how do i resolve this ode45 problem

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Omar Nicolas García Gómez
编辑： Jan 2022-5-11
Ran in:
I need to simulate a power multilevel inverter. For that i generate a vector (1x1000double) called Vo, represented by the blue signal:
The simulation is simple, it requires solving the following ecuation:
; with R=30 and L=0.0133 for t=[0 ,1/50].
when i try to solved it with "Vo" as a vector it returns an error, but then i try to transform this "Vo" vector into a function that fits in the time t=[0 1/50], with the following:
fo=50; mf=20;
t=linspace(0,1/fo,mf*fo);
Vof=@(t) Vo(1+ceil(t.*fo.*(length(t)-1));
Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.
the issue is that when i try to simulate the circuit the returned output it's a vector full of 0...
R=30; L=0.0133;
dio=@(t,io) (Vof(t)./L)-((R*io)/L);
tspan=[0 1/fo];
io0=0;
[tt,io]=ode45(dio,tspan,io0);
plot(tt,io),hold on
plot(t,Vof(t))
t = 1×1000
0 0.0000 0.0001 0.0001 0.0002 0.0002 0.0002 0.0003 0.0003 0.0004 0.0004 0.0004 0.0005 0.0005 0.0006 0.0006 0.0006 0.0007 0.0007 0.0008 0.0008 0.0008 0.0009 0.0009 0.0010 0.0010 0.0010 0.0011 0.0011 0.0012
how should i resolve this problem? any ideas?
PS: sorry for such weak explanation... first time asking.

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回答（1 个）

Jan
Jan 2022-5-11
编辑：Jan 2022-5-11
Your expression contains unbalances parentheses:
Vof=@(t) Vo(1+ceil(t.*fo.*(length(t)-1));
4 opening ( but only 3 closing ).
If this is fixed, the next error concerns "Vo". What is this?
Finally remember, that ODE45 is designed to integrate smoth functions. Your function does not look like it is differentiable. Then the step size controller of ODE45 can drive mad and the results can be dominated by rounding errors.
The integral of a piecewise constant function can be calculated by a sum more accurately and efficiently.
Prefer simple code. Compare these equivalent definitions:
dio = @(t,io) (Vof(t)./L)-((R*io)/L);
dio = @(t,io) Vof(t) / L - R * io / L;

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