How to best dissipate heat for high-power inverters?
Most high-power inverters and their associated electronic components are integrated into electrical cabinets. Inverters not only improve system efficiency, but the efficiency of the inverter itself is also very high, with a loss of only 2% to 4%. However, due to the large amount of power conversion in high-power inverters, even if the efficiency loss is low, it will lead to the generation of several kilowatts to tens of kilowatts of waste heat, which must be dissipated.
In open air-cooled cabinets, it is simple to remove this heat. However, in harsh environments where filtered fan cooling or cooling via direct air flow is not possible, thermal management of the enclosure becomes an important part of the design process. Strategies are essential to efficiently, passively, and economically cool medium and high power sealed enclosure drives in harsh environments.
01 Flow or Sealed
Open airflow cabinets allow ambient air to flow through the cabinet, effectively cooling the high power modules directly. However, this efficient cooling can result in external contaminants entering the enclosure, which are typically minimized by using a fan filter system to filter the air flowing into the cabinet. Filters help reduce dust and debris, but they require regular maintenance to clean or replace the filters.
In these systems, the high power components (insulated gate bipolar transistors, integrated gate commutated thyristors, silicon controlled rectifiers) are typically connected to a fluid-cooled cold plate. The fluid then rejects the heat to the ambient air using a vapor compression system or through a liquid-to-air heat exchanger. In either case, the required ambient air heat exchanger can be located inside or outside the facility. The primary drawback to these systems is the challenges of introducing fluid into the cabinet and piping coolant in and out of the cabinet.
02 Loop Thermosyphons
Loop Thermosyphons (LTS) are gravity driven two-phase cooling devices. They work similarly to heat pipes, where the working fluid evaporates and condenses in a closed loop to transfer heat over a given distance. The main advantage of loop thermosyphons over heat pipes is the ability to use a conductive working fluid, allowing for efficient, long-distance transmission of high power. Loop thermosyphons have no moving parts and are more reliable than active liquid coolants, vapor compression or pumped two-phase cooling systems. Loop thermosyphons are ideal for transferring high power waste heat from power electronics in a cabinet to the environment outside the cabinet.
03 Sealed Enclosure Heat Exchangers
Loop thermosyphons are an excellent method for removing large amounts of heat directly from high heat generating components. However, the waste heat load of secondary components still needs to be cooled. These secondary components, including many low power devices dispersed throughout the cabinet, are difficult to cool by direct contact. For these low power, low heat flux components, direct air cooling is the most practical method. Low power components can be easily cooled by air-to-air heat exchangers while maintaining the integrity of the enclosure seal.
In the loop thermosyphon and sealed heat exchanger combination, high-power insulated gate bipolar transistors (IGBTs) or integrated gate-commutated thyristors (IGCTs) are mounted on the loop thermosyphon cold plate, and its 10 kW load plus heat load is dissipated to the external cabinet air through the loop thermosyphon (see Figure 2). All secondary electronic components are cooled by a sealed air-to-air heat exchanger, which can remove about 1 kW of waste heat.
The water supply pumps of many power plants are also quite powerful. For example, a 2*300MW thermal power plant has a water supply pump with a power of 5500KW. With such a large power, medium and high voltage types are used, such as 6KV.
Some ball mills also have relatively large power, such as the Ф5500×8500 ball mill, whose motor power is 4500Kw.
There are also some large rolling mills with relatively large motor power, especially hot rolling equipment. For example, the motor power of some finishing mills is 11,000 kilowatts.
General heat dissipation methods for inverters
Based on the current structure of inverters, heat dissipation can generally be divided into the following three types: natural heat dissipation, convection heat dissipation, liquid cooling and external environment heat dissipation.
(I) Natural heat dissipation For small-capacity inverters, natural heat dissipation is generally used. The use environment should be well ventilated and free of dust and floating objects. This type of inverter is mostly used for household air conditioners, CNC machine tools, etc., with very low power and a relatively good use environment.
(II) Convection cooling dissipate heat
Convection cooling is a commonly used cooling method, as shown in Figure 2. With the development of semiconductor devices, semiconductor device heat sinks have also developed rapidly, tending to standardization, serialization, and generalization; while new products are developing in the direction of low thermal resistance, multi-function, small size, light weight, and suitable for automated production and installation. Several major heat sink manufacturers in the world have thousands of product series, all of which have been tested and provide power usage and heat sink thermal resistance curves, which provide convenience for users to accurately select. At the same time, the development of heat dissipation fans is also quite fast, showing the characteristics of small size, long service life, low noise, low power consumption, large air volume, and high protection. For example, the commonly used low-power inverter heat dissipation fan is only 25mm×25mm×10mm; Japan SANYO long-life fan can reach 200000h, and the protection level can reach IPX5; there is also Singapore LEIPOLE large air volume axial flow fan, with an exhaust volume of up to 5700m3/h. These factors provide designers with a very broad choice space.
Convection cooling is widely used because the components (fans, radiators) used are easy to choose, the cost is not too high, and the capacity of the inverter can be from tens to hundreds of kVA, or even higher (using units in parallel).
(1) Cooling with built-in fan of inverter
Cooling with built-in fan is generally used for small-capacity general-purpose inverters. By correctly installing the inverter, the cooling capacity of the built-in fan of the inverter can be maximized. The built-in fan can take away the heat inside the inverter. The final heat dissipation is carried out through the iron plate of the inverter box. The cooling method using only the built-in fan of the inverter is suitable for control boxes with separate inverters and control boxes with relatively few control components. If there are several inverters or other electrical components with relatively large heat dissipation in the inverter control box, the heat dissipation effect is not very obvious.
(2) Cooling with external fan of inverter
By adding several fans with ventilation convection function in the control box where the inverter is installed, the heat dissipation effect of the inverter can be greatly improved and the temperature of the inverter working environment can be reduced. The capacity of the fan can be calculated by the heat dissipation of the inverter. Let's talk about the general selection method: Based on experience, we calculated that for every 1kW of heat generated by power consumption, the fan exhaust volume is 360m³/h, and the power consumption of the inverter is 4-5% of its capacity. Here we calculate at 5%, and we can get the relationship between the inverter-adapted fan and its capacity: For example: the inverter power is 90 kilowatts, then: the fan exhaust volume (m3/h) = inverter capacity × 5% × 360m³/h/kW = 1620m³/h
Then select the fan model of different manufacturers according to the fan exhaust volume to obtain the fan that meets our conditions. Generally speaking, fan cooling is the main means of inverter cooling at this stage, especially suitable for relatively large control cabinets, and when the electrical components in the control cabinet work and heat at the same time. It is suitable for highly integrated centralized control cabinets and control boxes. In addition, due to the continuous advancement of technology in recent years, heat dissipation fans are no longer as huge as they were in previous years, and small and powerful fans are everywhere. The cost performance is also much better than other cooling methods.
