Nonlinear control of voltage-source converter systems

The nonlinear control method, associated with the books of A. Isidori, H. Nijmeijer, and A. J. van der Shaft, has so far been applied to the STATCOM (system order, N = 3). There have been two impediments to progress in applying the method: 1) difficulty in synthesizing the nonlinear transformation which is the key to the method; 2) the advanced mathematical language which makes the aforesaid books generally inaccessible. This paper describes the successful application of the nonlinear control method to control systems based on back-to-back pulsewidth modulation voltage-source converter. This paper is written in a tutorial form to explain how the nonlinear control method can be applied without using the advanced mathematical language. The SSSC and the UPFC (system order, N = 5) are chosen as illustrative examples.