Simulate Your Way out of a Difficult Real Time Control Problemisawwsymposium.com/wp-content/uploads/2013/08/W… · · 2013-09-11of a Difficult Real Time Control Problem ... •

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Simulate Your Way out of a Difficult Real Time Control Problem Automatically Controlling Gates to Reduce Combined Sewer Overflows (CSOs)

2013 ISA Water / Wastewater and Automatic Controls SymposiumAugust 6-8, 2013 – Orlando, Florida, USA

Speaker: Maxym Lachance, Eng. (Tetra Tech)

2013 ISA WWAC Symposium Aug 6-8, 2013 – Orlando, Florida, USA 2

Presenter

• Maxym Lachance, Eng., is a project engineer with Tetra Tech, holding a college degree in electronics and a bachelor's degree in automated production engineering (Montreal)

• 12 years of experience• 5 years with Tetra Tech (Wastewater Collection)

– Design, start-up, commissioning, calibration, etc.

• Involved in many RTC projects– Ottawa, ON; Edmonton, AB; Bordeaux, France;

Wilmington, DE; etc.

• Winner of the Tetra Tech 2012 Technical Achievement Award


Presentation Outline

• Background• RTC#4 Site Description• Control issues at the RTC#4 site• Methodology• Simulating the Existing Behavior• Development of New Command Rules• On-site performance• Benefits of the project


Background

• Edmonton, Alberta, Canada

• Early Action Control Plan for CSO Strategy

– New RTC Sites– W12 Syphon

(Diverting flows to the south side)

• RTC#4 site start-up in 2003

• Control issues despite efforts to improve site performance


RTC#4 Site Description

• Control objective:– Inline storage

• Type of Control:– Local reactive RTC based

on level measurements

• Control rules:– Rule 1 – maintain d/s level

at half pipe– Rule 2 – do not exceed

maximum u/s level

• Sensor locations:– u/s: 0.5m from gate – d/s: 40 m from gate



• Dry weather flow (DWF)• Gate open at 100%



• Wet weather flow (WWF)– Downstream level control initiate inline storage– Upstream level control override downstream control rule


Control Issues

• D/S set point overshoot during the beginning of event

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Methodology

• Objective: evaluate possible solution without any field instrumentation and civil change

• Development of off-site simulator– Not based on theoretical model simulation– Representative of field conditions and specific hydraulic

behaviors, validated with real data

• Validation of the simulator by reproducing exixting conditions

• Development of new control strategies• Implementation of new control strategy on site• Performance evaluation


Simulator - Data Collection

• Review of the current control strategy– Type of controller used– Data processing?

– Averaging– Sampling

– Requires a thorough review of the PLC code– Undocumented data manipulation

– Need to better understand the issues– Avoid repeating the same control mistakes



• Equipment specifications– Water level sensor

– Type– Location (invert)– Calibration range

– Actuator– Type– Speed– Positioning dead band– Modulating limitations

– Duty cycle– Maximum number of starts per hour

– Automation technology– PLC type

– Gate– Type– Size and shape– Location – Invert of the gate

– Sewer (u/s and d/s)– Size and shape– Slope



• Monitoring data collection– Accurate data– Validated data– Available at a good sampling rate

– One minute interval with fixed time stamp

• Identity type of events where control issues are prevalent• Retrieve data from specific rainfall events

– Measured levels– Gate position


Simulating the Existing Behavior

• Simulator input– Inflows (based on a real rainfall event)

• Simulator functional blocks to reproduce on-site hydraulics– Flow under the gate– Gate controller (actuator and gate)

– PID– Actuator

– Upstream level– Storage– Transient effect (i.e. surface waves caused by gate movement)

– Downstream level– Travel delay– Flow contraction



• Calculating simulator inflows– Measured flows are not available at RTC#4– Based on an actual measured rainfall event

• Flow under the gate (FUG) can be calculated– Upstream level– Downstream level– Gate position

• Stored volume (∆V)– Available upstream level

versus volume relationship

Site Inflow FUG V= − ∆



• Upstream level simulation– Sum of the steady state and

transient level– Steady state: Depth versus

storage relationship

– Transient effect: Function of the gate movement (exponential filter)

dVSite inflow FUG

dt= −



• Downstream level simulation– Based on the flow under the gate

– Upstream level– Downstream level– Gate position

– Account for d/s level sensor location

– Flow traveling time (40 m d/s)– Peak attenuation (exponential

filter)

– Convert flow to level with manning equation



• Controller – Gate position (actuator)– Programmable logic controller

– PID equation:

– Actuator– Speed– Dead band– Position error

1 ( )* ( ) * ( ) *c D

I

D PVOutput K E E dt T

T dt

= + +

∫




Development of New Command Rules

• Address control issues– Actuator not rated for modulation (60 starts/ hours)– Gate too large (opening between 0-10% to maintain desired level)– Upstream level meters too close to the gate (transient effect)– Downstream level meters far from the gate (travel delay)– Set point overshoot at beginning of the event

• Testing different controllers and parameters– PID and AI (Adaptive Integrative)– Gains, control loop update, dead band

• Testing the addition of data processing function– Using moving average to filter level data

• Testing of gate position during DWF


Development of New Command Rules


Major Findings from Off-site Test

• Confidence in Matlab® Simulator to reproduce field conditions for existing and new control rules

• Possibility to stabilize the site with new control rules without civil or instrumentation modifications– PID selected over AI (no predictive aspect)– Filtering of level data is important to provide stable input for the PID

controller– Control loop update longer than transient effect and travel time to

downstream sensor– U/S controller (100 seconds)– D/S controller (60 seconds)

– Dry weather gate opening at 25%


On-site Performance

• Performance follow-up for 5 rainfall events• Eliminated the set point overshoot

– Before: Overshoot of ≈40 cm– After: No overshoot

– One case where overshoot was 7 cm (reduction of 82%)

• Upstream level oscillation reduced by 80%– Before : ±50 cm (100 cm span)– After: ±10 cm (20 cm span)

• Downstream level oscillation reduced by 80%– Before : ±25 cm (50 cm span)– After: ±5 cm (10 cm span)


On-site Performance


Benefits of the Project

– Provides alternatives testing methodology where standard methods have failed

– Eliminates the risks related to on-site testing/calibration– Potential overflows– Potential flooding– Potential surcharge

– Off-site fine tuning of controller under various conditions– Eliminates the need to chase storm events– May take place in dry periods and be ready for the control season

– Eliminate costly site upgrades


Summary

– Simulation is a powerful tool to resolve RTC issues – It is only possible when onsite data is available

– Simulation requires good data collection– Current control strategy– Validated historical data (level and gate position)– Equipment specifications/limitations

– Simulations are reliable if validated by the reproduction of existing conditions

– Good identification of the control issues– Good characterization of the hydraulic behavior

– The simulation allowed for a wide range of controller testing– Gains, loop update, filtering, etc.– Quickly and safely

– Simulation results can be reproduced onsite


Questions

Thank you !

Documents

Simulate Your Way out of a Difficult Real Time Control Problemisawwsymposium.com/wp-content/uploads/2013/08/W… · · 2013-09-11of a Difficult Real Time Control Problem ... •