fix Td definition in LimPID

Author: baggepinnen

src/Blocks/continuous.jl

@@ -318,7 +318,7 @@ Proportional-Integral-Derivative (PID) controller with output saturation, set-po
 The equation for the control signal is roughly
 
 ```
-k(ep + 1/Ti * ∫e + 1/Td * d/dt(ed))
+k(ep + 1/Ti * ∫e + Td * d/dt(ed))
 e = u_r - u_y
 ep = wp*u_r - u_y
 ed = wd*u_r - u_y
@@ -389,7 +389,7 @@ function LimPID(; name, k = 1, Ti = false, Td = false, wp = 1, wd = 1,
         @named Izero = Constant(k = 0)
     end
     if with_D
-        @named der = Derivative(k = 1 / Td, T = 1 / Nd, x_start = xd_start)
+        @named der = Derivative(k = Td, T = 1 / Nd, x_start = xd_start)
         @named addD = Add(k1 = wd, k2 = -1)
     else
         @named Dzero = Constant(k = 0)

test/Blocks/continuous.jl

@@ -280,7 +280,7 @@ end
 @testset "LimPID" begin
     re_val = 1
     @named ref = Constant(; k = re_val)
-    @named pid_controller = LimPID(k = 3, Ti = 0.5, Td = 100, u_max = 1.5, u_min = -1.5,
+    @named pid_controller = LimPID(k = 3, Ti = 0.5, Td = 1/100, u_max = 1.5, u_min = -1.5,
                                    Ni = 0.1 / 0.5)
     @named plant = Plant()
     @named model = ODESystem([
@@ -342,7 +342,7 @@ end
     end
     @testset "set-point weights" begin
         @testset "wp" begin
-            @named pid_controller = LimPID(k = 3, Ti = 0.5, Td = 100, u_max = 1.5,
+            @named pid_controller = LimPID(k = 3, Ti = 0.5, Td = 1/100, u_max = 1.5,
                                            u_min = -1.5, Ni = 0.1 / 0.5, wp = 0, wd = 1)
             @named model = ODESystem([
                                          connect(ref.output, pid_controller.reference),
@@ -363,7 +363,7 @@ end
             @test all(-1.5 .<= sol[pid_controller.ctr_output.u] .<= 1.5) # test limit
         end
         @testset "wd" begin
-            @named pid_controller = LimPID(k = 3, Ti = 0.5, Td = 100, u_max = 1.5,
+            @named pid_controller = LimPID(k = 3, Ti = 0.5, Td = 1/100, u_max = 1.5,
                                            u_min = -1.5, Ni = 0.1 / 0.5, wp = 1, wd = 0)
             @named model = ODESystem([
                                          connect(ref.output, pid_controller.reference),