Distance Bulk Power Transmission Research Articles

Comparative Analysis of Inter-Inverter Interactions in Emerging Hierarchical-Infeed and Conventional Multi-infeed LCC-HVDC Systems

The emerging hierarchical-infeed LCC-HVDC (HIDC) system has been recently commissioned for the long distance bulk power transmission in China. Compared to the conventional multi-infeed LCC-HVDC (MIDC) system with inverters coupling only in the ac-side, different inter-inverter interactions exist in the HIDC system where inverters couple in both the ac- and dc- sides. It is beneficial to reveal the underlying difference of the inter-inverter interactions in the HIDC and MIDC systems for determining which system should be adopted in the planning study. However, this difference has not been clearly revealed yet in earlier works. Thus in this paper, the inter-inverter voltage interaction factor (IVIF) index is firstly introduced to quantitatively assess the inter-inverter interactions. The analytical calculation methods of the IVIF for the HIDC and MIDC systems are also presented for the satisfactory accuracy and efficiency. Moreover, these methods are further used for comparative analysis of parametric dependence of the IVIF in the HIDC and MIDC systems considering various system parameters, operation variables and dc control modes. The analysis results clearly reveal the underlying difference of the inter-inverter interactions in the HIDC and MIDC systems. Finally, the effectiveness of the theoretical assertions is verified by experiments based on the hardware-in-the-loop platform.

Fast and reliable differential protection based on traveling waves for HVDC transmission line

High voltage direct current (HVDC) technology is the ideal solution for long distance bulk power transmission. However, different from AC systems, differential protection of HVDC lines still faces a lot of challenges. We claim that from the perspective of state estimation, the essence of differential protection is to estimate state variables using measured data, of which the validity indicates whether there is a fault. Therefore, the performance of the differential protection is highly related to the model accuracy. Using a detailed distributed parameter line model, this paper developed a novel differential protection method for HVDC lines based on traveling waves with high reliability. The optimal differential point is also discussed to enhance protection rapidity. Experiments demonstrate that the proposed protection could soon detect internal faults with high fault resistance while maintaining reliability when external faults occur.

Modelling of HVDC Link for Power Quality Assessment

Conversion technique of HVDC has become a dominant technology for long distance bulk power transmission. The AC and DC system are interconnected by HVDC converter thus, it becomes the medium of the harmonic transfer. The presence of harmonic not only increases the losses, but it can also lead the system to collapse. In this study, the passive filter is used to mitigate the harmonics in both the AC and DC sides of the HVDC network by tuning it until satisfied with the harmonic standard. The test system of TNB-EGAT HVDC link is modelled using PSCAD software with AC voltage rating of 275 kV and 230 kV for rectifier and inverter side, respectively. The system is controlled by the control system that has been modelled according to CIGRE Benchmark. Comparison of the simulation results between before and after the implementation of passive filters in the system reveals that the harmonics have been mitigated effectively. The results show that the level of THD current at the AC side reduced to 0.2336% and 0.0154% at rectifier and inverter side, respectively.

A supplementary control for mitigation of successive commutation failures considering the influence of PLL dynamics in LCC-HVDC systems

Line commutated converter based high voltage direct current (LCC-HVDC) links are widely employed for long distance bulk power transmission and asynchronous alternating current (AC) grid connection. However, LCC-HVDC systems often suffer from commutation failures when AC voltage is distorted, oscillating or reduced by AC faults, which leads to overheating of converter valves and interruptions in transmitted power. Seriously, it would have adverse impact on the safety and stability of the entire power system. This paper proposes a supplementary control for mitigation of successive commutation failures on the basis of analyzing the influence of phase-locked loop (PLL) dynamics on the commutation process. By analyzing the impact of PLL dynamics on the actual leading angle, it is found that changes in the AC voltage phase remarkably influence commutation. Accordingly, the error between AC voltage phase and PLL's output angle is added to the output of the extinction angle or DC voltage control to mitigate the successive commutation failures of LCC-HVDC. Simulations conducted on the CIGRE benchmark model in PSCAD/EMTDC validate the performance of the supplementary control, which effectively mitigates successive commutation failures.

Performance Evaluation of Distance Relay in the Presence of Voltage Source Converters-Based HVDC Systems

Voltage source converters (VSC)-based high voltage direct current (HVDC) link is an economical option for the long distance bulk power transmission, and it can be used to interconnect the offshore wind farms with an AC grid. Due to the penetration of VSC-HVDC system into the AC grid, the performance of the distance relay gets affected when a transmission line close to the point of common coupling (PCC) subjected to power system disturbances. In such condition, the PCC voltage is increased due to the VSC-HVDC control action, that causes the Zone-2 fault can be seen as a Zone-3 fault. As a result, the miscoordination of Zone-2 protection can occur in the distance relays. This paper presents both the analytical and simulation studies carried out on a VSC-HVDC system influence on the distance relay performance under fault conditions using PSCAD/EMTDC. Simulation results show that the presence of VSC-HVDC system greatly affects the performance of the Zone-2 and Zone-3 relay in an AC transmission line. Besides, the maloperation of the Zone-2 and Zone-3 relay is mitigated by varying the AC voltage reference input of the decoupled d-q controller of VSC-HVDC. Also, the effect of fault resistance on Zone-1 ground relay performance is analyzed.

Review of DC fault protection for HVDC grids

The development of modular multilevel converter (MMC) and the increased needs for long distance bulk power transmission using underground and subsea cables have promoted the rapid development and application of voltage source converter (VSC) based high‐voltage DC (HVDC) systems. In this paper, recent advances in the area of DC fault protection in VSC‐based HVDC systems are reviewed. The main characteristics during DC faults are described and various converter topologies, which have DC fault blocking capability, are introduced and compared in terms of efficiency, cost, and control flexibility. The development of DC circuit breaker is introduced and various methods for DC fault detection and system level protection approaches for large scale HVDC grids are also discussed. WIREs Energy Environ 2018, 7:e278. doi: 10.1002/wene.278This article is categorized under: Energy Infrastructure > Systems and Infrastructure Energy Systems Economics > Systems and Infrastructure

A novel and comprehensive single terminal ANN based decision support for relaying of VSC based HVDC links

HVDC technology is increasingly important for long distance bulk power transmission, but existing protection relaying techniques for such a system are subject to limitations. This paper presents a novel Artificial Neural Network (ANN) based on an algorithm for fault detection, location and classification in VSC-HVDC systems. Taking advantage of the ability of ANNs to identify and classify patterns, the proposed algorithm is able to detect and correctly classify a fault occurring at either the rectifier substation on the DC line or at the inverter substation. Therefore, such a scheme can be used as a decision support tool or as a backup protection. Only local signals are used at the rectifier substation and no communication link is necessary, thus improving the system’s protection reliability and reducing the overall cost of the hardware implementation. A detailed VSC-HVDC system is described and used to simulate a number of fault scenarios in the system. Using the resulting fault waveforms, a comprehensive decision support scheme is developed and described, paying particular attention to the signal processing chain and design of the specific ANNs for each relaying task. Finally, a detailed analysis of the influence of key fault parameters on the limits of the algorithm’s performance is carried out.

Theoretical analysis of tuned HVAC line for low loss long distance bulk power transmission

One of the main objectives of the smart grid initiative is to enable bulk power transmission over long distance, with reduced transmission losses. Besides the traditional high-voltage alternating current (HVAC) transmission, with the advancement in power electronics, high-voltage direct current (HVDC) transmission is increasingly becoming important. One of the main factors impacting the transmission line parameters and the losses is the length of the transmission line (overhead). In this paper, a concept of tuned high-voltage AC line is presented for long (> 250 km) transmission line. A tuned line is where the receiving-end voltage and current are numerically equal to the corresponding sending-end values. This paper presents the detailed theoretical analysis of the tuned HVAC line, suggesting adaptation of the transmission frequency as per the length of the line. The simulation of a tuned HVAC line is performed using the PSCAD/EMTDC. Simulation results for two different line lengths, substantiate the theoretical analysis of reducing the reactive power absorbed in the line, while increasing the active power transmission.

Enhancement of power system dynamic performance through an on-line self-tuning adaptive SVC controller

Static VAr compensators (SVC) are used for voltage control of long distance bulk power transmission lines. By using a supplemental control loop an SVC can also be used to improve the dynamic and transient stability of a power system. Use of a self-tuning adaptive control algorithm as a supplementary controller for the SVC is presented in this article. The control derived is based on a pole-shifting technique employing a predicted plant model. Simulation studies on a simple power system model showed rapid convergence of the estimated plant parameters with an extremely good damping profile. The controller has been tested for ranges of operating conditions and for various disturbances. The effectiveness of the adaptive damping controller was also evaluated through an ‘optimized’ PI controller.

DESIGN OF VARIABLE STRUCTURE CONTROLLER FOR STATIC VAR COMPENSATOR

ABSTRACT Static Var Compensator (SVC) is a relatively new kind of reactive power and voltage control device. It can be used not only to improve dynamic and transient stability of power system, but is especially suitable for voltage control of long distance bulk power transmission lines. To enhance the performance of SVC, in addition to voltage control (main control), a supplementary control (auxiliary control) is required. Variable Structure (VS) Stabilizer is proposed in this paper, as supplementary controller to SVC. The machine, excitation and SVC dynamics are considered. In this paper, a systematic procedure for evaluating gains for sliding mode to occur is presented. The switching vector is constructed using pole-assignment method. Trial and error, and heuristics approach is completely avoided for evaluating the gains in the sliding mode

Power system stabilizing control by a superconducting magnetic energy storage with a high‐speed phase shifter

AbstractElectric power demand has increased rapidly and this is expected to continue. Undamped power swings with low frequency tend to occur in large power systems with complex configuration. Therefore, several stabilizing control schemes, e.g., a power system stabilizer (PSS), have already been investigated.On the other hand, superconducting magnetic energy storage (SMES) is expected to be an effective apparatus in power systems since any SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stabilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is difficult for SMES to serve two different purposes simultaneously.This paper proposes a combination of SMES with a high‐speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of a phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at a generator terminal. In addition, the effectiveness of both load change compensation and power system stabilization is confirmed numerically.

高速移相器を付加したSMESによる電力系統の安定化制御

Recently, electric power demand is rapidly increasing and will be in the future. In the large power systems with complex configuration, undamped power swing with low frequency tends to occur. Therefore several stabilizing control schemes, e. g. a power system stabilizer (PSS), have been investigated so far. On the other hand, superconducting magnetic energy storage (SMES) has been expected as an effective apparatus in power systems since a SMES located in power systems is capable of leveling load demand, compensating for load changes, maintaining bus voltages and stablilizing power swings. The effectiveness of each function, however, depends upon the location of the SMES in the power system because the output power from the SMES is distributed according to the impedance ratio of the transmission line at the SMES location. Therefore, it is rather difficult for realize a SMES to server for two different purpose at the same time. This paper proposes a combination of SMES with a high speed phase shifter (HSPS). The HSPS, which consists of a phase shift transformer and a set of power converters, is capable of controlling the power flow of the transmission line by adjusting the phase angle of phase shift transformer. Therefore, it is expected that the combination of SMES and HSPS can realize a highly effective controller independent of its location. Numerical examples demonstrate that the proposed apparatus located far from a generator in a long distance bulk power transmission system is capable of stabilizing the power swing as effectively as the SMES located at the generator terminal. In addition, the effectiveness on the load change compensation as well as on the power system stabilization is confirmed numerically.

Power system stabilization by superconducting magnetic energy storage with solid-state phase shifter

In this paper, a new configuration of power system controller with a combination of superconducting magnetic energy storage and phase shifter, is proposed to improve the stability of a long distance bulk power transmission system. A power system stabilizing control scheme is also proposed. A related simulation shows that the proposed controller is effective for enhancement of power system stability independent of the location of the controller in a long distance bulk power transmission system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

PERFORMANCE EVALUATION OF STATIC VAR COMPENSATED SYSTEM WITH AUXILIARY CONTROLS

ABSTRACT Static VAR system is a new kind of reactive power and voltage control equipment. It can be used not only to improve dynamic and transient stability of power system, but is especially suitable for voltage control of long distance bulk power transmission lines.To improve power system dynamic and transient stability, in addition to voltage feed-back, rotor speed of synchronous machines, bus frequency deviation, and derivative of bus voltage can be used as auxiliary control signals for SVS. The measurement of generator bus frequency deviations and transmission of rotor speed of generators are difficult in single/multi-machine power systems particularly when the SVS is located at the mid point on transmission line.But, power flow over transmission lines can be conveniently and locally measured. In this paper, an attempt is made to use power flow over lines (derivative of active power/reactive power) as auxiliary control signal for SVS. The auxiliary controller parameters are obtained using eigen-value...

Experimental study on stabilization of model power transmission system by using four quadrant active and reactive power control by SMES

This paper presents the experimental results of stabilization of a model power transmission system by using a Superconducting Magnet Energy Storage (SMES). The SMES, which was composed of two sets of GTO (Gate Turn Off thyristor) power converters and a superconducting coil, is capable of controlling active power (P) and reactive power (Q) simultaneously in four quadrants by changing the firing angles of power converters. The model power transmission system was designed to simulate the behavior of a real scale long distance bulk power transmission system with voltage of 500 kV, capacity of 2000 MVA and length of 280 km. In this study, we have experimented power system stabilizing control by applying P-Q simultaneous control ability of SMES. From the results of experiment it was demonstrated that stabilizing effect by means of SMES is very significant.