The inverter is a power adjustment device composed of semiconductor devices and is mainly used for converting DC power into AC power. It is generally composed of a boost circuit and an inverter bridge circuit. The boost circuit boosts the DC voltage of the solar cell to the DC voltage required for the output control of the inverter; the inverter bridge circuit converts the boosted DC voltage equivalently to an AC voltage of a common frequency. The inverter is mainly composed of a switching element such as a transistor, and the switching element is repeatedly turned on and off (ON-OFF) so that the DC input becomes an AC output. Of course, the output waveform of the inverter simply generated by the opening and closing loop is not practical. High-frequency pulse width modulation (SPWM) is generally required to narrow the width of the voltage near both ends of the sine wave, and the width of the voltage in the center of the sine wave becomes wider, and the switching element is always allowed to move in a direction at a certain frequency in the half cycle. A pulse train (quasi-sinusoidal wave). Then let the pulse wave form a sine wave with a simple filter.
The composition of components:
1. Current sensors Photovoltaic inverters generally use Hall current sensors for current sampling. The current sensors used vary from low power to high power. Some examples are given below:
100KW: Detection current is about 300A, generally use JCE308-TS7 current sensor
250KW: Detection current is about 500A, generally use JCE508-TS6 current sensor
500KW: The detection current is about 1000A, generally use JCE1005-FS current sensor
1MW: The detection current is about 2000A, generally using JCE2005-FS current sensor
For the current sensor requires high accuracy, fast response time, and low temperature, high temperature and other environmental requirements, many domestic manufacturers are using open-loop current sensors to replace closed-loop current sensors, such as: JCE1000-AXS, JCE1500-AXS, JCE2000-AXS, etc.
2, current transformer
Generally use BRS series current transformers, ranging from a few hundred to several thousand A, the output signal generally adopts 0-5A as the standard
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The first thing to determine is whether it is connected to the grid or off-grid. The configuration of the inverter shall be determined in addition to the technical specifications of the entire photovoltaic power generation system and with reference to the product catalog manual provided by the manufacturer. In general, we must also consider the following technical indicators.
1, rated output power
The rated output power represents the ability of the photovoltaic inverter to supply power to the load. Photovoltaic inverters with high rated output power can bring more power loads. When selecting a PV inverter, first consider that it has enough rated power to meet the requirements of the equipment for electrical power under the maximum load, as well as the expansion of the system and the access of some temporary loads. When the electrical equipment is made of pure resistive load or the power factor is greater than 0.9, the rated output power of the photovoltaic inverter is generally selected to be 10% and 15% larger than the total power of the electrical equipment.
2, the output voltage adjustment performance
The adjustment performance of the output voltage indicates the voltage regulation capability of the photovoltaic inverter output voltage. In general, PV inverter products give the percentage deviation of the output voltage of the PV inverter when the DC input voltage fluctuates in the allowable fluctuation range, which is usually called the voltage regulation rate. High-performance photovoltaic inverters should also give the percentage deviation of the PV inverter output voltage when the load changes from zero to 100%, which is usually called the load regulation ratio. The voltage regulation rate of a photovoltaic inverter with good performance should be less than or equal to ±3%, and the load regulation rate should be less than or equal to ±6%.
3, the overall efficiency
The overall efficiency represents the power loss of the PV inverter itself. Large-capacity photovoltaic inverters also have to give full efficiency and low-load efficiency. Generally, the efficiency of inverters below the KW level should be over 85%; the efficiency of the 10KW level should be over 90%; the efficiency of greater power must be above 95%. The efficiency of the inverter has an important impact on the photovoltaic power generation system to increase the effective power generation and reduce the cost of power generation. Therefore, it is necessary to compare the photovoltaic inverters and choose products with higher efficiency.
4, start performance
PV inverters should be guaranteed to start reliably under rated load. A high-performance photovoltaic inverter can be started multiple times at full load without damaging power switching devices and other circuits. Mini-inverters sometimes use soft-start or current-limiting start-up measures or circuits for their own safety.
1, power
Generally, according to the requirements of the system, inverters with corresponding power sections are configured. The power of the selected inverters should be matched with the maximum power of the solar cell array. Generally, the rated output power of the photovoltaic inverter is selected to be approximately the same as the total input power. This can save costs.
2. Key technical indicators
1) Select the appropriate input and output voltage range to ensure the best combination of products.
2) European efficiency of the inverter: Its level will directly affect the design cost and power generation efficiency of the photovoltaic power generation system.
3), solar cell square array maximum power tracking function (MPPT) and its efficiency.
4), should pay attention to the selected inverter should have basic protection functions, such as overcurrent / short circuit protection, over power protection, over temperature protection, lightning protection, island protection and other functions.
5) The output current waveform distortion ratio (THD%) of the inverter is less than 4%.
3, certification standards
As the core equipment of the photovoltaic power station, in order to ensure the stability, reliability and continuous operation of the power station, the grid-connected inverter must have high reliability. It should have safety certification for sales destinations, electromagnetic compatibility certification, and national grid certification: (in Europe, for example)
Safety regulations: EN62109-1, EN62109-2
Electromagnetic Compatibility: EN61000-6-1, EN61000-6-2, EN61000-6-3, EN61000-6-4
On-grid certification: VDE0126-1-1 (Germany)
4, brand and service
It is advisable to purchase a brand that has a good reputation on the market. Because a company with a good brand image usually has a large investment in technology and maintenance services, it can meet its commitment to customers.
1. Photovoltaic inverters require high efficiency. Due to the high price of solar cells in 2011, in order to maximize the use of solar cells and improve system efficiency, we must try to improve the efficiency of the inverter.
2. Photovoltaic inverters require high reliability. Photovoltaic power generation systems are mainly used in remote areas in 2012. Many power plants are unattended and maintained. This requires inverters to have a reasonable circuit structure, strict component screening, and require the inverter to have various protection functions, such as input DC polarity reverse protection, AC output short circuit protection, overheating, overload protection and so on.
3. The photovoltaic inverter requires a wide range of adaptation of the DC input voltage. Since the terminal voltage of the solar cell varies with the load and the sunlight intensity, although the battery has an important role in the voltage of the solar cell, the voltage of the storage battery depends on the remaining battery. The fluctuation of capacity and internal resistance fluctuates, especially when the battery ages, its terminal voltage varies widely. For example, in a 12V battery, the terminal voltage can vary from 10V to 16V. This requires that the inverter must be larger. The DC input voltage range guarantees normal operation and ensures the stability of the AC output voltage.
4. Photovoltaic inverter In the medium and large-capacity photovoltaic power generation system, the output of the inverter power supply should be a sine wave with small distortion. This is due to the fact that in medium- and large-capacity systems, if square-wave power is used, the output will contain more harmonic components, and higher harmonics will cause additional losses. The load of many photovoltaic power generation systems is communication or instrumentation equipment. The equipment has higher requirements on the quality of the power grid. When the large-capacity photovoltaic power generation system is connected to the grid, it is required that the inverter output a sine wave current in order to avoid power pollution with the public power grid.
Automotive Connector 27P External Thread Assembly
Automotive Connector 27P External Thread Assembly
Automotive Connector 27P External Thread Assembly
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