Switching converter is a negative feedback control system, and its control link is crucial. The control methods of the converter are divided into voltage mode and current mode. Voltage mode control is a single closed-loop control with only voltage feedback, and the error amplifier only detects the output voltage when the output current and output voltage change. The control is simple, but the dynamic and steady-state performance is not good enough. In addition, due to only adjusting the voltage without considering the impact of current changes on the system, it is impossible to adjust the power of the converter.
On the basis of voltage feedback, current mode control also introduces a current feedback loop, which essentially makes the output inductor current follow the value set by the error voltage. The inductor can be replaced by a constant current source, so that the system can be reduced to first order through second-order, simplifying the design of the control system regulator. In terms of control performance, it is far superior to voltage mode. It can be divided into peak current control, average current control, hysteresis current control and other modes. The peak current is the current peak value as the control object, and the average current is controlled as the average value of the current. The average current mode has a high gain current amplifier, which can accurately track the current setting value, strong noise suppression ability, and does not require slope compensation. It can be applied to any circuit topology favored by most designers.
The control system of a switching converter is usually designed based on a constant frequency. The resonant frequency of aseries resonantconverter will change with the variation of the equivalent inductance of the load, causing the working state of the circuit to shift and slide into the inductance or C. The working state of capacitors will greatly reduce the efficiency of the entire circuit. In order to maintain the resonant state of the circuit during load changes and track the operating frequency of the circuit, phase-locked loop technology is a commonly used frequency tracking method. This design adopts a combination of frequency tracking and power control to design the entire control system. The frequency tracking module adopts phase-locked loop technology. The power control module controls the output power by controlling the current of the output circuit. Fast dynamic response, good control performance, and can achieve good results. Control effect.
