Control Systems (TACS)

Transcription

1 U Transient Analysis of I Control Systems (TACS) Introduced in EMTP in 1976 Developed to model controls for HVdc converters (Pacific Intertie) Model interactions between system transients and control systems Each variant of EMTP has it own variant ATP has two: TACS and Models Intro to TACS 1 What TACS can do Model control systems» Generator excitation and governor control» Control loops for power electronic converters» Firing circuit for power electronics» Relay algorithms Intro to TACS 2 1

2 What TACS can do Monitor and post-process network variables» Analog and digital filters» RMS voltages and currents» Calculate P and Q» Compute motor/generator torque or flux» Reference frame transformations Intro to TACS 3 What TACS can do Simulate mechanical/electromechanical Non-linear reponses Create models for devices without built-in models for example, arc resistances Create harmonic sources Variable frequency sources Intro to TACS 4 2

3 U TACS Relationship to I Network Solution Control system models solved separate from network» Different equation formats» First network then TACS in each time step» Leads to on step time delay Power System (Network) Measurements Commands Controlled Sources TACS Intro to TACS 5 General Format TACS design from point of view of reproducing Laplace domain block diagram» Converted to difference equations» Arbitrary connections of blocks Signal and variable names limited to 6 characters Can implement digital controls Some limited FORTRAN expressions Intro to TACS 6 3

4 TACS and ATPDraw ATPDraw Interface for TACS» Not as nice as circuit interface, but much improved Not essentially to always draw connecting lines» Use the same variable names instead» Will generate a warning message about duplicate names when first run ATP file Several of the example cases shipped with ATPDraw have TACS modelling Intro to TACS 7 Built-in variables Enter these as input node names» TIMEX = simulation time in seconds (from 0.0)» ISTEP = number of time steps since the start of the simulation» DELTAT = simulation time step (TIMEX=ISTEP*DELTAT)» FREQHZ = system frequency in Hz (defined by first sinusoidal source in the Network part of the simulation)»omegar = 2 * * FREQHZ (rad/sec) Intro to TACS 8 4

5 Pre-Defined TACS Internal Sources» ZER0 = 0.0» MINUS1 = -1.0» UNITY = PLUS1 = 1.0» PI = FORTRAN Compiler Constant for PI Intro to TACS 9 User-Defined TACS Sources Used as inputs for other TACS blocks or to control a TACS source in the network User calls from TACS menu As is the case for network sources, the user defines start and stop time Intro to TACS 10 5

6 User-Defined TACS Sources Used as inputs for other TACS blocks or to control a TACS source in the network As is the case for network sources, the user defines start and stop time Options:» Type 11: DC Source (called Level Signal in rule book)» Type 14: Cosine (AC Source)» Type 23: Pulse (repeats, alternates between 0.0 and set amplitude» Type 24: Ramp (output rises from 0.0 to amplitude of set period and repeats until stop time for the source or end of simulation Intro to TACS 11 TACS Measurements from Network Used as inputs for other TACS blocks Type 90: Node voltage measurement» Node to ground voltage Type 91: Switch current» Must be connected to a switch Type 92: Internal variable from special ATP components (dynamic synchronous machine or universal machine) Type 93: Switch position (output = 0.0 for open switch and 1.0 for closed switch) Intro to TACS 12 6

7 Transfer Functions User can define general transfer functions Laplace domain polynomials in numerator and denominator Can have constant gain block (zero order on numerator and denominator) General Format: N 0 N 1 s N 2 s 2 N 3 s 3 Gs ( ) gain D 0 D 1 s D 2 s 2 D 3 s 3 N m s m D m s m Intro to TACS 13 Sample Transfer Function G(s) Intro to TACS 14 7

8 Limiters User can specify limits for transfer functions outputs»1 st order or zero order only» Can set hard (static) limits (enter numbers)» Can use outputs from other TACS functions (dynamic limits) Windup limiter» Zero order transfer function» TACS processes block and then looks at output» Prior to limit application, output can move far beyond limit» Time needed to back off of the limit Intro to TACS 15 Limiters (continued) Non-Windup limiter» Doesn t saturate and backs off limit quickly» Implement with first order transfer function One pole, no zeros in the function Additional poles and zeros are ignored Both windup and non-windup limits occur in practice» Need to understand behavior of the system you re modeling Intro to TACS 16 8

9 Built-In Devices Implement common functions difficult to make up» Frequency sensor» Externally controlled switch» Level switch» Transport delay» Pulse Delay» Digitizer» Point-by-point nonlinearity (lookup table)» Time controlled switch» Controlled integrator Intro to TACS 17» Derivative» Input-IF» Signal selector» Sample and track» Min/Max function» Min/Max tracking» Counter» True RMS Built-In Devices Intro to TACS 18 9

10 Free-Format FORTRAN Expressions Supplmental variables in rule book Somewhat free format ATP recognizes as device types 99, 98 and 88 Options:» Algebraic operators: +, -, *, /, **» Relational operators.eq.,.ne.,.lt.,.le.,.ge.,.gt. Ouputs are 0.0 or 1.0 Intro to TACS 19 Free-Format FORTRAN Expressions Allowed functions:» SQRT, ABS, EXP, LOG, LOG10» SIN, COS, TAN, COTAN (argument in radians)» ASIN, ACOS, ATAN (answer in radians)» SINH, COSH, TANH» TRUNC, MINUS, INVRS» RAD, DEG, NOT» SIGN (-1 for neg. number, +1 for pos. number or zero)» SEQ6, RAN (random number generator) Intro to TACS 20 10

11 Free-Format FORTRAN Expressions Limitations:» The user is allowed up to 20 levels of nesting.» Can't do SQRT(A**2+B**2) and similar» Can combine functions: SQRT(ABS(INVRS(X) ) )» Does not allow: GOTO, IF, DO, SUBROUTINE, or FUNCTION Intro to TACS 21 Outputs from TACS TACS controlled source in the network» Source type 60» The variable name in TACS and the name of the node the source is connected to must match» Including phase identifier (single phase source) TACS controlled switches Interface to type 59 (or 58) dynamic synchronous machine Interface to type 19 dynamic (universal machine) Plot data file Variable inductor.. Intro to TACS 22 11

12 Initial Conditions Can set initial conditions to improve start up behavior» Especially if correct outputs at time = 0+ are desired Network and TACS undergo separate steady-state initialization, with network computed first» TACS output to Network are initially zero unless specified Especially useful for:» First order or higher transfer functions» FORTRAN statements» Several of the built-in devices Intro to TACS 23 Accessing TACS Models Intro to TACS 24 12

13 TACS Sources Intro to TACS 25 TACS Devices Intro to TACS 26 13

14 TACS Measuring Source Intro to TACS 27 Source Dialog Intro to TACS 28 14

15 Transfer Function Intro to TACS 29 TACS Device Dialog Intro to TACS 30 15

16 FORTRAN Statement Intro to TACS 31 Slave Source Intro to TACS 32 16

17 Outputs from TACS TACS node: Type» 0=Output.» 1=Input signal positive sum up.» 2=Input signal negative sum up.» 3=Input signal disconnected.» (only necessary if node name is user specified) Intro to TACS 33 Node Dialog Intro to TACS 34 17

18 TACS Outputs Intro to TACS 35 Output Dialog Intro to TACS 36 18

19 RLC Circuit, Network and TACS Simple RLC circuit modelled as:» Network components» TACS only model» Results Compared Intro to TACS 37 ATPDraw Diagram GEN VSRC RL VLC U LDEL ISER VOUT LDEL U Intro to TACS 38 19

20 Compare Outputs 15 VOUT from TACS and VLC from Network * (file drawrlc.pl4; x-var t) t: VOUT v:vlc Intro to TACS 39 Example Results 15 Time Step Delay Between TACS and Network * (file drawrlc.pl4; x-var t) v:vlc v:ldel Intro to TACS 40 20