chore: changing IntegralPartDischargeFactor to IntegralPartDischargeT…

…imeConstant

Instead of using a factor equal to the inverse of a time constant,
the time constant itself is used instead, and the formula adapted accordingly.
Additional comments added.

antiwindupcontroller.go

@@ -28,8 +28,8 @@ type AntiWindupControllerConfig struct {
 	DerivativeGain float64
 	// AntiWindUpGain is the anti-windup tracking gain.
 	AntiWindUpGain float64
-	// Inverse of the time constant to discharge the integral part of the PID controller (1/s)
-	IntegralPartDischargeFactor float64
+	// IntegralDischargeTimeConstant is the time constant to discharge the integral state of the PID controller (s)
+	IntegralDischargeTimeConstant float64
 	// LowPassTimeConstant is the D part low-pass filter time constant => cut-off frequency 1/LowPassTimeConstant.
 	LowPassTimeConstant time.Duration
 	// MaxOutput is the max output from the PID.
@@ -84,11 +84,12 @@ func (c *AntiWindupController) Update(input AntiWindupControllerInput) {
 	c.State.ControlError = e
 }
 
-// TODO: Document me.
+// DischargeIntegral provides the ability to discharge the controller integral state
+// over a configurable period of time.
 func (c *AntiWindupController) DischargeIntegral(dt time.Duration) {
 	c.State.ControlErrorIntegrand = 0.0
 	c.State.ControlErrorIntegral = math.Max(
 		0,
-		math.Min(1-dt.Seconds()*c.Config.IntegralPartDischargeFactor, 1.0),
+		math.Min(1-dt.Seconds()/c.Config.IntegralDischargeTimeConstant, 1.0),
 	) * c.State.ControlErrorIntegral
 }

antiwindupcontroller_test.go

@@ -17,11 +17,11 @@ func TestAntiWindupController_PControllerUpdate(t *testing.T) {
 	// Given a saturated P controller
 	c := &AntiWindupController{
 		Config: AntiWindupControllerConfig{
-			LowPassTimeConstant:         1 * time.Second,
-			ProportionalGain:            1,
-			IntegralPartDischargeFactor: 0.1,
-			MinOutput:                   -10,
-			MaxOutput:                   10,
+			LowPassTimeConstant:           1 * time.Second,
+			ProportionalGain:              1,
+			IntegralDischargeTimeConstant: 10,
+			MinOutput:                     -10,
+			MaxOutput:                     10,
 		},
 	}
 	for _, tt := range []struct {
@@ -65,14 +65,14 @@ func TestAntiWindupController_PIDUpdate(t *testing.T) {
 	// Given a saturated PID controller
 	c := &AntiWindupController{
 		Config: AntiWindupControllerConfig{
-			LowPassTimeConstant:         1 * time.Second,
-			DerivativeGain:              0.01,
-			ProportionalGain:            1,
-			IntegralGain:                10,
-			AntiWindUpGain:              10,
-			IntegralPartDischargeFactor: 0.1,
-			MinOutput:                   -10,
-			MaxOutput:                   10,
+			LowPassTimeConstant:           1 * time.Second,
+			DerivativeGain:                0.01,
+			ProportionalGain:              1,
+			IntegralGain:                  10,
+			AntiWindUpGain:                10,
+			IntegralDischargeTimeConstant: 10,
+			MinOutput:                     -10,
+			MaxOutput:                     10,
 		},
 	}
 	for _, tt := range []struct {
@@ -119,11 +119,11 @@ func TestAntiWindupPID_FFUpdate(t *testing.T) {
 	// Given a saturated I controller
 	c := &AntiWindupController{
 		Config: AntiWindupControllerConfig{
-			LowPassTimeConstant:         1 * time.Second,
-			IntegralGain:                10,
-			IntegralPartDischargeFactor: 0.1,
-			MinOutput:                   -10,
-			MaxOutput:                   10,
+			LowPassTimeConstant:           1 * time.Second,
+			IntegralGain:                  10,
+			IntegralDischargeTimeConstant: 10,
+			MinOutput:                     -10,
+			MaxOutput:                     10,
 		},
 	}
 	for _, tt := range []struct {
@@ -197,14 +197,14 @@ func TestAntiWindupController_OffloadIntegralTerm(t *testing.T) {
 	// Given a saturated PID controller
 	c := &AntiWindupController{
 		Config: AntiWindupControllerConfig{
-			LowPassTimeConstant:         1 * time.Second,
-			ProportionalGain:            1,
-			DerivativeGain:              10,
-			IntegralGain:                0.01,
-			AntiWindUpGain:              0.5,
-			IntegralPartDischargeFactor: 0.1,
-			MinOutput:                   -10,
-			MaxOutput:                   10,
+			LowPassTimeConstant:           1 * time.Second,
+			ProportionalGain:              1,
+			DerivativeGain:                10,
+			IntegralGain:                  0.01,
+			AntiWindUpGain:                0.5,
+			IntegralDischargeTimeConstant: 10,
+			MinOutput:                     -10,
+			MaxOutput:                     10,
 		},
 	}
 	c.State = AntiWindupControllerState{

trackingcontroller.go

@@ -29,8 +29,8 @@ type TrackingControllerConfig struct {
 	DerivativeGain float64
 	// AntiWindUpGain is the anti-windup tracking gain.
 	AntiWindUpGain float64
-	// Inverse of the time constant to discharge the integral part of the PID controller (1/s)
-	IntegralPartDischargeFactor float64
+	// IntegralDischargeTimeConstant is the time constant to discharge the integral state of the PID controller (s)
+	IntegralDischargeTimeConstant float64
 	// LowPassTimeConstant is the D part low-pass filter time constant => cut-off frequency 1/LowPassTimeConstant.
 	LowPassTimeConstant time.Duration
 	// MaxOutput is the max output from the PID.
@@ -93,11 +93,12 @@ func (c *TrackingController) Update(input TrackingControllerInput) {
 	c.State.ControlError = e
 }
 
-// TODO: Document me.
+// DischargeIntegral provides the ability to discharge the controller integral state
+// over a configurable period of time.
 func (c *TrackingController) DischargeIntegral(dt time.Duration) {
 	c.State.ControlErrorIntegrand = 0.0
 	c.State.ControlErrorIntegral = math.Max(
 		0,
-		math.Min(1-dt.Seconds()*c.Config.IntegralPartDischargeFactor, 1.0),
+		math.Min(1-dt.Seconds()/c.Config.IntegralDischargeTimeConstant, 1.0),
 	) * c.State.ControlErrorIntegral
 }

trackingcontroller_test.go

@@ -11,12 +11,12 @@ func TestTrackingController_PControllerUpdate(t *testing.T) {
 	// Given a tracking P controller
 	c := &TrackingController{
 		Config: TrackingControllerConfig{
-			LowPassTimeConstant:         1 * time.Second,
-			ProportionalGain:            1,
-			AntiWindUpGain:              0,
-			IntegralPartDischargeFactor: 0.1,
-			MinOutput:                   -10,
-			MaxOutput:                   10,
+			LowPassTimeConstant:           1 * time.Second,
+			ProportionalGain:              1,
+			AntiWindUpGain:                0,
+			IntegralDischargeTimeConstant: 10,
+			MinOutput:                     -10,
+			MaxOutput:                     10,
 		},
 	}
 	for _, tt := range []struct {
@@ -98,14 +98,14 @@ func TestTrackingController_OffloadIntegralTerm(t *testing.T) {
 	// Given a tracking PID controller
 	c := &TrackingController{
 		Config: TrackingControllerConfig{
-			LowPassTimeConstant:         1 * time.Second,
-			ProportionalGain:            1,
-			DerivativeGain:              10,
-			IntegralGain:                0.01,
-			AntiWindUpGain:              0.5,
-			IntegralPartDischargeFactor: 0.1,
-			MinOutput:                   -10,
-			MaxOutput:                   10,
+			LowPassTimeConstant:           1 * time.Second,
+			ProportionalGain:              1,
+			DerivativeGain:                10,
+			IntegralGain:                  0.01,
+			AntiWindUpGain:                0.5,
+			IntegralDischargeTimeConstant: 10,
+			MinOutput:                     -10,
+			MaxOutput:                     10,
 		},
 	}
 	c.State = TrackingControllerState{