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AD2S100

AC Vector Processor

Analog Devices 

AD2S100

SIMPLE SLIP CONTROL

In an adjustable-frequency drive, the control strategy must en-

sure that motor operation is restricted to low slip frequencies,

resulting in stable operation with a high power factor and a high

torque per stator ampere. Figure 12 shows the block diagram of

simple slip control using the AD2S100. Here, the slip frequency

command ω2 and the current amplitude command are sent to

the microprocessor to generate two orthogonal signals, |I| Sin θ

and |I| Cos θ here (θ = ω2.) With the actual shaft position angle,

φ, (resolver-to-digital converter) and the orthogonal signals from

(I) SET

SLIP

FREQ

dθ

ω2 = dt

Ia

I Sinθ

µPROC I Cosθ AD2S100 Ib

Ic

PWM

+

INVERTER

AC

INDUCTION

MTR

φ

AD2S80A RDC

RESOLVER

Figure 12. Slip Control of AC Induction Motor with

AD2S100

the µP, the AD2S100 generates the inverter frequency and am-

plitude command into a three-phase format. The three-phase

sine wave reference currents are reproduced in the stator phases.

For general applications, both the steady-state and dynamic per-

formance of this simple control scheme is satisfactory. For de-

tailed information about this application, please refer to the

bibliography at the end of the data sheet.

ADVANCED PMSM SERVO CONTROL

Electronically commutated permanent magnet synchronous

motors (PMSM) are used in high performance drives for

machine tools and robotics. When a field orientated control

scheme is deployed, the resulting brushless drive has all the

properties required for servo applications in machine tool fed

drives, industrial robots, and spindle drives. These properties

include large torque/inertia ratio, a high peak torque capability

for fast acceleration and deceleration with high torsional stiff-

ness at standstill.

Figure 13 shows the AD2S100 configured for both forward and

reverse transformations. This architecture concludes both flux

and torque current components independently. The additional

control of Vd (flux component) allows for the implementation

of field weakening schemes and maintenance of power factor.

ω ref

+

PI

–

Iqref

+

–

+

Idref

–

Vq

PI

Vd

PI

AD2S100

e–jφ

2/3

INV +

PWM

Id

Iq e+jφ

Va

Vb

3/2 Vc

AD2S100

PMSM

φ

AD2S82

ω

Figure 13. PMSM Servo Control Using AD2S100

For more detailed information, please refer to the application

note “Vector Control Using a Single Vector Rotation Semicon-

ductor for Induction and Permanent Magnet Motors.”

MOTION CONTROL DSP COPROCESSOR

AC induction motors are superior to dc motors with respect to

size/power ratio, weight, rotor inertia, maximum rotating veloc-

ity, efficiency and cost for motor ratings greater than 5 HP.

However, because of nonlinear and the highly interactive multi-

variable control structure, ac induction motors have been con-

sidered difficult to control in applications demanding variable

speed and torque.

Field orientated control theory and practice, under development

since 1975, has offered the same level of control enjoyed by tra-

ditional dc machines. Practical implementation of these algo-

rithms involves the use of DSP and microprocessor based

architectures. The AD2S100 removes the needs for software

implementation of the rotor-to-stator and stator-to-rotor trans-

formations in the DSP or µP. The reduction in throughput

times from typically 100 µs (µP) and 40 µs (DSP) to 2 µs in-

creases system bandwidths while also allowing additional fea-

tures to be added to the CPU. The combination of the fixed

point ADSP-2101 and the AD2S100, the “advanced motion

control engine” shown in Figure 14, enables bandwidths previ-

ously attainable only through the use of floating point devices.

For more detailed information on the AD2S100 vector control

application and on this advanced motion control engine, please

refer to application notes “Vector Control Using a Single Vector

Rotation Semiconductor for Induction and Permanent Magnet

Motors.”

MEASUREMENT OF HARMONICS

Three-phase ac power systems are widely used in power genera-

tion, transmission and electric drive. The quality of the electric-

ity supply is affected by harmonics injected into the power main.

In inverter fed ac machines, fluxes and currents of various fre-

quencies are produced. Predominantly in ac machines the 5th

and 7th harmonics are the most damaging; their reaction with

the fundamental flux component produces 6th harmonic torque

pulsations. The subsequent pulsating torque output may result

in uneven motion of the motor, especially at low speeds.

The AD2S100 can be used to monitor and detect the presence

and magnitude of a particular harmonic on a three-phase line.

Figure 15 shows the implementation of such a scheme using the

AD2S100. Note, the actual line voltages will have to be scaled

before applying to the three-phase input of the AD2S100.

Selecting a harmonic is achieved by synchronizing the rotational

frequency of the park digital input, φ, with the frequency of the

fundamental flux component and the integer harmonic selected.

The update rate, r, of the counters is determined by:

r

=

4096

n×ω

2π

Here, r = input clock pulse rate (pulses/second);

n = the order of harmonics to be measured;

ω = fundamental angular frequency of the ac signal.

–10–

REV. A

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