Bidirectional DC-DC

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

Libraries:
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 Option Description

Parameter Option	Description
`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.

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.

If	Then
Volt_cmd > Src_Volt	Boost
Volt_cmd < Src_Volt	Buck

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	$\begin{array}{l} L d V o l t_{C m d} = \min (V o l t_{C m d}, \frac{P_{l i m i t}}{L d_{A m p}}, 0) \\ L d V o l t = L d V o l t_{C m d} \cdot \frac{1}{τ s + 1} \end{array}$
Power loss for single efficiency source to load	$P w r_{L o s s} = \frac{100 - E f f}{E f f} \cdot L d_{V o l t} \cdot L d_{A m p}$
Power loss for single efficiency load to source	$P w r_{L o s s} = \frac{100 - E f f}{E f f} \cdot \| L d_{V o l t} \cdot L d_{A m p} \|$
Power loss for tabulated efficiency	$P r w_{L o s s} = f (L d_{V o l t}, L d_{A m p})$
Source current draw from DC-to-DC converter	$S r c_{A m p} = \frac{L d_{P w r} + P r w_{L o s s}}{S r c_{V o l t}}$
Source power from DC-to-DC converter	$S r c_{P w r} = S r c_{A m p} \cdot S r c_{V o l t}$

Power Accounting

For the power accounting, the block implements these equations.

Bus Signal			Description	Variable	Equations
`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	P_src	$P_{s r c} = S r c P w r$
		`PwrBusLd`	Load power from DC-to-DC converter	P_bus	$P_{b u s} = - L d V o l t$
	`PwrNotTrnsfrd` — Power crossing the block boundary, but not transferred Positive signals indicate an input Negative signals indicate a loss	`PwrLoss`	Converter power loss	P_loss	$P_{l o s s} = P w r L o s s$
	`PwrStored` — Stored energy rate of change Positive signals indicate an increase Negative signals indicate a decrease		Not used

The equations use these variables.

Volt_Cmd	DC-to-DC converter commanded output voltage
Src_Volt	Source input voltage to DC-to-DC converter
Ld_Amp	Load current of DC-to-DC converter
Ld_Volt	Load voltage of DC-to-DC converter
Src_Amp	Source current draw from DC-to-DC converter
τ	Conversion time constant
V_init	Initial load voltage of the DC-to-DC converter
P_limit	Output power limit for DC-to-DC converter
Eff	Input to output efficiency
Src_Pwr	Source power to DC-to-DC converter
Ld_Pwr	Load power from DC-to-DC converter
Pwr_Loss	Power loss
LdVolt_Cmd	Commanded load voltage of DC-to-DC converter before application of time constant

Examples

Build Full Electric Vehicle Model

Build a vehicle with a motor-generator, battery, direct-drive transmission, and powertrain control algorithms using the electric vehicle (EV) reference application.

Ports

Inputs

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VoltCmd — Commanded voltage
`scalar`

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

SrcVolt — Input voltage
`scalar`

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

LdCurr — Load current
`scalar`

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

Output

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Info — Bus signal
bus

Bus signal containing these block calculations.

Signal			Description	Variable	Units
`SrcPwr`			Source power to DC-to-DC converter	Src_Pwr	W
`LdPwr`			Load power from DC-to-DC converter	Ld_Pwr	W
`PwrLoss`			Power loss	Pwr_Loss	W
`LdVoltCmd`			Commanded load voltage of DC-to-DC converter before application of time constant	LdVolt_Cmd	V
`PwrInfo`	`PwrTrnsfrd`	`PwrBusSrc`	Source power to DC-to-DC converter	P_src	W
	`PwrTrnsfrd`	`PwrBusLd`	Load power from DC-to-DC converter	P_bus	W
	`PwrNotTrnsfrd`	`PwrLoss`	Converter power loss	P_loss	W
	`PwrStored`	Not used

LdVolt — Load voltage
`scalar`

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

SrcCurr — Source current
`scalar`

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

Parameters

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Electrical Control

Converter response time constant — Constant
`1/1000` (default) | `scalar`

Converter response time, τ, in s.

Converter response initial voltage, Vinit — Voltage
`0` (default) | `scalar`

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

Converter power limit, Plimit — Power
`100000` (default) | `scalar`

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

Electrical Losses

Parameterize losses by — Loss calculation
`Single efficiency measurement` (default) | `Tabulated loss data` | `Tabulated efficiency data`

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

Parameter Option Description

Parameter Option	Description
`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.

Single efficiency measurement

Electrical loss calculated using a constant value for conversion efficiency.

Tabulated loss data

Tabulated efficiency data

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 DC to DC converter efficiency, eff — Constant
`98` (default) | `scalar`

Overall conversion efficiency, Eff, in %.

Dependencies

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

Vector of voltages (v) for tabulated loss, v_loss_bp — Breakpoints
`[0 200 400 600 800 1000]` (default) | `1`-by-`M` vector

Tabulated loss breakpoints for M load voltages, in V.

Dependencies

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

Vector of currents (i) for tabulated loss, i_loss_bp — Breakpoints
`[0 25 50 75 100]` (default) | `1`-by-`N` vector

Tabulated loss breakpoints for N load currents, in A.

Dependencies

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

Corresponding losses, losses_table — 2-D lookup table
`N`-by-`M` matrix

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.

Vector of voltages (v) for tabulated efficiency, v_eff_bp — Breakpoints
`[200 400 600 800 1000]` (default) | `1`-by-`M` vector

Tabulated efficiency breakpoints for M load voltages, in V.

Dependencies

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

Vector of currents (i) for tabulated efficiency, i_eff_bp — Breakpoints
`[25 50 75 100]` (default) | `1`-by-`N` vector

Tabulated efficiency breakpoints for N load currents, in A.

Dependencies

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

Corresponding efficiency, efficiency_table — 2-D lookup table
`N`-by-`M` matrix

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

Dependencies

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

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Version History

Introduced in R2017b

Bidirectional DC-DC