Multi-Level Inverter Vector Control for Bootstrap Voltage Stability
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Solution Overview
Problem
Existing multi-level inverters face challenges in reducing voltage drops in bootstrap circuits, which are not addressed by two-level inverter control methods.
Innovation Solution
A multi-level inverter design incorporating a DC power supply unit, inverter circuits, and a controller that utilizes a series connection of switching elements and diodes, along with gate drivers and bootstrap circuits, to control voltage vectors and minimize voltage drops by replacing specific voltage vectors with zero and double-magnitude vectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a two-level inverter control method is used, then the bootstrap circuit voltage can be maintained in two-level inverters, but the method is not applicable to multi-level inverters and cannot prevent voltage drops in multi-level inverter bootstrap circuits
Solution Approach 1:
The invention changes the control parameters by selecting and applying different voltage vectors (specifically replacing the first voltage vector with a zero vector and a second voltage vector) to ensure that the switching elements are properly controlled. This parameter change in the control strategy enables the bootstrap circuit to be charged appropriately in multi-level inverters, resolving the voltage stability issue that arises when applying two-level inverter control methods to multi-level systems.
2Power
If the first voltage vector is applied in multi-level inverters, then the output voltage control can be achieved, but voltage drops occur in the bootstrap circuits
Solution Approach 1:
The invention employs periodic action by controlling the switching elements to charge the bootstrap circuit at specific periodic intervals. The control unit is configured to apply voltage vectors in a sequence that ensures the bootstrap circuit receives charging pulses periodically, preventing voltage drops while maintaining output voltage control. This periodic charging strategy is implemented through the coordinated switching of elements in the inverter circuit.
Solution Approach 2:
The invention applies preliminary action by ensuring the bootstrap circuit is charged in advance before it is needed for gate driver operation. The control strategy proactively manages the switching states to charge the bootstrap capacitor during specific time intervals, so that when the gate driver requires voltage, the bootstrap circuit is already charged and ready, preventing voltage drops and ensuring reliable switching operation.
3Reliability
If switching control is optimized for two-level inverters, then voltage vector replacement can prevent bootstrap voltage drops, but the control method cannot be applied to multi-level inverters
Solution Approach 1:
The invention applies segmentation by dividing the control of multi-level inverter into distinct segments or stages. The control unit separately manages different voltage vectors (first voltage vector, zero vector, second voltage vector) and applies them in a segmented manner to different time intervals or switching cycles. This segmented control approach simplifies the overall control strategy by breaking down the complex multi-level inverter control into manageable segments that can be independently optimized, making the solution applicable to multi-level systems without excessive complexity.
Data Source
AI summary
A control unit replaces one first voltage vector out of two first voltage vectors with a zero vector and a second voltage vector. The two first voltage vectors belong to a plurality of voltage vectors, each have a reference magnitude, and are located closest to a command voltage vector. The zero vector is combination of potential levels at respective third connection nodes of a inverter circuits as high as a potential at a negative electrode. The second voltage vector has the same direction as, and twice as large a magnitude as, the first voltage vector. The control unit controls first to fourth gate drivers within a predetermined control cycle to make a synthetic vector of a voltage vector included in the plurality of voltage vectors but the first voltage vectors, the other first voltage vector, the zero vector, and the second voltage vector equal to the command voltage vector.