ST UM2975 Manuel utilisateur

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.

UM2975

UM2975 - Rev 1 page 2/63

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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Getting started

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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

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.

UM2975

Main characteristics

UM2975 - Rev 1 page 4/63

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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Reference design description

UM2975 - Rev 1 page 5/63

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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Reference design description

UM2975 - Rev 1 page 6/63

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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Reference design description

UM2975 - Rev 1 page 7/63

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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Reference design description

UM2975 - Rev 1 page 8/63

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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Reference design description

UM2975 - Rev 1 page 9/63

Figure 15. STDES-VRECTFD control board sections

Figure 16. STDES-VRECTFD MCU pin assignment

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Reference design description

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