Three-Inverter Power Conversion Device for Voltage Ripple Reduction
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Solution Overview
Problem
Existing power conversion systems face challenges in efficiently generating three-phase AC power from a DC bus while minimizing voltage ripple and maintaining reliable operation, particularly in systems with multiple inverters where voltage amplitude exceeds the DC voltage, leading to overmodulation and reduced reliability.
Innovation Solution
A power conversion device comprising three inverters that convert DC power to single-phase AC power, controlled by a controller generating a fundamental wave command and an adjustment wave command with triple frequency, superimposed to produce three-phase AC power. The controller calculates the phase and amplitude of the adjustment wave based on the power factor to reduce voltage ripple and includes modules for overmodulation correction and boost control to manage voltage amplitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If voltage amplitude is increased beyond DC voltage in multiple inverter systems, then output capacity is improved, but overmodulation occurs reducing reliability
Solution Approach 1:
The patent applies parameter changes by introducing an adjustment wave with triple the frequency of the fundamental wave and adjusting its amplitude and phase. This modifies the voltage waveform parameters to prevent overmodulation while maintaining high output capacity, resolving the contradiction between power output and system reliability
Solution Approach 2:
The patent employs periodic action through the adjustment wave that oscillates at triple the fundamental frequency. This periodic modulation of the voltage command signal enables continuous operation at high power levels without entering the overmodulation region, thereby maintaining reliability while increasing output capacity
2Device complexity
If capacitor capacity is reduced to minimize voltage ripple, then device complexity is improved, but voltage ripple control becomes difficult
Solution Approach 1:
The patent changes the waveform parameters by superimposing an adjustment wave at triple the fundamental frequency. This parameter modification shifts the ripple frequency spectrum, enabling effective ripple suppression with smaller capacitors and reducing overall device complexity while maintaining voltage stability
3Object-generated harmful factors
If adjustment wave amplitude is increased to reduce voltage ripple, then voltage ripple is reduced, but overmodulation may occur
Solution Approach 1:
The patent implements feedback control by calculating the adjustment wave amplitude based on the detected voltage ripple characteristics and power factor. This closed-loop approach dynamically adjusts the adjustment wave parameters to suppress ripple while preventing overmodulation, resolving the contradiction between ripple reduction and reliability
Solution Approach 2:
The patent employs dynamic adjustment of the adjustment wave amplitude and phase according to operating conditions such as power factor and load demands. This dynamic control enables the system to maintain optimal ripple suppression without entering overmodulation across varying operating points, balancing both objectives
Data Source
AI summary
A power conversion device includes three inverters configured to convert DC power of DC buses into single-phase AC power, and a controller configured to control the three inverters so as to generate three-phase AC power. The controller is configured to generate a fundamental wave command for generating one-phase AC power constituting the three-phase AC power, and to generate an adjustment wave command having triple the frequency of the fundamental wave command. Additionally, the controller is configured to output a phase voltage command, in which the adjustment wave command is superimposed on the fundamental wave command, and to determine an initial phase of the adjustment wave command to be offset from an initial phase of the fundamental wave command so as to reduce a voltage ripple occurring in the DC buses at double the frequency of the fundamental wave command.