EMC - EV

Electromagnetic Compatibility for Electric Vehicles

MF/EF Exposure Limits (Refereces)

Christian Rosu

EV pros and cons

Pros:

  • Fast Start, very quiet and very smooth, no engine vibration, no oil or gas smell.
  • High torque, very silent and responsive acceleration.  Tesla model S can go from zero to 60 mph 3.1 seconds. Electric drivetrains are generally much simpler and more reliable.
  • Home recharging for house owners. Perfect for EV drivers with home solar panels system.
  • Cheaper to operate & maintain (1/3 from gasoline cost, no exhaust systems, don’t need oil changes).
  • No carbon emissions if operated in regions with grid based on hydro, wind, or solar.

Cons:

  • Limited range (80 to 100 miles) and due to lack of charging stations infrastructure exploring new routes or road deviations are risky.
  • The cost of EV batteries is very high ($10,000), their life expectancy is modest (5 years), and their performance drops every year lowering the driving range. EV battery’s power will drop in very cold weather. Replacing & disposal of EV batteries in your garage is not anymore possible.
  • The average cost of EV is about $40,000 in spite of governmental incentives.
  • We still see a considerable number of EV makers recalls.

Christian Rosu

Switching to an electric car turns the environemnet green only in certain countries

The carbon emissions from electricity generation are measured in tones of CO2 emitted per gigawatt hour of electricity produced.

  • tCO2e/GWh = 0 for hydroelectric, nuclear and renewable energy
  • tCO2e/GWh = 500 to 600 for natural gas power plants
  • tCO2e/GWh = 1000 for coal-fired power plants

In countries that generate much of their electricity by burning coal charging EV's battery will significantly boosts carbon emissions. Even in Canadian provinces Alberta, Saskatchewan and Nova Scotia, electric cars generate more carbon pollution over their lifetimes than gas-powered cars. To really contribute to a greener environment you have to buy rather an HEV than EV. Sources


Christian Rosu

LISN (Line Impedance Stabilization Network) or AN (Artificial Network)

Purpose of the LISN:
1. Provide well defined RF impedance to the DUT.
2. The 1μF & 50μH filter isolates the noise that is put on the power lines from the DUT from feeding back to the power supply.
3. Provide a low impedance path for the noise to be measured at the output port of the LISN coupling the interference voltage generated by DUT via 0.1μF to the analyzer or receiver.

The role of the LISN is to isolate the DM current and CM current from the power supply, and to minimize the impact of the CM current by returning it to its sources. The wire harness inductance for large systems (aircraft) is 50μH whereas for small systems (automotive) is 5μH. However, the LISN selection criteria should be based on the frequencies of the measurements required.

     

Types of LISN

  1. V-LISN: Unsymmetrical emissions (line-to-ground)
  2. Delta-LISN: Symmetric emissions (line-to-line)
  3. T-LISN: Asymmetric emissions (mid point line-to-line)

 

There are two types of V-LISN with different impedances.

  • 5 µH inductance (CISPR 16-1-2, CISPR 25, ISO 7637, SAE J1113-41, DO160) are normally used to measure equipment for vehicles, boats and aircrafts connected to on-boards mains with DC or 400 Hz.
  • 50 µH according to CISPR 16-1-2, MIL STD 461 and ANSI C63.4 is intended to operate at mains frequencies of 50 Hz or 60 Hz.

The T-LISN measures the asymmetric disturbance voltage (common mode voltage) and provides it to an EMI Receiver. It is normally used for measuring telecommunication and data transmission equipment connected to symmetrical lines as e.g. twisted pairs.

CISPR-25 (Ed 3.0)
A network inserted in the supply lead or signal/load lead of apparatus to be tested which provides, in a given frequency range, a specified load impedance for the measurement of disturbance voltages and which may isolate the apparatus from the supply or signal sources/loads in that frequency range.
CISPR-25 (Ed 3.0) & ISO-11452-2:2004 & ISO-11452-4
The AN impedance ZPB (tolerance ± 20 %) in the measurement frequency range of 0.1 MHz to 100 MHz it is measured between the terminals P and B with a 50 Ω load on the measurement port and with terminals A and B short-circuited.

  

The 1μF capacitor is populated in CISPR-25 LISN; R=1Kohm.


ISO 7637-2:2011 & ISO-11452-2:2004 & ISO 7637-2:2004
The artificial network is used as a reference standard in the laboratory in place of the impedance of the vehicle wiring harness in order to determine the behavior of electrical/electronic devices.
ISO 7637-2:2011 & ISO 7637-2:2004
The resulting values of impedance ZPB, measured between the terminals P and B while terminals A and B are short-circuited, are given in figure below as a function of frequency assuming ideal electric components. In reality, the impedance of an artificial network shall not deviate more than 10 % from the given curve.

  

No 1μF populated in ISO 7637-2 LISN; R =50 ohm, C is function of voltage.


Sample setup: CISPR-25 require separate LISN for B+ and GND lines.

Christian Rosu

IEC 61000-4-4 (Electric Fast Transients / Burst)

A burst arc occurs when a mechanical contact is open during the switching process. Burst sources:
• Circuit Breakers in electrical circuits
• High Voltage switchgear
• 110/230V Power Supply systems
• 24V Control Lines

A burst has a single pulse rise time/duration of 5 ns / 50 ns from a 50 Ohm source impedance.
Bursts of 15 ms duration with a repetition rate of 5 kHz (or 100 kHz) are applied every 300 ms.

Voltage test levels:
• Power ports: 0.5 KV, 1 KV, 2 KV, 4 kV
• Signal and Control ports: 0.25 KV, 0.5 KV, 1 KV, 2 kV

• Coupling method is used to transfer the transient to the DUT.
• Decoupling method is used to block the transient from entering the mains and damaging other equipment connected in the network.

• Power line coupling is done with direct CDNs (Coupling/Decoupling Networks).
• Signal line coupling is done with a CCC (Capacitive Coupling Clamp): two metal plates which sandwich the line under test (cable) to provide a distributed coupling capacitance.

Test waveform verification is mandatory prior to each test.
For equipment connected to power ports all lines are coupled simultaneously.

Christian Rosu

Electromagnetic Spectrum

Spectrum is a continuum of all electromagnetic waves (EM) traveling at constant speed (300,000 km/s). An electromagnetic wave consists of electric and magnetic fields which vibrates thus making waves. EM wave wavelength decreases as its frequency increases. Shorter the wavelength, higher is the EM wave energy. Waves with higher frequency can carry a higher energy. The energy is measured in Joules or Electron-Volt (1 J = 6.241509 *10^18 eV).

Wave speed is independent of frequency. Frequency has an inverse relationship to the wavelength, λ (lambda). Lambda * Frequency = Speed





Frequency Allocation Charts:

US: 2011_US_rf_spectrum_chart.pdf (334.3KB)

CANADA: 2014_Canadian_Radio_Spectrum_Chart.pdf (279.1KB)

UK: uk_frequency_allocations_chart.pdf (325.8KB)

AUSTRALIA: aust_rf_spectrum_allocations_chart.pdf (296.7KB)

Automotive Cold Crank, Load Dump, and Reverse Polarity Protection

The suppliers of automotive electronic devices are competing these days to lower the cost of theirs designs. This is a sample of rather expensive solution to ensure proper function of an automotive electronic device during transients on supply lines (12V Battery).


Sample of less expensive solution to prevent reverse polarity, load dump, and cranking pulse from disturbing circuits sourced from a 5V voltage regulator or directly from the 12V B+ line.

Automotive 12V Battery - Voltage Drops

Simple simulation to prevent voltage drop issues for 9V to 16V operating voltage range devices.

All DUT's functions are required to perform as designed during battery voltage drops of up to 1 ms.  For drops above 1 ms the functions are allowed to be temporarily disrupted or fail in a safe mode. Upon return to the operating voltage range the DUT is supposed to auto-recover and resume its operation. In the above example the DUT's functions should not be disrupted (dropout = 1.3 ms, B+ = 9.36 V).


In the above example (dropout = 1.67 ms, B+ = 8.65 V) a fail safe behavior is acceptable. The software will prevent the DUT from resuming its operation as long as B+ is detected below the voltage range. Once B+ line is above 9V the auto recover process should be initiated.