PWM Rectifier Modulation Scheme Selector for Switching Loss Reduction
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Solution Overview
Problem
PWM rectifiers face increased switching losses and apparatus size due to high-speed switching, and previous solutions that reduce switching losses, such as using a two-phase modulation scheme, lead to degraded controller response and earlier activation of protective functions, resulting in reduced maximum output.
Innovation Solution
A motor drive PWM rectifier that dynamically selects between three-phase and two-phase modulation schemes based on detected current thresholds, switching to two-phase when current is large to reduce switching losses and back to three-phase when near maximum rated current to minimize current ripple, thus optimizing switching device usage without reducing output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a two-phase modulation scheme is used to reduce switching losses, then switching losses decrease, but controller response degrades and maximum output is reduced
Solution Approach 1:
The patent dynamically switches between two-phase and three-phase modulation schemes based on detected current levels. When current exceeds a first threshold, the system transitions to two-phase modulation to reduce switching losses. When current exceeds a second threshold, it switches to three-phase modulation to maintain maximum output capability. This dynamic adaptation resolves the contradiction by allowing the system to optimize for efficiency at moderate loads while preserving full power capability at high loads.
Solution Approach 2:
The patent changes the modulation scheme parameter (from two-phase to three-phase) based on operating conditions. By detecting current levels and comparing them against thresholds, the system adjusts the modulation approach to balance switching loss reduction with maintaining maximum output capability, thus resolving the contradiction between energy efficiency and productivity.
2Loss of energy
If a two-phase modulation scheme is used to reduce switching losses, then switching losses decrease, but current ripple increases causing earlier protective function activation
Solution Approach 1:
The system dynamically adjusts the modulation scheme based on current ripple implications. At moderate current levels, two-phase modulation is used to reduce switching losses. When current approaches maximum rated levels, the system switches to three-phase modulation to minimize current ripple and prevent protective function activation, thus resolving the contradiction between reducing switching losses and controlling harmful current ripple.
3Object-generated harmful factors
If high-speed switching is used in PWM rectifier, then power supply harmonics and reactive power are reduced, but switching losses and apparatus size increase
Solution Approach 1:
The patent uses dynamic modulation scheme selection to balance harmonic reduction with switching loss management. By switching between two-phase and three-phase schemes based on current thresholds, the system maintains effective PWM rectification for harmonic reduction while optimizing switching frequency and pattern to minimize switching losses at different operating points.
Data Source
AI summary
A motor drive PWM rectifier includes a control section which generates the PWM signal in accordance with either a three-phase modulation scheme or a two-phase modulation scheme in which a PWM voltage command for one phase selected from among three phases each constituting the PWM voltage command in the three-phase modulation scheme is set and held at a level equivalent to a maximum value or minimum value of the PWM carrier and in which a PWM voltage command for the other two phases created by also applying an offset, required to achieve the setting, to the other two phases, a detecting section which detects three-phase AC current and outputs a detected current value, and a selecting section which selects the two-phase modulation scheme when the detected current value is larger than a first threshold value but smaller than a second threshold value, and otherwise selects the three-phase modulation scheme.