Three-Phase Multilevel Inverter Control for Ripple Current Suppression
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The existing DPWM modulation scheme for three-phase multi-level inverters reduces switch loss but increases ripple current in the busbar capacitor, leading to increased costs due to the need for larger capacitors.
Innovation Solution
A control method that determines a modulation ratio and uses a common-mode voltage regulation signal to optimize the DPWM modulation scheme, reducing ripple current while maintaining low switch loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If DPWM modulation scheme is used to reduce switch loss, then switch loss is reduced, but ripple current in busbar capacitor is increased
Solution Approach 1:
The patent dynamically adjusts the modulation mode between DPWM and SPWM based on the modulation ratio. When modulation ratio is below a threshold, DPWM is used to minimize switch loss; when it exceeds the threshold, SPWM is used to suppress ripple current. This parameter-based switching resolves the contradiction by adapting the modulation strategy to operating conditions.
Solution Approach 2:
The patent implements a dynamic modulation strategy that transitions between DPWM and SPWM modes based on real-time modulation ratio monitoring. This dynamic adjustment allows the system to optimize switch loss reduction while preventing excessive ripple current generation, resolving the static contradiction through adaptive control.
2Object-generated harmful factors
If busbar capacitor size is increased to suppress ripple current, then ripple current is suppressed, but system cost is increased
Solution Approach 1:
Instead of increasing capacitor size, the patent changes the modulation parameter (switching between DPWM and SPWM modes) to control ripple current. This approach suppresses ripple current through control strategy optimization rather than hardware scaling, avoiding increased system cost.
Solution Approach 2:
The patent replaces the mechanical solution of increasing capacitor size with a control-theory-based solution (modulation mode switching). This substitution achieves ripple current suppression through electrical control parameters rather than physical component scaling, reducing system cost.
3Manufacturing precision
If SPWM technology is used to obtain high-quality sinusoidal output, then output voltage quality is improved, but switch loss is excessively large
Solution Approach 1:
The patent changes the modulation parameter (modulation ratio) to determine when to use SPWM for high output quality and when to use DPWM for low switch loss. By dynamically adjusting this parameter, the system achieves both high output voltage quality and low switch loss under different operating conditions.
Solution Approach 2:
The patent implements a dynamic modulation strategy that transitions between SPWM and DPWM modes based on real-time modulation ratio monitoring. This dynamic adjustment allows the system to optimize output voltage quality while minimizing switch loss, resolving the contradiction through adaptive control rather than static selection.
Data Source
AI summary
A control method of a three-phase multi-level inverter includes: determining a modulation ratio based on output of the three-phase multi-level inverter, where the modulation ratio indicates a ratio of an amplitude value of a sinusoidal modulation wave in pulse width modulation to an amplitude value of a carrier; generating, based on the modulation ratio and a modulation ratio threshold, a common-mode voltage regulation signal for regulating a common-mode voltage in phase voltages of the three-phase multi-level inverter; adding the common-mode voltage regulation signal and a differential-mode voltage regulation signal for regulating a differential-mode voltage in the phase voltages of the three-phase multi-level inverter to obtain a composite regulation signal, where the composite regulation signal is presented as a modulation wave for discontinuous pulse width modulation (DPWM); and generating, based on the composite regulation signal, drive signals for controlling switches of phases of the three-phase multi-level inverter.