DC/AC and DC/DC Conversion Device for Reducing Switching Losses
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Solution Overview
Problem
Existing DC-to-AC conversion devices suffer from high-frequency switching losses and waveform distortion, particularly due to high-frequency switching in DC/DC converters and AC reactors, leading to inefficiencies and distorted AC waveforms.
Innovation Solution
A conversion device with a filter circuit, DC/AC and DC/DC conversion units, and a control unit that determines control duties to convert DC voltage into a pulsating current waveform with alternating periods, performing step-down operations and polarity inversion to generate a smooth AC voltage, while minimizing high-frequency switching losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high-frequency switching is performed in DC/DC converter and inverter, then voltage conversion is achieved, but switching loss and reactor loss increase
Solution Approach 1:
The inverter performs polarity inversion at a frequency twice the commercial frequency rather than high-frequency switching. The DC/DC converter operates periodically with switching performed only during specific periods when the DC bus voltage is higher than the absolute value of the AC voltage, reducing continuous switching losses while maintaining voltage conversion capability.
Solution Approach 2:
The patent maintains continuous voltage conversion by combining the DC/DC converter and inverter operations, where the DC/DC converter replenishes energy to the DC bus during periods when the inverter cannot provide sufficient voltage, ensuring continuous power supply without requiring constant high-frequency switching in both stages.
2Loss of energy
If the inverter performs only polarity inversion at twice commercial frequency, then switching loss is reduced, but waveform distortion occurs near zero cross point
Solution Approach 1:
The DC bus acts as an intermediary energy storage element between the DC/DC converter and inverter. The DC/DC converter regulates the DC bus voltage to provide a stable energy reservoir, enabling the inverter to perform smooth polarity inversion without waveform distortion at zero cross points.
Solution Approach 2:
The DC/DC converter performs preliminary energy conversion and storage in the DC bus before the inverter performs polarity inversion. By pre-charging the DC bus to appropriate voltage levels, the system ensures that sufficient energy is available for smooth waveform generation during the inverter's polarity switching operations.
3Manufacturing precision
If feedback control is used to reduce output current distortion, then waveform quality improves, but control cycle becomes longer and response is delayed
Solution Approach 1:
The control unit performs preliminary calculation of the DC reactor current command value based on the output voltage command value and predetermined parameters before actual operation. This pre-calculation approach eliminates the need for iterative feedback control, providing both high waveform quality and fast response without control cycle delays.
Solution Approach 2:
The patent replaces the mechanical feedback control system with a direct calculation-based control approach. Instead of using feedback loops that require measurement and adjustment cycles, the system directly computes the required current command values from voltage commands and fixed parameters, achieving instantaneous control response with high precision.
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
The solution effectively suppresses high-frequency switching losses and achieves smooth AC waveforms by optimizing the control of DC/AC and DC/DC conversion units, reducing distortion and improving conversion efficiency.
Implementation Method 1
a DC/DC conversion unit provided between the DC bus and the DC power supply and including a DC reactor
Implementation Method 2
a DC/AC conversion unit provided between the filter circuit and a DC bus
Implementation Method 3
a filter circuit connected to the load and including an AC reactor and a first capacitor
Data Source
AI summary
Duties of control for DC/AC and DC/DC conversion units are determined by considering electric influences of a filter circuit, a capacitor connected to a DC bus, and a DC reactor for an output voltage command value for supplying an AC voltage to a load. The DC/DC conversion unit is controlled to convert a DC voltage into a DC bus voltage waveform alternately having a period of a pulsating current waveform corresponding to the absolute value of the AC voltage and a period of the DC voltage as a pulsating current minimum value. The DC/AC conversion unit is controlled to perform step-down operation during the period of the DC voltage and thus perform conversion into a waveform of the absolute value of the AC voltage corresponding to the period of the DC voltage, and also to perform polarity inversion per one pulsating current cycle.