Adjustable PWM Control for Low Speed Torque and Voltage Accuracy
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Solution Overview
Problem
Existing power conversion systems face challenges in accurately controlling switching inverters, particularly at low motor speeds, where the decreasing pulse width of switching control signals makes it difficult to estimate inverter output voltages and increases thermal stress on switches, while also requiring derating to prevent overheating.
Innovation Solution
The method involves selectively using zero vectors when the maximal pulse width value exceeds a threshold during a PWM half cycle and accumulating output control values for use in subsequent cycles, effectively reducing switching frequency and maintaining high control loop sampling, thereby mitigating thermal stress and improving torque capabilities without derating or adjusting nominal switching frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the pulse width of switching control signals is decreased to operate at low motor speeds, then the motor speed control range is extended, but the inverter output voltage estimation accuracy deteriorates and thermal stress on switches increases
Solution Approach 1:
The patent dynamically adjusts the PWM carrier frequency based on the operating speed range. At low speeds, the carrier frequency is reduced to increase the effective pulse width, improving voltage estimation accuracy. At higher speeds, the nominal carrier frequency is restored to maintain speed control performance. This dynamic adaptation resolves the contradiction between extended speed range and measurement precision.
Solution Approach 2:
The system changes the PWM carrier frequency parameter adaptively according to the motor speed operating point. By modifying this key parameter, the system maintains optimal pulse width duration across different speed ranges, ensuring accurate voltage estimation even when operating at low speeds where pulse widths would naturally be smaller.
2Speed
If the pulse width of switching control signals is decreased to operate at low motor speeds, then the motor speed control range is extended, but the thermal stress on switches increases
Solution Approach 1:
The patent dynamically adjusts the PWM carrier frequency based on the operating speed range. At low speeds, the carrier frequency is reduced to increase the effective pulse width, improving voltage estimation accuracy. At higher speeds, the nominal carrier frequency is restored to maintain speed control performance. This dynamic adaptation resolves the contradiction between extended speed range and measurement precision.
Solution Approach 2:
The system changes the PWM carrier frequency parameter adaptively according to the motor speed operating point. By modifying this key parameter, the system maintains optimal pulse width duration across different speed ranges, ensuring accurate voltage estimation even when operating at low speeds where pulse widths would naturally be smaller.
3Temperature
If the PWM switching frequency is reduced to mitigate thermal stress at low speeds, then the thermal stress on switches is reduced, but the control loop sampling rate decreases
Solution Approach 1:
The patent segments the PWM control into two independent frequency domains: the carrier frequency (affecting thermal stress) and the control loop sampling frequency (affecting productivity). By decoupling these frequencies, the system can independently optimize each - using a reduced carrier frequency at low speeds to minimize thermal stress while maintaining the nominal control loop sampling rate to preserve productivity and control performance.
Solution Approach 2:
The patent dynamically adjusts the PWM carrier frequency based on the operating speed range. At low speeds, the carrier frequency is reduced to increase the effective pulse width, improving voltage estimation accuracy. At higher speeds, the nominal carrier frequency is restored to maintain speed control performance. This dynamic adaptation resolves the contradiction between extended speed range and measurement precision.
Data Source
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AI summary
Methods, control apparatus and computer readable mediums are presented for controlling a switching inverter in which a controller selectively suspends PWM carrier signals to provide inverter switching control signals using zero vectors in response to a maximal pulse width value for a present PWM half cycle being greater than a threshold value, and accumulates a present output control value for individual output phases for use in a subsequent PWM half cycle for selective effective reduction in switching frequency for low-speed operation while maintaining high frequency control loop sampling.