link effectively reduces electromechanical inter-area oscillations under a wide range of composite static load characteristics. Response is however limited by the value of the voltage index for active power; the compensation loop is functional only when this index is greater than one. The effectiveness of the supplementary control scheme is barely affected by the value of the voltage index for reactive power; these results reduce the modeling considerations of the reactive power characteristics, which in practical circumstances are more variable and depending on several and sometimes unknown factors.
Transient Stability Analysis for Betterment of Power System Stability Adopting HVDC Controls
Incorporation of HVDC transmission subsystems in AC transmission networks has been a major change in power transmission during the last few years. This change required modifications in the performance evaluation procedures notably for load flow and stability analysis. The methodologies used for AC/DC system's load flow calculation and transient stability analysis are presented in this chapter. In this thesis, the investigations are carried out on the improvement of power system stability by utilizing auxiliary controls for controlling HVDC power flow. AC/DC load flow using eliminated variable method is utilized in the transient stability analysis. Transient stability analysis is done on single machine system and multi-machine system, using different control signals derived from the AC system.
2018
In this paper we introduce a HVDC transmission between two buses of an IEEE 9bus system with transient and dynamic analysis of rotor angle deviation of the three synchronous generators. The deviation of the generators is maintained in synchronization during steady state and after fault transient. Comparison of HVDC VSCs with different controllers is presented with P, PI and PID controllers. Modeling and simulation is carried out in MATLAB software with graphical representations. IndexTerms – HVDC links , Powerflow Controllers, Rotor angle deviation,VSCs
Transient stability analysis of VSC HVDC transmission with power injection on the DC-link
TURKISH JOURNAL OF ELECTRICAL ENGINEERING & COMPUTER SCIENCES, 2015
The utilization of a DC-link transmission corridor of embedded VSC HVDC for a DC power injection from renewable energy sources to increase the power flow capability and AC network stability support is a promising technology. However, DC faults on the DC transmission line are likely to threaten the system's operation and stability, especially when the DC power injection exceeds certain limits. A DC single line-to-earth fault is the most likely fault scenario and its effect on the VSC HVDC operation will depend on the earth-loop impedance. Adding an injection point on the DC-link will reduce the earth-loop impedance, hence imposing a danger of increasing the earth fault current. Therefore, in this paper, a VSC HVDC with a DC power injection on the DC-link is studied, the DC-line-to-earth fault is analyzed in the time domain, and its effects on the DC and AC sides of the system are presented. The analysis is based on a developed state-space representation of the system under a single-line-to earth fault. The zero-input zero-state (ZIZS) response is used to find the solution of the state-space representation. In order to correlate the state-space solution with a simulation, the system is modeled in MATLAB/Simulink. Interestingly, it was observed that a quick recharging of the DC-link capacitor due to a power injection created an additional damping of the postfault oscillations of the AC-side power angle and the DC-side voltage and power oscillations, hence enhancing transient stability.
Long extra high voltage (EHV) ac lines cannot be loaded to their thermal limits in order to keep sufficient margin against transient instability. With the scheme proposed in this paper, it is possible to load these lines very close to their thermal limits. The conductors are allowed to carry usual ac along with dc superimposed on it. The added dc power flow does not cause any transient instability. This paper presents the feasibility of converting a double circuit ac line into composite ac-dc power transmission line to get the advantages of parallel ac-dc transmission to improve stability and damping out oscillations. Simulation and experimental studies are carried out for the coordinated control as well as independent control of ac and dc power transmissions. No alterations of conductors, insulator strings, and towers of the original line are needed. Substantial gain in the loadability of the line is obtained. Master current controller senses ac current and regulates the dc current orders for converters online such that conductor current never exceeds its thermal limit. The present paper is implemented by using MATLAB/SIMULINK. Key word: Extra high voltage (EHV) transmission, flexible ac transmission system (FACTS), simultaneous ac-dc power transmission.
Dynamic Analysis of VSC-HVDC System with Disturbances in the Adjacent AC Networks
Distributed generation & alternative energy journal, 2023
VSC-HVDC systems are widely used to integrate wind farms, asynchronous generations and networks operating at different frequencies. The Multiterminal (MT) and multi-fed (MF) HVDC's are the system mainly constituted of VSC's, to integrate renewable sources and transmitting bulk power to conventional AC grids. A sudden change in the steady state even in adjacent networks may create severe disturbances in the operation of such HVDC systems. The disturbances in AC or DC networks directly influence the performance of systems, particularly in MT-HVDC and MF-HVDC systems. However, the HVDC systems are known for their intelligent control in modulating operational states as and when required. This paper presents the dynamic analysis of MF-HVDC system due to load changes, faults and other
Energies, 2021
High-voltage direct current (HVDC) has received considerable attention due to several advantageous features such as minimum transmission losses, enhanced stability, and control operation. An appropriate model of HVDC is necessary to assess the operating conditions as well as to analyze the transient and steady-state stabilities integrated with the AC networks. Nevertheless, the construction of an HVDC model is challenging due to the high computational cost, which needs huge ranges of modeling experience. Therefore, advanced dynamic modeling of HVDC is necessary to improve stability with minimum power loss. This paper presents a comprehensive review of the various dynamic modeling of the HVDC transmission system. In line with this matter, an in-depth investigation of various HVDC mathematical models is carried out including average-value modeling (AVM), voltage source converter (VSC), and line-commutated converter (LCC). Moreover, numerous stability assessment models of HVDC are outl...
Dynamic simulation of HVDC interconnection in large power system
2011 IEEE Power and Energy Society General Meeting, 2011
Generally the Power factor and Dynamic stability of a HVDC system plays vital role for maintaining the system stability and very effectively improves the system responses. The novel controller has demonstrated good responses with very weak inverter AC systems and widely changing AC parameters. In this paper it is studied that if it is possible to offer adequate replacement for synchronous condensers at weak HVDC-HVAC interconnection point. The actual HVDC system has excellent small signal responses with increased probability of commutation failure. To keep the same commutation failure probability, half of the synchronous condenser must be maintained in normal operation. Further synchronous condenser can also be disconnected, when the novel inverter control method is employed. However the nominal operating angle has to be somewhat increased. The financial benefits of the system are evident due to reduction of the synchronous condensers. The controller is designed with two primary objectives, one is the stability improvement of HVDC systems connected to very weak AC systems and the other is HVDC robustness with respect to the AC system parameter changes.