Switched Capacitor Line for AC to DC Power Factor Correction
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Solution Overview
Problem
Conventional AC to DC conversion methods face issues with low power factor, large capacitor size, and harmonic generation, especially in medium and high power applications, requiring significant circuitry for harmonic suppression and load switching.
Innovation Solution
The use of a switched capacitor line with a bi-directional switch comprising oppositely oriented uni-directional switches, controlled to manage capacitance charging and discharging, reducing the need for large smoothing capacitors and minimizing harmonic generation, while increasing the power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a large smoothing capacitor is used in parallel with the bridge rectifier to smooth out voltage variations, then the output voltage stability is improved, but the physical size and capacitance value increase significantly
Solution Approach 1:
The patent applies dynamic switching control to the capacitor, transitioning it from a static always-connected component to a dynamically controlled element. The capacitor is switched in only during specific portions of the AC cycle when needed for voltage regulation, and switched out during other portions, thereby maintaining voltage stability while dramatically reducing the average capacitance requirement and physical size
Solution Approach 2:
The patent implements periodic switching of the capacitor in synchronization with the AC input cycle. The capacitor is connected during specific intervals (e.g., during voltage peaks or when voltage drops below a threshold) and disconnected during other intervals, creating a periodic action that maintains output stability while minimizing capacitor size requirements
2Productivity
If conventional rectifier arrangements are used for AC to DC conversion, then the conversion function is achieved, but the power factor remains low (0.3-0.6)
Solution Approach 1:
The patent uses dynamic switching control to regulate the capacitor connection timing, which directly influences the input current waveform. By switching the capacitor in and out at optimally timed moments during the AC cycle, the system shapes the input current to be more in phase with the input voltage, thereby improving the power factor from the conventional 0.3-0.6 range to significantly higher values
Solution Approach 2:
The patent implements feedback control by monitoring the output voltage and using this information to control the switching timing of the capacitor. The switch is controlled based on the detected voltage level, creating a closed-loop system that maintains optimal power factor by adjusting capacitor connection timing in response to actual voltage conditions
3Productivity
If conventional rectifier arrangements are used, then the basic conversion is achieved, but harmonic generation in the current waveform occurs
Solution Approach 1:
The patent employs periodic switching of the capacitor in synchronization with the AC cycle to shape the input current waveform. This periodic action ensures that current is drawn in a more sinusoidal pattern rather than the distorted waveform produced by conventional rectifiers, thereby reducing harmonic generation without requiring additional suppression circuitry
Solution Approach 2:
The patent converts the potentially harmful effect of capacitor switching into a beneficial outcome. By carefully timing the capacitor switching events, the system uses the switching action itself to shape the current waveform and reduce harmonics, rather than the switching creating additional distortion that would require separate suppression circuitry
4Object-generated harmful factors
If circuitry for harmonic suppression is incorporated, then harmonic generation is reduced, but the device complexity increases
Solution Approach 1:
The patent makes the capacitor serve multiple functions simultaneously: it acts as a smoothing element for voltage regulation, a power factor correction device, and a harmonic reduction mechanism. This multi-functionality eliminates the need for separate harmonic suppression circuitry, thereby reducing device complexity while still achieving effective harmonic reduction
Solution Approach 2:
The patent enables the capacitor and its switching mechanism to self-regulate the harmonic content of the input current. The controlled switching of the capacitor inherently shapes the current waveform to reduce harmonics without requiring additional active compensation circuitry or complex control systems, allowing the system to self-correct its own harmonic issues
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 achieves a significantly higher power factor of up to 0.895, reduces capacitor size by 90%, and minimizes harmonic generation, simplifying power supply conversion without the need for additional harmonic suppression circuitry, particularly beneficial in medium and high power applications.
Implementation Method 1
a capacitance (18) and a bi-directional switch (20). The switch (20) is operable to control the timing of charging and discharge of the capacitance (18)
Data Source
Figure 1~3
Figure 4a~5c
Figure 6a~7c
AI summary
An electrical conversion apparatus is described which comprises a bridge rectifier (10) having an input side and an output side, and a switched capacitor line (16) arranged in parallel with the output side of the bridge rectifier (10), the switched capacitor line (16) comprising a capacitance (18) and a switch (20) arranged in series with one another so that the switch (20) can control charging and discharging of the capacitance (18). A method of electrical conversion is also disclosed wherein when the output voltage of the bridge rectifier is above a threshold level (26) and is rising the switch is closed so that the capacitance charges and a load is satisfied from the output of the bridge rectifier, when the output of the bridge rectifier is above the threshold level (26) and is falling the switch is opened so that the capacitance is isolated from the load, the load still being satisfied by the output of the bridge rectifier, and when the output of the bridge rectifier is below the threshold level (26), the switch is closed so that the load is served by discharge of the capacitance. The threshold level (26) may be dynamically controlled, for example in response to the output of a monitor circuit (32).