DC-Coupled Converter-Inverter Ripple Phase Matching
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Solution Overview
Problem
Existing power conversion systems experience increased pulsations in current flowing through the DC circuit between the converter and the inverter due to frequency differences between carrier waveforms used in PWM control, leading to unstable control and potential device damage.
Innovation Solution
A power conversion system is designed with a resonance circuit comprising capacitors in the DC voltage units of the converter and inverter, and an inductance component in the DC coupling unit. The switching frequency of both the converter and inverter is set higher than the resonance frequency of the circuit, and the phases of voltage ripples at the capacitors are controlled to be substantially matched.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the switching frequency is set higher than the resonance frequency of the resonance circuit, then pulsations in the current flowing through the DC coupling unit are reduced and control stability is improved, but the design constraints on the resonance circuit parameters become more stringent
Solution Approach 1:
The patent applies parameter changes by setting the switching frequency higher than the resonance frequency of the resonance circuit formed by the capacitors and DC coupling unit inductance. This frequency relationship parameter change ensures that the system operates in a stable region where pulsations are reduced, while the resonance circuit parameters are designed to satisfy this frequency constraint
2Reliability
If the phases of voltage ripples at the capacitors are controlled to be substantially matched, then pulsations in the current flowing through the DC coupling unit are reduced, but the synchronization control complexity increases
Solution Approach 1:
The patent employs feedback control by monitoring the voltage ripple phases at the capacitors and adjusting the switching operations to maintain substantially matched phases. This feedback mechanism ensures that the voltage ripples are synchronized, thereby reducing current pulsations in the DC coupling unit while providing a systematic approach to manage the synchronization requirement
3Volume of moving object
If capacitance of the capacitors in the DC voltage units is reduced to minimize device size, then the required device volume decreases, but current pulsations and control instability increase
Solution Approach 1:
The patent converts the potentially harmful effect of reduced capacitance (which would normally increase current pulsations) into a benefit by carefully designing the resonance circuit parameters and controlling the switching frequency to be higher than the resonance frequency. This approach allows smaller capacitors to be used while maintaining control stability through the resonance frequency relationship and phase-matched voltage ripple control
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively reduces pulsations in the current flowing through the DC coupling unit, stabilizes the control, and prevents potential overvoltage or excess current issues, while also minimizing the required capacitance.
Implementation Method 1
a switching frequency of each of the converter and the inverter is set to be the same and the switching frequency is higher than a resonance frequency of a resonance circuit that includes the first capacitor, the second capacitor, and the DC coupling unit
Data Source
AI summary
A power conversion system in which a converter and an inverter are coupled to each other via a DC coupling unit that has an inductance component is provided. A switching frequency of each of the converter and the inverter is set to be the same and the switching frequency is set to be higher than a resonance frequency of a resonance circuit that includes a first capacitor, a second capacitor, and the DC coupling unit such as a cable. A switching operation of at least one of the converter or the inverter is controlled such that phases of predetermined components of voltage ripples, at the first capacitor and the second capacitor, that are respectively generated by switching operations of the converter and the inverter are substantially matched.