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            星火太陽能和你一起了解更多太陽能資訊

            光伏儲能系統關鍵設備之離網逆變器

            返回列表 來源: 古瑞瓦特 發布日期: 2023.01.30 瀏覽次數:
            修正波與正弦波

            逆變器輸出波形主要分兩類,一類是正弦波,另一類是修正波 。修正弦波逆變器,采用PWM脈寬調制方式生成修正波輸出,由于存在20%左右的諧波失真,不能帶空調等感性負載,但可以帶電燈等阻性負載。修正弦波逆變器采用非隔離耦合電路,器件簡單,效率高。 純正弦波逆變器采用隔離耦合電路設計,電路較復雜,成本較高,可以連接任何常見的電器設備(包括電視機、液晶顯示器等,特別是冰箱等感性負載)而沒有干擾。

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            工頻隔離和高頻隔離

            純正弦波離網逆變器的輸入端和輸出端有電氣隔離,按照電氣結構分為高頻隔離和工頻隔離,高頻隔離變壓器放在直流升壓端,采用的方案是先把直流電逆變器高頻率的交流電,通過高頻變壓器升壓,然后整流為直流電,最后又逆變為工頻交流電,高頻逆變器采用的是體積小,重量輕的高頻磁芯材料,可以降低逆變器的重量,減少逆變器的體積,提高逆變器的效率,但電路較為復雜。工頻隔離變壓器放在交流端出端,逆變器電路較簡單,抗沖擊能力較強,但體積較大,重量比較重。

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            高頻逆變器應用場景
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            工頻逆變器應用場景
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            古瑞瓦特高頻隔離逆變器

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            古瑞瓦特工頻隔離逆變器


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            分體式與一體式

            離網系統由于多了一個蓄電池,因此必須要配置控制器,用于組件給蓄電池充電,控制器和逆變器分開,做成兩個設備,就是分體式。把控制器和逆變器集成在一起,就是一體式,也稱為控制逆變一體式。分體式系統,控制器和逆變器可以分別選型,但接線比較復雜,適應于組件和逆變器功率相差比較大的系統,以及系統功率很大的系統。控制逆變一體式系統結構簡單,用戶接線方便,適應于組件和逆變器功率相差比較小的系統。


            離網逆變器的重要技術參數

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            在選擇離網逆變器時,除了注意逆變器的輸出波形,隔離類型外,還有幾個技術參數也非常重要,如系統電壓、輸出功率、峰值功率、轉換效率、切換時間等等,這些參數的選擇對負載的用電需求影響較大。

            1)系統電壓:就是蓄電池組的電壓,離網逆變器的輸入電壓和控制器的輸出電壓是一致的,在設計選型時,要注意和控制器保持一致。

            2)輸出功率:離網逆變器的輸出功率表述有兩種,一種是視在功率表示法,單位是VA,這是參考UPS標記,實際輸出有功功率還需乘以功率因素,如500VA的離網逆變器,功率因素是0.8,實際輸出有功功率就是400W,也就是說能帶動400W的阻性負載,如電燈,電磁爐等;第二種是有功功率表示法,單位是W,如5000W離網逆變器,實際輸出有功功率就是5000W。

            3)峰值功率:在光伏離網系統中,組件、蓄電池、逆變器、負載構成電氣系統,逆變器的輸出功率,是由負載決定的,有些感性負載,如空調、水泵等,里面的電動機,啟動功率是額定功率的3-5倍,所以離網逆變器對過載有特別要求。峰值功率就是離網逆變器的過載能力。

            逆變器給負載提供啟動能量,一部分來自于蓄電池或者光伏組件,超出的部分由逆變器內部的儲能元件—電容和電感來提供 。電容和電感都是一種儲能元件,不同的是電容是以電場的形式儲存電能,電容的容量越大,儲存的電量越多。而 電感則是以磁場的形式存儲能量,電感器磁芯的磁導率越大,電感量也越大,則能夠儲存的能量也越多。 

            4)轉換效率:離網系統轉換效率包括兩方面,一是機器本身的效率,離網逆變器電路復雜,要經過多級變換,因此整體效率比并網逆變器稍低,一般在80-90%之間,逆變器整機功率越大效率越高,高頻隔離比工頻隔離效率要高,系統電壓越高效率也越高。二是蓄電池充放電的效率,這個是蓄電池的類型有關系,當光伏發電和負載用電同步時,光伏可以直接供給負載使用,不需要經過蓄電池轉換。

            5)切換時間:離網系統帶負載,有光伏、蓄電池、市電三種模式,當蓄電池能量不足,切換到市電模式時,存在切換時間,有的離網逆變器采用電子開關切換,時間在10毫秒內,臺式電腦不會關機,照明燈也不會閃爍。有的離網逆變器采用繼電器切換,時間可能超過20毫秒,臺式電腦可能會關機或者重啟。


            Modified wave and sine wave

            Inverter output waveform is mainly divided into two categories, one is sine wave, the other is the correction wave. Repair sine wave inverter, using PWM pulse-width modulation to generate corrected wave output, due to the existence of about 20% harmonic distortion, can not take inductive load such as air conditioning, but can take resistive load such as lights. The repair sine wave inverter adopts the non - isolated coupling circuit, the device is simple and the efficiency is high. Pure sine wave inverter adopts isolated coupling circuit design, the circuit is more complex, high cost, can be connected to any common electrical equipment (including TV, LCD, especially the inductive load such as refrigerator) without interference.

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            Power frequency isolation and high frequency isolation

            Pure sine wave off-grid inverter input and output end has electrical isolation, according to the electrical structure is divided into high frequency isolation and power frequency isolation, high frequency isolation transformer in the DC boost end, the scheme is to first put the DC inverter high frequency alternating current, through the high frequency transformer boost, and then rectifier to DC, and finally inverter for power frequency alternating current, High frequency inverter is small volume, light weight of high frequency magnetic core material, can reduce the weight of the inverter, reduce the volume of the inverter, improve the efficiency of the inverter, but the circuit is more complex. The power frequency isolation transformer is placed in the AC end out of the end, the inverter circuit is simple, strong impact resistance, but the volume is larger, the weight is heavier.

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            Application scenarios of high-frequency inverters

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            Application scenario of power frequency inverter

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            Guruwatt high frequency isolation inverter

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            Agent Gureva has a frequency isolation inverter

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            Split asanas versus uniasanas

            Off-grid system due to more than a battery, so it must be configured with a controller, used for battery charging components, controller and inverter separate, make two devices, is split. The controller and inverter integrated together, is the integral, also known as the control inverter integral. Split system, controller and inverter can be selected separately, but the wiring is more complex, suitable for the component and inverter power difference is relatively large system, as well as the system power is very large. The integrated control inverter system has the advantages of simple structure, convenient connection, and is suitable for the system where the power difference between the component and the inverter is relatively small.

            Important technical parameters of off-grid inverter

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            In the selection of off-grid inverter, in addition to pay attention to the output waveform of the inverter, isolation type, there are several technical parameters are also very important, such as system voltage, output power, peak power, conversion efficiency, switching time and so on. The selection of these parameters has a greater impact on the power demand of the load.

            1) System voltage: is the voltage of the battery. The input voltage of the off-grid inverter is consistent with the output voltage of the controller. In the design and selection, attention should be paid to keeping consistent with the controller.

            2) Output power: The output power of off-grid inverter is expressed in two ways, one is apparent power representation, the unit is VA, this is a reference to the UPS label, the actual output active power needs to be multiplied by the power factor, such as 500VA off-grid inverter, the power factor is 0.8, the actual output active power is 400W, that is to say, can drive 400W resistance load, such as lights, Induction cooker, etc.; The second is active power representation, the unit is W, such as 5000W off-grid inverter, the actual output active power is 5000W.

            3) Peak power: in the photovoltaic off-grid system, components, batteries, inverters and loads constitute the electrical system. The output power of the inverters is determined by the load. For some inductive loads, such as air conditioners and water pumps, the motor inside has a starting power 3-5 times of the rated power, so the off-grid inverters have special requirements for over-loading. Peak power is the overload capacity of the off-grid inverter.

            The inverter provides the load with starting energy, part of which comes from the battery or photovoltaic module, and the excess part is provided by the energy storage components inside the inverter -- capacitors and inductors. Capacitors and inductors are both energy storage components. The difference is that capacitors store electric energy in the form of electric fields. The larger the capacity of capacitors, the more electricity they store. Inductors store energy in the form of magnetic fields. The larger the permeability of the inductor's magnetic core, the larger the inductance, and the more energy can be stored.

            4) Conversion efficiency: off-grid system conversion efficiency includes two aspects, one is the efficiency of the machine itself, the off-grid inverter circuit is complex, after multistage transformation, so the overall efficiency is slightly lower than the grid-connected inverter, generally between 80-90%, the greater the inverter power efficiency is higher, high frequency isolation efficiency is higher than the power frequency isolation efficiency is higher, the higher the system voltage efficiency is higher. The second is the efficiency of battery charging and discharging. This is related to the type of battery. When photovoltaic power generation and load power consumption are synchronized, photovoltaic can directly supply the load, without the need for battery conversion.

            5) Switching time: off-grid system with load, there are three modes of photovoltaic, battery, mains, when the battery energy is insufficient, switch to the mains mode, there is a switching time, some off-grid inverter using electronic switch, time within 10 milliseconds, desktop computer will not shut down, lights will not blink. Some off-grid inverters use relay switches that may take longer than 20 milliseconds, and the desktop computer may shut down or restart.


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