Photovoltaic Anti-Backflow Grid-Connected Box

The clean power grid-connected power supply system operates in parallel with the public grid distribution system (supplied by a 10kV/0.4 kV distribution transformer). Given the special requirements for load variation control, on one hand, the power supply department must ensure the quality and reliability of the user's power supply while enabling the clean power source to function properly, fully leveraging the economic benefits of clean energy and its role in testing and demonstration. On the other hand, the operation of the clean power source should not affect the distribution system, and it is not allowed to feed power back to the power system through the distribution transformer. At the same time, the clean power supply should be used scientifically and rationally to reduce the user's electricity costs. Therefore, control of the clean power source is necessary.

The task of this device is to monitor the low-voltage side of the distribution transformer in real time and to control the clean power source. It employs a specially designed microcomputer device and control circuit to ensure rapid protection action and control accuracy.

I. Main Features of the Reverse Power Monitoring Device

1.1 The reverse power monitoring device can be centrally grouped on a panel or locally dispersed and installed on high-voltage switchgear cabinets. Each interval functions independently, with devices connected only via a network for information sharing. This not only enhances the flexibility of the entire system but also significantly improves reliability, as a failure of any single device only affects a local component.

1.2 The device utilizes a high-performance processor and a high-resolution A/D converter, sampling 32 points per cycle in combination with measurement CTs, ensuring high accuracy of telemetry data.

1.3 The protection function is completely independent of the communication network; network failure does not affect the normal operation of protection.

1.4 The device adopts a fully sealed design, along with carefully designed anti-interference components, greatly improving vibration resistance and electromagnetic interference resistance.

1.5 It features both hardware and software watchdog functions, enabling the entire system to achieve high measurement accuracy and strong anti-interference capability simultaneously.

1.6 With a user-friendly human-machine interface, the device uses a fully Chinese large-screen LCD display. Trip reports, alarm reports, telemetry, remote signaling, and setting adjustments are all clearly labeled in Chinese on the screen, making it easy for users to operate and understand.

1.7 The communication method employs a CAN port, i.e., Controller Area Network interface (or 485 port), characterized by: simple structure with only two wires connected externally; high transmission speed up to 1Mbps; long transmission distance up to 10KM; CRC verification with corresponding error handling capability; and non-destructive bus arbitration technology, giving the station communication high efficiency and strong anti-interference ability.

II. Brief Introduction of Main Functions

In addition to reverse power and reverse power recovery functions, during system operation, the device continuously monitors bus voltage and measures current, with alarm functions for abnormal current and voltage, set as follows:

(1) Overvoltage alarm

(2) Undervoltage alarm

(3) Overload alarm

(4) Reverse power

(5) Reverse power recovery

(6) Measurement and control functions: U, I, P, Q, cosΦ, F (requires measurement current and voltage input)