Multi-Stage LLC Converter Control for Wide Output Voltage Range
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Solution Overview
Problem
Existing power converters using LLC circuits face inefficiencies outside their input/output range, and the use of mechanical relays as changeover switches is costly and bulky, posing risks of surge currents during failures.
Innovation Solution
A power converter design with multiple LLC circuits that can switch between series and parallel connections without a changeover switch on the output side, utilizing a control unit to form a series resonant circuit in some stages and perform switching operations in others, optimizing efficiency and output voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a changeover switch is provided on the output side to switch between series and parallel connection, then the output voltage range can be widened, but the risk of surge current increases and mechanical relay is required which is expensive and large in size
Solution Approach 1:
The changeover switch function is extracted from the output side and relocated to the input side of the LLC circuits. The input side changeover switch SW1 switches between series and parallel connection of the LLC circuits before they connect to the battery, eliminating the need for output side switching and the associated surge current risks.
Solution Approach 2:
The mechanical relay on the output side is replaced by a semiconductor switch (MOSFET or IGBT) on the input side. The semiconductor switch can be controlled by the control unit to switch between series and parallel connection, providing the same functionality without the size, cost, and reliability issues of mechanical relays.
2Ease of operation
If a mechanical relay is used as the changeover switch, then the switching between series and parallel connection can be achieved, but the device becomes expensive, large in size, and cannot be replaced by semiconductor switch
Solution Approach 1:
The mechanical relay is completely replaced by a semiconductor switch (MOSFET or IGBT) with integrated control circuitry. The semiconductor switch is controlled by the control unit to achieve series/parallel switching, eliminating the need for mechanical components and reducing device size, cost, and complexity.
Solution Approach 2:
The semiconductor switch on the input side serves multiple functions: it acts as the changeover switch for series/parallel connection, provides surge current protection, and can be controlled dynamically by the control unit based on battery voltage requirements, replacing multiple separate components.
3Adaptability or versatility
If the operating frequency is increased to widen the output voltage range, then the output range can be expanded, but the efficiency deteriorates significantly outside the input/output range
Solution Approach 1:
The system dynamically switches between series and parallel connection configurations based on the required output voltage. The control unit monitors the battery voltage and switches the LLC circuit configuration accordingly, allowing the system to operate within its efficient input/output range while still providing a wide overall output voltage range.
Solution Approach 2:
The system changes the connection configuration parameter (series or parallel) of the LLC circuits based on the required output voltage level. By switching between these two configurations, the system can provide a wide output voltage range (V1 to V3) while maintaining high efficiency within the operating frequency range (X1 to X2).
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
Widens the output voltage range without a changeover switch, improving efficiency by setting the operating frequency near resonance, and preventing surge currents.
Implementation Method 1
causes a series resonant circuit of the resonant inductor and the resonant capacitor to be formed
Implementation Method 2
a primary winding of a transformer
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3(a)~3(d)
AI summary
A power converter 1 that converts a direct-current voltage Vin into an output voltage Vo by a switching operation of an upper switch element QH and a lower switch element QL using an LLC circuit 10 including a resonant inductor Lr connected to a connection point between the upper switch element QH and the lower switch element QL connected in series between a positive electrode and a negative electrode of the direct-current voltage Vin, a primary winding N1 of a transformer T, and a resonant capacitor Cr, the power converter 1 including: the LLC circuit 10 of each of a plurality of stages in which secondary windings N2 of the transformers T are connected in series; and a control unit 30 that causes a series resonant circuit of the resonant inductor Lr and the resonant capacitor Cr to be formed in any one or more of the LLC circuits 10 of the plurality of stages and causes the other LLC circuit 10 to perform the switching operation.