THDi Control Circuit for UPS Power Factor Correction
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Solution Overview
Problem
Current power factor correction circuits for small-capacity UPS applications have limitations in achieving low total harmonic current distortion (THDi) across a wide range of AC power inputs, leading to inefficiencies and increased costs due to complex digital control systems.
Innovation Solution
A THDi control circuit comprising a power factor correction circuit with a boost unit, inverter unit, and feedback unit, utilizing a current detection element to generate a sensing current for adjusting the pulse width modulation signal, allowing the circuit to operate effectively within a wider AC power range (190Vac to 250Vac) with a THDi of approximately 5%, enhancing adaptability and reducing distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a conventional power factor correction circuit is used for small-capacity UPS applications, then the circuit can operate within a limited AC power range (220V to 230V), but the total harmonic current distortion (THDi) remains high (approximately 10%) and the adaptability to wider voltage ranges is poor
Solution Approach 1:
The patent implements dynamic adjustment of the pulse width modulation signal duty cycle based on real-time detection of input voltage and current. The control circuit continuously monitors the AC power input conditions and dynamically modifies the switching characteristics of the power factor correction circuit to maintain low THDi across the expanded voltage range of 190V to 250V, transforming a static circuit into an adaptive dynamic system
Solution Approach 2:
The patent incorporates a feedback mechanism where the control circuit detects output voltage and current, calculates output power, and uses this information along with detected input current to generate appropriate pulse width modulation signals. This closed-loop feedback system enables the circuit to automatically adjust its operation to maintain low THDi across varying AC power conditions
2Object-generated harmful factors
If digital control with advanced digital signal processors is used to implement power factor correction circuits, then high performance power factor correction results can be achieved, but the cost and circuit complexity dramatically increase
Solution Approach 1:
The patent replaces expensive advanced digital signal processors with a simpler, more cost-effective control circuit implementation. The solution uses basic computational functionality to calculate output power from detected voltage and current, generating pulse width modulation signals through straightforward control logic rather than complex digital signal processing, thereby dramatically reducing cost while maintaining acceptable performance
Solution Approach 2:
The patent extracts and isolates the essential control functions needed for power factor correction, separating them from complex digital signal processing capabilities. By implementing only the necessary calculations for output power determination and pulse width modulation generation, the design eliminates unnecessary complexity and cost associated with over-engineered digital controllers
Data Source
AI summary
A total harmonic current distortion (THDi) control circuit includes a power factor correction circuit and a control circuit. The power factor correction circuit includes a boost unit, an inverter unit, and a feedback unit. The boost unit includes a switch element and a current detection element series-coupled to the switch element. The feedback unit operatively detects an output voltage and an output current of the power factor correction circuit. The control circuit calculates an output power according to the output voltage and the output current, and calculates an input voltage and an input current according to the output power. The control circuit outputs a pulse width modulation signal and controls a conduction current generated by the switch element according to the input current. The control circuit adjusts the duty cycle of the pulse width modulation signal according to the conduction current detected by the current detection element.