Committed to heatsink research and development  

Provide design and development services

Quality is everything

Efficient cooling solution

How can high power frequency converter dissipate heat better?

首页    How can high power frequency converter dissipate heat better?

Most high power converters and their associated electronic components are integrated into the electrical cabinet, as shown in Figure 1.
The inverter not only improves the system efficiency, but also the efficiency of the inverter itself is very high, with a loss of only 2% to 4%.
However, due to the large power conversion in the high-power converter, even if the efficiency loss is low, it will lead to waste heat of several kilowatts to tens of kilowatts, which must be dissipated somehow.

In an open air cooler, it's easy to get rid of that heat.
However, in harsh environments where filtering fans cannot be used for cooling or cooling through direct air flow, heat management of the housing becomes an important part of the design process.
The research strategy is critical for efficient, passive and economical cooling of medium - and high-power converters with sealed enclosures in harsh environments

1. Circulation or sealing

The open air cabinet can allow the ambient air circulation cabinet to directly and effectively cool the high-power module.
This efficient cooling, however, can cause external pollutants to enter the enclosure, often using a fan filtration system to filter air into the cabinet to minimize these contaminants.
Filters help reduce dust and debris, but they require regular maintenance to clean or replace the filters.

The sealed enclosure does not allow outside air to enter the cabinet. Instead, air inside the cabinet is used to cool the electronics, and heat is exported to ambient air through a heat exchanger.
The sealed enclosure prevents dirt, dust, humidity, salt spray and other corrosive substances in the air from entering the cabinet and affecting the service life of the electronic components.

Both systems are suitable for low-power cabinets.
However, for many high power converter cabinets, the power consumption level is higher than the air cooling level can be achieved.
Low-power components are generally cooled directly by air flow, while higher-power components are cooled directly or indirectly by facility cooling water, steam compression systems, or pumping liquid systems.

In these systems, the high-power elements (insulated gate bipolar transistors, integrated gate commutator thyristors, silicon controlled rectifiers) are usually connected to a fluid cooled cold plate.
The fluid then releases heat into the ambient air using a steam compression system or through a liquid-gas heat exchanger.
In either case, the required ambient air heat exchangers may be located inside and outside the facility.
The main disadvantage of these systems is the challenge of introducing fluids into and out of the cabinet and coolant lines.

2. Thermal siphon in the loop

Loop thermosiphon (LTS) is a gravity driven two - phase cooling device.
They work in a similar way to heat pipes, in that the working fluid can transfer heat over a given distance as long as it evaporates and condenses in a closed cycle.
Compared with heat pipe, the main advantage of loop thermosiphon is that it can use conductive working fluid, high efficiency and long distance transmission power.
Loop thermosiphons have no moving parts and are more reliable than active liquid coolant, steam compression, or pumped two-phase cooling systems.
The loop thermosiphon is ideal for transferring high-power waste heat from the power electronics in the cabinet to the external environment of the cabinet.

At the cabinet level, the advantages of the loop thermosiphon cooling system are significant.
Cabinets, electronics, and cooling systems can be installed in sealed, separate enclosures on the factory floor.
Each cabinet is self-contained, can be delivered independently, and is easy to install at the end customer.
The simplest form of implementation is the air-cooled loop thermosiphon condenser located at the top of the cabinet.
This way, the cabinet remains independent and only electrical connections are required for final installation.

The loop thermosiphon condenser can also be connected to a facility or cooling water system.
Waste heat can be further dissipated from the cabinet and multiple cabinets to work on the same loop.
With the loop thermosiphon and the cold water condenser, the pipe and water connections are on the outside of the cabinet so that the coolant is separated from the electronics.

3. Sealed enclosure heat exchanger

Loop thermosiphons are an excellent way to remove large amounts of heat directly from high heating components.
But the waste heat load of secondary components still needs to be cooled.
These auxiliary components, including many low-power devices scattered around the cabinet, are difficult to achieve by direct contact cooling.
For these components with low power consumption and low heat flow, direct air cooling is the most practical method.
The low-power components can be easily cooled by an air-air heat exchanger while maintaining the integrity of the enclosure seal.

In the combination of a loop thersiphon and a sealed heat exchanger, a high-power insulated gate bipolar transistor (IGBT) or an integrated gate directional thyristor (IGCT) is installed on the loop thersiphon cold plate, and its 10 kw load plus the heat load is dissipated through the loop thersiphon into the external cabinet air (see Figure 2).
All secondary electronic components are cooled by sealed gas-gas heat exchangers, which produce about 1 kilowatt of waste heat.


Loop thersiphon and seal the air-air heat exchanger to maintain the original NEMA cabinet class.
The combination of the two can maintain the sealing performance of the high power cabinet, which is not affected by the external airflow, and there will be no coolant flow in the cabinet.

Loop thermosiphon and sealed enclosure cooler provide many advantages for power electronic cooling applications.
Loop thermosiphons use conductive working fluids suitable for medium and high voltage applications to passively cool high power electronic components.
A sealed enclosure cooler removes the heat generated by the low-power, distributed components in the power electronics cabinet, while preventing pollutants in the external air from interacting with these components.
The combination of two cooling solutions provides reliable cooling of the high-power motor controller in a sealed enclosure required for harsh working conditions.

Which type of equipment will use the higher power converter?

The size is relative, the motor power is large, frequency converter power should be large.
If I have to say big, I believe that the power of frequency converter used in places like high-speed railway is relatively large, after all, the load requirement is placed there. In contrast, the power of frequency converter used in general factories is not so large.

The power of each kind of high-speed train also varies, but generally there are thousands of kilowatts or more. The big ones, such as CRH380A's 16 group, have a power of 19600 kilowatts, which is about 20,000 kilowatts. This is almost the limit of the power produced by domestic electric machinery factories (although domestic electric motors are rarely used in these occasions).
Generally, such high-voltage inverter is used in such places. The former Robin Hood was acquired by Siemens and many of them are used in these places.

General heat dissipation method of frequency converter

Based on the current structure analysis of frequency converter, heat dissipation can be generally divided into the following three types: natural heat dissipation, convection heat dissipation, liquid cooling heat dissipation and external environment heat dissipation.

(1) Natural heat dissipation

Natural heat dissipation mode is generally selected for frequency converters with small capacity. The operating environment should be well ventilated without dust and floating objects easily attached.
The objects of this kind of frequency converter are mostly household air conditioners, CNC machine tools, etc., with small power and good use environment.

Another way to use natural heat dissipation frequency converter capacity is not necessarily small, that is explosion-proof frequency converter.
For this kind of frequency converter small capacity can choose the general type of heat sink can, requires the heat dissipation area in the allowed range as much as possible, heat dissipation fin spacing smaller, as far as possible to increase the area of heat radiation.
For large capacity explosion-proof frequency converter, it is recommended to use heat pipe radiator if using natural heat dissipation method.
Heat pipe radiator is a new radiator in recent years, it is a combination of heat pipe technology and heat sink technology of a product, its heat dissipation efficiency is very high, the capacity of explosion-proof inverter can be relatively large, up to several hundred kVA.
This kind of radiator is opposite common radiator, the place differs is volume is opposite big, cost is tall.
Compared with water cooling, this method of heat dissipation has advantages: water cooling requires water cooling devices, water cooling radiators and essential water circulation system, etc., and its cost is higher than that of heat pipe radiators.
Industry reflects that heat pipe radiator performance is good, worthy of promotion.

Another way of natural heat dissipation is "through the wall" natural heat dissipation, which reduces the heat at most by 80%. Its characteristic is that the main body of the frequency converter is completely isolated from the heat dissipation fins through the electric control box, which greatly improves the heat dissipation effect of the frequency converter components.
The biggest advantage of this way of heat dissipation is that the radiator can be cleaned regularly and the protection level of the electric control box can be ensured to be higher.
As a common cotton spinning enterprise due to too much cotton batt, often easy to block the ventilation duct of the frequency converter, resulting in the frequency converter overheating fault, with the natural heat dissipation through the wall can be very good to solve this problem.

(2) convection heat dissipation

Convective heat dissipation is a common way of heat dissipation, as shown in Figure 2.
With the development of semiconductor devices, the radiators of semiconductor devices have also been developed rapidly and tend to be standardized, serialized and generalized.
And the new products to low thermal resistance, multi-function, small volume, light weight, suitable for automatic production and installation and other directions.
Several major radiator manufacturers in the world, the products up to thousands of series, and all have been tested, provide the use of power and heat resistance of the radiator curve, for the accurate selection of users to provide convenience.
Meanwhile, the development of cooling fan is also quite fast, showing the characteristics of small volume, long order, low noise, low power consumption, large air volume, high protection.
For example, the commonly used low-power inverter cooling fan is only 25mm×25mm×10mm;
Japan SANYO long life fan up to 200000h, protection level up to IPX5;
Moreover, there is a German EBM high-volume axial flow fan, with exhaust air up to 5700m3/h.
These factors provide designers with a wide range of choices.

The convective heat dissipation is widely adopted because the devices (fans and radiators) used are easy to choose and the cost is not too high. The capacity of inverter can be from dozens to hundreds of kVA or even higher (unit parallel connection mode is adopted).

(1) The inverter is equipped with a fan for heat dissipation

Internal fan heat dissipation is generally used for general purpose inverter with small capacity.
By properly installing the inverter, the heat dissipation capacity of the inverter's built-in fan can be maximized.
The built-in fan can take away the heat inside the converter.
The final heat dissipation is carried out through the iron plate of the box where the frequency converter is located.
The heat dissipation method that only the fan is installed in the frequency converter is applicable to the control box with a separate frequency converter and the control box with fewer control elements.
If the frequency converter control box, there are a number of frequency converter, or other large heat dissipation electrical components, then the effect of heat dissipation is not very obvious.

(2) External fan installed in the frequency converter for heat dissipation

By adding several fans with ventilation convection function in the control box of the inverter installed, the heat dissipation effect of the inverter can be greatly improved and the working environment temperature of the inverter can be reduced.
The ability to use the fan can be calculated by the heat dissipation of the frequency converter.
Here's a general selection method:

According to our experience, the heat generated by each 1kW power output requires the fan's exhaust air volume to be 360m /h, while the power consumption of the frequency converter is 4-5% of its capacity. Here, we calculate by 5%, and the relationship between the frequency converter's adaptive fan and its capacity can be obtained:

For example, the power of the frequency converter is 90 kW, then:

The exhaust air volume of the fan (m3/h)= converter capacity ×5%×360m /h/kW=1620m /h

Then through the exhaust volume of the fan to choose different manufacturers fan model to meet our conditions.
Generally speaking, fan heat dissipation is the main means of inverter heat dissipation at this stage, especially suitable for relatively large control cabinet, and the control cabinet has the electrical components work at the same time, at the same time under the condition of heating.
Suitable for highly integrated centralized control cabinet and control box.
And in recent years as a result of the continuous progress of science and technology, cooling fan has not as a few years before the giant, small and powerful fan everywhere.
Cost performance is also much better than other ways of cooling.

(3) Liquid cooling for heat dissipation

Water cooling is a common way of industrial liquid cooling, as shown in FIG. 3.
For the inverter this kind of equipment to choose the heat is very few, because of its high cost, in the small capacity inverter in big volume, again because of the general inverter capacity in a few kVA to nearly hundred kVA capacity is not very big, it is hard to make the ratio of the level of user acceptance, only on special occasions, such as explosion-proof) and particularly large capacity inverter only in this way.

Water-cooled frequency converter has a history of nearly ten years in Europe and is widely used in high-power and space-limited occasions such as steamships and locomotives.
Compared with the traditional air-cooled frequency converter, water-cooled frequency converter can solve the heat dissipation problem more effectively, so that the volume of high-power frequency converter is greatly reduced and the performance is more stable.
The reduction of volume means that the equipment installation space is saved, thus effectively solving the volume requirement of frequency converter for many special occasions.
For example, the 400kW water-cooled frequency converter of VACON, a Finnish company, is only one-fifth the size of the same grade of air-cooled frequency converter.

The data show that the heat dissipated can be increased by 10~15% under natural cooling and 20~30% under forced air cooling after electrophoretic painting or anodized blackening, and the surface pressure resistance after electrophoretic painting can be up to 500~800V.
So in the choice of heat sink and formulate processing technology, the heat sink for the above process processing will greatly improve its heat dissipation capacity, but also can enhance insulation, reduce due to improper installation caused by the creeping distance is too small, electrical clearance is not enough to bring adverse effects.

The heat dissipation effect is closely related to the installation process. During installation, the contact area between the power module and the radiator should be increased as much as possible to reduce the heat resistance and improve the heat transfer effect.
A thin layer of heat-conducting silicone grease between the power device and the radiator can reduce the thermal resistance by 25~30%.
If insulation or pad is needed between the power device and the radiator for easy installation, it is recommended to use low thermal resistance materials: thin mica, polyester film or copper block, aluminum block.
The position of components on the radiator should be arranged reasonably. The components should be located in the center of the radiator base surface during the installation of a single component, and the components should be evenly distributed during the installation of multiple components.
The torque should be consistent when fastening the device.
After the installation of the device and radiator should not be machined again, otherwise it will produce stress, increase thermal resistance.
Single-sided finned radiator, suitable for natural air cooling outside the equipment, which is conducive to the ventilation of power components and can reduce the temperature inside the machine.
In natural air cooling, the cross section of the radiator should be parallel to the direction of the horizontal plane;
When forced air cooling, the flow direction of airflow should be parallel to the fin direction of the radiator

(4) Heat dissipation in the external environment

With the progress of science and technology, air conditioning is gradually applied to more and more control cabinets, control box production, and become one of the important means of heat dissipation.
But for the inverter this kind of equipment to choose the heat of the very few, because of its high cost, relatively large volume, again because of the general inverter capacity in a few kVA to dozens of kVA, capacity is not particularly big, it is hard to make the ratio of the level of user acceptance, only on special occasions, such as special strict with work environment) and special big capacity inverter only in this way.
And in air conditioning, some still involve the discharge of waste water, so in the process of complete set of dish cabinet also want to consider more comprehensive, increased the design cost.
In addition, there are other reasons to consider the heat dissipation effect of the converter, such as high altitude (& GT;
1000m), due to the reduction of air density, the heat dissipation capacity should be appropriately increased;
In addition, switching frequency, the heating of frequency converter is mainly from IGBT (insulated gate bipolar transistor), and the heating of IGBT is concentrated at the moment of on and off.
Therefore, when the switching frequency is high, the calorific value of the frequency converter also increases.

No matter what kind of heat dissipation, should be based on the capacity of the frequency converter, determine its power consumption, choose the appropriate fan, and the appropriate radiator, to achieve excellent cost performance, at the same time should also be the frequency converter used by the environmental factors fully considered.
In view of the harsh environment (high temperature, high humidity, coal mine, oil field, offshore platform), corresponding measures must be taken to ensure the normal and reliable operation of the frequency converter.
From the inverter itself, should be as far as possible to avoid the impact of adverse factors, such as dust, sandstorm impact can be sealed processing, only the radiator duct and the outside air contact, to avoid the internal impact of the inverter;
For salt mist, moisture and other components of the frequency converter can be insulated spraying treatment;
Frequency converter used in field work should be protected against rain, sun, fog and dust.
Of equipment such as high temperature and high humidity environment can increase air conditioning cooling dehumidification, a good environment to frequency converter, to ensure reliable operation frequency converter, the facts show that handle the inverter heat dissipation not only requires the designer from the inverter itself, also requires users to correctly use in strict accordance with the instructions for installation, have adequate ventilation space, suitable for the use of the environment, and try to do regular maintenance, coal dust and industry, in particular, to use environmental dedusting, regularly for inverter air duct dust, so that the frequency converter, the cooling system function of the temperature rise within allowable values of frequency converter,
Frequency converter can run reliably and bring greater economic and social benefits to enterprises.


2020年11月8日 10:25