Real Time DSP Based 3phase Signal Synth

8/3/2019 Real Time DSP Based 3phase Signal Synth

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REAL TIME DSP-BASED3-PHASE SIGNAL

SYNTHESIZER


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DSP BASED REAL TIME TESTSIGNAL GENERATOR

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REAL TIME DSP-BASED3-PHASE SIGNAL SYNTHESIZER

OUTLINE

Motivation, issues

Example test signals

Signal generation: block diagram

Implementation in CProgramming organization, benefits, rules


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MOTIVATION

Example application: 3-phase powerelectronics - control synchronization

Requirement for various test signals: phase & frequency step modulation

amplitude step modulation

notching

imbalance

other distortion & noise types

OBJECTIVE: minimize code developmenteffort, from block diagram to code


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UNDERLYING ISSUES

Development testing in real timeAvailability and affordability of real time DSP, ex.:

Analog Devices ADSP-21161 200 MHz floatingpoint DSP

Programming: block diagram level programmingpreferred

object oriented approach

Ex.: MatLab/Simulink, C++

BUT: excessive underlying overhead and code,reduced efficiency and execution speed


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PROPOSED APPROACH

Given C language:popular

efficient compilation

interfaceable to assembly language code

struct-ure based syntax, and function pointersTransportability across different h/w platforms

Can effectively translate block / data flow diagramlevel design into C code, for most efficient

execution, development, and maintainability Important point: insist on rigorous, but simple,

programming rules


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EXAMPLE TEST SIGNALS

3-phase signal synthesis, with:

Harmonic distortion (BD)

Notching distortion (CDN)

AS BD CDN


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SYNTHESIS: FUNCTIONAL BLOCK DIAGRAM

Main functional blocks:

3-phase sinusoid generator, with FM and PM (here: fixedfrequency

3-phase harmonic addition

3-phase notching

DAC analog output

3- GENERATOR

A

B

Input C

Ko o

3- HARMONICS

A A

B B

C C

H(k)

3-phase

signals

ab

c

3- NOTCHING

A A

B B

C Notch C

specs

{ Ni }{ h1 , h2 , h3 }Ko o

DAC

0

1

2

3

4

5

6

7

V0V1V2V3V4V5V6

V7

AS BD CDNGen_3phase_0 Dist_3phase_0 Notch_3phase_0


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TOP LEVEL CODE IMPLEMENTATION IN C

// The translation of the block diagram into C code:

// 1. Refer to pre-defined data types and prototypes:

#include Gen_3phase.h // Pre-compiled building blocks

#include DSP_hardware.h // Hardware specific declarations

// 2. Declare functional blocks, assigning names (optional; required forward

// declaration when feedback is involved, ex. PLL):

//Type name user-defined (type names defined in Gen_3phase.h)

// variable (object)

// name

State_3phase Gen_3ph_0 ; // 3-phase clean signal generation unitDistortn_3ph Dist_3ph_0 ; // Harmonic distortion unit

Notching_3ph Notch_3ph_0 ; // Notching distortion unit

// NOTE: DAC output unit pre-existing in DSP hardware pre-compiled library


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DEFINE OBJECTS OPERATING PARAMETERS

// 3. Define functional block operating parameters:

State_3phase Gen_3ph_0 = // 3-phase generator unit{ Gen_3phase, 60*2*pi, 0, 0, 0 } ;

// Handler, 60 Hz freq, no frequency or phase modulation

Distortn_3ph Dist_3ph_0 = // Harmonic distortion unit

{ Dist_3phase, &Gen_3ph_0.A, &Gen_3ph_0.B, &Gen_3ph_0.C,// Handler, addresses of A-B-C and phase source signals

&Gen_3ph_0.Phase, { 0.3, 0.05, 0.03 } } ;// generator phase, and specify 3-rd to 15-th odd harmonic levels

Notching_3ph Notch_3ph_0 = // Define notching operator

{ Notch_3phase, &Dist_3ph_0.A, &Dist_3ph_0.B, &Dist_3ph_0.C,// Handler, addresses of A-B-C distorted signals

&Gen_3ph_0.Phase, // Signal phase0.2*pi, 0.25*pi, 0.2 , // Specs for 3 notches:1.2*pi, 1.30*pi, 0.5 , // start angle, end, depth1.6*pi, 1.70*pi, 0.0 } ;


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DEFINING A LIST OF OBJECTS FOR EXECUTION

// 4. Define a list of objectsto execute:

// Object: defined in file Gen_3phase.h

Object *Gen_3ph_list [ ] = // Define list of objects to execute

{ (void*) &Gen_3ph_0 , //Address of 3-phase sine generation unit

(void*) &Dist_3ph_0 , //Address of harmonic distortion unit(void*) &Notch_3ph_0 , //Address of notching distortion unit

0 } ; //0:mandatory end of list

// 5. Define list of signals of interest for DAC output and scope observation:

float Signals_3ph[8] = // 8 DAC outputs available

{ &Dist_3ph_0.A, &Dist_3ph_0.B, &Dist_3ph_0.C,

&Gen_3ph_0.Phase, &Dist_3ph_0.B, &Notch_3ph_0.C } ;


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MAIN PROGRAM: INITIALIZATION

// 6.Main program: initialize hardware and pointer to list of objects:

void main (void) {pDAC_signals = Signals_3ph ; // List of signals for DAC o/ppObject_list = Gen_3ph_list ; // List of objects to execute

Init_DSP_hardware (DSP_isr); // Hardware specific initialization// Execute function DSP_isr at sampling ratewhile (1) ; // Repeat forever, or process user input

} // main()

From perspective of main application programming: thats all,and the main present focus of interest


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CODE DEVELOPMENT: 3 STAGES

1. Application level: from block diagram to C code; as in previousexample

by application programmer: minimal C skills, follow

example template

specify:

- various objects (variables)- operating parameters

- connections, i.e. via addresses (C & syntax)

2. Underlying, pre-existing functional units:

> in pre-compiled (object) library

> defined (described) in pre-existing header (.h) file

3. Basic I/O at hardware level for specific platform


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BENEFITS

Application developed at level of block diagram: clearestand simplest

Simple rules to follow, easily copied from exampletemplate, minimal C programming skills required

Object-oriented approach, without undue underlying

overhead; minimal reduction of execution efficiency

C code easily transportable (compiled) for any hardwareplatform

MOST IMPORTANT: strict adherence to programmingrules, best captured in example templates


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EXECUTING A LIST OF OBJECTS

Given, in Gen_3phase.h:

typedef struct Object {pFunc (*pFn)(struct Object *pS) ; // Common to all objects

} Object ;

The following pre-exists in pre-compiled library:

void DSP_func (void){ // Executed at sampling rate

Object **pList = Gen_3ph_list ; // Point to object list

for ( ; *pList ; pList++ ) // Repeat till end of list(*pList) -> pFn(*pList) ; // Call function, pass Object address

} // DSP_func()


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TRANSLATING BLOCK SYMBOL TO CODE

3- GENERATOR

A

B

Input C

Ko o

SourceSignal

(variable)

Source

Signal

(variable)

Constant Constant

3- GENERATOR

Angle

Freq

*p

*pF

A

B

C

KO o

Signal

flow

Code:

Ref.

To

(addr)

SOURCE BLOCK

DIAGRAM NOTATION

Handler

function

*

(void*) &Gen_3ph_0


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OBJECT DEFINITION 3-PHASE SINE GENERATOR

underlying, pre-existing, previously defined, user-defined object types,found in file Gen_3phase.hC keywords: typedef and struct

// This defines, once and for all, the 3-phase generator data (object) type,// its interface, and internal state variables:

typedef struct State_3phase {pFunc (*pFn) (struct State_3phase *pG3ph) ; //MUST = Gen_3phasefloat Phase, // Current phase angle, rads

Wo , // Center frequency, rad./sec.Ko , // Freq. control sensitivity*pFctrl, // Freq. control signal addr.*pPhCtrl , // Phase control signal addr.A, B, C ; // 3-phase output signals

} State_3phase ; // Name of new data type


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INTERNAL OBJECT BEHAVIOUR

underlying, pre-existing, previously compiled, user-definedobject type handler function, in file Gen_3phase.Cof least interest to present discussion

void Gen_3phase (State_3phase *pG3ph) {// This defines the internal operation of the 3-phase sine generator, with phase and// frequency modulation

pG3ph->Phase += pG3ph->Wo ; // Advance phasepG3ph->Phase += (*(pG3ph->pFctrl)) * pG3ph->Ko ; // Freq ctrl input

if (pG3ph->Phase > pi) // Keep phase:pG3ph->Phase -= 2*pi ; // -pi < Phase < pi

pG3ph->A = sin (pG3ph->Phase + *pG3ph->pPh_ctrl) ; // Phase ctrl inputpG3ph->B = sin (pG3ph->Phase + *pG3ph->pPh_ctrl - 2*pi/3) ;pG3ph->C = - pG3ph->A - pG3ph->B ; // Phase C = -A B

} // Gen_3phase()


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CONCLUSIONS

Based on these simple organization and guidelines, andstrict adherence to simple rules, other functional unitscan be easily developed and added to library

Simplified programming at top, block diagram equivalent,level, with minimal to no C programming skills required

3 stages of development:

Main application level, simplest translation from block diagram toC code

Collection of functional objects, in C, transportable to anyplatform

Hardware level I/O for specific platform


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THANK YOU

Real Time DSP Based 3phase Signal Synth

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