Average-Value DC-DC Converter

R2026b

Average-value DC-DC converter

• 

Average-Value DC-DC Converter block

To add a block to a model, double-click the canvas and start typing the block name. Then, select the block from the list.

Libraries:
Simscape / Electrical / Semiconductors & Converters / Converters

Description

The Average-Value DC-DC Converter block represents a controlled DC-DC converter. You can model a buck, boost, or noninverting buck-boost converter. The block excludes switching events and uses a simple power balance to relate the converter output to the duty cycle, voltage reference, or current reference. This simplicity allows rapid simulation. Use this block for system-level applications such as designing outer-loop controllers or optimizing systems in which you deploy power electronics.

The Average-Value DC-DC Converter block supports two implementation modes. The behavioral model is simpler and does not include energy storage dynamics. You specify the efficiency, either as a constant value or as a function of output current. The average-value model uses a modification to the behavioral model which includes LC dynamics. You specify the inductance, inductor series resistance, capacitance, and capacitor effective series resistance. Losses arise from the inductor series resistance, capacitor effective series resistance, and the loading. Efficiency is an emergent result of these parasitics and the operating point. To control the inverter state variables, set the Implementation mode parameter to Average value. For fast simulation, set this parameter to Behavioral.

Behavioral Model

If you set the Control input parameter to Duty cycle, the input current and output voltage are functions of the duty cycle and efficiency. The voltage and current also depend on the converter type. The block enforces the ideal voltage transfer ratio for the selected topology.

This diagram shows the equivalent circuit for the ideal core of an average-value DC-DC converter. This ideal core is equivalent to the behavioral model with a duty cycle input and 100% efficiency. The circuit contains a controlled current source and a controlled voltage source.

This table shows the output voltage, v₂, and input current, i₁ of the ideal converter core. The output voltage and input current are functions of the input voltage, v₁, and output current, i₂, respectively.

Voltage and Current Equations

Converter Type	Output Voltage, $v_2$	Input Current, $i_1$
Buck	$$v_2=DutyCycle\cdot v_1$$	$$i_1=DutyCycle\cdot i_2$$
Boost	$$v_2=\frac{v_1}{1-DutyCycle}$$	$$i_1=\frac{i_2}{1-DutyCycle}$$
Buck-Boost	$$v_2=\frac{DutyCycle\cdot v_1}{1-DutyCycle}$$	$$i_1=\frac{DutyCycle\cdot i_2}{1-DutyCycle}$$

If the efficiency is less than 100%, the Average-Value DC-DC Converter block scales the input current accordingly.

If you set the Control input parameter to Current reference, the converter sets the output current and it computes the voltage. Similarly, if you set the Control input parameter to Voltage reference, the converter sets the output voltage and it computes the current.

Average-Value Model

Since R2025a

The average-value implementation uses the same ideal converter core as the behavioral implementation but with additional external Inductor and Resistor blocks from the Simscape™ Foundation library.

The diagrams below show the equivalent circuit for each converter topology. The ideal core represents the switches and diodes that you want to average the behavior of. The inductor and capacitor operate as they do in the switching converters. The Average-Value DC-DC Converter blocks in these diagrams, represent the ideal converter core, and have these parameter values:

• Implementation mode is Behavioral.

• Control input is Duty cycle.

• Converter efficiency is Constant.

• Efficiency (%) is 100.

This figure shows the equivalent circuit of an average-value model of a buck converter. The average-value model is equivalent to the behavioral model of a buck converter with an LC filter on output side.

This figure shows the equivalent circuit of an average-value model of a boost converter. The average-value model is equivalent to the behavioral model of a boost converter with an inductor connected to the positive input and a capacitor across the output..

This figure shows the equivalent circuit of an average-value model of a buck-boost converter. The average-value model uses two behavioral models in stages. The stages share the duty cycle control signal. The converter core on the input side is a buck converter and the converter core on the output side is a boost converter. The inductor connects between the two stages, from the positive output of the buck converter to the positive input of the boost converter. The capacitor connects across the output of the second stage.

Variables

Since R2025a

To enable the Initial Targets and Nominal Values sections, set the Implementation mode parameter to Average value.

To set the priority and initial target values for the block variables before simulation, use the Initial Targets section in the block dialog box or Property Inspector. For more information, see Set Priority and Initial Target for Block Variables.

Nominal values provide a way to specify the expected magnitude of a variable in a model. Using system scaling based on nominal values increases the simulation robustness. You can specify nominal values using different sources, including the Nominal Values section in the block dialog box or Property Inspector. For more information, see System Scaling by Nominal Values.

Examples

Average-Value DC-DC Converter Control

Control the output voltage of a buck-boost converter. To adjust the duty cycle, the Control subsystem uses a PI-based control algorithm. An average-value DC-DC converter model is used to speed up the simulation. The input voltage and the system load are held constant throughout the simulation. The total simulation time (t) is 0.25 s. At t = 0.15 s, the voltage reference changes and the system switches from buck mode to boost mode.

• Open Model

Linearize DC-DC Converter Model

Linearize a model of a DC-DC converter using averaged switching or an average-value converter.

• Since R2023b
• Open Live Script

Assumptions and Limitations

• The Average-Value DC-DC Converter block expects a positive input voltage. If the input voltage is negative, this block limits the voltage to 0 and throws a warning. (since R2026b)

  Before R2026b: The input voltage must be positive. If the input voltage is negative, this block throws an error.

• All converter types use the same polarity for input and output.

Ports

Conserving

DutyCycle — Duty cycle

physical | scalar

Electrical conserving port associated with the duty cycle.

Dependencies

To enable this port, set Control Input to Duty Cycle.

Data Types: double

Iref — Current reference

physical

Electrical conserving port associated with the current reference.

Dependencies

To enable this port, set Control Input to Current reference.

Data Types: double

Vref — Voltage reference

physical

Electrical conserving port associated with the voltage reference.

Dependencies

To enable this port, set Control Input to Voltage reference.

Data Types: double

1+ — Positive DC voltage 1

electrical | scalar

Electrical conserving port associated with the positive terminal of the first DC voltage.

Data Types: double

1- — Negative DC voltage 1

electrical | scalar

Electrical conserving port associated with the negative terminal of the first DC voltage.

Data Types: double

2+ — Positive DC voltage 2

electrical | scalar

Electrical conserving port associated with the positive terminal of the second DC voltage.

Data Types: double

2- — Negative DC voltage 2

electrical | scalar

Electrical conserving port associated with the negative terminal of the second DC voltage.

Data Types: double

Parameters

Implementation mode — Converter implementation mode

Behavioral (default) | Average value

Since R2025a

Option to specify the implementation mode of the converter. To control the inverter state variables, set this parameter to Average value. For fast simulation with no dynamics, set this parameter to Behavioral.

Converter type — Converter type

Buck converter (default) | Buck-boost converter | Boost converter

Type of converter.

Dependencies

To enable this parameter, set Control Input to Duty Cycle or Implementation mode to Average value.

Control input — Control input

Duty cycle (default) | Current reference | Voltage reference

Specify the control input to convert the electrical energy between the two sides.

Dependencies

To enable this parameter, set Implementation mode to Behavioral.

Converter efficiency — Converter efficiency parameterization

Constant (default) | Tabulated

Specify the parameterization of the converter efficiency. If you select Tabulated, the conduction losses depend on the provided output current.

Note

For tabulated efficiency, the extrapolation method is nearest. Therefore, the efficiency does not go above the highest value or below the lowest value in the Efficiency vector (%) parameter.

Dependencies

To enable this parameter, set Implementation mode to Behavioral.

Efficiency (%) — Converter efficiency

100 (default) | positive scalar

Efficiency of the converter, in percentage.

Dependencies

To enable this parameter, set Implementation mode to Behavioral and Converter efficiency to Constant.

Output current vector — Vector of output current magnitude

[0, 2, 5] A (default) | row vector of at least two elements

Vector of output currents.

Dependencies

To enable this parameter, set Implementation mode to Behavioral and Converter efficiency to Tabulated.

Efficiency vector (%) — Vector of efficiencies

[90, 95, 98] (default) | row vector of at least two elements

Vector of efficiencies for each output current specified in Output current vector, in percentage. This parameter must have the same size of Output current vector.

Dependencies

To enable this parameter, set Implementation mode to Behavioral and Converter efficiency to Tabulated.

Inductance — Inductance

1e-6 H (default) | positive scalar

Since R2025a

Inductance.

Dependencies

To enable this parameter, set Implementation mode to Average value.

Inductor series resistance — Series resistance of inductor

0 Ohm (default) | nonnegative scalar

Since R2025a

Series resistance of the inductor.

Dependencies

To enable this parameter, set Implementation mode to Average value.

Capacitance — Capacitance

1e-7 F (default) | positive scalar

Since R2025a

Capacitance.

Dependencies

To enable this parameter, set Implementation mode to Average value.

Capacitor effective series resistance — Series resistance of capacitor

1e-6 Ohm (default) | nonnegative scalar

Since R2025a

Series resistance of the capacitor.

Dependencies

To enable this parameter, set Implementation mode to Average value.

Extended Capabilities

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

Version History

Introduced in R2018b

R2025a: Support bidirectional power flow and model LC dynamics

The Average-Value DC-DC Converter block now supports bidirectional power flow. You can also model the converter LC dynamics. To model LC dynamics, set the Implementation mode parameter to Average value. This option exposes the LC parameters, including the inductance and the capacitance.