in a method for controlling bi - directional switches in power converters , with separate control signals for both current directions , preferably 3 × 3 matrix converters , a switching process from a base main state , into a secondary main state , and vice versa , occurs after a voltage controlled two - step process or a voltage controlled four - step process , without additional operational current - conducting components . after a first step , all uni - directional switches , apart from those at the interface of reference main state and target main state , are switched off and after a second step , all target main state switches are switched on . the switching processes can thus be carried out , at any time , by an appropriate choice of interval beginning and interval end , whereby a free - wheeling arm for both current directions permanently exists , the only requirement being the creation of a current interval for each phase in multi - phase systems . the method is applicable with practically all supply current frequencies .