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EMC standards and typical test methods for inverters
Release time:
2022-08-14 00:00
Source:
EMC is the abbreviation of Electromagnetic Magnetic Compatibility, Chinese is electromagnetic compatibility. EMC refers to "the ability of a device to function properly in an electromagnetic environment without causing intolerable interference to other devices in the environment".
The increasing use of power electronics in conjunction with microelectronics in increasingly complex systems means that electromagnetic compatibility has become an extremely important issue when ensuring the proper operation of complex systems and devices. Therefore, electromagnetic compatibility issues must be taken into account during the planning phase of equipment and systems.
The frequency converter is suitable for the EMC product standard GB 12668.3 of the variable-speed electric drive system (Power Drive Systems, referred to as PDS), the standard name: variable-speed electric drive system Part 3: electromagnetic compatibility requirements and specific test methods, which is equivalent to the international standard IEC61800-3. The following is a brief introduction to the standard's immunity requirements and electromagnetic emission requirements for PDS.
I. Overview
The GB 12668.3 standard defines the anti-interference requirements and interference emission limits according to the application environment conditions. According to the installation location, the environment is divided into "first class" and "second class".
first environment
It includes the environment of domestic buildings, and also includes the application environment directly connected to the low-voltage power supply network supplying civil buildings without intermediate transformers.
Second environment
Includes all environments except for applications directly connected to low-voltage power supply networks that supply buildings used for domestic purposes.
PDS products are divided into four categories (C1 to C4) according to the installation position and output current of the variable speed drive:
C1 PDS
Rated voltage < 1000V, for use with unrestricted drive systems in the "first" environment.
C2 PDS
Drive systems for rated voltage < 1000V, for use in fixed positions in the "second" environment. It is neither a plug-in device nor a mobile device, and when used in the first environment, it is prescribed as a PDS that can only be installed and commissioned by professionals. The warnings and installation information provided by the manufacturer must be followed.
C3 PDS
Rated voltage <1000V, unrestricted drive systems for use in the "second" environment.
C4 PDS
Rated voltage ≥ 1000V or rated current ≥ 400A, drive system for complex systems in the "second" environment.
In a "Class 1" environment (ie, a domestic environment), the permissible level of interference is lower. Therefore, equipment designed for use in the "Class 1" environment must have low interference emissions. At the same time, however, they require only relatively low interference immunity.
In "secondary" environments (ie industrial areas), the permissible interference level is higher. Equipment designed for use in the "second" environment allows a relatively high level of interference emission, but they also require a high level of interference immunity.
All test evaluations are carried out on the ports of the product. The internal interfaces and ports of the PDS product are shown as follows:
For the influence of PDS and its sub-components according to the given disturbance, the immunity test is divided into three acceptance (performance) criteria: A, B, and C:
2. Immunity test requirements: low frequency disturbance
Ideal power system: single frequency, single waveform (sinusoidal).
The emergence of a large number of modern power electronic devices, the application of nonlinear loads, the nonlinear interface circuit between the power supply and the electrical equipment, etc., will inevitably generate strong current harmonics and electromagnetic interference, which poses a potential threat to the safety of the power system. threat. To this end, GB 12668.3 specifies the immunity requirements for harmonics and commutation notches/voltage distortions on the PDS power port.
2.1 Harmonics and commutation notches/voltage distortion
PDS equipment shall withstand the immunity classes given in the table below.
2.2. Voltage deviation (variation, change, fluctuation), voltage drop and short-term interruption
Voltage dips are caused by occasional short circuits, ground faults in the grid, or sudden large changes in load. The short-term voltage interruption may be caused by continuous rapid reclosing under fault conditions, and the duration may be shorter than 0.5s.
GB 12668.3 stipulates the immunity requirements of PDS system or components for voltage deviation (variation, change, fluctuation), voltage dip and short-term interruption as follows.
2.3. Voltage unbalance and frequency change
There are many reasons for the imbalance. For example, there is a broken line. If the line is broken, there is no grounding or the isolation switch is not connected, it will lead to asymmetrical three-phase parameters, and the problem of voltage imbalance will directly occur.
Voltage unbalance is generally defined by the ratio of the negative sequence (or zero sequence) component to the positive sequence component.
The frequency change of the power system is determined by many factors. Small frequency fluctuations may be due to instability and load changes in renewable energy generation. Large frequency fluctuations are caused by failures of generator sets or important transmission lines.
GB 12668.3 specifies the immunity requirements for voltage unbalance and frequency variation of PDS system or components as follows.
3. Immunity test requirements: high frequency disturbance
3.1 The first type of environment
PDS products used in the first environment shall meet the following test requirements.
In the case of a CDM/BDM product, a written warning shall be included in the instructions for use stating that its intended use is not industrial equipment.
3.2, the second type of environment
The following immunity classes apply to PDS equipment intended for use in the second environment. It is also suitable for low-voltage ports or low-voltage interfaces (power supply, signal) of PDS with rated voltage higher than 1 000V.
Note: Examples of low-voltage ports and interfaces of PDS with rated voltage higher than 1000V:
Low-voltage enclosure ports: enclosures for auxiliary equipment, control and protection
Low-voltage power port: Low-voltage power supply for PDS
Low voltage power interface: Auxiliary power distribution within the main components of the PDS
Low-voltage signal interface: Low-voltage signal interface within the main components of the PDS
Low pressure process port: signal port of PDS
These phenomena are inappropriate for applications applied to ports with rated insulation voltages higher than 1 000 V. Such ports are called high voltage ports of PDS with rated voltage higher than 1000V.
Note: Examples of high-voltage ports and interfaces of PDS with rated voltage higher than 1000V:
High-voltage case ports: Cases for transformers, converter sections, and electric motors
High-voltage power port: primary side of the transformer
High-voltage power interface: High-voltage power distribution within the main components of the PDS
High-voltage signal interface: the high-voltage signal interface in the main part of the PDS
3.3 Supplementary instructions on electromagnetic field immunity
If the PDS is in the following situations, it should be tested according to GB/T 17626.3 and IEC 61000-4-6:
- the rated voltage is not higher than 500 V;
- the rated current is not more than 200 A;
- have a total mass of not more than 250 kg; and
- The height, width and depth are not greater than 1.9 m.
If the PDS rating is greater or higher than the value in the paragraph above, you will need to choose between the following two options:
- carry out the items in GB/T 17626.3 and IEC 61000-4-6 on the PDS; or
—— Carry out the items in GB/T 17626.3 and IEC 61000-4-6 on sensitive sub-components.
If the motor is too large to be put into use on the test site, a motor of smaller size may be substituted for the test as long as there is no adverse effect on the operation of the CDM/BDM.
Where only subcomponents have been tested, comparative tests with radiocommunication equipment for general industrial use should be carried out on the complete PDS. This test is only valid for the specific location, equipment installed and frequency tested.
4. Launch test
PDS shall meet the corresponding requirements according to the product categories, among which C1, C2, and C3 need to be verified for compliance, and for C4 category, the engineering design practice shall be completed according to standard 6.5.
Where the PDS does not comply with the limits for category C1, the following warning shall be included in the instructions for use:
5. Test plan
5.1 Anechoic chamber method
Brief introduction to the test project:
Standards such as CISPR 16 stipulate that the EUT needs to conduct a radiation emission test above 30MHz in an open field or an anechoic chamber. The EUT is placed on the ground plane at a specified height and arranged to simulate normal operating conditions. Antennas are placed at specified distances. Rotate the EUT in the horizontal plane and note the maximum reading. Then adjust the height of the antenna so that the direct wave and the ground reflected wave are close to or reach the same phase superposition, and find out the maximum disturbance value.
Measurement distance: refers to the distance between the point of the EUT closest to the antenna and the projection of the center of the antenna on the ground. The 10-meter method is preferred, and the 3-meter method is optional.
Antenna Height: The height of the antenna from the ground should vary within the specified range to obtain the maximum reading that would occur if the direct and reflected waves were in phase. When the measurement distance is less than or equal to 10 meters, the antenna height is preferably changed between 1m and 4m.
Radiated emission test layout diagram
The radio frequency electromagnetic field radiation immunity test is used to simulate the situation that the equipment is subjected to radio frequency radiation interference, especially to simulate the possible impact on the equipment when people around the equipment use mobile phones. Although the power of a single mobile phone is not large, due to the short distance, it may cause high local field strength. Others such as radio stations, TV transmitters, mobile radio transmitters, various industrial electromagnetic radiation sources, and electric welding machines, silicon controlled rectifiers, fluorescent lamps, etc. will also produce radiation to the equipment during work. The frequency range specified by the latest standard is: 80MHz - 6GHz; the test field strength is between 1 - 30V/m.
Schematic diagram of RF electromagnetic field test layout
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
The 10m anechoic chamber SAC-10 adopts the most advanced electromagnetic compatibility test solution. The darkroom project is fully controlled in Germany, with rigorous craftsmanship and standardized construction. The absorbing material adopts a unique nano-material, which replaces the traditional carbon powder technology absorbing material with excellent performance, stability, and excellent test consistency. And the absorbing material is completely non-combustible, and it is the only one in the world that meets the requirements of DIN4102 A2 fire protection level, so as to avoid fire incidents in darkrooms.
The main performance parameters of the anechoic chamber SAC-10 are as follows:
PDS and its sub-components test needs assessment:
The anechoic chamber system fully meets the RF electromagnetic field (RS) test in the 80MHz~1 000MHz frequency band of 3V/m in chapters 3.1 and 3.2 of PDS products, and the 10m field radiated emission (RE) 30MHz-1000MHz test requirements in chapter 4. And the anechoic chamber adopts 3 test axis design, EMI, EMS do not need to switch sites, which greatly saves site layout and instrument debugging time, making the test easier and more efficient.
5.2 Harmonic current and voltage flicker
Brief introduction to the test project:
Due to the extensive use of switching power supplies in electronic products, while improving power supply efficiency, a large amount of harmonic current will be injected into the power grid due to nonlinear power conversion, which will not only interfere with other equipment in the same power grid, but also make the neutral line of the power grid Current overload affects power transmission capacity. In addition, the phase control of the power supply will also cause changes in the effective value current of the grid, resulting in fluctuations in the effective value voltage on the load side, causing the lights of lighting fixtures to flicker.
The harmonic test mainly measures the harmonics injected into the power grid when the EUT is working. In the harmonic measurement circuit, the test power supply S is an idealized AC power supply with the characteristics of small internal resistance, pure waveform, stable voltage and accurate frequency. Measuring equipment M is a discrete Fourier transform time-domain analysis instrument, which can analyze harmonic current values of 1-40th order.
The voltage fluctuation and flicker test mainly measures the change of grid voltage caused by EUT. The interference effect caused by the voltage change depends not only on the magnitude of the voltage change, but also on the frequency of its occurrence. The voltage change is usually evaluated by two indicators, namely voltage fluctuation and flicker. The voltage fluctuation indicator reflects the degree of sudden large voltage changes, while the flicker indicator reflects the continuous voltage changes over a period of time. In the voltage fluctuation and flicker circuit, the composition of the reference impedance Z (at 50Hz) of the power supply S: RA=0.24Ω, jXN=0.15Ω; RN=0.16Ω, jXN=0.10Ω.
Schematic diagram of harmonic current and voltage flicker test layout
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
Harmonic and flicker analyzer DPA 503N, is a fully certified harmonic and flicker analyzer, which meets the latest editions of IEC/EN61000-3-2, IEC/EN61000-3-3 and JIS C 61000-3-2 standard requirement. It also meets the requirements of IEC/EN 61000-4-7:2002 and Am.1:2008 (Class A instruments) and IEC/EN 61000-4-15:2003. Fully meet the testing requirements of PDS product low-frequency emission (power port).
5.3 Conducted harassment
Brief introduction to the test project:
The test of power line conduction disturbance, although different products are regulated by different standards, but the basic method is the same, consisting of artificial power network (AMN or line impedance stabilization network LISN) and EMI test receiver, of which (50μH+5Ω) //50Ω or 50μH//50Ω V-shaped artificial power network can provide standard 50-ohm impedance for disturbance voltage measurement within a given frequency range, and isolate the equipment under test (EUT) from the power supply. When LISN is not applicable, a voltage probe can be used for measurement.
Conducted disturbance test diagram
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
The ESR receiver is fully compliant with the CISPR 16-1-1 standard. The receiver can measure electromagnetic interference with conventional stepped frequency sweeps or at very high speeds with FFT-based time domain sweeps. At the same time, the R&S®ESR can also be used as a comprehensive and powerful signal and spectrum analyzer. The conduction disturbance test system is also equipped with multiple sets of professional test instruments such as high-resistance-capacitance voltage probe CVP9222C, high-voltage probe TK9420 (2.5kV), artificial power network NNLK 8129 RC, etc., which can fully meet the measurement requirements of GB 12668.3 for power ports and telecommunication ports .
5.4 Electrostatic discharge
Brief introduction to the test project:
The electrostatic discharge immunity test mainly checks the discharge (direct discharge) caused by people or objects touching the equipment, and the impact on the operation of the equipment caused by the discharge (indirect discharge) of people or objects on adjacent objects of the equipment. During electrostatic discharge, a discharge current of 1-50A can be generated within 0.5-20ns. Although the current is large, the energy is small because the duration is very short. Therefore, general electrostatic discharge will not cause harm to people, but it may cause destructive harm to electronic products such as integrated circuit chips.
The test levels of electrostatic discharge test are: contact discharge 2kV, 4kV, 6kV, 8kV; air discharge: 2kV, 4kV, 8kV, 15kV.
Schematic diagram of electrostatic discharge test layout
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
EMTEST electrostatic discharge signal generator NX30, the test voltage of air discharge and contact discharge can reach up to 30 kV, the discharge frequency can reach up to 25 Hz, a variety of discharge modules and discharge heads can be easily replaced. The power supply battery supports 30,000 discharges at 30 kV, and supports the control and analysis software of the Windows 7 operating system.
The electrostatic discharge signal generator fully meets the test requirements of 8kV air discharge and 4kV contact discharge of PDS products, and NX30 is light, easy to move, ergonomically designed, and extremely convenient to operate.
5.5 Electrical fast transient bursts
Brief introduction to the test project:
The electrical fast transient burst immunity test is to simulate the interference generated by many mechanical switches in the power grid when switching inductive loads. The characteristics of this type of interference are: narrow pulses appearing in groups, high pulse repetition frequency (kHz-MHz level), steep rising edge (ns level), short duration of a single pulse (10-100ns level), and the amplitude reaches kV level. Groups of narrow pulses can charge the junction capacitance of semiconductor devices, and when the energy accumulates to a certain level, it can cause circuit or equipment errors. During the test, the pulse is superimposed on the power line and communication line to form interference to the equipment.
The test part of the equipment under test (EUT) mainly includes the power supply port of the equipment, protective earth (PE), signal and control ports.
Schematic diagram of electrical fast transient burst test layout
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
Compact NX5 ultra-small simulator is a multi-functional test equipment that can meet various requirements of international standards (basic standards and general standards) and product series standards for transient, pulse, etc. tests. The Compact NX5 is equipped with an easy-to-use color touchscreen, built-in single-phase coupling/decoupling network, and couples EFT/Burst pulses through an automatically controlled external coupling network NX-series three-phase coupling/decoupling network for EUT voltages up to 1000 VDC / 3 x 690 VAC. And the CCI capacitive coupling clamp that can test the cable diameter up to 40 mm and burst voltage 7 kV. Fully meet the 2kV/ 5 kHz test level requirements of PDS product power ports, process measurement and control line ports and signal interfaces.
5.6 Surge (shock) immunity
Brief introduction to the test project:
The surge (shock) immunity test is to simulate the impact of lightning strikes (indirect lightning) in nature and the voltage changes caused by large-scale switch switching in the power supply lines on the power supply lines and communication lines. Surge test
Two waveforms (1.2/50μs and communication wave 10/700μs) are specified, with an amplitude of 0.5kV to 4kV. The energy is particularly large, and the impact on the EUT may be destructive. 10/700μs (commonly known as communication wave) is suitable for long-distance symmetrical communication ports, and 1.2/50μs is suitable for power line ports and other signal line ports.
Schematic diagram of surge (shock) test layout
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
Compact NX5 ultra-small simulator is a multi-functional test equipment that can meet various requirements of international standards (basic standards and general standards) and product series standards for transient, pulse, etc. tests. Compact NX5 is equipped with an easy-to-use color touch screen, built-in single-phase coupling / decoupling network, through the automatic control of external coupling network NX series three-phase coupling / decoupling network coupling surge pulse, EUT voltage up to 1000 VDC / 3 x 690 VAC. It also has coupling and decoupling networks for various communication port tests. It fully meets the test level requirements of 1kV and 2kV for power ports, process measurement and control line ports and signal interfaces of PDS products.
5.7 Radio Frequency Field Induced Conducted Immunity
Brief introduction to the test project:
For low-frequency (150kHz-80MHz/230MHz) radio frequency signals, because their wavelength is much longer than the size of the EUT, the interconnection cables of the EUT (including power lines and signal lines) are more likely to become antennas and receive electromagnetic fields than the EUT itself, so the radio frequency For the low-frequency part of the immunity test, it is more direct to use the conduction test method. The injection methods include CDN direct capacitive coupling injection, electromagnetic clamp injection, current clamp injection and DC injection.
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
The NSG 4070C is a versatile device for EMC immunity testing and compliance testing according to IEC/EN 61000-4-6 and some automotive BCI standards. The NSG 407C0's modular setup allows the use of internal or external amplifiers to suit a wide variety of applications. Powerful and easy-to-use firmware makes the NSG 4070 independent of external PC and control software, but it can also control system operation remotely. The available frequency range of the power port coupling and decoupling network is 150 kHz - 80 MHz, the number of lines is 5, the maximum current is 100 A, the maximum voltage is 600 VAC, 6 mm safety banana head connector; the maximum diameter of the electromagnetic injection clamp is 20 mm, and the maximum RF input power is 100 W. Fully meet the 10V/m test requirements of PDS product power port, signal interface, process measurement and control line port and signal interface within the frequency range of 0.15MHz~80MHz.
5.8 Power Quality Immunity
Brief introduction to the test project:
Voltage sags and voltage interruptions are caused by failures of the grid, power facilities, or sudden large changes in load. Voltage variations are caused by continuous changes in loads connected to the grid. If the EUT cannot respond in time to the change of the power supply voltage, it may cause a failure.
The test level of the voltage sag is expressed in %UT (the remaining voltage after the sag is the percentage of the reference voltage): 0%, 40%, 70%, 80%.
A short interruption generally refers to a complete interruption of the power supply for 250 cycles (50Hz) or 300 cycles (60Hz).
The voltage change generally refers to the situation where it is maintained for one cycle after a sudden change to 70%, and then returns to the reference voltage after 25/30 cycles.
Century Huize (Suzhou) Testing Technology Co., Ltd. laboratory test plan:
Multifunctional programmable AC and DC power quality immunity simulator NetWave 67, built-in arbitrary waveform generator, easy to simulate complex waveforms. Power supply frequency range DC - 5 kHz, output power up to 270 kVA AC / 324 kW DC, output voltage up to 3 x 690 V AC (pn), ±1120 V DC. Built-in standard test procedures comply with IEC / EN standards, aviation standards and MIL-STD military standard test requirements.
The power failure simulator PFS503N is used for voltage dips, short interruptions and voltage change tests. The equipment is a fully compatible three-phase test system, in compliance with IEC 61000-4-11 Ed.2:2004 and IEC 61000-4-34 standards, suitable for delta and star power supply test. Rated voltage up to 3 x 690 V AC, 600 V DC nominal current up to 100 A per phase.
