LLC Resonant Power Converter Current Sensing
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Solution Overview
Problem
Current power converters face challenges in accurate current sensing due to low accuracy and high power loss, especially with increasing power density, and issues with parallel windings causing power circulation and magnetic flux unbalance.
Innovation Solution
The solution involves a power converter design with a transformer, capacitor, and inductor forming an LLC resonant circuit, using first and second current sensors to determine the current difference through the primary and magnetizing inductor, and optionally using parallel windings connected to different capacitors to prevent power circulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sampling resistor is used for current sensing, then the current can be sensed, but the accuracy is low and power loss is large
Solution Approach 1:
The patent replaces the traditional sampling resistor method with a current transformer (CT) based sensing system. The CT uses electromagnetic induction to sense current, eliminating the need for high-power resistors and reducing power loss significantly while improving measurement accuracy through transformer-based signal transformation.
Solution Approach 2:
The patent introduces an intermediary current transformer between the primary circuit and the sensing circuit. This CT acts as a mediator that transforms the high current into a measurable signal without directly dissipating power in a resistor, thus resolving the contradiction between accurate sensing and power loss.
2Loss of energy
If a current transformer is used for current sensing, then the power loss is reduced, but the accuracy is still low and additional space is required
Solution Approach 1:
The patent merges the current transformer sensing function with the existing LLC resonant circuit components. The sensing CT is integrated into the primary side of the transformer structure, and the magnetizing inductor current sensing is combined with the existing circuit topology, eliminating the need for separate additional components and improving accuracy through integrated design.
Solution Approach 2:
The patent makes the transformer primary winding serve dual functions: both as the power transmission path and as the sensing element for magnetizing inductor current. This multi-functionality approach improves measurement accuracy by using the existing high-precision transformer structure for both power and sensing purposes.
3Use of energy by moving object
If parallel windings are used in the transformer, then the direct current resistance is decreased, but magnetic flux unbalance occurs
Solution Approach 1:
The patent introduces asymmetry by connecting different capacitors to each parallel winding. This asymmetric configuration creates different impedance paths for each winding, preventing the symmetrical conditions that cause power circulation while maintaining the low DCR benefit of parallel windings.
Solution Approach 2:
The patent changes the electrical parameters by introducing different capacitance values to each parallel winding. This parameter modification alters the resonant characteristics and impedance of each winding, eliminating the power circulation issue while preserving the reduced winding loss advantage.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design reduces space, cost, and power loss while achieving higher accuracy in current sensing and preventing power circulation, ensuring efficient operation even under large loads and eliminating magnetic flux unbalance.
Implementation Method 1
a capacitor and an inductor serially connected with the primary of the transformer. The capacitor, the inductor and a magnetizing inductor of the primary of the transformer form an LLC resonant circuit
Implementation Method 2
The first current sensor comprises the inductor and is configured to sense, via the inductor, a current passing through the primary of the transformer. The second current sensor comprises the primary and is configured to sense, via the primary, a current passing through the magnetizing inductor
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A power converter comprises a transformer (Tr) with a primary and a secondary, and a capacitor (Cr) and an inductor (Lr) serially connected with the primary of the transformer. The capacitor, the inductor and a magnetizing inductor (Lm) of the transformer form an LLC resonant circuit. The power converter further comprises a first current sensor (CT1) and a second current sensor (CT2). The first current sensor comprises the inductor and is configured to sense, via the inductor, a current passing through the primary of the transformer. The second current sensor comprises the primary and is configured to sense, via the primary, a current passing through the magnetizing inductor of the transformer. A current passing through the secondary is determined from a difference obtained based on the sensed current passing through the primary of the transformer and the sensed current passing through the magnetizing inductor. The power converter has the advantage that it is possible to provide an accurate sensed current at a low cost without load limitation, and it is also possible to perform a cycle-by-cycle protection function since a load waveform can be restored. In addition, another power converter is also provided, which has a structure for reducing power circulation among parallel windings (Wa, Wb) of the transformer.