电能质量PQ-BOX 300超高频测试

Evaluating Supraharmonics up to 150 kHz in Electric Vehicles at the University of Applied Sciences Bingen
In the first part of the measurement campaign of 2016,
 
various electric vehicles were evaluated in terms of their
 
charging behavior and their loading effects on the power
 
grid. The evaluation covered from DC up to the 50th har-
 
monic or supraharmonics up to 20 kHz. As some electric
 
vehicles use a chopper frequency much higher than 20 kHz,
 
another measurement campaign was started at the Uni-
 
versity of Applied Sciences Bingen in September 2017 to
 
measure the emissions ranging up to 150 kHz. In addition,
 
the mutual interference between the different vehicles and
 
between the electric vehicle and a solar inverter was inves-
 
tigated at the University of Applied Sciences Bingen.


Basis of the evaluation of the loading effects
The IEC 61851-21 -1 standard (Electric vehicle on-board charger EMC requirements for conductive connection to AC/DC supply) will apply to electric vehicles in the future. This standard has already received the status of FDIS and will be published shortly.
 
At this time, the limits for current harmonics as given by IEC 61000-3-2 (Class A) up to 16 A and IEC 61000-3- 12 (asym-metrical devices, Rsce = 33) for 16 A up to 75 A apply to electric vehicles. These same compatibility levels are also used in IEC 61851-21-1. There are limits up to the 40th current harmonic (2 kHz) and compatibility levels from 150 kHz to 30 MHz. There are no limits now on the emitted interference from electric vehicles in the frequency range from 2.5 kHz to 150 kHz. This range is also not regulated for the public power grid using compatibility levels. However, there are efforts un-derway now in the standards committee aimed at closing this gap as quickly as possible using compatibility levels.
 
There are many examples today of the mutual interference between different electronic devices. For example, the frequency converter of a CNC machine emits an interference level > 2.5 kHz into the power grid and a kitchen appliance malfunctions, or a solar inverter can automatically switch touch-dimmer lamps on and off. Who is responsible for this problem?
 
Is the kitchen appliance improperly equipped for interference resistance or is the CNC machine causing too large an inter-ference level in the power grid at its connection? There can only be a fair regulation with the forthcoming limits for this fre-quency range. The interference can be remedied at both ends. Install a power filter on the device experiencing interference or reduce the emitted interference at its origin. Different customers always ask the question, „Who has to pay for it?“
 
The current draft of IEC 61000-2-2 (Compatibility levels for the public power grid) defined limits for the following ranges:
 

The range of 30 kHz to 150 kHz is being prepared; compatibility levels are being added in real time.
 
 
In the standard, intentional emissions, for example, PLC signals for communication, are distinguished from nonintentional emissions.
 
Power utilities make use of a power line signal in the frequency range up to 148 kHz for signal transmission over the power grid. So that this signal can be detected unambiguously by the receiver, there must be a gap between the nonintentional emission from the power electronics, such as that caused by electric vehicles, and the PLC signal. Consequently, two limit curves are given in the standard.

Measuring technology

Today, there are not many power quality measurement devices for permanent, uninterrupted monitoring of frequencies from DC to 150 kHz. This comes from the fact that there are no specifications as to how to evaluate in the future standard-com-pliant levels > 2.5 kHz to 150 kHz.
 
The measuring procedure for the frequency range from 2 kHz to 9 kHz is described in the standard for harmonics, IEC 61000-4-7 in the informative Annex B. In this case, a grouping procedure for frequency bands of 200 Hz is used.
 
For the range > 9 kHz to 150 kHz, there is a suggestion in the Annex to IEC 61000-4-30, Ed. 3. Here, a grouping pro-cedure for bands of 2 kHz is suggested. The final measuring procedure will only be specified in a few years in the future Edition 4 of IEC 61000-4-30. The frequency bands of 200 Hz or 2 kHz are under discussion. While a 200 Hz frequency band provides greater resolution in the spectrum, 10 times the quantity of data is measured than with a 2 kHz frequency band. Because of this, each procedure has advantages and disadvantages.
 
The PQ Box 300 from the A. Eberle company was used for the measurement campaign at the University of Applied Sciences Bingen. The power quality network analyzer measures frequencies from DC to 170 kHz with high accuracy. The grouping procedure of the measurement device can be configured for either 200 Hz or 2 kHz frequency bands. In this way, the different measurement results coming from the different grouping procedures can be verified.
 
For charging the various electric vehicles, a charging station with a type 2 charging plug and various 32 A CEE outlets and single-phase outlets was available.
 
The charging station was connected to the power grid of the University and uses a 25 mm² cable. The short-circuit perfor-mance at the charging station is about 2.5 MVA. A single-phase 5 kW inverter is connected at a distance of about 10 m. The distance, that is the length of the cable connections, between the electric vehicles connected to the charging station, was usually 10 m, 2 times a standard charging cable of 5 m.

Measurement results

The following electric vehicles were evaluated:
 
Renault Zoe, Nissan Leaf, BMW i3, Audi e-tron, VW Golf GTE, Ford Focus e-lectric, Mitsubishi Outlander and the Tesla Model 90D.
 
Measurements were performed in the following configurations:
 

• The electric vehicle alone to the power grid

• The electric vehicle in parallel with other electric vehicles

• The electric vehicle in parallel with the solar inverter of the University

 
The chopper frequencies of the vehicles measured were between 8 kHz and a maximum of 50 kHz for the different manufacturers.
 
In addition, there were large differences in the levels of the switching frequencies for the various vehicles. These were bet-ween 2 volts for vehicles with poor filtering and high interference levels as well as values that were undetectable by measu-rement in vehicles with an extremely low interference level.