Transformerless Medium-Voltage UPS With Multi-Level Inverter Control
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Solution Overview
Problem
Conventional uninterruptible power supplies (UPS) for data centers face challenges with high power and voltage requirements, inefficiencies due to the use of step-up transformers, and increased costs and losses associated with copper power supply cables, as well as current distortion from traditional PWM techniques.
Innovation Solution
A transformerless UPS system utilizing a multi-level two-stage DC-DC converter and a multi-level inverter to generate medium AC voltage without the need for an output transformer, incorporating a flying capacitor topology and space vector PWM control for efficient power conversion and harmonic reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a step-up transformer is used to step up battery voltage to medium voltage for data center power supply, then the voltage requirement is met, but the system size, cost, and energy losses increase
Solution Approach 1:
The patent removes the step-up transformer from the traditional UPS system architecture. Instead of using a transformer to step up battery voltage to medium voltage (6.6kV or 13.8kV), the invention directly generates medium voltage AC output through a multi-level inverter circuit that converts battery DC voltage without requiring transformer-based voltage transformation.
Solution Approach 2:
The patent replaces the mechanical/electromagnetic transformer system with an electronic multi-level inverter system. The inverter uses semiconductor switches and capacitor networks to directly synthesize medium voltage AC waves from DC battery input, substituting the traditional electromagnetic transformation mechanism with solid-state electronic conversion.
2Power
If a step-up transformer is used in the UPS system, then voltage conversion is achieved, but energy losses increase by approximately 5%
Solution Approach 1:
The patent replaces the electromagnetic transformer with an electronic multi-level inverter system that converts DC to AC directly at the desired voltage level. This electronic conversion process eliminates the copper losses and core losses inherent in transformer-based systems, achieving efficiency improvements of approximately 5% by avoiding transformer energy dissipation.
3Power
If traditional PWM techniques are used for power conversion, then voltage control is achieved, but current distortion increases
Solution Approach 1:
The patent employs a multi-level inverter architecture that segments the voltage output into multiple discrete levels (e.g., ±Vdc/2, 0, ±Vdc). This segmentation allows the synthesis of AC waveforms with reduced harmonic content compared to traditional two-level PWM inverters, as the stepped voltage approximation more closely resembles a sinusoidal waveform, thereby reducing current distortion.
Solution Approach 2:
The patent changes the voltage output parameters by generating multiple voltage levels instead of a single bipolar output. The multi-level voltage structure modifies the spectral characteristics of the output waveform, reducing harmonic distortion and improving power quality without requiring complex filtering.
4Device complexity
If medium voltage distribution is not used, then system simplicity is maintained, but copper cable size and cost increase by approximately 400%
Solution Approach 1:
The patent creates a UPS system that universally handles both low voltage and medium voltage applications through the same multi-level inverter architecture. This universal design enables direct connection to medium voltage distribution networks (6.6kV or 13.8kV), eliminating the need for separate transformer stages and reducing copper cable requirements by approximately 400% compared to traditional low voltage systems.
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 solution enhances efficiency to 98.5-99%, reduces the size and cost of copper cables, and minimizes losses and current distortion, providing a compact and efficient power supply for data centers.
Implementation Method 1
The DC-DC converter transforms a DC voltage from the energy storage device into a DC voltage
Implementation Method 2
The multi-level inverter converts the DC voltage into an AC voltage of medium level
Data Source
AI summary
Systems and methods for supplying power at a medium voltage from an uninterruptible power supply (UPS) to a load without using a transformer are disclosed. The UPS includes an energy storage device, a single stage DC-DC converter or a two-stage DC-DC converter, and a multi-level inverter, each of which are electrically coupled to a common negative bus. The DC-DC converter may include two stages in a unidirectional or bidirectional configuration. One stage of the DC-DC converter uses a flying capacitor topology. The voltages across the capacitors of the flying capacitor topology are balanced and switching losses are minimized by fixed duty cycle operation. The DC-DC converter generates a high DC voltage from a low or high voltage energy storage device such as batteries and/or ultra-capacitors. The multi-level, neutral point, diode-clamped inverter converts the high DC voltage into a medium AC voltage using a space vector pulse width modulation (SVPWM) technique. The UPS may also include a small filter to remove harmonics in the AC voltage output from the multi-level inverter.