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Application Specific Intelligent Power Modules -A Novel Approach to System Integration in Low Power Drives

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  Application Specific Intelligent Power Modules - A Novel Approach to System Integration in Low Power Drives Eric R. Motto  - Powerex Inc., Youngwood, Pennsylvania, USA A BSTRACT  Abstract - This paper reviews the system requirements and key technologies driving the development of highly integrated Application Specific Intelligent Power Modules (ASIPMs). New ASIPMs with power circuit topologies, control functions and packaging optimized to meet the performance, cost and size requirements of specific small motor control applications will be presented. I. I NTRODUCTION  When used with an inverter, three phase AC motors are smaller, more efficient and more reliable than the universal AC and brush type DC motors that are commonly used in light industrial and consumer applications. In order to realize these advantages, the cost of the inverter must be offset by energy savings, improved performance, and increased reliability. The widespread use of inverters in heavy industrial and precision motion control applications is evidence that these advantages are being realized. On the other hand, the use of inverters with small AC motors (100W - 2.2kW) is often limited by the cost and complexity of the inverter. In addition, limited space often prevents the use of general purpose inverters with fixed shape, size, and cooling requirements. For these applications, it is becoming increasingly desirable to simplify and miniaturize the power section so that the physical size, form factor, and cost requirements can more easily be met. This paper will examine the system requirements of some typical small motor drive applications and present five examples of  Application Specific Intelligent Power Modules (ASIPMs) targeted to address these requirements. The examples illustrate how power circuit topologies, integrated functions, and packaging can be optimized to meet the requirements of specific applications. II. T HE ASIPM C ONCEPT  Conventional IPMs (figure 1a) integrating power devices with low voltage ASICs (Application Specific Integrated Circuits) to provide gate drive and protection functions have been widely accepted for general purpose motor drive applications ranging from 200W to more than 150kW [ 3 ][ 5 ] [7]. The success of these modules is the direct result of several technical advantages including: (1) Reduced design time and improved reliability offered by the factory tested, built-in gate drive and protection functions; (2) Lower losses resulting from simultaneous optimization of power chips and protection functions; (3) Smaller size resulting from User Supplied Interface Power ChipsLV ASIC Over Current,Over Temp.,Cotrol supplyfailureGate DriveTemp. Sensor  LV ASIC Over Current,Control supplyfailureGate DriveIsolated ControlSignal Interface(Opto Couplers)Isolated Power Supply CPU HVICLV ASICPower Chips LevelShiftGate Drive andProtectionInput signalconditioningProtection, Fault Logicand Analog CurrentFeedback ProcessingGateDrive CPU Isolated ControlSignal Interface(Opto Couplers)Isolated Power SupplyCurrent sensor(s)Temp. sensor  Figure 1a: Conventional IPMFigure 1b: ASIPM  the use of bare power chips and application specific control ICs. (4) Improved manufacturability resulting from lower external component counts. Figure 2: HVIC Chip Unfortunately, in spite of these advantages, the conventional IPM’s generic, general purpose, design does not provide enough functional integration to meet the demanding cost and size requirements of some small motor control applications. In these cases, it is often desirable to increase the level of integration to include functions such as level shifting, high side power supplies and current sensing. The ASIPM shown in figure 1b has been developed to address these requirements. The ASIPM takes the integration a step farther than conventional IPMs by introducing HVIC (High Voltage Integrated Circuit) technology. The ASIPMs described in this paper utilize custom high and low voltage integrated circuits to provide input signal conditioning, protection logic, analog current feedback signal processing, level shifting and gate drive for the integrated power semiconductor devices. A photo of a typical high voltage integrated circuit (HVIC) is shown in figure 2. III. S ELECTING THE I NTEGRATED C ONTROL AND P ROTECTION F UNCTIONS  The addition of HVIC technology to the ASIPM makes it possible to integrate a wide range of sophisticated functions. Figure 3 is a block diagram showing some of the functions that can be implemented. In general, the cost and size of the  ASIPM increases with increasing complexity. To determine which functions should be integrated for a given application, it is necessary to consider the fundamental trade-off between performance, size and cost illustrated in figure 4. The key to developing a cost effective ASIPM is to integrate only the functions that provide both system and cost advantages. Table 1 gives a breakdown of the required functions in four different applications. By examining the requirements shown in table 1 and considering the trade-off of figure 4 an optimum combination of integrated functions can be realized. Clearly, the optimum combination will be different for different applications. To date, five families of ASIPMs have been developed to meet the needs of specific applications. These devices will be described in more detail NR S GateDriveGateDriveSC Prot.SC Prot.LevelShiftShoot-ThroughInterlockBootStrapSupplyUnder VoltageLock-OutFaultStatusFeedbackTSOver Temp.CurrentSensor(s)Under VoltageLock-Out U,V,WP ControlPower  CPU/DSP ControlnStatusn AnalogCurrentn Figure 3: ASIPM Integrated Functions Performance EfficiencyControl PrecisionI/O FunctionsReliability Cost Functional ValueDevelopment TimeManufacturability Size SystemRequirementsForm Factor  Figure 4: ASIPM Design Trade-off  Inverter  IGBTs & Free Wheel Diodes Converter  Diodes Brake IGBT & Diode Figure 5: ASIPM Power Circuit Requirements  Table 1: ASIPM Control and Protection Application Requirements Control and Protection Functions   High Performance General Purpose Industrial Inverter Compact High Precision  AC Servo and Vector Drives Basic General Purpose Industrial and Commercial Speed Control/Smart Motors Low Cost Consumer  Appliance and imbedded inverters Gate Drive Required Required Required Required Level Shift Required Required Required Required Boot Strap Supply Diodes Required Required Required Required P-Side Gate Drive Under Voltage Protection Required due to unstable nature of boot strap supplies Required due to unstable nature of boot strap supplies Required due to unstable nature of boot strap supplies Required due to unstable nature of boot strap supplies P-Side Short Circuit Protection Desirable, but may not be needed when high performance output current sensors are used with a high speed CPU Desirable, but may not be needed when high performance output current sensors are used with a high speed CPU Desirable if low enough cost. However, acceptable protection can usually be achieved using bus current sensors Usually unnecessary in imbedded inverter applications N-Side Gate Drive Under Voltage Protection Generally required for reliable power up/down Generally required for reliable power up/down Generally required for reliable power up/down Generally required for reliable power up/down N-Side Short Circuit Protection Desirable for low impedance faults and shoot-through survival Desirable for low impedance faults and shoot-through survival Desirable for low impedance faults and shoot-through survival. May be implemented using bus current sensor. Desirable for low impedance faults and shoot-through survival. May be implemented using bus current sensor Shoot Through Interlock Good safety feature. May be required depending on users design philosophy Good safety feature. May be required depending on users design philosophy Good safety feature. May be difficult to justify cost Desirable, but may not meet cost requirements Over Temperature Desirable Desirable Desirable if cost effective Usually unnecessary in imbedded inverter applications Current Sensors and Feedback Three phase output current feedback is required Three phase output current feedback is required DC Bus current feedback signal is usually sufficient Current feedback signal is usually not required Fault Status Feedback Multiple diagnostic fault signals are desirable Multiple diagnostic fault signals are desirable Single fault status signal is usually acceptable Single fault status signal is usually acceptable in the following sections. IV. S ELECTING T HE P OWER C IRCUIT T OPOLOGY  The power semiconductor requirements in the inverter power stage also differ from application to application. Figure 5 shows the typical power devices that may be included in a small motor control. Table 2 gives a breakdown of the requirements in four different applications. For lowest cost, the power stage should only include the necessary power devices. It can be observed from table 2 that the optimum power circuit topology depends on the application requirements. V. ASIPM E XAMPLES  Table 2: ASIPM Power Circuit Requirements  Power Circuit Component   High Performance General Purpose Industrial Inverter Compact High Precision  AC Servo and Vector Drives Basic General Purpose Industrial and Commercial Speed Control/Smart Motors Low Cost Consumer  Appliance and imbedded inverters Converter (Rectifier) Usually requires three phase rectifier Required for stand alone units Not required in DC feed multi axis applications Usually requires three phase rectifier May require three phase, single phase, or doubler* configurations Brake Usually required for rapid deceleration Braking function generally required but may be implemented in the bulk power supply of DC fed systems and size requirements vary widely depending on the application Usually not required Usually not required Inverter Required - High PWM Frequency (5kHz - 20kHz) Required - High PWM Frequency (5kHz - 20kHz) Required - High PWM Frequency (5kHz - 20kHz) Required - High and Low PWM frequencies  The following subsections present five examples of actual ASIPMs that have been optimized to meet the needs of specific applications. In each example the power circuit topology, package design and integrated functions have been tailored to a specific class of small motor control applications. At the same time care has been exercised to keep the integrated functions as generic as possible so that the module is suitable for a wide enough range of applications to take advantage of the economies of automated mass production. These examples each follow one of the application categories outlined in tables 1 and 2. Figure 6: PS212XX “DIP” ASIPM    A. ASIPM DIP Series For Consumer  Appliance Applications  The DIP ASIPM, PS212XX series, is designed for basic speed control in consumer appliance applications. For these applications, the ASIPM must provide a small, low-cost, efficient power stage that can be easily integrated into the finished equipment. In order to achieve these targets, a new transfer molded package was developed. A photograph of the new package is shown in figure 6 and a cross section diagram is shown in figure 7. Low cost is achieved by assembling bare power chips along with custom HVIC and LVIC die on a lead frame like a giant integrated circuit. The lead frame assembly is molded in epoxy resin along with an aluminum heat sink to provide good thermal characteristics. This process reduces cost and manufacturing time by eliminating the need for separate packaging of the power devices and control ICs. In addition, the IMS (Insulated Metal Substrate) or ceramic substrate that is used in conventional hybrid modules is not required. The transfer molded package is also well suited for high volume, low cost mass production.  Aluminum Heat SinkMold ResinPower ChipsIGBT, FWDi Al Bond Wire Au Bond WireHVICPower PinsControl Pins Figure 7: “DIP” ASIPM Package Cross SectionTable 3: “DIP” ASIPMs  “DIP” ASIPM Inverter Rating Line-up 400W 750W 1500W Low Frequency Type PS21204 PS21205 High Frequency Type PS21213 PS21214 The input voltage for these applications is generally between 100VAC and 240VAC. To cover this range, IGBTs and free wheel diodes with a 600V V CES  rating were selected. Most of the target applications are powered from a single phase AC source but flexibility to accommodate three phase sources and voltage doubler (figure 8) topologies was desired. Due to these requirements and the limited capabilities of the lead frame design, it was determined that the rectifier converter should not be integrated in the DIP ASIPM. The IGBT inverter section is a standard three phase bridge containing six IGBT+FWDi pairs. For optimum system cost, the decision was made to develop two different types of IGBT chips. High speed chips are used when the application requires switching frequencies greater than 5kHz and low speed (low saturation voltage) chips are used when the required switching frequency is less than 5kHz. At this writing, there are four DIP ASIPMs in production and several additional types under development. Table 3 shows the typical application and type names of these four devices. 330VDC120VAC Figure 8: Doubler Circuit Figure 9 is a block diagram showing the DIP ASIPM’s integrated control and protection functions

Henry Purcell

Jul 23, 2017

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Jul 23, 2017
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