Implements IEEE type AC5A excitation system model

Fundamental Blocks/Machines/Excitation Systems (sps_avr)

This block models a simplified brushless excitation system where the regulator is supplied from a permanent magnet generator. This model is good to represent simplified systems with rotating rectifiers.

This block is an adaptation of the AC5A excitation system of
the IEEE^{®} 421 standard, copyright IEEE 2005, all rights reserved.

**Low-pass filter time constant**The time constant Tr of the first-order system representing the stator terminal voltage transducer.

**Voltage regulator gain and time constant**The gain Ka and time constant Ta of the first-order system representing the main regulator.

**Voltage regulator output limits**The voltage regulator output limits VRmin and VRmax, in p.u.

**Damping filter gain and time constants**The gain Kf and time constants Tf1, Tf, and Tf3 of the second-order system representing the derivative feedback.

**Exciter gain and time constant**The gain Ke and time constant Te of the first-order system representing the exciter.

**Field voltage values**The exciter saturation function is defined as a multiplier of exciter alternator output voltage to represent the increase in exciter excitation requirements due to saturation [1]. The saturation function is determined by specifying two voltage points, Efd1 and Efd2 in p.u., on the air-gap line and constant resistance load saturation curve and providing the corresponding two saturation multipliers SeEfd1 and SeEfd2.

Typically, the voltage Efd1 is a value near the exciter expected maximum output voltage, Efd2 value is about 75% of Efd1.

**Exciter saturation function values**The exciter saturation function is defined as a multiplier of exciter alternator output voltage to represent the increase in exciter excitation requirements due to saturation [1]. The saturation function is determined by specifying two voltage points, Efd1 and Efd2 in p.u., on the air-gap line and Constant Resistance Load saturation curve, and providing the corresponding two saturation multipliers SeEfd1 and SeEfd2.

SeEfd1 and SeEfd2 multipliers are equal to A-B / B, A is the value of exciter field current on the Constant Resistance Load saturation curve corresponding to the selected Efd voltage, and B is the value of exciter field current on the air-gap line corresponding to the selected Efd voltage.

If you do not want to model the saturation effect, set SeVe1 and SeVe2 values to zero.

**Initial values of terminal voltage and field voltage**The initial values of terminal voltage Vt0 and field voltage Efd0, both in p.u. Initial terminal voltage is normally set to 1 pu. The Vt0 and Efd0 values can be determined using the Powergui Load Flow tool.

**Sample time**Specify a value greater than zero to discretize the block at the given sample time. Set to -1 to inherit the simulation type and sample time parameters of the Powergui block.

- Vref
The reference value of the stator terminal voltage, in p.u.

- Vt
The measured value in p.u. of the stator terminal voltage of the controlled Synchronous Machine block.

- Vstab
Connect this input to a power system stabilizer to provide additional stabilization of power system oscillations. When you do not use this option, connect to a Simulink ground block. The input is in p.u.

- Efd
The field voltage to apply to the

`Vf`

input of the controlled Synchronous Machine block. The output is in p.u.

The `power_machines`

example contains a Configurable
Subsystem block that allows you to select between seven types
of excitation systems to control the terminal voltage of the Synchronous
Machine block. This configurable block refers to the `power_machines_lib`

example
library that contains seven pretuned excitation system blocks that
fit simulation requirements for this example.

Right-click the EXCITATION configurable block, then select **AC5A** from
the **Block Choice** menu to control the Synchronous
Machine block using the AC5A Excitation System block.

[1] "IEEE Recommended Practice for
Excitation System Models for Power System Stability Studies." *IEEE Standard*,
Vol. 421, No. 5, 2005 (Revision of IEEE 521.5-1992).

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