In Julia, I am receiving the error message:

MethodError: no method matching connect(::ODESystem, ::ODESystem)
Closest candidates are:
connect(::Base.LibuvStream, ::Any…)

Below is the code:

using CairoMakie, AlgebraOfGraphics
using ModelingToolkit, ModelingToolkitStandardLibrary
using DifferentialEquations
set_aog_theme!()

@parameters t
const B = ModelingToolkitStandardLibrary.Blocks

@component function Thruster(; name, thrust, lever_arm)
    @named ctrl_input = B.RealInput()
    @named torque_out = B.RealOutput()

    sts = @variables u(t) M(t)
    ps = @parameters thrust=thrust lever_arm=lever_arm

    eqs = [
        M ~ u * lever_arm * thrust,

        u ~ ctrl_input.u,
        torque_out.u ~ M
    ]

    ODESystem(eqs, t, sts, ps; systems=[ctrl_input, torque_out], name = name)
end

@component function SimpleSpacecraftPlant(; name, J=100.0, ϕ0=0.0, ω0=0.0)
    @named torque_in = B.RealInput()

    @named ϕ_out = B.RealOutput()
    @named ω_out = B.RealOutput()

    sts = @variables ϕ(t)=ϕ0 ω(t)=ω0
    ps = @parameters J=J ϕ0=ϕ0 ω0=ω0

    D = Differential(t)

    eqs = [
        D(ϕ) ~ ω,
        D(ω) ~ torque_in.u / J,

        ϕ_out.u ~ ϕ,
        ω_out.u ~ ω
    ]

compose(
    ODESystem(eqs, t, sts, ps; name = name), torque_in, ϕ_out, ω_out
)
end

@component function BBController(; name, thruster_torque)
    @named ref_signal = B.RealInput()
    @named ctrl_output = B.RealOutput()

    sts = @variables ref(t) u(t)
    ps = @parameters thruster_torque=thruster_torque

    eqs = [
        u ~ thruster_torque*sign(ref),

        ref ~ ref_signal.u,
        ctrl_output.u ~ u
    ]

    compose(
        ODESystem(eqs, t, sts, ps; name = name), ref_signal, ctrl_output
    )
end

setpoint = deg2rad(10)
@named θ_ref = B.Constant(k=setpoint)

J = 100
ωn = 0.5
ζ = 1.3

Kp = J*ωn^2
Kd = 2*J*ωn*ζ

@named ref_controller = B.LimPID(k=Kp, Td=Kd, Ti=1, gains=true)

F = 1
L = 1
@named thruster = Thruster(thrust=F, lever_arm=L)

@named plant = SimpleSpacecraftPlant(J=J)

F = 1
L = 1
@named bangbang_controller = BBController(thruster_torque=L*F)

function simulate_system(controller; tspan=[0.0, 120.0], solver_kwargs...)
    system_eqs = [
        connect(θ_ref.output, ref_controller.reference),
        connect(ref_controller.ctr_output, controller.ref_signal),
        connect(controller.ctrl_output, thruster.ctrl_input),
        connect(thruster.torque_out, plant.torque_in),
        connect(plant.ϕ_out, ref_controller.measurement),
    ]

    @named model = ODESystem(
        system_eqs, t; systems = [
             θ_ref, ref_controller, thruster, plant, controller
        ]
    )
    sys = structural_simplify(model)

    prob = ODEProblem(sys, [], tspan, [])
    sol = solve(prob; solver_kwargs...)
end

tspan=[0.0, 180.0]

bb_sol = simulate_system(bangbang_controller; tspan=tspan)

times = 0:0.1:tspan[2]
interp = bb_sol(times)

fig1 = Figure()
ax11 = Axis(fig1[1,1], xlabel="Time (s)", ylabel="Angle (°)")

lines!(ax11, times, rad2deg.(interp[plant.ϕ]))
hlines!(ax11, [rad2deg(setpoint)], linestyle=:dash)

bracket!(120, 10, 180, 10, offset=5, text="Inset Area", style=:square, orientation=:down)

ax12 = Axis(fig1, bbox = BBox(400, 750, 200, 450))

lines!(ax12, 120:0.1:180, rad2deg.(bb_sol(120:0.1:180)[plant.ϕ]))
hlines!(ax12, [rad2deg(setpoint)], linestyle=:dash)

fig1

I believe the problem is to do with connectors. I tried looking up documentation but could not find which connector may not be working. Any suggestions?