knestronX · LPDC platform

Battery inverter built from three modules

The Low-Power DC Platform (LPDC platform) connects the 230 VAC grid to batteries from 12 to 65 VDC. AC/DC converter, galvanic isolation, and bidirectional DC/DC converter are separate modules rated at 3.6 kW each. They can be freely combined and connected in parallel.

Discuss your application View modules

230 VACGrid, generator

AFEAC/DC

380 VDC

ISOgalvanic isolation

70 VDC

DCDDC/DC

12–65 VDCBattery, PV, load

Energy flows in both directions: charging from the grid or a generator, discharging into the grid or into your own island grid.

3.6 kW

Rated power per module

5.8 kW

Peak power for 3 seconds

70 VDC

DC link below the 120 VDC limit for SELV and PELV

12–65 VDC

Adjustable battery voltage

The modules

One string, three tasks

Each module operates bidirectionally and is connected to the internal CAN bus. A higher-level master controls operating modes and setpoints.

AFE AC/DC conversion

Active front end between the 230 VAC grid and the 380 VDC DC link. As a PFC rectifier, it charges from the grid or a generator; as an inverter, it feeds back into the grid or forms its own grid.

Input current can be limited to 6, 10, or 16 A 3 modules for three-phase operation at 120° Grid-forming operation Charging at a charging station (CP/PP)

Monitoring: overload, short circuit, temperature, undervoltage and overvoltage

Parameter AC side DC side Voltage 230 VAC ±10 % 380 VDC Rated power 3.6 kW 3.6 kW Peak power (3 s) 5.4 kW 5.4 kW Rated current 16 A 10 A Peak current (3 s) 24 A 15 A

ISO Galvanic isolation

Isolated, bidirectional DC/DC converter from 380 VDC to 70 VDC. It safely separates the high-voltage DC link from the extra-low-voltage side.

Isolation voltage 2 kV Isolation voltage 4 kV

At 70 VDC, the bus stays below the 120 VDC limit and can be implemented as SELV or PELV.

Monitoring: overload, short circuit, temperature

Parameter HV side LV side Voltage 380 VDC 70 VDC Rated power 3.6 kW 3.6 kW Peak power (3 s) 5.4 kW 5.8 kW Rated current 10 A 52 A Peak current (3 s) 15 A 83 A

DCD DC/DC conversion

Bidirectional DC/DC converter between the 70 VDC bus and a battery, PV module, or DC load. The output voltage is adjustable between 12 and 65 VDC.

CAN to the battery management system Modbus for DTU and monitoring MPPT for PV input

Continuous power at 60 A battery current

12 V

720 W

24 V

1.44 kW

36 V

2.16 kW

48 V

2.88 kW

60 V

3.6 kW

Parameter Bus side Battery side Voltage 70 VDC 12–65 VDC Rated power 3.6 kW 3.6 kW Peak power (3 s) 5.8 kW 5.8 kW Rated current 52 A 60 A Peak current (3 s) 83 A 105 A

Monitoring: overload, short circuit, temperature, undervoltage and overvoltage

Scaling

More power with more modules

The system can be expanded independently at three points. The same modules can form a small single-phase storage system or a three-phase system in the double-digit kilowatt range.

AC side

AFE in parallel

More power per phase or additional 230 VAC connections. Via the sync bus, three AFEs form a three-phase grid with 120° phase shift.

Isolation point

ISO parallel

Each additional ISO module increases the power transferred between the high-voltage and extra-low-voltage sides.

DC side

One DCD per battery

The 70 VDC bus runs as many DCDs as there are batteries, PV modules or DC loads connected, even at different voltages.

21.6 kW

Example calculation: two AFEs per phase, three phases. 6 × 3.6 kW add up to 21.6 kW rated power, three-phase.

Applications

Where the LPDC platform is used

Battery inverter

Charge and discharge storage on the 230 VAC grid. With 48 V batteries, two DCDs share the power; from 60 V upward, one is enough.

3.6 kW single-phase 10.8 kW three-phase with three strings

UPS for data centers

Online double-conversion UPS: one AFE rectifies the grid to 380 VDC, and a second AFE uses it to form the supply for the servers. The battery is connected to the DC link via ISO and DCD and takes over during a power outage without any switchover. Racks with 48 V DC are supplied directly by a DCD.

Online double conversion, battery on the DC link 48 VDC rack supply via DCD

Generator Booster

The AFE operates in parallel with the generator and feeds in power from the battery. The storage covers load peaks, and the generator recharges it during low-load periods.

View the 27 kW configuration example

5.4 → 16.2 kW Generator 3 × 1.8 kW plus 3 × 3.6 kW from the battery

Emergency power supply

If the grid fails, the grid disconnect opens and the AFE forms the grid for the emergency circuit from the battery. Battery capacity determines the bridging time.

1~ or 3~ grid-forming, three-phase with three synchronized AFEs

PV storage

PV modules connect directly to the 70 VDC bus via a DCD with MPPT and charge the battery without going through the AC grid.

MPPT option for the DCD

Charging at a charging station

The AFE evaluates Control Pilot and Proximity Pilot. This allows the system to charge its battery at a wallbox or public charging station, for example as mobile storage.

CP / PP Option for the AFE, input current 6, 10 or 16 A

Further applications

Battery test bench

The DCD charges and discharges battery modules from 12 to 65 V. The energy is fed back into the grid via the AFE instead of being dissipated as heat in load resistors.

12–65 V devices under test, energy fed back

Onboard power systems

For special-purpose vehicles, boats and motorhomes: shore power is turned into an onboard power system with battery buffer via galvanic isolation. Multiple DCDs supply different voltage levels.

12 / 24 / 48 V from shore power, galvanically isolated

Radio sites

Buffered 48 VDC supply for radio and network equipment. With PV via a DCD with MPPT, also at remote sites.

48 VDC from grid, battery and PV

Peak shaving

The storage covers power peaks from machines or cooling systems, reducing the power drawn at the grid connection.

6 / 10 / 16 A AFE input current can be limited

Second-life storage

Used battery packs with different voltages each operate on their own DCD on the shared 70 VDC bus.

1 DCD per battery pack

Mobile power

For construction sites and events: the storage charges at a charging station and supplies power on site as an island grid, quietly and without exhaust fumes.

CP / PP charging, grid-forming on site

Configuration example

Generator support with 27 kW

A generator with 3 × 1.8 kW supplies loads whose peaks are far higher. Six strings of the LPDC platform raise the available power to 27 kW three-phase. A PV system additionally charges the storage.

Scroll the circuit diagram sideways to see all modules.

Why separate DC links? Each AFE operates between line conductor and neutral conductor. If the DC links of all phases were connected together, the phases would be interconnected via the AFEs. That is why each phase has its own 380 VDC DC link. Only after the galvanic isolation in the ISO module do all strings converge on the shared 70 VDC bus.

5.4 kW

Generator, 3 × 1.8 kW

+21.6 kW

from battery and PV via six AFEs, up to 32.4 kW for 3 seconds

27 kW

rated power, three-phase, for the loads

Bill of materials

Module Quantity Function AFE 6 Two per phase in parallel with the generator, synchronized via the sync bus ISO 6 Two per phase: connect the phase DC link to the shared 70 VDC bus, 6 × 3.6 kW in total DCD 8 Battery 48 V: 8 × 2.88 kW at 60 A, approx. 23 kW for a demand of 21.6 kW DCD with MPPT 1 PV modules on the 70 VDC bus Master 1 Operating modes and setpoints for all modules via CAN

Operating states

Low load

The generator covers the load. The AFEs use the surplus to charge the battery.

Load peak

The AFEs feed in power from the battery. The generator stays within its rated range.

Sun

The PV modules charge via the DCD with MPPT directly on the 70 VDC bus.

Generator off

The AFEs form the grid from battery and PV alone.

Sum of rated values. Sizing depends on load profile, generator and battery.

Interfaces

Networked via CAN

Interface Module Purpose CAN internal all Networking and control of the modules CAN battery DCD Battery management data Modbus DCD, option Connection to DTU and monitoring Sync bus AFE Phase angle in parallel and three-phase operation CP / PP AFE, option Charging at a charging station 24 VDC all Control voltage

Installation space

Compact string

AFE

150 × 200
× 80 mm

ISO

150 × 320
× 100 mm

DCD

150 × 160
× 40 mm

One string: AFE + ISO + DCD 320 × 370 × 120 mm

Two strings side by side 640 × 370 × 120 mm

Dimensions from the concept phase, subject to change during development.

Contact

Let's talk about your application

Tell us your grid connection, battery voltage and power requirement. We will suggest a suitable combination of modules.

KNESTEL
Technologie & Elektronik GmbH

vertrieb@knestel.de

Phone

08372- 7080

Address

Osterwalder Str. 12
87496 Hopferbach