Method for detecting whether a battery is disconnected, an online uninterruptible power system and an offline uninterruptible power system using the method

An online UPS, comprising:

• a charging circuit, for performing a DC-DC conversion operation and for charging a battery;
• a sensing circuit, for sensing an output of the charging circuit to generate a sensing result;
• and
• a control unit, comprising:
• a digital control circuit, for generating a PWM signal according to the sensing result, a duty cycle of the PWM signal being used to control an output voltage of the charging circuit;
• and
• a driving circuit, for generating a driving signal to drive the charging circuit according to the PWM signal,
• wherein when the digital control circuit determines that the charging circuit is in a constant voltage charging mode according to the sensing result, the digital control circuit executes a battery disconnection detection, and the battery disconnection detection comprises the following steps:
• alternately performing a first operation and a second operation on the PWM signal, wherein the first operation is increasing the duty cycle of the PWM signal by a first preset value for a first preset time, and the second operation is reverting the PWM signal to an original duty cycle for a second preset time;
• and
• determining whether the voltage at the output terminal of the charging circuit rises and reaches a second preset value.

An offline UPS, comprising:

• a charging circuit, for performing an AC-DC conversion operation, an output of the charging circuit being used to charge a battery and used as a system power;
• a sensing circuit, for sensing the output of the charging circuit to generate a sensing result;
• and
• a control unit, comprising:
• a digital control circuit, for generating a PWM signal according to the sensing result, a duty cycle of the PWM signal being used to control an output voltage of the charging circuit, wherein the digital control circuit further has a function of stabilizing the output voltage of the charging circuit;
• and
• a driving circuit, for generating a driving signal to drive the charging circuit according to the PWM signal,
• wherein when the digital control circuit determines that the charging circuit is in a constant voltage charging mode according to the sensing result, the digital control circuit executes a battery disconnection detection, and the battery disconnection detection comprises the following steps:
• alternately performing a first operation and a second operation on the PWM signal, wherein the first operation is increasing the duty cycle of the PWM signal by a first preset value for a first preset time, and stopping the function of stabilizing the output voltage of the charging circuit during the first preset time, and the second operation is reverting the PWM signal to an original duty cycle for a second preset time;
• determining whether a voltage at an output terminal of the charging circuit rises and reaches a second preset value;
• stopping performing the first operation and the second operation when the voltage at the output terminal of the charging circuit reaches the second preset value, and increasing the duty cycle of the PWM signal, thereby making a target level of the output voltage of the charging circuit rising to a third preset value and keeping for a third preset time, wherein the third preset value is greater than the second preset value;
• and
• determining whether the voltage at the output terminal of the charging circuit still reaches the second preset value within the third preset time.