AC-DC Rectifier Segmented Capacitor Topology
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Solution Overview
Problem
Existing AC-DC rectifiers in datacenters face issues with low efficiency, high switching losses, and reliability due to the use of internal electrolytic capacitors, which limit their power density and operational performance.
Innovation Solution
A non-isolated AC-DC rectifier topology is developed that minimizes the use of electrolytic capacitors, employing a front-end full-bridge Power Factor Correction (PFC) converter with single boost and buck switches operating in both positive and negative half cycles to charge capacitors efficiently, reducing switching losses and using polypropylene capacitors for improved reliability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If internal electrolytic capacitors are used in AC-DC rectifiers, then the rectifier can be manufactured with conventional components, but the reliability and power density are reduced
Solution Approach 1:
The output capacitor function is segmented into two separate capacitors (first output capacitor and second output capacitor) that are alternately charged during positive and negative half cycles respectively. This segmentation allows each capacitor to be smaller and eliminates the need for large electrolytic capacitors, thereby improving reliability while managing complexity through functional division.
Solution Approach 2:
The system employs periodic action by alternating the charging of the two output capacitors with each half cycle of the AC input. During positive half cycles, the first capacitor is charged; during negative half cycles, the second capacitor is charged. This periodic charging pattern enables the use of smaller capacitors with lower ESR, improving reliability without requiring complex capacitor configurations.
2Loss of energy
If conventional AC-DC rectifier topologies are used, then the design is straightforward, but switching losses are high and efficiency is low
Solution Approach 1:
The rectifier employs dynamic switching of the first and second switches based on the polarity of the AC input cycle. The controller dynamically adjusts which switch is active during each half cycle, enabling the output circuitry to efficiently charge the appropriate capacitor. This dynamic operation reduces switching losses by ensuring switches are properly timed and prevents simultaneous conduction, thereby improving rectification efficiency.
3Quantity of substance
If electrolytic capacitors are used for output filtering, then the filtering function is achieved, but the power density is limited
Solution Approach 1:
The total capacitance requirement is segmented into two separate capacitors that share the filtering function alternately. Each capacitor only needs to handle half-cycle charging, allowing the use of smaller, lower-volume capacitors. This segmentation dramatically reduces the total capacitor volume while maintaining adequate filtering performance, thereby increasing power density.
Solution Approach 2:
The invention changes the operational parameters of the capacitors by switching between two capacitors at line frequency rather than using a single capacitor continuously. This parameter change allows each capacitor to be sized for half the total energy storage requirement, reducing individual capacitor volumes and total ESR, which increases power density while maintaining filtering effectiveness.
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 solution achieves high reliability, high power density, low switching losses, and high efficiency by reducing the reliance on electrolytic capacitors and optimizing the charging process, resulting in improved performance and reduced switching voltages.
Implementation Method 1
a front-end full-bridge Power Factor Correction (PFC) converter with single boost and buck switches operating in both positive and negative half cycles
Implementation Method 2
a first output capacitor coupled between the positive output and ground, a second output capacitor coupled between the negative output and ground
Data Source
AI summary
According to one aspect, embodiments of the invention provide a method for operating an AC-DC rectifier, the method comprising receiving, with a converter, input AC power having an input AC voltage waveform, controlling, during a positive half line cycle of the input AC voltage waveform, the converter to couple a second DC bus to ground, controlling, during the positive half line cycle of the input AC voltage waveform, the converter to maintain a positive DC link voltage on a first DC bus, controlling, during the positive half line cycle of the input AC voltage waveform, output circuitry to charge a first output capacitor and provide a positive output voltage to a positive output, and discharging, during the positive half line cycle of the input AC voltage waveform, a second output capacitor to provide a negative output voltage to a negative output.