PFC Feedforward Control for Stable Vbulk Under Step Loads
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Solution Overview
Problem
Conventional power factor correctors (PFCs) experience significant overshoot or undershoot in output voltage when the DC/DC converter output experiences a high step load, disrupting stability and affecting dynamic load response.
Innovation Solution
A method and device for controlling a PFC, where the PFC controller receives a signal from the DC/DC controller indicating the load, derives an expected output control signal to stabilize the output voltage, and configures the voltage controller accordingly to maintain stability of the output voltage Vbulk.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the PFC voltage control loop responds quickly to load changes, then the dynamic load response improves, but the output voltage ripple increases and distorts the current reference signal affecting power factor
Solution Approach 1:
The patent applies preliminary action by using feedforward control to anticipate load changes before they affect the output voltage. The controller receives load information in advance and adjusts the voltage control signal proactively, preventing voltage drops or overshoots before they occur. This allows the system to respond to load changes without waiting for the slow feedback loop to detect the voltage deviation.
Solution Approach 2:
The patent introduces an intermediary feedforward control path that mediates between the load information and the voltage control signal. This intermediary path processes load information separately from the main feedback loop and combines it with the voltage error signal, allowing fast response without directly coupling the voltage control to high-frequency load variations that would cause distortion.
2Reliability
If the PFC voltage control loop has slow response to maintain low bandwidth, then the power factor and THD performance is maintained, but the dynamic load response becomes poor with significant voltage overshoot or undershoot
Solution Approach 1:
The patent combines feedback control with feedforward control. The feedback loop continues to operate at low bandwidth to maintain power factor and THD performance by providing accurate voltage error correction. The feedforward path adds fast response capability by anticipating load changes, creating a hybrid control system that leverages the strengths of both control approaches.
Solution Approach 2:
The patent merges feedback control and feedforward control into a unified control system. The feedback controller maintains reliability for power factor correction, while the feedforward controller enhances stability during load transitions. The two control paths are combined at the voltage control signal generation stage, allowing the system to achieve both objectives simultaneously.
3Power
If the PFC output capacitor is charged and discharged in each AC half cycle, then the rectified AC power is converted to DC, but the output voltage ripple with frequency equal to 2 times line frequency is generated
Solution Approach 1:
The feedforward control provides preliminary action by adjusting the voltage control signal in anticipation of load changes, preventing large voltage excursions before they occur. This proactive adjustment reduces the magnitude of voltage ripple that would otherwise be generated during AC half-cycle charging and discharging of the output capacitor.
Data Source
AI summary
A power factor corrector (PFC) is used to receive input power and supply power to a load via a DC/DC converter. A method of controlling a PFC is executed by a PFC controller used to control the PFC, where the PFC controller includes a voltage controller. The method includes receiving a first signal transmitted from a DC/DC controller used to control the DC/DC converter, where the first signal indicates the load, deriving a second signal based on the first signal, where the second signal is an expected output control signal of the voltage controller under the load indicated by the first signal, and configuring the voltage controller according to the second signal so as to keep an output voltage Vbulk of the PFC to the DC/DC converter stable.