Question

求电气工程及其自动化英文论文一篇 内容不限 题目要翻译好 谢谢

如题
要英文的 题目要翻译好 谢谢 只要是电气专业类别的都可以

Answer 1

用于分布式在线UPS中的并联逆变器的一种无线控制器
A Wireless Controller for Parallel Inverters in Distributed Online UPS Systems
Josep M. Guerrero', Luis Garcia de Vicufia", Jose Matas'*, Jaume Miret", and Miguel Castilla"
. Departament #Enginyeria de Sistemes, Automatica i Informhtica Industrial. Universitat Polithica de Catalunya
C. Comte d'Urgell, 187.08036 -Barcelona. Spain. Email: josep.m.guerrero@upc.es .. Departament #Enginyeria Electrbnica. Universitat Polit6cnica de Catalunya
AV. Victor BaLguer s/n. 08800I - Vilanova i la Geltrh. Spain
Absiract - In this paper, a novel controller for parallelconnected
online-UPS inverters without control wire
interconnections is presented. The wireless control technique is
based on the well-known droop method, which consists in
introducing P-oand Q-V schemes into the inverters, in order to
share properly the power drawn to the loads. The droop method
has been widely used in applications of load sharing between
different parallel-connected inverters. However, this method
has several drawbacks that limited its application, such as a
trade-off between output-voltage regulation and power sharing
accuracy, slow transient response, and frequency and phase
deviation. This last disadvantage makes impracticable the
method in online-UPS systems, since in this case every module
must be in phase with the utility ac mains. To overcome these
limitations, we propose a novel control scheme, endowing to the
paralleled-UPS system a proper transient response, strictly
frequency and phase synchronization with the ac mains, and
excellent power sharing. Simulation and experimental results
are reported confirming the validity of the proposed approach.
1. INTRODUCTION
The parallel operation of distributed Uninterruptible Power
Supplies (UPS) is presented as a suitable solution to supply
critical and sensitive loads, when high reliability and power
availability are required. In the last years, many control
schemes for parallel-connected inverters has been raised,
which are derived from parallel-schemes of dc-dc converters
[I], such as the master-slave control [2], or the democratic
control [3]. In contrast, novel control schemes have been
appeared recently, such as the chain-structure control [4], or
the distributed control [ 5 ] . However, all these schemes need
control interconnections between modules and, hence, the
reliability of the system is reduced since they can be a source
of noise and failures. Moreover, these communication wires
limited the physical situation ofthe modules [6].
In this sense, several control techniques has been proposed
without control interconnections, such as the droop method.
In this method, the control loop achieves good power sharing
making tight adjustments over the output voltage frequency
and amplitude of the inverter, with the objective to
compensate the active and reactive power unbalances [7].
This concept is derived from the power system theory, in
which the frequency of a generator drops when the power
drawn to the utility line increases [8].
0-7803-7906-3/03/$17.00 02003 IEEE. 1637
However, this control approach has an inherent trade-off
between voltage regulation and power sharing. In addition,
this method exhibits slow dynamic-response, since it requires
low-pass filters to calculate the average value of the active
and reactive power. Hence, the stability and the dynamics of
the whole system are hardly influenced by the characteristics
of these filters and by the value of the droop coefficients,
which are bounded by the maximum allowed deviations of
the output voltage amplitude and frequency.
Besides, when active power increases, the droop
characteristic causes a frequency deviation from the nominal
value and, consequently, it results in a variable phase
difference between the mains and the inverter output voltage.
This fact can be a problem when the bypass switch must
connect the utility line directly to the critical bus in stead of
its phase difference. In [9], two possibilities are presented in
order to achieve phase synchronization for parallel lineinteractive
UPS systems. The first one is to locate a particular
module near the bypass switch, which must to synchronize
the output voltage to the mains while supporting overload
condition before switch on. The second possibility is to wait
for the instant when phase matching is produced to connect
the bypass.
However, the mentioned two folds cannot be applied to a
parallel online-UPS system, since maximum transfer time
ought to be less than a % of line period, and all the modules
must be always synchronized with the mains when it is
present. Hence, the modules should be prepared to transfer
directly the energy from the mains to the critical bus in case
of overload or failure [lo].
In our previous works [11][12], we proposed different
control schemes to overcome several limitations of the
conventional droop method. However, these controllers by
themselves are inappropriate to apply to a parallel online-
UPS system. In this paper, a novel wireless control scheme is
proposed to parallel different online UPS modules with high
performance and restricted requirements. The controller
provides: 1) proper transient response; 2) power sharing
accuracy; 3) stable frequency operation; and 4) good phase
matching between the output-voltage and the utility line.
Thus, this new approach is especially suitable for paralleled-
UPS systems with true redundancy, high reliability and
power availability. Simulation and experimental results are
reported, confirming the validity of this control scheme.
Fig. 1. Equivalenl cimuif ofan invener connecled 10 a bus
t"
Fig. 2. P-odraop function.
11. REVlEW OF THE CONVENTIONAL DROOP METHOD
Fig. 1 shows the equivalent circuit of an inverter connected
to a common bus through coupled impedance. When this
impedance is inductive, the active and reactive powers drawn
to the load can be expressed as
EVcosQ - V2 Q=
where Xis the output reactance of an inverter; Q is the phase
angle between the output voltage of the inverter and the
voltage of the common bus; E and V are the amplitude of the
output voltage of the inverter and the bus voltage,
respectively.
From the above equations it can be derived that the active
power P is predominately dependent on the power angle Q,
while the reactive power Q mostly depends on the outputvoltage
amplitude. Consequently, most of wireless-control of
paralleled-inverters uses the conventional droop method,
which introduces the following droops in the amplitude E
and the frequency U of the inverter output voltage
u = w -mP (3)
E = E ' - n Q , (4)
being W* and E' the output voltage frequency and amplitude
at no load, respectively; m and n are the droop coefficients
for the frequency and amplitude, respectively.
Furthermore, a coupled inductance is needed between the
inverter output and the critical bus that fixes the output
impedance, in order to ensure a proper power flow. However,
it is bulky and increase:; the size and the cost of the UPS
modules. In addition, tho output voltage is highly distorted
when supplying nonlinezr loads since the output impedance
is a pure inductance.
It is well known that if droop coefficients are increased,
then good power sharing is achieved at the expense of
degrading the voltage regulation (see Fig. 2).
The inherent trade-off of this scheme restricts the
mentioned coefficients, which can be a serious limitation in
terms of transient response, power sharing accuracy, and
system stability.
On the other hand, lo carry out the droop functions,
expressed by (3) and (4), it is necessary to calculate the
average value over one line-cycle of the output active and
reactive instantaneous power. This can be implemented by
means of low pass filters with a smaller bandwidth than that
of the closed-loop inverter. Consequently, the power
calculation filters and droop coefficients determine, to a large
extent, the dynamics and the stability of the paralleledinverter
system [ 131.
In conclusion, the droop method has several intrinsic
problems to be applied 1.0 a wireless paralleled-system of
online UPS, which can he summed-up as follows:
Static trade-off between the output-voltage regulation
(frequency and amplitude) and the power-sharing
accuracy (active an4d reactive).
2) Limited transient response. The system dynamics
depends on the power-calculation filter characteristics,
the droop coefficients, and the output impedances.
Lost of ac mains synchronization. The frequency and
phase deviations, due to the frequency droop, make
impracticable this method to a parallel-connected
online UPS system, in which every UPS should be
continuously synchronized to the public ac supply.
1)
3)
111. PROPOSED CONTROL FOR PARALLEL ONLINE UPS
INVERTERS
In this work, we will try to overcome the above limitations
and to synthesize a novel control strategy without
communication wires that could be appropriate to highperformance
paralleled industrial UPS. The objective is to
connect online UPS inverters in parallel without using
control interconnections. This kind of systems, also named
inverter-preferred, should be continuously synchronized to
the utility line. When an overload or an inverter failure
occurs, a static bypass switch may connect the input line to
the load, bypassing the inve:rter [14][15].
Fig. 3 shows the general diagram of a distributed online
UPS system. This system consists of two buses: the utility
bus, which is connected lo the public ac mains; and the
secure bus, connected to the distributed critical loads. The
interface between these buses is based on a number of online
UPS modules connected in parallel, which provides
continuously power to the: loads [16]. The UPS modules
include a rectifier, a set of batteries, an inverter, and a static
bypass switch.
1
1638
Q ac mains
utility bus
I I I
j distributed loads !
Fig. 3. Online distributed UPS system.
syposr /
I 4
(4
Fig. 4. Operation modes of an online UPS.
(a) Normal operation. (b) Bypass operation. (c) Mains failure
The main operation modes of a distributed online UPS
1) Normal operation: The power flows to the load, from
the utility through the distributed UPS units.
2) Mains failure: When the public ac mains fails, the
UPS inverters supply the power to the loads, from the
batteries, without disruption.
Bypass operation: When an overload situation occurs,
the bypass switch must connect the critical bus
directly to the ac mains, in order to guarantee the
continuous supply of the loads, avoiding the damage
of the UPS modules.
For this reason, the output-voltage waveform should be
synchronized to the mains, when this last is present.
system are listed below (see Fig. 5):
3)
Nevertheless, as we state before, the conventional droop
method can not satisfy the need for synchronization with the
utility, due to the frequency variation of the inverters, which
provokes a phase deviation.
To obtain the required performance, we present a transient
P-w droop without frequency-deviation in steady-state,
proposed previously by OUT in [ 111
w=o -mP (5)
where is the active power signal without the dccomponent,
which is done by
. -
I t -1s
P= p ,
( s + t - ' ) ( s + o , )
being zthe time constant of the transient droop action.
The transient droop function ensures a stable frequency
regulation under steady-state conditions, and 'at the same
time, achieves active power balance by adjusting the
frequency of the modules during a load transient. Besides, to
adjust the phase of the modules we propose an additional
synchronizing loop, yielding
o=w'-m%k,A$, (7)
where A$ is the phase difference between the inverter and the
mains; and k, is the proportional constant of the frequency
adjust. The steady-state frequency reference w* can be
obtained by measuring the utility line frequency.
The second term of the previous equality trends to zero in
steady state, leading to
w = w' - k4($ -@'), (8)
being $and $* the phase angles of the output voltage inverter
and the utility mains, respectively.
Taking into account that w = d $ / d t , we can obtain the
next differential equation, which is stable fork, positive
d$ *
dt dt
- + km$ = - + k,$' . (9)
Thus, when phase difference increases, frequency will
decrease slightly and, hence, all :he UPS modules will be
synchronized with the utility, while sharing the power drawn
to the loads.
IV. CONTROLLIEMRP LEMENTATION
Fig. 5 depicts the block diagram of the proposed
controller. The average active power P , without the dc
component, can be obtained by means of multiplying the
output voltage by the output current, and filtering the product
........................................................................................
io
",.
L
Sj'nchronirorion loop
.......................................................................................
Fig. 5. Block diagram of the proposed controller.
using a band-pass filter. In a similar way, the average
reactive power is obtained, hut in this case the output-voltage
must be delayed 90 degrees, and using a low-pass filter.
In order to adjust the output voltage frequency, equation
(7) is implemented, which corresponds to the frequency
mains drooped by two transient-terms: the transient active
power signal term; and the phase difference term, which
is added in order to synchronize the output voltage with the
ac mains, in a phase-locked loop (PLL) fashion. The outputvoltage
amplitude is regulated by using the conventional
droop method (4).
Finally, the physical coupled inductance can be avoided by
using a virtual inductor [17]. This concept consists in
emulated an inductance behavior, by drooping the output
voltage proportionally to the time derivative of the output
current. However, when supplying nonlinear loads, the highorder
current-harmonics can increase too much the outputvoltage
THD. This can be easily solved by using a high-pass
filter instead of a pure-derivative term of the output current,
which is useful to share linear and nonlinear loads [I 1][12].
Furthermore, the proper design of this output inductance can
reduce, to a large extent, the unbalance line-impedance
impact over the power sharing accuracy.
v. SIMULATION AND EXPERIMENTARELS ULTS
The proposed control scheme, (4) and (7), was simulated
with the parameters listed in Table 1 and the scheme shown
in Fig. 6, for a two paralleled inverters system. The
coefficients m, n, T, and kv were chosen to ensure stability,
proper transient response and good phase matching. Fig. 7
shows the waveforms of the frequency, circulating currents,
phase difference between the modules and the utility line,
and the evolution of the active and reactive powers. Note the
excellent synchronization between the modules and the
ACmiiinr 4 j. ...L...I.P...S...1... ..........................B...u...n...r.r..r..e..s... ................................... i
Fig. 6. Parallel operation oftwa online UPS modules,
mains, and, at the same time, the good power sharing
obtained. This characteristik let us to apply the controller to
the online UPS paralleled systems.
Two I-kVA UPS modules were built and tested in order to
show the validity of the proposed approach. Each UPS
inverter consisted of a single-phase IGBT full-bridge with a
switching frequency of 20 kHz and an LC output filter, with
the following parameters: 1. = 1 mH, C = 20 WF, Vi" = 400V,
v, = 220 V, I50 Hz. The controllers of these inverters were
based on three loops: an inner current-loop, an outer PI
controller that ensures voltage regulation, and the loadsharing
controller, based on (4) and (7). The last controller
was implemented by means of a TMS320LF2407A, fixedpoint
40 MHz digital sigrial processor (DSP) from Texas
Instruments (see Fig. 8), using the parameters listed in Table
I. The DSP-controller also includes a PLL block in order to
synchronize the inverter with the common bus. When this
occurs, the static bypass switch is tumed on, and the droopbased
control is initiated.
1640
big 7 Wa\cfc)rms for twu.invencr, ;mnectcd in parallel. rpchrontred io Ihc ac mdnl.
(a) Frequencics ufhoth UPS (b) Clrculattng currcni among modulcs. (CJ Phmc d!Nercn;: betucen ihc UPS a#>dth e ai mum
(d) Ikiril uf the phze diNmncc (e) md (0 Activc and rcactlw pouerr "I ooih UPS
Note that the iimc-acs arc deliheratcly JiNercni due in thc disiinct timuion*uni) ofthe \ inrblrr
1641
TABLEI.
PARAMETEROSF THE PARALLELESDYS TEM.
Filter Order I I
Filter Cut-off Frequency I 0, I 10 I rags
Fig. 8 shows the output-current transient response of the
UPS inverters. First, the two UPS are operating in parallel
without load. Notice that a small reactive current is circling
between the modules, due to the measurement mismatches.
Then, a nonlinear load, with a crest factor of 3, is connected
suddenly. This result shows the good dynamics and loadsharing
of the paralleled system when sharing a nonlinear
load.
Fig. 8. Output current for the two paralleled UPS, during the connection of B
common nonlinear load with a crest factor of 3. (Axis-x: 20 mddiv. Axis-y:
5 Mdiv.).
VI. CONCLUSIONS
In this paper, a novel load-sharing controller for parallelconnected
online UPS systems, was proposed. The controller
is based on the droop method, which avoids the use of
control interconnections. In a sharp contrast with the
conventional droop method, the controller presented is able
to keep the output-voltage frequency and phase strictly
synchronized with the utility ac mains, while maintaining
good load sharing for linear and nonlinear loads. This fact let
us to extend the droop method to paralleled online UPS.
On the other hand, the proposed controller emulates a
special kind of impedance, avoiding the use of a physical
coupled inductance. Th.e results reported here show the
effectiveness of the proposed approach.

Answer 2

Welding Automation Research in the engineering school is largely focused on problems involving sensing, modeling, and control of welding processes, i.e., welding automation. Faculty and students from electrical engineering, mechanical engineering, and material science are involved in the welding automation research. The overall objective of this research is to provide both greater productivity and enhanced quality for welding in the manufacturing environment.

http://eecs.vanderbilt.edu/researchgroups/weldingautomation

Answer 3

我有一篇我本科毕设的小论文，英文中文都有，而且是我人工翻译的，8000字左右。你要的话PM我。我是电气工程及其自动化专业的。《Analysis of thyristor-controlled phase shifter applied in damping power system oscillations》

Answer 4

什么意思？要英文的？题目要汉语翻译？