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