1 Introduction
In existing technologies, the switching cabinet, control cabinet, transformer cabinet, and variable frequency power unit cabinet of a frequency converter are all independent cabinets, arranged sequentially. The switching cabinet is connected to the control cabinet and transformer cabinet via cables and control lines, and the variable frequency power unit cabinet is connected to the control cabinet and transformer cabinet via control lines and cables. Due to the existing structural layout, the interconnections are long, complex, and inconvenient for assembly and maintenance. This sequential layout results in a large overall size, large footprint, high cost, and low power density of the frequency converter.
2 Structural Scheme
2.1 Overall Structure
The overall structural diagram is shown in Figure 1.
The overall structural layout diagram is shown in Figure 2.
Figure 3 shows the axonometric view of the back of the inverter cabinet.
Figure 4 shows a schematic diagram of the airflow direction of a series ventilation and cooling system.
2.2 Working Principle
Figures 1, 2, and 3 are schematic diagrams of an embodiment of the integrated medium- and high-voltage frequency converter of the present invention, including a control unit 1, a frequency conversion power unit cavity 2, a switching unit 3, and a transformer unit cavity 4. The control unit 1 and the frequency conversion power unit cavity 2 are arranged on the left and right sides of the front of the frequency converter cabinet 5. The switching unit 3 and the transformer unit cavity 4 are located at the rear of the frequency converter cabinet 5, forming a square layout with the control unit 1 and the frequency conversion power unit cavity 2 in a front-to-back integrated structure.
Switching unit 3 is adjacent to transformer unit cavity 4 and connected by a cable. Variable frequency power unit 9 is adjacent to transformer 6 and connected by a plug-in connector and a short cable. The wiring between units is simple and convenient, with shortened lengths, significantly reducing costs. Control unit 1 is connected to variable frequency power unit 9 via optical fiber to transmit control signals, providing strong anti-interference capabilities.
The variable frequency power unit cavity 2 adopts a drawer-type structure, including multiple power units 9, which are arranged in three columns corresponding to the three phases. By configuring different numbers of power units 9 for each phase, variable frequency drives with different capacities and voltage levels can be produced.
Figure 4 shows a ventilation and cooling system between the frequency converter power unit cavity 2 and the transformer unit cavity 4, including a duct 7 and a fan 8. The duct 7 includes the frequency converter power unit cavity 2 and the transformer unit cavity 4. A partition 11 is provided between the frequency converter power unit cavity 2 and the transformer unit cavity 4. The transformer unit cavity 4 is also provided with a back plate 12. The fan 8 is located at the lower part of the transformer unit cavity 4. The inlet of the fan 8 is connected to the frequency converter power unit cavity 2, so that a negative pressure is formed in the frequency converter power unit cavity 2. The outlet of the fan 8 is located below the transformer unit cavity 4, so that a positive pressure is formed in the transformer unit cavity 4. The air inlet of the duct 7 is located at the front of the frequency converter power unit cavity 2. The air passes through the heat sink of each power unit 9 and enters the transformer unit cavity 4, blowing towards the transformer 6. The air outlet of the duct 7 is located at the top of the transformer unit cavity 4, so as to carry away the heat of the frequency converter power unit cavity 2 and the transformer unit cavity 4. To prevent rain from entering through the air outlet of the duct 7, a rain canopy 10 is provided on the top of the frequency converter cabinet 5.
3 Structural Advantages
Compared with existing technologies, the advantages of this structure are:
(1) The control unit, frequency conversion power unit, switching unit and transformer unit adopt an integrated structure, arranged in front and back rows, with a compact structure and a volume of only 1/3 of the split layout. The wiring between cabinet units is simple and convenient, and the cost is significantly reduced.
(2) The frequency converter power unit is installed vertically in a drawer structure, with each column corresponding to one phase, which reduces the floor space occupied;
(3) The power unit is installed using a quick-plug connection method, which facilitates the production, storage, installation, expansion, maintenance and transportation of the power unit. It is applicable to the production of frequency converters with different capacities and voltage levels and has strong versatility.
(4) The transformer unit and the frequency conversion power unit adopt series ventilation, which simplifies the cooling system.
4. Conclusion
Currently, high-voltage variable frequency speed control systems are used for the control and energy saving of large high-voltage motors. They are applied in various industries such as thermal power, steel, mining, coal, cement and building materials, and petrochemicals, and are considered the best choice for energy saving of large motors, offering advantages such as reduced energy consumption, increased efficiency, reduced impact on the power grid, and improved production processes. The integrated structure of medium-high voltage and medium-power frequency converters represents a significant innovation in frequency converter structure. This technology has been patented. Practical application has demonstrated its effectiveness and it has significant application and promotion value.
