Analyzing the Inner Workings of a Variable Frequency Drive’s Inverters
This teardown looks at the inner workings of the Hitachi SJ P1 Variable Frequency Drive, an inverter for industrial applications and part of a line of industrial inverters.
The SJ-P1 inverter can be used to drive both induction motors and permanent magnet motors. While induction motors are more commonly found in motor-driven systems, they are often larger in size and less efficient than permanent magnet motor solutions. While permanent magnet motor solutions tend to have a higher initial cost, they may offer a smaller size for more compact mechanical packages and higher efficiency. Although the permanent magnet motor offers many benefits, there is a problem of permanent magnet demagnetization when the inverter is overloaded over time. The SJ-P1’s over-current trip feature uses many isolated current detection and protection components to prevent the inverter from overloading and suppresses the demagnetization of permanent magnet motors.
Figure 1: The Hitachi SJ Series P1 variable frequency drive.
The SJ-P1 Series is designed for easy integration with various networks using optional Fieldbus modules like RS485-Modbus (built-in), RS422 port (built-in), Ethernet, EtherCAT, ProfiNET and Profibus-DP. The SJ-P1 inverter is used in a wide variety of applications including industrial fans, hydraulic pumps, cranes and lifts used in warehouse automation and injection molding machines. Now, let's take a look at the inner workings of this piece of equipment.
General Specifications
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Model and Ratings: SJ-P1, 15kW, 35A, 3-phase 400V class
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Sine-wave PWM system
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0.00 to 590.00 Hz output frequency range
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Protection functions: Overcurrent error, overload error, brake resistor overload, overvoltage error, memory error, undervoltage error, current detector, etc.
External and Enclosure
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Dimensions: 390mm x 245mm x 190mm
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Weight: 16kg
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Operating ambient temperature: -10° to 40°C
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Installation class: A maximum altitude of 1000m, without gases or dust
Figure 2: The Hitachi SJ Series P1 enclosure.
DC Bus Capacitor
- DC Bus Bulk Capacitor: Nippon Chemi-con (2pcs) 400V/4400µF electrolytic capacitors.
Figure 3: The DC bus capacitor
Main Controller Board
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PWM MCU: Renesas R5F571MFCDFC industrial equipment-specific real-time engine. A 32-bit microcontroller capable of operation up to 240 MHz.
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Programmable Logic Device: Altera EPM240T100I5N. The MAX® II family of instant-on, non-volatile CPLDs with densities from 240 to 2,210 logic elements (LEs) and non-volatile storage of 8Kbits.
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Isolation: Toshiba
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TLP2362 (4pcs) 10Mbd high-speed photocoupler
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TLP2301 (4pcs) 20 kbps photo-transistor with high-speed detector.
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TLP291 photo-transistor.
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TLP290 (4Pcs) photo-transistor with AC inputs.
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Relay: Panasonic JQ1-5V-F general purpose relays 5A, 5VDC, 400mW SPDT (1 Form C).
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Relay: Fujitsu FTR-F3AA012E general purpose relays, 12VDC, 200mW SPST (1 Form A).
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Line input and three-phase output contactor board.
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Current transducer: LEM HLSR 62-P (2pcs) open-loop 62A current transducer with galvanic separation.
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Capacitor: Okaya LE 105 310V 1µF film capacitor.
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Resistor: Iwaki 3.3/6.6ΩJ (8pcs) resistor.
Figure 4: The main controller board
Figure 5: Line input and three-phase output contactor board.
Line Input and 3-Phase Output Contactor Board
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Current Transducer: LEM HLSR 62-P (2pcs) open-loop 62A current transducer with galvanic separation.
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Capacitor: Okaya LE 105 310V 1µF film capacitor.
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Resistor: Iwaki 3.3/6.6ΩJ (8pcs) resistor.
Figure 6: The power electronics board
Figure 7: Another view of the power electronics board.
Power Electronics Board
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IGBT: Fuji Electric 7MBR100VR120-50 1200V 100A IGBT module with rectifier, brake, inverter and thermistor stage.
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Isolation: Broadcom (Avago Technologies)
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ACPL-W61L (3pcs) ultra-low-power 10MBd digital CMOS optocoupler.
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ACPL-C87A precision optically isolated voltage sensor with 0.5% high gain accuracy.
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ACPL-C79A precision miniature isolation amplifier with 0.5% high gain accuracy.
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Isolation: Broadcom (Avago Technologies)
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ACPL-336J (6pcs) 2.5A IGBT gate drive optocoupler with integrated (VCE) desaturation detection, active Miller clamping, fault, and UVLO status feedback.
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ACPL-W341 3A output current IGBT gate drive optocoupler with rail-to-rail output voltage.
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ACPL-W61L (4pcs) ultra-low-power 10MBd digital CMOS optocoupler.
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ACPL-C87A (2pcs) precision optically isolated voltage sensor with 0.5% high gain accuracy.
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Isolation: Toshiba TLP385 (13pcs) photo-transistor with 5000Vrms in a 4-pin SO6L package.
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Switching Power Supply: ON Semiconductor 2SK3748 N-channel 1500V 4A power MOSFET.
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Capacitor: Nichicon (2pcs) 400V/150µF electrolytic capacitor. Capacitor: Okaya
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LE 105 (3pcs) 310V 1µF film capacitor.
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HCP474 (2pcs) 0.47µF 1250VDC capacitor
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About the Author
Nilo Mitra is a freelance technical writer/editor specializing in writing on IT/software, Web/Internet and telecommunications topics, in which areas he has had 35+ years of professional experience. He is able to write on complex technical subjects in a way that makes these understandable to an educated, professional audience who are not necessarily subject matter experts.
This article originally appeared in the Bodo’s Power Systems magazine.