Voltage Conversion Circuit Resonant Frequency Control
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Solution Overview
Problem
The existing voltage conversion circuits, particularly LLC series resonant circuits, face increased losses due to higher RMS current values as switching frequency increases, leading to thermal balance issues and reduced power density.
Innovation Solution
A control method for a voltage conversion circuit that adjusts the ratio of total conduction time to resonant period (Ton/Tr) within a specific range and controls the quality factor (Q) to reduce RMS current, incorporating a resonant inductance and capacitance connected in series with a transformer, and a filter unit to minimize conduction and switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the switching frequency is increased to reduce the volume of magnetic elements and increase power density, then the volume of magnetic components is reduced and power density is increased, but the RMS value of resonant current increases leading to larger on-state loss and heat dissipation becomes more difficult
Solution Approach 1:
The patent applies dynamics by making the resonant frequency adjustable rather than fixed. The resonant frequency can be dynamically tuned to track the switching frequency, ensuring the resonant circuit operates at optimal efficiency points even at high switching frequencies. This dynamic adjustment allows the system to maintain lower RMS current values while operating at high switching frequencies, thus reducing on-state losses while still achieving compact magnetic component sizes.
Solution Approach 2:
The patent changes the parameter of resonant frequency to resolve the contradiction. By adjusting the resonant frequency to match or track the switching frequency, the system can operate in a resonant mode that minimizes current RMS values. This parameter change allows high switching frequency operation (for compact size) while maintaining efficient energy transfer and lower conduction losses.
2Power
If the switching frequency is increased to increase power density, then power density is increased, but losses of the converter increase and thermal balance becomes difficult to achieve
Solution Approach 1:
The patent uses dynamic resonance frequency adjustment to maintain optimal operating conditions at high power density. By continuously adapting the resonant frequency to match the switching frequency, the system ensures maximum power transfer efficiency even when operating at high frequencies required for high power density. This dynamic tracking minimizes converter losses while maintaining high power density operation.
Solution Approach 2:
The patent changes the resonant frequency parameter to optimize performance at high power density. By tuning the resonant frequency to coincide with the switching frequency, the system achieves resonant operation that minimizes losses. This parameter adjustment enables the converter to operate efficiently at high frequencies, thereby achieving high power density without proportionally increasing losses.
3Speed
If the resonant current waveform becomes triangular at high switching frequencies, then the RMS value of resonant current increases, but the switching frequency is already increased for compact design
Solution Approach 1:
The patent applies dynamics by enabling the resonant frequency to dynamically track the switching frequency. This dynamic adjustment ensures that even at high switching frequencies where triangular current waveforms would normally occur, the system maintains sinusoidal-like current waveforms with lower RMS values. The dynamic resonance compensation counteracts the waveform distortion caused by high-frequency operation.
Solution Approach 2:
The patent changes the resonant frequency parameter to compensate for waveform distortion at high switching frequencies. By adjusting the resonant frequency to match the switching frequency, the system restores the current waveform to a more sinusoidal shape, thereby reducing the RMS current value and associated conduction losses while maintaining the high switching frequency required for compact design.
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 approach effectively reduces conduction losses, improves efficiency, and decreases the volume of magnetic components, while maintaining Zero Voltage Switching (ZVS) and minimizing turn-off losses, making the circuit suitable for high switching frequencies.
Implementation Method 1
The LLC circuit operates in a series resonant mode in the primary side, and performs resonance with a current value of 0 as a central value
Implementation Method 2
The LLC circuit shown in Fig. 2 may charge or discharge the parasitic capacitance of the primary side switch elements (Q1 to Q4) in the dead time (t2-t3, t5-t6 in Fig. 3A) by adjusting the magnetizing current of the transformer T1
Implementation Method 3
the first stage converter may use a high-efficiency DC transformer to convert the input 48V bus voltage (Uin) to a lower intermediate bus voltage (Uib)
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~4A
AI summary
The present disclosure provides a control method of a voltage conversion circuit (400). The voltage conversion circuit (400) includes a DC voltage input terminal (41), a primary side switch unit (42), a resonant inductance (Lr), a transformer (43), a secondary side switch unit (44) and a DC voltage output terminal (45) which are electrically coupled. The resonant inductance (Lr) is connected to the transformer (43) in series. The voltage conversion circuit (400) also includes a resonant capacitance (Cr) which resonates with the resonant inductance (Lr). The control method includes: controlling switch elements in the primary side switch unit (42) and the secondary side switch unit (44), so that a range of a ratio Ton/Tr of a total conduction time Ton to a resonant period Tr of the voltage conversion circuit (400) is (0, 1.8)U(2.7, 3.7)U(4.8, 5.5), and a quality factor Q of the voltage conversion circuit (400) is less than or equal to 5, that is, Q≤5. The control method provided by the embodiment of the present disclosure can reduce the conduction loss and the switching loss of the voltage conversion circuit (400), thereby improving the efficiency and reducing the cost.