# Reference to pid controllers

#### Nasif at

Hi experts
I need a suggestion regarding a project
Currently i am doing a hydro electric project. I am using a siemens plc, g120 drive (2 no's) and 2 incremental encoders
We have turbine which contains a wicket gate through which water is entering the turbines. When water hits the turbine it rotates the turbine and a generator also.
And some power can be produced.
So our aim is to control the wicket gate movement(angular motion) to produce necessary power. The control should through a pid block. So my concern is
what should be the input to pid block??
Flow or power

#### TrojanPoem

The hydro-station can be used for two purposes.

1. Provide the deficit between the demand and generation to compensate for frequency deviation or voltage drop => Swing unit operation
2. Provide constant power output regardless of the grid state => PQ unit operation

If you're going to operate the hydro station as swing unit. You will need two PID blocks

PID-1 : The input is the reference frequeny (50Hz or 60 Hz) and the feedback is the grid frequency.
PID-2 : The input is the reference voltage (220 Hz or 120Hz) and the feedback is the grid voltage at PCC

If you're going to operate the hydro station as PQ unit. You will need two PID blocks

PID-1 : The input is the reference active power (you choose the amount) and the feedback signal is the actual output active power at the point of connection.

PID-2 : The input is the reference reactive power (you choose the amount) and the feedback signal is the actual output reactive power at the point of connection.

So the input of the PID is V/f/P/Q and the output is the angle of the gate.

From your query as to whether use power or flow , i assume you're trying to control the station as PQ unit. So , you should use power active/reactive.

The flow could also be used, but then you will need to scale it to get the actual power

P = (density * gravity * flow * pump head ) / (efficiency of turbine * efficiency of generator * pipe efficiency)

So , SP_INT of the PID is the power reference ( a value you choose).

While the PV of the PID block is the scaled power P

So you have to calculate the equation above using STL to get P, then use this P in the PID block.

#### Nasif at

First of all thanks for the quick response
Great help
I have to get a clarification from customer side whether it is swing operation or pq operation.

I am newbie in hydro power projects and i have to learn more about the operation. (Sorry for providing less data)

i am familiar with pid operation but not worked with 2 pid blocks. So i have to consider this equation while choosing the SP to pid block. And if i choose power as the reference to pid block flow can be automatically controlled to get the desired power by adjusting wicket gate.

well, definitely i can refer this message in the development stage. Thank u so much