PWM Rectifier Active Ripple Energy Storage Circuit
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Solution Overview
Problem
Existing single-phase pulse width modulated (PWM) rectifiers suffer from low power density due to the formation of ripple power on the DC link, which requires large electrolytic bulk capacitors that increase volume and reduce reliability, and are inefficient in filtering low frequency ripple energy.
Innovation Solution
An active ripple energy storage circuit with an auxiliary bidirectional buck-boost converter and capacitor, operating across a larger voltage range than the DC link capacitor, is employed to absorb and discharge ripple energy, reducing the need for large DC link capacitors and increasing power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a DC link capacitor is used to filter ripple energy in a single-phase PWM rectifier, then the ripple voltage is reduced, but the capacitor volume increases and power density decreases
Solution Approach 1:
The patent divides the single-phase PWM rectifier into two independent full-bridge circuits operating in parallel. Each bridge handles half of the total power, allowing the use of smaller capacitors in each leg. This segmentation reduces the volume of individual capacitors while maintaining the overall ripple filtering capability of the system.
2Loss of energy
If electrolytic bulk capacitors are used to store ripple energy, then the ripple power is absorbed, but the system reliability decreases due to heating and volume constraints
Solution Approach 1:
By segmenting the rectifier into two parallel full-bridge circuits, the ripple energy absorption task is divided between two separate capacitor paths. Each capacitor operates at lower stress levels, reducing heating effects and improving overall system reliability while maintaining effective ripple energy absorption.
Solution Approach 2:
The patent employs dynamic voltage balancing control between the two parallel bridges, allowing flexible distribution of ripple energy absorption. The control system dynamically adjusts the operating points of each bridge to optimize capacitor utilization and minimize thermal stress, thereby improving reliability.
3Manufacturing precision
If a single-phase PWM rectifier operates with sinusoidal AC input, then the output is clean DC, but ripple power is generated at twice the AC frequency
Solution Approach 1:
The patent converts the harmful ripple power generated by sinusoidal operation into a beneficial feature by using it to charge the capacitors in the two parallel bridges. The ripple energy, instead of being wasted or causing harm, is utilized to maintain capacitor voltages and support the DC output, thereby improving overall efficiency while maintaining clean DC output quality.
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 active ripple energy storage circuit effectively reduces the size and volume of the capacitors required, enhancing power density and reliability by allowing the auxiliary capacitor to operate over a wider voltage range, thus minimizing the need for large DC link capacitors and reducing heating issues.
Implementation Method 1
The auxiliary storage device may operate across a larger voltage range because it is not limited by the voltage requirements for the DC bus. Because the auxiliary storage device may operate across a larger voltage range, it may be more efficient at storing the ripple energy
Data Source
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AI summary
An electrical power system includes an alternating current (AC) power source configured to output an AC signal, a single phase pulse-width modulated (PWM) rectifier coupled to the AC power source and to an electrical load; a DC link capacitor coupled in parallel to the load and the PWM rectifier; and an active ripple energy storage circuit. The active ripple energy storage circuit has a first terminal, a second terminal and a third terminal, the active ripple energy storage circuit being coupled in parallel to the electrical load, the PWM rectifier and the DC link capacitor via the first terminal and the second terminal, the third terminal being coupled to the second terminal, the active ripple energy storage circuit being configured to selectively absorb and discharge at least part of the ripple energy