Three-Level Motor Inverter Control for Low-Torque Efficiency
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Solution Overview
Problem
Existing three-phase full-bridge two-level inverter circuits in electric vehicles suffer from high harmonic content, increased switching losses, low system efficiency, and high costs due to the continuous operation of switching transistors, which are prone to damage, especially in low-torque regions, leading to reduced endurance mileage.
Innovation Solution
A motor control unit with a three-phase full-bridge three-level inverter circuit that includes a horizontal bridge circuit with lower current capacity switching transistors, controlled based on motor torque, current, temperature, and voltage, switching to a two-level mode in high-torque conditions to prevent damage and reduce costs, while maintaining efficiency in low-torque regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a three-phase full-bridge three-level inverter circuit is used, then system efficiency is improved and harmonic content is reduced, but the quantity of switching transistors is doubled and costs increase
Solution Approach 1:
The inverter circuit is divided into a vertical bridge circuit and a horizontal bridge circuit. The vertical bridge circuit contains switching transistors with current capacity greater than or equal to the maximum motor current, while the horizontal bridge circuit contains switching transistors with lower current capacity. This segmentation allows the system to achieve three-level inverter functionality with reduced overall transistor count and lower cost.
Solution Approach 2:
Different parts of the circuit are assigned different current capacities based on their functional requirements. The vertical bridge circuit handles high-current operations, while the horizontal bridge circuit handles lower-current operations. This local differentiation optimizes component selection and reduces overall system cost while maintaining efficiency benefits.
2Device complexity
If all switching transistors have the same current capacity, then the circuit is simpler to design, but all switching transistors are prone to damage when continuously working
Solution Approach 1:
The patent assigns different current capacities to switching transistors based on their specific operational requirements. Vertical bridge switching transistors have current capacity ≥ maximum motor current, while horizontal bridge switching transistors have lower current capacity. This differentiated design improves reliability by matching component capabilities to actual workload, preventing over-stressing of transistors.
Solution Approach 2:
The current capacity parameter of switching transistors is changed based on circuit position and operational demands. By varying this key parameter across different circuit locations, the system achieves both improved reliability and optimized cost-effectiveness.
3Power
If switching transistors continuously work in high-torque region, then power output is maintained, but switching transistors are prone to damage
Solution Approach 1:
The control apparatus dynamically switches between two-level and three-level inverter working modes based on torque requirements. In high-torque regions, the system operates in two-level mode with vertical bridge circuit to maintain power output. In low-torque regions, it operates in three-level mode with horizontal bridge circuit to improve efficiency. This dynamic adaptation maintains power when needed while protecting transistors from continuous high-stress operation.
Solution Approach 2:
The system changes operational parameters (working mode, current capacity allocation) based on torque conditions. This allows the inverter to optimize between power output and component reliability across different operating regions.
Data Source
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AI summary
A motor control unit, a control method, and a power assembly relate to the field of inverter circuits, and are used to reduce costs of an inverter circuit and improve system efficiency of the inverter circuit. The motor control unit includes a three-phase full-bridge three-level inverter circuit (111) and a control apparatus (112). The three-phase full-bridge three-level inverter circuit (111) includes a vertical bridge circuit and a horizontal bridge circuit. A current capacity of a switching transistor in the vertical bridge circuit is greater than or equal to a maximum current of a motor. A current capacity of a switching transistor in the horizontal bridge circuit is less than the current capacity of the switching transistor in the vertical bridge circuit. The control apparatus (112) is configured to control the switching transistor in the horizontal bridge circuit based on torque of the motor, a current output by an output terminal of the vertical bridge circuit, a temperature of the switching transistor in the horizontal bridge circuit, and a terminal voltage of the switching transistor in the horizontal bridge circuit.