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From: Chris Woodruff on 15 Jul 2010 22:14
Hello,

I am trying to build a power converter model in simscape. When running the simulation, I receive this error message: "Number of variables exceeds number of equations. Check for missing reference node." I know that there is a problem with the solver configuration, but have no idea how to go about solving the problem. Is anyone familiar with this error message?

Thanks
From: neil on 16 Jul 2010 00:17
"Chris Woodruff" <christopher.woodruff(a)samsung.com> wrote in message <i1of9c$3nk$1(a)fred.mathworks.com>...
> Hello,
>
> I am trying to build a power converter model in simscape. When running the simulation, I receive this error message: "Number of variables exceeds number of equations. Check for missing reference node." I know that there is a problem with the solver configuration, but have no idea how to go about solving the problem. Is anyone familiar with this error message?
>
> Thanks
Hi Chris

I do not have the toolbox any more but have some experience using it and getting this error is common and frustrating. The error message doesn't really indicate what is wrong with the model

Generally what it means is that you have over simplified your equations or missed an element in the model. For example you cannot have a voltage connecting directly to a group with an impedance element between them.

A good method to avoid this is to start small and build up your system. Also try write out of the equations for your system and make sure they make sense and can be solved. Make sure that for each through variable you have an equation linking it to the across variables on either side.
Try post slightly more detail about your model.

Are you using the modelling language or just simscape blocks?
From: Chris on 16 Jul 2010 02:07
Hi Neil,

Thanks for your reply. I haven't used Simulink/Simscape much so I appreciate your advice. I'm just using Simscape blocks for the model. I was given a circuit diagram and told to model it in Simulink. Most of it is fairly simple, the part where I'm confused has a N-Channel Mosfet leading to a PWM generator.

I think the source of my problem is the PWM generator. I am unsure whether to use the Simscape 'Controlled PWM Voltage' or the SimPowersystems 'PWM generator' block. I was looking at this example using the simscape block:
http://www.mathworks.de/access/helpdesk/help/toolbox/physmod/elec/ug/briwjp4-15.html
I'm unsure of how to connect the different ports, mostly just the REF port (the help page is very brief).

When I use the SimPowersystems block, I get a different message-unable to solve the algebraic loop, but I don't think it is the right block for this.

Thanks!

"neil " <neil.iain(a)gmail.com> wrote in message <i1omg1$6t0$1(a)fred.mathworks.com>...
> "Chris Woodruff" <christopher.woodruff(a)samsung.com> wrote in message <i1of9c$3nk$1(a)fred.mathworks.com>...
> > Hello,
> >
> > I am trying to build a power converter model in simscape. When running the simulation, I receive this error message: "Number of variables exceeds number of equations. Check for missing reference node." I know that there is a problem with the solver configuration, but have no idea how to go about solving the problem. Is anyone familiar with this error message?
> >
> > Thanks
> Hi Chris
>
> I do not have the toolbox any more but have some experience using it and getting this error is common and frustrating. The error message doesn't really indicate what is wrong with the model
>
> Generally what it means is that you have over simplified your equations or missed an element in the model. For example you cannot have a voltage connecting directly to a group with an impedance element between them.
>
> A good method to avoid this is to start small and build up your system. Also try write out of the equations for your system and make sure they make sense and can be solved. Make sure that for each through variable you have an equation linking it to the across variables on either side.
> Try post slightly more detail about your model.
>
> Are you using the modelling language or just simscape blocks?
From: neil on 16 Jul 2010 02:33
"Chris " <christopher.woodruff(a)samsung.com> wrote in message <i1osua$itd$1(a)fred.mathworks.com>...
> Hi Neil,
>
> Thanks for your reply. I haven't used Simulink/Simscape much so I appreciate your advice. I'm just using Simscape blocks for the model. I was given a circuit diagram and told to model it in Simulink. Most of it is fairly simple, the part where I'm confused has a N-Channel Mosfet leading to a PWM generator.
>
> I think the source of my problem is the PWM generator. I am unsure whether to use the Simscape 'Controlled PWM Voltage' or the SimPowersystems 'PWM generator' block. I was looking at this example using the simscape block:
> http://www.mathworks.de/access/helpdesk/help/toolbox/physmod/elec/ug/briwjp4-15.html
> I'm unsure of how to connect the different ports, mostly just the REF port (the help page is very brief).
>
> When I use the SimPowersystems block, I get a different message-unable to solve the algebraic loop, but I don't think it is the right block for this.
>
> Thanks!
>
> "neil " <neil.iain(a)gmail.com> wrote in message <i1omg1$6t0$1(a)fred.mathworks.com>...
> > "Chris Woodruff" <christopher.woodruff(a)samsung.com> wrote in message <i1of9c$3nk$1(a)fred.mathworks.com>...
> > > Hello,
> > >
> > > I am trying to build a power converter model in simscape. When running the simulation, I receive this error message: "Number of variables exceeds number of equations. Check for missing reference node." I know that there is a problem with the solver configuration, but have no idea how to go about solving the problem. Is anyone familiar with this error message?
> > >
> > > Thanks
> > Hi Chris
> >
> > I do not have the toolbox any more but have some experience using it and getting this error is common and frustrating. The error message doesn't really indicate what is wrong with the model
> >
> > Generally what it means is that you have over simplified your equations or missed an element in the model. For example you cannot have a voltage connecting directly to a group with an impedance element between them.
> >
> > A good method to avoid this is to start small and build up your system. Also try write out of the equations for your system and make sure they make sense and can be solved. Make sure that for each through variable you have an equation linking it to the across variables on either side.
> > Try post slightly more detail about your model.
> >
> > Are you using the modelling language or just simscape blocks?


Hi Chris

I would keep to using the Simscape blocks only. If you are use simpowersystem blocks then model the entire system should use simpowersystems. As far as I know they are built on different technologies and do not work all that well together.

If I was to guess, I would think you might be missing a resistor between the Mosfet and the PWM block and/or ground? Do you have a resistor between the moseft and ground. This is something you might not have in a circuit diagram but may need in the model. Even if it is a nominal resistance.

Try take the moseft block out see if you still get the error. Then try make a simple moded using a mosek and no PWM block them build them together.
From: Arnaud Miege on 19 Jul 2010 09:50
"Chris " <christopher.woodruff(a)samsung.com> wrote in message <i1osua$itd$1(a)fred.mathworks.com>...
> Hi Neil,
>
> Thanks for your reply. I haven't used Simulink/Simscape much so I appreciate your advice. I'm just using Simscape blocks for the model. I was given a circuit diagram and told to model it in Simulink. Most of it is fairly simple, the part where I'm confused has a N-Channel Mosfet leading to a PWM generator.
>
> I think the source of my problem is the PWM generator. I am unsure whether to use the Simscape 'Controlled PWM Voltage' or the SimPowersystems 'PWM generator' block. I was looking at this example using the simscape block:
> http://www.mathworks.de/access/helpdesk/help/toolbox/physmod/elec/ug/briwjp4-15.html
> I'm unsure of how to connect the different ports, mostly just the REF port (the help page is very brief).
>
> When I use the SimPowersystems block, I get a different message-unable to solve the algebraic loop, but I don't think it is the right block for this.
>
> Thanks!
>
Hi Chris,

I agree with Neil, I would stick to Simscape. Make sur that you have an electrical ground somewhere in your model. Have a look at the documentation:
http://www.mathworks.com/access/helpdesk/help/toolbox/physmod/simscape/ug/bq22y4u.html

The Controlled PWM Voltage is from SimElectronics. There are various demos that shows how to use it, for example elec_controlled_dcmotor. Most of the time, you would connect the REF port to ground, it's probably what you're missing in your model.

You can always contact technical support if you need any more help:
http://www.mathworks.com/support/contact_us/index.html

HTH,

Arnaud
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