Hi Everybody,
I am trying to simulate PMSG based Wind Turbine that work in stand-alone mode using back to back inverter. Firstly i designed a grid-connected wind turbine system. In my simulation for the grid side inverter, the currents and dc voltage are perfectly controlled by using vector control. Also generator side converter which i am used field oriented control works fine. But when the wind turbine were disconnected from the grid(in stand-alone mode), each different load step, the inverter output voltage is always changing. What should I do to make it constant?
Note: Fig 1. shows the grid side converter Simulink model. The breaker block is switching on 1 second and off 2 second. The figure 2 show output voltage and current graphs of load.
Your load-side inverter needs to regulate output voltage, rather than current, as you would when grid-connected. This means that this inverter cannot regulate the DC link voltage, and this task then needs to be addressed by the turbine-side inverter. Thus, turbine loading is completely uncontrolled, and dictated solely by the output inverter load. Connecting energy storage at the DC link can allow more controlled operation. This is generally needed for a practical system. Otherwise, the output voltage will collapse during load transients, and the DC link will over-voltage during transient unloads.
The back-to-back converter has high control flexibility of a generator torque and current
In stand-alone mode, torque must go to zero when the output is unloaded to keep from pumping up the DC link. This unloads the turbine, which has it's own set of problems, though this may be beyond what the OP is currently investigating. I agree that the control loops for both inverters can be designed for this functionality. I'm not sure that it's clear to the OP that they are not the same as for grid tie.
- Badges
- Science topic
- Similar topics
- Engineering
- Control Theory
- Control Systems
- Control Systems Engineering