Converter High-voltage Direct Current Transmission Research Articles

Research on control parameter optimization of LCC-HVDC system based on zero-pole optimal position distribution

The proportional-integral (PI) control is widely adopted as the leading controllers of the line-commutated converter high-voltage direct current transmission system (LCC-HVDC), while unreasonable coefficients setting will result in the DC system instability and aggravate system dynamic performance. In order to improve the overall response performance of the system, a tuning method of the controller parameters guided by the linearized zero-pole transfer function of the DC system is proposed. Firstly, the small signal analysis method is used to formulate the closed-loop transfer function model at the stable operating point. According to the position of zero and pole, the objective function which can quantitatively reflect the dynamic and steady state characteristics of the DC system is derived. Furthermore, combined with the particle swarm optimization (PSO) intelligent optimization algorithm, the multi-group control parameters of the system are optimized. Finally, by comparing the time domain numerical simulation results before and after parameter optimization, it is verified that the proposed tuning method can effectively improve the dynamic and steady-state characteristics of the DC system.

The Unified Supplementary Damping Method Based on Voltage-Soured Converter High-Voltage Direct Current Transmission Through Robust Control

The VSC-HVDC system can damp the inter-area low-frequency oscillation effectively. To enhance the ability of the VSC-HVDC supplementary control, this article proposes a unified low-frequency oscillation controller design using the robustness theory. The unified control strategy uses both the active power control and reactive power control loop of the VSC to expand the supplementary control dimensions. To design the controller, the TLS-ESPRIT identification method is used to obtain the system small signal model and the oscillation characteristic. Based on the model identified out, the linear matrix inequality method based robust control theory is applied for the controller design, and the robust controllers for active power control and reactive power control loop are both designed to improve the control effect. Finally, the simulation results show that the controller can reach better control effect and the robustness can also be guaranteed.

Dynamic Surface Backstepping Control for Voltage Source Converter-High Voltage Direct Current Transmission Grid Side Converter Systems

This paper studies the coordination control of active and reactive power of the voltage source converter-high voltage direct current transmission (VSC-HVDC) grid side converter. Firstly, the high-order VSC-HVDC converter system is decomposed into three subsystems by using the backstepping control method, and the control laws are designed for each subsystem to realize the control of VSC-HVDC converter systems. Secondly, the dynamic surface control method is used to deal with the problem of “explosion of complexity” in the traditional backstepping control method. Finally, the simulation results demonstrate that the VSC-HVDC converter systems can provide a certain capacity of reactive power compensation under the proposed method in this paper. In addition, the control method proposed in this paper does not require the information of the second derivative of active power and reactive power.

Study on overvoltage of hybrid LCC‐VSC‐HVDC transmission

Hybrid line commutation converter-voltage-source converter high-voltage direct current transmission (LCC-VSC-HVDC) power transmission has unique technical advantages, but its overvoltage study is not sufficient at present. In this study, the typical overvoltage phenomenon of hybrid LCC-VSC-HVDC power transmission is analysed and verified by power systems computer-aided design/electro-magnetic transient design and control simulation. On the one hand, overvoltage mechanism of modular multilevel converter module caused by single-phase grounding fault at the valve side of VSC transformer is analysed, and arresters are configured for the protection of the valve. On the other hand, the stress of the arresters at the LCC side is analysed. Installing current reversing protection on the VSC side is proposed. The research of this study provides the recommended arresters configuration in the converter station of hybrid LCC-VSC-HVDC power transmission system.

Online dynamic voltage stability assessment method of AC/DC power systems

The reactive power absorption of conventional line commutated converter–high-voltage direct current transmission systems challenges on the voltage stability of AC/DC power systems. Many online dynamic voltage stability assessment approaches have been put forward to AC power systems, but the impact of DC transmissions is seldom taken into account for AC/DC power systems. In this study, an online dynamic voltage stability assessment method of AC/DC power systems is proposed. The proposed method models the converter as an equivalent AC voltage source in series with the internal impedance by utilising the control mode model of DC transmission systems and the measured data of the converter bus. The equivalent AC voltage source can identify the dynamic of DC transmissions. Then the AC/DC power system can be modelled by the equivalent AC power system. Based on the nodal equivalent method, the proposed method establishes a voltage stability index of the equivalent AC power systems for the dynamic voltage stability assessment of AC/DC power systems. The simulation demonstrated the effectiveness of the proposed method.