Inverter PWM Control for Voltage Error Reduction
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Solution Overview
Problem
Existing inverter devices face output voltage and phase errors due to imbalanced positive and negative voltage integration in high-frequency operations and overmodulation modes, leading to unstable motor control, particularly when the inclination of the modulated wave is steep near zero crossing.
Innovation Solution
The inverter device employs asynchronous PWM control by shifting the ON and OFF timing of PWM pulses to equilibrate positive and negative side output voltages through linear approximation of the modulated wave near zero crossing, generating PWM pulses that balance voltage levels and reduce phase errors, thereby stabilizing motor control at high-speed rotations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a 50% duty cycle is set near the zero crossing of inverter output voltage to minimize output voltage error, then output voltage error is reduced, but inverter output is reduced since the average voltage becomes 0V
Solution Approach 1:
The patent applies local quality by differentiating the PWM control strategy based on the operating region. In the linear modulation region, conventional PWM is used, while in the overmodulation region near zero crossing, a specialized duty cycle adjustment is applied. This localized approach ensures voltage error correction is applied only where needed (near zero crossing in overmodulation) without unnecessarily reducing output in other operating conditions.
Solution Approach 2:
The patent dynamically adjusts the duty cycle based on real-time operating conditions (modulation factor and zero crossing detection). The control system continuously monitors the modulation state and adaptively modifies the PWM duty cycle near zero crossing when in overmodulation mode, rather than using a fixed duty cycle strategy. This dynamic adjustment optimizes both voltage accuracy and output power across varying operating conditions.
2Measurement precision
If the modulation factor is suppressed to generate PWM pulses and reduce phase errors near zero crossing, then phase errors are reduced, but inverter output is reduced
Solution Approach 1:
The patent applies preliminary action by proactively adjusting the PWM pulse generation strategy before significant phase errors accumulate. The system detects the overmodulation condition and zero crossing point in advance, then pre-adjusts the duty cycle to prevent large phase errors from developing, rather than attempting to correct them after they occur. This proactive approach maintains both accuracy and output power.
3Measurement precision
If carrier frequency is changed according to inverter output frequency to reduce inverter output error, then output error is reduced, but control calculation load is increased
Solution Approach 1:
The patent changes the modulation factor parameter dynamically based on the detected overmodulation condition and zero crossing position, rather than changing the carrier frequency. This parameter adjustment achieves the same goal of reducing output error in overmodulation mode but with significantly lower computational complexity, as it involves simple duty cycle calculations rather than full frequency synchronization and schedule adjustments.
Data Source
Figure 1
Figure 2(a)~2(d)
Figure 3(a)~3(c)
AI summary
Provided are an inverter device deterring PWM voltage error even if high inverter output frequencies are used for overmodulation driving and an electric vehicle equipped with the inverter device. In an angular section where the output voltage from an inverter device (100) is linearly approximated with the zero cross point as the center thereof, a PWM generator (140) in the inverter device (100) changes either the time interval between the centers of PWM ON pulses or the time interval between the centers of PWM OFF pulses depending on the inverter operation state. An electric vehicle is equipped with the inverter device (100), which drives a motor (300).