Documentation

Bidirectional DC-DC

DC-to-DC converter that supports bidirectional boost and buck

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• Powertrain Blockset / Energy Storage and Auxiliary Drive / DC-DC

Description

The Bidirectional DC-DC block implements a DC-to-DC converter that supports bidirectional boost and buck (lower) operation. Unless the DC-to-DC conversion limits the power, the output voltage tracks the voltage command. You can specify electrical losses or measured efficiency.

Depending on your battery system configuration, the voltage might not be at a potential that is required by electrical system components such has inverters and motors. You can use the block to boost or buck the voltage. Connect the block to the battery and one of these blocks:

• Mapped Motor

• IM Controller

• Interior PM Controller

• Surface Mount PM Controller

To calculate the electrical loss during the DC-to-DC conversion, use Parameterize losses by.

Parameter OptionDescription

Single efficiency measurement

Electrical loss calculated using a constant value for conversion efficiency.

Tabulated loss data

Electrical loss calculated as a function of load current and voltage. DC-to-DC converter data sheets typically provide loss data in this format. When you use this option, provide data for all the operating quadrants in which the simulation will run. If you provide partial data, the block assumes the same loss pattern for other quadrants. The block does not extrapolate loss that is outside the range voltage and current that you provide. The block allows you to account for fixed losses that are still present for zero voltage or current.

Tabulated efficiency data

Electrical loss calculated using conversion efficiency that is a function of load current and voltage. When you use this option, provide data for all the operating quadrants in which the simulation will run. If you provide partial data, the block assumes the same efficiency pattern for other quadrants. The block:

• Assumes zero loss when either the voltage or current is zero.

• Uses linear interpolation to determine the loss. At lower power conditions, for calculation accuracy, provide efficiency at low voltage and low current.

Note

The block does not support inversion. The polarity of the input voltage matches the polarity of the output voltage.

Theory

The Bidirectional DC-DC block uses the commanded voltage and the actual voltage to determine whether to boost or buck (lower) the voltage. You can specify a time constant for the voltage response.

IfThen
Voltcmd > SrcVoltBoost
Voltcmd < SrcVoltBuck

The Bidirectional DC-DC block uses a time constant-based regulator to provide a fixed output voltage that is independent of load current. Using the output voltage and current, the block determines the losses of the DC-to-DC conversion. The block uses the conversion losses to calculate the input current. The block accounts for:

• Bidirectional current flow

• Source to load — Battery discharge

• Load to source — Battery charge

• Rated power limits

The block provides voltage control that is power limited based on these equations. The voltage is fixed. The block does not implement a voltage drop because the load current approximates DC-to-DC conversion with a bandwidth that is greater than the load current draw.

 DC-to-DC converter load voltage $\begin{array}{l}LdVol{t}_{Cmd}=\mathrm{min}\left(Vol{t}_{Cmd},\frac{{P}_{limit}}{L{d}_{Amp}},0\right)\\ LdVolt=LdVol{t}_{Cmd}\cdot \frac{1}{\tau s+1}\end{array}$ Power loss for single efficiency source to load $Pw{r}_{Loss}=\frac{100-Eff}{Eff}\cdot L{d}_{Volt}\cdot L{d}_{Amp}$ Power loss for single efficiency load to source $Pw{r}_{Loss}=\frac{100-Eff}{Eff}\cdot |L{d}_{Volt}\cdot L{d}_{Amp}|$ Power loss for tabulated efficiency $Pr{w}_{Loss}=f\left(L{d}_{Volt},L{d}_{Amp}\right)$ Source current draw from DC-to-DC converter $Sr{c}_{Amp}=\frac{L{d}_{Pwr}+Pr{w}_{Loss}}{Sr{c}_{Volt}}$ Source power from DC-to-DC converter $Sr{c}_{Pwr}=Sr{c}_{Amp}\cdot Sr{c}_{Volt}$

Power Accounting

For the power accounting, the block implements these equations.

Bus Signal DescriptionVariableEquations

PwrInfo

PwrTrnsfrd — Power transferred between blocks

• Positive signals indicate flow into block

• Negative signals indicate flow out of block

PwrBusSrc

Source power to DC-to-DC converter

Psrc

PwrBusLd

Pbus

PwrNotTrnsfrd — Power crossing the block boundary, but not transferred

• Positive signals indicate an input

• Negative signals indicate a loss

PwrLoss

Converter power loss

Ploss

PwrStored — Stored energy rate of change

• Positive signals indicate an increase

• Negative signals indicate a decrease

Not used

The equations use these variables.

 VoltCmd DC-to-DC converter commanded output voltage SrcVolt Source input voltage to DC-to-DC converter LdAmp Load current of DC-to-DC converter LdVolt Load voltage of DC-to-DC converter SrcAmp Source current draw from DC-to-DC converter τ Conversion time constant Vinit Initial load voltage of the DC-to-DC converter Plimit Output power limit for DC-to-DC converter Eff Input to output efficiency SrcPwr Source power to DC-to-DC converter LdPwr Load power from DC-to-DC converter PwrLoss Power loss LdVoltCmd Commanded load voltage of DC-to-DC converter before application of time constant

Ports

Inputs

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DC-to-DC converter commanded output voltage, VoltCmd, in V.

Source input voltage to DC-to-DC converter, SrcVolt, in V.

Load current of DC-to-DC converter, LdAmp, in A.

Output

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Bus signal containing these block calculations.

SignalDescriptionVariableUnits

SrcPwr

Source power to DC-to-DC converter

SrcPwr

W

LdPwr

LdPwr

W

PwrLoss

Power loss

PwrLoss

W

LdVoltCmd

Commanded load voltage of DC-to-DC converter before application of time constant

LdVoltCmdV

PwrInfo

PwrTrnsfrd

PwrBusSrc

Source power to DC-to-DC converter

Psrc

W

PwrBusLd

Pbus

W

PwrNotTrnsfrd

PwrLoss

Converter power loss

Ploss

W

PwrStored

Not used

Load voltage of DC-to-DC converter, LdVolt, in V.

Source current draw from DC-to-DC converter, SrcAmp, in A.

Parameters

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Electrical Control

Converter response time, τ, in s.

Initial load voltage of the DC-to-DC converter, Vinit, in V.

Initial load voltage of the DC-to-DC converter, Plimit, in W.

Electrical Losses

This table summarizes the loss options used to calculate electrical options.

Parameter OptionDescription

Single efficiency measurement

Electrical loss calculated using a constant value for conversion efficiency.

Tabulated loss data

Electrical loss calculated as a function of load current and voltage. DC-to-DC converter data sheets typically provide loss data in this format. When you use this option, provide data for all the operating quadrants in which the simulation will run. If you provide partial data, the block assumes the same loss pattern for other quadrants. The block does not extrapolate loss that is outside the range voltage and current that you provide. The block allows you to account for fixed losses that are still present for zero voltage or current.

Tabulated efficiency data

Electrical loss calculated using conversion efficiency that is a function of load current and voltage. When you use this option, provide data for all the operating quadrants in which the simulation will run. If you provide partial data, the block assumes the same efficiency pattern for other quadrants. The block:

• Assumes zero loss when either the voltage or current is zero.

• Uses linear interpolation to determine the loss. At lower power conditions, for calculation accuracy, provide efficiency at low voltage and low current.

Overall conversion efficiency, Eff, in %.

Dependencies

To enable this parameter, for Parameterize losses by, select Single efficiency measurement.

Tabulated loss breakpoints for M load voltages, in V.

Dependencies

To enable this parameter, for Parameterize losses by, select Tabulated loss data.

Tabulated loss breakpoints for N load currents, in A.

Dependencies

To enable this parameter, for Parameterize losses by, select Tabulated loss data.

Electrical loss map, as a function of N load currents and M load voltages, in W.

Dependencies

To enable this parameter, for Parameterize losses by, select Tabulated loss data.

Tabulated efficiency breakpoints for M load voltages, in V.

Dependencies

To enable this parameter, for Parameterize losses by, select Tabulated efficiency data.

Tabulated efficiency breakpoints for N load currents, in A.

Dependencies

To enable this parameter, for Parameterize losses by, select Tabulated efficiency data.

Electrical efficiency map, as a function of N load currents and Mload voltages, in %.

Dependencies

To enable this parameter, for Parameterize losses by, select Tabulated efficiency data.