Technical Article

Analyzing the Inner Workings of a Variable Frequency Drive’s Inverters

August 11, 2020 by Nilo Mitra

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.

 

The Hitachi SJ Series P1 variable frequency drive
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

  • Model and Ratings: SJ-P1, 15kW, 35A, 3-phase 400V class

  • Sine-wave PWM system

  • 0.00 to 590.00 Hz output frequency range

  • Protection functions: Overcurrent error, overload error, brake resistor overload, overvoltage error, memory error, undervoltage error, current detector, etc.

 

External and Enclosure

  • Dimensions: 390mm x 245mm x 190mm

  • Weight: 16kg

  • Operating ambient temperature: -10° to 40°C

  • Installation class: A maximum altitude of 1000m, without gases or dust

 

The Hitachi SJ Series P1 enclosure
Figure 2: The Hitachi SJ Series P1 enclosure.

 

DC Bus Capacitor

  • DC Bus Bulk Capacitor: Nippon Chemi-con (2pcs) 400V/4400µF electrolytic capacitors‎.

 

The DC bus capacitor
Figure 3: The DC bus capacitor

 

Main Controller Board

  • PWM MCU: Renesas R5F571MFCDFC industrial equipment-specific real-time engine. A 32-bit microcontroller capable of operation up to 240 MHz.

  • 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.

  • Isolation: Toshiba

    • TLP2362 (4pcs) 10Mbd high-speed photocoupler

    • TLP2301 (4pcs) 20 kbps photo-transistor with high-speed detector.

    • TLP291 photo-transistor.

    • TLP290 (4Pcs) photo-transistor with AC inputs.

  • Relay: Panasonic JQ1-5V-F general purpose relays 5A, 5VDC, 400mW SPDT (1 Form C).

  • Relay: Fujitsu FTR-F3AA012E general purpose relays, 12VDC, 200mW SPST (1 Form A).

  • Line input and three-phase output contactor board.

  • Current transducer: LEM HLSR 62-P (2pcs) open-loop 62A current transducer with galvanic separation.

  • Capacitor: Okaya LE 105 310V 1µF film capacitor.

  • Resistor: Iwaki 3.3/6.6ΩJ (8pcs) resistor.

 

The main controller board
Figure 4: The main controller board

Line input and three-phase output contactor board.

Figure 5: Line input and three-phase output contactor board.

 

Line Input and 3-Phase Output Contactor Board

  • Current Transducer: LEM HLSR 62-P (2pcs) open-loop 62A current transducer with galvanic separation.

  • Capacitor: Okaya LE 105 310V 1µF film capacitor.

  • Resistor: Iwaki 3.3/6.6ΩJ (8pcs) resistor.

 

The power electronics board

Figure 6: The power electronics board

Another view of the power electronics board.

Figure 7: Another view of the power electronics board.
 

Power Electronics Board

  • IGBT: Fuji Electric 7MBR100VR120-50 1200V 100A IGBT module with rectifier, brake, inverter and thermistor stage.

  • Isolation: Broadcom (Avago Technologies)

    • ACPL-W61L (3pcs) ultra-low-power 10MBd digital CMOS optocoupler.

    • ACPL-C87A precision optically isolated voltage sensor with 0.5% high gain accuracy.

    • ACPL-C79A precision miniature isolation amplifier with 0.5% high gain accuracy.

  • Isolation: Broadcom (Avago Technologies)

    • ACPL-336J (6pcs) 2.5A IGBT gate drive optocoupler with integrated (VCE) desaturation detection, active Miller clamping, fault, and UVLO status feedback.

    • ACPL-W341 3A output current IGBT gate drive optocoupler with rail-to-rail output voltage.

    • ACPL-W61L (4pcs) ultra-low-power 10MBd digital CMOS optocoupler.

    • ACPL-C87A (2pcs) precision optically isolated voltage sensor with 0.5% high gain accuracy.

  • Isolation: Toshiba TLP385 (13pcs) photo-transistor with 5000Vrms in a 4-pin SO6L package.

  • Switching Power Supply: ON Semiconductor 2SK3748 N-channel 1500V 4A power MOSFET.

  • Capacitor: Nichicon (2pcs) 400V/150µF electrolytic capacitor‎. Capacitor: Okaya

  • LE 105 (3pcs) 310V 1µF film capacitor.

    • HCP474 (2pcs) 0.47µF 1250VDC capacitor

 

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.