0 Introduction UPS power supply systems are essential power sources for industries such as power, telecommunications, and banking. They have undergone decades of development since their inception, and their protection functions have continuously evolved with technological advancements and improvements. UPS systems can be categorized based on the operating state of the inverter within the main unit: standby, online, and line-interactive. Their function is to filter and regulate the mains power to provide a more stable voltage to the load. Simultaneously, they convert electrical energy into chemical energy stored in batteries via chargers. In the event of a power outage, or if the mains voltage or frequency exceeds the UPS's input range, the system can quickly activate its backup power supply to power the load. The UPS intelligent monitoring system designed in this paper possesses the following features and functions: it can operate in various complex power grid environments; it does not generate additional interference to the mains power during operation; its output electrical performance indicators should be comprehensive and of high quality, meeting all load requirements; the UPS itself should have high efficiency and an output capacity close to that of actual mains power; it is a highly intelligent device with highly intelligent self-testing functions, automatic display, alarm, status memory functions, and communication functions. 1. Overall Design This design consists of several modules, including a main monitoring unit, an AC detection unit, a battery detection and inspection unit, a feeder detection and voltage regulation unit, and an insulation monitoring and grounding selection unit. These modules communicate internally via RS485 to achieve real-time monitoring, control, and alarm processing of AC power distribution, battery charging and discharging processes, battery status, voltage regulation status, bus-to-ground resistance, and feeder switch status. The entire system communicates with the host computer via RS232 for historical data querying and statistics. 2. Unit Introduction 2.1 Main Monitoring Unit The main monitoring unit manages the operation of the entire system. It consists of a main monitoring board, a 320x240 dot-matrix LCD display, a keyboard, and indicator lights. It manages battery charging and discharging, sets and displays operating and control parameters, stores and queries alarm records, communicates with the host computer via RS232, and controls internal units via RS485. 2.2 AC Detection Unit This unit mainly acquires three-phase AC voltage, current, and frequency; it also has alarm functions for AC power failure, phase loss, overvoltage, and undervoltage; the relay alarm contacts close when an alarm occurs. The three-phase AC voltage display value can be corrected by adjusting the potentiometer on the board. 2.3 Battery Detection and Inspection Unit This unit consists of a battery detection board and a battery inspection board (optional). It mainly acquires battery pack voltage (bus voltage), charging/discharging current, ambient temperature, and individual cell voltage; detects battery fuse status; and can control the voltage or current input of modules or phase-controlled power supply three-phase trigger boards from other manufacturers by outputting analog voltage and current inputs (specific details to be negotiated with the manufacturer), improving system compatibility; provides timely metering; and performs alarm functions for bus over/undervoltage, battery overcharge, battery depletion, and individual cell failure. The bus voltage and individual cell voltage display values ​​can be corrected by adjusting the potentiometers on the battery detection board and battery inspection board, respectively. As shown in Figure 2. 2.4 The feeder detection and silicon chain voltage regulation unit consists of a feeder detection CPU board and a digital input board, which monitors the feeder switch status of the busbar and control busbar in real time. It can detect 24 feeders through the digital expansion port. An alarm is triggered when a switch change occurs or the control busbar voltage exceeds the limit, and the control busbar voltage is automatically adjusted via silicon chains (up to 7 silicon chain sections). The control busbar voltage display value can be calibrated by adjusting the potentiometer on the feeder detection board. 2.5 The insulation monitoring and grounding selection unit consists of an insulation monitoring detection board and a grounding selection expansion board. Its main function is to monitor the busbar-to-ground resistance in real time and self-locate the grounding branch. When the busbar-to-ground resistance is lower than the alarm setting value, the alarm relay closes; it connects to the grounding selection port, supporting up to 24 selection channels. 3 Key Circuit Unit Design 3.1 Current Detection Circuit The magnitude of the battery charging and discharging current is particularly critical. The circuit diagram is shown in Figure 1. Because it detects both charging and discharging currents, the voltage across the small resistor has two directions. Two channels are used for detection in the circuit, which facilitates separate signal conditioning and allows measurement using only one input channel of the A/D converter. 3.2 Monitoring of Bus Voltage The bus voltage monitoring circuit is shown in Figure 2. The bus voltage flows through resistors R16, R17, and R54, and is sampled at resistor R17. Therefore, resistor R17 should be a high-precision resistor. Since R16 and R54 are much larger than resistor R17 and appear in the denominator, high-precision resistors are not necessary. LL's function is to suppress common-mode interference. The magnitude of the voltage to be monitored can be adjusted by changing the potentiometer Rp to meet the input voltage requirements of the A/D converter. 3.3 A/D Conversion The A/D conversion chip used is TLV1544. The main features of the TLV1544 are: wide-range single-supply operation (VCC can be 2.7–5.5V); high internal conversion rate (conversion time less than 10μs); four external input channels, which can be selected arbitrarily by programming different status words; four ports as synchronous serial interfaces, connecting to the microprocessor via SPI bus; and 11-bit A/D conversion, sufficient for system requirements. As shown in Figure 3, the control begins sampling of the analog signal input from the selected channel. A high-to-low transition initiates analog input signal sampling; a low-to-high transition puts the sample-and-hold function in hold mode and begins analog-to-digital conversion. Independent of the input/output clock signal, it starts working when high. The duration of the low position controls the duration of the switched-capacitor array sampling period. When not in use, it is connected to a high level. The EOC pin goes high at the end of the A/D conversion to indicate completion. This unit uses the EOC level to determine whether the conversion is complete and reads the data. 3.4 Communication Circuit Design The entire system communicates internally via RS485. The specific circuit is shown in Figure 4. Because the control chips all use AT89C52, the CPU, as the main monitoring unit, only has one serial port, and its parallel port is not fully utilized. Therefore, the serial port is expanded using the programmable serial interface chip 8250, and the parallel port is used to simulate the serial port. 3.5 X5045 Circuit Design The design of the X5045 circuit is shown in Figure 5. This device integrates four functions: power-on reset control, watchdog timer, buck management, and a serial EEPROM with block protection. It helps simplify the design of the application system, reduce the printed circuit board area, and improve reliability. It is connected to the CPC via an SPI bus, making reading and writing simple. Its internal EEPROM can also protect some important data. 3.6 System Clock Design The DS1306 clock chip, which has a full range of functions, is used. The time, calendar, and alarm of the DS1306 can be set and initialized by writing the corresponding register bits. The calendar and time can be obtained by reading the corresponding registers. The DS1306 has three operating modes for power supply. This system uses a rechargeable battery, as shown in Figure 6. 4 Conclusion (1) This intelligent power monitoring system performs intelligent battery charging and discharging management based on the characteristics of the battery, which plays a role in extending the battery life in actual use; (2) The 485 communication of each module enables the system to have complete alarm processing and accident recall functions, so as to fully grasp the system operating status.