Heat dissipation strategy for frequency converters – Schneider

Drives power and operate commercial and industrial motors, and thermal protection is necessary in accordance with their planning and operating environment. The main advantages of the frequency converters are flexible handling, smooth start-up and shutdown functions, and significant energy savings due to centrifugal fans and pumps operating under variable loads.

Heat dissipation strategy for frequency converters – Schneider

Heat dissipation strategy for frequency converters – Schneider

Most high-power drives and their associated electronics are integrated into the electronic chassis. The inverter not only improves the power of the system, but also the power of the inverter itself is very high, with a loss of only 2% to 4%. However, due to the large amount of electrical energy converted in a high-power drive, even low power losses can lead to the occurrence of waste heat in kilowatts to tens of kilowatts, and it is necessary to find ways to dissipate this heat.

In an open, air-cooled cabinet, it's simple to get this heat out. However, in harsh environments, where pre-filtered fan cooling or direct air flow is not possible, the heat management of the enclosure becomes an important part of the planning process. Strategies for researching drives are essential for efficient, forced and cost-effective cooling of drives in medium and high power hermetically sealed enclosures in harsh environments.

Flow or sealing

The open airflow cabinet allows ambient air to circulate through the cabinet and directly and efficiently cool the high-power modules. This efficient cooling can cause external contaminants to enter the enclosure, and a fan filtration system is often used to filter the air flowing into the cabinet and then minimize these contaminants. Filters help reduce dust and debris, but they need regular protection to clean or replace the filter.

The sealed enclosure does not allow outside air to enter the cabinet, but instead uses the air inside the cabinet to cool the electronics and export the heat through a heat exchanger into the ambient air. The sealed enclosure prevents dirt, dust, humidity, salt spray, and other corrosive airborne substances from entering the cabinet and affecting the service life of electronic components.

Both systems are suitable for low-power cabinets. However, for many high-power drive cabinets, power consumption levels are higher than what can be achieved with air cooling. Low-power components are typically cooled directly by the air stream, while higher-power components are cooled directly or directly by equipment cooling water, vapor compression systems, or pumped liquid systems.

In these systems, high-power components (insulated gate bipolar transistors, integrated gate commutated thyristors, silicon-operated rectifiers) are typically connected to a fluid-cooled cold plate. The fluid then dissipates heat into the ambient air using a vapor compression system or through a liquid-gas heat exchanger. In either case, the required ambient air heat exchanger can be housed in the equipment meter. The main drawback of these systems is the challenges posed by introducing fluid into the cabinet and coolant lines in and out of the cabinet.

Loop thermosiphon

Loop thermosiphons (LTS) are gravity-driven, two-phase cooling devices. They operate in a similar way to heat pipes, where the working fluid transfers heat over a given distance as long as it evaporates and condenses in a closed cycle. Compared with heat pipes, the main advantage of loop thermosiphons is that they can use conductive working fluids to transmit high power efficiently and over long distances. Compared to active liquid coolant, vapor compression, or pumped two-phase cooling systems, loop thermosiphons have no moving parts and are more reliable. Loop thermosiphons are ideal for transferring high-power waste heat from the power electronics in the cabinet to the outside of the cabinet.

At the cabinet level, the advantages of a loop thermosiphon cooling system are obvious. Cabinets, electronics, and cooling systems can be installed in sealed, free-standing enclosures on the factory floor. Each cabinet is self-contained, can be delivered independently, and is easy to install at the customer's disposal. The easiest way to do this is with an air-cooled loop thermosiphon condenser located at the top of the cabinet. In this way, the cabinet is self-contained, and only electrical connections are required for final installation.

Loop thermosiphon condensers can also be connected to equipment or cooling water systems. Waste heat can be further dissipated from the cabinet and multiple cabinets, which can then be operated on the same loop. With loop thermosiphons and cold water condensers, the connection between the pipes and water is outside the cabinet, which separates the coolant from the electronics.

Hermetically sealed enclosure heat exchanger

Loop thermosiphons are an excellent way to remove large amounts of heat directly from high-heat components. However, the waste heat load of the secondary components still needs to be cooled. These ancillary components, including many low-power devices scattered throughout the cabinet, make it easy to cool down with direct contact. For these low-power, low-heat flow components, direct air cooling is the most practical option. Low-power components can be easily cooled by an air-to-air heat exchanger, working together to maintain the integrity of the enclosure seal.

In a loop thermosiphon and sealed heat exchanger combination, a high-power insulated gate bipolar transistor (IGBT) or an integrated gate commutated thyristor (IGCT) is mounted on a loop thermosiphon cold plate, and its 10 kW load plus heat load is dissipated into the air of the external cabinet through the loop thermosiphon. All secondary electronic components are cooled by a sealed air-to-air heat exchanger, which can export about 1 kilowatt of waste heat.

Loop thermosiphons and sealed air-to-air heat exchangers adhere to the original NEMA cabinet rating. The combination of the two allows the high-power cabinet to remain sealed and unaffected by external airflow and with no coolant flowing through the cabinet.

Loop thermosiphons and sealed housing coolers offer many advantages for power electronics cooling applications. Loop thermosiphons use conductive working fluids that are ideal for medium and high voltage applications to cool the heat of high-power electronic components in a forced manner. Hermetically sealed enclosure coolers remove heat from low-power, distributed components in power electronics cabinets, preventing contaminants from the outside air from interacting with these components. The combination of the two cooling solutions reliably cools high-power motor manipulators in the sealed enclosures required for harsh operating environments.

Heat dissipation strategy for frequency converters – Schneider

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