AC-DC Converter Harmonic Control via Bidirectional Switching
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing alternating-current direct-current converters face challenges in controlling harmonic currents and improving power factors while minimizing costs, as they often require high-frequency PWM control, complex circuit configurations, large reactors, increased power consumption, or insufficient harmonic reduction.
Innovation Solution
An alternating-current direct-current converter with a rectifier, two series-connected capacitors, and bidirectional switches, where diodes are inversely parallel to the capacitors, and control means drive the switches to maintain sinusoidal terminal voltages and improve power factors, allowing for a more compact reactor and reduced switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If high-frequency PWM control is used to control harmonic currents and improve power factor, then the power factor is improved and harmonic currents are controlled, but the noise increases and costs increase
Solution Approach 1:
The patent applies periodic action by switching the bidirectional switches at specific periodic intervals synchronized with the AC power supply cycle. The switching occurs at predetermined timing within each half-cycle (e.g., when the reactor current reaches specific values), rather than using continuous high-frequency PWM. This periodic switching at line frequency or sub-harmonic frequencies reduces noise while maintaining effective harmonic control and power factor improvement.
2Object-generated harmful factors
If a large reactor is used to control harmonic currents, then harmonic control is improved, but the device size and cost increase
Solution Approach 1:
The patent employs dynamic switching control where bidirectional switches are activated at specific moments during the AC cycle to dynamically adjust the reactor current waveform. This dynamic control allows a smaller reactor to achieve the same harmonic filtering effect that would require a much larger passive reactor, because the switching actively shapes the current to be sinusoidal rather than relying solely on the reactor's inherent impedance.
Solution Approach 2:
The patent changes the operating parameters by controlling the switching timing and duration of the bidirectional switches. By adjusting when and how long the switches remain ON during each half-cycle, the system can control the reactor current waveform shape and amplitude, achieving harmonic suppression with a smaller reactor size compared to passive LC filter approaches.
3Object-generated harmful factors
If switching frequency is reduced to lower noise and cost, then noise and cost are reduced, but harmonic control capability may be compromised
Solution Approach 1:
The patent implements feedback control by detecting the reactor current and using this information to determine the appropriate switching timing. The control unit monitors the reactor current waveform and switches the bidirectional switches at moments when the current reaches predetermined values, ensuring that the current remains sinusoidal even at lower switching frequencies. This feedback mechanism maintains harmonic control effectiveness without requiring high-frequency switching.
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 configuration achieves a sinusoidal converter voltage, improves power factors, reduces noise-related costs, and provides a more compact reactor with lower switching frequency, effectively controlling harmonic currents and reducing overall costs.
Implementation Method 1
a rectifier which rectifies an alternating current voltage and outputs a direct current voltage
Implementation Method 2
a capacitor to which the direct current voltage output from the rectifier or the direct current voltage output via the reactor is applied via a diode, the capacitor acquiring a smoothed direct current voltage
Implementation Method 3
a reactor connected in series to an alternating current input side or a direct current output side of the rectifier
Data Source
AI summary
Provided is an alternating-current direct-current converter capable of controlling a harmonic current and improving a power factor at reduced costs. The alternating-current direct-current converter includes two capacitors connected in series between output terminals of a rectifier; a first switch connected between one input terminal of the rectifier and a connection point of the capacitors; a second switch connected between the other input terminal of the rectifier and the connection point of the capacitors; a voltage detector which detects terminal voltages of the capacitors; a current detector which detects a current input from the alternating current power supply; and a control means which drives and controls the first switch and the second switch, in which the control means drives and controls the first switch and the second switch such that the terminal voltages of the capacitors are fixed and a power supply power factor is improved using an active power component and a reactive power component obtained by conversion of detection results of the current detector and detection results of voltage detector.