WKT02a-22 Phase-by-phase Modulated DC to AC Inverter for Three-phase Unbalanced Load

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LI, Chentian
January 18, 2023 4:38 pm

Thank you for being interested in my project, yes, the major difference is :
The first topology is actually 3 isolated single-phase inverters which are synchronized by 120 degree of phase shift, the 3 inverters are independent, and they all have a complete DC-TO-AC circuit inside each of them, to share the power on the common DC bus, they all equipped with a DC-TO-DC isolation unit (the full-bridge DC isolator), which provides them with a electrically isolated sub DC bus from the common DC bus. As 3 inverters are completely isolated, they can bee regarded as 3 independent (which means one does not interefere another’s output), and Y-connected 3-phase AC voltage source, which is almost electrically equivalent to a traditional 3-phase+N step down transformer’s secondary output, which can surely drive 3 unbalanced loads.
The second topology is actually a 3-phase 3-line output inverter plus a N level management circuit, which can provide a neutral line equivalent voltage level under all designed (i.e., balanced or unbalanced; linear or non-linear; periodic or non-periodic) conditions, to make the inverter, viewing from output to inside, electrically equivalent to 3 Y-connected sinusoidal voltage sources with 120 degrees phase shift sequentially. The N level management circuit can be A: bi-directional buck-boost DC-TO-DC converter type, which employs inductor as energy consevation device; OR B: bi-directional charge pump type, which employs capacitor as energy consevation device, the engineering purpose of the management circuit is to maintain a 1/2 bus voltage level under inward and outward current flowing on the N output (of course, the current magnitude shoud be within designed ratings), and as the modulation strategy is bipolar modulation, which range the sine wave symmetrically reference to 1/2 bus voltage as center of symmetry, thus the 1/2 bus voltage can be regarded as the neutral line level.

And, I had started the design of the control logic, which is mainly a embedded MCU circuit and some analog front-ends. As the new topology have two more functional unit (one is the boost-type pre-regulator, another is the N level management circuit), the control logic will be more complicated when comparing with one of the single control logic in the “3-inverters” topology, but as there is only one set of power electronic circuit is required (the former needs 3 sets), the total hardware complexity is surely decreased. Which is basically a concept of “one comprehensive” compare with “three relative simple repetitions”. For the software strategy, the comparison is almost the same.

Last edited 1 year ago by LI, Chentian
ZHENG, Zheyang
January 18, 2023 2:50 pm
  1. Have you compared the two topologies you proposed?
  2. Have you also designed the control circuits for your new inverter? Will the new design significantly complicate the control logic?