DC-DC Converter
A model of the behaviour of an energy converter.
Description
The DC-DC Converter unit is a model of the behaviour of a DC-DC power converter. The converter regulates the voltage on the load side. To balance the input power, output power and losses, the required amount of energy is taken from the power supply side. Alternatively, the converter can maintain a recovered energy flow from the load side to the power supply.
The schematic below illustrates the behaviour of the converter.
The component consumes constant power and corresponds to inverter losses that are independent of the load current. The power consumption is defined by Converter losses at zero output power. The resistor corresponds to losses that increase with load current and is defined by Percentage efficiency at rated output power.
The voltage source is defined by the following equation:
,
where
-
- is the load side voltage reference value determined by the value of the Output voltage reference demand parameter. In addition, this value can be supplied to the Vref port input if the Voltage Reference parameter is set to
External; -
- this is the value that is set in the Output voltage droop with output current parameter. See Voltage drop for more information.
The source current value is calculated so that the power flowing into the inverter is equal to the sum of the power flowing out of the inverter plus the losses in the inverter.
Use the Power direction parameter to set the inverter behaviour when the voltage delivered by the load is higher than the inverter output voltage reference:
-
Unidirectional power flow from supply to regulated side- the current is blocked by a diode in the off state and the current source current is zero. Set the conductance of this diode using the Diode off-state conductance parameter. -
Bidirectional power flow- power is transferred to the power side and becomes negative.
The block can also enable voltage regulation dynamics. If `Specify voltage regulation time constant' is selected for the Dynamics parameter, a first order lag is added to the equation that determines the voltage source value. With dynamics enabled, a step change in load will cause the output voltage to transient, with the time constant defined by the Voltage regulation time constant parameter.
Voltage drop
Voltage drop is the reduction in output voltage for the device controlling the load. Voltage drop is important in voltage regulation schemes as it increases the systems resistance to load transients.
A separate voltage drop value allows controlling the load-dependent output voltage variation, independent of load-dependent losses. To enable voltage droop, select the Enable droop parameter. To set the droop value, set the Droop parameterization parameter to Droop parameterization:
-
By voltage droop with output current- set the voltage drop directly by setting the value of the parameter Output voltage droop with output current. -
By percentage voltage droop at rated load- the voltage drop in percentage of Output voltage reference demand depending on the value of Voltage droop percentage at rated load parameter is calculated from the equation:
,
,
where is the value of the Output voltage reference demand parameter. If Voltage reference is set to External, the unit uses the constant value of Voltage reference used to calculate droop percent instead.
The graph shows how the block calculates the voltage drop.
The voltage drop is the slope of the line where and .
Tabular efficiency
The efficiency of DC-DC converter can be obtained as a function of output current, input voltage and temperature.
These equations define the relationship between losses and efficiency:
if ( ),
if ( ),
where
-
- is the losses in the DC-DC converter;
-
- input voltage;
-
- input current;
-
- output current;
-
- device temperature, if the unit uses a thermal port;
-
- DC-DC converter efficiency as a function of output current, input voltage and temperature, which is set in Percentage efficiency table, eff(I2,V1,T).
If the output current is 0, the converter losses are equal to the value of Converter losses at zero output power.
The power loss as a function of output current is calculated as follows:
-
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, I2, the block uses the values of the Percentage efficiency table, eff(I2) parameter to find the corresponding efficiency value (using linear interpolation or nearest extrapolation) and then convert this value to losses.
-
Otherwise, the block carries the zero output current with the last negative or first positive point in the table, as shown in the figure.
If the Enable thermal port checkbox is selected, the block calculates the efficiency as a function of temperature in addition to the output current and input voltage. The loss calculation remains the same as when the thermal ports are hidden.
Modelling a situation where the supply voltage cannot match the load
The DC-DC Converter unit uses the Minimum supply voltage to function parameter to protect the network when the supply voltage cannot meet the load requirements. This occurs if a switch is connected in series with the power supply and then switched off, or if there is a series resistance in the power supply connection that drops too much voltage. During simulation, if the voltage falls below the Minimum supply voltage to function, the unit relaxes the output voltage regulation. Once the voltage falls below 90% of the value of Minimum supply voltage to function, the inverter input behaves as a fixed resistance equal to the value of Input resistance if not functioning. Similarly, the output of the DC-DC Converter behaves as a fixed resistance equal to Output resistance if not functioning.
Modelling thermal effects
This block has one additional thermal port. To enable the thermal port, select the Enable thermal port checkbox.
The block transfers heat generated by electrical losses through the Controlled Heat Flow Rate Source block to the Thermal Mass block. The electrical properties of the block do not change depending on the temperature. The thermal properties for this block are set using the Thermal mass and Initial temperature parameters.
Assumptions
-
The two electrical networks connected to the terminals on the supply side and on the control side must have their own block Electrical Reference.
-
The source-side equation defines the power constraint on the product of voltage and current . For modelling purposes, the solver must be able to uniquely define . To ensure that the solution is unique, the block implements two statements:
-
- this assertion ensures that the sign of is uniquely defined.
-
- this statement refers to the case when the supply voltage of the block has a series resistance.
In the presence of series resistance, there are two possible steady-state solutions for , satisfying the power constraint, the best being the one with the smaller value.
-
Ports
Non-directional
1+ - input positive terminal
electricity
An electrical non-directional port connected to the positive terminal of the input circuit.
1- is the input negative terminal
electricity
An electrical non-directional port associated with the negative terminal of the input circuit.
2+ is the output positive terminal
electricity
An electrical non-directional port connected to the positive terminal of the output circuit.
2- is the output negative terminal
electricity
An electrical non-directional port connected to the negative terminal of the output circuit.
Vref is the output negative terminal
scalar
An electrical non-directional port through which an external voltage reference signal is applied.
Dependencies
To use this port, set the Voltage Reference parameter to External.
H is a heat port
heat
A thermal non-directional port representing a thermal mass. For more information, see Modelling thermal effects.
Dependencies
To use this port, set Enable thermal port to `enabled'.
Main
Voltage reference - reference voltage
Internal (By default) | `External `
Option for the reference voltage modelling method.
Output voltage reference demand - set voltage value
10.0 V (by default).
The set value for the voltage regulator and the output voltage value when there is no output current.
Dependencies
To use this parameter, set Voltage Reference to Internal.
Rated output power - rated output power
10.0 W (By default).
Output power for which the efficiency value is set in per cent. This parameter is also used to calculate the voltage drop , if the drop is set in per cent.
Enable droop - take voltage drop into account
On (By default) | Off
The option for voltage drop detection.
Droop parameterization - voltage droop model
By voltage droop with output current (by default) | By percent voltage droop at rated load.
Select one of the following voltage drop parameterization methods:
-
By voltage droop with output current- specify the absolute value of the voltage drop . This is the option by default. -
By percent voltage drop at rated load- specify the voltage drop in per cent at rated load.
Dependencies
To use this parameter, set the Enable droop parameter to `enabled'.
Output voltage droop with output current - voltage drop at 1 A
0.1 V/A (By default).
The number of volts by which the output voltage drops from the set value at 1 A output current.
Dependencies
To use this parameter, set Enable droop to `enable' and Droop parameterization to `By voltage droop with output current'.
Voltage droop percent at rated load - voltage drop percentage at rated load
2 (By default).
The percentage by which the voltage drops compared to the rated output voltage when the rated load is consumed. If Voltage reference is set to Internal, the unit uses the Output voltage reference demand parameter to calculate the percentage of drop. If Voltage reference is set to `External', the unit uses the Voltage reference used to calculate droop percent.
Dependencies
To use this parameter, set Enable droop to on and Droop parameterization to `By percent voltage droop at rated load'.
Voltage reference used to calculate droop percentage - voltage reference used to calculate voltage drop percentage
10 V (By default).
The reference voltage that the Voltage droop percent at rated load parameter uses to calculate the voltage drop during simulation.
Dependencies
To use this parameter, set Enable droop to `enabled', Voltage reference to `External', and Droop parameterization to `By voltage droop percent at rated load'.
Power direction - power flow direction
Unidirectional power flow from supply to regulated side (by default) | Bidirectional power flow.
Select one of the following power conversion direction methods:
-
Unidirectional power flow from supply to regulated side- most low-power regulators are unidirectional. This is the By default option. -
`By percent voltage droop at rated load' - high power converters can be bidirectional, such as converters used in electric vehicles to provide regenerative braking.
*Diode off-state conductance` - unidirectional diode
1e-8 1/ohm (by default).
The ideal diode is switched on the output side to prevent current injection into the inverter in a unidirectional configuration.
Losses
Converter losses at zero output power - constant losses
`1 W (by default)
The power consumed by the component in the equivalent circuit, which corresponds to the converter losses independent of the load current.
Converter losses - conversion losses
Assume proportional to square of output current (by default) | Tabulate efficiency.
Parameterization of converter losses.
Percentage efficiency at rated output power - rated efficiency
80 (By default)
Efficiency defined as the ratio of load output power to input supply power in per cent.
Dependencies
To use this parameter, set Converter losses to `Assume proportional to square of output current'.
Variables for tabulation - tabular variables
| Output current (by default) | Output current and input voltage | `Output current and temperature | `Output current, input voltage, and temperature.
Specify the parameters on which efficiency depends: output current, input voltage, and temperature. To enable the temperature options, you must open the unit’s thermal port.
Vector of output currents for tabulated efficiencies, I2 - output currents for tabulated efficiencies
[-2, -1, 1, 2] A (by default) | vector of positive increasing scalars.
Vector of output currents for tabulated efficiencies. The dimensionality of this vector must be greater than or equal to three and equal to the dimensionality of Percentage efficiency table, eff(I).
Dependencies
To use this parameter, set the Converter losses parameter to `Tabulate efficiency'.
Percentage efficiency table, eff(I2) - tabulated efficiency values depending on current
[66, 76, 80, 74] (by default) | `Positive scalar matrix'.
Tabulated efficiency values in per cent as a function of current. The dimensionality of this vector must be equal to the dimensionality of Vector of output currents for tabulated efficiencies, I2.
Dependencies
To use this parameter, set Converter losses to `Tabulate efficiency' and Variables for tabulation to `Output current'.
Vector of input voltages for tabulated efficiencies, V1 - input voltages for tabulated efficiencies
[15, 30, 45] V (by default) | ` vector of positive increasing scalars`.
Vector of input voltages for tabulated efficiencies. The dimensionality of this vector must be greater than or equal to two.
Dependencies
To use this parameter, set Converter losses to `Tabulate efficiency' and Variables for tabulation to `Output current and input voltage' or `Output current, input voltage, and temperature'.
Percentage efficiency table, eff(I2,V1) - tabulated efficiencies as a function of current and voltage
[66, 66, 66; 76, 76, 76; 80, 80, 80; 74, 74, 74] (by default) | matrix of positive scalars.
Tabulated efficiency values in per cent as a function of current and voltage.
Dependencies
To use this parameter, set Converter losses to `Tabulate efficiency' and Variables for tabulation to `Output current and input voltage' or `Output current, input voltage, and temperature'.
Vector of temperatures for tabulated efficiencies, T - temperature values for tabulated efficiencies
[280, 300, 320] K (by default) | ` vector of positive increasing scalars'.
A vector of temperature values for tabulated efficiencies. The dimensionality of this vector must be equal to or greater than 2.
Dependencies
To use this parameter, set the Converter losses parameter to `Tabulate efficiency'.
Percentage efficiency table, eff(I2,T) - tabulated efficiency values as a function of current and temperature
[66, 66, 66; 76, 76, 76; 80, 80, 80; 74, 74, 74] (by default) | matrix of positive scalars
Tabulated efficiency values in per cent as a function of current and temperature.
Dependencies
To use this parameter, set Converter losses to `Tabulate efficiency' and Variables for tabulation to `Output current and temperature'.
Percentage efficiency table, eff(I2,V1,T) - tabulated efficiencies as a function of current, voltage and temperature
repeat([66.0, 76.0, 80.0, 74.0], 1, 3, 3) (by default) | three-dimensional matrix of scalars.
Tabulated efficiency values in per cent as a function of current, voltage and temperature.
Dependencies
To use this parameter, set Converter losses to `Tabulate efficiency' and Variables for tabulation to `Output current, input voltage, and temperature'.
Dynamics
Dynamics - dynamic model
No dynamics (by default) | Specify voltage regulation time constant
Specify whether to enable voltage regulation dynamics:
-
No dynamics- voltage regulation dynamics are not taken into account. -
Specify voltage regulation time constant- add a first order lag to the equation defining the source voltage value. With dynamics enabled, a step change in load will result in a transient change in output voltage.
*Voltage regulation time constant` - dynamics time constant
0.02 s (By default)
Time constant associated with voltage transients during step changes in load current.
Dependencies
To use this parameter, set the Dynamics parameter to Specify voltage regulation time constant.
Initial output voltage demand - Initial output voltage demand
`10 V (by default).
The value of at time zero. Normally is defined by the parameter Output voltage reference demand. However, if there is a need to initialise the model without transients when a steady load current is applied, it is possible to set the initial value of using this parameter and increase it accordingly to account for output resistance and voltage drop.
Dependencies
To use this parameter, set the Dynamics parameter to Specify voltage regulation time constant.
Off State
Minimum supply voltage to function - minimum supply voltage to function
`1 V (by default)
Minimum supply voltage to operate the converter and regulate the output voltage to the set value. When the supply voltage drops below 90% of the value of this parameter, the input of the DC-DC Converter behaves as a fixed resistance equal to the value of Input resistance if not functioning. Similarly, the output of the DC-DC Converter behaves as a fixed resistance equal to Output resistance if not functioning.
Input resistance if not functioning - input resistance if not functioning
1000 ohms (by default).
Input resistance when supply voltage drops below 90% of the Minimum supply voltage to function.
Output resistance if not functioning - output resistance if not functioning
`1000 ohms (by default).
Output resistance when supply voltage drops below 90% of the value of Minimum supply voltage to function.
Thermal
Thermal mass - thermal mass
100 J/K (by default)
The thermal mass associated with the heat port is H. It represents the energy required to raise the temperature of the thermal port by one degree.
Dependencies
To use this parameter, set Enable thermal port to `enable'.
Initial temperature is the initial temperature at the thermal port
298.15 К
Initial temperature associated with heat port H.
Dependencies
To use this parameter, set Enable thermal port to `enable'.