ST STDES-PFCBIDIR Manuale utente

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.

UM2979

UM2979 - Rev 1 page 2/70

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

UM2979

Getting started

UM2979 - Rev 1 page 3/70

• 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

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.

UM2979

Main characteristics

UM2979 - Rev 1 page 4/70

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

UM2979

Reference design description

UM2979 - Rev 1 page 5/70

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

UM2979

Reference design description

UM2979 - Rev 1 page 6/70

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.

UM2979

Reference design description

UM2979 - Rev 1 page 7/70

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

UM2979

Reference design description

UM2979 - Rev 1 page 8/70

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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Reference design description

UM2979 - Rev 1 page 9/70

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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Reference design description

UM2979 - Rev 1 page 10/70

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