Analytical Model of Electrical Machines in Business Software

This paper presents a possibility of using enterprise resource planning (ERP) business software for alternative analysis of electrical machines, with SAP ERP as an example of such software. Method presented is valid for all kinds of electrical machines. For the purpose of this paper, induction machine is processed. Analysis started with calculation of all six parameters of equivalent circuit, based on data determined by typical electrical measurements. Completion point is creation of steady-stay torqueslip curve. It is important to emphasize that only the standard SAP objects and functions are used for the whole procedure, without any additional programming.


INTRODUCTION
Power given by electrical machines is base source of mechanical energy for current industry requirement, so the need for finding a way for some alternative kinds of analysis and design of electrical machines is fully justified.This paper presents the new way of induction machine (IM) analysis done by typical ERP business software.
Dynamic states of electrical machines are described by voltage and mechanical nonlinear differential equations [1].By solving well known system for AC machines the steady state equivalent circuit of IM, together with formulas for calculation of the values of all six parameters of equivalent circuit can be defined.With further calculation it is easy to determine required expressions for impedance, torque, slip and current [2].This paper will not cover the process of finding correct formulas, but the process of including all required parameters and formulas in SAP and giving the final results in the form of steady-state characteristics.
The presented procedure has three basic steps: -calculation of IM parameters in SAP -preparation of the SAP structure for simulation -simulation in SAP and determining the needed values for steady-state curves creation.
Proposed solution is based on standard SAP objects (materials, classes, work centres, activity types, cost centres, routings and production orders) and three SAP business modules: Production Planning (PP), Variant Configuration (LO-VC) and Controlling (CO).All needed functionalities covered by these modules are described in detail in [3÷5].

CALCULATION OF IM PARAMETERS IN SAP
This procedure step has three technical steps in SAP: -creation of characteristics, classes and dependencies (for measured and calculated data) -creation of material and configuration profile -value calculation for all six IM equivalent circuit parameters (Fig. 1).
Symbols V1 and V2 stay for stator and rotor phase voltages, respectively.All parameters are defined in Tab.

Figure 1 Parameters of IM equivalent circuit
Nominal data of three phase slip-ring IM used in this example are: 1250 kW, 6000 V, 138 A and 1485 r/min [6].Some measured data were also available and for all of them SAP characteristics are created (Tab.1).In order to calculate all parameters of equivalent circuit, the standard form of LO-VC functionality is used.Based on measured data, three additional parameters should be calculated: Equivalent no-load power, Short circuit resistance and Short circuit reactance.For each of them, both characteristics and dependencies are created (Tab.2).Technical equations for them are well known [1].What will be shown is presentation of such equations in SAP, using characteristics and dependencies.Dependency for characteristic Equivalent no-load power (Z_FER_CO3) is shown in Figs.2a and 2b.Next task is calculation of all six equivalent circuit parameters (Tab.3).They should also be created in SAP as characteristics and their values are given by formulas in dependencies.All six dependencies from Tab. 3 are created in the same way as dependencies from Tab. 2. An example for Stator phase resistance (Z_FER_R01) is given in Fig. 5.After all parameters are connected and dependencies are created, the configuration object (SAP configurable material) should be defined (Fig. 6).After all dependencies are connected to material via configuration profile, configuration simulation can start.First step in configuration simulation is to enter measured values from Tab. 1.An easy way to use screen appears with possibility to enter all known values (Fig. 7).

Figure 7 Input of measured values
When all fields are filled, the final values for equivalent circuit parameters appear as calculated (Fig. 8).With values for these parameters, the system for simulation and creation of the steady-state characteristics is prepared.This process can be continued in the same way as calculating values for equivalent circuit parameters (using LO-VC as the only functionality needed), but in order to show different possibilities, some other options are tried out.needed for IM steady-state characteristic will be calculated by using two other SAP modules, PP and CO.

PREPARATION FOR SIMULATION
When using PP and CO modules, preparation for simulation consists of three technical steps in SAP: -creation of constants and formulas required for defining all parameters of IM equivalent circuit -creation of activity types, cost centres and work centres in order to collect all constants and formulas -creation of materials and routings.
All six parameters will be included in our procedure with the help of Formula constants, which are the basic part of Work centre master data.After all six parameters are defined, they can be used in formulas for electromagnetic torque and rotor / stator current.
What follows is the way for defining parameters and formulas in SAP.Fig. 9 shows the way for defining stator resistance R 1 .Parameter K1 is defined with the origin "Work centre constant":  For both of them User parameters in routings are used.Fig. 11 shows the way for defining synchronous speed as parameter with the origin "User defined field from operation".Slip will be used as main parameter for simulation.This parameter will be defined with the origin "General operational value" (Fig. 13).

Figure 13 Slip as SAP parameter
In parameter settings, existing connection with SAP field MGVRG (Operation quantity) is visible.

Formulas for Steady-State Analysis
Formulas from [2] will be used for static analysis.Five new parameters and five formulas for their calculation will be created in SAP.
The first parameter is σ 1 , the dissipation factor.It is defined as follows: In order to have the dissipation factor in SAP, a new parameter P01 (Fig. 14) with the origin "Standard value in the operation" and simple formula key F1 (Fig. 15) were created.
For breakdown slip s max , described by formula (2), SAP parameter P02 and formula key F2 are created: For breakdown torque T max , described by formula (3), parameter P03 and formula key F3 are created: Formula key F3, as a more complex example, is shown in Fig. 16.It is visible that space provided in SAP for formula definition could sometimes be a problem for complex technical equations.
Figure 16 Formula key for breakdown torque For electromagnetic torque T em , described by Eq. ( 4), parameter P04 and formula key F4 are created: For rotor current I' 2 , described by formula (5), parameter P05 and formula key F5 are created:

SAP Master Data
In order to include previously created formula keys and parameters in our analysis, three kinds of master data should be created in SAP: Materials, Work centres and Production routings.They will be simulation carriers.The first step is creation of material master data that will later be used for definition of slip value in percentage (Fig. 17).What follows is the inclusion of previously created parameters and formula keys in production work centres.

Figure 18 Simulation parameters as standard value key
For the beginning, the standard value key FER9 is specified, as group of parameters which will be monitored during simulation (Fig. 18).Then the formula keys F1 to F5 should be added to work centre and connect to corresponding parameter P01 to P05 (Fig. 19).

Figure 19 Formulas in Work centre
For existing material master data (slip), a Production routing should be created, as a basic set of master data needed for successful simulation (Work centre FER201 used in this example is one of parameters inside routing, Fig. 20).
After creating all parameters and formulas in SAP, the basic structure is ready for simulation and creation of steady-state characteristics.

SIMULATION
There are two more things to be done in SAP, in order to have a successful simulation with resulting steady-state characteristics: Technical Gazette 25, 2(2018), 582-586 -creation of Production order -several confirmations of Production order with collecting data for each confirmation.
For production order creation (Fig. 21) previously created Production routing is used as a template.Production order should be created for maximum slip value, 100 %.Simulation will be done through business activity named Production order confirmation.Orders will be confirmed for different slip values, from 1 % to 100 %.
Formulas F1 to F3 are slip independent, while formulas F4 and F5 are slip dependent.The last two formulas should be read for each simulation (Production order confirmation) step and given values for electromagnetic torque and rotor current should be collected.At the end, for these two parameters, simulation curves for steady-state model of induction machine can be created.All dots are calculated by SAP, but curve alone is created in excel.In the same way the curve for currentslip characteristic can be done.
In order to create such simulation curve in SAP, an additional ABAP (programming language used by SAP) program has to be created, because creation of such specific diagrams is not provided by standard SAP ERP software.

CONCLUSION
The possibility of using business software for analysis of electric machines is still an unknown area whose research requires specific combination of competent knowledge and experience in at least three scientific fields: electrical engineering, business processes and ERP systems.
This paper presents a case with induction machine analysis using SAP ERP as business software.Here, it is described how to calculate the values of equivalent circuit parameters, how to transform technical equations to SAP formula keys and how to get steady-state torque-slip characteristic.Three SAP modules are used, with only standard functionalities, and without any additional programming.
The next and third possible step in using ERP software for electrical machinery analysis is related to the area of business decision making.First research done in this field showed the possibility of helping highpositioned managers (as "natural" users of ERP software) in finding quick answers to critical questions regarding feasibility, costs and scheduling of possible projects.If such option is accepted, then this paper can be viewed as a solid base for the very first step in that direction.

Figure 2
a) Characteristics used in dependency Z_FER_CO3, b) Formula in dependency Z_FER_CO3 Dependency for characteristic short circuit resistance (Z_FER_CO4) is shown in Figs.3a and 3b.a) b) Figure 3 a) Characteristics used in dependency Z_FER_CO4, b) Formula in dependency Z_FER_CO4 Dependency for characteristic short circuit reactance (Z_FER_CO5) is shown in Figs.4a and 4b.a) b) Figure 4 a) Characteristics used in dependency Z_FER_CO5, b) Formula in dependency Z_FER_CO5

Figure 5
Figure 5 Dependency for stator phase resistance

Figure 6
Figure 6 IM as Configurable material FER_AM01

Figure 8
Figure 8 Calculated equivalent circuit parameters So, in the next section one different way of formula processing in SAP is described.Value of parameters

Figure 9
Figure 9 Stator resistance definitionFig.10 shows example of grouping all six parameters of IM equivalent circuit.

Figure 10
Figure 10 IM equivalent circuit parameters After all six parameters are included in SAP, two additional parameters should be created: -nominal voltage (KP1) -synchronous speed (KP2).

Figure 11
Figure 11 Synchronous speed as SAP parameterAfter both user parameters are defined, they should be grouped under User fields key (FER_01, Fig.12):

Figure 12
Figure 12 Voltage and synchronous speed as user fields

Figure 14 Figure 15
Figure 14 Dissipation factor as SAP parameter

Figure 17
Figure 17 Slip as material in SAP

Figure 20
Figure 20 Work centre as part of Production routing

Figure 21
Figure 21 Production order for simulation

Figure 22
Figure 22Results for slip = 10 % and 20 % Fig.22shows the SAP screens for production order confirmation for two simulation steps and slip's values of 10 % and 20 %.

Fig. 23
Fig.23shows the final curve (created in excel) for steady state torque-slip characteristic.All dots are calculated by SAP, but curve alone is created in excel.In the same way the curve for currentslip characteristic can be done.In order to create such simulation curve in SAP, an additional ABAP (programming language used by SAP) program has to be created, because creation of such specific diagrams is not provided by standard SAP ERP software.

Table 1
Measured data and SAP Characteristics