PV Power Converter Control for Black-Start MPPT and Bus Voltage Protection
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Solution Overview
Problem
Microgrid systems face challenges in accurately estimating the maximum photovoltaic power point before a black start, especially when not dependent on external power grids or loads, leading to frequent shutdowns and power-offs due to load power exceeding the maximum photovoltaic power point.
Innovation Solution
A power converter system with a controller that converts direct current from photovoltaic modules into alternating current, includes a direct current conversion circuit, an inverter circuit, and a controller. The controller adjusts the output power of the photovoltaic module to an operating power, then sets it to zero to prevent bus capacitor voltage from exceeding safe thresholds, ensuring safe operation and accurate estimation of maximum photovoltaic power.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the controller adjusts the output power of the photovoltaic module to operating power to enable MPPT mode operation, then the power converter can track maximum power point, but the bus capacitor voltage continuously increases and may exceed safe thresholds causing damage
Solution Approach 1:
The controller implements periodic action by alternating between MPPT mode and zero-power mode in cycles. During MPPT mode, the photovoltaic module operates at operating power to track maximum power point. When bus capacitor voltage reaches a preset threshold, the controller switches to zero-power mode, reducing output power to zero to allow voltage to decrease. This periodic switching resolves the contradiction between maintaining productivity through MPPT and preventing harmful voltage overload.
Solution Approach 2:
The system applies dynamics by making the output power of the photovoltaic module adjustable and switchable between two states: operating power for MPPT operation and zero power for voltage protection. The controller dynamically transitions between these states based on real-time bus capacitor voltage measurements, enabling the system to adapt its power output to prevent voltage overload while maintaining the ability to track maximum power point when safe.
2Adaptability or versatility
If the power converter operates without external load connection during black start, then the system can independently estimate maximum photovoltaic power point, but the bus capacitor voltage cannot be consumed and may become excessively high
Solution Approach 1:
During black start operation without external load, the controller employs periodic action by cycling between MPPT mode and zero-power mode. In MPPT mode, the system estimates maximum photovoltaic power point by operating at operating power. When bus capacitor voltage reaches the preset threshold, the controller switches to zero-power mode to allow voltage to decrease naturally without load consumption. This periodic switching enables independent black start capability while preventing voltage accumulation damage.
3Reliability
If the controller frequently switches the photovoltaic module output power between operating power and zero to protect bus capacitor voltage, then bus capacitor damage is prevented, but the system experiences frequent power adjustments and potential instability
Solution Approach 1:
The controller implements periodic action with carefully designed switching criteria to balance protection and stability. By using a preset voltage threshold for switching between MPPT mode and zero-power mode, the system prevents excessive frequency of power adjustments. The threshold-based control ensures that switching occurs only when necessary (when voltage reaches the threshold), avoiding unnecessary transitions that would cause instability, while still providing effective bus capacitor protection.
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 system effectively estimates the maximum power value of photovoltaic modules without external load connection, preventing bus capacitor damage and ensuring reliable system operation by accurately managing voltage levels and power output.
Implementation Method 1
an output of the direct current conversion circuit is connected to a bus capacitor of the inverter circuit, and the bus capacitor is configured to store electric energy from the photovoltaic module
Implementation Method 2
a power converter, a method for controlling a power converter, and a power supply system... convert a direct current from a photovoltaic module into an alternating current
Data Source
AI summary
A power converter includes a direct current conversion circuit, an inverter circuit, and a controller. An input of the direct current conversion circuit is configured to connect to the photovoltaic module, and an output of the direct current conversion circuit is connected to a bus capacitor of the inverter circuit. The controller is configured to change output power of the photovoltaic module. When power of the load is less than a specified threshold, the power converter is controlled to reduce the output power of the photovoltaic module from operating power to zero for at least once, where the operating power is greater than zero and less than rated output power, and when the output power of the photovoltaic module is the operating power, the power converter operates in a maximum power point tracking (MPPT) mode.