Download Project Statement - ECE Senior Design

Power Factor Correction
Input Circuit
ECE 4901 Fall 2016
Jethro Baliao (ECE)
Kevin Wong (ECE)
Paul Glaze (ECE)
Ethan Hotchkiss (ECE)
Lenze Americas
1-(508)-278-9100
[email protected]
www.lenze.com
Abstract: The goal of this project is to design an
input circuit that will improve the power factor
input of a frequency inverter designed and
manufactured by Lenze. Power factor is
important since it would improve efficiency and
lessen costs of energy. The parameters for this
project would have an input voltage of 115 VAC
single phase, at 60Hz. As for the output
requirements, they are to have an voltage output
of around 325 VDC and low voltage ripple. The
design would first be for a single-phase model. A
design for a three phase may also be
considered after completion of the single phase
product. In this paper, the basic planning stages
will be discussed on how to design the circuit as
well as the limitations, questions, and statement
of need.
I. Introduction
Power factor is one of the most
important elements in an AC electrical system.
Power factor is basically the ratio of real power
to apparent power in the circuit. The relationship
can be represented by the following equation
,
𝑃𝑜𝑤𝑒𝑟 𝐹𝑎𝑐𝑡𝑜𝑟(𝑃𝐹) = 𝑐𝑜𝑠𝜑 =
𝑃
𝑆
(1)
Another way of looking at this relationship is
from the power triangle.
Fig. 1. Power Triangle
In order to achieve a higher power factor
the average current waveform should follow the
phase and shape of the input voltage. The
behavior of the converter, whether it be
continuous conduction mode (CCM) and
discontinuous conduction mode (DCM), will be
what the PFC design will be based on. In other
words, if the voltage gain is independent of the
load and the input current is continuous CCM
would be ideal. On the other hand, if the input
current is variable and the voltage gain is
dependent on the load then DCM is appropriate.
We expect to operate in CCM given that we are
looking to maximize efficiency and minimize
current ripple.
II. Background Research
Here the apparent power, S can be determined
by taking the vector sum of the reactive power,
Q and the real power.
𝑆 = √𝑃2 + 𝑄2
Working with these VFD’s, a power
factor correction (PFC) circuit can further
improve the efficiency. These motors drives will
need a network to compensate for its reactive
power which lessens the burden on the power
supply. A PFC circuit will typically make use of
switching devices found in power electronics
such as, MOSFETs, BJTs, Diodes and
Thyristors, as well as static components such as
capacitors and inductors. The switching
characteristics of the active devices help control
the flow of energy in the circuit.
(2)
Frequency inverters also known as
variable-frequency drives (VFD) are instruments
that alter the input voltage frequency and
magnitude to obtain an AC output. This drive
would be connected to an inductive motor to
help control the frequency and voltage supplied.
We can find VFDs in many fields ranging from
large scale industrial networks to small gadgets.
Before we design a prototype, we first
need to determine what we need to know. To
start off, our main objective is to design an input
circuit that will improve the power factor input for
a VFD Lenze will provide for us. By studying
various topologies for power factor correction,
we would be able to determine which is
appropriate for our project.
Research papers and textbooks are
resources available to us. There are numerous
research papers written by members of the IEEE
which is a credible source. Furthermore, the
engineers at our sponsor’s location are willing to
provide assistance as well as the TA’s and
professors on campus who are knowledgeable
in power electronics and electric drives.
There is never enough information for
projects such as these since there are so many
possibilities and ways to reach our objective.
Considering how single-phase is the primary
goal, we also can work on a three-phase model.
Considering how this would be a much a more
difficult task to handle would further increase the
time spent on planning and designing.
More background research should be
looked into working with software. In order to
simulate our results, it is important to be familiar
with applications such as PSPICE, and Simulink.
Additionally if microcontrollers are considered,
knowledge of C is helpful.
III. Statement of Need
Power correction factor is needed to
reduce the total power needed. When a load is
capacitive or inductive, power is needed to
create the required electrical field or magnetic
field. The field must be created in one polarity,
broken down, and then created again in the
opposite polarity, and the cycle repeats. The
power consumed in this process is not used to
do any work. The ratio of power used to do work
vs the total power used is the power factor. By
adding technology to correct this it can reduce
the apparent power. If the power factor is very
low it may destabilize the power grid, or create
transients that can damage other devices on the
power grid. For these three reasons: saving
money, requirements from power companies,
and protecting other devices on the grid demand
power correction factor.
Power factor correction is in high
demand in today’s industrial world. Low power
factor is generally caused by inductive loads, ie.
motors. These inductive loads cause the current
to “lag” behind the voltage. The current and
voltage being out of phase is the driving factor in
lower power factor.
When apparent power rises without an
increase in real power, this leads to a needless
increase in current. As a result, this leads to
quadratically greater losses given that
conductive losses increase with the square of
the current.
Utility companies have always desired
higher power factors because just as low power
factor wastes money and resources within an
industry, it is also a waste for the utility company
to generate power that cannot be delivered due
to conductive losses. Many utility companies will
go as far as to penalize industrial accounts for
low power factor.
Prior to the rise of power electronics,
power factor correction was limited to the use of
capacitors, and or synchronous condensers.
These devices are effective at lowering the
power factor, but not without their drawbacks.
Using purely a capacitive power factor
correction circuit is the simplest method of
power factor correction, as it has the exact
opposite effect of an inductor. Capacitors force
the current to lead the voltage, therefore, if the
capacitance and the inductance are perfectly
balanced, the load will be at the unity power
factor. However, capacitors are fixed devices
and do not allow for adjustment and variation of
load without external control of connecting and
disconnecting capacitors to maintain power
factor. Another drawback to this setup is the
size, capacitor banks for power factor correction
are generally large units and would not fit in the
packaging of a small motor drive.
A second option for power factor
correction is the synchronous condenser. On a
basic level, a synchronous condenser is a no
load AC motor that uses the same
characteristics that absorb the reactive power to
produce reactive power in order to bring the load
to unity. This practice is very effective, however
it is also noisy and even larger than a capacitor
bank. Neither of these options are feasible for
installation in a small motor drive. This is where
the power electronics come in.
Research in power electronics began in
the 1950s and over the last 60 years, have
become a formidable force in the world of
electricity. The use of power electronics would
allow for an AC-DC rectification coupled with a
power factor correction DC-DC converter that
would draw power very close to the unity power
factor while still fitting into a small package.
While power electronics have existed for
many years, their practical industrial application
is a fairly recent development. At this time,
Lenze has no motor drives fitted with a power
correction circuit. This project will be the
pioneer for integrated power factor correction.
V. Basic Limitations
Lenze has not given us a strict budget
requirement, however the goal budget is below
$1,000 - $2,000. Given that the goal of this
device is to become a production model, cost
reduction is paramount. We will work to
maximize efficiency of all our components to
minimize cost while still satisfying all
requirements of the project. Lenze has also
requested that we build our final product to be
small enough to fit into an existing VFD with
minimal modifications to the chassis. This adds
an extra challenge for space efficiency given
that there is not a lot of extra space available for
the PFC components.
VI. Questions
IV. Preliminary Requirements
The preliminary requirements for this
product consist of simple input and output
requirements. Input would be single phase 115
VAC.The grid is to see a nearly resistive load
having a power factor above 0.95 under load. A
switching DC-DC converter circuit will be
needed to achieve this power factor.
The output of this product will feed an
inverter. This inverter will take an average of
about 325 VDC and about 4.5 Amps. We want
to accomplish this efficiently and reliably.
Simulations would be required to find the best
method for accomplishing this. We will begin by
optimizing the components of our circuit using
open loop control and then integrating closed
loop control for advanced adjustment to
minimize line and load regulation. Then a
prototype for our product will be built and tested.
Lenze is interested in a PCB being designed
and produced, but has not made it a strict
requirement.
Will we use active switching devices or
diodes for the rectifier?
Will we use feedforward or feedback
control?
Will the power converter be based on
DCM or CCM mode?
VII. Other Information
Lenze has expressed interest in
exploring options for three-phase input as well
as single phase input. However, they have not
made that a requirement and have left it as an
expansion option for our project. We are
interested in investigating this modification upon
completion of the single phase converter.