09-11-2012, 05:09 PM
Sequential Load Flow Solution Method for HVDC Links Embedded in AC Power Systems
Sequential Load Flow Solution.pdf (Size: 78.9 KB / Downloads: 647)
This demo illustrates a sequential AC-DC load flow method involving iteration between DC and AC solutions. The AC load flow is performed by the load flow tool of the Powergui. The DC load flow accommodates a two-terminal HVDC system taking into account tap changers of converter transformers. It is performed by a Simulink model LF_HVDC_2terminal containing the DC power flow algorithm. HVDC system parameters are specified in an initialization file LF_HVDC_2terminal_INI. A script LF_ACDC_solve controls the whole process and iterates until the convergence criteria have been reached. This solution technique can be extended to any number of HVDC links connected inside the same AC system or between isolated AC systems.
The AC network used in this demo is the 29-bus system provided with R2012a demos power_LFnetwork_29bus. A DC link has been added between LG27 bus (rectifier) and MTL7 bus (inverter). Once the AC-DC network has been initialized with the sequential solution method, you can run a simulation and observe that the specified power flow settings are respected.
Method Description
The AC-DC system is based on networks provided in two existing demos (power_hvdc12pulse_average and power_LFnetwork_29bus). The HVDC system transmitting 1000 MW at 500 kV through a 800 km line consists of two converter units (YYD transformer and 12-pulse thyristor bridge) represented by their average model1 and 600 Mvar AC filters. The 29-bus AC system uses a 735-kV series-and shunt-compensated transmission system and seven 13.8-kV power plants (total generation capacity of 27 000 MW) including detailed modeling of turbines, speed regulation, excitation systems and PSS. Please, refer to these demos for a detailed description.
Demonstration
The main rectifier control mode is the DC power, set at 1000 MW to be received at the inverter (the rectifier is chosen to be the slack station). The auxiliary mode, when there is a dip in AC voltage would be the alpha minimum mode, set to 5°. At the inverter, the main control mode is the DC voltage, set at 500 kV. The auxiliary mode, when there is a dip in AC voltage would be the minimum extinction angle gamma set to 17°. The tap changer control is set to hold α angle between 14° and 17° at the rectifier and the g angle between 20° and 23° at the inverter.