Power Conversion Device Impedance Control for Parallel Power Allocation
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Solution Overview
Problem
In parallel power conversion systems, existing technologies face challenges in uniformly allocating power among devices due to variations in output impedances, leading to instability and potential device overload during instantaneous power changes.
Innovation Solution
A power conversion device with a switching element unit, filter reactor, filter capacitor, output reactor, reactor current detection, output voltage detection, and a control unit that includes a voltage command generation, PWM signal generation, PLL, voltage correction calculation, and correction units to adjust output impedance based on reactor current, ensuring uniform power allocation among multiple devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional droop control methods are used to balance power allocation, then power distribution is uniformed, but the control requires one cycle or longer detection time making it impossible to respond to instantaneous power changes
Solution Approach 1:
The patent pre-calculates and stores the relationship between output current and voltage correction amounts in a lookup table before operation. During instantaneous power changes, the control unit directly retrieves the appropriate correction amount from this pre-prepared table based on the detected output current, eliminating the need for real-time one-cycle detection and calculation, thus achieving both rapid response and accurate power balancing
Solution Approach 2:
The patent creates a virtual model of the system's impedance characteristics through the lookup table that maps output current to voltage correction amounts. This virtual model allows the control system to simulate and compensate for impedance variations without requiring actual one-cycle measurement cycles, enabling instantaneous response while maintaining the effectiveness of droop control for power balancing
2Ease of manufacture
If power conversion devices operate in parallel with different output impedances, then manufacturing is simplified, but load allocation varies causing instability and potential overload
Solution Approach 1:
The patent dynamically changes the output voltage parameter based on the detected output current to compensate for impedance variations. By retrieving voltage correction amounts from a lookup table that maps current values to correction amounts, the system adjusts the output voltage in real-time to maintain stable and uniform power allocation among parallel-operating devices with different output impedances
Solution Approach 2:
The patent implements a feedback mechanism where the control unit continuously detects the output current and uses this information to retrieve appropriate voltage correction amounts from the lookup table. This closed-loop feedback ensures that devices with varying output impedances due to manufacturing tolerances can operate stably in parallel with uniform power allocation
Data Source
AI summary
In a control unit for drive-controlling a switching element unit of each power conversion device, a voltage correction amount calculation unit calculates a correction amount corresponding to voltage drop due to impedance between the switching element unit and filter reactor. A voltage command correcting unit corrects a voltage command generated by the voltage command generation unit, using the correction amount. Thus, for a power conversion device 21 that has a small output impedance, correction is performed so as to increase the output impedance, and a PLL unit changes the frequency in accordance with active power calculated from output voltage and output current of the power conversion device, so as to uniform power allocations.