boost PFC average current control with a precharge circuit

This circuit is my small contribution to get rid of the initial current overshoot for classical PFC control strategies

Average Current Control

Average current control is a method where the average value of the input current is regulated to match a reference current, which is derived from the desired power factor correction. This technique involves measuring the average input current over a switching period and comparing it with the reference value to generate a control signal.

Working Principle

1. Current Sensing: The PFC continuously monitors the input current using a current sensor. This sensor provides an instantaneous measurement of the current.
2. Reference Current Generation: A reference current waveform is generated based on the input voltage and desired power factor. This reference represents the ideal current that should be drawn by the load to achieve optimal power factor correction.
3. Average Current Calculation: The instantaneous current measurements are averaged over a specific period (typically one switching cycle). This average value is used for comparison with the reference current.
4. Error Calculation: The difference (error) between the average current and the reference current is calculated.
5. Control Signal Generation: This error signal is processed through a control algorithm (usually a proportional-integral (PI) controller) to generate a control signal. This signal adjusts the duty cycle of the power electronic switches (e.g., MOSFETs or IGBTs) in the PFC circuit.
6. Switching Control: The control signal is used to modulate the switching of the power electronic devices, ensuring that the input current waveform follows the reference current waveform closely.
7. Correction and Stabilization: The process of monitoring, averaging, comparing, and adjusting continues in real-time, maintaining the desired power factor correction dynamically.

Benefits

• Improved Efficiency: By ensuring the average current drawn matches the reference current, the PFC reduces energy losses and improves overall system efficiency.
• Reduced Harmonics: Average current control helps in minimizing harmonic distortion in the current waveform, leading to a cleaner and more stable power supply.
• Stable Operation: The average current control method provides a stable and robust control mechanism, making it suitable for a wide range of load conditions.
• Enhanced Performance: The dynamic adjustment capability ensures that the PFC responds quickly to changes in load, maintaining optimal performance at all times.

Applications

PFCs with average current control are commonly used in various applications, including:

• Industrial Equipment: To improve the efficiency and performance of large motors, transformers, and other heavy-duty machinery.
• Consumer Electronics: In power supplies for computers, televisions, and other electronic devices to ensure efficient power usage and compliance with regulatory standards.
• Renewable Energy Systems: To optimize power conversion and improve the efficiency of solar inverters and wind turbine systems.
• Electric Vehicles: To manage battery charging systems efficiently, enhancing the overall performance and range of electric vehicles.

Key Components

• Current Sensor: Measures the instantaneous input current.
• Voltage Sensor: Measures the input voltage to generate the reference current.
• Controller: Processes the error signal and generates the control signal (e.g., PI controller).
• Power Electronic Switches: Modulate the input current by adjusting the duty cycle based on the control signal.

Now what happens during the initial startup of this circuit is an initial overshoot of the current, this problem can be harmful to sensible components like diodes .

it is due to in rush current in the filter capacitor becaus of the variation of dV/dt thats suddent from 0 to 0.7V due to the diodes forward current, this causes a sudden rise in the current which is bad for the THD