MULTILEVEL INVERTERS

1. Multilevel Inverters
Mohd Faizan
17EEB014
Department of Electrical Engineering
ZHCET,AMU

2. Contents
 Introduction
 PWM inverters Vs Multilevel Inverters
 Types of MLI
 Diode Clamped Multilevel Inverters
 Flying Capacitor Multilevel Inverters
 Multilevel Inverters Using H-Bridges (HBs) Converters
 Some Other Kinds of Multilevel Inverters
 References

3. Introduction
 They are different from conventional
inverters as they accumulate the levels
to obtain the waveform.
 They contain several power switches,
sources and capacitors.
 Output voltage of the MLI are the sum
of voltages due to commutation of
voltages.
 They are receiving increasing attention,
due to their attractive features.
One phase leg of an inverter: (a) two levels, (b) three levels, and (c) m levels
Picture credit: Advanced DC/AC Inverters: Applications in Renewable Energy

4. Multilevel inverters Vs PWM Inverters
 The switching frequencies of most
switching devices are low.
 The pulse heights are quite low, it
causes low dv/dt and ignorable
electromagnetic interference (EMI).
 Inverter control circuitry is relatively
simple.
 The devices are not costly and thus the
whole inverter is economical.
 The carrier frequency must be very
high.
 The pulse height is very high, which
causes large dv/dt and strong
electromagnetic interference (EMI).
 The inverter control circuitry is
complex.
 The devices are costly and it leads to
the increase in the cost of whole
inverter.

5. Types of Multilevel Inverters
Family tree of multilevel inverters
Picture credit: Advanced DC/AC Inverters: Applications in Renewable Energy

6. Diode Clamped Multilevel Inverters
 The switching devices are connected in
series to make up the desired voltage
rating and output levels.
 The inner voltage points are clamped by
either two extra diodes or one high-
frequency capacitor.
 The switching devices of an m-level
inverter are required to block a voltage
level of Vdc/(m−1).
 An m-level diode clamped inverter has:
 Number of power electronic switches =
2(m – 1)
 Number of clamped diodes = 2(m – 2)
A three level Diode Clamped MLI
Output waveform of a 3 level Diode Clamped MLI
Picture credit: Advanced DC/AC Inverters: Applications in Renewable Energy

7. Flying Capacitor Multilevel Inverters
 The flying capacitor inverter has
dependent capacitors clamping the
device voltage to one capacitor voltage
level.
 The charge of capacitor is balanced by
proper selection of the 0-level switch
combination.
 The +ive top level and -ive top level
have only one combination to
implement their output values.
 Other levels have various combinations
to implement their output values.
A three level Capacitor Clamped MLI
A five level Capacitor Clamped MLI
Picture credit: Advanced DC/AC Inverters: Applications in Renewable Energy

8. Multilevel Inverters Using H-Bridges (HBs)
Converters
 The basic structure is based on the
connection of H-bridges.
 Each HB is supplied by a separate DC
source.
 The resulting phase voltage is synthesized
by the addition of the voltages generated
by the different HBs.
 If the DC link voltages of HBs are identical
 Cascaded multilevel inverter
 If the DC link voltages of HBs are not
identical
 Hybrid multilevel inverter Multilevel inverter based on the connection of HBs
Picture credit: Advanced DC/AC Inverters: Applications in Renewable Energy

9. Some Other Kinds of Multilevel Inverters
Generalized multilevel inverter structure A Mixed-Level Multilevel Inverter Topology
Picture credit: Advanced DC/AC Inverters: Applications in Renewable Energy

10. References
 Nabae, A., Takahashi, I., and Akagi, H. 1980. A neutral-point clamped PWM inverter.
Proc. IEEE APEC’80 Conf., pp. 761–766.
 Nabae, A., Takahashi, I., and Akagi, H. 1981. A neutral-point clamped PWM inverter.
IEEE Trans. Ind. Applicat., pp. 518–523.
 Mohan, N., Undeland, T. M., and Robbins, W. P. 2003. Power Electronics: Converters,
Applications and Design. New York: John Wiley & Sons.
 Advanced DC/AC Inverters: Applications in Renewable Energy Fang by Lin Luo and
Hong Ye