Motor Drive Control System Switching PWM Rectangular Wave
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Solution Overview
Problem
Existing motor drive control systems face challenges in stably driving motors from low speed to high speed due to limitations in PWM and rectangular wave energization methods, particularly because they require current sensors that cause power loss and instability during sensor breakdown.
Innovation Solution
A motor drive control system that switches between PWM and rectangular wave energization based on voltage command amplitudes and phases, calculated using motor parameters, without relying on current sensors, utilizing a voltage command generation unit, phase generation unit, control switching determination unit, PWM energization unit, and rectangular wave energization unit to manage switching operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If PWM energization is used, then the motor can be stably rotated at low speed, but the output voltage amplitude is restricted and the motor cannot be driven at high rotation
Solution Approach 1:
The system dynamically switches between PWM energization and rectangular wave energization based on the motor's rotation speed. At low speeds, PWM energization is used for stable rotation control. When the rotation speed exceeds a predetermined threshold, the system transitions to rectangular wave energization, which enables higher output voltage amplitude and supports high-speed motor operation. This dynamic switching strategy resolves the contradiction by adapting the energization method to the operating conditions.
2Power
If rectangular wave energization is used, then the output voltage is increased for high rotation, but control of the output voltage becomes difficult
Solution Approach 1:
The control system dynamically selects the energization method based on the desired output voltage level and motor speed. When high voltage amplitude is needed for high-speed operation, rectangular wave energization is activated. The switching decision is made by comparing the current rotation speed with a predetermined threshold, enabling automatic adaptation between control modes.
Solution Approach 2:
The system changes the energization mode parameter based on operating conditions. By switching between PWM mode (good for voltage control) and rectangular wave mode (good for high voltage output), the system optimizes the balance between voltage control precision and output voltage amplitude according to the motor's speed requirements.
3Reliability
If a current sensor is used to detect AC current, then switching determination between PWM and rectangular wave energization can be performed, but motor output is lowered due to electric power loss of the harness
Solution Approach 1:
The invention extracts the current detection function from the physical current sensor and implements it through software-based calculation. Instead of using a hardware current sensor that causes power loss in the harness, the system calculates the current value by measuring the voltage across a known impedance (the motor's back-EMF or winding resistance) and computing the current through Ohm's law. This virtual current sensing approach eliminates the power loss associated with physical current sensors while maintaining accurate current detection for switching determination.
4Measurement precision
If a current sensor is used, then current detection is possible, but the motor cannot be stably driven during the breakdown of the current sensor
Solution Approach 1:
The system extracts the current detection capability from the current sensor hardware and implements it through voltage measurement and calculation. By measuring the voltage across the motor terminals and calculating current based on known motor parameters (back-EMF constant, winding resistance), the system creates a software-based current sensing mechanism that is not susceptible to current sensor failures. This approach ensures continuous stable motor operation even when physical current sensors break down.
Solution Approach 2:
The invention introduces voltage measurement as an intermediary to indirectly obtain current information. Instead of directly measuring current with a vulnerable current sensor, the system measures voltage (which is more reliable) and uses motor parameters as intermediaries to calculate the current value. This indirect measurement approach provides a backup pathway for current detection that maintains system reliability during sensor failures.
Data Source
AI summary
Included are: a voltage command generation unit which generates a voltage command amplitude and a voltage command phase based on a current command value; a phase generation unit during rectangular wave energization, which generates a voltage command phase during rectangular wave energization; and a control switching determination unit which switches by determining as to which control of PWM energization or rectangular wave energization will be performed depending on the amount of the condition of a motor. A switching device unit is driven by the output from a PWM energization unit when switched to the PWM energization; and the switching device unit is driven by the output from a rectangular wave energization unit when switched to the rectangular wave energization. The voltage command generation unit calculates the voltage command amplitude and the voltage command phase by using parameters of the motor.