This paper presents a simple yet practical intelligent power monitoring system for UPS (Uninterruptible Power Supply) applications. Designed to function effectively in complex power grid environments, the system features high-level self-diagnostic capabilities, automatic display, alarm functions, status memory, and communication functionalities. It ensures reliable performance by continuously monitoring various critical parameters of the power system.
The system's modules communicate via internal RS485 to enable real-time monitoring, control, and alarm handling for AC power distribution, battery charging and discharging processes, battery state, voltage regulation, bus-to-ground resistance, and feeder line switch status. Additionally, it connects with the host computer through RS232 for historical data retrieval and statistical analysis, making it an efficient tool for long-term power management.
At the core of the system is the main monitoring unit, which manages the overall operation. This unit includes a main monitoring board, a 320x240 dot matrix LCD screen, a keyboard, and indicator lights. It handles battery charge and discharge management, sets and displays operational parameters, stores and retrieves alarm records, and communicates with the host computer via RS232. It also controls internal units through the RS485 interface, ensuring seamless integration and coordination across all components.
As shown in Figure 1, the circuit design for detecting battery charge and discharge current is crucial. The circuit measures both charging and discharging currents, resulting in voltage signals in two directions. To facilitate signal conditioning, the detection is done through two separate channels, which simplifies the process and allows for efficient measurement using a single A/D converter input channel.
The battery detection and inspection unit comprises a battery detection board and an optional battery inspection board. It collects data on battery voltage (mother voltage), charge/discharge current, ambient temperature, and cell voltage. It also monitors the fuse state and provides analog voltage and current references to control other manufacturers' modules or phase-controlled power supply boards. This enhances system compatibility and enables precise battery monitoring, including alarms for over-voltage, over-charging, battery feed issues, and single-cell failures. Adjustments to battery voltage and cell voltage display values can be made using potentiometers on the respective boards, as illustrated in Figure 2.
The mother voltage monitoring circuit, depicted in Figure 2, involves resistors R16, R17, and R54, with sampling occurring at R17. Due to the high value of R16 and R54 compared to R17, these resistors do not need to be precision types. The LL component suppresses common-mode interference, while the potentiometer Rp adjusts the monitored voltage to meet the A/D converter’s input requirements.
For A/D conversion, the TLV1544 chip is used. It supports a wide single-supply voltage range (2.7–5.5 V), offers a fast conversion time of less than 10 μs, and provides four external input channels that can be programmed for different configurations. The chip uses a synchronous serial interface connected via SPI to the microprocessor and performs 11-bit A/D conversion, which is sufficient for the system's needs. As shown in Figure 3, the conversion process begins with analog signal sampling, followed by holding the sampled value and initiating the conversion. The EOC pin goes high when the conversion is complete, signaling the system to check the result.
In summary, this paper introduces the circuit design of an intelligent power monitoring system tailored for effective battery charge and discharge management. By leveraging the unique characteristics of batteries, the system helps extend their lifespan and improve reliability in real-world applications.
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