OpenDSS Documentation

kWrating:double;

Rated power output for the Storage element, kW.

kWhRating :Double;

Rated energy storage capacity, kWh.

kWhStored :Double;

Present amount of energy in the storage element, kWh.

kWhReserve :Double;

Reserve level of storage element, kWh. The storage element would generally not be discharged below this level.

ChargeEff :Double;

Charging efficiency, pu.

DisChargeEff :Double;

Discharging efficiency, pu.

kVArating :Double;

Voltampere rating of inverter, kVA.

kVStorageBase:Double;

Base voltage for the Storage element, kV L-L or 1-phase kV.

kvarRequested:Double;

Reactive power output requested, kvar. Could be + or -.

RThev :Double;

Equivalent resistance used for simple Thevenin equivalent, ohms.

XThev :Double;

Equivalent reactance used for simple Thevenin equivalent, ohms.

Vthev :Complex;

Thevenin equivalent voltage (complex) for default dynamic model.

ZThev :Complex;

Thevenin impedance used for default dynamics model.

Vthevharm :Double;

Thevenin equivalent voltage magnitudefor Harmonic mode model.

Thetaharm :Double;

Thevenin equivalent voltage angle reference for Harmonic model.

VthevMag:Double;

Thevenin equivalent voltage magnitude for dynamic model.

Theta :Double;

Power angle between voltage and current for dynamic model.

w_grid:Double;

Grid frequency, radians/s.

TotalLosses:Double;

Present value of total losses in Storage element.

IdlingLosses :Double;

Idling losses in Storage element

NumPhases,

Number of phases in the Storage element terminal (only one terminal).

NumConductors,

Total Number of conductors in the Storage element terminal. 1-phase elements always have 2. If wye-connected, 3-phase, there will be 4.

Conn :Integer

Terminal connection. 0 = Wye (or L-N); 1 = Delta (or L-L)

Function New

( Var DynaData : TDynamicsRec; Var CallBacks : TDSSCallBacks) : Integer; Stdcall;// Make a new instance

This function creates a new instance of the model defined by the DLL. It returns an integer handle to the instance that may be used to specifically select this instance at a later time.

User-written DLLs should have some mechanism for keeping track of instances of the class represented by the DLL. This could be a simple array of pointers or a linked list or some other mechanism of the programmer’s choosing. There is no internal OpenDSS mechanism to support this. Each Storage object that creates a DynaDLL model will keep track of only the one that belongs to it and use the Select function to instruct the DLL with instance to make active.

Arguments:

DynaData: The TDynamicsRec structure is passed by reference. This contains the time variables for a typical dynamics simulation. This is defined as follows.

TDynamicsRec = Packed Record

h, // Time step size in sec for dynamics

t, // sec from top of hour

tstart,

tstop:Double;

IterationFlag:Integer;

{0=New Time Step; 1= Same Time Step as last iteration}

SolutionMode :Integer;

intHour :Integer; // time, in hours as an integer

dblHour :Double; // time, in hours as a floating point number including fractional part

End;

CallBacks: The callback structure is passed by reference. See OpenDSS Callback Routines documentation. The user-written DLL would typically keep a pointer to this structure and call the functions and procedure in it to obtain specific data or to use internal OpenDSS functions such as messaging.

Procedure Delete

(var ID:Integer); Stdcall; // deletes specified instance

This procedure deletes a specific instance referenced by the ID. This is the value returned by the New function when the instance was created.

Function Select

(var ID:Integer):Integer; Stdcall; // Select active instance

This function selects an instance of the objects instantiated by the DLL. The ID is the value returned by the New function. ID is passed by reference (i.e., expect a pointer to an integer).

If successful, the function retuns the ID as confirmation. If the return value is 0, there has been an error.

Procedure Init

(V, I:pComplexArray);Stdcall;

This procedure is called when the OpenDSS is entering Dynamics mode from one of the power flow modes. Two pointers to complex number arrays are passed representing the present voltage, V, and current, I, at the Storage element terminals. The user-written DLL uses these values to perform whatever calculations are required to initialize the active model.

Procedure Calc

(V, I:pComplexArray); stdcall;

This procedure invokes the main electrical calculation algorithm of the model. This will nearly always be to compute the terminal currents, I, given the present estimate of the voltages, V, and internal state variables.

V and I are pointers to complex number arrays. There will be one complex value for each conductor of the Storage element terminal. If there is any question how many conductors are present, the GetActiveElementTerminalInfo call back

function may be called or, for the Storage element, the values are available on the public data structure.

Procedure Integrate;

stdcall; // Integrates any state vars

This procedure is called by the OpenDSS in Dynamics mode when it is time to integrate the state variables if the model uses differential equations.

OpenDSS currently uses a two step predictor-corrector integration process. The IterationFlag variable of the TDynamicsRec structure indicates with step is currently being executed. If IterationFlag=0, the predictor step is being executed. If it is =1 the corrector step is being executed.

Most other models in the OpenDSS use a forward Euler for the predictor step and trapezoidal for the corrector step. The derivatives from the previous time step – necessary for the trapezoidal integration step – are captured during the predictor step.

Procedure Edit

(EditStr:pAnsichar; Maxlen:Cardinal); Stdcall;

The Edit procedure is called when the OpenDSS encounters the DynaData=(MyString) property definition in the script. MyString is passed to this procedure in the EditStr argument as a pointer to a null-terminated Ansi character string. It is up to the Edit procedure in the DLL to interpret the string and properly set any variables. The callbacks to the OpenDSS parser may be used to help interpret the string if an OpenDSS-like syntax is used.

The length of the string is passed in the Maxlen argument, which is pushed onto the calling stack in case it is expected by the language in which the DLL is implemented (some languages expect this argument).

Note that it is not necessary to support OpenDSS syntax. Any format may be used for the data required to define the model. If the model requires an extensive amount of data, one approach is to pass a file name in MyString and have the DLL’s Edit procedure read the data from the file.

Procedure UpdateModel;

StdCall;

This procedure is called by OpenDSS when it thinks it is necessary to recalculate model parameters from the present values of the data used to describe the models. Many models will not need this, but it is provided. It is typically called after calling the Edit procedure.

Function NumVars:

Integer;Stdcall; // Number of variables that can be returned for monitoring

This function returns the number of double-precision variables that can be accessed.

Procedure GetAllVars

(Vars:pDoubleArray);StdCall;

This Procedure is called by OpenDSS monitor elements and is expected to return the values of all the exposed model variables in an array of doubles. The OpenDSS will allocate the necessary space and pass a pointer to the buffer in the Vars argument.

Function GetVariable

(var i:Integer):double;StdCall; // returns a i-th variable value only

This function returns the value of the i-th variable. Note that i is passed by reference, That is, the user-written program should expect to receive a pointer to this index.

Procedure SetVariable

(var i:Integer;var value:Double); StdCall;

This procedure is provided to allow the user to set the value of a variable internal to the model. Both arguments are passed by reference. That is, the user-written program should expect to receive pointers to the values of these arguments.

The DLL is not obligated to set the internal variable to the value and should not permit it if it will break the model.

Procedure GetVarName

(var VarNum:Integer; VarName:pAnsiChar; maxlen:Cardinal); StdCall;

This procedure is provided to obtain the name assigned to a monitor or state variable. Monitor elements defined as Mode=3 will automatically query the names using this function.

VarNum is the index of the variable name requested and will be passed by reference (i.e., expect a pointer to an integer).

The OpenDSS will allocate space for VarName, a null-terminated Ansi character string, and pass the size of the allocation in the maxlen argument, which is an unsigned integer passed by value. The DLL implementation of this procedure will copy the string name of the requested variable into the buffer up to the limit given by maxlen.