Merge pull request #19 from JuliaComputing/onoff

add OnOffController

Author: baggepinnen

src/ModelingToolkitSampledData.jl

@@ -9,6 +9,7 @@ export DiscreteIntegrator, DiscreteDerivative, Delay, Difference, ZeroOrderHold,
        DiscretePIDParallel, DiscretePIDStandard, DiscreteStateSpace,
        DiscreteTransferFunction, NormalNoise, UniformNoise, Quantization,
        ExponentialFilter
+export DiscreteOnOffController
 include("discrete_blocks.jl")
 
 end

src/discrete_blocks.jl

@@ -971,3 +971,43 @@ Exponential filtering with input-output relation ``y(z) ~ (1 - a) y(z-1) + a u(z
     end
 end
 
+"""
+    DiscreteOnOffController(b = 0.1, bool = true)
+
+Discrete-time On-Off controller with hysteresis. The controller switches between two states based on the error signal `reference-input`. The controller is in the on-state if the error signal is within the bandwidth `b` around the reference signal, and in the off-state otherwise.
+
+# Connectors:
+- `reference`: The reference signal to the controller
+- `input`: The measurement feedback
+- `output`: The control signal output
+
+# Parameters:
+- `b`: Bandwidth around reference signal within which the controller does not react
+- `bool`: (structural) If true (default), the controller switches between 0 and 1. If false, the controller switches between -1 and 1.
+- `k`: Controller gain. The output of the contorller is scaled by this gain, i.e., `k = 2, bool = false` will result in an output of -2 or 2.
+"""
+@mtkmodel DiscreteOnOffController begin
+    @extend u, y = siso = SISO()
+    @components begin
+        reference = RealInput()
+    end
+    @structural_parameters begin
+        z = ShiftIndex()
+        bool = true
+    end
+    @parameters begin
+        b = 0.1, [description = "Bandwidth around reference signal"]
+        k = 1, [description = "Controller gain"]
+    end
+    @variables begin
+        s(t)=true, [description = "Internal variable"]
+    end
+    @equations begin
+        s(z) ~ (y(z-1) == k) & (u(z) < reference.u(z) + b/2) | (u(z) < reference.u(z) - b/2)
+        if bool
+            y(z) ~ k*s(z)
+        else
+            y(z) ~ k*(2*s(z) - 1)
+        end
+    end
+end

test/test_discrete_blocks.jl

@@ -461,6 +461,33 @@ end
     @test 0 ∈ uy
 end
 
+@testset "OnOff" begin
+    @info "Testing OnOff"
+    cl = Clock(0.1)
+    z = ShiftIndex(cl)
+    @mtkmodel OnOffModel begin
+        @components begin
+            onoff = DiscreteOnOffController(; z, bool=false)
+            c = Constant(k=1)
+        end
+        @variables begin
+            x(t) = 0 
+        end
+        @equations begin
+            onoff.u ~ Sample(cl)(x)
+            connect(c.output, onoff.reference)
+            D(x) ~ 0.1x + Hold(onoff.y)
+        end
+    end
+    @named m = OnOffModel()
+    m = complete(m)
+    ssys = structural_simplify(IRSystem(m))
+    prob = ODEProblem(ssys, [m.onoff.y(z-1) => 0], (0.0, 4.0))
+    sol = solve(prob, Tsit5(), dtmax=0.1)
+    # plot(sol, idxs=[m.x, m.onoff.y], title="On-off control of an unstable first-order system")
+    @test 0.89 <= sol(4, idxs=m.x) <= 1.11
+end
+
 
 @testset "ExponentialFilter" begin
     @info "Testing ExponentialFilter"