Modelling features of a VSC-HVDC transmission embedded in AC system

The paper considers specifics of mathematical model of DCTV continuous modes being included into power network calculation program developed in Labview software in the department of power plants, networks and systems. The program has such input parameters as network configuration, power line resistances, load and generation capacities, slack bus voltage and calculation accuracy. The paper presents analysis of network losses depending on DCTV load. Examples of post-fault network conditions were used to show positive features of DCTV in comparison with AC transmission. It is shown that applied DCTV extends the boundaries of network mode optimizations and enhances its safety in fault and post-fault modes. Special feature inherent to the model of DCTV continuous modes is that voltage vectors in the nodes of rectifier and inverter stations are not rigidly connected, and actual line power is regulated independently. In the model, nodes are connected through power consumption in one node and generation in another node, and it is specific that in continuous mode DC circuit of DCTV is described with the same equations as DCT on phase-control converters. Losses in converter transformers and reactors, and converters are factored as loads in the nodes of corresponding stations. Vector difference between rectifier station voltage and network voltage determines value and direction total capacity of transmission. The same is true for inverter station as related to its adjoining power system. Power-handling transmission capacity is limited to maximum actual current of converter that is limited to standardized current load of power semiconductor devices. Developed program is designed for educational purposes, and DCTV model can be integrated into industrial programs for calculation and optimization of power system modes.