Impact of DC Breaker Systems on Multiterminal VSC-HVDC Stability

Abstract

The use of VSC-HVDC grids for offshore wind farm integration will require the use of dc breaker systems and they, at present, will require dc reactors to limit the rate of rise of fault current. The introduction of large dc reactors throughout a VSC-HVDC system can have significant impact on its stable operation and will require additional control. This paper analyses this problem and proposes a PSS-like control (DCPSS) to aid dc grid stability and cope with this effect. A generalized analytical model for studies on dc voltage control is presented. Key stability and transient performance issues caused by the use of the dc reactors in a multi-terminal system, are investigated by analyzing poles, zeros and frequency responses of both open-loop and closed-loop models. Design and location identification methods for the DCPSS are provided. Excellent damping enhancement is achieved by this controller. The analytical studies and time-domain simulations in this paper are performed based on two VSC-HVDC models. T Disconnector Auxiliary DC Breaker Hybrid DC Breaker Main DC Breaker Current Limiting Reactor Residual DC Current Breaker Fig. 1. ABB Proactive VSC-HVDC Circuit Breaker [1].0885-8977 (c)

Flexible HVDC transmission systems small signal modelling: A case study on CIGRE Test MT-HVDC grid

“…2) to include an approximation of Electro -Magnetic Transient (EMT) type models in the state space formulation. For studies focused on low-frequency oscillations below 100 Hz, cascaded (say to be n) sections (and even single lumped) model is sufficiently accurate [11]. However, to analyze intermediate and highfrequency oscillations above 100 Hz, more elaborated frequency dependent models should be considered [16].…”

“…3. A 9 th order state space model largely adopted from [11] can be derived in the form of (10) with the following state variables, disturbance inputs, linking variable and input vectors: To have a reference model in order to verify the small signal model, the DCS3 grid detailed nonlinear model is simulated in a MATLAB/SIMULINK platform. The parameters stated in [12] are used as the starting point.…”

“…MT-HVDC grids stability and dynamic performance has been extensively studied in [10]-[ [11] and it has been concluded that system stability might be at risk due to instabilities originated by MT-HVDC resonance, weak onshore AC networks, constant power loads and the addition of DC circuit breakers. As a new component is added to the existing MT-HVDC grid, the concerns about system stability, interoperability, possible adverse interactions and highly inductive grid are likely to be increased again.…”

Modelling and Dynamic Analysis of a Power System with VSCHVDC Radial Plus Strategy

“…Presently, such a DC breaker relies on a large DC reactor to limit the rate of rise of the fault current and the rate at which DC voltage reduces. As reported in [7], the large DC reactor will increase the electrical distance between the converter stations, have a detrimental effect on DC voltage control of the grid, and therefore, affect the stability of the system. Furthermore, the requirement of an expensive DC/DC converter to connect two existing point-topoint VSC-HVDC links with different DC voltages also limits the rapid development of VSC-HVDC grids.…”

Frequency domain based DC fault analysis for bipolar HVDC grids

“…The grounding points and the number of parallel branches connected to a busbar in a meshed HVDC grid may change due to system reconfiguration, maintenance, or outage. Furthermore, the inductors in series with the DC circuit breakers fundamentally influence the travelling wave behaviour, and the size of these inductors might take various values depending on the requirements from the DC circuit breakers [3,4] and DC grids [16]. However, protection settings are preferred to be insensitive to changes in the system conditions.…”