PWM Rectifier Modulation Scheme Switching for Loss Reduction
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Solution Overview
Problem
PWM rectifiers using semiconductor devices face increased switching losses and converter size due to high-speed switching, and reducing PWM frequency to mitigate this issue degrades control system response.
Innovation Solution
A PWM rectifier that switches between a three-phase modulation scheme and a modified two-phase modulation scheme based on detected current amplitude, reducing switching operations and losses by minimizing switching in high-amplitude current regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-speed switching is performed using a semiconductor device in a PWM rectifier, then the rectifier can convert AC to DC effectively, but switching losses increase and converter size increases
Solution Approach 1:
The patent applies dynamics by making the PWM frequency variable rather than fixed. The control unit dynamically adjusts the PWM frequency based on the magnitude of the three-phase current: using high frequency when current is small and low frequency when current is large. This dynamic adaptation resolves the contradiction by optimizing switching frequency to current conditions, reducing unnecessary switching losses during high current operation while maintaining effective power conversion.
Solution Approach 2:
The patent changes the parameter of PWM frequency based on operating conditions. By detecting current magnitude and adjusting the PWM frequency accordingly (high frequency for small current, low frequency for large current), the system optimizes the balance between power conversion effectiveness and switching loss reduction, directly addressing the contradiction between power capability and energy loss.
2Loss of energy
If PWM frequency is reduced to reduce switching losses, then switching losses decrease, but control system response degrades
Solution Approach 1:
The system dynamically adjusts PWM frequency based on real-time current detection. When current magnitude is small, high PWM frequency is used to maintain fast control response. When current magnitude is large, low PWM frequency is used to reduce switching losses. This dynamic frequency adaptation resolves the contradiction by matching PWM frequency to operational demands rather than using a fixed frequency.
Solution Approach 2:
The patent changes the PWM frequency parameter according to current magnitude conditions. By switching between high frequency (for small current) and low frequency (for large current), the system optimizes both control response and switching losses, resolving the contradiction between these two opposing requirements.
3Volume of moving object
If PWM frequency is reduced to suppress converter size increase, then converter size is controlled, but control system response degrades
Solution Approach 1:
The patent applies dynamics by making PWM frequency variable based on current magnitude. High PWM frequency is used when current is small (maintaining control response), and low PWM frequency is used when current is large (reducing converter size). This dynamic adjustment resolves the contradiction between converter size and control response speed.
Data Source
AI summary
Disclosed is a PWM rectifier in which switching losses in a semiconductor device are reduced without degrading the response of a control system. In a PWM overmodulation region, the modulation scheme is set to a three-phase modulation scheme. In other regions, a switchover condition such as the amplitude of an input current is acquired and compared with a switchover level. If the switchover condition equals or exceeds the switchover level, the modulation scheme is switched over to a modified two-phase modulation scheme which reduces the number of switching operations to two thirds for the same PWM frequency.