Fast-Charging Equipment for EVs toward Carbon Neutrality

Introduction

With the aim of achieving Carbon Neutrality, the electrification of vehicles (EV adoption) is accelerating, and as part of the infrastructure, the installation of fast chargers that use only power derived from renewable energy is progressing.
Fast charging can support large-current output by the installation of a charging station (off-board charger) connected to the grid, enabling battery charging in a short time. As EV batteries continue to increase in capacity, the demand for installing fast chargers capable of fully charging the batteries in a short time is increasing. Especially from a sustainability perspective, the number of charging stations combining ESS and surplus renewable energy, such as solar power generated during the day, is increasing. And in terms of charging devices, high-voltage and large-current products are being developed to shorten charging times
* Off-board charger: Charging station. Also called EVSE (Electric Vehicle Service Equipment).

Challenges

Recent fast chargers are being developed with voltages ranging from 500 V DC to 1000 V DC and currents from 100 A DC to several hundred amperes DC.
As a result, there is rising demand for accurate measurement of high voltage and large current to evaluate their performance.
In addition, accurate measurement of charging capacity (Wh, Ah) is required, likely due to the connection between the power supplied to EV batteries and electricity costs.
Since a charger will contain several types of conversion circuits, minimizing the losses associated with these conversions is crucial. Additionally, because large currents are drawn from the grid into the fast charger, the harmonic components of the current need to be suppressed as well.
Therefore, it is necessary to check the distortion rate for each order of a harmonic current as well as the total harmonic distortion (THD).

Solutions provided by WT5000

• High-precision power measurement with a basic accuracy of ±0.03%
• Measuring high voltage and large current up to 1500 V DC and up to 2000 Arms
• High-precision measurement of the power factor and other power parameters
• High-precision measurement of AC/DC and DC/AC conversion efficiencies
• Measurement of integrated power and integrated current
• Harmonic data for each order and THD measurement
• Abnormality checks by continuous measurement of power values and waveform data

Figure 1. WT5000 Precision Power Analyzer

Proposals provided by WT5000

High-precision power measurement with a basic power accuracy of ±0.03%

The WT5000 delivers best-in-world class basic power accuracy of ±0.03% (50/60 Hz). It can measure the conversion efficiency of EV chargers with higher accuracy.
The WT5000 employs a modular architecture and can be fitted with up to seven power input elements.
YOKOGAWA’s design technology accumulated over the years has enabled an extremely high-precision measurement circuit to be housed inside a compact input element.
In addition, you can choose from three types of input elements (rated input 30 A, rated input 5 A, and an element dedicated to current sensor input) to suit your applications and can install, remove, or swap the input elements yourself.

Measuring high voltage and large current up to 1500 V DC and up to 2000 Arms

The output power of fast chargers for EVs is increasing year by year to enable rapid charging. Recently, they have been increasing in both voltage and current, with some models offering several hundred kW of output.
A single WT5000 can measure voltages up to 1500 V DC and measure currents up to 2000 Arms (3000 Apeak) with an AC/ DC current sensor. Additionally, installing up to seven power input elements on the WT5000 allows simultaneous measurement of seven single-phase power systems or several single-phase/3-phase power systems to accurately measure DC voltage, AC voltage, power factor, THD, and input/output efficiency.
Especially with respect to sensors, we offer large-capacity split core sensors that can have their core sections separated. This allows for measurement not only during development but also during maintenance once installed in the field, enabling connections to necessary wiring. As a result, you can choose and use them according to your specific applications.

Figure 2. AC/DC current sensor CT1000A (left) and CT2000A (right)

Figure 3. WT5000 and CT1000A AC/DC current sensors

Figure 4. Split core current sensor CT1000S

High-precision measurement of the power factor and other power parameters

Off-board chargers for EVs convert 50 Hz/60 Hz AC power from power grids to DC and supply power to EV batteries.
Since the power value of AC power varies depending on the voltage, current, and phase difference, it is important to minimize the phase difference and suppress harmonics to bring the power factor close to 1 in order to increase the power supply.
The WT5000 measures the power that passes through a PFC circuit and calculates the power factor. Parameters other than the power factor, such as voltage, current, active power, apparent power, and reactive power, can be measured and displayed simultaneously, enabling you to check changes in each parameter at the same time.

Figure 5. Example of displaying voltage, current, power factor, THD, etc.

High-precision measurement of AC/DC and DC/AC conversion efficiencies

In fast chargers for EVs, DC power is supplied to the battery through several conversion circuits, such as AC/DC conversion and DC/AC conversion. For these circuits, a design that minimizes power losses is extremely important.
By using the WT5000 with multi-channel input capability, the efficiency of each circuit can be measured with high accuracy.

Figure 6. Overview of an off-board charger

Measurement of integrated power and integrated current

The WT5000 has an integration function to measure power consumption (Wh) and current consumption (Ah) over a long period of time.
The integration function integrates the active power (watthour), current (ampere-hour), apparent power (volt-ampere hour), and reactive power (var-hour) values.
This function includes two modes: one to measure charging and discharging of, for example batteries, and the other to measure AC power sold/bought.

Figure 7. Example of integrated power and current measurement screen

[Detail of Integration function]

Charge/Discharge mode (Charge/Discharge)
Measure DC watt-hours (for each sampled data item) by polarity.
Sold/Bought mode (Sold/Bought)
Measure AC watt-hours (for each data update cycle) by polarity.

Measurement items related to the integration function

Abnormality checks by continuous measurement of power values and waveform data

When voltage, current, and power data need to be measured continuously for a long period of time, the IS8000 Integrated Software Platform, which is an application on PCs, can be used to check and save trends of power parameters in real time. Furthermore, the WT5000’s /DS (data streaming) option allows numerical power data and waveform data to be simultaneously monitored and recorded.
For example, by zooming in on the area where there is an abnormality in power measurements, the waveform data at that point can be observed with a single WT5000.

Figure 8. Voltage, current, and power trends displayed on the IS8000

Figure 9. Zooming in on the area of power drop to check abnormal waveforms

Additionally, by using the previously mentioned split core sensor, changing measurement locations becomes easy.
This makes it an effective way to identify areas where faults are present.