Main Content

Behavioral model of power converter

**Library:**Simscape / Electrical / Semiconductors & Converters / Converters

The DC-DC Converter block represents a behavioral model of a power converter. This power converter regulates voltage on the load side. To balance input power, output power, and losses, the required amount of power is drawn from the supply side. Alternatively, the converter can support regenerative power flow from load to supply.

This circuit illustrates the converter's behavior.

The *P _{fixed}* component draws a constant power and
corresponds to converter losses that are independent of load current. The power drawn is
set by the

The voltage source is defined by the following equation:

*v* = *v _{ref}* –

Where:

*v*is the load side voltage set point, as defined by the value you specify for the_{ref}**Output voltage reference demand**parameter. Alternatively, you can provide this value as input to the**Vref**port when the**Voltage reference**parameter is set to`External`

.*D*is the value you specify for the**Output voltage droop with output current**parameter. Having a separate value for droop makes control of how output voltage varies with load independent of load-dependent losses. Instead of specifying*D*directly, you can specify the**Percent voltage droop at rated load**.

The current source value *i* is calculated so that the power flowing
in to the converter equals the sum of the power flowing out plus the converter
losses.

To specify the converter behavior when the voltage presented by the load is higher than the
converter output voltage reference demand, use the **Power direction** parameter:

`Unidirectional power flow from supply to regulated side`

— Current is blocked by the off-state diode, and the current source current*i*is zero. Set the conductance of this diode using the**Diode off-state conductance**parameter.`Bidirectional power flow`

— Power is transmitted to the supply side, and*i*becomes negative.

Optionally, the block can include voltage regulation dynamics. If you select
`Specify voltage regulation time constant`

for the
**Dynamics** parameter, then a first-order lag is added to the
equation defining the voltage source value. With the dynamics enabled, a load step
change results in a transient change in output voltage, the time constant being defined
by the **Voltage regulation time constant** parameter.

You can tabulate the DC-DC Converter block efficiency depending on the output current and the temperature.

This equation defines the relationship between losses and efficiency:

$$loss\left({i}_{2}\right)=\left[1-eff\left({i}_{2}\right)\right]abs\left({v}_{1}{i}_{1}\right)$$

where

*loss(i*are the DC-DC converter losses._{2})*v*is the input voltage._{1}*i*is the input current._{1}*i*is the output current._{2}*eff(i*is the efficiency of the DC-DC converter as a function of the output current, as specified in_{2})**Percentage efficiency table, eff(I)**.

If the output current is equal to `0`

, the converter
losses are equal to **Converter losses at zero output power**.

These are the steps to compute the used power losses depending on the output current:

If the output current is less than the last negative current point or greater than the first positive current point in the

**Vector of output currents for tabulated efficiencies, I**parameter, the block uses the**Percentage efficiency table, eff(I)**parameter to find the corresponding efficiency (with linear interpolation or nearest extrapolation) and then convert that efficiency to losses.Else, the block blends the zero output current case to the last negative point or the first positive point in the table, as shown in this figure:

If you expose the thermal ports, the block tabulates the efficiency depending on both the current and temperature. The losses calculation remains the same as the non-thermal variant.

You can use the physical signal input port F to simulate both DC supply failure and converter failure. This type of event cannot be simulated by simply disconnecting the DC supply, for example by opening a switch, because the average value model will attempt to increase supply-side current to unrealistic values as supply-side voltage drops.

To expose the fault port, **F**, in the
**Faults** tab, set the **Enable output open-circuit
fault** parameter to `Yes`

.

You control the behavior in response to the physical signal fault input F by the
parameters on the **Faults** tab of the block dialog box. With the
default parameter settings:

**Fault condition**is`Output open circuit if F >= Fault threshold`

**Fault threshold**is`0.5`

If a signal is connected to port F, then the block operates according to the parameter
settings on the **Faults** tab. For example, if **Fault
condition** is ```
Output open circuit if F >= Fault
threshold
```

, then when the signal at port F rises above the
**Fault threshold** value, the converter stops operating. Zero
current is taken from the supply side, and zero current is supplied to the load
side.

The block has an optional thermal port, hidden by default. To expose the thermal port,
right-click the block in your model, and then from the context menu select
**Simscape** > **Block choices** >
**Show thermal port**. This action displays the thermal port
**H** on the block icon, and exposes the **Thermal
Port** parameters.

The block transfers heat generated from electrical losses through a Controlled
Heat Flow Rate Source to a Thermal Mass block. The
electrical properties of the block do not change with temperature. Specify the
thermal properties for this block using the parameters **Thermal
mass** and **Initial temperature**.

The two electrical networks connected to the supply-side and regulated-side terminals must each have their own Electrical Reference block.

The supply-side equation defines a power constraint on the product of the voltage,

*v*, and the current,_{s}*i*. For simulation, the solver must be able to uniquely determine_{s}*v*. To ensure that the solution is unique, the block implements two assertions:_{s}*v*> 0 — This assertion ensures that the sign of_{s}*v*_{s}is uniquely defined*i*<_{s}*i*— This assertion deals with the case when the voltage supply to the block has a series resistance_{max}

When there is a series resistance, there are two possible steady-state solutions for

*i*that satisfy the power constraint, the one with the smaller magnitude being the desired one. You should set the value for the_{s}**Maximum expected supply-side current**parameter,*i*, to be larger than the expected maximum current. This will ensure that when the model is initialized the initial current does not start at the undesired solution._{max}