Power Converter Black Start with Two-Stage Voltage Ramp Control
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Solution Overview
Problem
In power supply systems with parallel-connected inverters and power conversion systems, communication delays cause inconsistent voltage amplitudes and phases during black start, leading to circulating currents and potential shutdowns due to direct current bus overvoltage, necessitating a solution to achieve synchronous black start without additional hardware or communication mode changes.
Innovation Solution
A power converter with a controller that controls the voltage amplitude of alternating current output to be increased at different rates, first at a slower rate to maintain voltage differences below a threshold and then at a faster rate to complete black start within a fixed time, ensuring synchronized operation and reducing circulating currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If voltage amplitude is increased at a constant high rate during black start, then black start completion time is reduced, but circulating current among parallel devices increases due to voltage amplitude deviations
Solution Approach 1:
The patent applies dynamics by making the voltage increase rate variable rather than constant. The controller dynamically adjusts the voltage increase rate based on the current black start stage: using a first increase rate during an initial stage and a second increase rate during a subsequent stage, allowing optimization of both time and circulating current suppression
Solution Approach 2:
The black start process is segmented into multiple stages with different voltage increase rates. The controller divides the voltage increase process into at least two distinct phases, each with its own rate parameter, enabling differentiated control strategies for different stages of the black start sequence
2Object-generated harmful factors
If voltage amplitude is increased at a slower rate to suppress circulating current, then voltage difference between devices is reduced, but black start completion time increases
Solution Approach 1:
The controller dynamically switches between different voltage increase rates based on the black start stage. During the initial stage, a first increase rate is used to suppress circulating current; during the subsequent stage, a second increase rate is applied to accelerate voltage buildup and reduce overall completion time
Solution Approach 2:
The patent implements periodic action by applying different control parameters at different time intervals during the black start process. The controller transitions from one control mode (first increase rate) to another control mode (second increase rate) at predetermined stages, creating a time-based periodic control strategy
3Manufacturing precision
If additional hardware or communication mode changes are implemented to achieve synchronous black start, then synchronization accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system achieves synchronous black start through self-service control where each device's controller independently adjusts its voltage increase rate based on predefined control logic. The controller automatically determines the black start stage and applies appropriate increase rates without requiring additional synchronization hardware or communication infrastructure
Solution Approach 2:
The patent achieves synchronization by changing control parameters (voltage increase rates) rather than modifying hardware or communication modes. The controller adjusts the voltage increase rate parameter based on the black start stage, enabling precise synchronization control through parameter optimization alone
Data Source
AI summary
A direct current end of the power converter is configured to connect to a photovoltaic module or an energy storage battery, and an alternating current end of the power converter is configured to connect to a load or a power grid. The power converter includes a power conversion circuit and a controller. The power conversion circuit is configured to convert a direct current into an alternating current. The controller is configured to: during black start of the power converter, first control a voltage amplitude of the alternating current output by the power conversion circuit to be increased at a first rate, and then control the voltage amplitude of the alternating current output by the power conversion circuit to be increased at a second rate, where the second rate is greater than the first rate.