Three-Terminal DC Transformer Control for Circulating Current Suppression
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Solution Overview
Problem
The connection of devices with varying operating and output voltages in DC distribution networks, such as storage batteries, LED lights, and home appliances, to a static DC transformer results in large voltage differences between DC terminals, leading to safety impairments and degradation of conversion efficiency due to high current peaks and circulating currents.
Innovation Solution
A control apparatus for a three-terminal static DC transformer that generates rectangular AC-side voltages with three levels (positive, null, and negative) and adjusts the phase differences between self-excited single-phase inverters to equalize the voltage between DC terminals, minimizing peak and root mean square current values and circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If devices with varying operating voltages are connected to a static DC transformer, then the DC distribution network can accommodate diverse loading apparatuses, but large voltage differences between DC terminals occur leading to high current peaks and circulating currents
Solution Approach 1:
The patent applies dynamic control by adjusting the duty ratios of PWM signals for each inverter circuit based on real-time detection of DC terminal voltages. The control apparatus dynamically modifies the switching characteristics of inverters to adapt to varying voltage conditions, thereby suppressing harmful circulating currents while maintaining the ability to connect diverse voltage-level devices to the DC distribution network.
2Adaptability or versatility
If the voltage difference between DC terminals is large, then diverse voltage requirements are met, but the current peak value and effective current value become large impairing safety
Solution Approach 1:
The patent implements feedback control by detecting the actual DC terminal voltages and using this information to adjust the PWM duty ratios for each inverter. This closed-loop feedback mechanism ensures that the system automatically adapts to voltage variations, preventing excessive current peaks that would compromise safety while still accommodating diverse voltage requirements of connected devices.
3Adaptability or versatility
If the voltage difference between DC terminals is large, then different voltage levels are supported, but the circulating current that does not contribute to power transmission becomes large degrading conversion efficiency
Solution Approach 1:
The patent changes the operational parameters of the inverter circuits by adjusting PWM duty ratios according to the detected voltage differences between DC terminals. This parameter adjustment optimizes the power transmission characteristics, minimizing circulating currents that do not contribute to useful power transfer while maintaining support for multiple voltage levels across different terminal connections.
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
Effectively prevents safety impairments and conversion efficiency degradation even with large voltage differences between DC terminals by suppressing peak and root mean square current values and minimizing non-transmitting circulating currents.
Implementation Method 1
first, second, and third self-excited single-phase inverters which are connected parallelly to DC capacitors, respectively, at their DC sides are connected via a high frequency transformer at their AC sides
Implementation Method 2
connected via a high frequency transformer at their AC sides so as to supply electric power between first, second, and third DC terminals
Data Source
AI summary
With a control apparatus for a three-terminal static DC transformer for drive-controlling the three-terminal static DC transformer, a computing unit is provided with first, second, and third self-excited single-phase inverters so that each of voltages at their AC sides is caused to become a rectangular wave of three levels which are a positive voltage, a null voltage, and a negative voltage, wherein the rectangular wave is caused to undergo time changes so that the rectangular wave of the positive voltage is repeated in a half-cycle by being folded at the null voltage; and the computing unit drives each of the first, second, and third self-excited single-phase inverters so that a product of a length of a section in which the AC-side voltage of each of the first, second, and third self-excited single-phase inverters is not zero, and a voltage between the first, second, and third DC terminals becomes equal.