adding RLC load model

CHANGELOG.md

@@ -17,3 +17,4 @@
 * ![enhancement](https://img.shields.io/badge/PD-enhancement-%23a2eeef.svg) [Fourth Order Equation with Exciter, AVR and Governor](https://github.com/JuliaEnergy/PowerDynBase.jl/pull/53)
 * ![enhancement](https://img.shields.io/badge/PD-enhancement-%23a2eeef.svg) [`make` has now an `open-docs` target that builds the docs and then opens it](https://github.com/JuliaEnergy/PowerDynBase.jl/pull/55)
 * ![bugfix](https://img.shields.io/badge/PD-bugfix-%23d73a4a.svg) [removing accidentally added build file `.DS_Store`](https://github.com/JuliaEnergy/PowerDynBase.jl/pull/49)
+* ![enhancement](https://img.shields.io/badge/PD-enhancement-%23a2eeef.svg) [added RLC load model](https://github.com/JuliaEnergy/PowerDynBase.jl/pull/60)

src/NodeDynamics/RLC-Load.jl

@@ -0,0 +1,39 @@
+# (C) 2018 Potsdam Institute for Climate Impact Research, authors and contributors (see AUTHORS file)
+# Licensed under GNU GPL v3 (see LICENSE file)
+
+@doc doc"""
+```Julia
+RLCLoad(R,L,C)
+```
+A node type that represents the RLC load model according to
+"Power Systems Electromagnetic Transients Simulation",
+Neville Watson and Jos Arrillaga, IET 2007, p.59, eq. (3.47)
+
+# Keyword Arguments
+- `R`: resistance in [?]
+- `L`: inductance in [?]
+- `C`: capacitance in [?]
+
+
+# Mathematical Representation
+```math
+	\dfrac{du_C}{dt} = \frac{1}{C}i_L(t)\\
+    \dfrac{di_L}{dt} = -\frac{R}{L} i_L(t)+\frac{1}{L} u(t)
+```
+
+TODO: reference
+
+"""
+@DynamicNode RLCLoad(R,L,C) <: OrdinaryNodeDynamics()  begin
+    @assert R > 0 "Resistance should be >0"
+    @assert L > 0 "Inductance should be >0"
+    @assert C > 0 "Capacitance should be >0"
+
+end [[u_C, du_C],[i_L,di_L]] begin
+    i_L = i #?????
+    du_C = 1/C *i_L
+    di_L = R/L*i_L+1/L*u
+    du = du_C #????
+end
+
+export RLCLoad

src/PowerDynBase.jl

@@ -65,6 +65,8 @@ include("NodeDynamics/VoltageSourceInverterMinimal.jl")
 include("NodeDynamics/VoltageSourceInverterVoltagePT1.jl")
 include("NodeDynamics/CurrentSourceInverterMinimal.jl")
 include("NodeDynamics/ExponentialRecovery.jl")
+include("NodeDynamics/RLC-Load.jl")
+
 
 
 # the structures building the grid dynamics from the node dynamics

test/nodedynamics.jl

@@ -190,3 +190,15 @@ de_c = de_d + 1im*de_q
 @test expand(dint[6]) == expand((1 / T_sv) * (-P_sv + P - (1/R_d)*(((omega+(Ω*2PI))/(Ω*2PI))-1)))
 @test expand(dint[7]) == expand((1 / T_ch) * (-P_m  + P_sv))
 end
+
+@testset "RLC-Load" begin
+@syms R L C positive=true
+@syms du_C u_C di_L i_L real= true
+RLCdyn = construct_node_dynamics(RLCLoad(R=R,L=L,C=C))
+dint = [du_C,di_L]; int = [u_C,i_L];
+du = RLCdyn.rhs(dint, u, i, int, t)
+i_L=i
+@test expand(dint[1])==expand(1/C *i_L)
+@test expand(dint[1])==expand(du)
+@test expand(dint[2])==expand(R/L*i_L+1/L*u)
+end