儲(chǔ)能系統(tǒng)在光伏電站中的作用

1

保證系統(tǒng)穩(wěn)定

光伏電站系統(tǒng)中，光伏輸出功率曲線與負(fù)荷曲線存在較大差異，而且均有不可預(yù)料的波動(dòng)特性，通過儲(chǔ)能系統(tǒng)的能量存儲(chǔ)和緩沖使得系統(tǒng)即使在負(fù)荷迅速波動(dòng)的情況下仍然能夠運(yùn)行在一個(gè)穩(wěn)定的輸出水平。 

2

能量備用

儲(chǔ)能系統(tǒng)可以在光伏發(fā)電不能正常運(yùn)行的情況下起備用和過渡作用，如在夜間或者陰雨天電池方陣不能發(fā)電時(shí)，這時(shí)儲(chǔ)能系統(tǒng)就起備用和過渡作用，其儲(chǔ)能容量的多少取決于負(fù)荷的需求。 

3

提高電力品質(zhì)和可靠性

儲(chǔ)能系統(tǒng)還可防止負(fù)載上的電壓尖峰、電壓下跌和其他外界干擾所引起的電網(wǎng)波動(dòng)對(duì)系統(tǒng)造成大的影響，采用足夠多的儲(chǔ)能系統(tǒng)可以保證電力輸出的品質(zhì)與可靠性。 

No.2

儲(chǔ)能系統(tǒng)的主要模式

1

配置在電源直流側(cè)的儲(chǔ)能系統(tǒng)

配置在電源直流側(cè)的儲(chǔ)能系統(tǒng)主要可安裝在諸如光伏發(fā)電的直流系統(tǒng)中，這種設(shè)計(jì)可將蓄電池組合光伏發(fā)電陣列在逆變器直流段進(jìn)行配接調(diào)控，如圖1。該系統(tǒng)中的光伏發(fā)電系統(tǒng)和蓄電池儲(chǔ)能系統(tǒng)共享一個(gè)逆變器，但是由于蓄電池的充放電特性和光伏發(fā)電陣列的輸出特性差異較大，原系統(tǒng)中的光伏并網(wǎng)逆變器中的最大功率跟蹤系統(tǒng)(MPPT)是專門為了配合光伏輸出特性設(shè)計(jì)的，無法同時(shí)滿足儲(chǔ)能蓄電池的輸出特性曲線。因此，此類系統(tǒng)需要對(duì)原系統(tǒng)逆變器進(jìn)行改造或重新設(shè)計(jì)制造，不僅需要使逆變器能滿足光伏陣列的逆變要求，還需要增加對(duì)蓄電池組的充放電控制器，和蓄電池能量管理等功能。一般而言，該系統(tǒng)是單向輸出的，也就是說該系統(tǒng)中的蓄電池是完全依靠光伏發(fā)電充電的，電網(wǎng)的電力是不能給蓄電池充電的。

圖1、配置在電源直流側(cè)的儲(chǔ)能系統(tǒng)

該系統(tǒng)光伏發(fā)電陣列發(fā)出的電力在逆變器前端就與蓄電池進(jìn)行了自動(dòng)直流平衡，這種模式的主要特點(diǎn)是系統(tǒng)效率高，電站發(fā)電出力可由光伏電站內(nèi)部調(diào)度，可以達(dá)到無縫連接，輸出電能質(zhì)量好，輸出波動(dòng)非常小等，可大大提高光伏發(fā)電輸出的平滑、穩(wěn)定性和可調(diào)控性能，缺點(diǎn)是使用的逆變器需要特殊設(shè)計(jì)，不適用于對(duì)現(xiàn)有已經(jīng)安裝好的大部分光伏電站進(jìn)行升級(jí)改造。另一個(gè)缺點(diǎn)是，該儲(chǔ)能系統(tǒng)中的蓄電池組只能接受本發(fā)電單元的電力為其充電，而其他臨近的光伏發(fā)電單元或電站的多余電力無法為其充電。也就是說這種方案缺乏大電站內(nèi)部電力調(diào)配的功能。

2

配置在電源交流側(cè)的儲(chǔ)能系統(tǒng)

配置在電源交流側(cè)的儲(chǔ)能系統(tǒng)也可以稱之為配置在交流側(cè)的儲(chǔ)能系統(tǒng)，單元型交流側(cè)的儲(chǔ)能的模式如圖2所示，它采用單獨(dú)的充放電控制器和逆變器來給蓄電池充電或者逆變，這種方案實(shí)際上就是給現(xiàn)有光伏發(fā)電系統(tǒng)外掛一個(gè)儲(chǔ)能裝置，可在目前任何一種光伏電站甚至風(fēng)力發(fā)電站或其他發(fā)電站進(jìn)行升級(jí)安裝，形成站內(nèi)儲(chǔ)能系統(tǒng)，也可以根據(jù)電網(wǎng)需要建設(shè)成為完全獨(dú)立運(yùn)行的儲(chǔ)能電站。

這種模式克服了直流側(cè)儲(chǔ)能系統(tǒng)無法進(jìn)行多余電力統(tǒng)一調(diào)度的問題，它的系統(tǒng)充電還是放電完全由智能化控制系統(tǒng)控制或受電網(wǎng)調(diào)度控制，它不僅可以集中全站內(nèi)的多余電力給儲(chǔ)能系統(tǒng)快速有效的充電，甚至可以調(diào)度站外電網(wǎng)的廉價(jià)低谷多余電力，使得系統(tǒng)運(yùn)行更加方便和有效。

圖2、配置在交流低壓的側(cè)儲(chǔ)能系統(tǒng)

交流側(cè)接入的儲(chǔ)能系統(tǒng)的另一個(gè)模式是將儲(chǔ)能系統(tǒng)接入電網(wǎng)端，如圖3。顯然，這兩種儲(chǔ)能系統(tǒng)的不同點(diǎn)只是接入點(diǎn)不同，前者是將儲(chǔ)能部分接入了交流低壓側(cè)，與原光伏電站分享一個(gè)變壓器，而后者則是將儲(chǔ)能系統(tǒng)形成獨(dú)立的儲(chǔ)能電站模式，直接接入高壓電網(wǎng)。

交流側(cè)接入的方案不僅適用于電網(wǎng)儲(chǔ)能，還被廣泛應(yīng)用于諸如島嶼等相對(duì)孤立的地區(qū)，形成相對(duì)獨(dú)立的微型電網(wǎng)供電系統(tǒng)。交流側(cè)接入的儲(chǔ)能系統(tǒng)不僅可以在新建電站上實(shí)施，對(duì)于已經(jīng)建成的電站也可以很容易的進(jìn)行改造和附加建設(shè)，且電路結(jié)構(gòu)清晰，發(fā)電場(chǎng)和儲(chǔ)能電場(chǎng)可分地建設(shè)，相互的直接關(guān)聯(lián)性少，因此也便于運(yùn)行控制和維修。缺點(diǎn)是由于發(fā)電和儲(chǔ)能相互獨(dú)立，相互之間的協(xié)調(diào)和控制就需要外加一套專門的智能化的控制調(diào)度系統(tǒng)，因此造價(jià)相對(duì)較高。

3

配置在電源直流側(cè)的儲(chǔ)能系統(tǒng)

配置在負(fù)荷側(cè)儲(chǔ)能系統(tǒng)主要是指應(yīng)急電源和可移動(dòng)的電動(dòng)設(shè)備，譬如可充電式的電動(dòng)汽車，電動(dòng)工具和移動(dòng)電話等。

現(xiàn)階段，交叉補(bǔ)貼的存在和居民建筑用能局限性還不能刺激居民用戶側(cè)儲(chǔ)能的配套應(yīng)用，但隨著光儲(chǔ)技術(shù)成本的降低，工商業(yè)用戶側(cè)光儲(chǔ)應(yīng)用價(jià)值將顯現(xiàn)。

The role of energy storage system in photovoltaic power station  

 

 

 

1  

 

Ensure system stability  

 

In photovoltaic power station system, photovoltaic output power curve and load curve have great differences, and both have unpredictable fluctuation characteristics. Through energy storage and buffering of energy storage system, the system can still operate at a stable output level even in the case of rapid fluctuation of load.  

 

 

2  

 

The standby energy  

 

The energy storage system can play a backup and transition role when photovoltaic power generation cannot operate normally. For example, when the battery array cannot generate power at night or on rainy days, the energy storage system will play a backup and transition role. The amount of its energy storage capacity depends on the demand of the load.  

 

 

3  

 

Improve the quality and reliability of electricity  

 

The energy storage system can also prevent the voltage spike, voltage drop and other external disturbances on the load caused by the fluctuation of the grid to the system, the use of enough energy storage systems can ensure the quality and reliability of power output.  

 

 

No.2  

 

The main modes of energy storage systems  

 

 

 

1  

 

The energy storage system is configured on the DC side of the power supply  

 

The energy storage system configured on the DC side of the power supply can mainly be installed in the DC system such as photovoltaic power generation. In this design, the battery combination photovoltaic power generation array can be connected and regulated in the DC section of the inverter, as shown in Figure 1.   The photovoltaic power generation system and the battery energy storage system in the system share an inverter, but due to the large difference between the charging and discharging characteristics of the battery and the output characteristics of the photovoltaic power array, the maximum power tracking system (MPPT) in the photovoltaic grid-connected inverter in the original system is specially designed to match the photovoltaic output characteristics.  The output characteristic curve of the storage battery cannot be simultaneously satisfied.   Therefore, such systems need to transform or redesign the original system inverter, not only need to make the inverter can meet the requirements of photovoltaic array inverter, but also need to increase the battery charge and discharge controller, and battery energy management and other functions.  Generally speaking, the system is one-way output, that is to say, the battery in the system is completely dependent on photovoltaic power generation to charge, the power grid is not able to charge the battery.  

 

 

The picture  

 

Figure 1. Energy storage system configured at dc side of power supply  

 

 

 

Electricity from photovoltaic array in the system automatic dc inverter in front and battery balance, the main characteristic of this model is system of high efficiency and power output can be made of photovoltaic power station internal operation, can achieve a seamless connection, the output power quality is good, the output fluctuation is very small, etc., can greatly improve the photovoltaic output smooth, stability and control performance,   The disadvantage is that the inverter used needs special design and is not suitable for upgrading the existing photovoltaic power stations that have been installed.  Another disadvantage is that the batteries in the system can only receive power from the same unit to charge them, not the excess power from other nearby PHOTOVOLTAIC units or power stations.  In other words, it lacks the internal power distribution function of a large power station.  

 

 

 

 

2  

 

The energy storage system is configured on the AC side of the power supply  

 

 

 

Configuration is also called the power ac side of the energy storage system configuration in the ac side of the energy storage system, unit type ac side of the energy storage model shown in figure 2, it USES a separate charge and discharge controller and inverter to battery charging and inverter, this scheme is actually to the existing photovoltaic power generation system plugins an energy storage device,   It can be upgraded and installed in any kind of photovoltaic power station or even wind power station or other power station to form the in-station energy storage system, or it can be built into a completely independent energy storage power station according to the needs of the power grid.  

 

This model overcomes the dc energy storage system can't be extra electricity unified scheduling problem, the system charge or discharge completely controlled by the intelligent control system or controlled by the power grid scheduling, it not only can focus within the total surplus electricity to rapid and efficient energy storage system of charging, even cheap low excess power grid scheduling stand outside,   Make the system run more convenient and effective.  

The picture  

 

Figure 2. Side energy storage system configured at AC low voltage  

 

 

 

Another mode of the energy storage system connected to the AC side is to connect the energy storage system to the power grid, as shown in Figure 3.   Obviously, the difference between these two energy storage systems is only the access point. The former connects the energy storage part to the AC low-voltage side and shares a transformer with the original PHOTOVOLTAIC power station, while the latter forms an independent energy storage power station mode and directly connects the energy storage system to the high-voltage power grid.  

 

Ac side access scheme is not only suitable for power grid energy storage, but also widely used in relatively isolated areas such as islands, forming relatively independent micro-grid power supply system.   The ac side access energy storage system can not only be implemented in new power stations, but also can be easily transformed and additional construction for existing power stations. Moreover, the circuit structure is clear, and the power field and energy storage field can be constructed separately, with little direct correlation with each other, so it is also convenient for operation control and maintenance.   The disadvantage is that since power generation and energy storage are independent from each other, the coordination and control between them requires a special intelligent control and scheduling system, so the cost is relatively high.  

 

 

3  

 

The energy storage system is configured on the DC side of the power supply  

 

The load side energy storage system mainly refers to emergency power supply and mobile electric equipment, such as rechargeable electric vehicles, power tools and mobile phones.  

 

At present, the existence of cross-subsidy and the limitation of residential building energy consumption cannot stimulate the supporting application of residential user-side energy storage, but with the reduction of the cost of optical storage technology, the application value of industrial and commercial user-side optical storage will appear.