UPS Converter Circuit for Fast Filter Capacitor Discharge
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Solution Overview
Problem
Existing UPS systems face challenges in efficiently and quickly discharging filter capacitors to prevent current inrush during re-closure of contactors, especially with increasing converter ratings, leading to potential reliability issues and inefficiencies.
Innovation Solution
A UPS converter circuit with a controlled switching element and split DC output capacitors, utilizing a PWM-modulated signal to alternately discharge filter capacitors based on polarity, minimizing current through an inductor to the DC-link mid-point, thereby ensuring rapid discharge without additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive discharge with parallel resistor is used, then capacitor discharge time constant is extended, but discharge speed is reduced and losses increase
Solution Approach 1:
The patent employs a dynamic discharge mechanism where the controlled switching element actively adjusts the discharge path based on operational requirements. The switching element can connect the filter capacitor to either the plus DC capacitor or minus DC capacitor, enabling controlled bidirectional discharge that adapts to different operational states, thereby achieving fast discharge without excessive losses.
Solution Approach 2:
The filter capacitor discharges through the existing DC link capacitors (plus and minus DC capacitors) rather than requiring external discharge resistors. This self-service mechanism utilizes the system's own energy storage elements to absorb the discharge energy, eliminating the need for separate passive discharge components and reducing overall losses.
2Power
If converter rating is increased, then filter capacitance increases linearly, but discharge capability does not scale proportionally
Solution Approach 1:
The controlled switching element serves multiple functions: it operates as part of the main converter circuit during normal operation and simultaneously provides the discharge path for the filter capacitor. This multi-functionality allows the same component to handle both power conversion and capacitor discharge tasks, enabling discharge capability to scale with converter rating without additional dedicated discharge components.
Solution Approach 2:
The discharge function is merged with the main converter circuit operation. The filter capacitor discharge path is integrated into the existing DC link structure, combining the energy storage function of the DC capacitors with the discharge function. This integration allows the discharge capability to naturally scale with the converter rating as the DC link capacitors increase in size.
3Speed
If input contactor recloses quickly after opening, then system response time is reduced, but current inrush is magnified
Solution Approach 1:
The filter capacitor is actively discharged before the input contactor recloses by controlling the switching element to connect the capacitor to the DC link capacitors. This preliminary discharge action reduces the voltage on the filter capacitor to a safe level before reclosure, preventing dangerous inrush currents while allowing quick system response.
Solution Approach 2:
The control circuit monitors the operational state and automatically activates the discharge mechanism when needed, such as after contactor opening. This feedback-based control ensures the capacitor is discharged at the appropriate moment before reclosure, dynamically preventing inrush currents while maintaining fast system response capability.
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 enables fast and efficient discharge of filter capacitors, reducing inrush current and improving reliability, allowing for quicker restarts and reduced component requirements, thus enhancing UPS system performance.
Implementation Method 1
The controlled switching element is configured to be controlled such that a current from the AC point via the inductor element flows alternatingly to either the plus DC capacitor in case of a positive polarity or the minus DC capacitor in case of a negative polarity
Data Source
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AI summary
Uninterruptible power supply converter circuit (100, 200, 300, 400), comprising a controlled switching element (102), a filter capacitor (104), and a split DC capacitor comprising a plus DC capacitor (106) and a minus DC capacitor (116) split at a DC-link mid-point (112). The controlled switching element (102), the filter capacitor (104), the plus DC capacitor (106) and the minus capacitor (116) are connected to each other at the DC-link mid-point (112) on a respective first side. A second side of the input filter capacitor (104) at an AC point (114) is coupled via an inductor element (110) to a second side of the controlled switching element (102), the second side of the controlled switching element being coupled to the second side of the plus DC capacitor (106) and the minus capacitor (116). The controlled switching element (102) is configured to be controlled such that a current from the AC point (114) via the inductor element (110) flows alternatingly to either the plus DC output capacitor (106) or the minus DC capacitor (116), and to the DC-link mid-point, respectively, thereby discharging the input filter capacitor (104).