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We are planning to make a system that can run a BLDC motor and charge a battery with a PV array using a boost MPPT.

Current aiming spec on output side: Nominal voltage 96V.

I am nt sure if there are gaps in my understanding, but this is kind of what I need help understanding.

  1. If we use an MPPT algorithm that controls the input voltage and current, which would mean the output voltage and current of the boost converter would change, does this mean that we could possibly damage the line/components connected on the line since we need a 96V DC bus on the output side, or is the output voltage regulated to 96V by the battery even though it would be connected via a BMS and/or a bidirectional converter?

  2. Another way I have read is using a secondary DC to DC converter between the output of the MPPT to the battery and to the motor as well. Would this be a good solution in terms of the efficiency of the overall system? From what I know, multiple DC-DC converters do reduce your overall efficiency.

In summary, what are some of the best ways to approach this kind of design problem, while thinking about maximizing efficiency as well as getting the best performance/lifespan out of your loads/devices?

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  • \$\begingroup\$ I think the answer depends on the specification of the MPPT controller. If it has a built-in DC-DC converter, then it shoukdn't need another one. \$\endgroup\$
    – Simon B
    Commented Aug 14, 2022 at 17:13
  • \$\begingroup\$ All the DC output MPPTs I have seen are designed to charge a battery. They probably won't really work correctly with a DC-DC converter as a load. There are also grid-tie DC to AC inverters that do MPPT, but those are designed to be connected to the grid and they assume the grid will happily accept however much power they put out. \$\endgroup\$
    – user57037
    Commented Aug 17, 2022 at 2:50

1 Answer 1

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If you have a PV system with a PV panel driving a (MPPT-regulated) DCDC converter whose load is a battery and/or a motor, then the DCDC will adjust the input current it consumes (and the PV will respond with different voltages) to maximize power (MPPT). That input power (V*I) will be converter by the DCDC to a current which drives the battery (at the voltage the battery is charged to).

Thus as the input (PV) changes, the DCDC will absorb maximum power from it (at the PV's V & I levels), and convert it to a current at the voltage of the battery. If the system was 100 % efficient, then V_PV * I_PV = V_BATT * I_BATT.

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  • \$\begingroup\$ Hey @jp314, thanks for the info, how would you go about designing one your self, with one controller, would you have two control loops one for MPPT and the other for output voltage? \$\endgroup\$ Commented Aug 14, 2022 at 22:29
  • \$\begingroup\$ just one loop for MPPT. then you need a comparator (not a control loop) that turns the system off (with a little hysteresis if VBATT indicates 100 % charged. If the PV is capable of generating too much current for the battery, then you'd need to override the MPPT in that case. \$\endgroup\$
    – jp314
    Commented Aug 14, 2022 at 23:17
  • \$\begingroup\$ oh right that makes sense, but then what if the battery is charged and I want the PV array to now power the motor, how would this work. Thanks for all your guidance! \$\endgroup\$ Commented Aug 15, 2022 at 0:56
  • \$\begingroup\$ If the motor is connected to the battery, then as soon as it turns on, the VBATT will fall and the MPPT controller will start to work and supply power to both. \$\endgroup\$
    – jp314
    Commented Aug 15, 2022 at 0:58
  • \$\begingroup\$ Alright Thanks alot. This makes alot more sense now. Thanks \$\endgroup\$ Commented Aug 15, 2022 at 11:27

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