Inverter Torque Control via Normalized Speed Ratio
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Solution Overview
Problem
Inverter-fed permanent magnet synchronous motors (PMSMs) face challenges in efficiently controlling torque output due to limitations in switching states and voltage levels, leading to suboptimal operating points that result in inefficiencies and mismatched torque delivery in applications like electric vehicles.
Innovation Solution
A method is introduced to compute a normalized speed and use it to determine torque settings, allowing the controller to switch among inverter states based on a constant ratio of speed to voltage, using either six-step or PWM control methods, and regulating the electrical bus voltage to maintain efficient operation across varying conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional inverter switching states are used to control PMSM torque, then the motor can operate in standard voltage and speed ranges, but the torque control becomes suboptimal and inefficient at varying operating conditions
Solution Approach 1:
The patent applies dynamics by making the inverter switching strategy adaptive to changing operating conditions. The controller dynamically selects between six-step and PWM switching modes based on real-time torque and speed requirements, allowing the system to optimize torque control efficiency across varying operating conditions rather than being constrained by fixed switching patterns
Solution Approach 2:
The patent changes the switching state parameters of the inverter based on normalized speed and torque demands. By computing optimal switching states as a function of normalized speed and torque, the system adjusts the electrical parameters to maintain optimal operating points, thereby improving torque control efficiency and reducing energy losses
2Manufacturing precision
If the inverter switches rapidly among multiple states to maintain optimal torque, then torque control precision improves, but the complexity of control increases and mode transitions become frequent
Solution Approach 1:
The patent applies preliminary action by pre-computing optimal inverter switching states based on normalized speed and torque requirements. The controller determines the appropriate switching mode (six-step or PWM) and optimal switching states in advance based on the calculated normalized speed, reducing the need for frequent real-time adjustments and mode transitions while maintaining precise torque control
Solution Approach 2:
The patent achieves universality by creating a unified control framework that handles multiple operating conditions through a single normalized speed-based approach. The same control algorithm determines both six-step and PWM switching states using normalized speed as the key parameter, simplifying the control structure while maintaining precision across the entire operating range
3Speed
If the motor operates at high speeds with fixed voltage, then voltage limit is exceeded and torque capability is reduced, but increasing voltage increases system complexity and cost
Solution Approach 1:
The patent changes the voltage parameter adaptively by regulating the electrical bus voltage based on the normalized speed and torque requirements. When operating at high speeds, the system increases the bus voltage to maintain torque capability, and reduces voltage at lower speeds, thereby extending the motor's effective operating range without requiring a fixed high-voltage system
Solution Approach 2:
The patent applies dynamics by making the bus voltage a dynamic parameter that adjusts with operating conditions. The voltage regulator modifies the bus voltage in response to changing speed and torque demands, allowing the system to maintain optimal performance across a wide speed range while adapting to different operating conditions rather than being constrained by a fixed voltage level
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
This approach ensures consistent and efficient torque control, reducing mode transitions and improving motor performance by maintaining optimal operating points even as rotor speed and bus voltage vary, thereby enhancing vehicle acceleration and engine behavior.
Implementation Method 1
Inverters are utilized to convert the non-oscillating voltage Vdc into three oscillating voltages
Implementation Method 2
These winding currents induce a rotating magnetic field which may be out of phase with the rotor. The resulting shaft torque depends upon both the magnitude of the magnetic field and the phase angle relative to the rotor
Data Source
AI summary
A vehicle includes one or more inverter-fed electric machines such as permanent magnet synchronous motors. In response to a torque request, a controller issues commands to an inverter calculated to cause the motor to produce the requested torque. A method of operating the inverter may determine the commands based on the ratio of rotor speed to inverter input voltage, reducing the approximation error associated with multi-dimensional lookup tables. When the speed and voltage vary while maintaining a constant ratio and constant torque request, the issued commands produce a winding current in the electrical machine with constant direct and quadrature components.