1 frequency conversion technology developing
process
The frequency conversion technology is should the
alternating current machine stepless speed regulation need to be born.
The 20th century 60's latter half issue starts, the electric
power electronic device from SCR (crystal thyratron), GTO (gate
extremely may shut off crystal thyratron), BJT (double pole power
transistor), MOSFET (metal oxidizes object field effect tube), SIT
(electrostatic induction transistor), SITH (electrostatic induction
crystal thyratron), MCT (MOS control transistor), MCT (MOS control
crystal thyratron) develops today IGBT (insulation grid double pole
transistor), HVIGBT (bears high-pressured insulation grid double pole
crystal thyratron), the component renewal urges the electric power
transformation technology the unceasing development. The 20th
century 70's start, the pulse-duration modulation live pressure
frequency conversion (PWM-VVVF) modulated velocity the research to
cause the people highly to take. The 1980s, are attracting
people's strong interest as the frequency conversion technology core
PWM pattern optimization question, and obtain many optimized patterns,
are best by the saddle shape wave PWM pattern effect. The 1980s
latter half issue starts, America, the date, Germany, England and so
on the developed country VVVF frequency changer sixth branch invests
the market and the widespread application.
VVVF frequency changer control relatively simple, physical
characteristics degree of hardness is also better, can satisfy the
general transmission the smooth velocity modulation request, obtained
the widespread application in industrial each domain. But, this
control mode when low frequency because output voltage smaller, quite
is been remarkable the stator resistance pressure drop influence,
therefore creates the output biggest torque to reduce. Moreover,
its physical characteristics eventually does not have the direct
current motor to be hard, dynamic torque ability and static velocity
modulation performance all also not entirely as desired, therefore the
people study the vector control frequency conversion velocity
modulation.
The vector control frequency conversion velocity modulation
procedure is: Exchanges iA, iB, iC the asynchronous motor under
three-phase coordinate system stator through the three-phase - two
phase transformation, equivalent becomes under two static coordinate
systems the alternating currents i alpha, i beta, again through
presses the rotor magnetic field direction detection to revolve the
transformation, equivalent becomes synchronization to revolve under
coordinate system direct current IM, IT (IM is equal to direct current
motor exciting current, IT is equal to has direct ratio with torque
armature electric current). Then the imitation direct current
motor control method, obtains the direct current motor the control
quantity, passes through the corresponding coordinates inverse
transformation, realizes to the asynchronous motor control.
The vector control method proposed has the epoch-making
significance. However in practical application, because the
rotor flux linkage accurately observes with difficulty, system
performance electric motor parameter influence bigger, also uses
矢量旋转 the transformation in the equivalent direct current motor
controlled process to be more complex, causes the actual control
effect to achieve the ideal analysis with difficulty the result.
In 1985, German Lu you university's Professor Dcpenbrock
proposed the direct torque control frequency conversion technology for
the first time. This technology has solved the above vector
control insufficiency in the very great degree, and by the novel
control thought, the succinct bright system structure, the fine sound
of something astir condition performance obtained the rapid
development. On the other day, this technology successfully has
applied in the high efficiency exchange transmission which the
electric locomotive tows.
The direct torque control directly analyzes the motor under the
stator coordinate system the mathematical model. Control motor
flux linkage and torque. It does not need to turn into the motor
the equivalent direct current motor, thus has omitted 矢量旋转 in
transformation many complex computations; It does not need to
imitate the direct current motor the control, also does not need as
解 to simplify the motor the mathematical model.
The VVVF frequency conversion, the vector control frequency
conversion, the direct torque control frequency conversion all hands
over - is straight - hands over in the frequency conversion one kind.
Its common shortcoming is the power input factor low, the
harmonic current is big, the direct current return route needs the big
stored energy electric capacity, the regeneration energy cannot feed
back the electrical network, namely cannot carry on four quadrants
movements. Therefore, the matrix type hands over - hands over
the frequency conversion to arise at the historic moment.
Because the matrix type handed over - hands over the frequency
conversion to omit the middle direct current link, thus omitted the
volume to be big, the price expensive electrolysis electric capacity.
It can realize the power factor is 1, the input current for the
sine also can four quadrants movements, the system power density be
big. This technology at present although not yet was mature, but
still attracted the multitudinous scholar thoroughly to study.
2 frequency conversion technologies and domestic
electric appliances
The 20th century 70's, the domestic electric appliances
start the gradually frequency conversion, appeared the
electromagnetism cooking, the frequency conversion illumination
appliance, the frequency conversion air-conditioner, the frequency
conversion microwave oven, the frequency conversion electric
refrigerator, IH (感应加热) the food ? the frequency conversion
washer and so on.
The 1990s latter half issue, the domestic electric appliances
depend on the frequency conversion technology, mainly aims at the high
function and the province electricity. For instance, the request
has high speed high strives, the control performance well, small
轻量, large capacity, the high comfortable feeling, the long life,
safe is reliable, static merit and so on sound, province electricity.
First is the electric refrigerator, because it is in the
around-the-clock, after uses the frequency conversion refrigeration,
the compressor throughout occupies the low speed running status, may
thoroughly eliminate the noise which because the compressor starts
causes, the energy conservation effect is more obvious.
Next, after the air-conditioner use frequency conversion,
expanded the compressor operating region, does not need the compressor
to move under off and on the condition may realize, the warm control
coldly, achieved reduces the power consumption, eliminates ill feeling
which causes as a result of the temperature change. In recent
years, the new style air-conditioner has used not brushes the direct
current motor realization frequency conversion velocity modulation,
its energy conservation effect comparatively exchanges the
asynchronous motor frequency conversion to enhance approximately 10% ~
15%. In order to further enhances the installment the potency,
in recent years, Japan's air-conditioner gradually changed the PWM+PAM
mixture control way from the pure PWM control. Namely compares
when the low speed uses the PWM control, maintains U/f is certain;
When the rotational speed is bigger than a definite value, will
modulate fixes nearby the maximum value, will lead through the change
direct current chopper passes occupies empties compared to, will
enhance the inversion input DC voltage value, thus the maintenance
frequency changer output voltage and will transfer the intensive
proportion, this region will be called the PAM area. After
selects the mixture control method, frequency changer power input
factor, electrical efficiency, equipment synthesis efficiency all
compared to alone PWM control when has a larger scale enhancement.
In recent years, the new style frequency conversion freezer
storage not only the power consumption reduced, realizes the static
sound, moreover used high speed transports the behavior to realize the
large scale sharp freezing; In the washer aspect, used the
frequency conversion realization to be possible in the past to change
speed the control, enhanced the cleaning performance, new popular
washer besides energy conservation and static sound, but also was
guaranteeing the clothing gently to wash and so on the aspect promotes
the new control content; The electromagnetism cooking use high
frequency 感应加热 causes the bowl directly to give off heat, does
not have the fuel gas and the electric heating blazing part, therefore
not only is safe, but also the large scale enhancement heats up the
efficiency, its operating frequency is higher than above the sense of
hearing frequency, thus eliminated the noise which the rice cooker
vibrates causes; The IH electric cooking pot obtains the
firepower is stronger than the electric heater, moreover may carry on
the firepower trimming using the frequency conversion, so long as
reasonably designs heats up the induction coil, may obtain free heats
up the layout, cooked a meal in the food performance a scale;
The frequency conversion microwave oven use high frequency
electrical energy essential rises for the magnetron to press the
actuation, the power source structure slightly, in the stove the space
is more spacious, the new style microwave oven can wilfully adjust the
electric power, and best heats up the way according to the different
food choice, reduces the time, reduces the electricity to consume;
The illumination aspect, the fluorescent lamp use high frequency
illumination, may enhance the luminous efficiency, the realization
energy conservation, not glitters, Yi Diaoguang, the frequency
wilfully may move, ballast small 轻量.
The frequency conversion technology is bringing the new
revolution for the of all forms electrical appliances, and will bring
a bigger gospel to the user. The next frequency conversion
technology also along with the electric power electronic device, the
new electric power will transform the analysis situs electric circuit,
the filter and the shield technology progress develops. The home
use solar energy generating system also will increase the new energy
to the electrical appliances.
3 electric powers electronic installation brings harm and
countermeasure
In the electric power electronic installation controls
the rectification and not the controllable diode rectification causes
the input current profile to have the serious distortion, not only
greatly reduced the system power factor, but also has caused the
serious overtone pollution. Moreover, in the hardware electric
circuit the voltage and the electric current rapid change, causes the
electric power electronic device withstanding very big electric
stress, and creates the serious electronmagetic interference for the
periphery electrical equipment and the electric wave (EMl), moreover
the situation is day by day serious. Many countries have all
formulated the limit overtone national standard, international
electrical electron engineer the association (1EEE), the international
electrician committee (1EC) and the international big electrical
network conference (CIGRE) has promoted own overtone standard in
abundance. Our country government also separately and in 1993
has formulated the limit overtone related stipulation in 1984.
3.1 overtones suppressions
In order to suppress the overtone which the electric
power electronic installation produces, one method is carries on the
overtone to compensate, namely the establishment overtone compensation
system, causes the input current to become the sine wave.
The traditional overtone compensation system uses the LC
harmonious filter, it both may compensate the overtone, and may
compensate the reactive power. Its shortcoming is, compensates
the characteristic the electrical network impedance and the running
status influence, is easy and the phylogeny antiresonance, causes the
overtone to enlarge, makes the LC filter to overload even burns down.
In addition, it only can compensate the fixed frequency the
overtone, the effect also insufficient ideal. But this kind of
compensation system structure is simple, at present still widely is
applied.
After the electric power electronic device popularizes the
application, the utilization active electric power filter carries on
the overtone to compensate into the important direction. Its
principle is, from compensates in the object to examine the harmonic
current, then produces with this harmonic current size equal polarity
opposite bucking current, thus enable the electrical network electric
current only to include the fundamental wave component. This
kind of filter can the overtone which all changes to the frequency and
the peak-to-peak value carry on the track to compensate, also
compensates the characteristic not the electrical network impedance
influence. It will obtain people's value, and gradually will
promote the application.
Another method is reforms the converter the work mechanism,
achieves both the suppression overtone, and enhances the power factor,
this kind of converter calls the specific power factor converter.
The large capacity converter reduction overtone main method is
uses the multiple technology: Many square-waves superimposition
will eliminate a number of times lower overtone, thus will obtain
approaches the sine the steps and ladders wave. Renumbers many,
the profile more approaches the sine, but the electric circuit
structure is more complex.
Mainly use the PWM rectification technology several kilowatts to
several hundred kilowatts powers factors converter. It directly
various electric powers electronic device carries on the sine PWM
control to the rectification bridge on, causes the input current to
approach the sine wave, its phase and the power source phase voltage
phase is same. Thus, in the input current on only contains with
the turn-on frequency related higher harmonic, these harmonic orders
high, is easy to filter, simultaneously also enable the power factor
to approach 1. Uses the PWM rectifier to take AC/DC the
transformation the PWM inversion, is the so-called double PWM
frequency changer. It has the input voltage, the electric
current 频率固定, the profile is the sine, the power factor
approaches 1, the output voltage, the power frequency variables,
current waveform also for sine characteristic. This kind of
frequency changer may realize four quadrants movements, thus achieves
the energy the bidirectional transmission.
The low-power converter in order to realize the low overtone and
the power factor, generally uses the diode rectification to add PWM to
cut the wave, often called it adjusts (PEC) the power factor.
The typical electric circuit has rises 压型, to fall 压型,
the fluctuation 压型 and so on.
3.2 electronmagetic interferences suppression
countermeasure
Solves the EMI measure is overcomes the switch component
leads passes and shuts off when appears oversized electric current
climbing rate di/dt and voltage climbing rate du/dt, what at present
quite is noticeable is the zero current breaker (ZCS) and the zero
potential switch (ZVS) the electric circuit.
(1) realizes the zero current breaker (ZCS) and the
zero potential switch (ZVS) method:
On the l switch component the series inductance,
may suppress the switch component leads passes when di/dt like this,
causes on the component not to have the voltage, the electric current
重叠? reduced the switch to damage ?
On l switch component shunt capacitance, when the
component shuts off 后抑?the du/dt rise, on the component does
not have the voltage, the electric current 重叠? reduced the
switch loss;
On l component counter- parallel diode. Leads
in the diode passes the period, the switch component assumes the zero
potential, the zero electric current condition, this time actuates the
component to lead passes or shuts off can realize ZVS, the ZCS
movement.
(2) present more commonly used soft switch technology
L partial resonance PWM. In order to
cause the efficiency as far as possible with the hard switch time
approaches, must prevent the component electric current 有效?
increase. Therefore, in a switch cycle, only clears when the
component and shuts off causes the electric circuit resonance, calls
it the partial resonance.
L non- loss cushion electric circuit. On
series inductance either when shunt capacitance electrical energy
release does not pass through the resistance or the switch component,
called the non- loss cushion electric circuit, often does not use the
counter- parallel diode.
The main switch component uses when the electrical machinery
control IGBT, IGBT shuts off has the rear part electric current, to
shuts off the loss to be very influential. Therefore, shuts off
time uses zero electric current time long ZCS to be more appropriate.
3.3 power factor compensation
The early method uses the synchronous condenser, it is
specially uses for to produce the reactive power synchronous machine,
the use 过励?and owes the excitation separately to send out the
different size Rong Xinghuo the perceptual reactive power.
However, because it is the rotating machine, noise and loss all
bigger, movement maintenance also complex, the speed of response is
slow. Therefore, has been unable the request in very many
situations which adapts the fast reactive power to compensate.
- A method is in addition uses the saturable reactor the static
idle work compensation system. It has static and the speed of
response quick merit, but because its iron core must magnetize to the
saturated condition, the loss and the noise very are all big, moreover
has the nonlinear circuit some special questions. Also cannot
the phase splitting adjustment compensate the load not to be
balanced, therefore has not been able to occupy the static idle work
compensation system the mainstream.
Along with the electric power electron technique water unceasing
development, used SCR, GTO and IGBT and so on the static idle work
compensation system obtained the considerable development, was most
superior by the static idle work generator. It has the
adjustable speed to be quick, the movement scope width merit, moreover
after adopts multiple measure and so on, multi- levels or the PWM
technology. May greatly reduce in the bucking current the
harmonic content. More importantly, the static idle work
generator use reactor and the capacitance section is small, greatly
reduces the installment the volume and the cost. The static idle
work generator is representing the dynamic idle work compensation
system development direction.
|
