ST STDES-PFCBIDIR User manual

Introduction
The STDES-PFCBIDIR reference design represents a complete solution for high-power, three-phase active front end (AFE)
rectifier applications based on the three-level T-Type topology.
This reference design topology is mostly used for DC fast charging applications related to industrial and electric vehicles.
It features full-digital control. The embedded STM32G474RET3 mixed-signal high-performance microcontroller provides the full
control of the power factor (PF), the DC voltage, and the auxiliary task to manage the grid connection and the soft startup
procedure.
The high-bandwidth continuous conduction mode (CCM) current regulation allows the maximum power quality in terms of total
harmonic distortion (THD) and power factor (PF).
Figure 1. DC charging station
How to use the STDES-PFCBIDIR reference design
UM2979
User manual
UM2979 - Rev 1 - February 2022
For further information contact your local STMicroelectronics sales office.
www.st.com

Figure 2. STDES-PFCBIDIR reference design - power board
Fully assembled board developed for
performance evaluation only,
not available for sale
Figure 3. STDES-PFCBIDIR reference design - control board
Fully assembled board developed for
performance evaluation only,
not available for sale
The high switching frequency of the SiC MOSFETs (70 kHz) and the multilevel structure allow an efficiency of almost 99% as
well as the optimization of passive power components in terms of size and cost.
The high efficiency bidirectional rectifier is designed for several end applications such as electric vehicle (EV), industrial battery
chargers, and industrial equipment, which requires a very high PF and low THD.
The STDES-PFCBIDIR is a fully assembled kit developed for performance evaluation only, not available for sale.
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1Getting started
1.1 Safety information
Caution: This reference design is intended for demonstration purposes only and is not for domestic or industrial
installations.
Danger: The high-voltage levels used to operate the reference design can cause serious injury,
electrical shock, and even death.
This reference design is intended for use by experienced power electronics professionals
who understand the necessary precautions against potential dangers and risks while
operating this board, even when it is not powered. The qualified personnel must be familiar
with the installation, use, and maintenance of power electrical systems. During operation, do
not touch the board as some of its components could reach a very high temperature.
1.2 Block diagram
Figure 4. STDES-PFCBIDIR block diagram
1.3 Features
• 3-phase, 3-level bidirectional AC-DC power converter:
–Rated nominal DC voltage: 800 VDC
– Rated nominal AC voltage: 400 VAC at 50 Hz
– Nominal power: 15 kW
• AC to DC rectifier mode:
– Power factor: PF >0.99
– Inrush current control and soft startup
• DC to AC inverter mode:
– Active and reactive power control
– Integrated grid connection solution
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• Power section based on SiC MOSFETs:
–High frequency operation (100 kHz)
– High efficiency: >98%
– Passive element weight and size reduction
• Control section based on STM32G474RET3 microcontroller:
– P2P compatible with other STDES 3-phase power converters
– Four integrated high-performance op-amps
– Control and monitoring interfaces: SWD, UART, I²C, DACs
– 64-pin digital power connector
– Overcurrent and overvoltage protection
1.4 Main characteristics
Table 1. Main characteristics
Description Symbol Min. Typ. Max. Unit Comments
Three-phase input voltage VAC 208 400 VACLL
AC line frequency Hz 47 63 Hz
Maximum output power POUTmax
15
7kW
VAC = 230 VRMS IAC = 21 VRMS
VAC = 110 VRMS IAC = 21 VRMS
Output voltage VDC 800 V
Power factor PF >0.99 - From 20% of load
Total harmonic distortion THDi <5 % From 20% of load
Switching frequency fsw 70 kHz
Table 2. Protection characteristics
Description Symbol Min. Typ. Max. Unit
HVDC overvoltage protection VDCovp 900 V
HVCAP overvoltage protection VCAPovp 500 V
AC overcurrent protection IACovp 30 A
1.5 Reference design description
1.5.1 Power board
The figure below shows the power board of the STDES-PFCBIDIR reference design.
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Figure 5. STDES-PFCBIDIR reference design - power board
The following figure shows the main sections of the power board.
Figure 6. STDES-PFCBIDIR power board sections
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1.5.2 Power stage
1.5.2.1 Boost inductor
Boost inductors are part of the LCL-R AC side filter. They allow obtaining the converter PFC operation by
controlling the inductor current using a proper conduction pattern in the power device section.
Continuous conduction mode (CCM) performs the PFC operation of this reference design. The inductance value
is related to several parameters: the current ripple, the available converter voltage levels, the switching frequency,
and the rated DC-AC operation voltages.
Table 3. Boost inductor parameters
Parameter Symbol Value
DC voltage (V) V0800
Switching frequency (kHz) fsw 70
Rated AC voltage (VRMS) VAC 230
Max. ripple current (%) ΔiLppmax 10
Boost inductance (H) L 470e-6
1.5.2.2 Inrush current limiter
Figure 7. Three and four-wire connections
Figure 8. Passive NTC
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Figure 9. STDES-PFCBIDIR NTC specifications
Figure 10. Active relays
1.5.2.3 Sensing
1.5.2.3.1 AC current
An isolated sensor measures the AC input current. It represents the boost inductor current to be controlled for the
proper operation of the PFC behavior of the power converter.
The output voltage of the Hall effect transducer is not in scale and contains a DC component of 2.5 V with respect
to the ADCs.
A conditioning circuit allows obtaining the correct value for the ADCs. The circuit shown below is replicated for
each phase.
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Figure 11. AC current sensing block diagram
1.5.2.3.2 AC voltage
The three-phase AC voltages are obtained using a two-stage sensor circuit. The first part represents an isolated
op-amp that allows measuring the HV through a voltage divider with an isolation barrier.
Isol-Op-AMP output is limited in volts and is scaled with a second stage of op-amps with a proper gain and bias.
This circuit allows measuring an AC voltage referenced by a virtual or grid neutral point. The circuit is replicated
for each phase.
Figure 12. AC voltage sensing block diagram
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1.5.2.3.3 DC current
An isolated sensor measures the DC output current. Hall sensors are taken into consideration. A conditioning
circuit allows obtaining the correct value for the ADCs.
Figure 13. DC current sensing block diagram
1.5.2.3.4 DC voltage
The DC voltages are obtained using two-stage sensing. The total DC bus voltage is split exploiting two voltage
dividers. Both voltages are needed to obtain the monitoring of each capacitor to avoid overvoltage, offering
independent DC voltages for the control.
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Figure 14. DC voltage sensing block diagram
1.5.3 Control board
The figure below shows the control board of the STDES-PFCBIDIR reference design.
Figure 15. STDES-PFCBIDIR reference design - control board
The following figure shows the main sections of the control board.
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Figure 16. STDES-PFCBIDIR control board sections
Figure 17. STDES-PFCBIDIR MCU pin assignment
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1.6 Power factor correction (PFC) benefits
The figure below highlights the PFC benefits in terms of rest factor and power factor.
Figure 18. PFC benefits
1.7 Converter operation
The figure below shows the current paths of the Vienna topology. To simplify the scheme, we considered the
single phase representation.
Figure 19. Switching paths of the Vienna topology
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2How to use the STDES-PFCBIDIR reference design
2.1 System setup
To use the STDES-PFCBIDIR, you need:
•a programmable AC emulator or a programmable AC source;
• a DC electronic load;
• a power analyzer;
• a digital oscilloscope.
You can test the STDES-PFCBIDIR up to 15 kW at 230 VAC RMS and 6 kW at 110 VAC RMS in a frequency
between 47 and 63 Hz.
2.2 How to connect the reference design
To operate the reference design power converter properly, consider the operating limits shown below.
Table 4. Operation condition limits
Description Value Unit
Three-phase input voltage range 208-400 VAC
Line frequency range 47-63 Hz
Maximum output power at 230 VAC 15 kW
Voltage limit of the bulk capacitors 500 V
Step 1. Connect the power board as shown in the figure below.
The figure shows the three-phase connection sequence (A-B-C). The neutral connection is optional.
The power board handles the input connection exploiting the four input relays. The polarity influences
the DC load connection.
Figure 20. STDES-PFCBIDIR connection
Step 2. The auxiliary power supply can be externally provided. Connect an external fan to manage the thermal
dissipation.
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2.3 MCU programming and debugging
You can program and debug the microcontroller unit (MCU) through different tools.
Step 1. Use ST-LINK/V2 and a 20- to 10-pin JTAG adapter to connect the platform to the PC.
Figure 21. ST-LINK/V2 and adapter
Figure 22. ST-LINK/V2 connected to the control board
Step 2. Select the main.c file in the project/Application/User path.
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Step 3. Click on the [Download and debug] button to start programming and debugging.
Figure 23. IAR EWARM program procedure
Step 4. Click on the [Run] button to start the code execution.
Figure 24. IAR EWARM debug procedure
2.4 Board configuration
The STDES-PFCBIDIR is a customizable reference design. You can customize the power supply, the driving
section, the grid relays, the inrush current limiter, and the DC current sensing technique.
2.4.1 Power supply section
Two different input voltages are required for the power supply. An embedded SMPS based on the VIPER26HD
provides self-powering from the DC-link.
As shown in the figure below, you can select either an internal or external connection. Specific LEDs allow
identifying the selected configuration.
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Figure 25. Example of power supply configuration
2.4.2 Driver section
The driving section allows configuring the driving voltage.
Figure 26. Example of driver configuration
Table 5. Example of driving section configuration
Configuration SB1 SB2 SB3 SB4 SB5 SB6
+20 V -5 V Closed Open Closed Closed Open Open
2.4.3 Relay section
The STDES-PFCBIDIR allows managing the power in both directions (AC-DC rectifier mode a DC-AC inverter
mode).
To customize the AC side connection with the power converter, we considered four relays. Three of them are for
the three-line connection and one is for the neutral.
You can manually manage each relay (on|off state). The MCU can manage the relays for the grid connection or if
a fault occurs.
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Figure 27. Example of relay configuration
2.5 Preliminary test procedure
2.5.1 AC sensing
To verify the proper operation of the AC sensing, analyze some test points for voltages and currents as shown in
the figures below.
Figure 28. AC sensing section
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Figure 29. AC voltage sensing test procedure
Figure 30. AC grid voltage sensing test procedure
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Figure 31. AC grid current sensing test procedure
2.5.2 DC sensing
To verify the proper operation of the DC sensing, analyze the test points for voltages and currents as shown in the
figures below.
Figure 32. DC voltage sensing test procedure (1 of 2)
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Figure 33. DC voltage sensing test procedure (2 of 2)
2.5.3 AC connection
Connect the STDES-PFCBIDIR AC main as shown below.
A correct ABC sequence is mandatory for the proper operation of the power converter.
Figure 34. AC main connection and sequence
2.5.4 DC connection
The figure below shows the output DC connection. Ensure to apply the correct polarity.
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