In hybrid and electric vehicles, there are multiple opportunities for the application of auxiliary three-phase motor drives. These systems are rated in the 5-8kW range and are used on systems like: air conditioning drives, electric superchargers and electric turbochargers. Often these systems are realized using discrete device designs, but integrated power module designs are rapidly becoming more popular.
The ON Semiconductor line of Automotive Smart Power Module (ASPM), three-phase modules, are a perfect fit. These modules are a compact and efficient choice for the construction of a threephase auxiliary motor drive system (Figure 1).
These modules have a six device IGBT power-bridge along with soft recovery anti-parallel diodes, optimized for motor control applications (Figure 2). Three high-side gate drivers, single low-side gate driver and is constructed on an isolated ceramic substrate. The ASPM modules are constructed using a Direct Bond Copper (DBC) substrate process. This construction sandwiches a ceramic sheet between two thin copper layers. The top copper is patterned to create the circuit interconnections, while the bottom copper is used to conduct the heat away to the heatsink. Different types of ceramic substrate materials are available for various levels of thermal performance. Both Alumina (Al2O3) and Aluminum Nitride (AIN) substrates are available. The circuit components are soldered on to the top DBC layer and the entire package is epoxy encapsulated. The final product is housed into a rugged, hermetically sealed, thermally efficient package. These modules are automotive qualified to both AQG324 and AEC-Q10x specifications.
ASPM modules are available in both 650V (ASPM27) and 1200V (ASPM32) voltages and in multiple current levels. The current available product offerings are shown in Table 1. Each of these module offerings can provide the heart of a high-voltage motor drive system. With the addition of current sense resistors and high quality current sense amplifiers (CSA), for example the NCV21x series, proper over-current protection can be obtained. CSAs can provide the system with the information needed to implement sensor-less motor speed control algorithms. A microcontroller would be added to provide the control needed to produce the switching signals used to drive each off the six module inputs.
The value proposal for a module design versus a discrete design varies by application, but the improved performance of the ASPM design solution cannot be denied. It provides superior thermal performance, which can often be impossible to provide using a PCB to transfer the heat from discrete devices to a heatsink. It also offers a vast improvement in EMI performance, due primarily to the close proximity of the high current components, unachievable in most discrete designs. Motor drive systems using the ASPM modules can be used to produce compact and highly efficient designs.
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