The established advantage of DIgSILENT PowerFactory software is its comprehensive integrated performance and its ability to model production, transmission, distribution and industrial networks as well as analyzing the interoperability of these networks and restoring power to the network. Electric networks, planning trends and their operational trends are becoming increasingly complex as the market grows, network interconnection develops and distribution continues to expand. This increases the demand for tools that are computer programs that are reliable in terms of data quality, flexibility and manageability. Along with new versions of PowerFactory software, DigSILENT has been able to take a step forward in integrating functionality and data management seamlessly into a team work environment. Creating and organizing plans, scenarios, versions, and sustainable arrangements are available for better organization.

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It will cover the philosophy, creation, initialisation and testing of dynamic models for use in time-domain power systems simulations. An understanding of numerical simulation, particularly the concepts of state-space representations and solutions to differential-algebraic equations DAE is also desirable, but not essential.

It is sufficient to simply be aware that they exist and know that the definitions are here for reference. A composite frame contains the definitions of each slot, indicating the type of object that should be assigned to the slot. Frames are type objects that belong in the equipment type library. The user must define what type of object the slot represents. It links the composite frame which contains slots to the actual network elements, measurement devices and DSL common models in the grid.

It can be seen as the design or blueprint for a piece of equipment e. Model definitions are type objects that belong in the equipment type library.

Whereas the block definition could be seen as the design or model for a piece of equipment, the common model can be seen as a specific physical instance of the equipment item itself e. Common models are grid elements that belong in the grid.

Block definitions can be built from both equations and graphical block diagrams. Primitive blocks are often re-used in other composite model definitions. A block definition can be assigned as a macro by ticking the macro checkbox in the block definition dialog. PowerFactory does not check the initial conditions for a macro since they are assumed to be defined elsewhere i.

Higher-level representations such as graph- ical block diagrams and nested block structures are automatically converted to a set of DSL equations, which are then parsed and interpreted during the simulation.

For example, when creating a transformer, the user must create both a transformer type e. Multiple transformer elements can use the same type, and changing the type parameters will affect all of the transformers that inherit or reference this type. There are type objects in the library i. These grid elements inherit the properties of the type objects e.

A table of type versus element analogies are shown in Table 2. Suppose that the frame represents the connections of a generator Slot A to a voltage controller Slot B. Both diagrams depict two generators network elements 1 and 2 , each connected to a voltage controller common models 1 and 2. Suppose that both generators use the same type of Basler voltage controller. Instead of defin- ing the block diagram for each voltage controller individually, the PowerFactory philosophy is to define the Basler voltage controller once as a type model definition and then create two differ- ent instances common models for each of the generators each with their own local parameter settings.

This configuration is reflected in Figure 2. We can create a new common model based on the AVK block diagram and replace the Basler controller in the composite model all the while using the same composite model and frame. There are few restrictions on how a user can construct models and with this freedom, a user can create models with very complicated structures.

This has an obvious drawback in that some model structures are fundamentally unsound, but can be created nevertheless. Rather than impose restrictions, the philosophy adopted by PowerFactory is to provide tools for error detection and testing instead. As a result, disturbances such as faults, load steps, etc will likely cause unstable frequency and voltage excursions since there are no governor or AVR actions to control these quantities.

It is therefore necessary to specifically define the generator controls and their dynamic response to system disturbances. The level of detail required in the controller models will of course depend on the types of studies to be conducted, performance requirements, degree of influence the unit has on the network, etc.

Consider the hydroelectric generation system shown in Figure 2. In this system, the amount of water flowing into the penstock is controlled by a control gate at the intake. The water in the penstock flows through the turbine and rotates it, before being discharged through the draft tube.

The turbine is coupled to a synchronous generator, which is then connected to the network. The gate position is controlled by a governor system, which tries to keep the output of the generator at a constant frequency. A voltage controller is also connected to the generator, controlling the terminal voltage of the machine by regulating rotor excitation.

We can see from this stylised system that there are control signals i. This can be summarised by a block diagram as shown Figure 2. The blocks that represent the generator, governor, etc are called slots and are placeholders for the models that describe their dynamic behaviour. At this stage, we have just seen an overview for how the hydro generation control system is structured i.

We still have to define the individual dynamic models for the governor, turbine and voltage controller. Note that as mentioned earlier, there is already a built-in model for the synchronous generator element and therefore does not require an additional definition.

This block diagram represents the model definition for the voltage controller. We can perform a similar exercise and define model definitions for the governor and turbine not shown here.

Once we have finished creating these model definitions, we will have then defined complete blueprints for the hydro generation control system, i. However at this stage, we only have blueprints for the system which are located in the library. We still need to create actual instances of the equipment inside the grid.

Built-in grid elements such as synchronous generators can be created by the drawing tools in the PowerFactory GUI. We can first create a composite model and link it to the composite frame we defined earlier see Figure 2.

The slots for the generator, governor, turbine and voltage controller now need to be filled. For the generator slot, we can select the relevant generator element in the grid. For the other slots, we will have to create common models and link them to the relevant model definition. In the end, the complete composite model is shown in Figure 2. The same composite model as seen from inside the data manager is shown in Figure 2.

Figure 2. Consider the structure of the system to be modelled and how it can be broken down into discrete blocks that can be modelled separately 2. Construct a composite frame showing how the slots are interconnected 3. Create each of the model definitions and set appropriate initial conditions see Section 4 4.

Create a composite model and fill the slots with the relevant grid elements, e. Test the complete model see Section 5. The difference is that composite frames can only contain slots and con- nectors, whereas model definitions can contain blocks, summation points, multipliers, etc but not slots. PowerFactory recognises whether the block definition is a composite frame or a model definition based on the first block or slot that is drawn in the diagram.

If a block is drawn, the slot icon is automatically deactivated so that slots and blocks cannot be mixed up in the same diagram and vice versa if a slot is drawn first. Composite frames are purely graphical and contain no equations. Refer to Chapters A model definition containing only equations is called a primitive block definition, while a model definition with a graphical block diagram is referred to as a composite block definition.

Both primitive and composite block definitions can be reused inside other higher-level model definitions PowerFactory supports an arbitrary number of layers. A composite model references a composite frame and inherits its structure i. The relevant system components, e. Composite models are created from within a data manager e. Once a frame is selected, the relevant system components for example, see Figure 3.

It is best practice to store elements such as common models and measurement devices inside the composite model object for example, see Figure 2. A common model inherits the block diagram of the linked model definition, but has its own local parameter settings.

Common models are created from within a data manager e. Once a model definition has been selected, the parameters of the common model can be entered for example, see Figure 3. In other words, prior to the start of a time-domain simulation, the system is operating in a steady state condition and network voltages, active and reactive power flows, loadings, etc. This also means that the operational configuration defined for the load flow calculation e.

It is recom- mended that the steady-state load flow is configured correctly before running a time-domain simulation. This is because the outputs of the model are usually known e. Model initialisation typically starts at the grid elements and then works backward through the other blocks, initialising each block completely one at a time.

In most models, a number of variables or signals will need to be manually initialised. This is generally for variables or signals that cannot be determined directly from the load flow solution. Note that not all of the variables and signals in a model need to be manually initialised. When a variable or signal is not known or manually initialised, PowerFactory will try to use the model equations to compute its initial value.

An error will be thrown if the model equations have undefined variables or signals e. For example, consider Figure 4. Figure 4. The signals pt and speed are calculated automatically based on the steady- state load flow solution and are known. The output signal pt is known from the generator element, but the input signal g is unknown, and must be manually initialised. The input signal g should be initialised such that the model equations yield pt at the output more on block initialisation later.

Lastly, the governor block is initialised. However, any internal state variables in the block need to be manually initialised. Note that it may also be possible for the output signal g to be calculated using the model equa- tions from the speed input. If this is possible, then the calculated g should be the same as the g initialised in the turbine block. The general rule is that in the steady state, all derivates are zero, i. The output yo is the steady state value yo,ss , which can be calculated from known initial values e.


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