October 7, 20241 yr Hi folks, Recently I was wondering about the purpose of implementing the buck circuit in the middle between DC-DC and DC-AC circuits in solar inverter Can anyone describe it well? Thanks in advance
October 9, 20241 yr This post was recognized by Energy-Jason! Coulomb was awarded the badge 'Superstar' and 15 points. On 2024/10/07 at 8:19 PM, Adnano said: I was wondering about the purpose of implementing the buck circuit in the middle between DC-DC and DC-AC circuits in solar inverter My understanding is that it's only used for battery charging (only utility battery charging for low PV voltage models). The problem is that the bus voltage depends on many factors, such as loads and solar power, and the battery needs a very carefully controlled voltage to get the desired current into the battery when charging it. The DC-DC converter has a fixed ratio between high voltage side and battery voltage. This ratio can be 8:1 or 7:1 or various fixed values in between for various 48 V models. Varying the duty cycle of the isolating transformer drive does not change this ratio. In fact, the DC-DC converter is fed fixed 50% duty cycle (with dead time) square waves from the SG3525 chip. So the buck converter is used to vary the voltage between the bus voltage and the high side of the DC-DC converter, and this to the battery voltage and thus the battery charge current. You can think of the high side of the DC-DC converter as the battery, transformed up by the turns ratio of the isolating transformer. So if the battery is at 50.0 V and the turns ratio is 7.0:1, then it's effectively a 350 V battery to be charged. Say the bus voltage is 400 V; that 50 V gap is dropped in a low loss manner by the buck stage. Effectively, the buck stage IS the battery charger, just operating at high voltage. When power flow is away from the battery, this stage does not boost, but instead switches off and the flywheel diode allows power to pass through unaltered (1:1). It must get tricky if conditions are such that the power flow is alternating between charging and discharging the battery. I assume that the battery can't instantaneously support the load in that scenario, and has to wait a few tens of milliseconds for the bus voltage to fall to the transformed battery voltage.
October 12, 20241 yr On 2024/10/09 at 6:45 AM, Coulomb said: My understanding Bro … your explanation are always legendary.. keep shining ⭐️
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