数理解析研究所講究録
第 841 巻 1993 年 60-71

60

Transient Analysis of Nonlinear Transmission
Lines by Hybrid Harmonic Balance Method
Akio Ushida
Department of Electrical and Electronic Engineering, Faculty ofEngineering, Tokushima University, Tokushima 770 Japan

Abstracb We discuss a transient analysis of transmission lines terminated by nonlinear subnetworks. In this analysis, the circuit is partitioned into the transmission
line and nonlinear subnetwork by using substitution source. The transmission line
is solved by the phasor technique or perturbation method, and the nonlinear subnetwork by a numerical integration technique. We calculate the the substitution
source giving rise to the transient response by application of the relaxation hybrid
harmonic balance method.

1

Introduction

For a computer-aided design of nonlinear systems, it is very important to calculate thetransient responses. Especially, for the high operating frequency, VLSI chips and printed circuit boards must be considered as distributed circuits. For the linear transmission lines, thetransient responses are usually calculated by the nume rical inverse Laplace transformations[1-4] $and/or$ frequency-domain approach [5-7]. Especially, Wang and Wing [6] have proposeda bilevel waveform relaxation algorithm to get the transient responses of transmission lines
terminated by nonlinear loads.
In this paper, we present an efficient and simple frequency-domain method for getting thetransient responses of the linear $and/or$ nonlinear transmission line terminated by nonlinear
subnetwork [8]. For the first step, the distributed circuit is partitioned into the transmission
line and nonlinear subnetwork with a substitution source. The response of the transmission line
can be calculated by a frequency-domain technique such as phasor or perturbation technique.
On the other hand, the response of nonlinear subnetwork to the substitution source can becalculated by a time-domain numerical integration technique. The substitution source giving
rise to the transient response is evaluated by an iterational method. We call our method a relaxation hybrid harmonic balance method. Especially, in the case of the linear transmission line,
the variational value at each iteration is calculated by the application of a relaxation techniqueto the time-invariant sensitivity circuit having an associated current source corresponding to
the residual error at the partitioning point [8].
For the nonlinear transmission line, it is equivalently replaced by the linear transmission
line containing the distributed sources decided by the perturbational technique. Therefore, theresponse can be calculated by the application of the two-point boundary value problem.

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In section 2, we show the idea of our relaxation hybrid harmonic balance method to the linear
transmission lines. In section 3, we show an algorithm for solving the nonlinear transmission
lines.

Linear transmission line terminated by nonlinear subnetwork

2

To understand the idea of our method, we consider a simple circuit in Fig.l(a), whereisis a nonlinear subnetwork. Using the substitution theorem,
a linear transmission line andlet us partition the circuit into two subnetworks as shown in Fig.l(b).
$N_{L}$$N_{N}$

Fig. 1(a) A transmission line $tel\cdot Ulitlatcd$ by a uonlinear subnetwork(b) Partition tbe circuit into linear and nonlinear subnetwork using

a $substitutio\iota 1$ source $v(t)$(c) Sensitivity circuit for getting tlxe $valiation_{C}\sqrt{}$ value$\triangle\iota’(t)$where the input impulse is described by the Fourier expansion as follows:$e_{in}(t)=E_{0}+ \sum_{k=1}^{M}(E_{2k-1}\cos k\omega t+E_{2k}\sin k\omega t)$

where$\omega=\frac{2\pi}{T}$(1). For the linear transmission line, the circuit equation is described by$(\begin{array}{l}EI_{s}\end{array})=(\begin{array}{llll}cosh \theta l \end{array})(\begin{array}{l}VI_{L}\end{array})$

(2)

where
and are the characteristic impedance and propagation constant, respectively. Hence,the current through partitioning point is given by$Z_{0}$$\theta$$I_{L}= \frac{E-V\cosh\theta l}{Z_{0}\sinh\theta l}$

(3)

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with phasor techThus, we can easily calculate the response of linear transmission linenique.
On the other hand, the response of the nonlinear subnetwork to the substitution voltage
source $v(t)$ is calculated by a numerical integration technique such as backward difference formula. The substitution theorem says that the transient response $v(t)$ satisfies$i_{L}(t)$(4)$F(v(t))=i_{L}(v)-i_{N}(v)=0$

where $i_{N}(v)$ is a response of the nonlinear subnetwork in Fig.1(b).
Let us calculate the steady-state periodic response satisfying (4) with an iterational method.
Assume the waveform at $jth$ iteration by(5)$v^{j}(t)= t_{0^{j}}^{r}/+\sum_{k=1}^{M}(V_{2k-1}^{j}\cos k\omega t+V_{2k}^{j}\sin k\omega t)$of the linear transmission line given by (3) can be calculated
In this case, the responseby the superposition theorem to each frequency component of (1) and (5). On the other hand,from afor the nonlinear subnetwork, we can calculate the steady-state periodic response
time-domain approach. Note that when the damping term is sufficiently large, we can directly
calculate the steady-state response by simply numerical integration technique. To estimate thesolution at the $j+1st$ iteration, put the solution$i_{L}^{j}(t)$$i_{N}^{j}(t)$(6)$v^{j+1}(t)=v^{j}(t)+\triangle v(t)$where$\triangle v(t)$is a variational voltage waveform described by$\triangle v(t)=\triangle V_{0}+\sum_{k=1}^{M}(\triangle V_{2k-1}\cos k\omega t+\triangle V_{2k}\sin k\omega t)$

Substituting$v^{j+1}$(7)

from (6) into (4), we obtain$F(v^{j}+\triangle v)$$=$$\simeq$$i_{L}(v^{j+1})-i_{N}(v^{j+1})$$y_{L}^{j}(\triangle v)-y_{N,t}^{j}(\triangle v)+\epsilon^{j}(t)=0$(8)

It is not easy to solve the time-varying circuit given by (8) even if it is a linear. Hence, we
introduce the following approximate time-invariant system:$y_{L}^{j}(\Delta v)-y_{N,0}^{j}(\triangle v)+\epsilon^{j}(t)=0$

where the residual error$\epsilon^{j}(t)$(9)

is defined by(10)$\epsilon^{j}(t)\equiv i_{L}(v^{j})-i_{N}(v^{j})$andin (8) and (9) denote linear opemtors which
The symbols
transform
into the time-domain response of the associated variational subnetwork, where
the subscript
denotes the time-varying operator andthe time-invariant operator, respectively.
The solution of (9) is calculated in the following manner: i.e., After getting the steady-state, every nonlinear element in the subnetwork
response to jth substitution sourceis$y_{L}^{j}(\triangle v),$$y_{N,t}^{j}(\triangle v)$$y_{N,0}^{j}(\triangle v)$$\triangle v$“ $t$ ’“$v^{j}(t)$$0$’$N_{N}$

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replaced by a linear time-invariant element as follows:
For nonlinear resistors $i_{G}=i_{G}(v_{G})$ :(11)$G_{0}^{j}= \frac{1}{T}\int_{0}^{T}\frac{\partial\hat{i}_{G}}{\partial v_{G}}dt|_{v_{G}=v_{G}^{j}}$For nonlinear capacitors$q_{C}=\hat{q}_{C}(v_{C})$:(12)$C_{0}^{j}= \frac{1}{T}\int_{0}^{T}\frac{\partial\hat{q}_{C}}{\partial v_{C}}dt|_{v_{C}=v_{C}^{j}}$For nonlinear inductors$\phi_{L}=\hat{\phi}_{L}(i_{L})$:(13)$L_{0}^{j}= \frac{1}{T}\int_{0}^{T}\frac{\partial\hat{\phi}_{L}}{\partial i_{L}}dt|_{i_{L}=i_{L}^{j}}$Observe thatandare equal to the average values in the period $[0, T]-$ at the th
substitution voltage.
Now, consider the equivalent circuit for determining
using algorithm (9). It has thesame circuit configuration as the original one, except that the voltage source is short-circuitedand all of the nonlinear elements are replaced by time-invariant elements defined by (11)-(13).
Furthermore, at the partitioning point, it has a current source equal to the residual error
given by (10). Thus, we have the equivalent circuit as shown in Fig.1(c). The variationalcan be independently calculated by the applications of the superposition theorem
voltage.
to each frequency component of
The iteration is continued until the variation satisfies
for a given small . The
residual error after convergence of the iteration is given by$G_{0}^{j},$$C_{0}^{j}$$j’$$L_{0}^{j}$$\triangle v(t)$$\epsilon^{j}(t)$$\triangle v(t)$$\epsilon^{j}(t)$$\Vert\triangle V\Vert<\epsilon$$\epsilon^{j}=\frac{1}{T}\int_{0}^{T}[i_{L}(t)-i_{N}(t)]^{2}dt$$\epsilon$(14)

If the residual error is not small enough, we must choose the more frequency components givenby (1) and repeat again the same iteration.

3

Nonlinear transmission line terminated by nonlinear
subnetwork

3.1

Perturbational techniqueNow, consider a nonlinear transmission line whose circuit equation is described by the following partial differential equation:$- \frac{\partial v}{\partial x}=\frac{\partial\phi_{L}}{\partial t}+v_{R}$$- \frac{\partial i}{\partial x}=\frac{\partial q_{C}}{\partial t}+i_{G}$

(15)

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Assume that the transmission line is uniform for the distance, and the nonlinear characteristics
per unit length are fUnctions of voltage $v(x)$ and current $i(x)$ as follows:$\phi_{L}$$q_{C}$$=$$=$$L_{0}i+\epsilon\hat{\phi}_{L}(i)$,$C_{0}v+\epsilon\hat{q}_{C}(v)$$v_{R}=R_{0}i+\epsilon\hat{v}_{R}(i)$,$i_{G}=G_{0}v+\epsilon\hat{i}_{G}(v)$

(16)
(17)

where means a small constant.
Let us apply a perturbation method to the analysis of the nonlinear transmission line. As
shown in section 2, we partition the circuit into the transmission line and the nonlinear subnetwork with the substitution source. Applying an iterational technique, we try to find out thegiving rise to the same responses at the partitioning point. Assume
substitution source
the waveform as follows:$\epsilon$$v^{j}(t)$$\dot{d}(x, t)=V_{0}^{j}(x)+\sum_{k=1}^{M}(V_{2k-1}^{j}(x)\cos k\omega t+V_{2k}^{j}(x)\sin k\omega t)$(18)$i^{j}(x, t)=I_{0}^{j}(x)+ \sum_{k=1}^{M}(I_{2k-1}^{j}(x)\cos k\omega t+I_{2k}^{j}(x)\sin k\omega t)$(19)

Applying the perturbational technique to the nonlinear transmission line, we describe (16)-(17)as follows:$\phi_{L}(i^{j})$$\simeq$$L_{0}i^{j}+\epsilon\hat{\phi}_{L}(i^{j-1})v_{R}(i^{j})\simeq R_{0}i^{j}+\epsilon\hat{v}_{R}(i^{j-1})$$q_{C}(v^{j})$$\simeq$$C_{0}v^{j}+\epsilon\hat{q}_{C}(v^{j-1})i_{G}(v^{j})\simeq G_{0}v^{j}+\epsilon i_{G}(v^{j-1})\wedge$

(20)
(21)

Substituting (20)-(21) into (15) and applying the harmonic balance method, we have the following relations.

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Hence, it can be uniquely solved only if the boundary conditions are given. Note that theconditions at the input terminal are given from (1) as follows:

Now, consider the responses of nonlinear subnetwork which is partitioned by a substitution
given by (5). Assume that the steady-state response to the substitution source
source$v^{j}(t)$$v^{j-1}(l, t)$

is described by the Fourier expansion as follows:$i_{N}^{j-1}(t)= \hat{I}_{N,0}^{j-1}(x)+\sum_{k=1}^{M}(\hat{I}_{N,2k-1}^{j-1}(x)\cos k\omega t+\hat{I}_{N,2k}^{j-1}(x)\sin k\omega t)$

We approximate$i_{N}^{j}(t)$(29)

by the following relation:$i_{N}^{j}(t)\simeq y_{N,0}^{j-1}(v^{j})+\{i_{N}^{j-1}(t)-y_{N,0}^{j-1}(v^{j-1})\}$(30)

is a linear operator defined in section 2 which transforms
towhere the symbol
were the sensitivity circuit at
the corresponding time-domain response. Observe that if–lth iteration, the algorithm would be exactly equal to the Newton method. Therefore, we
can hope the large convergence ratio for the weakly nonlinear subnetwork because the operator
will be a good approximation of
from the sensitivity circuit. Let us describe thesecond term of (30) in the Fourier series as follows:$v^{j}(t)$$y_{N,0}^{j-1}(v^{j})$$y_{N,0}^{j-1}$$j$$y_{N,0^{1}}^{i-}$$y_{N,t}^{j-1}$$i_{N}^{j-1}(t)-y_{N,0}^{j-1}(v^{j-1})=I_{N,0}^{j-1}+ \sum_{k=1}^{M}(I_{N,2k-1}^{j-1}\cos k\omega t+I_{N,2k}^{j-1}\sin k\omega t)$(31)

Therefore, from (18), (19) and (31), we have another boundary conditions as follows:$G_{N}^{j-1}(0)V_{0^{j}}(l)+I_{N,0}^{j-1}=I_{0}^{j}(l)$(32)$G_{N}^{j-1}(k\omega)V_{2^{j}k-1}(l)+B_{N}^{j-1}(k\omega)V_{2k}^{j}(l)+I_{N,2k-1}^{j-1}=I_{2k-1}^{j}(l)$(33)$G_{N}^{j-1}(k\omega)V_{2k}^{j}(l)-B_{N}^{j-1}(k\omega)V_{2k-1}^{j}(l)+I_{N,2k}^{j-1}=I_{2k}^{j}(l)$(34)

where the input impedance of the sensitivity subnetwork is assumed by$Y_{N,0}^{j-1}(k\omega)=G_{N}^{j-1}(k\omega)+jB_{N}^{j-1}(k\omega)$

Observe that eqs.(28) and (32)-(34) are the boundary conditions for solving the differential
equations (22)-(23) and (24)-(27). Thus, we can estimate the Fourier coefficients with the twopoint boundary value problem. The algorithm is a kind of perturbation method so that it isefficiently applied to the relatively weakly nonlinear transmission lines.

3.2

Two-point boundary value problem

Now, we consider to solve the differential equations (22)-(23) and (24)-(27) under the boundary conditions (28) and (32)-(34). Let us rewrite their relations for dc component and kth
frequency component simply:

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For the case of generality, put $N_{i}=2$ , and $N_{f}=4$ . Let us solve the two-point boundary
value problem (38)-(40). Consider the adjoint system to (38) as follows:$\frac{dw}{dx}=-A^{T}w$(41)$\frac{d}{dx}\sum_{i=1}^{N_{j}}w_{i}(x)\oint_{i}(x)=\sum_{i=1}^{N_{f}}w_{i}(x)f_{\dot{i}}(x, y^{j-1})$(42)

From (38) and (41), we have [9]On integrating (42) over $[0, l]$ , we have$\sum_{i=1}^{N_{f}}w_{i}(l)y_{i’}(l)-\sum_{i=1}^{N_{f}}w_{i}(0)y_{i}^{j}(0)=\int_{0}^{l}\sum_{i=1}^{N_{f}}w_{i}(x)f_{i}(x, y^{j-1})dx$(43)This gives the relation betweenof the original equation andof the adjoint equation
at the two end points $x=0$ and $x=l$ . Let us integrate the adjoint equations backward from
$x=l$ with the terminal
cond.itions as follows:$w_{i}^{j}(x)$$\dot{\oint}_{i}(x)$$w_{m}^{n}(l)$$=$$\alpha_{n,m}^{j-1}$, $m=1,$$\cdots$,$N_{f},$$n=N_{i}+1,$$\cdots$,$N_{f}$(44)

Then, the fundamental identity (43) gives$\sum_{i=1}^{N_{f}}\alpha_{n,i}^{j-1}\dot{\oint}_{i}(l)-\sum_{i=1}^{N_{f}}w_{i}^{n}(0)\oint_{i}(0)=\int_{0}^{l}\sum_{i=1}^{N_{f}}w_{i}^{n}(x)f_{i}(x, y^{j-1})dx$$n=N_{i}+1,$ $\cdots,$ $N_{f}$(45)Substituting (40) and (44) into (45), we have$\sum_{i=N.+1}^{N_{f}}w_{i}^{n}(0)\dot{\oint}_{i}(0)=I_{n}^{j-1}-\sum_{i=1}^{N_{i}}w_{i}^{n}(0)E_{i}-\int_{0}^{l}\sum_{i=1}^{N_{f}}\cdot w_{i}^{n}(x)f_{i}(x, y^{j-1})dx$

(46)

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,
for $n=N_{i}+1,$. Thus, combining (39) and (46), we can estimate theinitiala conconditof kth frequency component at jth iteration.
The iteration is continued until the variational value satisfies$\cdots$$N_{f}$$1t_{1}on$$y_{i^{l}}(0)$$\sum_{i=N_{i}+1}^{N_{f}}$lf$\dot{\oint}_{i}(0)-y_{i}^{j-1}(0)\Vert\leq\epsilon$(47)

for every frequency component.

4

Illustrative examples

4.1

Transient response of linear circuit

To understand the efficiency of our frequency-domain analysis,
we consider a sim$pe$le Clrcul
circuit asshown in Fig.2(a). The response at distance from the terminalload
is given as follows:$y$$Z_{L}$(48)$I^{r}/(y)=V_{s}\frac{Z_{L}\cosh\theta y+Z_{0}\sinh\theta y}{Z_{L}\cosh\theta l+Z_{0}\sinh\theta l}$(b)$|1tS0(|$(c)$[\mathfrak{l}\mathfrak{l}\cc|$Fig.2(a) Transmission line terminated by a linear load(b) No distortion waveform at end terlllinal $Z_{L}=1[k\Omega]$
Parameters of transmission line per unit length $[?nm]$ ;$Z_{L}$$R=0.o1[k\Omega],$ $L=0.01[\mu H],$ $C=0.01[t^{\iota F],G=0.01[\eta\iota S]}$(c) Transient response of transmission line terminated byby a linear load $Z_{L}=R_{L}+sL_{L}:R_{L}=0.5[k\Omega],$ $L_{L}=0.5[\mu H]$
Parameters of transmission line per unit length $[?nm]$ :$R=0.2[k\Omega],$$L=0.01[/H],$ $C=0.O1[\ell\iota F],$ $G=0.O1[mS]$$I(y)= \frac{V_{s}}{Z_{0}}\frac{Z_{0}\cosh\theta y+Z_{L}\sinh\theta y}{Z_{L}\cosh\theta l+Z_{0}\sinh\theta l}$

(49)

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and the propagation constant .
where the characteristic impedance isNow, consider a no-distortion transmission line $l=6[mm]$ . Then, the load impedance must
, and is given by $Z_{L}=1k\Omega$ in this example.
be matching to the characteristic impedance
Assume the impulse waveform of $E=2$ and period $T=1$ [nsec]. The waveform is describedby Fourier series with 1024 frequency components. The transient response by our frequencydomain is shown in Fig.2(b). The amplitude at terminal load is slightly decreased, but the
waveform is exactly the same shape as the input.
Next, consider a circuit terminated by R-L series load ( $R_{L}=0.5[k\Omega]$ and $L_{L}=0.5[\mu H]$ ). The
response at terminal point is given by Fig. 2(c). The transient phenomena continues much
longer than the above example, and has remarkable reflection phenomena from the two end
points.
Note that we can get these responses in a second by SUN SPARC station IPX. We foundfrom two examples that the frequency components for this kind of problem is enough at most
1024 frequency components. The algorithm can be applied to much larger systems such as
multi-conductor transmission lines.
$\theta$$Z_{0}$$Z_{0}$

4.2

Analysis of a transmission line terminated by a diodeConside an application of our relaxation hybrid harmonic balance method to a stiff circuit asshown in Fig. 3(a). Note that we can not neglect the nonlinear capacitor in the high frequency
domain, so that their characteristics are given as follows: Nonlinear resistor :$i_{d}=I_{s}[exp(\lambda v_{d})-1]$(50)$q_{d}=T_{F}I_{s}[exp( \lambda v_{d})-1]-\frac{p_{d}C_{jd}}{1-m_{d}}[(1-\frac{v_{d}}{p_{d}}-1](1-m_{d})$(51)Nonlinear capacitor :where $I_{s}=10^{-16}[A],$ $\lambda=40,$ $T_{F}=50\lceil psec$] $C_{jd}=0.1[pF],$ $m_{d}=0.4,$ $p_{d}=0.8$ . The bothcharacteristics are sharply changed around $v_{d}=0.7-0.8[V]$ . For this example, our hybrid
harmonic balance method has never converged because of the stiff nonlinearity. Hence, wehave introduced the compensation resistor , and it is partitioned into the linear transmission
line and nonlinear subnetwork by the substitution voltage $v(t)$ as shown in Fig.3(b). For thesteady-state analysis of nonlinear subnetwork, we used the backward difference formula. The
impulse response at the partitioning point is given by Fig.3(d), where the input amplitude is$E=5[V]$ . The convergence ratios for the different compensation resistors (see Appendix) are
shown in Fig. 3(e). We found that the iteration algorithm is stable for wide range of thecompensation resistor value.
$,$$R_{c}$

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5

Conclusions and remarks

We have presented an algorithm for calculating transient response of a transmission line
terminated by nonlinear subnetworks, which belongs to a class of frequency-domain technique.
At the first step, a circuit is partitioned into the transmission line and the nonlinear subnetwork

70
with the substitution source. At the second step, the transmission line is solved by the phasor
technique $and/or$ perturbational technique. On the other hand, the nonlinear subnetwork issolved by a numerical integration formula. The variation at each iteration is calculated by
the phasor method to the linear transmission line and the two-point boundary value problem
to the nonlinear transmission line. The both algorithms are very simple and can be applied
wide classes of transmission line terminated by nonlinear subnetworks. We also have shown animportance of introducing the compensation elements to the stiff nonlinear subnetworks. The
technique is usefully applied to the circuits containing transistors and diodes.
Acknowlegedment
The author would like thank to Professor K. Okumura and Dr. T. Ichikawa at Kyoto
University for useful discussions and suggestions concerning to the frequency-domain transient
analysis of distributed circuits.

References[1] T.Hosono,Fast Laplace Transformation by BASIC, Japanese, Kyouristu Publisher Co.,

1987.

[2] T.K.Tang and M.S.Nakhla,”Analysis of high-speed VLSI interconnects using the as ymptotic waveform evaluation technique”,IEEE Trans. on Computer-Aided Design, Vol.11,
No.3, pp.341-352, 1992.
$|$[3] D.S.Gao, A.T. $Yangand/|$ S.M.Kang, “ Modeling and simulation of interconnection delays
and crosstalks in hight-speed integrated circuits”, IEEE Trans. Circuits Syst. Vol.CAS-37,
pp.1-9, Jan. 1990.
[4] C.Gordon, T.Blazeck and R.Mittra,”Time-domain simulation of multiconductor transmission lines with frequency-dependent losses”, IEEE Trans. on Computer-Aided Design,
Vol.11, No. 11, pp.1372-1387, 1992.

[5] T.Ichikawa,”Analysis of transmission lines with distributed sources”, IEICE of Japan,
Vol.J68-A,No.2, pp. 166-172, 1985.
[6] R.Wang and O.Wing,”Tlransient analysis of dispersive VLSI interconnects terminated in
nonlinear loads”, IEEE. Trans. on Computer-Aided Design, Vol.11, No.10, pp.1258-1277,

1992.

[7] F.Y.Chang,”Waveform relaxation analysis of nonuniform lossy transmission lines characterized with frequency-dependent parameters”, IEEE Trans. on Circuits Syst. Vol.CAS-38,
No. 12, pp.1484-1500, 1991.
[8] A.Ushida, T.Adachi and L.O.Chua, “Steady-state analysis of nonlinear circuits based on
hybrid methods“, IEEE Trans. on Circuits Syst. Vol.CAS-38, No.8, pp.649-661, 1992.

[9] S.M.Roberts and J.S. Shipman, Two-Point Boundary Value Problems: Shooting Method,
American Elsevier Publishing Co. Inc. 1972.

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Appendix
Consider the convergence condition of the compensation technique in the example 4.2, whichandas shown in Fig. 4. For the simplicity, we assume
has two compensation resistor
that the nonlinear subnetwork at jth and $j+1$ iteration has the same sensitivity circuit.
$R_{c}$$-R_{c}$Now, set the residual current at jth iteration (9) by

Fig.4 Compensation technique$\epsilon^{j}(t)=\epsilon_{0}^{j}+\sum_{k=1}^{M}(\epsilon_{2k-1}^{j}\cos k\omega t+\epsilon_{2k}^{j}\sin k\omega t)$(52)

and the impedances of the linear and the nonlinear sensitivity circuit at kth frequency component$Z_{L,k}$$=$$R_{L,k}+jX_{L,k}$$Z_{N,k}^{j}$$=$$R_{N,k}^{j}+jX_{N,k}^{j}$

(53)
(54)

Then, the total impedance at the partitioning point is given$Z_{k}^{j}= \frac{(R_{L,k}-R_{c}+jX_{L,k})(R_{N,k}^{j}+R_{c}+,jX_{N,k}^{j})}{R_{L,k}+R_{N,k}^{j}+j(X_{L,k}+-\lambda_{Nk}^{\prime j})}$(55)

is the compensation resistor.
where
Hence, the variational voltage at jth iteration is given by$R_{c}$$\triangle V_{2k-1}+j\triangle V_{2k}=\overline{Z}_{k}^{j}(\epsilon_{2k-1}^{j}+j\epsilon_{2k}^{j})$where denotes the complex conlugate ofiteration is given by$\overline{Z}$

$Z$

(56)

. Therefore, the variational current at $j+1th$$\hat{c}_{2k-1}^{j+1}+j\epsilon_{2k}^{j+1}=\frac{R_{N,k}^{j}-R_{L,k}+2R_{c}-j(X_{N,k}^{j}-X_{L,k})}{R_{L,k}+R_{N,k}^{j}-j(X_{L,k}+arrow\lambda_{N,k}^{\prime j})}(\epsilon_{2k-1}^{j}+j\epsilon_{2k}^{j})$(57)Hence, the relaxation hybrid harmonic balance method will converge if the compensation resistor
satisfies$R_{c}$(58)

for $k=0,1,$$\cdots,$$M$.