Problem 7.8: Harmonic Power Flow with one Nonlinear Bus and Two Sets of Harmonic Nonlinear Device Currents
To the three-bus system of Fig. P7.8 apply the Newton–Raphson harmonic load flow analysis technique. Assume that bus 1 is the swing or slack bus, bus 2 is a linear PQ bus, and bus 3 is a nonlinear bus, where the fundamental real and reactive powers are specified. In addition, at bus 3 the real and imaginary harmonic nonlinear device currents are given as
The 5th and 7th nonlinear currents are referred to the harmonic voltages V˜(5)3 and V˜(7)3, respectively.
a)Find the fundamental and harmonic (5th and 7th) bus admittance matrices in polar form.
b)Make an initial guess for the bus vector U¯¯¯0=[δ(1)2,∣∣V˜(1)2∣∣,δ(1)3,∣∣V˜(1)3∣∣,δ(5)1,∣∣V˜(5)1∣∣,δ(5)2,∣∣V˜(5)2∣∣,δ(5)3,∣∣V˜(5)3∣∣,δ(7)1,∣∣V˜(7)1∣∣,δ(7)2,∣∣V˜(7)2∣∣,δ(7)3,∣∣V˜(7)3∣∣]t and compute the nonlinear load device currents G(1)r,3,G(1)i,3,G(5)r,3,G(5)i,3,G(7)r,3 and G(7)i,3, which are referred to the swing bus.
c)Evaluate the initial mismatch vector ΔM¯¯¯¯0=[ΔW¯¯¯¯,ΔI¯(5),ΔI¯(7),ΔI¯(1)]t.
d)Find the Jacobian J¯¯0 for this power system configuration and compute the bus correction vector ΔŪ0. The Jacobian J¯¯0 is of the form
In particular, this matrix (Eq. P8-3 or Eq. P8-4) has the following 16 unknowns: δ(1)2,∣∣V˜(1)2∣∣,δ(1)3,∣∣V˜(1)3∣∣,δ(5)1,∣∣V˜(5)1∣∣,δ(5)2,∣∣V˜(5)2∣∣,δ(5)3,∣∣V˜(5)3∣∣,δ(7)1,∣∣V˜(7)1∣∣,δ(7)2,∣∣V˜(7)2∣∣,δ(7)3,∣∣V˜(7)3∣∣, (see identification of columns of Eq. P8-4) and the following 16 equations: ΔP2(1), ΔQ2(1), ΔIr,1(5), ΔIi,1(5), ΔIr,2(5), ΔIi,2(5), ΔIr,3(5), ΔIi,3(5), ΔIr,1(7), ΔIi,1(7), ΔIr,2(7), ΔIi,2(7), ΔIr,3(7),ΔIi,3(7), ΔIr,3(1), ΔIi,3(1), (see identification of rows of Eq. P8-4). Note there are no H¯¯¯ matrices (e.g., H¯¯¯(1),H¯¯¯(5) and H¯¯¯(7)) related to α3 and β3. This reduces the equation system by two equations. In this case we can define the matrix J¯¯0 (Eq. P8-4).
e)Update the bus vector U¯¯¯1=(U¯¯¯0−ΔU¯¯¯0) and recompute the updated mismatch vector ΔM¯¯¯¯1.
Hint: The top row – not part of the Jacobian – of Eq. P8-4 lists the variables: