Solar power system an overview:

The adoption of solar power systems has continued to rise globally in recent years.  A solar power system converts sunlight into electrical energy using photovoltaic (PV) panels. A typical solar power system features PV cells, a charge controller, an inverter, a battery bank, power optimizers, and connecting cables. 

PV panels convert sunlight to DC power. The charge controller stores this power in the battery. The inverter converts DC to AC power. The power optimizers are electronic devices (DC to DC converter technology), often located close to the individual solar modules, to maximize the energy output from each solar panel. Solar power systems can be off-grid, grid-tied, or hybrid.

Figure: Hybrid solar power system

• The off-grid system supplies electrical energy for an individual user (e.g., for a home) and does not supply power to the electrical utility grid.  Off-grid inverters are typically designed to provide one of three waveforms: square wave, modified square wave, or sine wave outputs.  
• The grid-tied system supplies electrical power for an individual user (e.g., for a home) or to be sold to the utility grid. The grid-tied inverter is designed to deliver a pure sine wave in phase with the grid.  
• The hybrid system uses a hybrid inverter that performs dual functions, i.e., it can operate as an Off-Grid inverter and as a Grid-Tied inverter at the same time. 

The solar power system provides renewable energy solutions in various environments, including residential areas, industries, hospitals, offices, etc.   

EMC testing for solar power systems:

Electronics such as inverters and power optimizers used in solar power systems can generate electromagnetic interference (EMI) and be affected by EMI from external sources like nearby power lines and other electronic devices. Electromagnetic interference (EMI) refers to high-frequency EM noise generated during the normal operation of electrical and electronic equipment, which can affect or interfere with the operation of nearby equipment in two ways: by traveling through connected lines/cables (called conducted EMI) and through the air (called radiated EMI). 

Figure: Understanding Conducted EMI (propagate via power line) and Radiated EMI (unwanted electromagnetic energy emissions, propagate via air)

For example, inverters and power optimizers in solar power systems can emit both conducted and radiated electromagnetic emissions, which may destabilize the power grid, and interfere with the operation of other connected devices and co-located wireless communication systems or devices. Electromagnetic disturbances are emitted from the inverter due to switching actions and clock signals.

Electromagnetic compatibility (EMC) refers to electrical and electronic equipment’s ability to operate satisfactorily without disturbing any other nearby equipment or system in its real-world electromagnetic environment. To ensure that electronic devices used in solar power systems are safe and reliable, it is important to subject them to electromagnetic compatibility (EMC) testing. EMC testing plays a crucial role in verifying that devices meet the necessary EMC standards to operate safely and reliably in a diverse electromagnetic environment. 

EMC standards are documents published by international and national organizations that provide EMI emission limits, immunity levels, EMC testing procedures, and other details to ensure the electromagnetic compatibility of equipment. An electrical and electronic product can get into the market of a country when it meets the relevant EMC standards requirements of that country. 

How is EMC testing performed for solar power systems?

EMC testing is performed for electronic devices such as inverters used in solar power systems to ensure that the device can operate properly without disturbing any other nearby devices in its intended electromagnetic environment. This testing ensures the device is reliable to use and meets its relevant EMC standards.  

The EMC testing typically involves two types of testing: emission testing and immunity testing. These tests are usually performed in a laboratory environment (e.g., anechoic chamber) with necessary equipment, according to the relevant EMC standard requirements. Several different types of EMC tests may be performed on electronic devices used in solar power systems, including:

 Emission testing:                                                                                

The emission testing measures the levels of EMI emitted by a device during operation. The purpose of this testing is to ensure that the device under test (DUT) does not exceed the emission limits specified in the EMC standards, thereby ensuring that the DUT does not interfere with other nearby devices in the same environment. The emission testing includes the following tests: 

Conducted Emission (CE) Test: This test measures the levels of conducted EMI emitted by a device during normal operation to ensure that the device under test (DUT) does not exceed the conducted emission limits specified in the EMC standards, thereby ensuring that the DUT does not interfere with other connected devices on the same line during operation.

Radiated Emission (RE) Test: This test measures the levels of radiated EMI emitted by a device during normal operation to ensure that the DUT does not exceed the radiated emission limits described in the EMC standards, thereby ensuring that the DUT does not interfere with other nearby devices on the same environment. 

Harmonics and Flicker Testing: This test measures harmonic currents and voltage fluctuations (i.e., flicker) caused by the DUT and compares the results with the limits specified in the relevant EMC standards. The purpose of this test is to ensure that the DUT does not exceed the harmonic emission and voltage fluctuation limits set by the standards, thereby ensuring the quality of the power supply.

Immunity testing:

Immunity testing is conducted to assess a device's ability to withstand external electromagnetic disturbances, such as conducted disturbances, radiated disturbances, electrostatic discharge (ESD), and electrical fast transients (EFT)/bursts that may occur in real-world environments. The purpose of immunity testing is to ensure that the device can withstand external EMI and operate properly in its intended real-world environment. 

The EMC immunity testing includes the following tests:

Conducted immunity testing: Assesses the device's ability to withstand electrical noise conducted through power lines and cables.

Radiated immunity testing: Determines the device's ability to withstand radiated EM noise from external sources. 

Electrostatic discharge (ESD) testing: Evaluates a device's ability to withstand electrostatic discharges.

Electrical Fast Transients (EFT)/Burst testing: Evaluates the device's ability to withstand EFT disturbances.

Voltage dips - short interruptions - voltage variations testing: Determines the device's ability to withstand voltage dips, short interruptions, and voltage variations disturbances.

Power frequency magnetic field immunity testing: Assesses the device's to withstand the power frequency (50/60 Hz) magnetic field, which can be caused by nearby power line conductors or other nearby equipment (e.g., motors, transformers).

After completing the EMC testing, the results are analyzed to determine if the device meets the EMC standards requirements and specifications. If the product does not comply with the requirements of standards, the manufacturer may need to make changes or modifications to improve its EMC performance. Thereby, EMC testing ensures the reliability of electronic devices and the safe & reliable operation of solar power systems.

EMC testing standards for solar power systems:

At present, there are no specific dedicated EMC standards for solar inverters. Because, at various times, solar inverters are considered as household appliances, ISM (industrial, scientific, medical) equipment, or as information technology components. Therefore, based on the environment used,  EMC standards defined for residential, commercial, multimedia equipment, industrial, scientific, and medical equipment can apply to solar inverters.

Here are some key standards relevant to EMC testing for electronics (e.g., inverters) used in solar power systems:

IEC 61000-6-1: This is an international generic EMC immunity standard that specifies immunity requirements for equipment used in residential, commercial, and light-industrial environments.

IEC 61000-6-2: This is an international generic EMC immunity standard that specifies immunity requirements for equipment designed for use in industrial environments.

IEC 61000-6-3: This is an international generic EMC emission standard that specifies emission requirements (conducted and radiated) for equipment intended for use in residential environments (indoor and outdoor). This standard also applies to equipment used in commercial and light-industrial environments. 

IEC 61000-6-4: This is an international generic EMC emission standard that specifies emission requirements (conducted and radiated) for equipment intended for use in industrial environments (indoor and outdoor).

IEC 61000-3-2: This is an international standard that specifies limits for harmonic current emission from electrical equipment connected to the low-voltage power supply network (equipment input current ≤16 A per phase).

IEC 61000-3-3: This is an international standard that specifies limits on voltage fluctuations and flicker in low-voltage power supply networks (for equipment with rated current ≤16 A per phase and not subject to conditional connection).

IEC 61727:   Specifies requirements for the interconnection of PV systems to the utility distribution system, including EMC aspects, to ensure that the systems do not adversely affect grid stability or other connected equipment.

CISPR 11: This is an international standard that specifies emission limits and methods of measurement for conducted and radiated emissions from industrial, scientific, and medical (ISM) equipment. 

CISPR 14-1: This is an international standard that specifies emission limits and methods of measurement for conducted and radiated emissions from household appliances, electric tools, and similar apparatus.

CISPR 32: This is an international standard that specifies emission limits and methods of measurements for conducted and radiated emission from multimedia equipment.

EN 61000-6-3: It is a European standard equivalent to IEC 61000-6-3.

EN 61000-6-4: It is a European standard equivalent to IEC 61000-6-4. 

EN 61000-3-2: It is a European standard equivalent to IEC 61000-3-2. 

EN 61000-3-3: It is a European standard equivalent to IEC 61000-3-3.

IEEE 1547:  It is an IEEE standard prepared for Interconnecting Distributed Resources with Electric Power Systems.

UL 1741: Applies in the USA to inverters, converters, controllers, and interconnection system equipment for use with distributed energy resources. 

These standards ensure that electronics in the solar power system are reliable enough to operate in their intended real-world environments. Typically, solar inverters are designed with EMI filters at their inputs, outputs, and any signal/control connections. They are also well-shielded and use other good EMC design practices (e.g., use of shielded cables) to meet the EMC standards requirements.