Transformerless Medium-Voltage UPS With Multilevel Conversion
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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 connects the battery through a DC-DC converter and inverter to the medium voltage grid, eliminating the bulky transformer component while maintaining the required voltage output capability
Solution Approach 2:
The patent replaces the electromagnetic transformation mechanism (transformer) with an electronic conversion mechanism (DC-DC converter and inverter). The transformerless UPS uses power electronic devices to convert DC battery voltage to AC medium voltage, substituting the mechanical/electromagnetic field-based transformer with an electronically controlled conversion process
2Power
If a step-up transformer is used in the UPS system, then voltage conversion is achieved, but energy losses increase by approximately 1-1.5%
Solution Approach 1:
The patent replaces the transformer's electromagnetic induction mechanism with electronic switching and control circuits. The DC-DC converter and inverter use solid-state power devices to convert voltages with significantly lower losses compared to transformer core and copper losses, achieving the 98.5-99% efficiency reported in the patent
3Ease of operation
If traditional PWM techniques are used for power conversion, then simple control is achieved, but current distortion and harmonics increase
Solution Approach 1:
The patent employs space vector PWM (SPWM) technique which modifies the control parameters and switching patterns compared to traditional PWM. SPWM uses a rotating reference frame and space vector mathematics to generate switching signals that produce sinusoidal output currents with reduced harmonics, improving power quality while maintaining control effectiveness
Solution Approach 2:
The patent incorporates feedback control mechanisms in the DC-DC converter and inverter stages. The control system continuously monitors output currents and voltages, adjusting switching duty cycles and phases to minimize harmonics and maintain sinusoidal waveforms, thereby reducing current distortion while maintaining stable operation
4Power
If high power cables are used to supply megawatt-range power to data centers, then power delivery is sufficient, but cable size and cost increase due to copper price increases
Solution Approach 1:
The patent changes the voltage parameter in the power transmission system by implementing a transformerless medium voltage UPS that outputs directly at 6.6kV or 13.8kV. By operating at higher voltage levels without transformation losses, the system reduces the current required for the same power delivery (P=VI), thereby reducing the copper cable cross-section and quantity needed
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 more compact and efficient power supply for data centers.
Implementation Method 1
The DC-DC converter generates a DC output voltage that is higher than the DC input voltage from the energy storage device
Implementation Method 2
The inverter converts the DC output voltage from the DC-DC converter to an AC output voltage
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.