Sub-resonant DC-DC Converter Control for Transformer Saturation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing DC-DC converters face inefficiencies and high costs in converting low voltage direct current (LVDC) from wind turbines or photovoltaic plants to medium voltage direct current (MVDC) due to transformer saturation and high power requirements, especially in megawatt-scale applications.
Innovation Solution
A DC-DC converter design featuring a transformer with a resonant tank on the secondary side and a control method that applies voltage pulses separated by zero voltage periods, using phase shift and frequency control to prevent transformer saturation and reduce power losses, allowing for efficient conversion of LVDC to MVDC.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional DC-DC converters are used for LVDC to MVDC conversion, then power conversion can be achieved, but transformer saturation occurs and power requirements increase
Solution Approach 1:
The patent applies periodic voltage pulses to the transformer primary winding, separated by zero voltage periods. This periodic action allows the transformer core to reset during zero voltage periods, preventing saturation while maintaining efficient power transfer during active periods. The resonant tank circuit naturally oscillates at its resonant frequency, creating periodic current flow that further prevents DC bias and saturation.
Solution Approach 2:
The patent operates the converter at a switching frequency lower than the resonant frequency of the LC tank circuit. This parameter choice ensures that the tank circuit has sufficient time to complete its resonant oscillation and return to zero current before the next voltage pulse, enabling zero current switching and preventing transformer saturation. The operating frequency is carefully selected to balance efficiency and saturation prevention.
2Power
If high power conversion is implemented, then megawatt-level output is achieved, but cooling requirements and power losses increase
Solution Approach 1:
The patent converts the potentially harmful effect of resonant oscillations into a beneficial zero current switching mechanism. The resonant tank circuit naturally oscillates when energized, and by timing the voltage pulses to allow complete oscillation cycles, the current naturally returns to zero. This transforms what could be a harmful high-current condition into a beneficial zero-current switching state, eliminating switching losses and reducing power dissipation in semiconductor devices.
Solution Approach 2:
The periodic application of voltage pulses with zero voltage intervals allows the resonant tank to complete its oscillation cycles. During these zero voltage periods, current in the tank circuit naturally decays to zero, enabling lossless switching. This periodic action maintains high efficiency even at megawatt power levels by ensuring that switching occurs only when current is zero, minimizing I²R losses and reducing cooling requirements.
3Speed
If conventional switching frequency is used, then power conversion speed is maintained, but zero current switching cannot be achieved
Solution Approach 1:
The patent deliberately selects a switching frequency lower than the resonant frequency of the LC tank circuit. This parameter change ensures that each voltage pulse allows the tank circuit to complete at least one full resonant oscillation cycle, returning current to zero before the next pulse. This lower frequency enables zero current switching, eliminating switching losses in the semiconductor devices while maintaining adequate power conversion speed for megawatt applications.
Solution Approach 2:
The periodic voltage pulsing at sub-resonant frequency allows the resonant tank circuit to naturally oscillate and return to zero current between pulses. This timing ensures that switching transitions occur when current is zero, enabling lossless switching. The periodic nature of this operation maintains consistent efficiency across all switching cycles, preventing energy losses that would occur with conventional continuous switching.
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 approach achieves high efficiency (above 99%) with reduced transformer size and power requirements, enabling efficient megawatt-level power delivery while minimizing transformer saturation and cooling needs, suitable for offshore wind farms and large photovoltaic plants.
Implementation Method 1
an input of the secondary side comprising inductor-capacitor (LC) circuitry... a frequency of the switching of the switching circuitry being lower than the resonant frequency of the LC circuitry
Implementation Method 2
a transformer, a primary side connected to a primary winding of the transformer, a secondary side connected to a secondary winding of the transformer
Data Source
AI summary
A DC to DC power converter is described that includes a transformer, a primary side connected to a primary transformer winding, and a secondary side connected to a secondary transformer winding. The secondary side comprises inductor-capacitor (LC) circuitry at an input, and a plurality of diodes providing uncontrolled rectification. A controller controls switching of the switching circuitry to apply voltage pulses to the primary transformer winding. The voltage pulses are separated by zero-voltage periods. A switching frequency of the switching circuitry is less than the resonant frequency of the LC circuitry.