Bakez
Member level 1
I am testing the efficiency of brand new MOSFETs in wind turbine applications. However rather than building an entire 3 phase AC-DC-AC converter, I am instead emulating one leg of the converter by building a single phase DC-AC inverter with an inductive load or H-Bridge:
I want to control the sinusoidal current through the inductive load so I can correctly emulate the working point that would be seen in real wind turbine operation. To do this I know that I have to have some method of controlling the duty cycle of the control half bridge MOSFETs in order to get the correct voltages across the inductor and hence the correct current. I need to design a PI controller where the I will have a reference sinusoidal current as an input and sample the actual current through the inductor in order to find the error. I will also have to implement this into a DSP so I need to design it discretely.
The problem I have is I am not good at control theory. Although I know I have to design this in the z domain as I will have to implement the controller digitally, and I have to incorporate some sort of delay as the duty cycle of the PWM can only change once per cycle, as well as including dead time compensation. Also I think the half bridge under testing (DUT) can be controlled open loop so I only have to design a PI controller for the control side so that I can regulate the difference between the two half bridges.
Basically I think I have this transfer function in the S-Domain and have no idea how to get it into the Z domain:
and then I use this PI controller:
I will post another post below with my working
All help appreciated
- - - Updated - - -
I think that the transfer function in the S domain for the load is:
and the transfer functions for the control inverters are:
And therefore the gain of the inverter bridge can be Vdc
A delay of half a period can be taken as (according to a book):
I want to control the sinusoidal current through the inductive load so I can correctly emulate the working point that would be seen in real wind turbine operation. To do this I know that I have to have some method of controlling the duty cycle of the control half bridge MOSFETs in order to get the correct voltages across the inductor and hence the correct current. I need to design a PI controller where the I will have a reference sinusoidal current as an input and sample the actual current through the inductor in order to find the error. I will also have to implement this into a DSP so I need to design it discretely.
The problem I have is I am not good at control theory. Although I know I have to design this in the z domain as I will have to implement the controller digitally, and I have to incorporate some sort of delay as the duty cycle of the PWM can only change once per cycle, as well as including dead time compensation. Also I think the half bridge under testing (DUT) can be controlled open loop so I only have to design a PI controller for the control side so that I can regulate the difference between the two half bridges.
Basically I think I have this transfer function in the S-Domain and have no idea how to get it into the Z domain:
and then I use this PI controller:
I will post another post below with my working
All help appreciated
- - - Updated - - -
I think that the transfer function in the S domain for the load is:
and the transfer functions for the control inverters are:
And therefore the gain of the inverter bridge can be Vdc
A delay of half a period can be taken as (according to a book):