Cascaded Power Conversion Modules With Bypass-Boost-Hold Control
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Solution Overview
Problem
Conventional cascaded solid-state transformers experience low efficiency during light load conditions due to high switching and transformer losses, and require high-capacity filtering capacitors, increasing costs.
Innovation Solution
The cascaded power conversion system operates DC/DC conversion units in bypass, boost, and hold modes, allowing for low switching and transformer losses, and eliminates the need for high-capacity bus capacitors by immediately outputting DC energy, reducing system costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the AC/DC conversion circuit is operated in high frequency rectification mode to uniformly distribute power between modules, then power distribution is improved, but switching loss increases and system efficiency decreases
Solution Approach 1:
The patent dynamically adjusts the operating mode of the AC/DC conversion circuit based on input voltage conditions. When input voltage is high, it operates in power frequency rectification mode with DC/DC conversion; when input voltage is low, it operates in high frequency rectification mode. This dynamic adaptation resolves the contradiction by selecting the appropriate mode to minimize switching loss while maintaining power distribution uniformity.
Solution Approach 2:
The patent changes the operating parameters of the AC/DC conversion circuit by switching between power frequency rectification mode and high frequency rectification mode based on input voltage thresholds. This parameter change allows the system to optimize between switching loss and power distribution uniformity under different operating conditions.
2Stability of the object's composition
If the DC/DC conversion circuit is operated in hold mode with switching frequency equal to resonant frequency, then voltage regulation is maintained, but transformer power loss increases
Solution Approach 1:
The patent dynamically adjusts the DC/DC conversion circuit operating mode based on the relationship between input voltage and threshold values. When input voltage is high (above second threshold), it operates in bypass mode to minimize transformer loss; when input voltage is moderate (between first and second thresholds), it operates in hold mode to maintain voltage stability. This dynamic adjustment resolves the contradiction between voltage stability and transformer power loss.
Solution Approach 2:
The patent implements periodic mode switching in the DC/DC conversion circuit based on input voltage conditions. The circuit alternates between bypass mode, hold mode, and boost mode depending on the input voltage level, which allows the system to periodically optimize between transformer power loss and voltage regulation requirements.
3Power
If the DC bus voltage contains double-frequency ripple, then power conversion is achieved, but filtering capacitor capacitance must be increased, raising system cost
Solution Approach 1:
The patent dynamically controls the DC/DC conversion circuit to operate in different modes (bypass, hold, boost) based on input voltage conditions. This dynamic control suppresses double-frequency ripple in the DC bus voltage by coordinating the operation of multiple power conversion modules, thereby reducing the required filtering capacitor capacitance while maintaining power conversion capability.
Solution Approach 2:
The patent combines multiple power conversion modules in a cascaded configuration where the output of one module serves as input to the next. This merging of modules allows the system to share the power conversion function across multiple units, reducing the ripple magnitude in each individual module's DC bus and thereby reducing the required capacitor size.
4Stress or pressure
If multiple power conversion modules are connected in series to withstand high input voltage, then voltage handling capability is improved, but system efficiency decreases under light load conditions
Solution Approach 1:
The patent dynamically controls each module's AC/DC and DC/DC conversion circuits to operate in different modes based on the overall input voltage level and load conditions. Under light load conditions, the system can reduce the number of active modules or adjust their operating modes to minimize systematic loss while still maintaining the required voltage withstanding capability through the series connection of modules.
Data Source
AI summary
A cascaded power conversion system is used for receiving an AC input power having an AC input voltage. The cascaded power conversion system includes N power conversion modules. Each of the N power conversion modules includes an AC/DC conversion unit, a DC bus and a DC/DC conversion unit. In every ¼ period of the AC input voltage, the DC/DC conversion units of the N power conversion modules are operated in a bypass mode, a boost mode and a hold mode, and a total voltage of DC bus voltages of the N power conversion modules are changed in a consecutive manner.