UPS uninterruptible power supply immediately enters the battery inversion state; In order to prevent the mains from switching back and forth, UPS will turn into the mains inverter state only when the mains is restored to170 ~ 270 V ~ 270 V. Detection and control of commercial power frequency The purpose of detecting commercial power frequency is to serve as the basis of inverter phase locking, and adjust the inverter phase by adjusting the zero-crossing point of the inverter, so that the inverter output and the commercial power input in the commercial power state are basically in the same frequency and phase. When the commercial power is connected, UPS detects the frequency of the input commercial power as the output frequency of the inverter; When the battery is turned on, the frequency output by the frequency converter is set to the previously output frequency.

When the commercial power is normal, phase locking is implemented. The inverter frequency follows the mains frequency first, and the frequency is the same before tracking the phase. By changing the inverter frequency, the inverter and the mains are in phase. After phase locking, the phase difference between inverter and commercial power is less than 3 degrees, and the frequency error is less than 0.0 1Hz. When the mains frequency exceeds the range of 47 ~ 53 Hz, UPS will immediately switch to the battery inverter state without phase locking. Only when the mains frequency returns to 48 ~ 52 Hz, UPS will phase lock again and switch to the mains inverter state.

The square wave of 38.4kHz emitted by the CPU of the triangular wave generator is converted into a square wave of 19.2kHz by a frequency dividing circuit composed of an operational amplifier, and then integrated into a triangular wave by an integrator. The CPU of the standard sine wave generator sends out an analog sine wave with a frequency division of 128, which is filtered by a second-order low-pass filter to generate a standard sine wave. The standard sine wave of PWM signal is compared with the sine wave feedback signal of inverter output voltage, and the PWM signal is generated by triangle wave cutting. The inverter voltage regulating CPU reads the inverter voltage value every 16ms and compares it with the set voltage value. When the difference is higher than 10V, the CPU immediately adjusts the standard sine wave, thereby adjusting the PWM signal, so that the output voltage is correspondingly increased or decreased by 5V to narrow the difference. When the difference is lower than 10V, the CPU accumulates the difference. When the accumulated value reaches 30V, the CPU adjusts the standard sine wave to increase or decrease the output voltage by 2V.

A/D reading of CPU The CPU reads the battery voltage, positive and negative bus voltages and internal temperature once every half cycle, and reads the mains voltage, inverter voltage and inverter current once every eight standard sine wave points (at the beginning of each cycle, the CPU changes the initial position of the reading point to make it read once every eight standard sine wave points, and the scanning effect is achieved by A/D reading at 128 points, and the reading value is stored in RAM).