Development of models and algorithms for power flow calculation

In electrical systems, power flow algorithms are applied to calculate the quasi-stationary voltages and currents. The voltage magnitudes in these systems are tightly linked to the provision of reactive power from appropriate sources such as thermal generators in particular as well as static devices like shunt reactors and capacitors. The feasible reactive power output (maximum and minimum) is usually modeled in a strongly simplified way using constant, voltage-independent values. This assumption is acceptable for a narrow range around the generator’s terminal voltage, but during a disturbance-induced voltage decline this may lead to results on the insecure side. That’s why a model is being developed which allows for sufficient accurate results on the secure side over the entire operational feasible voltage range. It shall require only a few, commonly available, input data.

In this research activity, the following objectives are pursued:

• Development of new models of generation units and other reactive power sources for power flow algorithms in electrical systems. These models shall be valid for the entire operational feasible voltage range.
• Verification of their applicability through implementation in network calculation programs
• Comparative simulations against fully dynamic models.
  
  

As a total result of the project, operational models as well as a new software module for power flow calculations to determine the explicit voltage stability margin shall be developed. They shall be applicable in other quasi-stationary calculation methods, too.

The approach is divided into the following steps:

• Conception:
  The available literature about control and protection of generation units shall be evaluated. With the consultation of operators and manufacturers, the structure of current models and their implementation in power flow calculation programs along with their disadvantages shall be identified. Based on the gathered information suggestions for optimization are developed and new, advanced models are created.
• Implementation:
  To implement the new models for generation units and reactive power compensation devices suitable algorithms are developed which can handle the versatile effects of a change inreactive power output on the reactive power balance, the operational voltage in particular and the demand for reactive power in the grid.
• Validation:
  The test and verification of the models is done by comparison with disturbance reports and by comparison against fully dynamic network simulations based on sample networks.
  
  

M.Sc. Hendrik Acker

[1]  H. Acker, S. Loitz, W. Wellssow, “Improving the Accuracy of System
 Security Assessment in Highly Stressed Transmission Grids,” in 
 Innovative Smart Grid Technologies (ISGT), 2013

[2]  S. Loitz, H. Acker, and W. H. Wellssow, “Improving the system voltage stability assessment by using advanced reactive power generation models,” in Security in Critical Infrastructures Today, Proceedings of International ETG-Congress 2013; Symposium 1, 2013, pp. 1–6.