Abstract: Achieving stability and good performance of a voltage-source converter (VSC) connected to a weak grid – that is, with a low short-circuit ratio (SCR) – is often challenging. Moreover, it is desirable to use the same controller tuning irrespective of the SCR. This is because the SCR may be varying, perhaps in an unknown way. This objective is called robust control – a well-studied topic in the field of process control. Roughly 15 years ago it was recognized that the conventional method vector current control (VCC) is not robust, as it generally gives unsatisfactory performance for weak grids. Due to the particular system structure, cut-and-dried methods from robust process control are not immediately applicable to converter control. Instead, the problem was circumvented by emulating the dynamics of a synchronous machine, called power-synchronization control (PSC). However, PSC was found to be inferior to VCC for strong grids, that is, neither PSC is robust. In this webinar, we present the key evolutionary steps in which VCC and PSC were robustified to both perform well irrespective of the SCR. The somewhat surprising end result of this process is that the two schemes become near identical and can be unified in a universal controller.
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