Coordinated multiple HVDC modulation emergency control for enhancing power system frequency stability

Abstract

High‐voltage direct current (HVDC) power modulation can effectively improve the system frequency stability after high power shortage fault disturbance. This study presents an emergency control method by coordinating the active powers of multiple HVDC lines for enhancing the frequency stability. Firstly, the system frequency response model with HVDC modulation is built, and then a simplified method for calculating the sensitivity of maximum frequency to HVDC modulation is proposed based on the first‐order differential method. Next, based on a functional relationship of the AC bus voltage and the actual HVDC modulation capacity, the methodology for calculating the HVDC real‐time modulation capacity is proposed. Finally, the coordinated multiple HVDC modulation emergency control model is established which aims to minimise the modulation cost considering the maximum frequency threshold. The proposed methodology has been tested in a real‐power system. The simulation results of different scenarios have verified its effectiveness in suppressing the rise of maximum frequency and enhancing frequency stability.

Coordinated emergency control strategy of high‐voltage direct current transmission and energy storage system based on Pontryagin minimum principle for enhancing power system frequency stability

“…When the power support of VSC‐HVDC is used to improve the dynamic frequency, the security constraint of the AC system should also be considered to avoid power flow over the limit of AC transmission [20]. In order to ensure the power flow of the AC transmission lines within the limit, the transfer ratio is defined [21] $$$$\begin{equation}{\sigma }_i = \frac{{{P}_{i,1} - {P}_{i,0}}}{{\Delta {P}_H}}\end{equation}$$$$where P i ,0 and P i ,1 is the power flow of the i th important power transfer interface before and after the power support of VSC‐HVDC, respectively; Δ P H is the magnitude of the power support of VSC‐HVDC. The transfer ratio is a constant, which is determined by the network of the AC system.…”

“…Therefore, when the stability limitation of the important interface power flow P i ,max and the initial power flow at fault time are given, we can calculate the maximum power support of VSC‐HVDC [21] $$$$\begin{equation}\Delta {P}_{H\max ,{\rm{ac}}}{\rm{ = }}\frac{{{P}_{i,\max } - {P}_{i,0}}}{{{\sigma }_i}}\end{equation}$$$$To sum up, when the short‐time overload capability of HVDC and security constraint of AC system are considered, the maximum power support of VSC‐HVDC can be obtained: $$$$\begin{equation}\Delta {P}_{H\max } = \min (\Delta {P}_{H\max ,o},\Delta {P}_{H\max ,{\rm{ac}}})\end{equation}$$$$…”

“…When the power support of VSC-HVDC is used to improve the dynamic frequency, the security constraint of the AC system should also be considered to avoid power flow over the limit of AC transmission [20]. In order to ensure the power flow of the AC transmission lines within the limit, the transfer ratio is defined [21] 𝜎…”

“…There are few studies on the emergency frequency coordinated control. In [20, 21], a coordinated multiple HVDC emergency optimization control problem is solved, which aims to minimize the control cost considering the frequency threshold, the power of important interfaces and the operating conditions of HVDC. But the frequency variation of the non‐disturbed systems connected to HVDCs and the overload capacity limit of HVDC are not considered.…”

Equal‐area criterion and analytical model for transient stability assessment of hybrid AC–DC transmission system using voltage sourced converter

“…In all those presentations, the focus has been on the transient analysis of AC power systems. To achieve high controllability and economical transmission over long distances, high-voltage direct current (HVDC) systems using voltage sourced converters (VSCs) are seen as a promising option for grid extension [4][5][6]. The availability of an equal-area criterion for combined AC and VSC-HVDC trans-mission would be very valuable.…”