Interline DC Power Flow Controller Research Articles

Power Flow Study of MT-HVDC Grid Compensated by Multiport Interline DC Power Flow Controller

DC power flow controllers (DCPFCs) are emerging devices to control power flow in voltage source converter (VSC)-based multi-terminal HVDC (MT-HVDC) grids. In this paper, a novel Newton-Raphson (NR)-based DC power flow solver (DCPFS) is proposed to solve the DC power flow problem (DCPFP) by using a novel multiport interline DC power flow controller (MIDCPFC), where physical and control state variables of the whole system (MIDCPFC and MT-HVDC grid) are modified simultaneously to achieve predetermined control objectives. The static model (SM) and the power injection model (PIM) of the considered MIDCPFC have been derived and their equations are embedded within the proposed DCPFS. Since there are no fictitious buses in the proposed DCPFS, the original conductance matrix of the system and its symmetry are preserved, and only minor modifications are needed on the original system's Jacobin matrix. It is very straightforward to implement the proposed DCPFS as the voltage of intermediate capacitor of the MIDCPFC is treated as an independent variable, and thus, an external process to control its value is not needed. In this study, comprehensive models have been proposed to model losses of the MIDCPFC and VSCs for the first time; and the shunt conductance of HVDC lines have also been considered. Finally, a modified 15-bus MT-HVDC grid is proposed for verification purposes. The obtained results verify the accuracy and efficacy of the proposed concepts, models, and formulations of this study.

Stability Analysis and Control Design for Multiterminal HVDC Network With Power Flow Controller

The power flow control in high-voltage direct current (HVDC) grids can be improved by employing the interline dc power flow controller (IDCPFC). This article presents an improved control scheme using IDCPFC to balance power flow in the dc networks. In this work, a differential-mode transformer (DMT) is used in combination with a bidirectional buck converter to form a variable DMT. In comparison to the existing methods, the proposed system is scalable to higher voltages and powers, which makes it suitable for high-voltage dc transmission systems. Analysis of a small-signal model of the proposed method and design of compensator for improvement of transient behavior is performed. A simulation is performed with independent feed-forward and feedback control to show the effectiveness of the proposed method. The proposed method is also validated through a 600-W experimental prototype. The experimental results show that the current flow between lines is controlled for unbalance load conditions.

Technical Constrained Power Flow Studies for IDC-PFC Integrated Into the MT-HVDC Grids

Power flow (PF) flexibility in the multi-terminal HVDC (MT-HVDC) grids is a thought-provoking issue. It leads to employing the active DC power flow controller (DC-PFC)s. Hence, this paper examines the static average model (AM) and power injection model (PIM) of an interline DC-PFC (IDC-PFC). It is to provide a suitable base for DC PF studies and easy embedding of the DC-PFCs into MT-HVDC grids’ PF equations. In this regard, this paper proposes a new DC PF solver (DC-PFS) for the IDC-PFC compensated MT-HVDC grids within the well-accepted Newton-Raphson (NR) framework. It requires a few modifications in the main structure of the system's Jacobin (J) matrix compared to the uncompensated MT-HVDC grid. Also, the system's admittance matrix and its symmetry are preserved. In the proposed concept, the IDC-PFC cooperates with other MT-HVDC grid's state variables to satisfy the predetermined control objective(s). Furthermore, this paper proposes a new solution procedure (SP) to handle various system's limitations during the processes of solving the DC PF problem. Meanwhile, there is no need to modify the related J matrix. The effective and accurate performance of the IDC-PFC's models, as well as presented NR-based DC-PFS and SP, are verified by performing several simulations on the 8-bus CIGRE MT-HVDC grid.

Modular Interline DC Power Flow Controller

DC power flow controller (DCPFC) is regarded as an effective technology to improve the active power distribution capability in a complex dc grid. Among different types of DCPFCs, the interline dc power flow controller (IDCPFC) can realize multiline power flow control functions in a complex dc grid. In this article, a modular multiline IDCPFC has been proposed via a transformerless structure. Specifically, the n -line IDCPFC can actively control ( n −1)-line power flow based on the theoretical analysis. The proposed technology is analyzed in detail, including topology, operation principle, and control strategy. As a case study, a three-line IDCPFC is implemented in this article. Both simulation and experimental results are obtained to show that the proposed IDCPFC can effectively control multiline power flows under various conditions.

Interline dc power flow controller with fault current‐limiting capability

Power flow control and fault current limitation are two major problems that require an urgent solution in a direct current (dc) grid. This study proposes a novel interline dc power flow controller having a fault current limitation capability (FCL–PFC). The proposed controller is expected to realise overall control of the internal power flow in a dc grid and to limit the fault current under fault conditions. FCL–PFC exhibits small capacity and low loss and does not require energy from an alternating current (ac) system. The topological structure of FCL–PFC is first introduced. Then, the principles of power flow control and self-power balance using the dc voltage and ac circulating current, respectively, is discussed. The control strategy under stable conditions is further designed. Based on the proposed FCL–PFC action sequence under fault conditions, this study describes the calculation and analysis of the dc fault current in different periods for maximising the fault current limitation ability of FCL–PFC. Finally, a simulation model is used in PSCAD/EMTDC to verify the power flow control and fault current limitation capabilities of the proposed FCL–PFC. The economy of combining FCL–PFC with direct current circuit breakers is analysed.

Investigate on a Simplified Multi-Port Interline DC Power Flow Controller and Its Control Strategy

A DC power flow controller (DCPFC) can help to facilitate power flow routing in the multi-terminal high-voltage direct current (HVDC) transmission system. Realizing its multi-port output can effectively improve the device regulate range and capability. Based on analysis of the traditional multi-port interline DC power flow controller (MI-DCPFC), this paper presents a switches reduced topology of MI-DCPFC. In addition, for solving the problem of coupling of the port-output voltage of the traditional MI-DCPFC, a novel control strategy based on carrier phase shifting pulse width modulation (CPS-PWM) is proposed. It implements the decoupling of the port-output voltage of MI-DCPFC, which can ensure completely independent tracking of the power flow regulating commands for different controlled lines. Moreover, key relationships between the system state variables are also analyzed and detailed in this study. Finally, the performance of the proposed controller and control strategy are confirmed with the simulation and experiment studies under different conditions.

A Novel Interline DC Power-Flow Controller (IDCPFC) for Meshed HVDC Grids

Power-flow control ability of meshed high-voltage direct-current grids can be improved by inserting a dc power-flow controller into the grids. Based on the study of existing dc power-flow controllers, this paper proposes a novel interline dc power-flow controller (IDCPFC) which has the benefit of fewer active switching devices, simpler control, little side effect on meshed grids, no external power source needed, and wide application occasions. The performance of the IDCPFC is validated by simulation and experimental tests. The results show that the proposed IDCPFC can achieve stable power-flow control in different conditions.