Application Example 03/2017 Closed-Loop Control With PID . - Siemens

3 Basics of Control Engineering2.4 Hardware and software components3Basics of Control EngineeringOverviewControl engineering is a branch of engineering that researches how to specificallyinfluence given variables in technical systems. The aim is to achieve and maintainthe desired value of this variable under certain conditions.This chapter provides a very brief outline of “control engineering”.The “SIMATIC S7-1200, S7-1500 PID Control” Function Manual covers the basicsof control engineering (\4\).Controlled systemA controlled system contains the variable to be controlled, such as the temperatureof a room. To identify the type of a system and then dynamically control it in anoptimal way, the system to be controlled must be analyzed in detail.One option to identify the type is to look at the step response of a controlledsystem. As an example, the following figure shows the step response of a PTnsystem (for example, temperature in a room). Siemens AG 2017 All rights reservedThe time response can be approximately defined by the following variables: Delay time Tu Compensation time Tg Maximum value Xmax.Figure 3-1 PTn system step responseTuTgyxClosed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/2017delay timecompensation timeoutput valueprocess value9

3 Basics of Control Engineering2.4 Hardware and software componentsControllerThe controller controls an actuator to bring the controlled system to a desired state.The simplest controllers are two-position controllers that only know the states “ON”and “OFF” and use them to control the controlled system via the actuator.The frequently used PID controllers consist of three parts: The P component generates an output signal proportional to the systemdeviation. The I component integrates the system deviation over time and, due to thisintegration, affects the controlled system. The D component, however, responds to the changed system deviation (timederivation of the system deviation).These three components of the ideal PID controller are weighted by the coefficientsproportional gain, integral action time and derivative action time.With the “PID Compact”, “PID 3Step” and “PID Temp” blocks, the SIMATICS7-1500 offers a software control option that is already integrated in the firmware.This application uses “PID Compact”. For more information on “PID 3Step” and“PID Temp”, please refer to manual \4\, the TIA Portal Help and applicationexamples \9\ and \10\. Siemens AG 2017 All rights reservedNoteControl loopIn a control loop, the system deviation between setpoint and process value isdetermined by the controller and a manipulated variable is derived from thisdeviation. The manipulated variable acts on the controlled system via an actuator(see Figure 3-2).Figure 3-2 Simple control ariableCon-ProcessvaluetrolledsystemA simple example of a control loop is the control of the room temperature using aheater. The room temperature is measured with a sensor and fed to a controller.This controller compares the current room temperature to a setpoint and calculatesan output value (manipulated variable) for controlling the heater.Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201710

4 Function mechanisms4.1 Structure of the sample projectFunction mechanisms4StructureThis chapter introduces the individual scenarios of the STEP 7 program anddescribes the individual blocks in greater detail.It describes the exact behavior of the two scenarios and provides a figure of theentire control loop for each scenario.Project engineeringThis chapter does not describe the configuration, commissioning and optimizationof “PID Compact”. For the appropriate step-by-step instructions, please refer tochapter 5.4.1Structure of the sample projectScenariosThe sample project consists of the scenarios listed in chapter 2.2 that areindependent of each other. Siemens AG 2017 All rights reservedProgram overviewThe S7 program of the CPU 1516-3 PN/DP has the following structure:Figure 4-1FBPID CompactOB30Scenario1Scenario1FBLSim PT3FBPID CompactFBLSim PDT1FBLSim PT2oscOB31Scenario2FBLSim PT1FBLSim LaggingScenario2AssignmentExcept for the “PID Compact” FB (FB1130) used in all scenarios, the individualblocks can be clearly assigned to the existing scenarios.Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201711

4 Function mechanisms4.1 Structure of the sample projectUser blocksTable 4-1 Blocks and instructions of the simulation librarySymbolic nameDescriptionScenario1Cyclic interrupt OB: Implements the scenariodescribed in chapter 4.2:Closed-loop control of a PT3 system with theaid of the “PID Compact” controllerDB2PidCompact1Instance DB for the “PID Compact” blockDB100Scenario1TagsBlock with parameters for supplying the blockcalls in Scenario 1FB54LSim PT3Simulation of a PT3 elementDB101InstLSim PT3Instance DB of FB “LSim PT3” (FB54)OB31Scenario2Cyclic interrupt OB: Implements the scenariodescribed in chapter 4.3:Closed-loop control of a simulated controlledsystem consisting of PT1, PDT1, lag and PT2element with the aid of the “PID Compact”controller.DB6PidCompact2Instance DB for the “PID Compact” block.DB200Scenario2TagsBlock with parameters for supplying the blockcalls in Scenario 2.FB50LSim PT1Simulation of a PT1 element.DB201InstLSim PT1Instance DB of FB “LSim PT1” (FB50).FB52LSim PT2oscSimulation of a periodic PT2 element.DB202InstLSim PT2oscInstance DB of FB “LSim PT2osc” (FB52).FB55LSim PDT1Simulation of a PDT1 element.DB203InstLSim PDT1Instance DB of FB “LSim PDT1” (FB55).FB59LSim LaggingSimulation of a lag element.DB204InstLSim LaggingInstance DB of FB “LSim Lagging” (FB59).FB1130PID CompactSystem block: Digital PI/PID controller; called in eachscenario.Always used as a PID controller – not as a PIcontroller – in this application.Scenario1OB30Scenario2 Siemens AG 2017 All rights reservedElementBlocks of the “LSim” simulation libraryThe project also uses blocks from the “LSim” simulation library that is provided onthe same HTML page as this document.The following blocks are from the library: LSim PT3 LSim PT1 LSim PDT1 LSim Lagging LSim PT2oscThe “LSim” simulation library provides more simulation blocks for simulatingcontrolled systems.For a detailed description of the individual simulation blocks, please refer to thelibrary description document (Table 2-5).Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201712

4 Function mechanisms4.2 Scenario 1: Calling and commissioning “PID Compact”FB “PID Compact” (FB1130) software controllerThe “PID Compact” system block (FB1130) implements a PID software controllerwith the following interface:Figure 4-2 Siemens AG 2017 All rights reservedFor a detailed description of FB “PID Compact” (FB1130) and its parameters,please refer to the TIA Portal Help.4.2Scenario 1: Calling and commissioning“PID Compact”4.2.1Task: Control a simulated PT3 systemTaskShow how to simulate a PT3 controlled system with the simulation library.Control the PT3 controlled system with the “PID Compact” block.Schematic diagramFigure 4-3Reference variablePIDcontrollerManipulatedvariablePT3 controlledsystemFeedbackStep responseThe figure below shows the step response of the PT3 controlled system when theinput jumps from 0 50:Figure 4-4TriggerProcess value (step response)Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201713

4 Function mechanisms4.2 Scenario 1: Calling and commissioning “PID Compact”4.2.2ProcedureOverviewThe following tasks have to be performed to implement the user program: Insert the PT3 system simulation into the user program and parameterize it. Add the “PID Compact” block to the user program. Configure the “PID Compact” block. Commission the software controller with pretuning and fine tuning.Step-by-step descriptionFor the associated step-by-step description for the individual actions, please referto chapter 5. Siemens AG 2017 All rights reservedNote4.2.3If you do not want to reprogram the individual actions with the aid of chapter 5,you can also access the sample project directly. The sample project containsScenario1 that has already been commissioned.Controlled system: Scenario1OverviewAfter commissioning the sample project as described in chapter 6, you can directlymonitor the behavior of the controlled system.Parameters and formula for “PID Compact”After fine tuning, the following parameters are active in the “PID Compact”software controller:Table 4-2 Symbols and parametersSymbolDescriptionValueKpProportional gain10.770338TIIntegral action time21.10933TDDerivative action time5.337515aDerivative delay coefficient0.1bProportional action weighting0.2586402cDerivative action weighting0.0yOutput value of the PID algorithm-sLaplace operator-wSetpoint-xProcess value-The PID algorithm of “PID Compact” (FB1130) is based on the following formula:Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201714

4 Function mechanisms4.2 Scenario 1: Calling and commissioning “PID Compact”𝑦 𝐾𝑝 [(𝑏 𝑤 𝑥) 1𝑇𝐷 𝑠(𝑤 𝑥) (𝑐 𝑤 𝑥)]𝑇𝐼 𝑠𝑎 𝑇𝐷 𝑠 1Monitoring the controlled systemChapter 7 describes how to monitor and control the controlled system with the aidof the provided visualization using WinCC Runtime Advanced.Control response of the systemAfter commissioning Scenario1, a setpoint step-change from 0 50% results in thefollowing response: Siemens AG 2017 All rights reservedFigure 4-5Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201715

4 Function mechanisms4.3 Scenario 2: Simulation and closed-loop control of a more complex controlled system4.3Scenario 2: Simulation and closed-loop control of amore complex controlled system4.3.1Task: Control a simulated more complex controlled systemTaskSimulate a more complex controlled system with the aid of the “LSim” controlledsystem simulation library and control it using the “PID Compact” block. Use the“pretuning” and “fine tuning” functions for commissioning.The controlled system should consist of the following elements:Table 4-3 Siemens AG 2017 All rights reservedTypeNoteSchematic step responseExample:real processPT1 elementControlled system speed,inverterPDT1 elementUse in step change-capablesystemsLag element (lagging)Conveyor system, gearPT2 element (periodic)Oscillating mechanicalsystem, strokes/rotationsSimulating a real controlled system can save time and costs whencommissioning a controller!Schematic diagramThe more complex controlled system consists of the following elements:Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201716

4 Function mechanisms4.3 Scenario 2: Simulation and closed-loop control of a more complex controlled systemFigure 4-6Controlled T1PT2oscFeedbackStep responseThe step response of the combined controlled system is shown below:Figure 4-7 Siemens AG 2017 All rights reservedTriggerStep responseThe following parameters are used for the individual elements:Table 13.05.01.0-Lag---5 ( 1.5 s)Periodic PT20.4 (omega)0.65 (damp)1.0-ProcedureOverviewThe procedure for this scenario corresponds to the one in Scenario 1:Note Insert the individual elements of the controlled system into the program andparameterize them. Add, parameterize and commission the “PID Compact” software controller.If you do not want to reprogram the individual actions with the aid of chapter 5,you can also access the sample project directly. The sample project contains“PID Compact” that has already been commissioned.Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201717

4 Function mechanisms4.3 Scenario 2: Simulation and closed-loop control of a more complex controlled systemStep-by-step descriptionFor the step-by-step description, please refer to chapter 5.Monitoring the controlled systemChapter 7 describes how to monitor and control the controlled system with the aidof the provided visualization using WinCC Runtime Advanced.“PID Compact” parametersThe following fine-tuned parameters result for the “PID Compact” block:Table 4-5 Complex controlled system parameter setPID CompactKp0.9506688TI [s]8.276175TD [s]2.224364a0.1b0.532196c0.0 Siemens AG 2017 All rights reservedControl response of the systemA setpoint step-change from 0 to 50 in the steady-state control loop results in thefollowing response at the inputs and outputs of the “PID Compact” controller.Figure 4-8Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201718

5 Configuration and Programming4.3 Scenario 2: Simulation and closed-loop control of a more complex controlled system5Configuration and ProgrammingContentsThis chapter discusses the configuration and project engineering implemented onthe S7-1500 CPU side in the sample project (Table 2-5).Step-by-step instructions show you how to set up and optimize a simulated controlloop.OutlineThe following chapters are available for handling FB “PID Compact” (FB1130): Inserting FB “PID Compact” (FB1130). Parameterizing FB “PID Compact” (FB1130). Commissioning FB “PID Compact” (FB1130). Siemens AG 2017 All rights reservedThe following chapters describe how to handle the “LSim” simulation library: Inserting a function block of the simulation library. Simulation of a controlled system with multiple elements.The following table shows the chapters relevant for the different scenarios:Table 5-1 Necessary configuration steps in the scenariosTaskScenario12Descriptionin chapter (link)Parameterizing “PID Compact”XXChapter 5.1 and chapter 5.2.Commissioning (pretuning and fine tuning)XXChapter 5.3.1.Inserting a single simulation elementXInterconnecting multiple controlled systemsClosed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/2017Chapter 5.4.XChapter 5.5.19

5 Configuration and Programming5.1 Inserting FB “PID Compact” (FB1130)Inserting FB “PID Compact” (FB1130)5.1VariantsThere are several options for inserting FB “PID Compact” into a project as atechnology object.Please note that calling “PID Compact” as a multi-instance does not generate atechnology object. You can continue to use the FB – however, without graphicssupport of the technology object.ProcedureThe following table shows one option of adding the “PID Compact” technologyobject to a project.Table 5-2No. Siemens AG 2017 All rights reserved1.ActionInsert a cyclic interrupt OB ( ), for example, with a cycle time of 300 ms ().The cycle time used is the sampling time of your controller.To ensure a constant sampling time of the controller, a PID controller must always be called in acyclic interrupt OB.12.2.In the instructions, double-click to add an instance of “PID Compact” to any network of the cyclicinterrupt OB created in step 1.Closed-Loop Control with "PID Compact" V2.3Entry-ID: 79047707, V3.0.0, 03/201720

5 Configuration and Programming5.1 Inserting FB “PID Compact” (FB1130)No.3.ActionSelect a name for the instance data block/technology object.Note!Wh

S7-1500 CPUs for closed-loop process control. 1.2 Overview of the automation task The automation task is to set up a control loop for influencing physical parameters in a technical process. The control loop is to consist of the following elements: "PID_Compact" as the controller. Simulated technical processes as the controlled system.