As national policies continue to tilt toward distributed photovoltaics, photovoltaic innovation technology is improved, the cost of electricity is reduced, state subsidies remain unchanged, and investment in distributed photovoltaic power stations is now very cost-effective. However, many people still have some concerns. With so many photovoltaic modules installed on the roof, the inverter outputs so much current that there is no electromagnetic radiation, and it has no effect on the human body and household appliances.
What is electromagnetic radiation?
What is radiation? It refers to the process by which an object emits energy into the surrounding space in the form of waves or particles. As long as the temperature of each object in the natural world is above absolute zero, it will constantly transmit energy to the outside world in the form of electromagnetic waves or particles. In other words, everything in the world has radiation, including the human body, and it is always radiating outward. For example, bask in the sun, in fact, is to accept the sun's radiation. However, not all radiation is harmful, and some are even inseparable. For example, the sun's radiation, sunlight, and the growth of all things on the earth require sunlight.
Although electromagnetic radiation will not change the molecular nature of organisms and cause direct damage, if the energy is large, it will also cause certain effects on organisms, which are reflected in two aspects: thermal effects and induced currents. It also causes interference with home appliances such as mobile phones, radios, and televisions.
Electromagnetic Radiation Protection Regulations (GB8702-88) and Sanitary Standards for Environmental Electromagnetic Waves (GB9175-88). The electromagnetic radiation exposure limit is stipulated: 50Hz frequency is calculated according to the standard of magnetic field strength, and the specific unit is μT. If the radiation is stronger than 0.4μT, it has certain harm to the human body. If radiation is below 0.4μT, it is relatively safe. The RF electromagnetic field is calculated based on the power density or the field strength. The specific unit is μW/c m2 or V/m, and the standard limit within the public's most sensitive range of 30-3000 MHz is 40 μW/cm 2 . Under this standard, it is safe.
The generation of electromagnetic radiation
According to the basic theory of electromagnetism, there will be a corresponding electric field distribution around the charged particles. The charged particles that change with time will produce a changing electric field. Because there is a potential difference between two points with different potentials around the charged particles, they form between the two points. Voltage; When a large number of charged particles move directionally, a current is formed, and a magnetic field is generated around the current. A current that changes with time will produce a changing magnetic field. Similarly, a magnetic field that changes over time can also generate an electric field, so that alternating electric and magnetic fields that are generated alternately, perpendicular to each other and continuously propagated into space, produce electromagnetic radiation. The amount of energy carried by electromagnetic radiation depends on the level of its frequency. The higher the frequency, the greater the energy.
Photovoltaic system electromagnetic radiation
Photovoltaic system is composed of photovoltaic modules, brackets, DC cables, inverters, AC cables, power distribution cabinets, transformers, etc. Among them, the brackets are not charged and naturally will not produce electromagnetic interference. Photovoltaic modules and DC cables, which are DC currents, have no change in direction and can only generate an electric field and cannot generate a magnetic field. Although the output transformer is AC, but the frequency is very low, only 50Hz, the resulting magnetic field is very low. The inverter is a device that converts DC power into AC power. There are power electronic conversions. The frequency is generally 5-20 KHz. Therefore, an alternating electric field is generated, and electromagnetic radiation is also generated. The country has strict standards for the electromagnetic compatibility of photovoltaic inverters.
Radiated Emissions: Inverters used in households or directly connected to residential low-voltage power supply network installations should meet the Class 1 Group B limits in GB 4824-2004, as shown in the following table.
Photovoltaic Inverter EMC Electromagnetic Interference Solution Photovoltaic inverter electromagnetic radiation, compared with household appliances, about the same as a laptop, lower than the induction cooker, hair dryer, refrigerator. So don't worry about it.
Photovoltaic inverter as a power electronic equipment, the switching frequency is relatively high, the string inverter is usually up to about 20K, the current is relatively large, if you do not take measures, there will be a lot of electromagnetic interference. The usual methods include shielding, filtering and grounding. Shielding can effectively suppress electromagnetic interference transmitted through space. There are two purposes for shielding, one is to limit the internal radiated electromagnetic energy from leaking out of the control area, the other is to prevent external radiated electromagnetic energy from entering the internal control zone, and the inverter is fully metal-encapsulated with conductors such as aluminum or iron. Filtering is the control of EMI conducted interference and is usually implemented using three devices: decoupling capacitors, EMI filters, and magnetics. Inverter input and output terminals have X and Y capacitors, common-mode inductors, and magnetic beads, magnetic rings and other magnetic components. Irrespective of the method used to suppress EMI interference, it is ultimately necessary to discharge the static electricity through the ground. Therefore, the grounding of the inverter is very important. In addition to suppressing EMI interference, grounding also provides zero potential reference points and safety protection.
Conducted emission: Inverters used in households or directly connected to residential low-voltage power supply network installations shall meet the Class 1 Group B limits in GB 4824-2004.
Summary: Photovoltaic systems have electromagnetic radiation, but they are relatively small, and the use of qualified equipment will not cause harm to human bodies and cause interference to household appliances. Photovoltaic modules are direct current and do not generate radiation. The inverter's radiation is strictly controlled within the safe range. The following points must also be observed when installing the inverter: Do not install the inverter in the bedroom and the living room, and try to install outdoors. Ground (PE) Must be connected, the corresponding grounding system must be complete and in line with the specification.
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