Multilevel AC/DC Converter Control for Efficiency
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Solution Overview
Problem
Current AC/DC conversion solutions using DC/DC converters in 'Simple Bridge' mode face inefficiencies, including variable intermediate voltages, unoptimized losses, and challenging transitions between power transfer modes, limiting the full utilization of AC/DC conversion systems.
Innovation Solution
A multi-level AC/DC converter control process with n power cells, each featuring an AC/DC input converter and an isolated DC/DC converter, allowing operation in either closed-loop 'Double Bridge' mode for voltage regulation or open-loop 'Simple Bridge' mode for maximum efficiency, with a control system regulating output voltage and managing power transfer modes to optimize efficiency and minimize losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If DC/DC converter operates in single-bridge mode with one switching bridge controlled as diode bridge, then control is simplified and efficiency is improved, but intermediate voltages become dependent on operating point and transitions between power transfer modes are difficult
Solution Approach 1:
The patent implements dynamic switching between single-bridge and double-bridge modes based on operating conditions. The system automatically transitions from single-bridge mode (for normal operation) to double-bridge mode (when intermediate voltage regulation is needed), making the control system adaptive to different operational requirements rather than static.
Solution Approach 2:
The patent changes the operational parameters of the DC/DC converter by switching between different bridge configurations. By altering the number of active switching bridges (from one to two), the system changes its voltage regulation characteristics to match the required operating conditions.
2Device complexity
If DC/DC converter operates in single-bridge mode, then control electronics are simplified, but losses are not optimized and transition between power transfer modes requires constant monitoring and precise timing
Solution Approach 1:
The system dynamically adjusts the number of active switching bridges based on power flow direction and magnitude. During high-power transfer, both bridges operate in double-bridge mode to optimize efficiency. During low-power or steady-state conditions, the system switches to single-bridge mode to reduce control complexity and switching losses.
Solution Approach 2:
The patent applies partial action by using only one switching bridge when full double-bridge operation is not required. This reduces the excessive action of keeping both bridges active all the time, thereby reducing unnecessary switching losses and control complexity during steady-state operation.
3Reliability
If dual-bridge DC/DC converter is used, then soft switching techniques can be implemented, but operating in single-bridge mode limits the full potential of the converter architecture
Solution Approach 1:
The system dynamically selects between single-bridge and double-bridge modes based on operational requirements. When soft switching and high reliability are priorities, the system operates in double-bridge mode. When full converter potential and efficiency are needed, the system transitions to single-bridge mode, thereby fully utilizing the converter architecture's capabilities.
Solution Approach 2:
The patent makes the DC/DC converter universal by enabling it to perform both single-bridge and double-bridge operations. This multi-functionality allows the same hardware architecture to adapt to different operational modes, maximizing its utility and preventing underutilization of the dual-bridge capability.
Data Source
Figure 1~2
Figure 3A~3B
Figure 3C~5
AI summary
The invention concerns a method for controlling an AC/DC converter (1 ) which comprises n power cells Ci, and wherein: - each power cell comprises an AC/DC input converter (In i) and an isolated DC/DC converter (Conv_i); - each input converter (In i) of a cell Ci being connected in series to the input converter (ln_i+1) of the cell Ci+1 in order to form an input stage (IN); - the DC/DC converter (Conv_i) of each cell Ci being connected in parallel to the DC/DC converter (Conv_i+1) of the cell Ci+1 in order to form an output stage (OUT). The input stage (IN) is controlled in order to regulate the output voltage (Uout) at a reference value (Uout_ref) by controlling the input current (lac). Each DC/DC converter (Conv_i) is controlled in a first operating mode (DAB) or in a second operating mode (SAB).