FGPID Class Reference

Detailed Description

Encapsulates a PID control component for the flight control system.

Configuration Format:

<pid name="{string}" [type="standard"]>
  <input> {[-]property} </input>
  <kp> {number|[-]property} </kp>
  <ki type="rect|trap|ab2|ab3"> {number|[-]property} </ki>
  <kd> {number|[-]property} </kd>
  <trigger> {property} </trigger>
  <pvdot> {property} </pvdot>
</pid>

For the integration constant element, one can also supply the type attribute for what kind of integrator to be used, one of:

• rect, for a rectangular integrator
• trap, for a trapezoidal integrator
• ab2, for a second order Adams Bashforth integrator
• ab3, for a third order Adams Bashforth integrator

For example,

<pid name="fcs/heading-control">
  <input> fcs/heading-error </input>
  <kp> 3 </kp>
  <ki type="ab3"> 1 </ki>
  <kd> 1 </kd>
</pid>

Configuration Parameters:

The values of kp, ki, and kd have slightly different interpretations depending on whether the PID controller is a standard one, or an ideal/parallel one - with the latter being the default.

By default, the PID controller computes the derivative as being the slope of the line joining the value of the previous input to the value of the current input. However if a better estimation can be determined for the derivative, you can provide its value to the PID controller via the property supplied in pvdot.

kp - Proportional constant, default value 0. ki - Integrative constant, default value 0. kd - Derivative constant, default value 0. trigger - Property which is used to sense wind-up, optional. Most often, the trigger will be driven by the "saturated" property of a particular actuator. When the relevant actuator has reached it's limits (if there are any, specified by the <clipto> element) the automatically generated saturated property will be greater than zero (true). If this property is used as the trigger for the integrator, the integrator will not continue to integrate while the property is still true (> 1), preventing wind-up. The integrator can also be reset to 0.0 if the property is set to a negative value. pvdot - The property to be used as the process variable time derivative.

Author

Jon S. Berndt

Definition at line 125 of file FGPID.h.

#include <FGPID.h>

Inheritance diagram for FGPID:

Collaboration diagram for FGPID:

Public Types
enum	eIntegrateType {   eNone = 0 , eRectEuler , eTrapezoidal , eAdamsBashforth2 ,   eAdamsBashforth3 }
	These define the indices use to select the various integrators. More...
Public Types inherited from FGJSBBase
enum	{ eL = 1 , eM , eN }
	Moments L, M, N. More...
enum	{ eP = 1 , eQ , eR }
	Rates P, Q, R. More...
enum	{ eU = 1 , eV , eW }
	Velocities U, V, W. More...
enum	{ eX = 1 , eY , eZ }
	Positions X, Y, Z. More...
enum	{ ePhi = 1 , eTht , ePsi }
	Euler angles Phi, Theta, Psi. More...
enum	{ eDrag = 1 , eSide , eLift }
	Stability axis forces, Drag, Side force, Lift. More...
enum	{ eRoll = 1 , ePitch , eYaw }
	Local frame orientation Roll, Pitch, Yaw. More...
enum	{ eNorth = 1 , eEast , eDown }
	Local frame position North, East, Down. More...
enum	{ eLat = 1 , eLong , eRad }
	Locations Radius, Latitude, Longitude. More...
enum	{   inNone = 0 , inDegrees , inRadians , inMeters ,   inFeet }
	Conversion specifiers. More...

Public Member Functions
	FGPID (FGFCS *fcs, Element *element)
void	ResetPastStates (void) override
bool	Run (void) override
void	SetInitialOutput (double val)
Public Member Functions inherited from FGFCSComponent
	FGFCSComponent (FGFCS *fcs, Element *el)
	Constructor.
virtual	~FGFCSComponent ()
	Destructor.
std::string	GetName (void) const
double	GetOutput (void) const
virtual double	GetOutputPct (void) const
std::string	GetType (void) const
virtual void	SetOutput (void)
Public Member Functions inherited from FGJSBBase
	FGJSBBase ()
	Constructor for FGJSBBase.
virtual	~FGJSBBase ()
	Destructor for FGJSBBase.
void	disableHighLighting (void)
	Disables highlighting in the console output.

Additional Inherited Members
Static Public Member Functions inherited from FGJSBBase
static const std::string &	GetVersion (void)
	Returns the version number of JSBSim.
static constexpr double	KelvinToFahrenheit (double kelvin)
	Converts from degrees Kelvin to degrees Fahrenheit.
static constexpr double	CelsiusToRankine (double celsius)
	Converts from degrees Celsius to degrees Rankine.
static constexpr double	RankineToCelsius (double rankine)
	Converts from degrees Rankine to degrees Celsius.
static constexpr double	KelvinToRankine (double kelvin)
	Converts from degrees Kelvin to degrees Rankine.
static constexpr double	RankineToKelvin (double rankine)
	Converts from degrees Rankine to degrees Kelvin.
static constexpr double	FahrenheitToCelsius (double fahrenheit)
	Converts from degrees Fahrenheit to degrees Celsius.
static constexpr double	CelsiusToFahrenheit (double celsius)
	Converts from degrees Celsius to degrees Fahrenheit.
static constexpr double	CelsiusToKelvin (double celsius)
	Converts from degrees Celsius to degrees Kelvin.
static constexpr double	KelvinToCelsius (double kelvin)
	Converts from degrees Kelvin to degrees Celsius.
static constexpr double	FeetToMeters (double measure)
	Converts from feet to meters.
static bool	EqualToRoundoff (double a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, float b)
	Finite precision comparison.
static bool	EqualToRoundoff (float a, double b)
	Finite precision comparison.
static bool	EqualToRoundoff (double a, float b)
	Finite precision comparison.
static constexpr double	Constrain (double min, double value, double max)
	Constrain a value between a minimum and a maximum value.
static constexpr double	sign (double num)
Static Public Attributes inherited from FGJSBBase
static char	highint [5] = {27, '[', '1', 'm', '\0' }
	highlights text
static char	halfint [5] = {27, '[', '2', 'm', '\0' }
	low intensity text
static char	normint [6] = {27, '[', '2', '2', 'm', '\0' }
	normal intensity text
static char	reset [5] = {27, '[', '0', 'm', '\0' }
	resets text properties
static char	underon [5] = {27, '[', '4', 'm', '\0' }
	underlines text
static char	underoff [6] = {27, '[', '2', '4', 'm', '\0' }
	underline off
static char	fgblue [6] = {27, '[', '3', '4', 'm', '\0' }
	blue text
static char	fgcyan [6] = {27, '[', '3', '6', 'm', '\0' }
	cyan text
static char	fgred [6] = {27, '[', '3', '1', 'm', '\0' }
	red text
static char	fggreen [6] = {27, '[', '3', '2', 'm', '\0' }
	green text
static char	fgdef [6] = {27, '[', '3', '9', 'm', '\0' }
	default text
static short	debug_lvl = 1
Protected Member Functions inherited from FGFCSComponent
void	CheckInputNodes (size_t MinNodes, size_t MaxNodes, Element *el)
void	Clip (void)
void	Delay (void)
Static Protected Member Functions inherited from FGJSBBase
static std::string	CreateIndexedPropertyName (const std::string &Property, int index)
Protected Attributes inherited from FGFCSComponent
bool	clip
FGParameter_ptr	ClipMax
FGParameter_ptr	ClipMin
bool	cyclic_clip
unsigned int	delay
double	delay_time
double	dt
FGFCS *	fcs
int	index
std::vector< FGPropertyValue_ptr >	InitNodes
double	Input
std::vector< FGPropertyValue_ptr >	InputNodes
std::string	Name
double	Output
std::vector< double >	output_array
std::vector< SGPropertyNode_ptr >	OutputNodes
std::string	Type
Static Protected Attributes inherited from FGJSBBase
static constexpr double	radtodeg = 180. / M_PI
static constexpr double	degtorad = M_PI / 180.
static constexpr double	hptoftlbssec = 550.0
static constexpr double	psftoinhg = 0.014138
static constexpr double	psftopa = 47.88
static constexpr double	fttom = 0.3048
static constexpr double	ktstofps = 1852./(3600*fttom)
static constexpr double	fpstokts = 1.0 / ktstofps
static constexpr double	inchtoft = 1.0/12.0
static constexpr double	m3toft3 = 1.0/(fttom*fttom*fttom)
static constexpr double	in3tom3 = inchtoft*inchtoft*inchtoft/m3toft3
static constexpr double	inhgtopa = 3386.38
static constexpr double	slugtolb = 32.174049
	Note that definition of lbtoslug by the inverse of slugtolb and not to a different constant you can also get from some tables will make lbtoslug*slugtolb == 1 up to the magnitude of roundoff.
static constexpr double	lbtoslug = 1.0/slugtolb
static constexpr double	kgtolb = 2.20462
static constexpr double	kgtoslug = 0.06852168
static const std::string	needed_cfg_version = "2.0"
static const std::string	JSBSim_version = JSBSIM_VERSION " " __DATE__ " " __TIME__

Member Enumeration Documentation

eIntegrateType

enum eIntegrateType

These define the indices use to select the various integrators.

Definition at line 135 of file FGPID.h.

                      {eNone = 0, eRectEuler, eTrapezoidal, eAdamsBashforth2,
                       eAdamsBashforth3};

Constructor & Destructor Documentation

FGPID()

FGPID	(	FGFCS *	fcs,
		Element *	element
	)

Definition at line 50 of file FGPID.cpp.

                                         : FGFCSComponent(fcs, element)
{
  Element *el;
 
  I_out_total = 0.0;
  Input_prev = Input_prev2 = 0.0;
  Trigger = nullptr;
  ProcessVariableDot = nullptr;
  IsStandard = false;
  IntType = eNone;       // No integrator initially defined.
 
  CheckInputNodes(1, 1, element);
 
  auto PropertyManager = fcs->GetPropertyManager();
  string pid_type = element->GetAttributeValue("type");
 
  if (pid_type == "standard") IsStandard = true;
 
  el = element->FindElement("kp");
  if (el)
    Kp = new FGParameterValue(el, PropertyManager);
  else
    Kp = new FGRealValue(0.0);
 
  el = element->FindElement("ki");
  if (el) {
    string integ_type = el->GetAttributeValue("type");
    if (integ_type == "rect") {            // Use rectangular integration
      IntType = eRectEuler;
    } else if (integ_type == "trap") {     // Use trapezoidal integration
      IntType = eTrapezoidal;
    } else if (integ_type == "ab2") {      // Use Adams Bashforth 2nd order integration
      IntType = eAdamsBashforth2;
    } else if (integ_type == "ab3") {      // Use Adams Bashforth 3rd order integration
      IntType = eAdamsBashforth3;
    } else {                               // Use default Adams Bashforth 2nd order integration
      IntType = eAdamsBashforth2;
    }
 
    Ki = new FGParameterValue(el, PropertyManager);
  }
  else
    Ki = new FGRealValue(0.0);
 
 
  el = element->FindElement("kd");
  if (el)
    Kd = new FGParameterValue(el, PropertyManager);
  else
    Kd = new FGRealValue(0.0);
 
  el = element->FindElement("pvdot");
  if (el)
    ProcessVariableDot = new FGPropertyValue(el->GetDataLine(), PropertyManager, el);
 
  el = element->FindElement("trigger");
  if (el)
    Trigger = new FGPropertyValue(el->GetDataLine(), PropertyManager, el);
 
  bind(el, PropertyManager.get());
}

~FGPID()

~FGPID

(

)

Definition at line 132 of file FGPID.cpp.

{
  delete Kp;
  delete Ki;
  delete Kd;
  delete Trigger;
  delete ProcessVariableDot;
  Debug(1);
}

Member Function Documentation

ResetPastStates()

void ResetPastStates ( void  )

overridevirtual

Reimplemented from FGFCSComponent.

Definition at line 144 of file FGPID.cpp.

{
  FGFCSComponent::ResetPastStates();
 
  Input_prev = Input_prev2 = Output = I_out_total = 0.0;
}

Run()

bool Run ( void  )

overridevirtual

Reimplemented from FGFCSComponent.

Definition at line 153 of file FGPID.cpp.

{
  double I_out_delta = 0.0;
  double Dval = 0;
 
  Input = InputNodes[0]->getDoubleValue();
 
  if (ProcessVariableDot) {
    Dval = ProcessVariableDot->getDoubleValue();
  } else {
    Dval = (Input - Input_prev)/dt;
  }
 
  // Do not continue to integrate the input to the integrator if a wind-up
  // condition is sensed - that is, if the property pointed to by the trigger
  // element is non-zero. Reset the integrator to 0.0 if the Trigger value
  // is negative.
 
  double test = 0.0;
  if (Trigger) test = Trigger->getDoubleValue();
 
  if (fabs(test) < 0.000001) {
    switch(IntType) {
    case eRectEuler:
      I_out_delta = Input;                         // Normal rectangular integrator
      break;
    case eTrapezoidal:
      I_out_delta = 0.5 * (Input + Input_prev);    // Trapezoidal integrator
      break;
    case eAdamsBashforth2:
      I_out_delta = 1.5*Input - 0.5*Input_prev;  // 2nd order Adams Bashforth integrator
      break;
    case eAdamsBashforth3:                                   // 3rd order Adams Bashforth integrator
      I_out_delta = (23.0*Input - 16.0*Input_prev + 5.0*Input_prev2) / 12.0;
      break;
    case eNone:
      // No integrator is defined or used.
      I_out_delta = 0.0;
      break;
    }
  }
 
  if (test < 0.0) I_out_total = 0.0;  // Reset integrator to 0.0
 
  I_out_total += Ki->GetValue() * dt * I_out_delta;
 
  if (IsStandard)
    Output = Kp->GetValue() * (Input + I_out_total + Kd->GetValue()*Dval);
  else
    Output = Kp->GetValue()*Input + I_out_total + Kd->GetValue()*Dval;
 
  Input_prev2 = test < 0.0 ? 0.0:Input_prev;
  Input_prev = Input;
 
  Clip();
  SetOutput();
 
  return true;
}

SetInitialOutput()

void SetInitialOutput ( double  val )

inline

Definition at line 138 of file FGPID.h.

                                    {
    I_out_total = val;
    Output = val;
  }

---

The documentation for this class was generated from the following files:

• FGPID.h
• FGPID.cpp