Unidirectional Converter and Switch for PV Energy Storage
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Solution Overview
Problem
Photovoltaic devices face energy waste due to power limitations of bidirectional inverters, leading to suboptimal power generation benefits, as excess energy cannot be efficiently stored and reused.
Innovation Solution
A charging and discharging system comprising a unidirectional converter, a unidirectional switch, an energy storage device, and a controller, which connects the photovoltaic device to the energy storage device and bidirectional inverter, allowing for charging during excess energy production and discharging when energy is needed, using a unidirectional switch and controller to manage power flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If power limitation is set for photovoltaic device output, then bidirectional inverter can operate within its power capacity, but excess energy from photovoltaic device is wasted
Solution Approach 1:
An energy storage device is introduced as an intermediary component between the photovoltaic device and the bidirectional inverter. The storage device absorbs excess energy when photovoltaic output exceeds inverter capacity, and releases energy when inverter demand exceeds photovoltaic output, thereby eliminating energy waste while protecting the inverter from overload
Solution Approach 2:
The system dynamically adjusts the operating parameters of the bidirectional inverter based on real-time conditions. When excess energy is available, the inverter operates at maximum capacity; when energy is deficient, the inverter reduces output. This parameter adjustment is coordinated with charging/discharging operations of the energy storage device to optimize overall system efficiency
2Productivity
If energy storage device is directly connected to bidirectional inverter, then energy can be stored and released, but voltage mismatch and current control complexity increase
Solution Approach 1:
The power conversion function is segmented into two independent parts: a unidirectional converter dedicated to charging the energy storage device from the photovoltaic device, and a bidirectional inverter dedicated to powering loads and interacting with the grid. This segmentation simplifies control by assigning specific functions to each converter, avoiding the complexity of managing a single bidirectional device handling all operations
Solution Approach 2:
A DC bus serves as an intermediary electrical connection between the unidirectional converter, energy storage device, and bidirectional inverter. This DC bus decouples the voltage and current characteristics of the two converters, allowing them to operate independently at their optimal parameters while still enabling coordinated energy management through the common DC link
3Speed
If unidirectional switch is used for discharging, then energy can be rapidly provided to inverter, but switch timing and voltage coordination must be precisely controlled
Solution Approach 1:
The controller continuously monitors the voltage of the energy storage device and the operational state of the bidirectional inverter. Based on this feedback, the controller determines the optimal timing for closing the unidirectional switch and adjusts the discharge rate to maintain voltage coordination. This closed-loop feedback control ensures rapid discharging while preventing voltage mismatches and protecting system components
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 system effectively stores excess energy from photovoltaic devices and provides it back to the bidirectional inverter, reducing waste and enhancing power generation benefits by optimizing energy utilization.
Implementation Method 1
the controller controls the unidirectional converter to charge the energy storage device with first charging power
Implementation Method 2
the controller controls the unidirectional switch to close, wherein the voltage-reducing-signal is used to instruct the bidirectional inverter to reduce the voltage
Data Source
Figure 1~2
Figure 3~5
AI summary
A charging and discharging system, a charging and discharging method, and a photovoltaic power generation system are provided. The charging and discharging system includes: a unidirectional converter, a unidirectional switch, an energy storage device and a controller; where an input terminal of the unidirectional converter is connected to an output terminal of a photovoltaic device of a photovoltaic power generation system to which the charging and discharging system is applied, and an output terminal of the unidirectional converter is connected to an input terminal of the energy storage device; the unidirectional switch is connected between an output terminal of the energy storage device and an input terminal of a bidirectional inverter of the photovoltaic power generation system to which the charging and discharging system is applied; the controller is connected to the unidirectional converter, the unidirectional switch, the energy storage device and the bidirectional inverter. With the charging and discharging system, excess energy of the photovoltaic device can be stored, and the stored energy is provided to the bidirectional inverter efficiently and rapidly, thereby avoiding waste of the excess energy of the photovoltaic device and improving gains of power generation of the photovoltaic device.