Start-Up Control of a Synchronous Condenser Integrated HVDC System With Power Electronics Based Static Frequency Converter

Abstract

The operation of thyristor-based high-voltage direct current (HVDC) system requires abundant reactive power support. Synchronous condensers, as rotating devices with large capacity of reactive power compensation, are generally utilized in HVDC systems. In this paper, the start-up control of a synchronous condenser integrated HVDC system with power electronics based static frequency converter (SFC) is investigated with the following 3 contributions: (1) Three different variable frequency starting methods are proposed regarding the main start-up control component, SFC. (2) Dynamic behaviors of AC voltages, reactive power of the system are studied when the synchronous condenser is integrated into the HVDC with different startup control methods. An evaluation index, including successive rates of integration, reactive power surges, and lengths of start-up period, are established using different start-up control methods. (3) Synthesizing the characteristics of three different start-up control methods, an optimized variable frequency starting control is proposed and the control strategy is further developed. A simulation model of a synchronous condenser integrated HVDC system with an SFC is established in PSCAD/EMTDC. Simulation results justify the effectiveness and superiority of the optimized start-up control strategy proposed. INDEX TERMS Synchronous condenser, different start-up control mode, static frequency converter (SFC), optimized variable frequency control strategy.

Improving Grid-Connection Reliability and Safety of Synchronous Condensers With Start-Up Process Optimization

“…1) The SFC system and the start-up excitation system are activated. With the rotor current controlled by the start-up excitation system in a closed-loop manner, the SFC system drags the rotor and accelerates its speed to 1.05 times rated speed [20].…”

“…8. In other words, if the phase angle difference falls within the range of [ , ], the freewheeling speed ratio regulation method can assure the synchronous condenser connected to the grid successfully, where (20) However, if the phase angle difference falls beyond the above successful range, further actions are required to assure the grid-connection success rate, as detailed in the following sub-section.…”

“…Considering the urgent demand of voltage support after the CF and the requirement of fast reactive power regulation in the multi-fed HVDC transmission system, it is desirable to use the new-type synchronous condenser with smaller sub-transient reactance to address this issue. Though other start-up solutions are available [16], the new-type 300MVar synchronous condenser mainly adopts the static frequency converter (SFC) start-up mode [17]- [19] followed by a freewheeling grid-connection process, during which the SFC is disconnected and the condenser speed is self-decreasing [20]. Because this freewheeling speed is uncontrollable, the success of the grid connection operation depends on the "catching" of the speed when the frequency of the condenser terminal voltage approaches the grid frequency (i.e.…”

Quantitative Assessment for Commutation Security Based on Extinction Angle Trajectory

“…The suppression of CF is important to reduce the risk of DC blocking and increase the transmission capacity of HVDC links. So far, there have been a number of solutions to reduce the risk of CF, which can be classified as follows: the modification of converter topology [3]- [5], the improvement of voltage stability [6], [7], the modification of HVDC control systems [8]- [12], and the application of system emergency control strategies [13], [14], etc. However, the determination of control quantity and control time as well as the assessment of control effects depends on the accurate judgment and evaluation of CF.…”

Highly reliable Coordinated Control Strategy for Static Frequency Converters applied to Large Synchronous Condensers

“…The variable frequency start system is then stopped. After confirming the exit of the inverter startup system, auxiliary excitation is switched to main excitation [12][13][14][15][16][17] . The rated terminal voltage is established by controlling the excitation system.…”