PFC Current Shaping With DC Offset Harmonic Control
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Solution Overview
Problem
Existing power supply systems face challenges in reducing harmonic content in current drawn from the grid, especially at higher power levels, and fail to actively damp resonance circuits formed by grid impedances and EMI capacitors, leading to potential malfunctions or destruction.
Innovation Solution
A method to generate a reference signal for a current regulator in a PFC circuit by adding a value dependent on the current conduction angle, increasing lower harmonic components and decreasing higher harmonic components, thereby reducing grid distortion and enabling higher input power draw without exceeding harmonic limits, and actively damping resonance circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a standard sinusoidal reference signal is used for PFC current regulation, then the control is simple and stable, but the harmonic content of the input current exceeds regulatory limits at higher power levels
Solution Approach 1:
The patent modifies the reference signal parameters by adding a DC offset component to the standard sinusoidal signal. This parameter change transforms the current waveform to reduce lower-order harmonics (5th, 7th) while maintaining the fundamental frequency, thereby reducing total harmonic distortion to comply with IEC 61000-3-2 standards without complicating the control structure
Solution Approach 2:
The patent uses a simplified mathematical model to generate the modified sinusoidal reference signal that copies the essential characteristics of ideal PFC current waveforms. By using a predefined formula with DC offset instead of complex real-time harmonic compensation algorithms, the system achieves low harmonic content while maintaining control simplicity
2Object-generated harmful factors
If the current conduction angle is reduced to lower harmonics, then the power factor improves, but the input power capability is limited to below 500W
Solution Approach 1:
The patent changes the reference signal formulation to include a DC offset term that enables operation at higher power levels. This parameter modification allows the PFC circuit to maintain reduced harmonic content while increasing the current conduction angle and input power capability beyond the 500W limitation of conventional approaches
Solution Approach 2:
The patent implements dynamic adjustment of the reference signal characteristics based on operating conditions. The modified sinusoidal signal with DC offset dynamically adapts to different power levels, enabling the system to maintain optimal harmonic performance across a wide power range from low to high power applications
3Object-generated harmful factors
If passive PFC choke or per-phase active PFC circuits are used for three-phase input, then the harmonic content is reduced, but the device complexity and component count increase
Solution Approach 1:
The patent creates a universal PFC control solution that works effectively for both single-phase and three-phase input configurations using the same modified sinusoidal reference signal approach with DC offset. This multi-functional control method eliminates the need for separate passive chokes or complex per-phase active PFC circuits, reducing overall system complexity while maintaining harmonic compliance across different phase configurations
Data Source
Figure 1~4
Figure 2
Figure 5~6
AI summary
A PFC circuit (10) according to the invention is connected to a grid (1), includes an input filter (2) and a rectifier (3) connected to a converter (4). A control circuit (5) generates the reference current for the current regulator of the converter (4) that controls its input current. Thereby, the reference current is generated by adding an offset current (I0) to a standard reference current and adapting the magnitude of the standard reference current to compensate for a change of the input power resulting from the addition of the offset current (I0). However, due to the addition of the offset current (I0) the magnitudes of some lower harmonic components of the input current of the power supply unit are increased and the magnitudes of some higher harmonic components of the input current are decreased such that the power supply may draw more current from the grid.