AC Converter Zero-Crossing Switching Pulse Density Modulation
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Solution Overview
Problem
Conventional AC converters for converting high-frequency AC power from wireless power transmission systems to low-frequency AC power suffer from efficiency losses due to power conversion to DC and switching losses, as well as cost and durability issues related to capacitor use.
Innovation Solution
The AC converter performs switching operations when the input high-frequency AC voltage is zero, using pulse density modulation to directly convert the AC voltage to a three-phase AC voltage with a lower frequency, eliminating the need for DC conversion and reducing switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional inverter technology is used to convert high-frequency AC power to low-frequency AC power through DC conversion, then frequency conversion is achieved, but power loss increases and conversion efficiency decreases
Solution Approach 1:
The patent extracts and eliminates the DC conversion stage from the conventional AC-DC-AC conversion process. By removing this intermediate step, the system directly converts high-frequency AC to low-frequency AC through pulse density modulation, thereby eliminating the power losses associated with DC conversion while maintaining effective frequency conversion.
Solution Approach 2:
Instead of following the conventional approach of converting AC to DC and then DC to AC, the patent inverts the process by directly modulating the high-frequency AC input to produce low-frequency AC output. This inversion eliminates the need for DC conversion and reduces overall power loss.
2Loss of energy
If multiple switching elements are used for AC to DC and DC to AC conversion, then frequency conversion is achieved, but switching losses increase
Solution Approach 1:
The patent removes the dual conversion stages (AC-DC and DC-AC) that require multiple switching elements. By implementing direct pulse density modulation on the high-frequency AC input, the system achieves frequency conversion with minimal switching operations, thereby reducing switching losses and improving conversion efficiency.
3Ease of manufacture
If rectifying section with capacitor is used for AC to DC conversion, then power conversion is achieved, but cost and durability problems occur
Solution Approach 1:
The patent extracts and eliminates the rectifying section with capacitor from the conversion system. By using direct pulse density modulation on the high-frequency AC input, the system achieves frequency conversion without requiring expensive and less durable capacitor-based rectification, thereby reducing cost and improving durability while maintaining conversion efficiency.
4Device complexity
If high-frequency AC power is converted to DC power and then to low-frequency AC power, then frequency conversion is achieved, but device complexity increases
Solution Approach 1:
The patent removes the intermediate DC conversion stage and associated components (rectifying section, capacitor, multiple switching elements for DC-AC conversion). This simplification reduces device complexity while maintaining effective frequency conversion through direct pulse density modulation, thereby improving conversion efficiency.
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
An AC converter includes: a switching section 101, which converts the input AC voltage in response to a control signal and which outputs the converted voltage to a phase that has been selected in accordance with the control signal; a filter section 104, which filters out high frequency components from the converted voltage, thereby converting the converted voltage into the output AC voltage; and a switching control section 103, which performs a pulse density modulation on a phase-by-phase basis and in response to a reference signal with the frequency fl, which is associated with the output AC voltage of each phase, synchronously with a zero cross of the input AC voltage, thereby generating the control signal according a pulse generation status by the pulse density modulation and the polarity of the input AC voltage and sending out the control signal to the switching section 101.