Solar String Injection Circuit for Maximum Power Point Optimization
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Solution Overview
Problem
Solar power generation systems face inefficiencies due to impaired cells in series strings, which cause power loss and damage, and existing solutions like boost circuits are expensive and inflexible, while conventional inverters require complex MPPT circuits for each string, leading to high costs and strain on the electrical grid from variable power output.
Innovation Solution
The implementation of injection circuits that monitor and adjust the voltage of impaired strings to maintain maximum power point operation, allowing strings to operate independently and reducing the need for complex inverter designs, with the option to connect to a DC bus or external power sources for power compensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bypass diodes are used to protect impaired cells, then cell damage is prevented, but power generation efficiency deteriorates because unimpaired cells are forced to operate away from their maximum power point
Solution Approach 1:
The patent segments the array management by introducing independent injection circuits for each string, allowing individualized control of each string's operating point rather than forcing all strings to operate at a common voltage. This segmentation enables unimpaired cells to operate at their maximum power point while still providing protection to impaired cells through controlled voltage adjustment.
Solution Approach 2:
The patent changes the voltage parameter dynamically by using injection circuits to add or remove voltage from individual strings based on their specific conditions. This allows the operating voltage of each string to be independently adjusted, enabling unimpaired cells to operate at their optimal voltage while impaired cells receive protective voltage adjustment, thereby resolving the contradiction between protection and efficiency.
2Productivity
If conventional inverters with MPPT circuits for each string are used, then maximum power point tracking is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the maximum power point tracking function from the inverter and implements it through simple injection circuits connected to each string. Instead of requiring a complex MPPT circuit within the inverter, the patent removes this complexity by placing simple voltage-injecting circuits at the string level, which can be independently controlled to achieve optimal power extraction without complicating the inverter design.
Solution Approach 2:
The injection circuit acts as an intermediary device between the solar string and the inverter. Rather than requiring the inverter to perform complex MPPT functions, the injection circuit pre-adjusts the string voltage to the optimal operating point, serving as a mediator that simplifies the inverter's task while maintaining power optimization capabilities.
3Power
If strings are connected in parallel to form arrays, then substantial power at convenient voltages is achieved, but power loss occurs when impaired cells force other cells to operate away from their maximum power point
Solution Approach 1:
The patent applies preliminary action by using injection circuits to pre-adjust the voltage of each string before it connects to the parallel array. By proactively adjusting the voltage of individual strings to account for impaired cells, the system prevents power loss from occurring in the first place, allowing all strings to contribute optimally to the array without forcing unimpaired cells to operate at suboptimal voltages.
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
This approach enhances solar array efficiency by maintaining maximum power production even with impaired cells, reduces power dissipation, and allows for flexible and cost-effective management of power output, minimizing strain on the electrical grid by controlling power delivery rates.
Implementation Method 1
The injection circuit is connected to a string of cells in an array. The injection circuit adjusts the voltage of the string to enable maximum power point operation of unimpaired cells in the string.
Implementation Method 2
Bypass diodes are diodes connected in parallel with the module's cells, in the direction to allow current to flow from what is normally the negative terminal to the positive. This is illustrated for a 3-module string, in FIG. 4. The effect of the bypass diode is to allow whatever current is being generated by the unimpaired cells to flow around the impaired cells, while limiting the negative voltage drop across the impaired cells to the very small value of the diode's forward bias.
Data Source
AI summary
An apparatus and method that controls the power produced by a string of solar cells, enabling the string to operate at its maximum power point when connected to a bus that operates at an externally controlled voltage. The apparatus and method can also be used to increase or decrease the output power of a string to any desired operating point.