You need to know this knowledge when using an inverter, otherwise you will be in vain?

1. Rated output voltage

The rated voltage value that the inverter should output when outputting the rated current within the allowable fluctuation range of the specified DC input voltage. The output voltage stability of the inverter characterizes the voltage stabilization ability of the inverter output voltage. Most inverter products give the deviation percentage of the inverter output voltage within the allowable fluctuation range of the input DC voltage, which is usually called Voltage regulation rate. The stable accuracy of the output rated voltage value is specified as follows.

(1) During steady-state operation, the voltage fluctuation range should be limited. The voltage fluctuation range is: single-phase 220 V ± 5%, three-phase 380 V ± 5%.

(2) The high-performance inverter should also give the deviation percentage of the output voltage of the inverter when the load changes from 0% to 100%, which is usually called the load regulation rate. The voltage regulation rate of inverter with good performance should not be greater than ± 3%, and the load regulation rate should not be greater than ± 6%.

(3) Under 10% asymmetric load, the asymmetry of the output voltage of the three-phase inverter with fixed frequency should not be greater than 10%. Asymmetry of output voltage Under normal working conditions, the load of each phase is symmetrical, and the asymmetry of output voltage should not be greater than 5%. Under normal working conditions, the three-phase voltage imbalance (the ratio of reverse sequence component to forward sequence component) output by the inverter should not exceed a specified value, generally expressed in%, such as 5% or 8%.

(4) When the battery with a voltage of 12V is in the floating charge state, the terminal voltage can reach 13.5 V, and the short-time overcharge state can reach 15V. The terminal voltage of the battery can drop to 10.5 V or lower when the battery discharge is terminated under load. The fluctuation of battery terminal voltage can reach about 30% of the weighed voltage. This requires the inverter to have good voltage regulation performance, so as to ensure that the solar photovoltaic power generation system is powered by stable AC voltage. For a qualified inverter, when the input terminal voltage changes within this range, the change of its steady-state output voltage should not exceed 5% of the rated value, and when the load suddenly changes, the deviation of its output voltage should not exceed ± 10% of the rated value.

(5) Waveform distortion and maximum harmonic content of output voltage. When the output voltage of the inverter is sine wave, the allowable maximum waveform distortion (or harmonic content) should be specified. It is usually expressed as the total waveform distortion of the output voltage, and its value should not exceed 5%. For sine wave inverter, under resistive load, the maximum harmonic content of output voltage should not exceed 10%. Because the high harmonic current output by the inverter will produce additional losses such as shallow current on the inductive load, if the waveform distortion of the inverter is too large, it will cause serious heating of the load components, which is not conducive to the safety of electrical equipment and seriously affects the operation efficiency of the system.

2. Rated output frequency

Under the specified conditions, the frequency of the AC voltage output by the inverter should be a relatively stable value, usually the power frequency is 50Hz. Under normal working conditions, the deviation should be within ± 1%. China's AC load works at the frequency of 50Hz. However, high-quality equipment needs accurate frequency, because frequency deviation will lead to the performance degradation of electrical equipment.

3. Load power factor

The load power factor characterizes the inverter's ability to carry inductive load or capacitive load. Under sine wave conditions, the load power factor is 0.7 ~ 0.9 (hysteresis), and the rated value is 0.9. The cosine of the phase difference between the current and voltage generated by the inverter is the power factor. For resistive loads, the power factor is 1, but for inductive loads (commonly used loads in household systems), the power factor will decrease, sometimes It may be lower than 0.5. The power factor is determined by the load rather than by the inverter. When the load power is constant, if the power factor of the inverter is low, the required capacity of the inverter will increase. On the one hand, the cost will increase; on the other hand, the apparent power of the AC loop of the photovoltaic power generation system will increase. If the power increases, the loop current will increase, the loss will inevitably increase, and the system efficiency will also decrease.

4. Rated output current (or rated output capacity)

Rated output current refers to the rated current value that the inverter should output under the specified output frequency and load power factor. Some inverter products give rated output capacity, which is expressed 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).

5. Inverter efficiency

The efficiency of the inverter refers to the ratio of its output power to input power under specified working conditions, expressed as a percentage. The efficiency of the inverter will vary greatly due to different loads. The efficiency value of the inverter represents its own power loss, usually expressed as a percentage. The actual efficiency of 10kW general-purpose inverter is only 70% ~ 80%. When it is used in solar photovoltaic power generation system, it will bring 20% ~ 30% power loss of total power generation. In the design of special inverter for solar photovoltaic power generation system, special attention should be paid to reducing its own power loss and improving the efficiency of the whole machine. This is an important measure to improve the technical and economic indicators of solar photovoltaic power generation systems. In terms of overall machine efficiency, the requirements for special inverters for solar photovoltaic power generation are: the rated load efficiency of inverters below kilowatt level should be no less than 85%, and the low load efficiency should be no less than 75%; The rated load efficiency of 10kW inverter should not be less than 90%, and the low load efficiency should not be less than 80%. Inverters with larger capacities should also give full load efficiency values and low load efficiency values. The efficiency of inverter has an important impact on improving the effective power generation and reducing the power generation cost of solar photovoltaic power generation system.

6. Protection function

An inverter with excellent performance should have complete protection functions or measures to deal with various abnormal situations that occur during actual use and protect the inverter itself and other components of the system from damage. For example, during the normal operation of the solar photovoltaic power generation system, the overcurrent or short circuit of the power supply system will be caused by load failure, personnel misoperation and external interference. Inverse

The converter is the most sensitive to the overcurrent and short circuit phenomenon of external circuit, and it is the weak link in the solar photovoltaic power generation system. Therefore, the inverter should be equipped with overvoltage protection, undervoltage protection, overcurrent protection, short circuit protection, lightning protection and overtemperature protection.

(1) Voltage protection: If the input end of the inverter is a battery pack, and the DC input voltage of the inverter will exceed the nominal value when the battery is overcharged. For example, after a 12V battery is overcharged, the voltage may reach 16V or higher, which may damage the subsequent inverter. Therefore, it is necessary to control the charging state of the battery. The inverter must have a protection circuit to detect the input voltage and overvoltage. When the voltage is higher than the set value, the protection circuit will disconnect the inverter. For inverters without voltage stabilization measures, there should be protective measures against output overvoltage to protect the load from the damage of output overvoltage. When the input voltage is lower than 85% of the rated voltage, the inverter should be protected and displayed. When the input voltage is higher than 130% of the rated voltage, the inverter should have protection function and fault display function.

(2) Overcurrent protection: The overcurrent protection circuit of the inverter should act in time when the load is short-circuited or the current exceeds the allowable value to protect it from inrush current damage. When the working current exceeds 150% of the rated current, the inverter should be able to automatically protect.

(3) Short-circuit protection: The action time of inverter short-circuit protection should not exceed 0.5 s.

(4) Input reverse connection protection: When the positive and negative input terminals are connected reversely, the inverter should have a protection function and display.

(5) Lightning protection: The inverter should have lightning protection.

(6) Over-temperature protection. In addition, for inverters without voltage stabilization measures, there should also be output overvoltage protection measures to protect the load from overvoltage damage.

7. Start-up characteristics

The start-up characteristics characterize the ability of the inverter to start with load and its performance when operating dynamically. Inverters should ensure reliable start under rated load. High-performance inverters can start at full load multiple times in a row without damaging power devices, while small inverters sometimes use soft start or current limiting start for their own safety. Under normal working conditions, the inverter should be able to start normally five times in a row under full load and no-load operating conditions.

8. Noise

Components such as electronic switches, transformers, filter inductors, electromagnetic switches and fans in inverters all produce noise. When the inverter is running normally, its noise should not exceed 65dB. Inverters that are not frequently operated, monitored and maintained should not be greater than 95dB; Inverters that are frequently operated, monitored and maintained should not be greater than 80dB.

9. Environmental conditions of use

The normal operation conditions of the inverter are that the altitude is not more than 1000m and the air temperature is 0 ~ + 40 ℃

10. Interference and anti-interference

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

11. Display

The inverter should be equipped with the data display function of AC output voltage, output current and output frequency, as well as the signal display function of input live, energized and fault state.