Modelling SW damping of slim DC-link capacitors


Companies / Organizations


South Jutland

When using slim DC-link in frequency inverters, the inverter is more sensitive to transients at mains and sensitive for inductance at mains. The setpoint at inverters are often a speed, which means at lower mains voltage the current will increase, which is equivalent to negative resistance. The more load, the more negative the resistance becomes.
In the cases where inductance in mains grid is more significant than the resistive part, there is a risk that ringing/oscillation will happen between the mains inductance and the slim (low ESR) dc-link capacitors. This oscillation can be dampened by software, so that the motor increases the speed during overvoltage, or reduce speed at low voltage.

Project description
The task is to do modelling of the motor control along with the hardware in for example the simulation program Simetrix and then add on a dampening element (SW-block), so that DC-link capacitance is fully protected by inverter software. No software will be implemented in inverter during this project, but simulations should prove the concept of the additional dampening element. 

The project is also expected to include system overview, block schematics and calculations, to guide the simulations into the right direction (not just trial and error).

The approach could be:
• Model the motor control along with the slim DC-link and mains hardware • Investigate/ model the oscillations
• Simulate the dampening element

Further information
Please contact Hans Jørgen Nørgaard (Lodam employee) by email:  or by phone: +45 73 42 37 37.

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