ST UM2975 User manual

Introduction
The STDES-VRECTFD reference design represents a complete solution for high-power, three-phase active front end (AFE)
rectifier applications based on the three-level Vienna 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 protections and the soft start-up
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 15 kW three-level three-phase Vienna rectifier with digital control
for power factor correction
UM2975
User manual
UM2975 - Rev 1 - January 2022
For further information contact your local STMicroelectronics sales office.
www.st.com

Figure 2. STDES-VRECTFD reference design - power board
Fully assembled board developed for
performance evaluation only,
not available for sale
Figure 3. STDES-VRECTFD 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 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-VRECTFD 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-VRECTFD block diagram
1.3 Features
• Three-phase, three-level AC-DC power converter
–Nominal rate for DC voltage: 800 VDC
– Nominal rate for AC voltage: 400 VAC at 50 Hz
– Maximum power: 15 kW
– Power factor: >0.99
– Inrush current control and soft start-up
– THD lower than 5% at nominal operation
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• Power section based on SiC MOSFETs and SiC diodes:
–High frequency operation (70 kHz)
– High efficiency: >98.6%
– Passive element weight and size reduction
• Control section based on the STM32G474RET3 microcontroller:
– Control and monitoring interfaces: SWD–UART, I²C and DACs
– 64-pin digital power connector
– LED status as UI
– Four integrated high-performance op-amps for additional features
1.4 Main characteristics
Table 1. Main characteristics
Description Symbol Min. Typ. Max. Unit Comments
Three-phase input voltage VAC 208 480 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-VRECTFD reference design.
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Figure 5. STDES-VRECTFD reference design - power board
The following figure shows the main sections of the power board.
Figure 6. STDES-VRECTFD power board sections
1.5.2 Power stage
1.5.2.1 Boost inductor
Boost inductors represent the energy storage elements that allow the PFC operation of the converter. This is
obtained by controlling the inductor current and using a proper conduction pattern in the power device section.
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Continuous conduction mode (CCM) performs the PFC operation of this reference design. The inductance is
related to several parameters: the desired 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 Unit
DC voltage V0800 V
Switching frequency fsw 70 kHz
Rated AC voltage VAC 230 VRMS
Max. ripple current ΔiLppmax 10 %
Boost inductance VAC 470-6 H
1.5.2.2 Passive current limiter NTC
Figure 7. Three and four-wire connections
Figure 8. Focus on the STDES-VRECTFD NTC
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Figure 9. STDES-VRECTFD NTC specifications
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 power converter. Hall sensors are taken into consideration. A conditioning circuit allows
obtaining the correct value for the ADCs. The circuit shown below is replicated for each phase.
Figure 10. 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.
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Figure 11. AC voltage sensing block diagram
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 12. 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 13. DC voltage sensing block diagram
1.5.3 Control board
The figure below shows the control board of the STDES-VRECTFD reference design.
Figure 14. STDES-VRECTFD reference design - control board
The following figure shows the main sections of the control board.
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Figure 15. STDES-VRECTFD control board sections
Figure 16. STDES-VRECTFD MCU pin assignment
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