DC/DC Converter Voltage Target Selection for Photovoltaic Control Accuracy
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Solution Overview
Problem
In power conversion devices for photovoltaic generation, low DC voltages inputted to the device result in significant reactive power due to smoothing capacitors, which affects control accuracy and efficiency.
Innovation Solution
A power conversion device with a control unit that calculates and sets voltage target values for DC/DC and DC/AC converters to manage switching operations, ensuring the DC/DC converter performs step-up operations when the DC voltage is low, reducing reactive power and maintaining control accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the DC voltage is low, then the reactive power due to smoothing capacitors increases significantly, but the control accuracy deteriorates
Solution Approach 1:
The control unit performs preliminary voltage assessment before controlling the converters. It calculates whether the DC voltage is lower than the peak value of the absolute value of the AC voltage, and based on this preliminary judgment, it selectively activates the DC/DC converter to perform step-up operation in advance, preventing the harmful effect of low voltage on control accuracy before it occurs
Solution Approach 2:
The DC/DC converter acts as an intermediary device between the DC power supply and the DC/AC converter. When the DC voltage is low, the DC/DC converter performs step-up operation to raise the voltage to an appropriate level, thereby eliminating the harmful effect of low DC voltage on control accuracy without requiring changes to the control algorithm itself
2Measurement precision
If the DC/DC converter performs step-up operation at low DC voltage, then control accuracy is maintained, but device complexity increases
Solution Approach 1:
The control unit dynamically adjusts the operation mode of the DC/DC converter based on real-time voltage conditions. The converter operates in step-up mode only when the DC voltage is lower than the peak AC voltage, and remains inactive or operates in bypass mode when the voltage is sufficient. This dynamic adaptation avoids the complexity of always having the converter active while maintaining control accuracy when needed
Solution Approach 2:
The control unit changes the operational parameters of the DC/DC converter based on the DC voltage level. When the DC voltage is low, the converter is activated with specific switching parameters to perform step-up operation. When the DC voltage is sufficient, the converter parameters are changed to disable or bypass operation. This parameter-based control allows a single converter design to handle multiple voltage conditions without requiring additional hardware complexity
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 the reduction in control accuracy and reactive power issues at low DC voltages, enhancing the overall efficiency and accuracy of power conversion.
Implementation Method 1
a DC/DC converter provided between the DC power supply and a DC bus
Implementation Method 2
a capacitor connected to the DC bus
Implementation Method 3
a DC/AC converter provided between the DC bus and the filter circuit
Data Source
AI summary
A control unit of a power conversion device calculates a current target value and a voltage target value for a DC/AC converter on the basis of an output current target value, to control the DC/AC converter, and calculates a current target value for the DC/DC converter on the basis of the current target value and the voltage target value, and a voltage target value for the DC/DC converter, to control the DC/DC converter, thereby controlling output of an AC power. The control unit selects, as the voltage target value for the DC/DC converter, a greatest value at a present time, from among a DC voltage value of the DC power supply, an absolute value of a voltage target value for an AC side of the DC/AC converter, and a DC voltage lower limit value which is a predetermined value smaller than a peak value of the absolute value.