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光伏逆变器的主要技术指标

Time: 2020-03-16 15:58:23

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The main technical indicators of photovoltaic inverter

1、输出电压的稳定度

光伏系统中,太阳电池发出的电能先由蓄电池储存起来,然后经过逆变器逆变成220V或380V的交流电。但是蓄电池受自身充放电的影响,其输出电压的变化范围较大,如标称12V的蓄电池,其电压值可在10.8~14.4V之间变动(超出这个范围可能对蓄电池造成损坏)。对于一个合格的逆变器,输入端电压在这个范围内变化时,其稳态输出电压的变化量应不超过额定值的±5%,同时当负载发生突变时,其输出电压偏差不应超过额定值的±10%。

2、输出电压的波形失真度

对正弦波逆变器,应规定允许的最大波形失真度(或谐波含量)。通常以输出电压的总波形失真度表示,其值应不超过5%(单相输出允许l0%)。由于逆变器输出的高次谐波电流会在感性负载上产生涡流等附加损耗,如果逆变器波形失真度过大,会导致负载部件严重发热,不利于电气设备的安全,并且严重影响系统的运行效率。

3、额定输出频率

对于包含电机之类的负载,如洗衣机、电冰箱等,由于其电机最佳频率工作点为50Hz,频率过高或者过低都会造成设备发热,降低系统运行效率和使用寿命,所以逆变器的输出频率应是一个相对稳定的值,通常为工频50Hz,正常工作条件下其偏差应在±l%以内。

4、负载功率因数

表征逆变器带感性负载或容性负载的能力。正弦波逆变器的负载功率因数为0.7~0.9,额定值为0.9。在负载功率一定的情况下,如果逆变器的功率因数较低,则所需逆变器的容量就要增大,一方面造成成本增加,同时光伏系统交流回路的视在功率增大,回路电流增大,损耗必然增加,系统效率也会降低。

5、逆变器效率

逆变器的效率是指在规定的工作条件下,其输出功率与输入功率之比,以百分数表示,一般情况下,光伏逆变器的标称效率是指纯阻负载,80%负载情况下的效率。由于光伏系统总体成本较高,

在光伏系统中,太阳电池发出的电能先由蓄电池储存起来,然后经过逆变器逆变成220V或380V的交流电。但是蓄电池受自身充放电的影响,其输出电压的变化范围较大,如标称12V的蓄电池,其电压值可在10.8~14.4V之间变动(超出这个范围可能对蓄电池造成损坏)。对于一个合格的逆变器,输入端电压在这个范围内变化时,其稳态输出电压的变化量应不超过额定值的±5%,同时当负载发生突变时,其输出电压偏差不应超过额定值的±10%。

6、额定输出电流(或额定输出容量)

表示在规定的负载功率因数范围内逆变器的额定输出电流。有些逆变器产品给出的是额定输出容量,其单位以VA或kVA表示。逆变器的额定容量是当输出功率因数为1(即纯阻性负载)时,额定输出电压为额定输出电流的乘积。

7、保护措施

一款性能优良的逆变器,还应具备完备的保护功能或措施,以应对在实际使用过程中出现的各种异常情况,使逆变器本身及系统其他部件免受损伤。

(1)输入欠压保户:

当输入端电压低于额定电压的85%时,逆变器应有保护和显示。

(2)输入过压保户:

当输入端电压高于额定电压的130%时,逆变器应有保护和显示。

(3)过电流保护:

逆变器的过电流保护,应能保证在负载发生短路或电流超过允许值时及时动作,使其免受浪涌电流的损伤。当工作电流超过额定的150%时,逆变器应能自动保护。

(4)输出短路保户

逆变器短路保护动作时间应不超过0.5s。

(5)输入反接保护:

当输入端正、负极接反时,逆变器应有防护功能和显示。

(6)防雷保护:

逆变器应有防雷保护。

(7)过温保护等。

另外,对无电压稳定措施的逆变器,逆变器还应有输出过电压防护措施,以使负载免受过电压的损害。

8、起动特性

表征逆变器带负载起动的能力和动态工作时的性能。逆变器应保证在额定负载下可靠起动。

9.噪声

电力电子设备中的变压器、滤波电感、电磁开关及风扇等部件均会产生噪声。逆变器正常运行时,其噪声应不超过80db,小型逆变器的噪声应不超过65db。

1. Stability of output voltage

In the photovoltaic system, the electrical energy generated by the solar cell is first stored by the storage battery, and then converted into 220V or 380V alternating current through the inverter. However, the storage battery is affected by its own charge and discharge, and its output voltage has a large range of change. For example, a nominal 12V battery can have a voltage value ranging from 10.8 to 14.4V (beyond this range may cause damage to the battery) . For a qualified inverter, when the input terminal voltage changes within this range, the change in the steady-state output voltage should not exceed ± 5% of the rated value, and when the load changes suddenly, the output voltage deviation should not exceed ± 10% of rated value.

2. Waveform distortion of output voltage

For sine wave inverters, the maximum allowable waveform distortion (or harmonic content) should be specified. Usually expressed as the total waveform distortion of the output voltage, its value should not exceed 5% (single-phase output allows l0%). The higher harmonic current output by the inverter will cause additional losses such as eddy current on the inductive load. If the waveform distortion of the inverter is too large, it will cause the load components to heat up seriously, which is not conducive to the safety of electrical equipment and seriously affects the system Operating efficiency.

3. Rated output frequency

For loads including motors, such as washing machines, refrigerators, etc., because the optimal frequency operating point of the motor is 50Hz, the frequency is too high or too low will cause the device to heat, reduce the system operating efficiency and service life, so the inverter The output frequency should be a relatively stable value, usually 50 Hz power frequency, and the deviation should be within ± 1% under normal operating conditions.

4. Load power factor

Characterize the inverter's ability to carry inductive or capacitive loads. The load power factor of the sine wave inverter is 0.7 to 0.9, and the rated value is 0.9. In the case of a certain load power, if the power factor of the inverter is low, the capacity of the required inverter will increase, on the one hand, the cost will increase, and the apparent power of the AC circuit of the photovoltaic system will increase. As current increases, losses will inevitably increase, and system efficiency will also decrease.

5. Inverter efficiency

The efficiency of the inverter refers to the ratio of its output power to the input power under specified working conditions, expressed as a percentage. Under normal circumstances, the nominal efficiency of the photovoltaic inverter refers to pure resistance load, 80% load s efficiency. Due to the higher overall cost of photovoltaic systems,

In the photovoltaic system, the electrical energy generated by the solar cell is first stored by the storage battery, and then converted into 220V or 380V alternating current through the inverter. However, the storage battery is affected by its own charge and discharge, and its output voltage has a large range of change. For example, a nominal 12V battery can have a voltage value ranging from 10.8 to 14.4V (beyond this range may cause damage to the battery) . For a qualified inverter, when the input terminal voltage changes within this range, the change in the steady-state output voltage should not exceed ± 5% of the rated value, and when the load changes suddenly, the output voltage deviation should not exceed ± 10% of rated value.

6. Rated output current (or rated output capacity)

Indicates the rated output current of the inverter within the specified load power factor range. Some inverter products are rated output capacity, the unit is expressed in VA or kVA. The rated capacity of the inverter is when the output power factor is 1 (that is, purely resistive load), the rated output voltage is the product of the rated output current.

7. Protection measures

An inverter with excellent performance should also have complete protection functions or measures to cope with various abnormal situations that occur during actual use, so as to protect the inverter itself and other system components from damage.

(1) Enter under-voltage protection account:

When the input voltage is lower than 85% of the rated voltage, the inverter should have protection and display.

(2) Enter the overvoltage protection account:

When the input voltage is higher than 130% of the rated voltage, the inverter should have protection and display.

(3) Overcurrent protection:

The overcurrent protection of the inverter should ensure that it can act in time when the load short-circuits or the current exceeds the allowable value, so as to protect it from the damage of surge current. When the working current exceeds 150% of the rated value, the inverter should be able to automatically protect.

(4) Output short circuit protector

Inverter short-circuit protection action time should not exceed 0.5s.

(5) Input reverse connection protection:

When the positive and negative poles of the input terminal are connected in reverse, the inverter should have protection function and display.

(6) Lightning protection:

The inverter should have lightning protection.

(7) Over-temperature protection, etc.

In addition, for inverters without voltage stabilization measures, the inverter should also have output overvoltage protection measures to protect the load from overvoltage damage.

8. Starting characteristics

Characterize the inverter's ability to start under load and its performance during dynamic operation. The inverter should ensure reliable start under rated load.

9. noise

Transformers, filter inductors, electromagnetic switches and fans in power electronic equipment will generate noise. When the inverter is operating normally, its noise should not exceed 80db, and the noise of a small inverter should not exceed 65db.


  
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