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TIDA-01606: Isolated/Non-isolated High Voltage Sensing

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Prodigy 10 points
Part Number: TIDA-01606
Other Parts Discussed in Thread: AMC1301

Hi,

We are evaluating TIDA-01606(10-kW, bidirectional three-phase three-level (T-type) inverter and PFC) and TIDA-01000(Vienna Rectifier-Based, Three-Phase Power Factor Correction) reference designs for PFC application.

I noticed, while both the designs use CC2000 series controller, the 3-Level T-Type reference design does not use isolation between the high voltage and the CC2000 controller. On the other hand the Vienna Rectifier-Based uses AMC1301 for sensing the line voltages and the two half DCbus Voltages.

My questions:

1.) Why does the Vienna Rectifier Design need the AMC1301s? Is it possible to get away without the AMCs?

2.) I also saw the Line Voltages being sense this way(non-isolated) in another design, where the C2000 & all the other digital circuitry was powered from a mains isolated powered supply and yet the Line Voltages were connected directly to CC2000 with a simple resister divider, i.e. without any isolation device. This was an energy meter design. I understand that the isolation requirements are specific to an application and the required standards. But It feels like I am missing some fundamental understanding here. Are the CC2000 ADCs (Presumably the differential inputs / Sigma-Delta Modulators) have any built in isolation? If so what is the isolation voltage?

It would be helpful if you can shine some light on what's going on with isolated / non-isolated ways of sensing the high voltages the two cases?

Thanks in advance,

Best Regards

  • 0
    TI__Intellectual 2110 points

    Hi,

    below, you can find my answers.

    1.) Why does the Vienna Rectifier Design need the AMC1301s? Is it possible to get away without the AMCs?

    From a functional point of view, it is not mandatory to have an isolation barrier between the high voltage and the low voltage. System can always work. If the application does not need proper isolation barrier the AMC can be removed.  

    2.) I also saw the Line Voltages being sense this way(non-isolated) in another design, where the C2000 & all the other digital circuitry was powered from a mains isolated powered supply and yet the Line Voltages were connected directly to CC2000 with a simple resister divider, i.e. without any isolation device. This was an energy meter design. I understand that the isolation requirements are specific to an application and the required standards. But It feels like I am missing some fundamental understanding here. Are the CC2000 ADCs (Presumably the differential inputs / Sigma-Delta Modulators) have any built in isolation? If so what is the isolation voltage?

    You are right. The micro controller is connected to the high voltage lines by using a high impedance voltage divider. There is no isolation barrier build in the C2000. The insulation barrier is kept by applying the Ohmic Law. The high voltage will be across the SMD resistors, this means that the insulation distance is respected by the distance between the pads. From an insulation coordination point of view, you have to consider the distance between the pads of the resistors.

    It would be helpful if you can shine some light on what's going on with isolated / non-isolated ways of sensing the high voltages the two cases?

    “No isolated voltage measurement” is composed of a voltage divider plus an operational amplifier. Operational amplifier is used in order to decouple the high impedance from the input of the ADC converter. This measurement method is cheap and easy. Do not require any power supply on the secondary side. Drawbacks: if your small resistor in the chain breaks and becomes an open circuit, voltage will start to rise. If there is not clamping circuit high voltage problem can be present. I will recommend this measurement method for basic and functional insulation. Furthermore, I am not quite sure if you can standardize your device as reinforced isolation when you have this kind of measurement method.

    “Isolated voltage measurement” you can use isolated delta sigma modulator. They will allow the user to guarantee the safety isolation propriety of the system. Furthermore, you avoid any issues of leakage currents going in your isolated logic region. In conclusion, system will be more robust by using device like AMC for line voltage measurements.  

    I hope that I have fully answered to all your questions.

    Best regards

    Riccardo