Constant Extinction Angle Control Research Articles

Stability Analysis via Impedance Modelling of a Real-World Wind Generation System with AC Collector and LCC-Based HVDC Transmission Grid

Stability Analysis via Impedance Modelling of a Real-World Wind Generation System with AC Collector and LCC-Based HVDC Transmission Grid

Research on CIGRE benchmark model and improved DC control strategy

The safe and stable operation of the HVDC transmission system greatly depends on the control system. The DC control system realizes a series of control strategies such as constant-current, constant-voltage, and constant-extinction angle control by controlling the trigger phase. The CIGRE Benchmark model is often used as a standard test model for research, but it is usually necessary to improve in actual project. First of all, taking the CIGRE Benchmark model as the research object, the DC control mode and basic control functions are introduced systematically. On this basis, the improved control strategy is studied. At the same time, PSCAD / EMTDC simulation software is used to build an improved control system model. The transient response of CIGRE Benchmark and improved control system is simulated and analyzed. Furthermore, the control mode conversion and control system response under different control strategies are studied.

Current-limit control method to prevent subsequent commutation failure of LCC-HVDC based on adaptive trigger voltage

With the wide construction of the line-commuted converter-based high-voltage direct current (LCC-HVDC), a large-scale AC/DC hybrid grid pattern has gradually formed. LCC-HVDC is prone to subsequent commutation failure (SCF) during the recovery process of first commutation failure (FCF). This phenomenon poses a great threat to the safe and stable operation of the power grid. LCC-HVDC is equipped with several controllers to prevent SCF. However, these controllers adopt preset fixed parameters and ignore the fault severity and LCC-HVDC self-regulation. The controller effect may not match the dynamic demand of the FCF recovery and even become the driving force of SCF. Accordingly, a new method is proposed on the basis of the quantification of the FCF recovery consequence, and it can avoid SCF by dynamically adjusting the DC current command according to a variable slope of Ud--Id - ord curve. First, the causes and influencing factors of SCF are presented by analyzing the recovery process of CF under the AC grid fault. Second, the correlation factors of the FCF recovery path are analyzed, and the idea of adaptive control against SCF based on the critical slope is proposed. Third, the critical slope of the Ud-Id - ord curve is derived with considering the influence of the initial state of the fault and constant extinction angle control. Then, a current-limit control method to prevent SCF based on the adaptive trigger voltage is proposed with considering the influence of the DC current variation on power angle stability. Finally, simulation results verify the effectiveness of the proposed method in preventing SCF.

Comparative Study on Small-Signal Stability of LCC-HVDC System With Different Control Strategies at the Inverter Station

The constant extinction angle control and constant DC voltage control are widely used for the inverter station of Line Commutated Converter based High Voltage Direct Current (LCC-HVDC) system in practical engineering. Under different control strategies, the control system parameters would have totally different effects on the stability of the LCC-HVDC system. In this paper, the small-signal models of the LCC-HVDC system with constant extinction angle control and LCC-HVDC system with constant DC voltage control are developed, respectively. Based on the eigenvalue analysis, this paper conducts a comprehensive comparison of the effects of a phase-locked loop (PLL) and LCC controller on the small-signal stability of LCC-HVDC system with different control strategies at the inverter station under weak AC grid condition. Then, the coupling effect between the PLL and LCC controller parameters is investigated when LCC-HVDC system adopts different control strategies. This paper can provide useful guidance for the systematic design and control parameter selection of LCC-HVDC projects.

Analysis of the commutation failure of inverters during open-conductor faults at the AC side

Summary Commutation failures (CFs) in inverter stations disturb the power system greatly. Open-conductor fault (OCF) is a longitudinal fault. When it occurs in the alternating current (AC) system, the three-phase voltages are unbalanced. Under this circumstance, it is generally considered that inverters can maintain normal commutation order for the voltage support provided by other transmission lines in normal operation. In this paper, the possibility of the inverter CF during OCF is established. The sensitivities of the CF to the AC voltage disturbances caused by the changes of the AC superposition voltage are analyzed. It is concluded that the sensitivities of the CF with different transformer wiring schemes and fault types are diverse. Before the CF happens in the inverter station during OCF, the CF may occur in other inverter stations of the multi-terminal direct current systems with the constant current and constant extinction angle control strategies. Simulation studies are performed in the PSCAD/EMTDC software (Copyright(C)2006, Manitoba HVDC Research Centre, Canada), and the theoretical analysis is validated by the simulation results. Copyright © 2014 John Wiley & Sons, Ltd.

Modeling of effective margin angle characteristics and AC voltage stability analysis of CCC

AbstractA capacitor commutated converter (CCC) has a simple circuit topology of a series capacitor placed between the valve and the converter transformer in each phase. The series capacitor mitigates the inverter operation of a CCC by assisting the commutation with the voltage charged in it. However, it does not guarantee complete commutation in any conditions, for a valve does not have self‐extinction ability. Therefore, precise analysis of the commutation process of a CCC is required to secure its operation. First, the formulation of the interrelation among the converter parameters—AC voltage, DC voltage, firing delay angle, overlap angle, and effective commutation margin angle—is presented. The firing delay angle at a given effective margin angle is calculated by using the obtained equations, which can be applied to constant extinction angle control. Next, we assess the AC voltage stability of an AC/DC link, when constant extinction angle control is applied to the inverter of CCC. The calculated voltage stability factor (VSF) shows that the commutation capacitor improves the AC voltage stability of constant extinction angle control at the inverter linked to a weak AC system, but it differs by the rectifier operation mode and compensation factor of the commutation capacitor. © 2001 Scripta Technica, Electr Eng Jpn, 137(4): 38–47, 2001

直流送電の電流制御と余裕角制御の組み合わせにおける安定性に関する考察

直流送電の電流制御と余裕角制御の組み合わせにおける安定性に関する考察

Microcomputer Control of Power Converters

Thyristor power converters are charac terized by an inherent discrete control action and are, therefore, particularly well suited to on-line control by microcomputers. The paper presents a new design of digital controllers based upon powerfull 16-bit or bit-slice microprocessors, which provide high firing time resolution and enough computing power to implement sophis ticated control strategies. Both hardware and software are discussed, with special emphasis on the firing con trol algorithms. The properties of Pulse Frequency Con trol (PFC) and Pulse Phase Control (PPC) are examined and small-signal discrete models are presented. These models are used in the analysis of constant current and constant extinction angle control through the z-transform method.

Minicomputer online control of d.c. link convertors

The implementation of a scheme using an online minicomputer to control the convertor of a model d.c. transmission system is described. The reasons for, and the limits of, the present investigation are defined. A brief description is given of the hardware designed to link the minicomputer to the model simulator. The development of algorithms to execute constant current, constant firing-angle and constant extinction-angle control, the last with predictive capability, are then described. These programs utilise the unique characteristics of a computer in terms of logical processing ability and memory storage. Test results demonstrating the performance and advantages of this control system are presented.

Hybrid simulation of fuel cell power conversion systems

Simulation techniques and results are presented for hybrid computer studies of line-commutated and self-commutated three phase bridge inverters. The line-commutated bridge system included constant extinction angle control of the inverter, power regulation of the DC source, and power factor correction capacitors. Simulation of this system was performed in real-time which allowed testing of prototype control hardware. The self-commutated system consists of three bridges operating in a phased sequence which permits elimination of harmonics by cancellation. System performance is evaluated with the inverters operating into a three phase load, part of which is supplied by the utility system. The paper discusses the computational techniques used in simulating systems of this type, including the role of the digital and analog computers in each study. This work supports the conclusion that hybrid simulation is a valuable tool for analysis and evaluation of power conversion systems which contain current switching devices.

A New Constant Extinction Angle Control for AC/DC/AC Static Convertors

Maximum utilization of an invertor's capacity and minimum consumption of reactive power demands an accurate constant extinction angle control. A new scheme for such a control is presented that is based on the integration of each commutating voltage waveform from -π + δc, thereby obtaining a simulation of the steady- state commutation equation. The resulting control is capable of fresh computation of the firing angle every cycle. The control is extended to cover the convertor operation over its full range from a minimum permissible angle of delay to the minimum permissible extinction angle.