Power Converter Waveform Distortion Reduction
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Solution Overview
Problem
Existing inverter devices experience waveform distortion due to phase lag between output voltage and current, leading to increased oscillation and distortion in load voltage, which requires larger filter circuits to mitigate.
Innovation Solution
The inverter device employs a power converter with bidirectional switches and anti-parallel diodes, operating modes that alternate switching elements based on PWM signals to synchronize voltage and current polarities, thereby synthesizing alternating current voltage unaffected by idle periods, reducing waveform distortion without enlarging filter circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a reactor is used in the filter circuit to eliminate harmonic components, then the output current becomes phase-lagged with respect to the output voltage, but this causes waveform distortion and oscillation in the load voltage
Solution Approach 1:
The patent introduces a bidirectional switch as an intermediary component between the switching elements and the filter circuit. This bidirectional switch actively compensates for the phase lag caused by the reactor, preventing waveform distortion while maintaining the harmonic elimination function. The bidirectional switch acts as a mediator that reconciles the conflict between current phase lag and waveform quality.
Solution Approach 2:
The patent changes the operational parameters of the switching elements by introducing specific on/off timing control. By adjusting the switching timing to account for the reactor's phase lag effect, the system maintains sinusoidal waveforms despite the presence of the reactor. This parameter adjustment allows the system to operate effectively with the phase-lagging current.
2Object-generated harmful factors
If the filter circuit size is increased to reduce waveform distortion, then the load voltage oscillation is reduced, but the device complexity and cost increase
Solution Approach 1:
The bidirectional switch serves as an active intermediary that compensates for waveform distortion without requiring a larger passive filter circuit. By actively controlling the switching timing and using the bidirectional switch to manage current flow, the system reduces waveform distortion while maintaining a compact filter circuit design.
Solution Approach 2:
The patent replaces the passive mechanical approach of simply enlarging the filter circuit with an active control system. Instead of increasing the physical size of passive components, the system uses active switching control and bidirectional switch operation to achieve waveform distortion reduction, thereby avoiding increased device complexity.
3Reliability
If idle period is added to prevent short-circuiting of switching elements, then the switching safety is improved, but the output voltage waveform distortion increases
Solution Approach 1:
The patent implements dynamic control of the switching elements by adjusting their on/off timing based on the operational state. The switching timing is dynamically modified to account for the idle period requirement while maintaining waveform quality. This dynamic approach allows the system to adapt the switching schedule to prevent short-circuiting without introducing significant waveform distortion.
Solution Approach 2:
The patent changes the timing parameters of the PWM signals to optimize the balance between switching safety and waveform quality. By adjusting the pulse width and timing to account for the idle period, the system maintains switching safety while minimizing the impact on output voltage waveform. This parameter optimization resolves the contradiction between reliable switching and waveform distortion.
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
In a period in which the polarities of output voltage and output current of a power converter differ, a pulse train voltage corresponding to a PWM signal is output by a switching element Q1 and switching element Q2 being turned off, one element of a switch element S1 and switch element S2 being turned on, and the other element being turned on and off based on an inverted signal of a PWM signal pulse width modulated in accordance with an output voltage command.