Input / Output

Inputs and outputs are variables related to synchronous machines. Each type of input and output is associated with a machine regulator: Automatic Voltage Regulator (AVR) and Speed Governor (GOV).

:::warning Warning! The control system must have at least one input and one output. :::

The inputs and outputs of the control system are defined by these blocks, which differ for each type of scope. The figure below shows an example of a form for editing the inputs and outputs of an AVR:

Input and Output Variables

The user must specify the block type as input or output and then select the desired variable from a list. The following control variables are currently available in the program:

• Terminal voltage (input: AVR): Magnitude of the voltage at the synchronous machine bus, in $p.u.$, time-varying. This variable is normally used in calculating the error of the AVR reference voltage;
• Speed (input: AVR and GOV): Speed of the synchronous machine, in rad/s, time-varying. Commonly used in calculating the speed error in speed regulators, as well as input to the PSS in AVRs;
• Active and reactive power (input: AVR): Active power supplied by the synchronous machine, in $p.u.$, time-varying. Usually used as input to the PSS (active power) and for excitation under- and overcurrent control in AVRs;
• Initial terminal voltage (input: AVR): Magnitude of the voltage at the synchronous machine bus prior to the dynamic study, derived from load flow, in $p.u.$, fixed over time. This variable is normally associated with the AVR voltage reference;
• Initial speed (input: AVR and GOV): System speed ($2 \pi f_{ref}$), defined in the simulation options, in rad/s, fixed over time. This variable is typically used as the speed reference in SRs and for speed normalization;
• Initial mechanical power (input: GOV): Initial mechanical power, calculated after initialization of synchronous machines using data from the load flow, in $p.u.$, fixed over time. Usually used as the mechanical power reference in speed regulators;
• Variation of speed and active power (input: AVR): Calculation of the variation of these inputs between integration steps normalized by the integration step, according to the equation: $$\Delta x = \frac{x_n - x_{n-1}}{h}$$ Where:
  • $\Delta x$ is the variation of the input (speed or active power);
  • $x_n$ and $x_{n-1}$ are the variable at the current and previous step, respectively;
  • $h$ is the integration step.
  :::info Information Normalization is necessary for the correct use of the control step ratio, defined in the simulation settings. :::
• Field voltage (output: AVR): Defines the voltage applied to the synchronous machine field, in $p.u.$ Used as an output of AVRs, mainly controlling the voltage at the connected bus and/or the machine's power factor;
• Mechanical power (output: SR): Defines the mechanical power applied to the synchronous machine shaft. Used as an output of speed regulators, mainly controlling the active power injected by the machine and its frequency.