1-axis fourth order equation

[WouterVer]

Possible numerical error going from a 2-axis to a 1-axis fourth order equation:

PowerDynBase.jl/src/NodeDynamics/FourthOrderEquation_1A.jl

Line 6 in e2a2431

# FourthEq(H, P, D, Ω, E_f, T_d_dash ,T_q_dash ,X_q_dash ,X_d_dash,X_d, X_q)

PowerDynBase.jl/src/NodeDynamics/FourthOrderEquation_1A.jl

Line 71 in e2a2431

# de_d = (1 / T_q_dash) * (- e_d + (X_q - X_q_dash) * i_q)

PowerDynBase.jl/src/NodeDynamics/FourthOrderEquation_1A.jl

Lines 74 to 75 in e2a2431

	e_d = (X_q - X_q_dash) * i_q
	de_d = 0

[timziebart]

similar to

PowerDynBase.jl/src/NodeDynamics/SwingEquation.jl

Line 42 in 55d7866

du = u * im * dϕ

vs

PowerDynBase.jl/src/NodeDynamics/SwingEquation.jl

Line 93 in 55d7866

du = u/v * dv + swing_eq_rhs!(dint, u, i, int, t)