At the moment, you can buy “open” development kits for motor control and inverters where the end user can load their algorithms and software into them. However, such development kits are small and their primary purpose is to enable the user/engineer to get acquainted with DSP and development environment.
The Open4Lab converter joins the openness of the motor control and inverter power with the IGBT module of 1200V 100A power level. It’s the only such product of that power, the only one that is “open” and allows users to develop their algorithm and load it into a converter.
Our intention was to make this inverter as a flexible part of laboratory equipment that can be tailored to your applications (eg. motor drive, power supply, or power grid connection).
The Open4Lab inverter provides a wide variety of user interfaces (optically isolated USB to JTAG / RS-232, CAN, SPI …) together with built-in protection including overcurrent, over voltage, overheat protection, instrument amplifier, “stopped DSP”, desaturation protection and electronic switch for emergency shutdown (E-STOP).
Logic voltage supply:
• Synchronous AC motor with permanent magnets
• Induction AC motor
750 V DC bus max.
100 A Ic (Tc=84°C)
200 A Ic max.
35 A RMS (depends on cooling)
12 V ili 24 V
CAN (or by order)
• Incremental encoder
• Magnetic position sensor
• 4 phases
• IGBT high performance module
• Integrated gate drivers with fault control and protection
• Isolated power supplies for gate drivers
• Low inductive plate lines (DC Bus)
• Measurement of output current with feedback
• Possibility of winding through the current sensor
• Current sensors on DC side
• Short circuit detection
• Detection of interrupt DSP operation with shut down
• Fan controlled via I²C interface
• DSP temperature via I²C interface
• Filtered power supply 5 V; ± 15 V
• Voltage supply: 24 V
• Light-emitting diodes for system status and error detection
• Plexigalss housing (with an easy access cover for DSP)
• USB → JTAG, optically isolated
• USB → RS232, optically isolated
• External connector for JTAG emulator
• R/D converter, adjustable resolution (10, 12, 14 or 16 bits)
• 5 isolated +/- voltage inputs
• 8 12-bit D/A outputs with +/- 10 V output range
• Emergency electronic switch (E-STOP)
• 4 double IGBT modules 100A 1200V
• 5 current sensors with feedback
• 4 temperature sensors
• Cooling fans with diameter of 80 mm
This open inverter is intended for laboratory and research applications. A single package provides both a four phase (four half bridges) power assembly and DSP carrier board.
DSP carrier board:
There is no DSP on the DSP carrier board itself; instead there is a 100 pin DIMM socket that accepts a variety of control cards conforming to Texas Instruments DIM100 standard, such as TI TMDSCNCD28343 Delfino. If a commercially available control card is not adequate, a custom designed control card can be used.
For programming and debugging purposes, the DSP carrier board provides optically isolated USB to JTAG interface. This interface also provides isolated USB to RS232 for communication from the host PC to the DSP on card. Use of this USB to JTAG interface is not required; if desired an JTAG emulator can be connected via a 14 pin header.
There is circuitry to connect five closed loop current sensors to the DSP carrier board. For each current sensor, the signal is converted to a voltage and level shifted to place the zero current point at the center voltage of the A/D converter. The signal is clamped to prevent any damage to the DSP’s A/D converter. In addition, each signal is compared against the outputs of its own dual channel D/A converter. If the magnitude – in either the positive or negative range – exceeds the limit set by the DSP, the open collector output will be activated. This open collector output can be used to activate a “trip zone” input on the DSP or to disable gate drive to the IGBTs.
Five isolated +/- voltage inputs are on the DSP carrier board. For each input, the voltage is encoded via sigma delta modulator, passed through an isolation barrier, decoded, and converted back to analog. This is repeated every 25 microseconds or less. There is also an open collector fault pin; it is activated when the magnitude of the input voltage reaches about 125% of the nominal input range.
There is a hardware level emergency stop (ESTOP) circuit. An external switch can be connected or the switch function can be disabled via a jumper. In addition to the switch function, an open collector output can trigger an emergency stop. An open collector output from the current or voltage inputs can be connected to trigger an emergency stop in response to a high current or voltage.
The resolver to digital interface is based on the AD2S1210 chip. Resolution is software configurable to 10, 12, 14, or 16 bits depending upon resolution and speed requirements of the application. The excitation amplitude is programmable so no potentiometer is required. Sine and cosine signals from the resolver pass through instrumentation amplifiers on their way to the AD2S1210 chip; this gives good common mode noise immunity.
There are eight digital to analog outputs (12 bit resolution) with a +/- 10V output range. They are not committed to any particular function and can be used for whatever desired.
A standard CAN bus transceiver is connected to the CAN-TX and CAN-RX pins on the DIMM100 socket. This allows the DSP to communicate via CAN bus.
Additional functionality can be added via SPI (serial peripheral interface) bus. The SPI signals data in, data out, clock, two chip selects, as well as 5V, 3.3V, and GND are accessible via a 10 pin header.
Power section and current measurement:
The power section consists of four 100A 1200V dual IGBT modules comprising four half bridges. Two 220uF polypropylene capacitors are mounted on a laminar bus structure very close to the IGBT modules, making a low inductance DC bus.
The power section is mounted to a black anodized heat sink. Three thermal sensors are mounted to the heat sink (in between the four IGBT modules). Three 80mm cooling fans can independently be energized to cool the heat sink as required.
There are five closed loop current sensors. Four sensors measure current for each half bridge; one measures DC bus current. The mechanical construction allows for both measurement of high current and accurate measurement of low current. For high current the sensor is placed directly around the bus bar. For low current the sensor is moved away from the bus bar. A wire is wound multiple times through the current sensor and connected to the bus bar. This enables the inverter to be used for both high and low current applications.
IGBT control board:
The IGBT control board performs many functions and brings everything together to make a functional laboratory inverter. This board carries the IGBT gate drive boards, provides the required power supplies, controls the three 80mm cooling fans, and implements IGBT protection.
The DSP carrier board is connected to the IGBT control board via a 40 pin ribbon cable. All signals and power supplies pass through this ribbon cable. The IGBT control board provides 5V, +15V, and -15V to the DSP carrier board via this cable.
Four IGBT gate drive boards are mounted to the IGBT control board. Each gate drive board drives the two IGBTs in one module. Each gate drive board also provides IGBT desaturation status back to the IGBT protection circuit. High and low side IGBTs are protected via desaturation protection – all eight IGBTs are protected. A desaturation fault is latched via the IGBT protection circuit. The DSP communicates with the protection circuit; it can check the fault status as well as reset any faults.
The IGBT protection circuit also implements “stopped DSP” protection. If the DSP is stopped via the JTAG interface, the PWM outputs are frozen. This can lead to a situation where current keeps increasing until desaturation protection is activated. This behavior is not desirable; a more elegant shut down mechanism is required. Before the IGBT protection circuit allows the IGBTs to be turned on, the DSP must communicate a “timeout” value to the protection circuit. One output on the DSP is reserved for the “heartbeat” function. This output is is periodically toggled by the DSP. If it does not toggle within the specified timeout period, all eight IGBTs are turned off.
Thermal control is implemented via I2C bus. The DSP can read all three temperature sensors and control all three fans via I2C bus.
Texas Instruments DIM100 cards are used in a number of development kits, eg. for motor control, power supply, etc. Our 4-phase inverter uses the advantages of this fact. First, anyone who has experience with the Texas Instruments sets mentioned above can apply that experience on our 4-phase inverter. Second, the existing software infrastructure can be used. The inverter can be programmed directly from the Code Composer Studio™ program (via built-in, optically isolated JTAG interface) as any Texas Instruments kit. Integration with tools such as VisSim™ and MATLAB® is also possible.
Motor control and supply:
•A synchronous or induction AC motor control. The fourth phase can be connected to the brake resistor.
• Synchronous AC motor / generator control. The fourth stage is used for rotor excitation.
• 3-phase AC motor drive with DC low voltage source. The fourth phase is used to raise the voltage above the DC power level (boost converter).
• DC motor drive.
• Drive two DC motors two-way – two half-bridges per motor.
• Multiple (up to 4) converter (buck converter) from one DC power supply.
Isolated voltage inputs can be connected to the AC network. The inverter can besoftware synchronized to the network (PLL), enabling various applications. Here are some examples of network connectivity:
•Two inverters are connected back-to-back between the AC network and the motor with current flow in both directions. • Three phases can be connected to the AC network. The fourth connects to the battery and is used as a converter (boost + buck) for the current flow in both directions between the battery and the AC network.
Only a few possible configurations are listed above – there are numerous other options. Our intention was to make this inverter as a flexible part of the lab equipment. We hope to be able to adapt to your application. However, we acknowledge that it will not be sufficient for all applications, so please feel free to contact us. We will be very happy to make changes and additions to make it suitable for your application.
A sample example of FOC for a 3-phase permanent magnet motor that you get with Open4Lab can be used as a basis for your own applications.