Abstract
To achieve better control performance, a comprehensive control parameter design method that considers economics, stability and dynamic performance is essential for hybrid multi-terminal HVDC systems. In this paper, a hierarchical model for the control system of Hybrid-MTDC is constructed and the parameters are optimized on two layers. On the system layer, using the normalization processing method, a system-layer objective function that considers both the minimum network loss and the voltage offset is formed for Hybrid-MTDC systems and solved with the proposed penalty interior point method. On the converter layer, using the state-space matrix method, a generic small-signal stability range of each control parameter can be obtained by the traversal calculation of the eigenvalues. Then, to identify the stricter stable operating region for the DC voltage controller under severe conditions, an additional stability criterion based on the mixed-potential theory is deduced, and the design-oriented boundaries are generated and added to the feasible region. Finally, within the design-oriented boundaries, a general dynamic performance evaluation function is constructed to determine the optimal control parameters. Utilizing the proposed method, a typical Hybrid-MTDC system is investigated, and experimental verifications are provided to validate the effectiveness and accuracy.
Highlights
In traditional HVDC projects, line commutation converters (LCC) have benefits such as high transmission capacity and low cost [1], [2]
To propose a comprehensive control parameter design method for Hybrid-MTDC systems, the main contributions of this paper are listed as follows: (i) Considering the economics of operating Hybrid-MTDC systems in the steady state, an objective function on the system layer that includes both the minimum network loss and the voltage offset is formed for Hybrid-MTDC systems
To identify the stricter stable operating region for the DC voltage controller under severe conditions, an additional stability analysis based on the mixed-potential theory is performed and the design-oriented boundaries are generated and added to the feasible region. (iii) Within the design-oriented boundaries, a dynamic performance evaluation function is constructed using the damping ratio and the negative real part of the eigenvalue, which can describe the dynamic performance of all oscillation modes of the system
Summary
In traditional HVDC projects, line commutation converters (LCC) have benefits such as high transmission capacity and low cost [1], [2]. The power flow control parameters on the system layer affect network losses and voltage offsets, which determines the economics of operating Hybrid-MTDC systems in the steady state. 3) Efficient global dynamic performance analysis: Reference [18] proposed a quantitative dynamic performance evaluation for Hybrid-MTDC systems based on a time-domain mathematical model This method can only perform an inverse Laplace transform for one of the outputs to analyse the dynamic indicators, which cannot be used as the global optimal term for all outputs of the dynamic performance analysis. To propose a comprehensive control parameter design method for Hybrid-MTDC systems, the main contributions of this paper are listed as follows: (i) Considering the economics of operating Hybrid-MTDC systems in the steady state, an objective function on the system layer that includes both the minimum network loss and the voltage offset is formed for Hybrid-MTDC systems.
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