Download presentation

Presentation is loading. Please wait.

Published byRemington Wolfington Modified over 3 years ago

1
A 2-day course on POWER ELECTRONICS AND APPLICATIONS (DC Motor Drives) Universiti Putra Malaysia August, Dr. Nik Rumzi Nik Idris Department of Energy Conversion Universiti Teknologi Malaysia

2
**Contents Introduction Trends in DC drives DC motors**

Modeling of Converters and DC motor Phase-controlled Rectifier DC-DC converter (Switch-mode) Modeling of DC motor Closed-loop speed control Cascade Control Structure Closed-loop speed control - an example Torque loop Speed loop Summary

3
INTRODUCTION DC DRIVES: Electric drives that use DC motors as the prime movers DC motor: industry workhorse for decades Dominates variable speed applications before PE converters were introduced Will AC drive replaces DC drive ? Predicted 30 years ago AC will eventually replace DC – at a slow rate DC strong presence – easy control – huge numbers

4
Introduction DC Motors Advantage: Precise torque and speed control without sophisticated electronics Several limitations: Regular Maintenance Expensive Heavy Speed limitations Sparking

5
**DC Motors Introduction Rotor: armature windings Stator: field windings**

Current in Current out Stator: field windings Rotor: armature windings Mechanical commutator Large machine employs compensation windings

6
**dt di L i R v = Introduction Lf Rf if + ea _ La Ra ia Vt Vf**

Electric torque Armature back e.m.f.

7
**Introduction Armature circuit: In steady state,**

Therefore speed is given by, Three possible methods of speed control: Field flux Armature voltage Vt Armature resistance Ra

8
Introduction Armature voltage control : retain maximum torque capability Field flux control (i.e. flux reduced) : reduce maximum torque capability For wide range of speed control 0 to base armature voltage, above base field flux reduction Te Maximum Torque capability Armature voltage control Field flux control base

9
**MODELING OF CONVERTERS AND DC MOTOR**

POWER ELECTRONICS CONVERTERS Used to obtain variable armature voltage Efficient Ideal : lossless Phase-controlled rectifiers (AC DC) DC-DC switch-mode converters(DC DC)

10
**Modeling of Converters and DC motor**

Phase-controlled rectifier (AC–DC) 3-phase supply + Vt ia T Q1 Q2 Q3 Q4

11
**Modeling of Converters and DC motor**

Phase-controlled rectifier 3-phase supply + Vt Q1 Q2 Q3 Q4 T

12
**Modeling of Converters and DC motor**

Phase-controlled rectifier F1 F2 R1 R2 + Va - 3-phase supply Q1 Q2 Q3 Q4 T

13
**Modeling of Converters and DC motor**

Phase-controlled rectifier (continuous current) Firing circuit –firing angle control Establish relation between vc and Vt firing circuit current controller controlled rectifier + Vt – vc iref -

14
**Phase-controlled rectifier (continuous current)**

Modeling of Converters and DC motor Phase-controlled rectifier (continuous current) Firing angle control linear firing angle control Cosine-wave crossing control

15
**Modeling of Converters and DC motor**

Phase-controlled rectifier (continuous current) Steady state: linear gain amplifier Cosine wave–crossing method Transient: sampler with zero order hold T GH(s) converter T – 10 ms for 1-phase 50 Hz system – ms for 3-phase 50 Hz system

16
**Modeling of Converters and DC motor**

Phase-controlled rectifier (continuous current) Output voltage Control signal Td Cosine-wave crossing Td – Delay in average output voltage generation 0 – 10 ms for 50 Hz single phase system

17
**Modeling of Converters and DC motor**

Phase-controlled rectifier (continuous current) Model simplified to linear gain if bandwidth (e.g. current loop) much lower than sampling frequency Low bandwidth – limited applications Low frequency voltage ripple high current ripple undesirable

18
**Modeling of Converters and DC motor**

Switch–mode converters Q1 Q2 Q3 Q4 T + Vt - T1

19
**Modeling of Converters and DC motor**

Switch–mode converters + Vt - T1 D1 T2 D2 Q1 Q2 Q3 Q4 T Q1 T1 and D2 Q2 D1 and T2

20
**Modeling of Converters and DC motor**

Switch–mode converters Q1 Q2 Q3 Q4 T + Vt - T1 D1 T2 D2 D3 D4 T3 T4

21
**Modeling of Converters and DC motor**

Switch–mode converters Switching at high frequency Reduces current ripple Increases control bandwidth Suitable for high performance applications

22
**Modeling of Converters and DC motor**

Switch–mode converters - modeling + Vdc − vc vtri q when vc > vtri, upper switch ON when vc < vtri, lower switch ON

23
**Modeling of Converters and DC motor**

Switch–mode converters – averaged model vc q Ttri d Vdc Vt

24
**Modeling of Converters and DC motor**

Switch–mode converters – averaged model Vtri,p -Vtri,p vc d 1 0.5

25
**Modeling of Converters and DC motor**

DC motor – small signal model Te = kt ia ee = kt Extract the dc and ac components by introducing small perturbations in Vt, ia, ea, Te, TL and m ac components dc components

26
**Modeling of Converters and DC motor**

DC motor – small signal model Perform Laplace Transformation on ac components Vt(s) = Ia(s)Ra + LasIa + Ea(s) Te(s) = kEIa(s) Ea(s) = kE(s) Te(s) = TL(s) + B(s) + sJ(s)

27
**Modeling of Converters and DC motor**

DC motor – small signal model + -

28
**CLOSED-LOOP SPEED CONTROL**

Cascade control structure 1/s converter torque controller speed position + - tacho Motor * T* * kT It is flexible – outer loop can be readily added or removed depending on the control requirements The control variable of inner loop (e.g. torque) can be limited by limiting its reference value

29
**CLOSED-LOOP SPEED CONTROL**

Design procedure in cascade control structure Inner loop (current or torque loop) the fastest – largest bandwidth The outer most loop (position loop) the slowest – smallest bandwidth Design starts from torque loop proceed towards outer loops

30
**CLOSED-LOOP SPEED CONTROL**

Closed-loop speed control – an example OBJECTIVES: Fast response – large bandwidth Minimum overshoot good phase margin (>65o) Zero steady state error – very large DC gain BODE PLOTS Obtain linear small signal model METHOD Design controllers based on linear small signal model Perform large signal simulation for controllers verification

31
**CLOSED-LOOP SPEED CONTROL**

Closed-loop speed control – an example Ra = 2 La = 5.2 mH J = 152 x 10–6 kg.m2 B = 1 x10–4 kg.m2/sec kt = 0.1 Nm/A ke = 0.1 V/(rad/s) Vd = 60 V Vtri = 5 V fs = 33 kHz Permanent magnet motor’s parameters PI controllers Switching signals from comparison of vc and triangular waveform

32
**CLOSED-LOOP SPEED CONTROL**

Torque controller design Tc vtri + Vdc − q – kt Torque controller + - Torque controller Converter DC motor

33
**CLOSED-LOOP SPEED CONTROL**

Torque controller design Open-loop gain kpT= 90 kiT= 18000 compensated compensated

34
**CLOSED-LOOP SPEED CONTROL**

Speed controller design Assume torque loop unity gain for speed bandwidth << Torque bandwidth Torque loop 1 Speed controller * T* T – +

35
**CLOSED-LOOP SPEED CONTROL**

Speed controller Open-loop gain kps= 0.2 kis= 0.14 compensated compensated

36
**CLOSED-LOOP SPEED CONTROL**

Large Signal Simulation results Speed Torque

37
**CLOSED-LOOP SPEED CONTROL – DESIGN EXAMPLE**

SUMMARY Speed control by: armature voltage (0 b) and field flux (b) Power electronics converters – to obtain variable armature voltage Phase controlled rectifier – small bandwidth – large ripple Switch-mode DC-DC converter – large bandwidth – small ripple Controller design based on linear small signal model Power converters - averaged model DC motor – separately excited or permanent magnet Closed-loop speed control design based on Bode plots Verify with large signal simulation

Similar presentations

Presentation is loading. Please wait....

OK

DC Machines.

DC Machines.

© 2018 SlidePlayer.com Inc.

All rights reserved.

To make this website work, we log user data and share it with processors. To use this website, you must agree to our Privacy Policy, including cookie policy.

Ads by Google