Switched-mode power supply capacitor voltage balancing
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Solution Overview
Problem
Existing switching power supply systems for variable speed drives face challenges in balancing the voltages across multiple electrolytic buffer capacitors, leading to uneven leakage currents and reduced lifespan, necessitating the use of bulky and costly sharing resistors to mitigate these issues.
Innovation Solution
A switching power supply system with two input terminals, two series-connected buffer capacitors, and a primary inductive assembly, featuring a current injection module and a balancing circuit to automatically balance the leakage currents across the capacitors, eliminating the need for sharing resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If multiple electrolytic buffer capacitors are connected in series to reduce voltage stress on each capacitor, then the voltage rating requirement for each capacitor is reduced, but the leakage current imbalance between capacitors causes voltage imbalance and reduces system reliability
Solution Approach 1:
The control circuit continuously monitors the voltage across each capacitor and dynamically adjusts the switching duty cycles of individual switches to compensate for leakage current differences. This feedback mechanism maintains voltage balance across capacitors despite variations in leakage current, solving the reliability issue while keeping capacitors in series configuration.
Solution Approach 2:
The system changes the operating parameters (switching duty cycle, switching frequency) of individual capacitor branches based on real-time voltage measurements. By dynamically adjusting these parameters, the system compensates for leakage current imbalances and maintains equal voltage distribution across series-connected capacitors.
2Reliability
If sharing resistors are added in parallel with each buffer capacitor to balance voltages, then voltage balance is achieved, but the resistors increase device complexity, power consumption, and heat generation
Solution Approach 1:
The control circuit uses the existing switching devices and control infrastructure to actively balance capacitor voltages without requiring additional passive balancing resistors. The system serves its own balancing needs through intelligent control algorithms that adjust switching patterns based on real-time voltage measurements, eliminating the need for external balancing components.
Solution Approach 2:
The patent replaces the passive electrical balancing mechanism (resistors) with an active electronic control mechanism. Instead of using resistive voltage division, the system uses controlled switching and duty cycle adjustment to achieve voltage balance, substituting a more complex control system with simpler passive components.
3Reliability
If sharing resistors are used to balance capacitor voltages, then voltage distribution is improved, but power losses and heat generation increase
Solution Approach 1:
The control circuit continuously monitors capacitor voltages and adjusts switching duty cycles in real-time to maintain voltage balance. This active feedback control eliminates the need for continuous power dissipation through balancing resistors, as balance is achieved through controlled switching rather than resistive voltage division.
Solution Approach 2:
The system dynamically changes switching parameters (duty cycle, frequency) to achieve voltage balance without relying on fixed resistive elements. By adjusting these parameters based on real-time conditions, the system achieves balancing with minimal power loss compared to static resistor-based approaches.
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 effectively balances the voltages across the capacitors, reducing the need for sharing resistors, minimizing heat losses, and extending the lifespan of the capacitors while maintaining efficient power delivery.
Implementation Method 1
a primary inductive assembly connected in series with the switches, at least one secondary winding coupled magnetically with the primary inductive assembly
Implementation Method 2
at least one secondary winding coupled magnetically with the primary inductive assembly to deliver a DC output voltage
Data Source
Figure 1~2
Figure 3~6
AI summary
The system has a secondary winding (Ns) magnetically coupled to a primary inductive assemblies (Np1, Np2) to output direct current output voltage (Us). The assembly is connected in series between a positive input terminal (A2) and two MOSFETs or insulated gate bipolar transistor switches (SW1, SW2). A drain (D2) of the switch (SW2) has a current injection module for injecting current at a mid-point (PMC) of two buffer capacitors (CB1, CB2). One end of a balancing circuit (15) is connected to the mid-point, to balance leakage currents of the capacitors. An independent claim is also included for a speed variator.