Inter-Ing 2007
„INTERDISCIPLINARITY IN ENGINEERING”
SCIENTIFIC INTERNATIONAL CONFERENCE,
TG. MUREŞ – ROMÂNIA, 15 -16 November 2007.
DEVICE FOR THE D.C. – D.C. CONVERTERS PWM COMMAND
Alexandru MORAR
“Petru Maior” University of Tg.-Mures, Romania
morar@upm.ro
Abstract: The author presents in this paper an electronic device for the PWM command of the twoquadrant of four-quadrant choppers. A simple construction and enhanced operation safety, very smooth
regulation of the duty cycle, 11 values programming for the working frequency (500Hz – 5KHz), TTL or
CMOS compatibility are some of the advantages presented by this electronic device.
Keywords: PWM device, 2-Q chopper, 4-Q chopper, saw tooth voltage generator.
1. Introduction
A spectacular evolution in the field of the electric energy conversion has been produced
by the emergence and development of new power semiconductor devices which facilitated the
power converter improvement and diversification, interposed between the power supply and the
electrical device motor.
The d.c.– d.c. converter, also known as chopper, is frequently used for the separatelyexcited d.c. motors speed regulation, being a converter which transforms a d.c. voltage, applied
to the input, into rectangular pulses to the output. The average value of a chopper’s output
voltage can be modified between zero and the feeding voltage, using the “Pulse Wawe
Modulation” principle of constant frequency pulses. In this way it is possible to achieve the
regulation by voltage of the d.c. motors speed [1],…,[5].
The block diagram of such an electrical drive system is presented in Fig. 1.
IBM PC
COMPUTER
FOUR QUADRANT CHOPPER
V+
+U
T1
PWM1
DBUS ABUS
PWM SIGNAL
GENERATOR
V+
K
u
PWM
PROT
Lf
D3
DIGITAL
PART
CBUS
INTERFACE
T3
D1
T2
PWM2
T4
D2
DRIVER
D4
-
?
LOAD
+
COMP
-
LEM
OPTICAL
ENCODER
V+
A BN
P1
(FREQUENCY)
P2
(DUTY CYCLE)
Fig. 1. Block diagram of d.c. electrical drive system.
IV-24-1
Ex
M
i
+
There are schemes of chopper operating in two or four quadrants, largely used in practice.
The H bridge converters are widely utilized in the adjustable electrical drives with d.c. motors.
An arm of this bridge is obtained by serially connecting two controllable power switching
devices (bipolar transistors, MOSFET, IGBT, GTO, MCT). Each device has an antiparallel
diode, called “free-wheeling diode”. The two devices of an arm structure work anti-phase like. In
practice, for passing from a state into another, the devices will be simultaneously blocked for a
short length of time, called “dead time ”[4], [5], [9]. The PWM command signal can be
generated either with the IBM-PC computer, in this case being necessary a specialized interface
and the required software tools, or with a special electronic device. Taking into consideration
what has already been revealed the authors present in this paper an electronic device for PWM
commanding the two or four quadrant chopper.
2. Device’s description
The command circuit for choppers, realized with traditional electronic means, are widely
used. The block diagram from where it can be deduced the operating principle of the device for
the chopper’s PWM command is presented in Fig. 2. There has been made the following
notations: OSC-astable circuit; M-monostable circuit; CD1, CD2-discharging circuits, GTLV1,
GTLV2-variable linear voltage generators; CS-selection circuit; CE-output circuit.
DUTY CYCLE=50%
I0
K
V+
+
K1
[50-0]%
K2
R1
C1
R2
OSC
CD1
I1
C1
C2
GTLV1
V+
= =
T
T
+
[50-100]%
T
-
FOUR QUADRANT CHOPPER
I2
CE
PWM-CMOS
C2
BS
PWM
K3
R3
C3
M
PWM1
DP
R4
CD2
PWM-TTL
T
V+
C4
GTLV2
+
T
TWO QUADRANT CHOPPER
-
[0-100]%
PROT
I3
PWM2
T
C3
A1
A0
K1
K0
V+
P
(DUTY CYCLE)
Fig. 2. Block diagram of the PWM device.
The signal from the astable circuit output, of programmable frequency and duty cycle
50%, is applied to a sawtooth voltage generator, composed by the discharging circuit CD1 and
the variable linear voltage generator GTLV1.
In the four-quadrant choppers case, the sawtooth voltage is compared to a reference
voltage fixed with the potentiometer P by the comparators COMP1 and COMP2. At the output of
these comparators there are obtained PWM signals with adjustable duty cycle in the range of
[50-100]% (clockwise drive) respectively [50-0]% (anticlockwise drive).
In the two-quadrant chopper case, the signal from the astable circuit output is applied at
the monostable circuit M input. The very short time pulses from the monostable output command
a second sawtooth voltage generator made in the CD2 discharging circuit and the variable linear
IV-24-2
voltage generator GTLV2. The sawtooth voltage is compared with the same reference voltage by
the COMP3 comparator, at whose output it is obtained PWM signal with the duty cycle
adjustable in the range [0-100]%.By means of the switches K0, K1 and of the selection circuit CS
it is selected: the signal with the duty cycle 50% from the OSC astable circuit output (resting
motor),the PWM signal with the duty cycle adjustable in the range [50-100]% (clockwise
electrical drive motor), the PWM signal with the duty cycle adjustable range [50-0]%
(anticlockwise electrical drive motor), or the PWM signal with the duty cycle adjustable in the
range [0-100]% (two-quadrant choppers command).Through the intermediary of the CE output
circuit , the device provides PWM signal TTL or CMOS compatible. Meantime, through the
intermediary of a DP digital command part, there are also generated PWM command signals with
“dead time” for the power semiconductor devices of the half-bridge and full-bridge converter.
The electrical schematic of the programmable oscillator is shown in Fig. 3.
1K10
1K9
1K8
1K7
1K6
1K5
1K4
1K3
IC1
+5
OSC
14
13
OSC
10
11
+5
+5
TRIGTRIG+
OSCO
AST
AST
Q
Q
EXT RES
RETRIG
C
R
R-C COM
GND
1K2
6
8
4
5
9
12
1K1
C2
R2
S1
S2
S3
S4
S5
S6
S7
S8
S9
S10
R1
1
2
3
C1
7
CD4047BE
RESET
Fig. 3. Electrical schematic of the programmable oscillator.
Nowadays, the CMOS integrated circuits imposed them selves as a dominant family
among the other families of digital circuits [6], [7].There are to be emphasized the following
advantages: low consumption power, enhanced immunity at perturbations, absence of input
current. Consequently, it has been utilized the integrated circuit MMC 4047. There has also been
utilized a rotating switch K with 3 sections and 11 positions each. The first section 1K1-1K10 is
utilized for the working frequency programming (11 values in the range 500Hz-5kHz ), the other
2 section (2K1-2K10 and 3K1-3K10) being utilized within the two variable linear voltage
generators. The 11 working frequencies values are established by means of 10 multiturn
adjustable resistances S1-S10.
In Fig. 4 it is presented the electrical block diagram of the PWM generator for the fourquadrant choppers command.
The variable linear generator is realized with constant current generator and with the
capacitor C1 [8] whereas the discharging circuit is realized with the transistor T2.The 10 multiturn
adjustable resistances S1-S10 are in or off the circuit trough the intermediary of the second section
of the rotating switch K. Thus, for any value of the working frequency, the maximum amplitude f
the sawtooth remains the same, Umax (see Fig.5).Consequently, the smoothness of the duty cycle
regulation remain the same, very good, for every selected value of the working frequency. Led
with the emitter-repeater realized with the operational amplifier I2A of type TLO84, the sawtooth
voltage is applied to the comparators I3A, I3B of type betaM 339, where it is compared with the
prescribed command voltage by means of the multiturn potentiometer P.
The electrical schematic of the PWM generator for the two-quadrant chopper command is
presented in Fig. 6. The constant current generator realized with the transistor T1 together with
the capacitor C1 forms a second variable linear voltage generator.
IV-24-3
+15
2K10
2K9
2K8
2K7
2K6
2K5
2K4
2K3
2K2
2K1
R3
S1'
S2'
S3'
S4'
S5'
S6'
D1
S7'
D2
D3
S8'
S9'
T2
S10'
C3
R4
-15
+5
IC3AF
PM2
15
PM4
+15
C5
CD4050BCN
IC3AE
11
R8
R7
6
5
2
6
I1A
C_PM4
R6
9
IC4C
TL084ACN
8
P_PM3
COM
+5
R9
C7
PM5
+15
R12
9
R13
8
I2A
C_PM5
C_PM2
C9
CD4050BCN
+15
Fig. 4. Electrical schematic of the PWM generator for the 4-Q choppers.
Fig. 5. Logic timing diagram of the PWM generator for the 4-Q choppers.
IV-24-4
C8
R15
IC5C
KA339
14
3
3
T1
NPN
C
4
CD4050BCN
IC3AA
R11
R14
IC5B
KA339
1
4
CD4050BCN
IC3AB
R5
10
11
C4
7
7
PM3
12
CD4050BCN
IC3AC
OSC
R10
12
14
+15
3K10
3K9
3K8
3K7
3K6
3K5
3K4
3K3
3K2
3K1
R16
S1''
S2''
S3''
S4''
S5''
D4
S6''
S7''
D5
D6
S8''
S9''
T4
S10''
C11
R17
IC3BD
9
CD4050BCN
IC3BB
+5
6
8
OSC
4
5
+5
9
12
RESET
R18
C12
1
2
3
7
IC2
TRIGTRIG+
+5
OSCO
AST
AST
Q
EXT RES
RETRIG
C
R
R-C COM
GND
CD4047BE
Q
14
10
5
PM6
10 C_PM6
4
CD4050BCN
IC3BE
13
11
11
12
CD4050BCN
IC3BA
3
2
C13
R21
R19
T3
NPN
6
B
+5
PM8
R22
10
R23
11
IC5D
KA339
13
R24
I3A
C_PM8
R20
CD4050BCN
IC3BF
14
5
PM7
IC4B
TL084ACN
7
C_PM7
15
COM
CD4050BCN
Fig. 6. Electrical schematic of the PWM generator for the 2-Q choppers
By means of the multiturn adjustable resistances S1”-S10” as well as of the third section of the
rotating switch K, it is modified the variable linear voltage slope so that, indifferent of the
working frequency value, the maximum amplitude is the same Umax. The discharging circuit,
realized with the transistor T2, is commanded by the very short-time pulses obtained at the I1
monostable circuit output of the type MMC 4047(see Fig. 7).
Fig. 7. Logic timing diagram of the PWM generator for the 2-Q choppers.
IV-24-5
The signal provided by the astable circuit OSC (duty cycle 50%) as well as the signals of
the PWM command of the four-quadrant (I1a and I2a) and the two-quadrant (I3a) choppers are
applied to the dual 4-line to 1-line multiplexer I3 of type CDB 4253E (see Fig. 8).Thus, through
the intermediary of the switches K1, K0 the desired PWM signal is selected (see Table 1).
+5
R27
1
OSC
DM7407N
I1A
I2A
I3A
SN7400N
R25
11
13
+5
SN7400N
R28
DM7407N
C?
+5
7
R?
U?B
Y2
9
3
4
DM7407N
SN74153N
R?
C?
C?
+15
+15
1
U?A
DM74ALS04BN
6
6
8
4
5
9
12
1
2
3
7
6
8
4
5
9
12
1
2
3
7
2
U?A
3
2
13
10
TRIG- VCC
14
TRIG+
OSCO
Q
+15
AST
AST
U?
CD4047BE
EXT QRES
11
RETRIG
R-C COM
GND
13
10
TRIG- VCC
14
TRIG+
OSCO
Q
+5
U?
CD4047BE
AST
AST
SN7400N
R30
EXT QRES
11
RETRIG
2
R-C COM
3
1
C
R
C
R
R26
IC6A
GND
+5
PWM_TTL
GND
R?
SN7400N
D8
PWM_CMOS
R?
IC6B
5
1
P?
4
+5
R29
4
16
+15
Y1
2OE
2C0
2C1
2C2
2C3
8
C?
+5
K2
1OE
1C0
1C1
1C2
1C3
15
10
11
12
13
IC6D
VCC
U?B
3
4
PM12
D7
+5
A
B
1
6
5
4
3
8
10
12
14
2
2
IC6C
U?
R?
U?A
KA339
2
3
9
K1
+5
U?A
+5
5
12
R?
2
CD4011BCN
PROT1
5
P?
U?B
5
4
6
U?B
6
CD4011BCN
C?
P?
3
CD4001BCN
P?
PROT1
+15
U?A
1
PWM1
P?
4
CD4001BCN
PWM2
C?
Fig. 8. Electrical schematic of the selection circuit, output circuit and digital part.
K1
0
0
1
1
K0
0
1
0
1
PWM-TTL
50%
[50-0]%
[50-100]%
[0-100]%
Table 1
The working modes.
PWM-CMOS
Obs.
50%
STOP
[50-0]%
FOUR-QUADRANT CHOPPER
[50-100]%
FOUR-QUADRANT CHOPPER
[0-100]%
TWO-QUADRANT CHOPPER
The output circuit CE is composed by the TTL-CMOS interface realized with the
comparator I4A of type betaM 339 and the noninverting buffers I2B of type MMC 4050 for
obtaining the CMOS-PWM signal and I5A of type CDB 407E for obtaining the TTL-PWM signal.
In Fig. 8 it is also presented the electrical schematic of the digital command part by means of
which there are obtained the “dead-time” command signals PWM1, PWM2 of the power
semiconductor devices within the half-bridge and full-bridge converter.
3. Experimental results.
The experimental researches has been made in the Electrical Drives Laboratory of the
Engineering Faculty, “Petru Maior” University of Targu- Mures. The general view of the PWM
IV-24-6
devices is shown in Fig. 9. It is has been integrated in a high-performance trial stand dedicated to
the separately-excited d.c. motors driving systems command.
As experimental results, the command PWM signal of a different working frequency, are shown
in Fig. 10.
Fig. 9. General view of the PWM device.
4. Conclusions
The electronic device for the choppers PWM command presented in this paper has the following
advantages:
• Very smooth regulation of the duty cycle indifferent of the working frequency value;
• The programming possibility, in the range of 500Hz – 5kHz, of the working frequency
value;
• Offers complementary PWM signals with “dead-time”;
• Offers PWM signal, TTL or CMOS compatible, for commanding two or four quadrant
choppers.
References
1 . Leonard W., Control of Electrical Drives, Springer-Verlage, Berlin, 1985.
2 . Mohan N., Undeland T., Robbins W., Power Electronics-Converters, Application and Design, John Wiley
& Sons , New York, 1989.
3 . Străinescu I., Variantelor statice de tensiune continuă. Editura Technică, Bucureşti, 1983.
4. Bogdanov I., Microprocesorul în comanda acţionărilor electrice.Editura Facla, Timişoara, 1989.
5 . Kelemen A., Imecs M., Electronică de putere. Editura Didactică şi Pedagogică, Bucureşti, 1980.
6. Ardelean I., Giurgiu H., Petrescu L., Circuite integrate CMOS. Manual de utilizare. Editura Technică,
Bucureşti, 1986.
IV-24-7
Fig. 10. PWM command signals of different working frequencies
IV-24-8
7. Băluţa Gh., Circuite logice şi structuri numerice.Proiectare şi aplicaţii. Editura Marix Rom, Bucureşti, 1999.
8 . Mitrofan Gh., Generatoare de impulsuri şi de tensiune liniar variabilă. Editura Technică, Bucureşti, 1980.
9 . Băluţa Gh., Insulated Gate Bipolar Transistors Based Reversible PWM Converter for D.C. Motors. Bul.
Inst. Polit., Iaşi, XLIV (XLVIII), 1-4, s. IV, 49-57 (1998).
10. Morar A., Diaconescu I., Circuite digitale. Circuite logice combinaţionale, Editura Universităţii “Petru
Maior” Tg. Mureş, 2003 .
11. .Morar A., Diaconescu I., Circuite digitale. Circuite logice secvenţiale, Editura Universităţii “Petru
Maior” Tg. Mureş, 2005
12. Morar, A. Electronică digitală –Aplicaţii şi probleme- Editura MEDIAMIRA cluj Napoca, 2007.
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