Control method for soft switch circuit in switch power source

1. A control method for a soft switch circuit in a switch power source comprising:

generating an alternating primary power filter current by controlling first and second primary power switching devices to be closed and opened;

generating an intermittent alternating resonant current in the same direction as the primary power filter current in a resonant branch by controlling forward and backward auxiliary switching devices to be closed and opened to thereby achieve closing of the first and second primary power switching devices at a zero voltage; and

generating a balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch in at least a period of time during the resting of the resonant current by further controlling the forward and backward auxiliary switching devices to be closed and opened, to thereby achieve an average current of zero in the resonant branch during a switching cycle.

2. The control method for a soft switch circuit in a switch power source according to claim 1 , wherein said generating the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch comprises:

in the positive half of a cycle, i.e., when the primary power current is in the positive direction, controlling the forward auxiliary switching devices to be closed after the first primary power switching device is closed and to be opened at the moment when the first primary power switching device is opened, to generate the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch to thereby achieve an average current of zero in the resonant branch during the positive half of a cycle; and

in the negative half of a cycle, i.e., when the primary power current is in the negative direction, controlling the backward auxiliary switching devices to be closed after the second primary power switching device is closed and to be opened at the moment when the second primary power switching device is opened to generate the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch to thereby achieve an average current of zero in the resonant branch during the negative half of a cycle.

3. The control method for a soft switch circuit in a switch power source according to claim 2 , wherein at least one of the primary switching devices and the auxiliary switching devices is an IGBT, MOSFET, GTO or SCR.

4. The control method for a soft switch circuit in a switch power source according to claim 1 , wherein said generating the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch comprises:

in the positive half of a cycle, i.e., when the primary power current is in the positive direction, controlling the forward auxiliary switching devices to be closed after the first primary power switching device is closed and to be opened in a period of first dead area to generate the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch to thereby achieve an average current of zero in the resonant branch during the positive half of a cycle; and

in the negative half of a cycle, i.e., when the primary power current is in the negative direction, controlling the backward auxiliary switching devices to be closed after the second primary power switching device is closed and to be opened in a period of second dead area to generate the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch, to thereby achieve an average current of zero in the resonant branch during the negative half of a cycle.

5. The control method for a soft switch circuit in a switch power source according to claim 4 , wherein at least one of the primary switching devices and the auxiliary switching devices is an IGBT, MOSFET, GTO or SCR.

6. The control method for a soft switch circuit in a switch power source according to claim 1 , wherein said generating the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch comprises:

in the positive half of a cycle, i.e., when the primary power current is in the positive direction, controlling the forward auxiliary switching devices to be closed after the first primary power switching device is closed and to be opened prior to the moment when the first primary power switching device is opened to generate the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch to thereby achieve an average current of zero in the resonant branch during the positive half of a cycle; and

in the negative half of a cycle, i.e., when the primary power current is in the negative direction, controlling the backward auxiliary switching devices to be closed after the second primary power switching device is closed and to be opened prior to the moment when the second primary power switching device is opened to generate the balance current with the same magnitude as and in the opposite direction to the resonant current in the resonant branch, to thereby achieve an average current of zero in the resonant branch during the negative half of a cycle.

7. The control method for a soft switch circuit in a switch power source according to claim 6 , wherein at least one of the primary switching devices and the auxiliary switching devices is an IGBT, MOSFET, GTO or SCR.

8. The control method for a soft switch circuit in a switch power source according to claim 1 , wherein at least one of the primary switching devices and the auxiliary switching devices is an IGBT, MOSFET, GTO or SCR.