Brief Analysis of DC Power System

The DC power system mainly consists of two parts, a battery cabinet (battery screen) and a DC screen (DC charging screen). Among them, the DC screen is composed of a high-frequency switching power supply module, a control unit, a step-down silicon chain measurement module, a switch quantity module, an insulation detection module, a battery test module, and multiple power distribution units such as AC input, DC voltage display, and power display. The following describes each component in detail.

1. Rectifier module

Power rectifier modules are stand-alone modules that convert alternating current to direct current. It is usually rated according to the magnitude of the current. Due to the different instrument concept, it can also be divided into air cooling modules and independent air. Duct Modules, Self-Cooling Modules, Self-Saving Air Cooling Modules, and Self-Saving and Self-Cooling Modules. It can be used in parallel with multiple units for N1 redundancy. The module output is a stable, adjustable 110 V, 220 V DC voltage. The module itself has various protection functions, such as input overvoltage protection, output overvoltage protection, output current limit protection and output short circuit protection.

2. Monitoring system

The monitoring system is the core of the control and management of the entire DC system. Its main task is to automatically monitor each functional unit and battery in the system for a long time, record various operating parameters, the state in the system and the time. It processes according to the measurement data and operating conditions, and controls the system according to these data, realizes the automatic management of the power system, and ensures the continuity, reliability and safety of the work. (Zhongruihong monitoring module is divided into intelligent monitoring module and integrated performance monitoring module. Currently, a more intelligent monitoring module is being used.)

3. Insulation monitoring unit

The DC system insulation monitoring unit is a device that monitors the DC system insulation and can monitor the leakage resistance of the line in real time. This value can be adjusted according to the situation. If the line insulation falls to the set value, an alarm signal is issued. The DC system insulation monitoring unit currently includes bus insulation monitoring and branch insulation monitoring.

4. Battery inspection unit

The battery check unit is a device that checks the online voltage of the battery. The voltage of each battery can be detected in real time, an alarm signal is given based on which battery voltage is above or below a setting, and the monitoring system can indicate which battery has failed. The battery check unit can typically detect 2V to 12V batteries and monitor 1 to 108 batteries.

5. Switch detection unit

The switching amount detection unit is a device used to record the switching amount online and alarm the output of the drying node. For example, a digital detection unit sends an alarm signal across the system about which circuit breaker has tripped or which fuse has blown, indicating which circuit breaker has failed or which fuse has tripped the monitoring system, and the data can also be viewed. Currently, the switch detection unit can detect 1 to 108 switches and multiple passive dry node alarm outputs.

6. Step-down unit

A buck unit is a buck regulator which is a combination of a buck unit for the bus voltage input and a buck unit for output to the control bus and sets the control bus voltage within a set range (110 V) or 220 V). If the bus voltage changes, the step-down unit is automatically adjusted to stabilize the output voltage. The drop unit is also evaluated based on the magnitude of the output current. There are currently two types of step-down devices: one is a step-down silicone chain, and the other is a stepless step-down chopper. The step-down silicon chain consists of 5 steps and 7 steps, and the voltage set points are both 3.5V, that is, if the coupled bus voltage increases or decreases by 3.5V, the step-down silicon chain automatically adjusts the stable control bus voltage. The stepless step-down chopper is a step-down module, which is smaller than the step-down silicon chain and has no voltage regulation point. Therefore, the output voltage is more stable than the step-down silicon chain, and there are functions such as overvoltage, overcurrent, and battery overcharge. However, buck silicone chains are still widely used because current continuously variable buck chopper technology is not very mature and often fails.

7. Power distribution unit

The power distribution unit is mainly used for DC screen, AC input, DC output, voltage display, current display and other functions, using devices such as power cords, cable clamps, AC circuit breakers, DC circuit breakers, contactors, lightning protection devices, shunts device, fuse, transfer switch, push button switch, indicator light, current, voltmeter, etc.