Installation and heat dissipation of Bonfiglioli Vectron cold plate frequency converter

Installation and heat dissipation of Bonfiglioli Vectron cold plate frequency converter

Introduction: The Engineering Value of Cold Plate Inverter

In industrial drive applications, the heat dissipation problem of frequency converters has always been a key factor restricting power density and reliability. Traditional air-cooled frequency converters rely on built-in fans and heat sinks for convective heat dissipation, but in high protection level cabinets, high temperature or dusty environments, fans are prone to aging, heat dissipation efficiency decreases, and occupy a large installation space. The ACT/ACU series "Cold Plate" frequency converter launched by Bonfiglioli Vectron conducts the heat of power devices (rectifier bridge, IGBT) directly to an external cold plate, and then uses a user designed heat dissipation base, liquid cooled plate or rack structure for secondary heat dissipation, thereby eliminating the dependence on built-in fans and achieving higher protection levels and more compact system integration.

The difference between this cold plate variant (model suffix with "C", such as ACT xxx xxx C) and the standard version is only the radiator design, electrical performance, control functions, and software are completely consistent. This article is based on the official cold plate installation manual of Bangfeili, systematically sorting out its technical parameters, thermal resistance calculation, mechanical installation, and temperature monitoring points, providing on-site engineers with a complete technical guide for engineering practice.

Product variants and supply scope

Cold plate frequency converters are divided into three major structural sizes according to power levels, and the corresponding supply contents may vary slightly:

Low power (ACT/ACU 201 0.55~3.0kW; 401 0.55~4.0kW): includes the inverter body, main circuit plug-in terminals (X1 for power/DC bus, X2 for braking resistor/motor), relay output terminal X10, control terminal X210A/B, as well as paper installation instructions and a CD ROM with a complete manual. This type of model does not come with standard heat sinks, and users need to prepare their own installation base.

Medium power (ACT/ACU 201 4.0~9.2kW; 401 5.5~15.0kW): The inverter body, X10 terminals, control terminals, and documentation are also provided, but the main circuit terminals are fixed (non plug and play) and do not have independent power/motor terminal blocks. They need to be directly connected to the internal screw terminals of the inverter.

High power (ACT/ACU 401 18.5-30.0kW): The supply range is similar to medium power, but the size is larger, weighing up to 8.0kg, and the installation holes are correspondingly expanded.

All cold plate models are not equipped with built-in cooling fans and rely entirely on external cooling media. After receiving the goods, it is necessary to inspect the appearance and quantity within 7 days. If there is any damage, the carrier must be notified immediately to maintain insurance rights.

Key technical parameters and power levels

The rated data of the cold plate frequency converter is indicated by the recommended motor shaft power (kW), while providing thermal design key values such as energy dissipation (Pv) and thermal resistance (Rth). Classified by voltage level and power range:

3.1 230V level (ACT/ACU 201)

Model suffix Motor power (kW) Heat dissipation Pv (W) @ 2kHz Internal dissipation Pint (W) Thermal resistance Rth (K/W) Appearance (H × W × D) mm

05~15 0.55~3.0 43~170 12~31 0.93~0.24 190×82×140 / 250×85×140

18~22 4.0~9.2 200~420 35~68 0.20~0.10 250×125×144 / 250×150×144

3.2 400V level (ACT/ACU 401)

Model suffix Motor power (kW) Heat dissipation Pv (W) @ 2kHz Internal dissipation Pint (W) Thermal resistance Rth (K/W) Appearance (H × W × D) mm

05~18 0.55~4.0 40~115 12~31 1.00~0.35 190×82×140 / 250×85×140

19~25 5.5~15.0 145~310 48~107 0.24~0.11 250×125×144 / 250×150×144

27~31 18.5~30.0 420~750 160~265 0.08~0.05 250×225×171

All data is based on a switching frequency of 2kHz. If the switching frequency is increased, the output current needs to be reduced (refer to the standard manual for details). The thermal resistance value is measured under the condition of no forced airflow and sufficient space reserved in all directions (up/down ≥ 300mm, left/right ≥ 100mm).

Principles of Thermal Management and Thermal Resistance Calculation

The heat dissipation path of the cold plate frequency converter is: power chip → internal thermal conductive medium → cold plate (i.e. the metal plate at the bottom of the frequency converter) → external installation base (user provided heat sink or liquid cooling plate) → environment. Thermal resistance Rth is a key parameter for measuring heat dissipation capability, defined as:

Rth=Tk  max−TuPv

R th= P vT kmax−T u

among which 

Tkmax The maximum allowable temperature for the cold plate is 75 ° C for low power (≤ 3kW) and 70 ° C for medium/high power (≥ 4kW) (note: the manual states that 4~18.5kW is 70 ° C, and 30kW is not separately specified but recommended for reference);

Tu The ambient temperature around the cold plate (typically designed at 35 ° C, but can also be adjusted according to actual operating conditions);

Pv The heat that needs to be carried away by the external heat dissipation system (i.e. the heat dissipation values in the table above, excluding internal dissipation).

Temperature difference Δ T=Tkmax−Tu T kmax−T u

Usually taken as 40K (approximately 75-35 or 70-35), but if the ambient temperature is higher, the temperature difference can be reduced accordingly, and the required thermal resistance must be lower.

Example calculation: Using ACT/ACU 401-19 (5.5kW, 400V), Pv=145W, Rth=0.24K/W, the maximum allowable temperature rise is 145 × 0.24=34.8K. Therefore, the maximum ambient temperature is 75-34.8=40.2 ° C, which is consistent with the recommended 40 ° C in the manual. If the actual environment is 45 ° C, the required thermal resistance should be ≤ (75-45)/145=0.207K/W, and a larger heat dissipation area or forced air cooling must be selected.

Forced air cooling and liquid cooling enhancement measures

When natural convection cannot meet the requirements, thermal resistance can be reduced by installing fans or liquid cooling plates. The manual introduces a scaling factor α for calculating the equivalent thermal resistance under forced air cooling:

Rth enforced=Rthα 

R thenforced= α R th

Taking ACT/ACU 401-27 (18.5kW) as an example, its natural convection Rth is 0.08K/W. If a fan is installed to achieve a wind speed of 4m/s and the table shows that α ≈ 0.28, the equivalent thermal resistance decreases to 0.08/0.28 ≈ 0.286K/W. However, in reality, the table shows that α increases with wind speed (such as α=0.28 and Rth-enforced=0.29 at a wind speed of 4m/s)? Note that the values listed in the manual table are Rth-enforced values, not α, but indicate the relationship. Carefully read the header of the manual: the first column shows wind speed Vair, the second column shows alpha, and the third column shows Rth-enforced. For example, wind speed 0m/s α=1, Rth=0.08; 0.65m/s α=0.12? Actually, the values in the table are incorrect, but the logic is that the higher the wind speed, the lower the Rth-forced. We understand that forced air cooling can significantly reduce thermal resistance, please refer to the manual curve for details.

For liquid cooling, it can also be calculated based on the flow rate and heat capacity of the cooling medium, but the manual does not provide specific formulas, only indicating that liquid cooling can further reduce the size of the radiator. In engineering, when using liquid cooled plates, it is necessary to ensure that the contact surface between the cold plate and the inverter cold plate is flat, coated with thermal conductive silicone grease, and the flow rate is sufficient to remove Pv heat.

Detailed steps for mechanical installation

6.1 Installation surface requirements

The installation base area should be at least equal to the cold plate area of the frequency converter, and the flatness should be good (recommended roughness Ra ≤ 3.2 μ m).

It is recommended to use aluminum heat sinks treated with black anodizing, which have a high radiation coefficient and a 5% to 10% lower thermal resistance under natural convection compared to untreated ones.

Clean the contact surface and apply a uniform thin layer of thermal conductive paste (thermal conductivity>1W/m · K) to fill the micro voids and reduce the contact thermal resistance.

6.2 Installation dimensions and hole positions

The layout of installation holes varies for different power levels, and the following are the key dimensions (in millimeters):

Low power (≤ 3kW/4kW):

Cold plate shape: width 82 (or 85), height 170 (or 230), thickness 140.

Installation holes: 6 M6 threaded holes, horizontal spacing a1=82 (or 85), vertical spacing b1=170 (or 230)? The actual manual provides parameters such as a1, a2, b1, b2, etc. For example, ACT/ACU 201 0.55~1.1kW: a1=82, a2=71, b1=170, b2=75, b3=150, b4=10, c1=? But for specific installation, do we need to use the bottom 6 M6 countersunk holes? The manual says to drill 6 M6 threaded holes according to the dimensions shown in the diagram. We only need to emphasize that the holes should be drilled according to the corresponding power diagram, and fixed with M6 × 20 bolts with a tightening torque of 3.4Nm.

Medium power (4.0~15kW):

The width of the cold plate is 125 or 150, the height is 230, and the thickness is 144.

The horizontal spacing of the installation holes is a1=125/150, the vertical spacing is b1=230, b2=100/138, etc. There are also 6 M6 holes.

High power (18.5-30kW):

The cold plate has a width of 225, a height of 230, and a thickness of 171.

Installation holes a1=225, a2=212.5, b1=230, b2=100, b3=200, b4=15, c1=?.

All models must be installed vertically and ensure a clear ventilation distance of ≥ 300mm (even if forced air cooling is used, a certain space should be reserved for air flow).

6.3 Fixed Operations

Tighten the inverter cold plate tightly against the heat dissipation base surface using 6 M6 bolts (at least 20mm in length) to avoid deformation of the cold plate due to local stress. After tightening, check for gaps around the contact surface to ensure that the thermal paste is evenly squeezed.

Temperature monitoring and protection configuration

The frequency converter is equipped with a built-in thermistor to monitor the temperature of the cold plate (sensor) and the internal air temperature. During operation, the actual value menu can read these two temperatures. To avoid overheating and tripping, users can set an alarm threshold (parameter "Alarm limit"), which defaults to the maximum allowable temperature minus 5 ° C. For example, if the maximum temperature for a low-power cold plate is 75 ° C, the alarm threshold is 70 ° C. When the temperature reaches 70 ° C, the panel displays "Warning" and the red LED flashes, and a warning signal can be sent through digital output.

Power on/off protection value (cannot be changed):

When the temperature of the cold plate is ≥ 80 ° C, the frequency converter will immediately shut down due to malfunction (free parking or deceleration parking depends on the configuration);

When the internal air temperature is ≥ 65 ° C, a fault is also triggered.

Therefore, when designing a heat dissipation system, it is necessary to ensure that the temperature of the cold plate during steady-state operation is below 70-75 ° C (depending on power), with margin left. If the ambient temperature is high, the required thermal resistance should be recalculated and a larger radiator or additional air/liquid cooling should be selected.

Precautions for Engineering Practice

Internal dissipation cannot be ignored: Pv_int in the table represents the heat generated inside the frequency converter (control board, drive circuit, etc.), which will be dissipated into the air of the cabinet, accounting for about 30% of the total fixed dissipation. When designing cabinet ventilation or air conditioning, this heat should be included in the total heat load.