Download Advanced Techniques for Controlling Output Voltage of Inverter

MIT International Journal of Electronics and Communication Engineering, Vol. 3, No. 2, August 2013, pp. 83–86
ISSN No. 2230-7672 ©MIT Publications
83
Advanced Techniques for Controlling
Output Voltage of Inverter
Amit Kumar Sharma
M.Tech
SITM, Lucknow, UP, INDIA
E-mail: [email protected]
Vivek Mishra
Asst. Prof ECE Deptt.
TMU, Moradabad, UP, INDIA
E-mail: [email protected]
Amit Sharma
Neeraj Kaushik
M.Tech
IIMT, Meerut, UP, INDIA
E-mail: [email protected]
Manas Singhal
M.Tech
IIMT, Meerut, UP, INDIA
E-mail: [email protected]
ME Scholar
NITTTR, Chandigarh, INDIA
E-mail: [email protected]
ABSTRACT
The full-bridge pulse-width-modulation (PWM) single-phase inverter is widely used in uninterruptable power supplies
(UPS), wind and solar power dc-ac interfacing, stand-alone voltage regulators in distributed power systems, and many
other applications. In many applications it is required that the output of the inverter must be varied as demanded by the
load. The main goal of this report is to study the various methods for controlling the output voltage of the inverter.
Though the output voltage can be controlled externally to the inverter either from DC side or from AC side but these
methods needs external component for controlling the inverter output.
Output voltage from an inverter can also be adjusted by exercising a control within the inverter itself. The most efficient
method of doing this is by pulse-width modulation control used within an inverter. This method is called the internal voltage
control of the inverter.
This paper mainly gives the brief of –Single Pulse Modulation, Multiple Pulse Modulation, Sinusoidal Pulse Width
Modulation (SPWM) or Carrier based Pulse Width Modulation Technique., Modified sinusoidal pulse width modulation.
Keywords: PWM, Modulation index, Undermodulation, SPWM, pulsating.
I. INTRODUCTION
to control the output voltage of inverter in various applications.
This paper gives the brief of techniques used to control the
DC-AC inverters are electronic devices used to produce AC output voltage of inverter.
power from low voltage DC energy (from a battery or solar
panel). This makes them very suitable for when required to use II. OUTPUT VOLTAGE CONTROL
AC power tools or appliances but the usual AC mains power is
TECHNIQUES
not available. It is the first and foremost requirement that the
output of three phase inverter should be purely sinusoidal[1]. The various methods for the control of output voltage of
However the waveforms of the practical inverter are non- inverters can be classified as:
sinusoidal and contain certain harmonics. These harmonics are
(a) External control of ac output voltage
generated by the semiconductor devices used in implementing
(b) External control of dc input voltage
three phase inverter is in the generation of harmonics. The
(c) Internal control of the inverter.
power electronics devices when used in practical circuits like
converter/controller circuits generate harmonics in the output
The first two methods require the use of peripheral
voltage supply. The harmonics generate undesirable effects in components whereas the third method requires no external
power supply circuits like generation of humming noises[2], components. Mostly the internal control of the inverters is
de-rating of the machines and torque pulsations which make dealt, and so the third method of control is discussed in great
the operation of the machine pulsating. This is also important detail in the following section.
MIT International Journal of Electronics and Communication Engineering, Vol. 3, No. 2, August 2013, pp. 83–86
ISSN No. 2230-7672 ©MIT Publications
Output voltage from an inverter can also be adjusted by
exercising a control within the inverter itself. The most efficient
method of doing this is by pulse-width modulation control used
within an inverter. This method is called the internal voltage
control of the inverter.
signal of amplitude Vc with triangular carrier signal Vcar.
The frequency of the control signal determines the fundamental
frequency of ac output voltage. The amplitude modulation
index is defined as:
(1)
2.1 External Control of ac Output Voltage
In this type of control as shown in Figure 2.1 an ac voltage
controller is used to control the output of inverter . Through
the firing angle control of ac voltage controller the voltage
input to the ac load is regulated.
84
The rms value of ac output voltage
(2)
where
(3)
Figure 2.1: External control of ac output voltage
By varying the control signal amplitude Vc from 0 to Vcar the
pulse width ton can be modified from 0 sec to T/2 sec and the
rms value of output voltage Vo from 0 to Vs.
2.2 External Control of dc Input Voltage
When the available voltage souecr is ac then the dc voltage
input to the inverter can be controlled through fully controlled
rectifier, uncontrolled rectifier and chopper,ac voltage
controller and uncontrolled rectifier as showh in Figure 2.2(a),
(b) and (c).
Figure 2.3: Gating signals of Single pulse-width
modulated inverter
2.5 Sinusoidal Pulse Width Modulation (SPWM)
Figure 2.2: External control of DC input voltage
2.3 Internal Control of Inverter
Inverter output voltage can also be adjusted by exercising a
control with in the inverter itself.Pulse width modulation is the
most commonly used technique to control the output voltage
of inverter, the various techniques are:
2.4 Single-Pulse-Width-Modulation
In single pulse width modulation control, there is only one
pulse per half cycle and the output rms voltage is changed by
varying the width of the pulse. The gating signals of single
pulse-width modulation are shown in Figure 2.3. The gating
signals are generated by comparing the rectangular control
In sinusoidal pulse width modulation there are multiple pulses
per half-cycle and the width of the each pulse is varied with
respect to the sine wave magnitude. Figure 2.4 shows the
gating signals and output voltage of SPWM with unipolar
switching. In this scheme, the switches in the two legs of the
full-bridge inverter are not switched simultaneously, as in the
bi-polar scheme.
In this unipolar scheme the legs A and B of the full-bridge
inverter are controlled separately by comparing carrier
triangular wave vcar with control sinusoidal signal vc and
-vc respectively. This SPWM is generally used in industrial
applications. The number of pulses per half-cycle depends upon
the ratio of the frequency of carrier signal (fc) to the modulating
sinusoidal signal. The frequency of control signal or the
modulating signal sets the inverter output frequency (fo) and
the peak magnitude of control signal controls the modulation
index ma which in turn controls the rms value of output voltage.
The area of each pulse corresponds approximately to the area
under the sine wave between the adjacent midpoints of off
MIT International Journal of Electronics and Communication Engineering, Vol. 3, No. 2, August 2013, pp. 83–86
ISSN No. 2230-7672 ©MIT Publications
85
Fig 2.5(g) shows the output waveform of inverter. Observe
that there are four pulses in each half cycle.
Figure 2.4: Sinusoidal Pulse Width Modulation
periods on the gating signals. If ton is the width of nth pulse, the
rms value of output voltage can be determined by:
(4)
2.6 Multiple Pulse Width Modulation
Principle: Multiple pulses are used to reduced the harmonic
contents and to control the output voltage. the width of all the
pulses is same.
In this modulation there are multiple number of output
pulses per half cycle and all pulses are of equal width. The Figure 2.5: Waveforms of Multiple Pulse Width Modulation
gating signals are generated by comparing a rectangular
reference with a triangular reference. The frequency of the
Thus by varying the width, output rms voltage can be
reference signal sets the output frequency (fo) and carrier changed.
frequency (f c). The number of pulses per half cycle is
determined by p = fc/2f0
Advantages
The rms ac output voltage
1. Distortion factor is reduced compared to single pulse
V0 = vs(pα/π)1/2
(5)
modulation.
Where α = duty ratio = ton/T
2. As value of p increases amplitude of lower harmonics
reduces.
The variation of modulation index (MI) from 0 to 1 varies
the pulse from 0 to π/p and the output voltage from 0 to Vs.
Disadvantages
2.7 Waveforms and Explanation
Figure shows the waveform of multiple pulse width
modulation.
Figure 2.5(a) shows the carrier signal and the reference
signal. The signal is a triangular waveform and reference
signal is the DC voltage.
They are compared and the pulsed waveform of
Figure 2.5(b) is obtained. The width of the pulses can be varied
by changing the amplitude of the DC reference signal.
Figure 2.5(c) and (d) shows two 50 Hz out of phase masking
square wave. The pulsed waveform of Figure 2.5(b) is ANDed
with these masking signals to obtain the base drivers.
Figure 2.5(e) shows the base drive of T1 and T2. Similarly
Figure 2.5(f) shows the base drives of T3 and T4 .
1. With increase in number of pulse switching losses
are increased.
2. Control scheme is complex.
2.8 Modified Sinusoidal PWM (MSPWM)
The widths of the pulses near peak of the sine wave do not
change much when modulation index is changed. Hence carrier
is suppressed at +30° and –30° in the neighborhood of peak
of sine wave. Such scheme is shown in Figure 2.6. Observe
that the triangular wave is present for the period of first 60°
and last 60° of the half cycle of sine wave.
The middle 60° of the sine wave do not have the triangular
wave. Hence the generated PWM has less number of pulses.
The rms value is more for the same modulation index.
MIT International Journal of Electronics and Communication Engineering, Vol. 3, No. 2, August 2013, pp. 83–86
ISSN No. 2230-7672 ©MIT Publications
86
Output voltage from an inverter can be control by exercising
a control within the inverter itself. The most efficient method
of doing this is by pulse-width modulation control used within
an inverter. This method is called the internal voltage control
of the inverter.
Pulse width modulation is the most adaptable method which
control the output voltage of the inverter by exercising the
internal control of the inverter . the various PWM techniques
include:
1. Single pulse modulation.
2. Multiple pulse width modulation.
3. Sinusoidal pulse width modulation.
4. Modified sinusoidal pulse width modulation.
We
also note that though there is various advantage
Figure 2.6: Waveforms of Modified Sinusoidal PWM
of PWM techniques, it also poses some of the limitations
The harmonic contents are also reduced. This control the most important limitation is that by the implementation
scheme also reduced switching losses. The implementation of of these techniques the switching loss in the inverter
increases.
this scheme is relatively complex then sine PWM.
2.9 Phase Displacement Control
The two inverters are connected in parallel. Output of one
inverter is phase shifted with respect to another inverter. The [1]
net output depends upon phase shift between the two inverter
output.
III. CONCLUSION
[2]
The report presents output voltage control of inverter. There
are various techniques to control the output of inverter whether
they are three phase or single phase The various methods for [3]
the control of output voltage of inverters can be classified as:
(a) External control of ac output voltage
[4]
(b) External control of dc input voltage
(c) Internal control of the inverter.
The first two methods require the use of peripheral [5]
components whereas the third method requires no external
components. Mostly the internal control of the inverters is
dealt, and so the third method of control is discussed in great
detail in this report.
REFERENCES
M. Depenbrock, “Pulse width control of a three-phase inverter
with non-sinusoidal phase voltage of a three-phase PWM
inverter”, Proc. IEEE Int. semiconductor Power Conversion
Conf., Orlando, Florida, USA, pp. 399-403, 1977.
G. Dong, “Sensorless and efficiency optimized induction
motor control with associated converter PWM schemes”, Ph.D.
Thesis, Faculty of Graduate School, Tennessee Technological
University, Dec. 2005.
A.M. Hava, “Carrier based PWM-VSI drives in the
overmodulation region”, Ph.D. Thesis, University of
Wisconsin-Medison, 1998.
A.M. Hava, “Kerkman R.J. and Lipo T.A”, A High Performance
Generalized Discontinuous PWM Algorithm, IEEE Trans. on
Industry Appl., Vol. 34, No. 5, Sept./Oct. 1998.
S. Haykin, “Neural Networks”, ND Prentice Hall, New York,
USA, Holmes D.G., 1996. The significance of zero space
vector placement for carrier-based PWM schemes, IEEE
Trans. Industry Appl.,Vol. 32, No. 5, pp. 1122-1129 Sept./
Oct. 2004.