Download PWM - Altervista

Elevator Drives - Discussion
•
•
•
•
•
History
Requirements
Motor and Control Types
Industry Trends
Future Drives
History
• 236 BC – First Passenger Lift,
Archimedes
• 1853 – Safe Elevator Demo,
Elisha Otis
• 1857 – First Safe Elevator
Installation,
Cooper Union, NYC
• 1861 – Otis Elevator Patent
Otis Patent 1861
History
• 1873 – First Modern DC Motor
• 1874 – J. W. Meaker Door Opener Patent
• 1880 – First Electric Motor Controlled
Elevator Siemens / Sprague
• 1882-1889 – Tesla AC Induction Motor
3-Phase Squirrel Cage Design
• 1889 – Otis Elevator Uses DC Motor
Otis
DC
Elevator
Motor
Circa 1889
History
• 1891 – Ward Leonard Variable
Speed Control
– AC Induction Motor Turning DC Dynamo
– Rheostat to Control Generated Voltage
– DC Voltage Controls DC Motor Speed
• 1900-1970’s – Ward-Leonard M-G Sets
and DC Motors Used for
Variable Speed Elevators
• AC Motors Used 1 and 2 Speed Starters
Otis No. 1 Geared DC Machine
with DC Motor
Circa 1915
Otis Gearless DC Machine
Circa 1919
M-G Set Controls
(Otis Elevator, 1920’s)
Otis Type
84 26
Broadway,NYC
Circa 1930’s
History
• 1975-Present
– Thyristor (SCR) DC Drives
Control Elevators
– All Analog Components in the 70’s
– Replaces Aging M-G Sets
• 1980’s – Microprocessors Improve
– Car Dispatch and Motor Drive Controllers
Otis type 84,NYC
with Encoder
Westinghouse #205
with Encoder
History
• Late 1980’s –
– Variable Frequency Inverters AC Induction Motors,
Geared Applications Only
• Early 1990’s –
– More AC Inverters and Motors Begin to Displace
Small DC, 3-15 HP
• Mid-1990’s –
– Vector Control AC Inverters 10-40 HP Almost as
Good as SCR-DC.
– KONE Introduces PM EcoDisc AC Machine
History
 Late 1990’s –
– Custom Gearless AC Induction Machines
– First Fully Regenerative AC
Elevator Drives
– Much Discussion on PM-AC and MRL
– SCR-DC Still Used for Medium and
Large Building Mods
History
2000-Present –
– More PM-AC Motor Manufacturers. PM Gearless Begins to
Replace AC Geared
– EU Focus on Efficiency and Harmonics/EMC
– Lower Cost IGBT Inverter Components
– North America Begins to Focus on Energy Reduction
– New Construction Leaning toward AC
– SCR-DC Still Used on Medium-Large Building Mods
Four Quadrant Operation
LSC
Umot, Imot
Linear power stage
Vcc
time
controller
R
M
Gnd
UT
Umot
advantages
– simple, low priced controller
– low electromagnetic noise level
– no minimum inductance needed
disadvantages
– high power losses at the final stage at
high currents or low motor voltages
(PV = R I2)
– for small nominal power up to 100 W
advantages
Pulsed
power
stage (PWM)
V
– low power losses
– high efficiency
– for higher nominal
power
disadvantages
– electromagnetic
noise in the radio
frequency range
– high power losses
in the motor at
standstill
cc
pulse
generator
Gnd
Umot, Imot
Umot
M
power
stage
ADS,
DEC, AECS, DES,
MIP, PCU, EPOS
time
cycle time: 20 - 50 ms
Imax 
Pulsed power stage: current
general measures:
ripple
V
 reduce motor voltage
cc
2  fS  (Lmot  L choke )
 enhance total inductance
- motor choke in controller
- additional motor choke
 enhance PWM frequency
50% 50%
low motor inductance
additional motor choke
Umot, Imot
30% 70%
frequency kHz
50
Time
scales
in1 control
loops
10
5
2
0.5 0.2
0.1
0.05
20
mechanical time constants
"slow" position controller
position controller MIP
speed controller
speed controller as "link" between
fast current controller and a slow
position control (PLC)
current
controller
PWM cycle time
0.02
0.05
0.1
0.2
0.5
1
2
5
10
20 ms
cycle time
PWM
• PWM(Pulse Width Modulation
• Cambiando il duty cycle, la velocità cambierà
 Lo scopo è :
1. Ridurre la dissipazione di potenza.
2. Ridurre I problemi di raffreddamento dei transistors)
Duty Cycle 20%
Lowest Speed
Cycle
Duty Cycle 50%
Middle Speed
Duty
Cycle
(DT)
Duty Cycle = DT / T (%)
Figure : PWM Control Signal
Duty Cycle 80%
High Speed
Duty cycle
• si definisce duty cycle d il rapporto tra la
durata del segnale "alto" ed il periodo
totaleT del segnale, e serve ad esprimere per
quanta porzione di periodo il segnale è a
livello alto:
t
d

T
• PWM
Un segnale PWM (Pulse Width Modulation
ovvero modulazione a variazione della
larghezza d'impulso) è un' onda quadra di
duty cycle variabile che permette di
controllare l'assorbimento (la potenza
assorbita) di un carico elettrico(nel nostro
caso il motore DC), variando modulando)
il duty cycle.
• Un segnale PWM è caratterizzato dalla
frequenza (fissa) e dal duty cycle
(variabile);
• si deduce dalla Figura, il duty cycle è il
rapporto tra il tempo in cui l'onda
assume valore alto e il periodo T
(l'inverso della frequenza: T=1/f)
• Es. un duty cycle dell'80% corrisponde
ad un'onda quadra che assume valore
alto per l'80% del tempo e basso per il
restante 20%,
DC Motor Drives
DC motor speed control using Switching Control or PWM
Voltage
Source
Vs
Vout
Diode
rectifier
Filter
capacitor
P ulse Widt h
%Dut y cycle =
x 100
Cycle
Full-bridge
DC-DC
converter
PWM
Pluse-width-modulation
Vout = % Duty cycle x Vs
M
Power Electronic converter
H-bridge converters circuit
Vcc
A
ON
G
Q1
D1
D3
Q3
G
D2
Q2
G
OFF
B
ON
D
M
C
OFF
G
Q4
D4