Cascaded Power Conversion Modules With Dynamic 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, leading to increased 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 cost.
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 applies dynamic operation by switching the AC/DC conversion circuit between high frequency rectification mode and power frequency rectification mode based on load conditions. During light load conditions, the circuit operates in power frequency rectification mode to reduce switching losses, while during heavy load conditions, it operates in high frequency rectification mode to maintain uniform power distribution. This dynamic mode switching resolves the contradiction between power distribution uniformity and switching loss reduction.
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 stable operation is achieved, but transformer power loss increases
Solution Approach 1:
The patent dynamically adjusts the operating mode of the DC/DC conversion circuit based on load conditions. During light load conditions, the circuit operates in bypass mode to eliminate transformer losses entirely. During heavy load conditions, it operates in hold mode to maintain stable operation. This dynamic switching between operational modes resolves the contradiction between operational stability and transformer power loss reduction.
3Stability of the object's composition
If high capacity bus capacitors are used to filter DC bus voltage with double-frequency ripple, then voltage filtering is improved, but system cost increases
Solution Approach 1:
The patent employs dynamic mode switching where the AC/DC conversion circuit operates in power frequency rectification mode during light load conditions, which produces minimal ripple on the DC bus voltage. This eliminates the need for high-capacity filtering capacitors. During heavy load conditions, the circuit switches to high frequency rectification mode where standard filtering capacitor designs are sufficient. This dynamic operation resolves the contradiction between voltage stability and system cost reduction.
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 complexity increases
Solution Approach 1:
The patent merges the operational control of multiple series-connected power conversion modules through a unified control strategy. The control unit coordinates the operation of all modules, switching them between different operational modes based on overall system load conditions. This unified control approach manages the complexity of multiple series modules while maintaining their voltage withstanding capability, effectively resolving the contradiction between voltage handling and system complexity.
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 enhances efficiency and reduces costs by minimizing switching and transformer losses, while allowing for a lower capacitance bus capacitor, thereby improving the overall efficiency and economic viability of the cascaded power conversion system.
Implementation Method 1
The AC/DC conversion unit is an AC/DC conversion circuit
Implementation Method 2
The DC/DC conversion unit is a DC/DC conversion circuit
Data Source
Figure 1A
Figure 1B
Figure 1C
AI summary
A cascaded power conversion system (1,1a, 1b, 1c, 1d, 1e, 1f) is used for receiving an AC input power having an AC input voltage. The cascaded power conversion system (1,1a, 1b, 1c, 1d, 1e, 1f) includes N power conversion modules (2). Each of the N power conversion modules (2) includes an AC/DC conversion unit (24, 24a, 24b), a DC bus (23) and a DC/DC conversion unit (25, 25a, 25b, 25c). In every 1/4 period of the AC input voltage, the DC/DC conversion units (25, 25a, 25b, 25c) of the N power conversion modules (2) are operated in a bypass mode, a boost mode and a hold mode, and a total voltage of DC bus voltages (Vdc) of the N power conversion modules (2) are changed in a consecutive manner.