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DENSO Develops High Output Power Control Unit and Battery Cooling System for Hybrids; Applied in the LS 600h

The new structure for DENSO’s PCU handles the greater cooling requirements of the high-output unit.

DENSO Corporation has developed a new high-output power control unit (PCU) and battery cooling system for hybrid vehicles. The products are installed on the Lexus LS 600h and the Lexus LS 600hL (earlier post).

The high-output PCU consists of a boost converter that raises the main battery voltage (288V) up to the maximum system voltage (650V), and two inverters that convert direct current (DC) into alternating current (AC) to drive the main traction motors.

Denso’s new PCU can produce higher output power by approximately 60% per unit volume, compared to the company’s conventional technology, thus improving the hybrid system performance. When the PCU is designed to produce the same output as the conventional technology, it can be reduced approximately 30% in size and approximately 20% in volume.

For this PCU, DENSO developed a new structure to handle the increased cooling requirements. To deliver a higher PCU output, the power devices must handle more power, resulting in more heat generation by the devices. Using a conventional cooling structure where power devices are mounted horizontally on a cooling unit through a heat sink so that only the side facing the cooling unit is cooled made it difficult to adequately cool the higher power devices.

In DENSO’s new cooling structure, the power devices are sandwiched between two heat sinks and inserted in layers between stacked cooling tubes. This structure allows both sides of the power devices to be cooled, which substantially enhances the cooling performance. The new cooling structure also is more compact than the conventional structure.

Since both sides of the power devices are soldered to the heat sinks, DENSO reduced the thickness of each power device to ease stress on joint portions, ensuring high reliability. The new PCU design can easily be used in hybrid systems with different output levels by changing the number of stacked power devices and cooling tubes.

Battery cooling system. In some conventional battery cooling systems, the battery blower draws only cabin air to cool the hybrid vehicle’s main battery. DENSO’s newly developed battery cooling system can use cooled air from the cooling unit of the rear air conditioning system as well as cabin air to cool the main battery.

Accordingly, the new battery cooling system provides comparable cooling performance with approximately half the amount of air required by previous models. This reduces noise from blowing air by approximately 30%, contributing to the quieter vehicle cabins of the Lexus LS600h and the Lexus LS600hL.

In addition to the high output PCU and battery cooling system, other DENSO hybrid vehicle products including the DC-DC converter, the battery-monitoring unit, the system main relays, and the current sensor are installed on the Lexus LS600h and the Lexus LS600hL.


Charles S

I may as well use this topic to relay some observations that I've seen in EVs and battery technologies.

When I test drove the Phoenix Motorcar SUT, the vehicle was not completely silent. There was some kind of whiny noise that got me worried, that there is something else other than the electric motor that's driving the vehicle. The rep says it was the cooling fan (of some kind of a coolant pump/system?) and then I realize that future EVs will probably more complex than just software, batteries, and a motor.

Every time I go to the dealership, I always hate it when they push all sorts of work on my car. I long for the day when we don't have to worry about scams and just deal with some basic components; they either work or they don't. I realize the addition of a coolant pump isn't a big deal, but my fantasy of a simple EV (like I see in the DIY projects) is probably an over-simplification of what the future, advanced vehicles will be.

On a side note, since people have been complaining that EVs (or EV mode in Prius) are too quiet, maybe designers should work on housing that will "tune" the cooling fans to some desirable notes and market it as sporty upgrades. 8D


Charles: Your now near the top of my jealousy hit list for the chance to drive the Phoenix. Did you not hear any noise from the motors themselves. Me e-cycle makes a sound sort of like a hair dryer. I don't have a battery cooling system (not big enough to need one)


With very powerful motors, you will probably have to liquid cool them. This is one of the features of hub motors, you distribute the power.

One large drive motor will give off a lot of heat and if it is permanent magnet, it needs to be kept below a safe maximum temperature so that the magnets do not lose their magnetism.



EV will still be far simplier then ICEV(Internal Combustion Engine...). Cooling fans and a radiator will be needed anyways if the EV is going to have AC.

hampden wireless

SJC, the motors used in electric cars dont need much in the way of cooling. The electronics and batteries on the other hand have had heat problems and need fans or liquid cooling. New technologies will reduce or eliminate this.


I thought that the large drive motor in the Prius was liquid cooled. I have not looked closely, but I think that the 70kw motor in the Escape hybrid is as well.


NiMH will need cooling as it has relatively high internal resistance and so a fair amount of in/out current is wasted in heating up the battery. Newer LiIon types have very much lower charge/discharge losses and could be put together with much less cooling in mind.

Bud Johns

SJC, the drive motor in the Prius (aka mg2) is not cooled, but it and mg1 and the power split device are all attached to the ICE and everything is aluminum, so plenty of heat transfer.


Nice discussion. All the components need cooling - some more so than others. Prius and everyone cool the electronics with water-glycol. Most motors in EVs or HEVs are cooled also with water glycol or with circulating oil inside the housings.

This dual sided cooling concept has been around for a long time, but it is great to see Denso getting it to a practical implementation. Power density improvements are key to getting BEVs and HEVs into widespread, economical, profitable production.


If you could make the batteries not have as high an internal resistance, they would not generate as much heat under heavy loads and would be more efficient.

I like the idea of getting to the root causes and not treating the symptoms. More complexity is more to go wrong and break down. I agree that simpler is better, by being more reliable and lower cost.

Charles S

"Did you not hear any noise from the motors themselves?"

Well, in the cabin, during acceleration, I think there was a slight whiny noise, but road noise was probably louder than the engine noise. From the outside, as the vehicle was coming to park, it was the fan noise that was most noticeable. As the vehicle was speeding away, I think it's really by the tire noise that you can tell the vehicle is accelerating. Otherwise, as I recall, the engine itself is fairly quiet.

Jack Rosebro

SJC and Bud Johns: Both motors in the Prius transaxle are cooled by inverter coolant as well as transaxle fluid via dedicated passages. The powersplit device itself does not produce significant heat, and requires lubrication, but nothing additional in the way of cooling.

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