State-of-the-art DC fast-chargers convert 3-phase AC from the power grid to high-voltage DC. Systems are made up of:

• Power factor correction and AC/DC converter
• DC/DC converter
• Control systems and power management
• User interfaces
• LAN / cellular communications
• High voltage charging and communication vehicle port
   

Each of these blocks requires testing. Explore the solutions below to learn more.

Chargers designed to connect to public utilities must limit the impact on the local grid or operators will be subjected to higher energy rates or penalties. Most utilities charge for power factor below 90 to 95% and many require compliance with harmonics standards.

The input stages of DC fast charging equipment are not only responsible for converting 3-phase AC to DC, but it must also ensure high power factor and low harmonic distortion, while maintaining high efficiency and reliability.

Oscilloscope-based systems with advanced power analysis software facilitate accurate, repeatable measurements, including:

• Line-side power quality
• Power Factor
• Harmonics
• Overvoltage/undervoltage protection
• Switching characteristics
• Timing (e.g. dead time)
• Dynamic switching loss
• Double-Pulse Testing
• Output ripple
• Efficiency

High power DC/DC converters provide isolation between the PFC block and voltage regulation for the vehicle charging port. High frequency transformers are often used for isolation and energy storage. New designs may use fast SiC MOSFETs to add efficiency and power density.

The fast switching speeds and voltage levels of SiC MOSFETS introduce measurement challenges due to high bandwidth and common mode voltages. EVSE test equipment solutions, including oscilloscopes with optically isolated probes and analysis software, Oscilloscopes with optically isolated probes and analysis software deliver accurate measurements even on high slew-rate, high common mode voltage signals. These include:

• Peak inrush current
• Overvoltage/undervoltage protection
• Switching analysis
• Miller duration and capacitance
• Gate resistance and charge parameters
• Dead time
• Switching loss
• In-circuit transformer and inductor measurements
• Control loop performance (e.g. PSRR and gain/phase margin)
• Ripple and noise
• EMI/EMC analysis

Embedded controllers are the brains behind the charging process. During charging they handle communication with the vehicle, regulate power flow, and monitor safety conditions. They also communicate with the user interface and digital networks.

These subsystems typically include processors or FPGAs, clocks, power rails, memory systems, and communications ICs, often operating on GHz signals with low amplitude. Since these systems operate in harsh physical and electrical environments, they require high noise immunity and power integrity.

Key measurements for validating and debugging these systems include:

• Power rail ripple and noise analysis
• Impedance measurements
• Power supply sequencing
• AC-DC Converters
• Switching and Timing Analysis
• Dead time analysis between Low side and High side switches
• Magnetic analysis for Transformers and Inductors
• Control loop analysis
• Communications signal integrity
• EMI/EMC analysis

Reliable communication between the charging station and vehicle battery management system is critical to manage the charging process and maintain safety.

Chargers that comply with IEC61851 incorporate a control pilot (CP) signal. The duty cycle of the CP signal conveys the maximum available current from the EVSE to the EV. This signal can be verified using an oscilloscope. Power line communications (PLC) may also be superimposed on this line for communication during the charging process. Some interfaces rely on serial data carried over CAN for communication between the EVSE and EV.

In both cases oscilloscopes are invaluable for checking signal quality throughout the system, looking for attenuation, noise and incorrect termination. Most Tektronix oscilloscopes can be outfitted with CAN bus decoding and triggering to display transactions synchronized with other system level activity.

In addition to conducting data communication, the charging interface must maintain current and voltage within specified limits. For example, the charger must limit the impact of line voltage transients, surges and sags on the DC output to the vehicle to specified levels and durations.

Key measurements for validating and debugging EVSE, include:

• Communication signal integrity / noise
• Duty cycle of the DP signal
• System timing
• Noise on DC output
• Output regulation

User interface devices often connect into the control system over standard serial buses such as RS-232, SPI or USB. Network communication provides key information for both charging station operators and users. Oscilloscopes and active probes are well-suited for signal and timing evaluation for user interface connections, LAN and wireless communications. Tektronix oscilloscopes support decoding on over 25 serial buses from RS-232 to wireless NFCs.

Key measurements include:

• Signal integrity / noise
• System timing
• CAN Bus decode
• LAN
• NFC decode
• Baseband RF
• EMI/EMC analysis

EVSE Testing Reference Solution

To guide you in creating an effective testing setup including an EA battery simulator tailored to your needs, we've included the table below. Here you'll find key instruments, probes, and options, along with their quantities and descriptions, each of which can be adjusted to suit your own individual requirements.