A Post-Contingency Power Flow Control Strategy for AC/DC Hybrid Power Grid Considering the Dynamic Electrothermal Effects of Transmission Lines

Abstract

The blocking of large-capacity HVDC or the tripping of AC transmission lines by accident will cause power flow transfer sharply and increase the risk of cascading faults in AC/DC hybrid power grid. Therefore, it is needed to take reasonable safety control measures in time to interdict the spreading of the accident. In this paper, a post-contingency power flow control (PPFC) strategy for AC/DC hybrid power grid was proposed. This strategy brings the dynamic electrothermal effects of the conductor into the safety constraints to fully excavate the short-time overload endurance capability of transmission lines, and coordinates the active power adjustment of generators, power transmission adjustment of HVDC, and load shedding measures, to realize the dynamic optimal power flow control in multiple time sections. The proposed optimization control model takes minimum total cost as the objective function, and accounts for the influence of different weather conditions along the transmission lines and load fluctuations after the accident on the electrothermal safety of transmission lines, which can quickly provide the economical and reasonable power flow control scheme, to prevent the AC/DC hybrid power grid from unexpected cascading tripping effectively. Finally, the effectiveness and superiority of the proposed strategy were verified through case studies on the modified IEEE 10-machine 39-node power systems.

Using the Thermal Inertia of Transmission Lines for Coping with Post-Contingency Overflows

“…))] ≤ 0 into the master problem; 33: end if 34: end for 35: end while Output: The active power output of each unit in the preventive stage and its adjusted amount in the corrective stage. The power flow distribution and variations of line conductors.…”

“…A temperature dependent power flow model has been established in [34] where the dependence of line resistances on conductor temperature was taken into account. In [35], the dynamic electrothermal effect has been brought into safety constraints of the post-contingency power flow control to excavate the overload endurance capability of lines.…”

“…An approximate quadratic relationship between the temperature and the square of current has been derived by some reasonable approximations in [34], and the analytical solution of HBE was obtained for a step change in currents. Reference [35] has proposed that, through transforming the HBE into algebraic difference equations by a numerical integration method, the optimal solution can be realized by combining those transformed equations with other algebraic equations.…”

AC Tie-Line Power Oscillation Mechanism and Peak Value Calculation for a Two-Area AC/DC Parallel Interconnected Power System Caused by LCC-HVDC Commutation Failures

“…Once continuous CFs occur, they could result in significant direct current increases and thus lead to an overheating of converter valves that would shorten their lifespans [24,25]. To reduce the probability of a CF occurring, many papers have focused on improving algorithms [26][27][28], improving the DC control strategy [29][30][31] and adjusting the network topology [32]. A hybrid configuration had been proposed that inserted a dynamic series capacitor and added fixed parallel capacitors at the valve side of the converter transformer [33][34][35].…”

Bi‐level optimised emergency load/generator shedding strategy for AC/DC hybrid system following DC blocking

“…Online control and corrective control coordination strategy for UHVDC blocking faults are put forward in [20], which can solve the problem of transmission section overload caused by UHVDC blocking. Hu et al [21] presented a post-contingency power flow control strategy for AC/DC hybrid power grid considering the dynamic electro-thermal effects of transmission lines. A dispatching and control strategy of the UHVDC blocking fault in the sending-end power grid is proposed in [22], which is based on big data technology and guarantee the grid frequency and voltage do not exceed the limit.…”