Medium-Voltage PV Control Using DC Bus Voltage Communication
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Solution Overview
Problem
Medium-voltage photovoltaic distribution systems face challenges in achieving rapid real-time communication between distributed DC-DC converters and centralized DC-AC converters due to their large number and wide distribution, making traditional signal line communication inefficient.
Innovation Solution
A control system that utilizes a DC bus voltage sampling circuit and DC-DC converter control circuits to replace signal lines for communication, enabling energy management through bus voltage changes, thereby simplifying the communication system and improving reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional signal line communication is used between DC-DC converters and DC-AC converter, then communication can be established, but communication speed is slow and real-time control is difficult to achieve
Solution Approach 1:
The patent uses DC bus voltage as an intermediary carrier to transmit control information. Instead of using traditional signal lines for communication, the system modulates control commands onto the DC bus voltage by intentionally creating voltage drops or rises, which are then detected by DC-DC converters to change their power output. This eliminates the need for separate communication signal lines and achieves fast real-time control through the existing power transmission medium.
2Reliability
If communication signal lines are introduced for energy dispatching, then control functionality is achieved, but system complexity increases and reliability decreases
Solution Approach 1:
The patent merges the communication function with the power transmission function by using the DC bus voltage - which already exists for power delivery - as the communication medium. Control commands are embedded in voltage variations on the same DC bus that carries power, eliminating the need for separate communication infrastructure. This reduces system complexity and improves reliability by reducing the number of components and potential failure points.
3Speed
If DC bus voltage is used as communication medium, then communication speed and reliability are improved, but voltage stability may be affected
Solution Approach 1:
The patent implements periodic voltage modulation on the DC bus to encode control information. Instead of creating large, unstable voltage deviations, the system uses small, periodic voltage variations that are sufficient for communication but minimal enough to maintain overall voltage stability. The DC-AC converter periodically adjusts the DC bus voltage within tight tolerances to convey control commands, ensuring both fast response and voltage stability.
Data Source
AI summary
The embodiments of the present invention provide a control system and method for a medium-voltage photovoltaic distribution system. The medium-voltage photovoltaic distribution system includes N photovoltaic modules, N DC-DC converters, a DC-AC converter and a line-frequency transformer. Outputs of the N DC-DC converters are connected in parallel to a DC bus. The DC bus is connected to the DC-AC converter. The line-frequency transformer is configured to connect to a medium-voltage AC grid. The control system includes a bus voltage sampling circuit and N DC-DC converter control circuits corresponding to the N DC-DC converters respectively. Each DC-DC converter control circuit includes a bus voltage sampling circuit, a photovoltaic sampling circuit, a droop controller, a maximum power point tracking controller, an input voltage loop regulator and a pulse width modulation wave generating circuit. It can greatly simplify the communication system and improve the reliability of the control system that the DC bus voltage is used to replace a signal line for communication.