A method used to control the operation of a converting device such that it can provide multi-level output voltage for loads. This method comprises at least the steps of: determine whether the load which the converter is providing electricity for is operating under the first condition or the second condition; generate the first pulse signal after determining that this load is operating under the first condition, select at least one of at least three different current paths, such that when the converter is selecting any of the current paths, it can provide output voltage at the same level; as well as generate the second pulse signal after determining that this load is operating under the second condition, such that the converter can perform the regular energy conversion operations.