Switching Power Converter Filter for Radiated Emission Reduction
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Solution Overview
Problem
Switching power converters, such as motor drives, generate radiated emissions due to rapid switching, which can interfere with other electronic equipment, and existing solutions like ferrite cores and common mode inductors increase conductor size and expense without proportional emission reduction.
Innovation Solution
A filter is implemented in motor drives, using capacitors connected in parallel between output phases and a common connection, such as ground, to minimize current conducted by the capacitors, reducing radiated emissions effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If ferrite core or common mode inductor is used to reduce radiated emissions, then emissions are reduced, but conductor size and expense increase
Solution Approach 1:
A common mode choke is introduced as an intermediary component between the inverter output and the motor. This choke selectively attenuates common mode noise currents (radiated emissions) while allowing differential mode power currents to pass through with minimal impedance. The choke acts as a mediator that separates and treats different current modes differently, reducing emissions without requiring oversized conductors throughout the entire system.
Solution Approach 2:
The invention changes the impedance parameter of the output circuit by introducing a common mode choke with frequency-dependent characteristics. The choke presents high impedance to high-frequency common mode noise currents while maintaining low impedance to low-frequency differential mode power currents. This parameter change allows selective filtering of emissions without affecting the overall current-carrying capacity of the system conductors.
2Object-generated harmful factors
If ferrite core or common mode inductor is used to reduce radiated emissions, then emissions are reduced, but device cost increases
Solution Approach 1:
The common mode choke serves as a cost-effective intermediary solution that targets only the noise problem rather than requiring oversized conductors throughout the entire system. By placing the choke at a specific location (inverter output), the system pays for emission reduction only where needed, rather than increasing conductor size everywhere, thus reducing overall device cost.
Solution Approach 2:
The invention segments the current path into differential mode (power) and common mode (noise) components, and applies different impedance characteristics to each segment. The common mode choke is placed only in the common mode path, allowing differential mode power currents to flow through low-impedance conductors. This segmentation enables cost-effective emission reduction without requiring expensive oversized conductors throughout the entire system.
3Ease of operation
If rapid switching is used to generate desired average output voltage, then output voltage control is improved, but radiated emissions increase
Solution Approach 1:
The common mode choke acts as an intermediary that decouples the rapid switching operation from the radiated emissions problem. It allows the inverter to maintain rapid switching for precise output voltage control while the choke absorbs and attenuates the resulting common mode noise currents, preventing them from radiating outward. This mediator enables both rapid switching and emission reduction to coexist.
Solution Approach 2:
The invention converts the harmful rapid switching action into a beneficial control mechanism by using pulse width modulation (PWM) techniques. The rapid switching generates the desired average output voltage through controlled duty cycles, and the common mode choke then handles the resulting emissions. The harm of rapid switching is transformed into a controllable parameter that achieves precise voltage regulation, with emissions managed separately by the choke.
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 filter significantly reduces radiated emissions by drawing noise current through a shielded path, minimizing interference with other electronic equipment while maintaining efficient output current handling without the need for oversized conductors.
Implementation Method 1
A capacitor is electrically connected between each terminal of the output and one of the ground connections
Data Source
AI summary
A filter for reducing radiated emissions in switching power converters such as a motor drive is disclosed. The switching power converter modulates a DC voltage input to generate a desired AC voltage output. Capacitors are connected in parallel between each output phase and a common connection, which may be a ground connection. The magnitude and layout of the capacitors are selected to minimize current conducted by the capacitors. The capacitors may be surface mount technology located proximate to the switching devices or the capacitors may be incorporated in the circuit board on which the switching devices are mounted. The filter may be applied to any of the switching elements in a motor drive, such as the inverter section, an active rectifier section, or a switched mode power supply.