Bidirectional DCDC
DCtoDC converter that supports bidirectional boost and buck
Libraries:
Powertrain Blockset /
Energy Storage and Auxiliary Drive /
DCDC
Description
The Bidirectional DCDC block implements a DCtoDC converter that supports bidirectional boost and buck (lower) operation. Unless the DCtoDC 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 DCtoDC conversion, use Parameterize losses by.
Parameter Option  Description 


Electrical loss calculated using a constant value for conversion efficiency. 

Electrical loss calculated as a function of load current and voltage. DCtoDC 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. 

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:

Note
The block does not support inversion. The polarity of the input voltage matches the polarity of the output voltage.
Theory
The Bidirectional DCDC 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 DCDC block uses a time constantbased 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 DCtoDC 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 DCtoDC conversion with a bandwidth that is greater than the load current draw.
DCtoDC converter load voltage  $$\begin{array}{l}LdVol{t}_{Cmd}=\mathrm{min}(Vol{t}_{Cmd},\frac{{P}_{limit}}{L{d}_{Amp}},0)\\ LdVolt=LdVol{t}_{Cmd}\cdot \frac{1}{\tau s+1}\end{array}$$ 
Power loss for single efficiency source to load  $$Pw{r}_{Loss}=\frac{100Eff}{Eff}\cdot L{d}_{Volt}\cdot L{d}_{Amp}$$ 
Power loss for single efficiency load to source  $$Pw{r}_{Loss}=\frac{100Eff}{Eff}\cdot \leftL{d}_{Volt}\cdot L{d}_{Amp}\right$$ 
Power loss for tabulated efficiency  $$Pr{w}_{Loss}=f\left(L{d}_{Volt},L{d}_{Amp}\right)$$ 
Source current draw from DCtoDC converter  $$Sr{c}_{Amp}=\frac{L{d}_{Pwr}+Pr{w}_{Loss}}{Sr{c}_{Volt}}$$ 
Source power from DCtoDC converter  $$Sr{c}_{Pwr}=Sr{c}_{Amp}\cdot Sr{c}_{Volt}$$ 
Power Accounting
For the power accounting, the block implements these equations.
Bus Signal  Description  Variable  Equations  



 Source power to DCtoDC converter  P_{src}  ${P}_{src}=SrcPwr$ 
PwrBusLd  Load power from DCtoDC converter  P_{bus}  ${P}_{bus}=LdVolt$  
 PwrLoss  Converter power loss  P_{loss}  ${P}_{loss}=PwrLoss$  
 Not used 
The equations use these variables.
Volt_{Cmd}  DCtoDC converter commanded output voltage 
Src_{Volt}  Source input voltage to DCtoDC converter 
Ld_{Amp}  Load current of DCtoDC converter 
Ld_{Volt}  Load voltage of DCtoDC converter 
Src_{Amp}  Source current draw from DCtoDC converter 
τ  Conversion time constant 
V_{init}  Initial load voltage of the DCtoDC converter 
P_{limit}  Output power limit for DCtoDC converter 
Eff  Input to output efficiency 
Src_{Pwr}  Source power to DCtoDC converter 
Ld_{Pwr}  Load power from DCtoDC converter 
Pwr_{Loss}  Power loss 
LdVolt_{Cmd}  Commanded load voltage of DCtoDC converter before application of time constant 
Examples
Ports
Inputs
Output
Parameters
Extended Capabilities
Version History
Introduced in R2017b