LLC Converter Ripple Compensation Using Secondary-Side Voltage Tracking
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Solution Overview
Problem
Conventional power supply apparatuses with LLC resonant converters suffer from double-frequency ripple issues when connected to the power grid, which can lead to instability and failure, and existing solutions are inadequate for handling varying capacitance, frequency, and load conditions, particularly failing to provide comprehensive ripple compensation for both constant resistance and constant current loads.
Innovation Solution
A power supply apparatus featuring a voltage tracking circuit that detects an auxiliary voltage and generates a reverse waveform to control the LLC converter operations, allowing for optimized ripple compensation regardless of input capacitance, frequency, or load changes, with a secondary side controller capable of customizing compensation methods based on ripple source magnitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If an uncontrolled rectifier bridge is used to connect the power supply apparatus to the power grid, then the circuit structure is simple, but double-frequency ripple is generated which harms the stable operation of the power supply apparatus
Solution Approach 1:
The patent detects the double-frequency ripple generated by the uncontrolled rectifier bridge and converts this harmful effect into a useful control signal. The controller uses the detected ripple information to generate compensation signals that actively cancel the ripple, transforming the harmful double-frequency ripple into a basis for stabilization control.
Solution Approach 2:
The patent implements a feedback mechanism where the controller detects the ripple on the DC link voltage, processes this information, and generates compensation signals fed back to the PFC circuit. This closed-loop feedback system continuously adjusts to maintain stable operation despite the presence of the uncontrolled rectifier bridge.
2Reliability
If isolators such as optical couplers are arranged to transmit input voltage to the controller on the secondary side, then the controller can reconstruct the waveform and adjust reference voltage for ripple offsetting, but the method is not comprehensive and only adjustment to a certain extent is permitted due to changes in capacitance values and frequency
Solution Approach 1:
The patent employs a self-service mechanism where the system detects its own ripple characteristics and automatically generates compensation signals without requiring external adjustment or complex isolation circuits. The controller directly monitors the DC link voltage ripple and adjusts the PFC circuit accordingly, making the system self-regulating across varying conditions.
Solution Approach 2:
The patent dynamically adjusts control parameters based on detected ripple characteristics. The controller modifies reference voltages and switching frequencies in real-time according to the detected ripple magnitude and frequency, enabling comprehensive adaptation to varying capacitance values, input frequencies, and load conditions.
3Ease of operation
If the controller detects the ripples of the output voltage on the secondary side, then the method is suitable for handling constant resistance loads, but it is unable to handle constant current loads and requires combination with current feedback mechanism
Solution Approach 1:
The patent performs preliminary detection of the DC link voltage ripple at the input side before it propagates to the output. By detecting and compensating for the ripple source at the PFC stage, the system proactively prevents ripple transmission to both constant resistance and constant current loads, eliminating the need for separate load-specific control mechanisms.
Data Source
AI summary
A power supply apparatus includes a power factor correction circuit, an LLC converter, an auxiliary conversion circuit, a secondary side controller and a voltage tracking circuit. The power factor correction circuit is used for converting a DC link voltage into a first voltage. The LLC converter includes a primary side circuit and a secondary side circuit, which are coupled with each other. The primary side circuit receives the first voltage. The first voltage is converted into an auxiliary voltage by the auxiliary conversion circuit. The voltage tracking circuit detects the auxiliary voltage and issues a detection signal to the secondary side controller. The secondary side controller tracks a ripple change of the DC link voltage and instantly generates a reverse waveform opposite to a waveform of the DC link voltage. The secondary side controller controls the operations of the LLC converter according to the reverse waveform.