Diode Rectifier Harmonic Reduction via Control Device Injection
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Solution Overview
Problem
Diode rectification methods generate high levels of undesired harmonics in the input current, leading to inefficiencies and compliance issues with harmonic standards, particularly in AC/DC conversion for motor applications.
Innovation Solution
A circuit arrangement with a DC voltage controller and control device that impresses specific harmonic current signals onto the DC current, using a storage capacitor to reduce harmonic content in the input current, including the use of 5th, 11th, and 17th harmonics to absorb energy from the grid while minimizing other harmonics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If diode rectification method is used, then device complexity is reduced and temperature rise of power switching elements is lower, but harmonic content in input current increases significantly
Solution Approach 1:
A control device is introduced as an intermediary between the AC power supply and the diode rectifier. This control device generates harmonic current signals (5th, 11th, 17th harmonics) that are superimposed on the rectifier input, causing the diode rectifier to absorb these harmonics and reduce the overall harmonic content in the input current while maintaining the simple diode rectifier structure
Solution Approach 2:
The invention converts the harmful harmonic currents into a beneficial feature by deliberately injecting specific harmonic signals (5th, 11th, 17th) that the diode rectifier absorbs. This transforms the rectifier's natural tendency to generate harmonics into a mechanism for harmonic absorption and cancellation, reducing total harmonic distortion while maintaining rectification efficiency
2Object-generated harmful factors
If PWM rectification method is used, then harmonic content in input current is reduced, but device complexity and cost increase due to additional switching elements
Solution Approach 1:
The invention replaces the expensive and complex PWM switching elements with inexpensive diode rectifier components. By using a control device to generate harmonic signals that the simple diode rectifier absorbs, the system achieves PWM-like harmonic performance using much simpler, cheaper, and more reliable diode-based components
Solution Approach 2:
The invention substitutes the active PWM switching mechanism with a passive diode rectifier system controlled by harmonic signal injection. Instead of using complex electronic switching to achieve harmonic reduction, the system uses signal processing and harmonic resonance principles to achieve the same effect with simpler components
3Object-generated harmful factors
If traditional EMC filters are used to reduce harmonics, then harmonic content is reduced, but filter volume and cost increase
Solution Approach 1:
The invention extracts the harmonic reduction function from the traditional EMC filter and relocates it to the rectifier input stage through control device signal injection. This allows harmonic cancellation to occur before the rectifier, eliminating or reducing the need for large downstream filter components
Solution Approach 2:
The control device performs preliminary harmonic cancellation by injecting compensating harmonic signals before they enter the rectifier. This preliminary action prevents harmonics from being generated in the first place, eliminating the need for large filter volumes that would be required if harmonics were addressed after rectification
Data Source
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AI summary
The invention relates to a method and a circuit arrangement (1) for reducing the harmonics of the input current of a rectifier (10) connected to an AC power supply (N) for providing a DC voltage for a DC load (40) having a storage capacitor (CZK), comprising a DC voltage controller (20) connected downstream of the rectifier (10) and a control device (30) configured to impose a specific current on the DC voltage controller (20), in particular to impose a harmonic current signal in the form of an approximate DC current, so that the harmonic content in the input current is reduced.