---

Component 156: Power Converter

---

Specification

Line Connection
1	Power Inlet
2	Power Outlet
3	Power Loss

General     User Input Values     Physics Used     References     Displays     Example

 

General

Component 156 (Power Converter) is used to model a power inverter that changes direct current (DC) to alternating current (AC), or a power rectifier that converts from AC to DC. In practice, the conversion may be performed either by means of electronic circuits or utilizing rotating mechanical equipment. In the simulation model, the heat losses of the electronics and the necessary shaft power to drive the rotating equipment are both expressed in terms of the conversion efficiency relative to the inlet power.

For simulation of photovoltaic inverters the performance model for grid-connected PV inverters developed by Sandia National Laboratories, USA (SAND2007-5036) can be used.  For this performance model, an extensive collection of data sets has been implemented in the default values library of component 156.

 

User Input Values

FMODE	Flag to set the calculation mode Design / Off-design Like in Parent Profile (Sub Profile option only) Expression =0:   Global =1:   local off-design (i.e. always off-design mode, even when a design calculation has been done globally) =-1: local design (i.e. always design mode, even when a off-design calculation has been done globally)
FEFF	Method for specification of efficiency model Like in Parent Profile (Sub Profile option only) Expression =0: Use FEFFand curve CEFF =1: Use SANDIA performance model (SAND2007-5036)
FVOLT	Method for specification of outlet voltage Like in Parent Profile (Sub Profile option only) Expression =0: Defined by specification value VOLT =1: Set externally
U2	Outlet voltage
FFREQ	Method to specify outlet frequency Like in Parent Profile (Sub Profile option only) Expression =0: Use specification value FREQ =1: Frequency given externally on electrical outlet
FREQ	Outlet frequency
NPHAS	Flag to set the type of outlet current Like in Parent Profile (Sub Profile option only) Expression =0: Direct Current =1: One-phase alternating current =3: Three-phase alternating current (Note: The specification of the current type at the inlet of the component is made via component 1 / component 33 on the electrical inlet line)
EFF	Efficiency
FEFFOD	Method for part load calculation Like in Parent Profile (Sub Profile option only) Expression =0: Constant design efficiency EFFN =1: Use correction curve CEFF (Q1/Q1N)
SMODEL	Inverter Model Name
VAC	AC voltage output
PACO	Maximum  AC power rating
PDCO	DC power level at which the AC power rating is achieved
VDCO	DC voltage level at which the AC power rating is achieved
PSO	DC power required to start the inversion process (self-consumption)
C0	parameter defining the curvature (parabolic) of the relationship between AC power and DC power at the reference operating condition, default value of zero gives a linear relationship, (1/W)
C1	empirical coefficient allowing PDCO to vary linearly with DC voltage input, default value is zero, (1/V)
C2	empirical coefficient allowing PSO to vary linearly with DC voltage input, default value is zero, (1/V)
C3	empirical coefficient allowing C0 to vary linearly with DC voltage input, default value is zero, (1/V)
PNT	AC power consumed by inverter at night (night tare) to maintain circuitry required to sense PV array voltage, (W)
VDCMAX	Maximum DC voltage
IDCMAX	Maximum DC current
MPPTLOW	Maximum power point lower voltage limit
MPPTHIGH	Maximum power point upper voltage limit
Q1N	Nominal inlet power
EFFN	Nominal efficiency

Result values

RLOAD	Calculated load
REFF	Calculated efficiency
QLOSS	Calculated losses
QAPP	Calculated apparent outlet power
QREAL	Calculated outlet power
QREACT	Calculated reactive outlet power
COSPHI2	Outlet power factor

Physics Used

Design Calculations

In design mode of the simple efficiency model, the user has to specify

For the current input into the transformer, the following are defined

• the active power
• the current type (number of phases), setting via boundary value or start value.
   (The forwarding of NPHAS takes place in the direction of flow. If lines with different NPHAS are brought together, the value of the main input is used).
   main input is used). 
   and
• the input voltage is determined by the upstream component or the power factor cos(phi) by the downstream components.

In design mode of the simple efficiency model, the user has to specify the conversion efficiency with the parameter EFF.  The resulting outlet power Q2 will be calculated as Q2 = Q1*EFF, and if a logic line is connected to port 3, the respective losses will be written into the stream value Q (energy flow).  Type of current, voltage and frequency of the electric line connected to the outlet port 2 of the power converter will  be set as per the specifications of the user.   

The SANDIA PV Inverter Performance Model (selected with Efficiency Model FEFF = 1) allows for describing the performance characteristic of a specific PV inverter type with a set of parameters. Since these data are derived from experiments with commercially available PV inverters, thus they already represent a fixed design.  If a pre-configured data set for a specific inverter type is selected from the default value library, the respective value for PDCO (DC power level at which the AC power rating is achieved) will be used for the nominal inlet power Q1N, and design point efficiency EFFN will be derived from the ratio PACO/PDCO. 

Off-Design Performance with Simple Model

Depending on the setting of the method flag FEFFOD, the off-design calculation will use the design efficiency (FEFFOD = 0: Constant design efficiency EFFN), or the efficiency will depend on the ratio of inlet power to nominal inlet power as per the correction factor defined in the characteristic CEFF. The outlet power will then be calculated as Q2 = Q1*EFFN*CEFF(Q1/Q1N). 

Off-Design Performance with SANDIA PV Inverter Performance Model

The Sandia performance model for grid-connected PV inverters (SAND2007-5036) describes the AC power output of the inverter (PAC) as a function of DC inlet power (PDC) with the following set equation:

 

    PAC = [(PACO/(A - B)) - C * (A - B)] * (PDC - B) + C * (PDC - B)^2

 

The coefficients A, B and C are calculated with linear dependency of the DC inlet voltage (VDC) and type-specific parameters that describe DC power and voltage at rated AC power and the self-consumption at nominal DC voltage.

   A = PDCO * [1 + C1 * (VDC - VDCO)]

   B = PSO* [1 + C2 * (VDC - VDCO)]

   C = C0* [1 + C3 * (VDC - VDCO)]

The individual parameters and coefficients are displayed with the same variable name as used in component 156, see the section User Input Values above. In addition, the data set for the PV inverter may include operating limits for maximum DC power and DC voltage, the range for DC voltage at the maximum power point which are checked in the calculation, if present. For information, the AC power consumed by the inverter at night to maintain circuitry required to sense PV array voltage is listed, but not actively used in the calculation.

 

Characteristics Lines

Characteristic line 1 (CEFF):  electrical efficiency

Characteristic line 1:  electrical efficiency

X-Axis         1          Q1/Q1N                    1st point                         2          Q1/Q1N                    2nd point                         .                         N         Q1/Q1N                    last point      Y-Axis          1        electrical efficiency EFF/EFFN (CEFF)          1st point                         2         electrical efficiency EFF/EFFN (CEFF)          2nd point                         .                         N        electrical efficiency EFF/EFFN (CEFF)          last point

---

 

Component Displays

Display Option 1

Example

Click here >> Component 156 Demo << to load an example.