I am designing a modular solar-powered DC microgrid consisting of MPPT boost converters, a 4-switch buck-boost interfaced with a battery and step-down load modules. All the individual modules are interfaced with a common DC bus whose voltage is being regulated by the 4-switch buck-boost. I am trying a plug-in, plug-out topology with a load module (buck converter). During plug-in, my grid voltage shows very high current and voltage transients, which are affecting the I-V characteristics of each module. I’m looking for any solution to minimise these transients.
The step-down converters are interfaced with the DC bus via an input filter, and a manual switch is used to plug in.
The battery is a SOC-based 1-RC Thevenin model where OCV is represented as a function of SOC. The SOC estimation is done by coulomb counting method, where battery current is a dependable parameter for SOC.
Hi bhaskar_245,
It is difficult to fully understand what is happening without a model.
From the schematic, I suspect you may be experiencing extremely large inrush currents, since there does not appear to be any pre-conditioning circuitry. As currently shown, the only element limiting the inrush current is the resistor labeled ESR in series with the filter capacitor.
I’m not deeply familiar with how this is typically handled in systems like yours, but in charging applications it is usually addressed using:
- NTC resistors for lower-power systems (for example, phone or laptop chargers)
- Pre-charge circuits for higher-power systems (for example, EV onboard chargers), often implemented using a resistor and a parallel relay or contactor. The resistor limits the initial current, and once the voltage difference between the two sides becomes sufficiently small, the relay bypasses the resistor.
I would also suspect that your MPPT algorithm and PV models depend heavily on the bus voltage. Depending on the size of your capacitors, the system may experience a sharp voltage collapse during startup or transient operation.
Is your PV model designed to account for this type of behavior? Also, what is the expected behavior of the real hardware during this scenario?
