DC Bus Discharge Control Using Stator Coordinate System
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Solution Overview
Problem
Residual power on a high-voltage DC bus cannot be quickly discharged due to the impossibility of preventing a stator current from generating mechanical torque when a rotor position sensor fails in high-voltage systems using permanent magnet synchronous motors.
Innovation Solution
A DC bus discharge control method that converts motor current signals into a stator coordinate system, generates a voltage control signal based on a random current reference instruction, and controls a switching device using PWM signals to manage the discharge process without relying on rotor position information, ensuring almost no effective torque is generated during discharge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rotor position sensor is used to control stator current according to the current active discharge method, then the discharge control can be implemented, but when the rotor position sensor fails, the stator current cannot be prevented from generating mechanical torque and residual power cannot be quickly discharged
Solution Approach 1:
The patent extracts the discharge control function from the rotor coordinate system (which requires rotor position sensor) and implements it independently in the stator coordinate system. This separation allows the discharge control to operate without relying on rotor position information, solving the reliability problem when the sensor fails while maintaining fast discharge capability.
Solution Approach 2:
The patent makes the discharge control system universal by enabling it to function in both normal conditions (with rotor position sensor) and fault conditions (without rotor position sensor). The stator coordinate system control method provides a universal solution that works regardless of rotor position sensor status, ensuring both reliability and productivity.
2Measurement precision
If the current control method in rotor coordinate system is used, then torque control is precise, but the system becomes dependent on rotor position sensor and cannot operate when it fails
Solution Approach 1:
The patent segments the control system into two independent coordinate systems: rotor coordinate system for normal torque control and stator coordinate system for discharge control. This segmentation allows each system to operate independently, with the stator coordinate system providing a backup that doesn't require rotor position sensor, thus improving adaptability while maintaining precision through proper control algorithms.
Solution Approach 2:
The patent changes the control parameters from rotor-based (requiring position sensor) to stator-based (independent of position sensor). By transforming the control equations and using different parameter sets in the stator coordinate system, the system maintains control capability without relying on the rotor position sensor, improving versatility.
3Object-generated harmful factors
If a random current reference instruction with zero mean is used in stator coordinate system, then mechanical torque is prevented from being generated, but the control complexity increases compared to traditional methods
Solution Approach 1:
The patent uses a random current reference instruction with zero mean, which can be viewed as a stochastic periodic action that continuously varies around zero. This approach prevents sustained torque generation while maintaining relatively simple control structure, as the random signal with defined statistical properties (zero mean, specific variance) can be generated and processed using standard control algorithms.
Data Source
AI summary
The present disclosure relates to a DC bus discharge control method, including that: an active discharge instruction is received; a motor current signal is acquired according to the active discharge instruction; the motor current signal is converted into a current signal in a stator coordinate system; a voltage control signal in the stator coordinate system is output based on the current signal in the stator coordinate system and a random current reference instruction of a preset stator coordinate system; and the voltage control signal in the stator coordinate system is converted into a three-phase voltage control signal, and a working state of a switching device is controlled according to the three-phase voltage control signal.