Bài giảng Điện tử công suất: Bộ nghịch lưu, biến tần Power Inverter (phần 2) - PGS.TS Lê Minh Phương

Bài giảng Điện tử công suất: Bộ nghịch lưu, biến tần Power Inverter (phần 2) cung cấp cho người học những kiến thức về bộ nghịch lưu áp 3 pha. Trong bài này chúng ta sẽ tập trung vào nguyên lý làm việc, phương pháp điều khiển và mô phỏng Matlab-Simulink của bộ nghịch lưu áp 3 pha. Mời tham khảo.

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PGS.TS Lê Minh Phương

Khoa Điện –Điện Tử

Trường Đại Học Bách Khoa

TPHCM

2012

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d Mô hình hóa bằng Matlab-Simulink

3 Bộ nghịch lưu dòng

b Nguyên lý làm việc

d Mô hình hóa bằng Matlab-Simulink

Contents – Nội dung

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The switches of any leg of the

inverter (S1 and S4, S3 and S6,

or S5 and S2) cannot be

switched on simultaneously because this would result in a short circuit across the dc link voltage supply

Bộ nghịch lưu áp 3 pha

Bộ nghịch lưu áp - VSI

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Period VI: Q4, Q5 and Q6 on

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VcN=1/3(2Vc0-Va0-Vb0) Vca=Vs(g5-g1)

Waveforms, phase voltage on load

Note:

vg1 and vg4 are complimentary

Va0 is controlled by g1, g4

Vb0 is controlled by g3, g6

Vc0 is controlled by g5, g2

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Analysis

PGS.TS Le Minh Phuong

1/21/2013

Trị hiệu dụng điện áp dây có thể tính

Điện áp tải tức thời theo phân tích Fourier

2 0,8165 3

V  V  V

1,3,5,

4 sin sin sin

s ab

s an

V  V  V

Trị hiệu dụng hài cơ bản điện áp tải:

Dòng điện tải tức thời theo phân tích Fourier

4 sin 60

0.770 2



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Note: In practical design, the neutral of capacitors is not grounded

because of the grounded three phase power supply

vn: voltage of load neutral respect to ground

vA0: voltage of node A respect to ground

vB0: voltage of node B respect to ground

vC0: voltage of node C respect to ground

Neutral point grounded three-phase inverter

Load neutral voltage

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 Thành phần hài bậc bộ số của 3 bằng 0 (triple -

order harmonics are not presented)

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(1) Modulating waves: three-phase

sinewaves (vmA, vmB, vmC) with

adjustable amplitude and frequency (2) Carrier wave: triangular wave, fixed amplitude, frequency may be adjusted, depends on applications (3) vmA≥vc →Q1 on

vmA<vc →Q4 on vg1 and vg4 are complementary

(4) vmB≥vc →Q3 on vmB<vc →Q6 on vg3 and vg6 are complementary

(5) vmC≥vc →Q5 on vmC<vc →Q2 on vg5 and vg2 are complementary

Điều chế độ rộng xung Sin (SINPWM)

Also, the inverter output voltage has the following features:

ƒ PWM frequency is the same as the frequency of Vtri

ƒ Amplitude is controlled by the peak value of Vcontrol

ƒ Fundamental frequency is controlled by the frequency of Vcontrol

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(4) vmB≥vc →Q3 on→vB0=Vs/2 vmB<vc →Q6 on→vB0=-Vs/2 vg3 and vg6 are complementary

(5) vmC≥vc →Q5 on→vC0=Vs/2 vmC<vc →Q2 on→vC0=-Vs/2 vg5 and vg2 are complementary

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Phân tích phổ điện áp dây tải

The three-phase VSI Ideal waveforms for

the SPWM (ma = 0.8, mf = 9):

(d) ac output voltage;

(e) ac output voltage spectrum;

The harmonics in the ac output voltage appear at normalized

frequencies fh centered around

mf and its multiples, specifically,

at h = l mf ±k l= 1, 2,

where l = 1, 3, 5, for k = 2, 4,

6, and l = 2, 4, For k = 1,5,

7, Such that h is not a

multiple of 3 Therefore, the

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Phân tích phổ dòng điện DC-link

The three-phase VSI Ideal waveforms for

the SPWM (ma = 0.8, mf = 9:

(g) dc current; (h) dc current spectrum;

For nearly sinusoidal ac load current, the harmonics in the dc link current are at frequencies

given by h = l mf ± k ± 1 l = 1, 2, where l = 0, 2, 4, for k =

1, 5, 7, and l = 1, 3, 5, for

k = 2, 4, 6, such that h = l ·

mf ± k is positive and not a

multiple of 3 For instance, Fig

shows the sixth harmonic (h =

6), which is due to h = 1 · 9 − 2

− 1 = 6

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The three-phase VSI Ideal waveforms for the SPWM (ma = 0.8, mf=9):

(i) switch S1current; and

(j) diode D1 current

In the linear region (ma ≤ 1) the maximum amplitude of the

fundamental ac output line voltage is √3vi /2 Therefore, one can write

To further increase the amplitude of the load voltage, the amplitude of

the modulating signal ˆvc can be made higher than the amplitude of the

carrier signal ˆv, which leads to overmodulation The relationship

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Square-wave Operation of Three-phase VSIs

(c)ac output voltage; and

(d) ac output voltage spectrum

Large values of ma in the

SPWM technique lead to full

overmodulation This is known as square-wave operation as illustrated in Fig, where the power valves are

on for 180◦

The ac line output voltage

contains the harmonics fh,

Where h = 6 · k ± 1 (k = 1, 2,

3, ) and they feature amplitudes

that are inversely proportional

to their harmonic order

Sinusoidal PWM with Zero Sequence Signal Injection

This approach expands the range of the linear region as it allows

the use of modulation indexes ma up to 2/√3 without getting into the

overmodulating region

A zero sequence signal is added to the modulating signals before they are compared to the carrier

signal

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Zero sequence signal generator (ma = 1.0, mf = 9):

(b) modulating signals; and

(c) zero sequence and modulating signals with zero sequence injection

The addition of the zero sequence reduces the peak amplitude of the resulting modulating

signals (uca , ucb , ucc ),

while the fundamental

components remain

unchanged

The maximum amplitude of the fundamental phase voltage in the linear

region ma ≤ 2/√3 is vi /2, thus, the maximum amplitude of the

fundamental ac output line voltage is vi

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The three-phase VSI Ideal

waveforms for the SPWM (ma = 0.8,

mf = 9) with zero sequence signal injection:

(a) modulating signals;

(b) carrier and modulating signals with zero sequence signal injection;

(c) switch S1 state;

The three-phase VSI

Ideal waveforms for the

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Selective Harmonic Elimination in Three-phase VSIs

As in single-phase VSIs, the SHE technique can be applied to

three-phase VSIs

The harmonics multiples of 3 (h = 3, 9, 15, ), could be present in the

phase voltages (vaN , vbN , and vcN ), and will not be present in the

load voltages (vab, vbc , and vca )

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Chopping angles for SHE and fundamental voltage

control in three-phase VSIs: fifth and seventh harmonic elimination

The three-phase VSI Ideal waveforms for the SHE technique: (a)

phase voltage vaN for fifth and seventh harmonic elimination;

(b) spectrum of (a); (c) line voltage vab for fifth and seventh harmonic

elimination; and (d) spectrum of (c)

Selective Harmonic Elimination in Three-phase VSIs

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(2) At t1, ia reaches the UBL→vg1=“0”→vg4=“1”→

G4on→ia↓ until t2 (3) At t2, ia reaches the LBL

→vg1=“1”→vg4=“0”→G1

on→ia↑

As a result, the actual current ia will be

kept within the upper and lower band limits

If reference current is sine wave, actual current is also sine wave on which some high order harmonics are superimposed High order harmonics can be filtered out easily

No low order harmonics

Inverter output current can be accurately

controlled

Phương pháp điều chế theo dòng điện

Delta Modulation

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Power Electronics

For Building

THANK YOU FOR YOUR ATTENTION



1/21/2013

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