coordination of controls of renewable power plants to meet...

Coordination of Controls of Renewable Power Plants to Meet Steady State and Dynamic Response Requirements for Voltage Control and Reactive Power Supply

Presented by Daniel Feltes, Siemens PTI

Unrestricted

11-Nov-16

Overview

Discussion of the control strategy developed for a large renewable facility compromised of four wind farms:

• Control Requirements

• Available Controls

• Time Frames

• Controllers

• Example Responses

• Other Points to Consider

11-Nov-16

The Wind Farm Layout

Utility(POI) 500kV

121kV

4x30MVAR7.8miles

121kV

34.5kV

WindFarm173.5MW

9.7miles 7.0miles

121kV 121kV

WindFarm360MW

34.5kV

WindFarm2150MW

34.5kV9.1miles

WindFarm4100MW

34.5kV 121kV

11-Nov-16

The Wind Farm Equipment

• Every turbine, padmount transformer and feeder cable section was modeled in the simulations

• Four 121 kV lines – total length of 33.6 miles

• Approximately 171 miles of 34.5 kV collector cables

Wind Farm # Turbines MW Turbine

Manufacturer1 45 73.5 GE2 92 150.0 GE3 37 60.0 GE4 46 100.0 Siemens

Total 220 383.5

11-Nov-16

Control Requirements

ISO Requirements

• Inject or withdraw reactive power continuously (i.e. dynamically) at the POI point up to 33% of rated active power at all levels of active power output

• Exhibit connection point performance comparable to an equivalent synchronous generation unit with characteristic parameters within typical ranges

11-Nov-16

Available Controls

The control of voltage and reactive power is accomplished by the following controls:

• On-Load Tap Changer (OLTC) controls to adjust the taps on the 525/121 kV autotransformers

• OLTC controls to adjust the taps on the 121/34.5 kV transformers at each of the four wind farms

• Switching of the four 30 Mvar capacitor banks at the 121 kV bus• The wind farm controllers (i.e., GE WindCONTROL and Siemens Park Pilot)• The wind turbine generator controls

Each of these controls has unique characteristics with respect to its impact and timing. Thus careful coordination of these controls is necessary to ensure the desired accuracy, robustness and speed of response is obtained without undesirable interactions.

11-Nov-16

Control Time Frames

Transient Timeframe (0 to 5 seconds)

• The voltage and reactive power controls that are active in the transient time frame are the controls of the wind farm controllers and the controls of the wind turbine generators

• The OLTC tap controls and the capacitor bank controls are not active in this time frame

Steady State Timeframe (5 Seconds to Minutes)

• All of the controls are active, but the response is dominated by the OLTC tap controls and the capacitor bank controls

• The goal is to meet the steady state requirements while maintaining as much dynamic reserve capability as possible

11-Nov-16

Wind Farm Controllers and Turbine Controls

GE Wind Farms

• Doubly-fed induction machines

• Very fast terminal voltage control

• Reactive power setpoint sent to each turbine from the GE WindCONTROL.

One WindCONTROL controls all 3 of the wind farms with GE turbines.

• The WindCONTROL adjusts the WTG setpoints to controls the main 121 kV

bus voltage, using line drop compensation.

• Overall response time of 1 to 2 seconds

11-Nov-16

Wind Farm Controllers and Turbine Controls

Siemens Wind Farm

• Wind Farm 4 only

• Full inverter machines

• Very fast terminal voltage control

• A voltage reference setpoint is sent to each turbine from the Siemens Park

Pilot controller.

• The Park Pilot adjusts these setpoints to controls the reactive flow at the

121 kV bus of Wind Farm 4.

• Overall response time of 1 to 2 seconds

11-Nov-16

Wind Farm 4 Reactive Power Boost

Wind Farm 4 controls the reactive power at its 121 kV bus

• To supply a transient reactive power contribution for large voltage changes,

the reactive setpoint is adjusted.

• The steady state contribution is not changed

• The controller is implemented in a PLC located at Wind Farm 4

11-Nov-16

Outer Loop Controller to Implement Reactive Power Droop at the POI

• The steady state requirements are to supply reactive power to the 500 kV

system with a 4% reactive droop setting

• The controller adjusts the voltage reference of the GE WindCONTROL wind

farm controller

• The controller is implemented in a PLC

D

DIP sT

sKsKK

+++1

S-

-

+

DesiredV500

MeasuredV500

Droop

TotalQ 500

referenceV121Vmax

Vmin

1/QMax

csT+11

11-Nov-16

121 kV Capacitor Bank Controller

• The objective of the control of the capacitor banks is to supply steady state reactive power when needed

• The capacitors should only be switched in when those system reactive needs are required for a longer period of time

• This “frees up” the reactive capability of the turbines in case it is needed for transient support

• This controller is also implemented in the PLC

11-Nov-16

500/121 kV Transformer OLTC Control

• Analysis performed to look at the operation of the wind farm over a range of system operating conditions and from low power output to full power output.

• Desired 500/121 kV transformer tap defined as a function of measured 500 kV voltage

• No adverse interaction with droop controller

V500If |D tap| >1.5 * average tap step,move tap one tap position in the desireddirection

Tap Selection Table

Tap# Tap(kV) -16 577.500 -15 574.225

.

.

. -1 528.275 0 525.000 1 521.725

.

.

. 15 475.775 16 472.500

+

+

Offset

asT+11

–

+

Present Tap

Approximate Tap

Average tap step = 3.281 kV = 0.00656 pu

(Time delay between tap change is Td seconds)

Δ tap

“Averaging” filter

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121/34.5 kV Transformer OLTC Control

• Conventional OLTC controls at each of the four wind farms

• Each controls the main 34.5 kV collector bus to a selected voltage setpoint(within a voltage band)

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Fast Transient Response

• Actual staged test of switching of the 121 kV capacitor banks• Comparison of the measured response to the ISO requirement

Actual Response

ISO Requirement

11-Nov-16

Slow Controls – Steady State Response

• Simulation of an event that changes the system voltage

• Demonstrates reactive droop control and operation of the taps and capacitor banks to maintain reactive reserve on the turbines

11-Nov-16

Slow Controls – Steady State Response

• Simulation of an event that changes the Wind Farms power output

• Demonstrates reactive droop control and operation of the capacitor banks to maintain reactive reserve on the turbines

11-Nov-16

Other Points to Consider

When multiple controls are present, it is important to ensure that they are well coordinated:

• Active only in the proper time frame (and these time frames are well separated)

• Not controlling the same quantity as other controllers or quantities that are

highly dependant

• Reach of the controllers does not overlap

The paper gives a few example of problematic strategies.

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Example of a Suboptimal Control Strategy

• Simulation of an event that changes the system voltage

• Demonstrates a suboptimal control strategy that leads to an undesirable control action

11-Nov-16

Conclusions

• The facility may need to demonstrate their capabilities to meet grid codes to be able to interconnect.

• Simulation to develop the control strategy, tune controller response and to test and remedy any interactions is much preferred to debugging control problems in the field

• While the controls and equipment are unique to this facility and may not be directly applicable to other facilities, but the general approach is.

• It is possible to achieve both a fast transient response to system events while coordinating the slower controls

11-Nov-16

Questions? And Thank You for listening!

11-Nov-16

Contact Information

Siemens Industry, Inc.Energy Management DivisionDigital Grid Business UnitSiemens Power Technologies International400 State Street, Schenectady, NY 12305 USA

James Feltes, Senior Manager, Consulting+1 (518) [email protected]

Dinemayer Silva, Staff Consultant+1 (518) [email protected]

Daniel Feltes, Consultant+1 (518) [email protected]

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