Multilevel DC to AC Converter with Segmented Phase Modules
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Solution Overview
Problem
Existing DC-to-AC converters face challenges in meeting network standards for harmonic content and impedance matching, particularly in high power ranges and high voltage applications, where traditional solutions like sinusoidal filters and multilevel converters are either bulky or costly and complex.
Innovation Solution
A DC-to-AC converter design featuring six phase modules connected to a transformer with three-phase primary and secondary windings, using a mixed switching pattern with sawtooth and sinusoidal carrier signals to achieve nine output voltage levels, reducing the need for filters and mitigating impedance variations, and allowing for reactive power compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If sinusoidal filters are used to meet harmonic injection levels, then harmonic content compliance is improved, but device bulk and impedance matching complexity increase
Solution Approach 1:
The patent changes the voltage level parameter by generating a five-level voltage output (0, +Vdc/4, +Vdc/2, +3Vdc/4, +Vdc) instead of traditional two-level output. This parameter change inherently reduces harmonic distortion, allowing compliance with harmonic injection standards without requiring bulky sinusoidal filters or complex impedance matching circuits.
Solution Approach 2:
The patent segments the single power converter into six independent phase modules, each capable of generating five voltage levels. This segmentation allows each module to operate independently with simplified filtering requirements, reducing overall device bulk and complexity while maintaining harmonic compliance through the multilevel voltage structure.
2Device complexity
If multilevel converters are used to decrease filter size, then filter bulk is reduced, but output distortion increases
Solution Approach 1:
The patent implements a five-level voltage output parameter that fundamentally reduces output distortion through its stepped voltage structure. The multiple voltage levels (0, ±Vdc/4, ±Vdc/2, ±3Vdc/4, ±Vdc) create a waveform that more closely approximates a sine wave, inherently reducing total harmonic distortion and allowing filterless operation in most cases.
Solution Approach 2:
The phase modules are designed with universal functionality to generate five voltage levels each, and when combined with the transformer's winding configuration, produce a nine-level output. This multi-functional design achieves both filter size reduction and low distortion simultaneously through the synergistic interaction of module outputs and transformer magnetizing inductance.
3Adaptability or versatility
If cells connected in series are used to achieve multilevel converters, then output voltage levels increase, but adaptability to power range and network voltage decreases
Solution Approach 1:
Instead of connecting cells in series, the patent segments the converter into six parallel phase modules, each handling a portion of the total power. This segmentation provides flexibility to adapt to different power ranges (tens of kVA to tens of MVA) and network voltages by simply adjusting the number and rating of modules, without requiring complex series connection configurations.
Solution Approach 2:
The patent employs dynamic control of the six phase modules with phase-shifted commands, allowing the system to adapt dynamically to different operating conditions, power levels, and network voltage requirements. The modular architecture enables flexible configuration and scaling, providing superior adaptability compared to fixed series connections.
4Adaptability or versatility
If a large number of lower-voltage power converters are used in parallel, then voltage levels are achieved, but implementation complexity and cost increase
Solution Approach 1:
The patent merges six phase modules with a common transformer core, where the transformer's magnetizing inductance serves as a shared interphase inductor. This merging eliminates the need for separate expensive transformers or additional interphase converters for each module, significantly reducing implementation complexity and cost while achieving the required voltage levels through the combined output of all modules.
Solution Approach 2:
The transformer serves multiple functions simultaneously: it provides voltage transformation, acts as an interphase inductor for the parallel modules, and enables the nine-level voltage output through its winding configuration. This multi-functionality reduces the overall component count and system complexity compared to using separate transformers for each module.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design eliminates the need for filters in most cases, reduces distortion, and effectively compensates for reactive power, while maintaining low voltage stress and simplifying transformer design, thus addressing the challenges of harmonic content and impedance matching.
Implementation Method 1
a transformer provided with a three-phase primary winding and with at least two secondary windings, each with three phases
Implementation Method 2
the first capacitance being connected between the positive portion of the DC voltage bus and the midpoint of the DC voltage bus, the second capacitance being connected between the negative portion of the DC voltage bus and the midpoint of the DC voltage bus
Data Source
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AI summary
A DC-to-AC converter (B) including six phase modules (A1-A6) and two capacitors (C1,C2), a transformer (T) with a three-phase primary winding (P) and with two three phase secondary windings (S1,S2), each phase module (A1-A6) receiving a DC voltage from a DC voltage bus and capable of transmitting an AC current, and including a transistor, able to modulate the output voltage according to five intensity levels, the first capacitance (CI) connected between the positive portion and the midpoint of the DC voltage bus, the second capacitance connected between the negative portion and the midpoint of the DC voltage bus, the first, second and third phase module (A1,A2,A3) are linked by their output to a different phase of the first secondary winding (S1). The fourth, fifth and sixth phase module (A4,A5,A6) are each linked by their output to a different phase of the second secondary winding (S2) of the transformer (T), the primary winding (P) of the transformer (T) is linked to an electrical power supply network (2).