Three-Phase Power Converter Pre-Charge Using Active Current Injection
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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 increased volume.
Innovation Solution
An electrical converter with a first converter stage comprising a three-phase bridge converter and a phase selector using active switches, along with a second converter stage including a buck-boost circuit for current injection, allows for controlled pre-charging by disconnecting intermediate nodes from phase terminals during start-up and using pulse width modulation to manage current flow, thereby minimizing hardware additions and optimizing operation.
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 extracts the pre-charging function from the main converter circuit by using the phase selector and current injection circuit to isolate and control the pre-charge path separately. This allows pre-charging without requiring a dedicated resistive element, eliminating the associated power losses and volume increase.
Solution Approach 2:
The phase selector acts as an intermediary component that enables controlled connection between phase terminals and intermediate nodes during start-up. By using the existing current injection circuit as a mediator, the patent achieves pre-charging functionality without adding separate resistive pre-charge components.
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 makes the phase selector and current injection circuit multi-functional by using them for both pre-charging during start-up and normal operation during steady state. This eliminates the need for separate dedicated pre-charge hardware, reducing overall device volume while maintaining pre-charging functionality.
Solution Approach 2:
The pre-charging function is extracted and implemented through the existing control circuitry (phase selector and current injection circuit) rather than adding separate resistive pre-charge components, thereby avoiding volume increase.
3Loss of energy
If the phase selector and current injection circuit are used for controlled pre-charging, then power losses are reduced and device volume is minimized, but the control complexity increases
Solution Approach 1:
The patent merges the pre-charging control with the existing phase selector and current injection circuit control. By combining these functions into a unified control strategy using PWM signals, the patent reduces overall system complexity despite the sophisticated pre-charging operation.
Solution Approach 2:
The controller monitors the DC bus voltage and uses feedback control to regulate the pre-charging process. By adjusting PWM duty cycles based on voltage feedback, the system achieves precise control without requiring complex additional circuitry, managing control complexity through intelligent feedback mechanisms.
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
The solution enables a controlled and efficient pre-charge of DC bus voltage with minimal added hardware, improving ease of operation and service life while reducing 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. The first converter stage can comprise a three-phase bridge converter/rectifier
Implementation Method 2
The second switches are advantageously configured to form a current injection circuit connecting the middle intermediate node to the DC terminals, e.g. the second switches are operated through pulse width modulation. The current injection circuit is advantageously a buck-boost circuit.
Data Source
AI summary
An electrical converter includes first and second converter stages, an output filter, and a controller having a first mode for converting a three-phase AC signal into a DC signal. The first converter stage has a three-phase bridge rectifier connecting three phase terminals to an upper intermediate node and a lower intermediate node, and a phase selector having first switches connecting the terminals to a middle intermediate node. The second converter stage includes a switch node connected to the middle intermediate node and a pair of second switches connecting the switch node to one of the DC terminals. In a second mode, the first switches are operated while keeping the upper or lower intermediate node disconnected from all the phase terminals to allow a current to flow between the middle intermediate node and the output filter, allowing for stepwise increasing a voltage across the DC terminals during start-up.