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What is a solar inverter

Inverters, also known as power conditioners and power regulators, are an essential part of a photovoltaic system. The main function of the photovoltaic inverter is to convert the direct current generated by the solar panels into alternating current for home appliances, and all the electricity generated by the solar panels has to be processed by the inverter before it can be output to the outside world.

The common solar power system consists of four parts, namely, solar panel, charge controller, solar inverter and battery. Solar panel is to provide direct current device, can be converted into solar energy; charge controller is mainly responsible for controlling the conversion of energy; solar inverter is the panel of direct current into alternating current, for battery storage, battery is mainly AC power storage for people's use. The solar inverter plays a role in the whole solar power generation system.

Through the full-bridge circuit, generally using SPWM processor after modulation, filtering, boosting, etc., to get with the lighting load frequency, rated voltage and other matching sinusoidal alternating current for the system end-users. With an inverter, a DC battery can be used to provide AC power to appliances. The solar AC power generation system is. , consisting of solar panels, charge controllers, inverters, and batteries; solar DC power generation systems do not include inverters. The process of converting AC electrical energy into DC electrical energy is called rectification, the circuit that performs the rectification function is called a rectifier circuit, and the device that implements the rectification process is called a rectifier device or rectifier.

Correspondingly, the process of converting direct current energy into alternating current energy is called inversion, the circuit that performs the inversion function is called an inverter circuit, and the device that realizes the inversion process is called an inverter device or inverter. The core of the inverter device is the inverter switching circuit, referred to as the inverter circuit. This circuit accomplishes the inverter function through the conduction and shutdown of power electronic switches. The on-off of the power electronic switching device requires certain driving pulses which may be regulated by changing a voltage signal. The circuitry that generates and regulates the pulses is commonly referred to as a control circuit or control loop. The basic structure of an inverter device, in addition to the inverter and control circuits described above, includes protection circuits, output circuits, input circuits, and output circuits.

solar inverter
solar inverter

The function and role of solar inverter

The inverter not only has the function of direct AC conversion, but also has the function of maximizing the function of the solar cell and the function of system fault maintenance. In summary, there are active operation and shutdown function, maximum power tracking and throttling function, anti-alone operation function (for grid-connected system), active voltage adjustment function (for grid-connected system), DC detection function (for grid-connected system), DC grounding detection function (for grid-connected system). Here is a brief introduction to the active operation and shutdown function and the maximum power tracking control function.

1.Active operation and shutdown function: after sunrise in the morning, the intensity of solar radiation is gradually strengthened, and the output of the solar cell is also increased, and when the output power required for the inverter task is reached, the inverter will start to run actively. After entering into operation, the inverter will watch the output of the solar cell module every time, only if the output power of the solar cell module is greater than the output power required by the task of the inverter, the inverter will continue to operate; until the sunset shutdown, even if the inverter can operate on cloudy and rainy days. When the output of the solar cell module becomes small and the output of the inverter is close to 0, the inverter constitutes a standby mode.

2.Maximum power tracking and throttling function: The output of the solar cell module is transformed with the intensity of solar radiation and the temperature of the solar cell module itself (chip temperature). In addition, because the solar cell module has the characteristic that the voltage decreases with the increase of current, so there is the best task point that can get the maximum power. The intensity of solar radiation is shifting, obviously the optimal task point is also shifting. Related to these transformations, has been to let the solar cell module task point in the maximum power point, the system has been from the solar cell module to obtain the maximum power output, this control is the maximum power tracking control. The most important feature of the inverter for solar power generation system is that it includes the function of maximum power point tracking (MPPT).

Solar inverter
Solar inverter

Performance Parameters of Solar Inverters

There are many parameters and technical conditions describing the performance of the inverter, here is only a brief description of the commonly used technical parameters when evaluating the inverter.

1.the use of the inverter environmental conditions, inverter normal use conditions: altitude of not more than 1000m, air temperature -30 ~ +40 ℃.

2.DC input power conditions, input DC voltage fluctuation range: ± 15% of the rated voltage of the battery pack.

3.Rated output voltage, in the specified input DC voltage allowable fluctuation range, it indicates that the inverter should be able to output the rated voltage value. The stable accuracy of the output rated voltage value is generally specified as follows:

(1) In steady state operation, the voltage fluctuation range should have a limit, for example, its deviation does not exceed ±3% or ±5% of the rated value.

(2) In the dynamic situation where there is a sudden change of load or the influence of other disturbing factors, its output voltage deviation should not exceed ±8% or ±10% of the rated value.

4.Rated output frequency, the frequency of the inverter output AC voltage should be a relatively stable value, usually for the frequency of 50 Hz. under normal operating conditions, the deviation should be within ± 1%.

5.Rated output current (or rated output capacity), said in the specified load power factor range of the inverter's rated output current. Some inverter products give the rated output capacity in VA or kVA. The rated capacity of the inverter is the product of the rated output voltage and the rated output current when the output power factor is 1 (i.e. pure resistive load).

6.Rated output efficiency, the efficiency of the inverter is in the specified operating conditions, its output power to the input power ratio, expressed in %. The efficiency of the inverter under the rated output capacity is the full load efficiency, and the efficiency at 10% of the rated output capacity is the low load efficiency.

7.The maximum harmonic content of the inverter, sine wave inverter, under resistive load, the maximum harmonic content of the output voltage should be ≤ 10%.

8.The overload capacity of the inverter, in the specified conditions, in a relatively short period of time, the inverter output exceeds the rated current value of the ability. The overload capacity of the inverter should meet certain requirements under the specified load power factor.

9.The efficiency of the inverter, in the rated output voltage, output current and specified load power factor, the inverter output active power and input active power (or DC power) ratio.

Solar inverter
Solar inverter
  1. Load power factor, characterizing the inverter's ability to carry inductive or capacitive loads. Under sinusoidal conditions, the load power factor is 0.7 to 0.9 (lagging), and the rated value is 0.9.

11.The asymmetry of the load, under 10% asymmetric load, the asymmetry of the output voltage of the three-phase inverter with fixed frequency should be ≤ 10%.

12.The output voltage unbalance, under normal operating conditions, the inverter output three-phase voltage unbalance (the ratio of the reverse sequence component to the positive sequence component) should not exceed a specified value, generally expressed in %, such as 5% or 8%.

13.Starting characteristics, under normal operating conditions, the inverter in full load and no-load operating conditions, should be able to start 5 times in a row normally.

14.Protection function, the inverter should be set up: short circuit protection, over current protection, over temperature protection, over voltage protection, under voltage protection and phase loss protection. Over-voltage protection means that for the inverter without voltage stabilization measures, there should be output over-voltage protection measures to protect the negative cut-off from the damage of output over-voltage. Overcurrent protection refers to the overcurrent protection of the inverter, should be able to ensure that the load occurs in a short circuit or the current exceeds the permissible value of timely action, so that it is free from the damage of the inrush current.

15.Interference and anti-interference, the inverter should be able to withstand electromagnetic interference in the general environment under the specified normal operating conditions. The anti-interference performance and electromagnetic compatibility of the inverter should be in line with the provisions of the relevant standards.

16.Infrequent operation, monitoring and maintenance of the inverter, should be ≤ 95db; frequent operation, monitoring and maintenance of the inverter, should be ≤ 80db.

17.Display, the inverter should be equipped with data display of parameters such as AC output voltage, output current and output frequency, and signal display of input charged, energized and fault status.

18.Communication function, the remote communication function enables the user to check the running status of the machine and the stored data without having to go to the site.

19.Waveform distortion of the output voltage, when the output voltage of the inverter is sinusoidal, the maximum permissible waveform distortion (or harmonic content) should be specified. Usually expressed in terms of the total waveform distortion of the output voltage, the value should not exceed 5% (10% allowed for single-phase output).

20.Starting characteristics, characterizing the inverter with load starting ability and dynamic performance. The inverter should ensure reliable starting under the rated load.

21.Noise, power electronic equipment, transformers, filter inductors, electromagnetic switches and fans and other components will produce noise. When the inverter is in normal operation, its noise should not exceed 80dB, and the noise of small inverters should not exceed 65dB.

Solar inverter
Solar inverter

Boland Renewable Energy Co.,LTD As an integrated new energy power company, providing you with high quality integrated wind energy , solar energy and energy storage system solutions.Boland is now a subsidiary of CRRC, and is responsible for the overseas expansion of  CRRC's wind power & solar power business. We have a relatively complete internal supply chain, service network and excellent product quality and technology.

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