Modular Multilevel Converter Full-Wave Control Low Frequency
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional modular multilevel DC/AC converters face challenges in supplying low-frequency signals without being bulky or expensive, particularly for variable speed AC motor applications, due to the high cost and size of energy storage devices required for floating capacitance, which limits their use in medium voltage applications.
Innovation Solution
A modular multilevel power conversion device with AC output and AC or DC input, utilizing a modular multilevel DC/AC converter with full-wave control and PWM control strategies to minimize the usage and size of energy storage devices, allowing for efficient operation at low frequencies and reduced passive component requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional modular multilevel DC/AC converters use floating capacitance energy storage devices to supply low-frequency signals, then the converter can operate at low frequencies, but the energy storage devices become oversized and expensive
Solution Approach 1:
The patent changes the operating parameters by introducing full-wave control mode that operates the switching modules differently during positive and negative half-cycles. This parameter change allows the energy storage devices to be charged and discharged more efficiently, reducing the required capacitance size while maintaining low-frequency operation capability
Solution Approach 2:
The patent implements periodic charging and discharging of the energy storage devices through full-wave control, where each switching module undergoes regular charge-discharge cycles synchronized with the output frequency. This periodic action ensures that the energy storage devices are fully utilized and sized appropriately for the application rather than being oversized for continuous low-frequency operation
2Power
If conventional modular multilevel DC/AC converters are designed for medium voltage applications, then the converter can handle high power, but the device becomes bulky and expensive
Solution Approach 1:
The patent divides the power conversion system into multiple independent switching modules connected in series, where each module handles a portion of the total voltage and power. This segmentation allows the use of smaller, more manageable components while achieving high power capability through modular aggregation, reducing overall device bulk
Solution Approach 2:
The patent designs universal switching modules that can operate in multiple modes (full-wave control and PWM control) and handle both voltage and current regulation functions. This multi-functionality reduces the need for separate dedicated components for each function, thereby reducing overall device size and cost while maintaining high power capability
3Manufacturing precision
If conventional modular multilevel DC/AC converters use PWM control for low-frequency operation, then the converter can maintain good waveform quality, but the energy storage devices must be oversized
Solution Approach 1:
The patent implements dynamic control that adapts the switching module operation based on the instantaneous output frequency and load conditions. At low frequencies, full-wave control is used to optimize energy storage device utilization, while PWM control is applied when appropriate. This dynamic adaptation maintains waveform quality across different operating conditions without requiring oversized energy storage devices for all scenarios
Data Source
Figure 1
Figure 2A~2D
Figure 3
AI summary
The invention relates to a modular multi-level power converter device having an AC output, comprising a modular multi-level DC/AC converter (21) having a plurality of arms (1.1, 1.2, 1.3) in parallel, the ends of which define input terminals (27, 28), each arm comprising two lines of modules (4.11, 4.12, 4.13, 4.14, 4.15, 4.16) in series, each switching module having a pair of switches in series (T111, T211), mounted on the terminals of an energy-storage device (4.3), the DC/AC converter adjusting the frequency at the output of the converter device. The device also comprises a converter having a DC output (20), comprising two output terminals (A, 22, 91, 92) connected to the input terminals (27, 28) of the DC/AC converter (21), said converter having a DC output (20) adjusting the amplitude at the output of the converter device, the DC/AC converter (21) also comprising means (29) for controlling the switches (T111, T211) of the modules, which apply a full-wave command to the switches during at least one time interval, the modules of a single line being in the same state simultaneously.