62 Frequency Converters 2.6.3.2 60° AVM If 60° AVM (Asynchronous Vector Modulation) is used – as opposed to the SFAVM principle – the voltage vectors are determined as follows: • Within one switching period, only one zero vector (000 or 111) is used • A zero vector (000 or 111) is not always used as the starting point for a switching sequence • One phase of the inverter is held constant for 1/6 of the period (60°). The switch state (0 or 1) remains the same during this interval. In the two other phases, switching is performed in the normal way Fig. 2.18 Switching sequence of the 60° AVM and SFAVM methods for a number of 60° intervals and Fig.
2.19 Switching sequence of the 60° AVM and SFAVM methods for several periods compare the switching sequence of the 60° AVM method with that of the SFAVM method – for a short interval (Fig. 2.18) and for several periods (Fig. 2.19). Fig. 2.18 Switching sequence of the 60° AVM and SFAVM methods for a number of 60° intervals Fig. 2.19 Switching sequence of the 60° AVM and SFAVM methods for several periods