Danfoss NXP DCGuard Design guide

Design Guide

VACON® NXP DCGuard™

Design Guide | VACON® NXP DCGuard™	Contents

Contents

1 Introduction		5
1.1	Purpose of this Design Guide	5
1.2	Additional Resources	5
1.3	Manual Version	5
1.4	Type Approvals and Certifications	5

2	Safety			6
	2.1	Safety Instructions		6
3	Product Overview			7
	3.1	DC Grids and Selectivity		7
	3.2	Selectivity with Fuses		7
	3.3	Application Functionality		8
	3.4	Protection Functions		9
		3.4.1	Instant Current Cut-Off	9
		3.4.2	Rapid Current Cut-Off	10
		3.4.3	High Current Cut-Off	10
		3.4.4	Overload Detection	10
	3.5	Controlled Voltage Ramp-Up		10
		3.5.1	Controlled Voltage Ramp-Up of a Loaded System	10
		3.5.2	Controlled Voltage Ramp-Up into a Short Circuit	10
	3.6	System Control Principle		10
	3.7	Application Requirements		11
	3.8	System Integrator Responsibilities		11
	3.9	System Selectivity		12
4	Component Overview			14
	4.1	Fuses		14
	4.2	Filters		15
		4.2.1	Calculating the Filter Impedance	15
	4.3	Mechanical Disconnectors		16
		4.3.1	Closing the Mechanical Disconnectors	17
		4.3.2	Opening the Mechanical Disconnectors	18
5	Specifications			19
	5.1	Technical Data		19
	5.2	Nameplate		20
	5.3	Voltage and Current Rating Guidelines		20
	5.4	Operation Temperature Range		21
	5.5	Power Ratings		21

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Design Guide | VACON® NXP DCGuard™			Contents
	5.5.1	Air-Cooled 500 V Units	21
	5.5.2	Air-Cooled 690 V Units	22
	5.5.3	Liquid-Cooled 500 V Units	23
	5.5.4	Liquid-Cooled 690 V Units	24
5.6	Total Capacitance, Inductance, and Resistance		25
6 Electrical Installation Guidelines			26
6.1	DCGuard Topologies		26
	6.1.1	Directional Topology	26
	6.1.2	Peer-to-peer Topology	26
	6.1.3	Ring Topology	27
6.2	Parallel Installation		28
6.3	Bus-Tie Cables		28
6.4	HF Capacitors		29
6.5	Cabling		29
	6.5.1	Wiring Diagrams for Air-Cooled Inverter Units	30
	6.5.2	Wiring Diagrams for Liquid-Cooled Inverter Units	32
6.6	Terminal Definitions		36
	6.6.1	Terminal Locations in Air-Cooled Inverter Units	36
	6.6.2	Terminal Locations in Liquid-Cooled Inverter Units	39
6.7	Control I/O Configuration		42
7 How to Select the VACON® NXP DCGuard™			44
7.1	VACON® Select Web Tool		44

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Design Guide | VACON® NXP DCGuard™	Introduction

1 Introduction

1.1 Purpose of this Design Guide

This design guide is intended for qualified personnel, such as:

•Project and systems engineers.

•Design consultants.

•Application and product specialists.

The design guide provides technical information to understand the capabilities of VACON® NXP DCGuard™ for integration into DC supply systems. Its purpose is to provide design considerations and planning data for integration of the device into a system. It caters for the selection of the drive units and options for the application in a diversity of installations. Reviewing the detailed product information in the design stage enables developing a well-conceived system with optimal functionality and efficiency.

1.2 Additional Resources

Other resources are available to understand installation, programming, operation, and options.

•The VACON® NXP DCGuard™ operating guide provides information about the installation and operation of the VACON® NXP DCGuard™ application.

•The VACON® NXP DCGuard™ application guide provides greater detail on how to work with the application software and how to set the parameters of the AC drive modules.

•VACON® NXP Common DC Bus and VACON® NXP Liquid-cooled Common DC Bus user manuals provide detailed information for the installation, commissioning, and operation of the AC drive modules.

•The operating and installation guides for VACON® options give detailed information about specific drive options.

Supplementary publications and manuals are available from Danfoss. See www.danfoss.com for listings.

1.3 Manual Version

This manual is regularly reviewed and updated. All suggestions for improvement are welcome.

The original language of this manual is English.

Table 1: VACON® NXP DCGuard™ Design Guide Version

Version	Release date	Remarks
A	04.12.2018	First release

1.4 Type Approvals and Certifications

VACON® NXP DCGuard™ is type approved as a circuit breaker/DC-bus tie breaker. For a list of the approvals and certifications, see the VACON® NXP DCGuard™ product page at www.danfoss.com.

NOTICE

VACON® NXP DCGuard™ acts as a protection device in a DC power distribution system. Separate approvals as a DC-bus tie breaker can be required.

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Design Guide | VACON® NXP DCGuard™	Safety

2 Safety

2.1 Safety Instructions

A safety guide is included in the product delivery. Read the safety instructions carefully before starting to work in any way with the system or its components.

The warnings and cautions in the safety guide give important information on how to prevent injury and damage to the equipment or the system. Read the warnings and cautions carefully and obey their instructions.

The product manuals with applicable safety, warning, and caution information can be downloaded from https://www.danfoss.com/en/ service-and-support/.

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Design Guide | VACON® NXP DCGuard™	Product Overview

3 Product Overview

3.1 DC Grids and Selectivity

Utilizing DC grids rather than AC grids enables power distribution with lower power losses. However, there are few or no international standards for building a DC grid, especially in marine applications. Short circuit handling is a challenge in DC grids and it is difficult to ensure the required system functionality by using fuses. Ensuring selectivity and limited short circuit energy requires more sophisticated protection devices.

Ensuring selectivity in a common-DC system is a challenge, and it becomes even more challenging when there are several inverters connected to the same DC bus. In a short circuit in the DC bus, the protection fuses burn, but often so do the fuses feeding other vital equipment in the same system. Even fuses which are not connected directly (nearest) to the short circuit can burn, for example, the fuses feeding inverters in another place in the same DC bus.

During the first 100–200 μs after a short circuit occurs, the capacitors inside each inverter will supply current to the fault. Since capacitors can feed out current extremely fast, selectivity is difficult to achieve by only using fuses. One way to improve the total selectivity in a common-DC-bus system is to split the system in two separate DC grids by using a fast-current cutter/DC-bus tie device.

Danfoss Drives has developed a new fast-current cutter/DC-bus tie device, the VACON® NXP DCGuard™. The semiconductor protection device is based on standard VACON® NXP inverter hardware and new software. During a short circuit, the VACON® NXP DCGuard™ disconnects the healthy side from the faulty side in microseconds, before the short circuit affects the healthy side. The fast isolation ensures that the healthy side can continue to operate as normal, also after the short circuit situation. The DCGuard cannot influence what happens inside the faulty DC grid during a short circuit situation.

3.2 Selectivity with Fuses

In some demanding applications (for example, marine applications) there is a requirement that a single fault must not shut down the complete system. Because of this requirement, it is required to build the system so that it can withstand a fault without having a total blackout.

Maintaining the required DC voltage on the healthy side of the DC grid during a fault is one of the main challenges when using fuses to disconnect the healthy part of the DC grid from the faulty part in a short circuit situation. When a short circuit happens, the voltage on the faulty side is close to 0 V. Because of the low resistance inside the fuses, also the voltage on the healthy side decreases. It takes time for the fuses to clear the fault, so there is a significant risk that also the voltage on the healthy side decreases below the undervoltage trip limit for the inverters in the healthy side. The result is a total blackout.

illustration 1 shows the DC voltage in grids 1 and 2, and the DC current through the fuses when there is a fault in DC grid 2.

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Design Guide | VACON® NXP DCGuard™	Product Overview

Overvoltagetrip	DC Current	Overvoltagetrip
DC Voltage		DC Voltage
Undervoltagetrip		Undervoltagetrip

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Short	Fuses	Time	Short	Fuses	Time	Short	Fuses	Time
circuit	clearance		circuit	clearance		circuit	clearance

DC grid 1	DC grid 2
DC+	DC+
DC-	DC-

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Illustration 1: Example of Selectivity with Fuses in a Fault Situation

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3.3 Application Functionality

VACON® NXP DCGuard™ is a fast DC current cutter device that detects and cuts off an outgoing short-circuit current. The main function is to isolate the faulty DC grid from the healthy DC grid, before that fault affects the healthy DC grid.

Two inverter units in a DCGuard peer-to-peer topology are required to be able to cut off short-circuit current both ways.

VACON® NXP DCGuard™ consist of VACON® NXP inverter units and application software ADFIF102. To ensure the correct functionality and safety level, always use the following components together with the DCGuard in a peer-to-peer system:

•An upstream mechanical disconnector if safe disconnection is required.

•Type aR supply fuses in each DC supply line (see the VACON® NXP DCGuard™ design guide for instructions).

•A dU/dt filter (a standard VACON® dU/dt filter can be used).

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Design Guide | VACON® NXP DCGuard™	Product Overview

DCGuard 1

DCGuard 2

DC grid 1	DC+	=	U	DC+	W	=	DC+	DC grid 2
	DC-	=	V	DC-	V	=	DC-

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Illustration 2: VACON® NXP DCGuard™ Peer-to-Peer Topology

3.4 Protection Functions

The VACON® NXP DCGuard™ application has different short-circuit protection levels. The levels can be used to ensure correct system selectivity. The instant current cut-off is non-programmable, but the other functions can be programmed. The protection functions also have separate programmable responses.

Instant trip

Short-circuit protection

Over load detection

Nom. current

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	Instant current cut-off
	Rapid current cut-off
	High current cut-off
	Bus tie cables over load protection

Operational area

Time

Illustration 3: VACON® NXP DCGuard™ Safety Layers

3.4.1Instant Current Cut-Off

•Non-programmable short-circuit current cut-off.

•VACON® NXP DCGuard™ trips within μs to fault F1 in a low impedance short circuit.

•The functionality is handled by the VACON® NXP inverter hardware.

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Design Guide | VACON® NXP DCGuard™	Product Overview

3.4.2 Rapid Current Cut-Off

•Programmable short-circuit current cut-off.

•VACON® NXP DCGuard™ trips within 10–100 μs to fault F63, F64, or F65 in a low to medium impedance short circuit.

•This functionality is handled by the system software and requires enough inductance in the output filter. If there is a short circuit in the bus-tie cables, a standard dU/dt filter does not have enough inductance to ensure an exact tripping level.

•For details about programming this function, see the VACON® NXP DCGuard™ Application Guide.

3.4.3High Current Cut-Off

•Programmable high circuit current cut-off.

•VACON® NXP DCGuard™ trips within 100 ms to fault F86, F87, or F88 if the current is too high for a too long time.

•This functionality is handled by the VACON® NXP DCGuard™ application software.

•For details about programming this function, see the VACON® NXP DCGuard™ Application Guide.

3.4.4Overload Detection

•Programmable overload detection.

•VACON® NXP DCGuard™ trips within 100 ms to fault F83, F84, or F85 in an overload situation in the DC cables out from the DCGuard.

•This functionality is handled by the VACON® NXP DCGuard™ application software.

•For details about programming this function, see the VACON® NXP DCGuard™ Application Guide.

3.5 Controlled Voltage Ramp-Up

To prevent a high inrush current when a VACON® NXP DCGuard™ is connecting to the bus-tie cables, a controlled voltage ramp up of the bus-tie cable voltage is always performed before closing the DCGuard. The voltage is ramped up from the current level to full DC voltage. Typically, the voltage rise time from 0 V to full DC voltage is 200–400 ms. The voltage rise time and switching frequency are programmable.

3.5.1 Controlled Voltage Ramp-Up of a Loaded System

VACON® NXP DCGuard™ can perform a controlled voltage ramp-up of a loaded system, but the voltage rise time must be adjusted case by case. The maximum current must stay below the tripping limit for the VACON® NXP DCGuard™ units during the controlled voltage ramp-up.

3.5.2 Controlled Voltage Ramp-Up into a Short Circuit

If a controlled voltage ramp-up is performed to a system where a short circuit is present, the VACON® NXP DCGuard™ detects the short circuit and trips.

3.6 System Control Principle

VACON® NXP DCGuard™ is only one component in a complete system, which often includes different layers of controls with different responsibilities.

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Design Guide | VACON® NXP DCGuard™	Product Overview

•The Energy Management System (EMS) optimizes the energy efficiency of the system. The optimization can include selecting and prioritizing the use of different energy sources. Normal time scales are from tens of seconds to hours.

•The Power Management System (PMS) includes controlling the power balance in a system which has multiple energy/power sources. Normal time scales are from grid cycle (20 ms/50 Hz) to seconds.

•The Power Conversion System (PCS) is the system relevant to the VACON® NXP DCGuard™. The PCS includes Power Conversion Control (PCC) and Power Conversion Hardware (PCH), which is the VACON® NXP hardware. The PCS controls the power conversion between the energy storage and the system. Normal time scales are from micro seconds to grid cycles.

•The Storage System (SS) includes the Battery Management System (BMS) and the battery. The BMS monitors the storage system and the storage cell level phenomena.

Energy Management System (EMS)

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Power Management System (PMS)

Power Conversion System

Power Conversion Control

(PCC)

Power Conversion

Hardware

Storage System

Battery Management

System

Battery

Illustration 4: Typical Layers in a Control System

3.7 Application Requirements

The VACON® NXP DCGuard™ application requires:

•NXP3 control board VB761 revision D or newer.

•System software version NXP00002V193 or newer.

3.8 System Integrator Responsibilities

The VACON® NXP DCGuard™ is developed to be used as a component in a common-DC system. System design and control must be done by the system integrator.

The VACON® NXP DCGuard™ peer-to-peer system is made of two independent DCGuard units, although they operate as a pair. It is the responsibility of the system integrator to implement the two DCGuard units in to the system, to ensure correct functionality, and to ensure correct safety level.

Especially consider the following when designing the system:

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Design Guide | VACON® NXP DCGuard™	Product Overview

•A fault in one of the two DCGuard units must lead to the opening of the other DCGuard unit.

•To ensure safe disconnection of the VACON® NXP DCGuard™ and the bus-tie cables, a mechanical disconnector is required in front of each DCGuard.

•The mechanical disconnector in front of each DCGuard unit must only be closed when the voltage level on both sides of the mechanical disconnector is within the limits of the mechanical disconnectors closing capacity. Meaning that the inrush current is within the mechanical disconnectors closing capacity.

•The mechanical disconnector in front of each DCGuard unit must only be opened when the conducted current is less than the maximum breaking capability of the mechanical disconnector.

•Closing a DCGuard unit must only be possible when the other side of the system is ready to be powered up.

•VACON® NXP liquid-cooled inverters do not control or monitor the cooling liquid flow through their own cooling elements. The system integrator must therefore take responsibility of implementing sufficient control and monitoring of the cooling liquid circuit.

•If the active control place for the DCGuard unit is keypad, make sure that there is a possibility to stop the DCGuard also in case the keypad is removed from the drive. In case the parameter Keypad/PC fault mode (ID 1329) is set to 0/No response or 1/Warning, it must be ensured on system level that there is the possibility for local control. This can be done, for example, by forcing to I/O or fieldbus control by a digital input.

3.9 System Selectivity

VACON® NXP DCGuard™ has received several Type approval certificates, but often the approval societies require an approval of the whole system. To get such a system approval, a selectivity study of the faulty side is required.

MATLAB®/Simulink® can be used to simulate what happens inside the faulty side of the DC grid during a short circuit. Contact the nearest Danfoss Drives representative for more information.

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Illustration 5: Model of a Complete DC-Supply System

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Design Guide | VACON® NXP DCGuard™	Product Overview

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Illustration 6: VACON® NXP DCGuard™ Library in Simulink®

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Design Guide | VACON® NXP DCGuard™	Component Overview

4 Component Overview

4.1 Fuses

Always protect the VACON® NXP DCGuard™ with aR-type fuses in each DC-supply line.

If there is a short circuit inside the VACON® NXP DCGuard™ unit, the aR-type fuses in each DC-supply line disconnect the unit from the feeding DC grid. The fuses are back-up fuses for semiconductor protection and only give protection against the effects of short circuit current. The fuses do not give any overload protection.

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	B
	C
	D
	E
	F
A	End plate	B	Screw
C	Ceramic body	D Reduced sections of element ("weak spots")
E	Element	F	End fitting

Illustration 7: Structure of a Type aR Fuse

C

D

B

A

E			F

G

A Start of fault

C Peak fault current reached at start of arcing

E Pre-arcing time

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B Actual current

D Possible unrestricted fault current

F Arcing time

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Design Guide | VACON® NXP DCGuard™	Component Overview

G Total clearing time

Illustration 8: Fuse Functionality in a Fault Situation

See the VACON® NXP user manuals for instructions for the fuse selection. The fuses are not included in the VACON® NXP DCGuard™ delivery.

CAUTION

INCORRECT FUSE CONFIGURATION

In certain cases, the correct fuse configuration can differ from the default configuration given in the VACON® NXP user manual!

-To find the correct fuse configuration, do a system calculation.

4.2Filters

VACON® NXP DCGuard™ requires a dI/dt filter in each of the connected output phases (U, V, W).

The purpose for the inductance is to limit the current rise time, so that the programmable protection functionality of the VACON® NXP DCGuard™ can detect the short circuit and cut the current. If there is a short circuit in the terminals, the dI/dt filter has a higher dI/dt, but is protected by the overcurrent protection of the VACON® NXP inverter hardware.

The filters for VACON® NXP DCGuard™ must fulfill these specifications:

•Approximately 2% inductance. See 4.2.1 Calculating the Filter Impedance.

•Full continuous DC current.

•Short time 5 kHz switching frequency.

A standard VACON® dU/dt filter has about 1.5–2% inductance and it can be used as the required dI/dt filter for VACON® NXP DCGuard™. All VACON® dU/dt filters are designed for 0–70 Hz and can therefore conduct the same amount of DC current as the AC current rating. For more information, see the VACON® NX Filters User Manual.

DCGuard 1

DCGuard 2

DC+	=	U	DC+	W	=	DC+
DC-	=	V	DC-	V	=	DC-

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L

L Inductor

Illustration 9: VACON® NXP DCGuard™ with Serial-Connected Inductances in Each Output Phase

4.2.1 Calculating the Filter Impedance

If the required inductance (L) value is known, the impedance (Z) in percentage can be calculated from:

(%) = 2 3 RMSLL

VLL is the line-to-line voltage, IRMS is the RMS current and f is the frequency.

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