Active Damping of Common Mode Resonance in Power Converters
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Solution Overview
Problem
Power conversion systems face issues with common mode resonance, which can lead to insulation failure and thermal issues due to high peak voltages and magnetic saturation, and existing solutions like damping resistors increase costs and reduce reliability.
Innovation Solution
The implementation of active damping in power conversion systems through special inverter or rectifier switching to mimic virtual resistors connected in parallel with capacitors, allowing for selective activation to mitigate common mode resonance currents and associated adverse effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If damping resistors are connected to the output neutral node to damp common mode resonance, then common mode resonance is suppressed, but system cost, size and reliability deteriorate due to high wattage requirements
Solution Approach 1:
The patent replaces the passive mechanical damping resistor with an active control system that uses switching devices and control circuits to generate damping effect. The control system processes feedback signals and generates compensating control signals to suppress common mode resonance without requiring physical damping resistors, thereby eliminating the reliability issues associated with high-power resistor components.
Solution Approach 2:
The patent introduces an intermediary control system that acts between the common mode resonance source and the damping effect. This control system uses feedback from the resonant loop and generates compensating signals through switching devices, serving as an intermediary mechanism that achieves damping without direct connection of high-power resistors to the neutral node.
2Object-affected harmful factors
If damping resistors are connected to the output neutral node to damp common mode resonance, then common mode resonance is suppressed, but device complexity and space requirements increase
Solution Approach 1:
The patent makes the switching devices and control circuits serve multiple functions: they perform both the primary power conversion function and the secondary common mode resonance damping function. By utilizing existing components for dual purposes, the system avoids adding separate damping resistor components, thereby reducing overall device complexity and space requirements.
Solution Approach 2:
The patent merges the damping function with the existing power conversion circuitry by integrating the damping control into the switching devices and control circuits. This consolidation eliminates the need for separate damping components and reduces the overall system complexity compared to adding independent damping resistors.
3Object-affected harmful factors
If high wattage damping resistors are used to suppress common mode resonance, then resonance currents are reduced, but power loss and thermal issues increase
Solution Approach 1:
The patent employs periodic switching action of the switching devices to generate the damping effect. By periodically switching the devices based on feedback signals, the control system creates an active damping effect that suppresses resonance currents without the continuous power dissipation inherent in passive resistor-based damping, thereby reducing energy loss.
Solution Approach 2:
The patent replaces the energy-dissipating resistor mechanism with an active control mechanism that uses switching devices and feedback control. This substitution transforms the damping approach from passive energy dissipation to active energy management, reducing continuous power loss while maintaining effective suppression of resonance currents.
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 approach effectively dampens common mode resonance without the need for additional damping resistors, improving system reliability and reducing costs while maintaining efficient operation.
Implementation Method 1
One example is a pulse width modulated (PWM) current source converter used in high-power motor drives with a switching rectifier with AC input power being selectively switched
Implementation Method 2
A common mode choke can be employed to absorb common mode voltages, where the input side line neutral and the neutral of the motor load are connected to form a loop consisting of line side capacitance, a rectifier circuit, the link choke, an output inverter and the motor side capacitance. The high impedance of the CM choke results in a low amplitude common mode current flow through the loop
Implementation Method 3
However, the energy storage components in the common mode loop form a resonance, which can be excited by the back emf of the motor operating at certain speeds leading to excessive oscillatory current thru the common mode choke
Implementation Method 4
The present disclosure presents power conversion systems and methods for damping common mode resonance in which special inverter or rectifier switching is employed to mimic the presence of one or more virtual resistors connected in parallel with the output or input capacitor(s)
Data Source
AI summary
Power conversion systems and methods are presented for damping common mode resonance, in which inverter or rectifier switching control signals are selectively modified according to a damping resistance current value computed using a predetermined virtual damping resistance value in parallel with an output or input capacitor and a measured output or input voltage value to mitigate or reduce common mode resonance in the converter.