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

gr,35=|V~31|cosδ31+|V~35|2cos2δ35+|V~37|cosδ37,

si711_e  (P8-1a)

gi,35=|V~31|sinδ31+|V~35|2sin2δ35+|V~37|sinδ37,

si712_e  (P8-1b)

gi,37=|V~31|cosδ31+|V~35|cosδ35+|V~37|2cos2δ37,

si713_e  (P8-2a)

gi,37=|V~31|sinδ31+|V~35|sinδ35+|V~37|2sin2δ37.

si714_e  (P8-2b)

f07-35-9780128007822
Figure P7.8 Three-bus power system consisting of two linear (swing bus = bus 1, PQ bus = bus 2) buses and one nonlinear bus (bus 3). The negative sequence impedance (≈ subtransient reactance at 60 Hz) of the swing bus is Z2 = jX = j0.10 pu and there are two sets of harmonics.

The 5th and 7th nonlinear currents are referred to the harmonic voltages V~35si715_e and V~37si716_e, 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=δ21V~21δ31V~31δ15V~15δ25V~25δ35V~35δ17V~17δ27V~27δ37V~37tsi717_e and compute the nonlinear load device currents Gr,31,Gi,31,Gr,35,Gi,35,Gr,37si718_e and Gi,37si719_e, which are referred to the swing bus.

c) Evaluate the initial mismatch vector ΔM¯0=ΔW¯,ΔI¯5,ΔI¯7,ΔI¯1t.si720_e

d) Find the Jacobian J¯0si721_e for this power system configuration and compute the bus correction vector ΔŪ0. The Jacobian J¯0si722_e is of the form

J¯0=J¯1J¯5J¯7YG¯(5,1)YG¯(5,5)YG¯(5,7)YG¯(7,1)YG¯(7,5)YG¯(7,7)YG¯(1,1)YG¯(1,5)YG¯(1,7).

si723_e  (P8-3)

In particular, this matrix (Eq. P8-3 or Eq. P8-4) has the following 16 unknowns: δ21,V~21,δ31,V~31,δ15,V~15,δ25,V~25,δ35,V~35,δ17,V~17,δ27,V~27,δ37,V~37,si724_e (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)Ii,3(7), ΔIr,3(1), ΔIi,3(1), (see identification of rows of Eq. P8-4). Note there are no H¯si725_e matrices (e.g., H¯1,H¯5si726_e and H¯7si727_e) related to α3 and β3. This reduces the equation system by two equations. In this case we can define the matrix J¯0si728_e (Eq. P8-4).

e) Update the bus vector U¯1=U¯0ΔU¯0si729_e and recompute the updated mismatch vector ΔM¯1.si730_e

Hint: The top row – not part of the Jacobian – of Eq. P8-4 lists the variables:

δ21V~21δ31V~31δ15V~15δ25V~25δ35V~35δ17V~17δ27V~27δ37V~37,

si731_e

and the right-hand side column – not part of the Jacobian – lists the mismatch quantities which must be satisfied:

ΔP21ΔQ21ΔIr,15ΔIi,15ΔIr,25ΔIi,25ΔIr,35ΔIi,35ΔIr,17ΔIi,17ΔIr,27ΔIi,27ΔIr,37ΔIi,37ΔIr,31ΔIi,31t.

si732_e

These two identifications help in defining the partial derivatives of the Jacobian. For example,

J3,50=ΔIr,15δ15,J3,100=ΔIr,15V35,J8,50=ΔIi,35δ15,

si733_e

J8,100=ΔIi,35V35,J9,110=ΔIr,17δ17,and

si734_e

J12,160=ΔIi,27V37.

si735_e

δ21V~21δ31V~31δ15V~15δ25V~25δ35V~35δ17V~17δ27V~27δ37V~37J¯0=19.81.989.90.990000000000001.9819.80.999.90000000000000000J3,50J3,60J3,70J3,80J3,90J3,1000000000000J4,50J4,60J4,70J4,80J4,90J4,1000000000000J5,50J5,60J5,70J5,80J5,90J5,1000000000000J6,50J6,60J6,70J6,80J6,90J6,1000000000000J7,50J7,60J7,70J7,80J7,90J7,1000000010001J8,50J8,60J8,70J8,80J8,90J8,10000000.100000000000J9,110J9,120J9,130J9,140J9,150J9,1600000000000J10,110J10,120J10,130J10,140J10,150J10,1600000000000J11,110J11,120J11,130J11,140J11,150J11,1600000000000J12,110J12,120J12,130J12,140J12,150J12,1600001000000J13,110J13,120J13,130J13,140J13,150J13,1600010000000J14,110J14,120J14,130J14,140J14,150J14,1609.900.9921.31.480000000000000.999.92.5118.3000000000000ΔP21ΔQ21ΔIr,15ΔIi,15ΔIr,25ΔIi,25ΔIr,35ΔIi,35ΔIr,17ΔIi,17ΔIr,27ΔIi,27ΔIr,37ΔIi,37ΔIr,31ΔIi,31.

si736_e  (P8-4)

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