Multi-level Rectifier for Medium Voltage Conversion
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Solution Overview
Problem
Emerging applications require efficient conversion of medium voltage AC levels to controlled DC voltage, but existing configurations rely on high voltage power semiconductor devices that are either unavailable or expensive.
Innovation Solution
A multi-level rectifier system comprising an input inductor, diodes, switches, and a DC link of capacitors, which provides multiple DC voltage points, allowing for sinusoidal voltage synthesis and reduced Total Harmonic Distortion without increasing switching frequency, and is coupled with a medium voltage to low voltage DC/DC converter for power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high voltage power semiconductor devices are used for medium voltage AC to DC conversion, then voltage conversion capability is improved, but device availability decreases and cost increases
Solution Approach 1:
The patent divides the high voltage conversion task into multiple lower voltage stages using a multi-level rectifier topology. Instead of using a single high voltage device, the system segments the voltage conversion into several steps, each handled by fractionally-rated switches and diodes operating at lower voltage levels, thereby improving device availability while maintaining overall voltage conversion capability.
Solution Approach 2:
The patent introduces multiple DC voltage points (three or more levels) in the voltage domain, creating a multi-level structure. This dimensional expansion allows the system to synthesize the desired output voltage through combinations of multiple lower voltage levels rather than relying on a single high voltage device, thus resolving the contradiction between voltage capability and device availability.
2Manufacturing precision
If switching frequency is increased to reduce harmonic distortion, then voltage synthesis precision is improved, but switching losses increase
Solution Approach 1:
The patent changes the voltage level parameter by operating switches at fractionally-rated lower voltage levels in a multi-level configuration. This parameter change allows for effective voltage synthesis with reduced harmonic distortion without requiring high switching frequencies, thereby reducing switching losses while maintaining voltage synthesis precision.
3Device complexity
If single-level rectifier topology is used for medium voltage conversion, then device complexity is reduced, but voltage conversion efficiency decreases
Solution Approach 1:
The patent segments the voltage conversion process into multiple levels with intermediate DC voltage points, allowing fractionally-rated devices to work in coordination. This segmentation improves voltage conversion efficiency by reducing stress on individual components and enabling softer switching, while the modular nature of the segmentation keeps device complexity manageable.
Solution Approach 2:
The multi-level rectifier topology serves multiple functions simultaneously: it performs voltage conversion, reduces harmonic distortion, limits peak stress on components, and enables the use of fractionally-rated devices. This multi-functionality improves overall voltage conversion efficiency without proportionally increasing device complexity.
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
The system effectively converts medium AC voltages to low DC voltages with reduced harmonic distortion and peak stress on components, achieving unity power factor and efficient voltage regulation, while minimizing the use of high voltage semiconductor devices.
Implementation Method 1
One end of an input inductor may be coupled to an AC voltage source and the other end of the input inductor may be coupled to a pair of diodes that are series connected
Implementation Method 2
the other end of the input inductor may be coupled to a pair of diodes that are series connected
Implementation Method 3
a DC link comprising a set of capacitors. The set of capacitors may be coupled in series such that the DC link provides three or more DC voltage points
Data Source
AI summary
Multi-level rectifiers are provided. A multi-level rectifier may convert a medium AC voltage to a medium DC voltage. A multi-level rectifier may comprise an input inductor, a set of diodes, a set of switches, and a DC link comprising a set of capacitors. One end of the input inductor is coupled to the input AC voltage and the other end of the input inductor is coupled to a pair of diodes that are series connected. The set of switches may be regulated such that the inductor may be coupled to a DC voltage point of the DC link. A multi-level rectifier may operate under a set of operation modes. Each operation mode may be determined from the input voltage and the inductor current. Accordingly, a sinusoidal voltage at the fundamental frequency of the input voltage may be synthesized by selectively switching between adjacent operation modes of the set of operation modes. A multi-level rectifier may be used in connection with a medium voltage to low voltage DC/DC converter to form a power conversion system that converts a medium AC voltage to a low DC voltage.