Power Converter Pre-Charge Using Active Switches and Phase Selector
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Solution Overview
Problem
Existing three-phase rectifiers face challenges in smooth and safe pre-charging (start-up) procedures, particularly due to the use of resistive elements which result in power losses and require large volumes.
Innovation Solution
An electrical converter design featuring a three-phase bridge converter with active switches, a phase selector, and a buck-boost circuit for controlled pre-charging, allowing for stepwise voltage increase without additional hardware, utilizing pulse width modulation and interleaved control signals to minimize stress on output filter capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resistive element connected through a relay is used for pre-charging, then the pre-charging function is achieved, but the device volume increases and power losses occur in the resistive element
Solution Approach 1:
The patent removes the resistive pre-charging element from the system entirely. Instead, it uses the existing active switches (S1-S6) in the three-phase bridge rectifier to perform pre-charging by controlling them to connect only the middle intermediate node to the DC+ terminal during start-up, eliminating energy losses associated with resistive pre-charging.
Solution Approach 2:
The existing active switches S1-S6 in the three-phase bridge rectifier are made multi-functional. During normal operation, they perform rectification, but during pre-charging, they are controlled to connect the middle intermediate node to DC+ for pre-charging. This eliminates the need for separate pre-charging hardware while achieving the same function.
2Reliability
If a resistive element connected through a relay is used for pre-charging, then the pre-charging function is achieved, but the device volume increases
Solution Approach 1:
The patent removes the resistive pre-charging element and relay from the system. Pre-charging is achieved by controlling the existing active switches S1-S6 to connect the middle intermediate node to the DC+ terminal, eliminating the need for additional pre-charging hardware and reducing device volume.
Solution Approach 2:
The existing active switches S1-S6 are made multi-functional, serving both rectification during normal operation and pre-charging during start-up. This eliminates the need for separate pre-charging hardware, thereby reducing device volume while maintaining pre-charging capability.
3Ease of operation
If additional hardware is added for pre-charging, then pre-charging control is improved, but the device complexity and cost increase
Solution Approach 1:
The controller makes the existing active switches S1-S6 multi-functional by controlling them to perform both rectification during normal operation and pre-charging during start-up. This approach improves pre-charging control without adding any hardware, thereby reducing device complexity and cost.
Solution Approach 2:
The patent removes the need for additional pre-charging hardware by using the existing active switches. The controller alone provides pre-charging control by appropriately switching S1-S6, eliminating hardware complexity while maintaining operational ease.
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
Enables a controlled and efficient pre-charge of DC bus voltage with minimal hardware additions, improving ease of operation and service life at reduced costs.
Implementation Method 1
a first converter stage operable to convert the AC signal at three phase terminals to a first DC signal at an upper intermediate node and a lower intermediate node
Implementation Method 2
a second converter stage arranged between the first converter stage and the output filter, the second converter stage comprising a switch node and a pair of second switches connecting the switch node to a respective one of the DC terminals
Data Source
Figure 1
Figure 2A~2C
Figure 2D~2E
AI summary
An electrical converter (100) comprises a first converter stage (11), an output filter (15), a second converter stage (12) arranged between the first converter stage and the output filter and a controller (40) implemented with a first mode of operation for converting a three-phase AC signal into a DC signal. The first converter stage comprises a three-phase bridge rectifier (24) connecting three phase terminals to an upper intermediate node (x) and a lower intermediate node (y), and a phase selector (25) comprising first active switches (S aza , S bzb , S czc ) connecting the three phase terminals to a middle intermediate node (z). The second converter stage comprises a switch node (t) connected to the middle intermediate node (z) and a pair of second switches (S Pz , S zN ) connecting the switch node (t) to a respective one of the DC terminals (P, N). The electrical converter is configured to disconnect the upper intermediate node (x) and/or the lower intermediate node (y) from all the phase terminals (A, B, C). The controller (40) is implemented with a second mode of operation wherein the first switches (S aza , S bzb , S czc ) are operated while keeping the upper intermediate node (x) or the lower intermediate node (y) disconnected from all the phase terminals (A, B, C), so as to allow a current to flow between the middle intermediate node (z) and the output filter (15), allowing for stepwise increasing a voltage across the DC terminals (P, N) during start-up.