Motors are used to drive a wide variety of loads – fans used in air conditioning systems, pumps that provide fresh water, and motors used to drive manufacturing equipment in factories are just a few examples. Traditionally, these motors are directly connected to the power supply of the grid. Because the working frequency of the power grid is fixed, the motor runs at a constant speed without direct torque control. Nowadays, the motor drive adopts frequency conversion to control the speed and torque of the motor.

The first advantage of using a frequency converter is to improve efficiency at full speed, because the inverter can maximize torque with a given excitation current. The second advantage of frequency conversion is to further save energy. In the traditional driving mode, the motor is either turned off or fully turned on (imagine that you can drive a car when you only allow the accelerator pedal to be fully lowered or your foot to be completely disengaged). Allowing the motor to run at different speeds saves energy and allows smoother opening and closing.

Intelligent power module (IPM) is an enabling technology of variable speed drive, which includes inverter and internal driver in one module. They are the preferred modules for single-phase AC input applications. The transfer molding manufacturing method used for these modules has excellent robustness as well as power cycling and temperature cycling capabilities. These modules may contain power factor correction (PFC) stages, but they usually do not contain input rectifier stages. The off the shelf availability of single-phase AC bridge rectifier components means that this is not an issue. The main benefit of using IPMS is that the driver is integrated – additional pins are added to the driver.

For three-phase AC input applications, IPMS becomes very large due to leakage and gap requirements to determine the minimum spacing between conductive parts to stop arc or track. Since the IPMS provides additional pins for the driver, the minimum spacing requirement makes the IPM larger than the module without the driver. Leakage and gap spacing must be carefully calculated for each application. These factors include the maximum operating height of the driver, the effective voltage in the system, the isolation used in the system, the degree of contamination of the modules and printed circuit boards, and the comparison tracking index (CTI).

Figure 1 shows the schematic diagram of a three-phase AC input module without integrated door drive. We will review the required spacing based on the general calculation covering most three-phase AC input motor drives.

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Figure 1: schematic diagram of Inverter Brake (CIB) module of three-phase AC input converter

The distance between NTC terminals and any other terminals must be at least 5.5 mm. This distance includes the distance between the outer edges of the pins. However, if the pins are soldered or inserted into pads, the relevant distance is between the external distances of each pad. The wide tolerance of hole size and the width of ring gasket help to improve manufacturability, but reduce leakage and gap distance.

A gap distance of 5mm is required between the R, s, t, dbminus and dbplus pins and any other pins. U. The required distance between V and W depends more on the application, and the minimum value here is usually 2.5mm to 3mm.

Add in all these gap distances, via tolerances and ring (PAD) sizes, and the result is a fairly large module – at least about 70 mm. If the additional signal required for high side control is added to the IPM, the minimum size of the module will become larger, making it too large and expensive for low-power three-phase input applications.

For low-power industrial three-phase AC input applications, IPM module and gel filling module are widely used: IPM module has no rectifier, and gel filling module has no driver. The gel filling module has a pin matrix, while the IPMS is usually located in a dual in-line package. Gel filled modules have low thermal cycling capacity, but the new manufacturing method greatly improves their power cycling capacity. When gel is used to fill the module, the flexibility of PCB layout is less than IPMS installed with dip, because the pins from the pin matrix of gel filling module often hinder the wiring of PCB.

Due to the wide application of robotic welding equipment, the new design trend is to use welding pins in gel filling and IPM modules. Some types of crimped pins are susceptible to corrosive environments, but this problem has not been found in soldered pin applications..

Figure 2 shows the cross section of the new tmpim (transmission molded PIM) module of on semiconductor. The first part of the manufacturing process is similar to the gel filling module. The die and thermistor are welded to the DBC and then wired. In IPM module, DBC and some parts are welded on leadframe. This reduces tool flexibility and requires additional tools. In contrast, as long as the pins are not changed, the die layout and structure of tmpim in DBC are completely flexible.

The next stage is to weld the leadframe to the DBC. The last stage is the transfer molding process in which the module is encapsulated in epoxy resin. The lead bond wire is cut and then bent into shape in a process called trimming and molding.

The advantage of this method over the module soldered to the leadframe is that it is easy to change the configuration or chip in the module. Different pins require a new leadframe and trim molding tool. Since the cost of this tool can reach hundreds of thousands of dollars, this method is used for modules with standard pins, such as six components, frequency converter Inverter Brake (CIB) module (Figure 1) and six components with staggered PFC.

The gel filled module is more flexible to change the custom way, but does not have the same thermal cycling capability as the transfer molded module. For the same DBC welding and wire bond connection, the transfer molding module will have better power cycle capability than the gel filled module.

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Figure 2: cross section of the new tmpim (transfer molded PIM) module.

Figure 2 shows a clear advantage of tmpim over existing modules. This scale has been stretched for illustration. The total thickness of the module is 8mm. The gap between the top of the pin and the top of the radiator is 6mm, which is greater than the required 5.5mm gap. Gel filled modules also meet this requirement, but they are much thicker (12 mm compared to 8 mm for tmpim); The IPM module is thinner. Therefore, the mechanical designer needs to shape the radiator, which usually adds additional manufacturing costs.

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Table 1 shows the spacing between pad edges after considering 0.5mm pad ring width, 0.3mm drilling tolerance and pin size. When designing tmpim products, the spacing requirements are widely considered.

Table 1: Pad to pad spacing for TMPIM DIP-C2 CIB module

Table 1: pad spacing of tmpimdip-c2 CIB module

The IGBT used in tmpim is a robust field resistance II 1200 V IGBT, which has a short-circuit rating of more than 10 s under 150 ℃, 900 V bus voltage and 15V grid drive. Prior to release, these modules were extensively tested in motor drive testing, including bench testing. NCP 57000 isolation gate driver from on semiconductor is ideal for driving tmpim. Each tmpim uses six isolated drivers. NCP 57000 has desat function, which detects overload current and then performs soft shutdown of IGBT to prevent excessive voltage spike from closing too quickly under short circuit conditions.

Tmpim series can realize more than 1000 thermal cycles. A standard gel filled module without any heat sink typically only achieves 200 thermal cycles. The power cycle curve of the module shows a good power cycle capability, which depends on the change of junction temperature. For high-power modules in tmpim, high-performance alumina substrates are used. When the power cycle curve is read, the lower thermal resistance leads to a reduction in thermal change, resulting in a higher power cycle capacity.

The current tmpim series of semiconductors includes 1200 V CIB modules, high-performance substrates rated at 25A, 35A, 35A and 50A. The new design of the series will include 650V CIB module, 650V 6-Pack, 1200V 6-Pack and 650V module, staggered PFC and 6-pack.

In a word, the method adopted by tmpim series can expand the use of transfer molding module to a higher power level, and also provide a convenient, compact and reliable solution for the designer of industrial motor drive inverter.

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