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Proceedings Article•DOI•

A 43-level 33 kV 3-phase modular multilevel cascaded converter for direct grid integration of renewable generation systems

Rabiul Islam1, Youguang Guo1, Mohammad Jafari1, Zahra Malekjamshidi1, Jianguo Zhu1 •
University of Technology, Sydney1
20 May 2014-pp 594-599
TL;DR: In this paper, the authors proposed a 43-level 3-phase 33 kV modular multilevel cascaded (MMC) converter for direct grid integration of renewable generation systems, where a high-frequency magnetic link is considered to generate isolated and balanced multiple dc sources for all of the H-bridge inverters of the MMC converter.
Abstract: This paper proposed a 43-level 3-phase 33 kV modular multilevel cascaded (MMC) converter for direct grid integration of renewable generation systems. A high-frequency magnetic-link is considered to generate isolated and balanced multiple dc sources for all of the H-bridge inverters of the MMC converter. The proposed converter is designed and analyzed taking into account the specified system performance, control complexity, cost and market availability of the semiconductors. The simulation results demonstrate the excellent feature of the proposed medium-voltage converter. It is expected that the proposed new technology will have great potential for future renewable power plants and smart grid applications.

Summary (2 min read)

Jump to: [A. Selection of Number of Level of 33 kV converter] – [B. Power Circuit of 43-Level 33 kV MMC Converter] – [C. Switching Circuit of 43-Level MMC Converter] – [III. SIMULATION RESULTS] and [CONCLUSION]

A. Selection of Number of Level of 33 kV converter

  • Each H-bridge inverter cell commutation voltage of a 13level converter is about 4044 V. Moreover, the control complexity increases with the number of converter levels.
  • The arithmetic and logic operations (ALOs) for switching section, THD of output power, and cost of semiconductors are calculated.
  • The THD are calculated through the MATLAB/Simulink environment.
  • Fig. 3 plots the component number and complexity of different level converters for 33 kV system.

B. Power Circuit of 43-Level 33 kV MMC Converter

  • The available cheap and mature 2.5 kV IGBT can be used to design the 33 kV 43-level converter, because this IGBT is recommended for 1200 V maximum applications.
  • About 96% device voltage utilization factor (DVUF) can be obtained with the 2.5 kV IGBTs.
  • In total, 21 H-bridge inverter cells are on each phase-leg and 252 active switching devices are required for the 3-phase 43-level converter.
  • The MMC converter requires multiple isolated and balanced dc sources.
  • The grid electrical isolation and voltage imbalance problems are solved through the common high-frequency magnetic-link [18] .

C. Switching Circuit of 43-Level MMC Converter

  • The phase-shifted carriers are specially conceived for FC [19] and MMC [20] converters.
  • Since each FC cell is a twolevel converter, and each H-bridge cell is a 3-level inverter, the traditional bipolar (using one carrier signal that is compared to the reference to decide between two different voltage levels, typically the positive and negative busbars of a voltage source converter) and unipolar pulse width modulation (PWM) techniques can be used, respectively.
  • Due to the modularity of these topologies, each cell can be modulated independently using the same reference signal in a phase.
  • The inverted form of this switching signal drives the bottom switching device.
  • For the left half-bridge cell, one is asserted when the reference signal value is greater than or equal to the carrier signal value, and the other is asserted when the reference signal value is less than the carrier signal value.

III. SIMULATION RESULTS

  • A total of 231 ALOs are involved with the switching scheme.
  • The semiconductor cost is about 41% lower than that of the 15-level converter, due to the cheap cost of low voltage rated devices.
  • Due to small step size, the line voltage waveforms are found to be very consistent with the reference sine waveforms.
  • The output power quality of a 43level converter is good enough to feed into the grid.

CONCLUSION

  • The designs of 33 kV converter systems have been analyzed, which helps in selecting the optimal number of levels for a medium-voltage converter.
  • All possible MMC converter topologies have been considered for the 33 kV converter systems.
  • In order to ensure a cost effective design, the DVUFs were calculated and only the selected converters with high DVUF were considered.
  • During the design process, the availability of the semiconductor devices was considered in the first instance.
  • After checking the availability of devices, the converter systems were designed taking into account three main factors: the specified converter output power quality, complexity of the switching controller, and cost of the semiconductors.

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A 43-Level 33 kV 3-Phase Modular Multilevel
Cascaded Converter for Direct Grid Integration of
Renewable Generation Systems
Md. Rabiul Islam, Youguang Guo, Senior Member, IEEE, Mohammad Jafari, Zahra Malekjamshidi, and Jianguo Zhu,
Senior Member, IEEE
School of Electrical, Mechanical and Mechatronic Systems
University of Technology Sydney
PO Box 123, Broadway, Sydney, Australia
Md.Islam@uts.edu.au and Rabiulbd@hotmail.com
Abstract—This paper proposed a 43-level 3-phase 33 kV
modular multilevel cascaded (MMC) converter for direct grid
integration of renewable generation systems. A high-frequency
magnetic-link is considered to generate isolated and balanced
multiple dc sources for all of the H-bridge inverters of the MMC
converter. The proposed converter is designed and analyzed
taking into account the specified system performance, control
complexity, cost and market availability of the semiconductors.
The simulation results demonstrate the excellent feature of the
proposed medium-voltage converter. It is expected that the
proposed new technology will have great potential for future
renewable power plants and smart grid applications.
Index Terms—Modular multilevel cascaded converter, medium-
voltage, photovoltaic power plants, grid integration.
I. INTRODUCTION
Different power electronic converters have been developed
using conventional topologies to fulfill the requirements of
renewable generation systems [1], [2]. However, it is hard to
connect the traditional converters to the grids directly, as the
distortion in generated output voltages is high and a single
switch cannot stand the grid voltage level. Many power
semiconductor vendors such as Semikron, ASEA Brown
Boveri (ABB), IXYS, Siemens and Mitsubishi Electric
produce devices specially designed for the diode rectifier
based converter and back-to-back converter for wind turbine
generator systems. All of the devices are in a pack, which
reduces the cost and complexity of the power conditioning
system. Semikron developed compact modules
SKS660FB6U+E1C+B6CI250V06 and IGDD6-4-426-D3816-
E1F2-BL-FA for the diode rectifier based power conditioning
systems. According to the internal circuit configuration, the
module SKS660FB6U+E1C+B6CI250V06 is suitable for
permanent magnet synchronous generator (PMSG)-based
wind turbine generator systems and IGDD6-4-426-D386-
E1F2-BL-FA is suitable for wound rotor synchronous
generator (WRSG)-based wind turbine generator systems.
Mitsubishi Electric developed the module CM00MXA-24S
with this converter topology which can be used for both the
WRSG and PMSG-based wind turbine generator systems.
Semikron also developed the module SKSC120GDD69/11-
A3AWAB1B for power conditioning of synchronous and
doubly-fed generator-based wind power systems.
ABB central inverters are especially designed for medium
scale photovoltaic (PV) power plants. The PVS800 version is
a 3-phase inverter with a power capacity in the range of 100–
500 kW. The transformer steps-up the inverter output voltage
from 300 V ac to grid voltage level (e.g., 6–36 kV). Siemens
developed the SINVERT PVS inverter for medium scale PV
power plants. The ac output voltage and power capacity of the
PVS version inverters are in the range of 288–370 V and 500–
630 kW, respectively.
With these converters, the conventional renewable
generation systems possessing the power-frequency (i.e., 50
or 60 Hz) step-up transformer and the line filter and booster
not only increase the size, weight and loss but also increase
the cost and complexity of the system operation [1]. Today,
the industrial trend is to move away from these heavy and
large size passive components to power electronic systems
that use more and more semiconductor elements controlled
by a digital circuit. In such a way, smart operation is ensured.
In comparison with conventional two level converters,
multilevel converters present lower switching losses, lower
voltage stress on switching devices, and better total harmonic
distortion (THD) [3]–[7]. These remarkable features enable
the connection of renewable energy systems directly to the
grid without using large, heavy and costly power transformers
and also minimize the input and output filter requirements
[8]–[14]. Although several multilevel converter topologies
have been used in low voltage applications, most of the
topologies are not suitable in medium voltage applications.
Because of some special features (e.g., the number of
components scale linearly with the number of levels and
individual modules are identical and completely modular in
constriction hence enabling high level attainability), the
modular multilevel cascaded (MMC) converter topology can
be considered as the best possible candidate for medium-
voltage applications [15], [16]. The high number of levels
means that medium-voltage attainability is possible to
connect the renewable generation units to the medium-
voltage grid directly and it is also possible to improve the
output power quality. The component number and control
complexity increase linearly with the increase in the number
of levels [1], [17]. Fig. 1 plots the component number and
complexity of different level converters.
5 10 15 20
20
40
60
80
100
120
Number of levels
Number of IGBTs/Complexity
Number of IGBTs
Control complexity
Fig. 1. Number of IGBTs/Control complexity versus converter level numbers
of 11 kV system.
8 10 12 14 16 18 20
4
6
8
10
12
Number of levels
THD (%)/Cost (×10000)
Semiconductor cost
(AUD)
THD (%)
Fig. 2. THD (%)/Semiconductor cost versus converter level numbers of 11
kV system.
On the other hand, the distortion in generated output
voltage and semiconductor cost of the converter decrease
dramatically with the increase of the converter number of
levels. Fig. 2 plots THD (%) and semiconductor cost of
different number of MMC converter levels for an 11 kV
system. Due to the unavailability of rated insulated gate
bipolar transistors (IGBTs), the 13 and 17 level converters
used the IGBTs that are used in the 11 and 15 level
converters, respectively. Hence, the semiconductor cost curve
is up-and-down in nature. Moreover, lower switching
frequency, even fundamental switching frequency, can be
used with the high level number converter, which
significantly reduces the switching losses of the converter.
Therefore, the optimal selection in the number of converter
levels is important for the best performance/cost ratio of the
medium-voltage converter systems and this is one of the
central contentions of this paper [17]. In this paper, a 33 kV
system is designed and analyzed taking into account the
specified system performance, control complexity, and cost
and market availability of the power semiconductors. It is
found that the 43-level converters are the optimal choice for
the 33 kV systems. The design and analysis of a 33 kV MMC
converter system is presented in detail in the following
sections.
II. D
ESIGN OF 43-LEVEL 33 KV MODULAR MULTILEVEL
CASCADED CONVERTER
A. Selection of Number of Level of 33 kV converter
Each H-bridge inverter cell commutation voltage of a 13-
level converter is about 4044 V. The highest voltage rating of
a commercially available IGBT is 6.5 kV, which is
recommended for a maximum voltage of 3600 V. Therefore,
a 13-level or lower level converter cannot be used to design
the 33 kV converter. Each H-bridge inverter cell
commutation voltage of a 15-level topology based 33 kV
converter is 3467 V which may be supported by the 6.5 kV
IGBT. Owing to this, at least 15-level topology is required to
design a 33 kV converter. The output power quality of a 55-
level inverter is good enough to directly feed into the 33 kV
ac grid. The cheap 1.7 kV IGBT can be used to design the 55-
level inverter. There are no significant performance
improvements or cost reductions with converters of more
than 55-levels. Moreover, the control complexity increases
with the number of converter levels. Due to these, 15-level to
55-level MMC converter topologies are considered for a 33
kV inverter system.
The arithmetic and logic operations (ALOs) for switching
section, THD of output power, and cost of semiconductors
are calculated. The number of ALOs is used to compare the
complexity of the converters. The THD are calculated
through the MATLAB/Simulink environment. Fig. 3 plots the
component number and complexity of different level
converters for 33 kV system. Fig. 4 plots THD (%) and
semiconductor cost of different number of MMC converter
levels for a 33 kV system. Normalized index values are
calculated. Fig. 5 plots the normalized total index values of
different converters. For the 33 kV converter, the total index
value is the lowest at the 43-level, because there is no
significant output power quality improvement and
semiconductor cost reduction for converters with more than
43 levels. In addition, the component number and control
complexity increase linearly with the increase in the number
of levels. Therefore, 43-level topology is considered as
optimal for 33 kV converter systems.
15 20 25 30 35 40 45 50 55
0
100
200
300
400
Number of levels
Number of IGBTs/complexity
Number of IGBTs
Control complexity
Fig. 3. Number of IGBTs/control complexity versus converter level numbers
of 33 kV system.
15 20 25 30 35 40 45 50 55
2
4
6
8
10
Number of levels
THD (%)/Cost (x30000)
Semiconductor cost
(AUD)
THD (%)
Fig. 4. THD (%)/Semiconductor cost versus converter level numbers of 33
kV system.
15 20 25 30 35 40 45 50 55
1
1.5
2
Number of levels
Normalized total index
Normalized total index
(performance, complexity, and cost)
Fig. 5. Normalized total index versus converter level numbers of 33 kV
system.
B. Power Circuit of 43-Level 33 kV MMC Converter
Each H-bridge inverter dc-link voltage rating of a 33 kV
43-level converter is 1156 V. The available cheap and mature
2.5 kV IGBT can be used to design the 33 kV 43-level
converter, because this IGBT is recommended for 1200 V
maximum applications. About 96% device voltage utilization
factor (DVUF) can be obtained with the 2.5 kV IGBTs. In
total, 21 H-bridge inverter cells are on each phase-leg and 252
active switching devices are required for the 3-phase 43-level
converter. Fig. 6 shows the circuit diagram of 43-level
converter.
Fig. 6. Circuit diagram of a 43-level MMC converter.
However, the MMC converter requires multiple isolated
and balanced dc sources. A high-frequency magnetic-link is
considered to generate multiple isolated and balanced dc
supplies for all of the H-bridge inverter cells of the MMC
converter from a single or multiple renewable source. The grid
electrical isolation and voltage imbalance problems are solved
through the common high-frequency magnetic-link [18].
C. Switching Circuit of 43-Level MMC Converter
The phase-shifted carriers are specially conceived for FC
[19] and MMC [20] converters. Since each FC cell is a two-
level converter, and each H-bridge cell is a 3-level inverter,
the traditional bipolar (using one carrier signal that is
compared to the reference to decide between two different
voltage levels, typically the positive and negative busbars of a
voltage source converter) and unipolar pulse width
modulation (PWM) techniques can be used, respectively. Due
to the modularity of these topologies, each cell can be
modulated independently using the same reference signal in a
phase. If the peak to peak amplitude of the carriers is A
c
, the
amplitude modulation index can be calculated from
c
m
ap
A
A
m
. (1)
Fig. 7 shows the basic block diagram of the phase-shifted
switching scheme for a 3-phase 43-level converter. If
B
n
is
the number of the H-bridge inverter cell or pair on a
particular phase leg and
m the number of converter levels, the
carrier phase-shifting for that particular cell or pair can be
calculated from
)1(
)1(360
m
B
n
o
ps
. (2)
Each compare unit generates one switching signal for the
top switching device of a half-bridge cell or a pair. The
inverted form of this switching signal drives the bottom
switching device. For the left half-bridge cell, one is asserted
when the reference signal value is greater than or equal to the
carrier signal value, and the other is asserted when the
reference signal value is less than the carrier signal value. For
the right half-bridge cell, one is asserted when the inverted
carrier signal value is greater than or equal to the reference
signal value, and the other is asserted when the inverted carrier
signal value is less than the reference signal value. Fig. 8
shows the gate pulse generation technique for the top
switching device and the technique to generate gate pulse for
the bottom switching device is illustrated in Fig. 9.
Fig. 7. Switching control scheme of 43-level MMC converter
For the flying capacitor (FC) multilevel converter, the
advantage of the even power distribution is that once the
flying capacitors are properly charged (initialized to their
corresponding values) no imbalance will be produced due to
the self balancing property of this topology [21], [22] and as a
result there is no need to control the dc-link voltages. Another
interesting feature is that the total output voltage has a
switching pattern with k (number of the power cells) times the
frequency of
the switching pattern of each cell. This
multiplicative effect is produced by the phase shifts of the
carriers. Hence, better THD is obtained at the output, using the
k time’s lower frequency carriers. With the phase-shifted
carrier based modulation scheme, the control signal
assignment to the appropriate semiconductor of the MMC
converter is easy and this remains simple even when the level
number increases to higher values.
Fig. 8. Generation of gate pulse PS
1
with phase shifted carrier.
Signals
Fig. 9. Generation of gate pulse PS
2
with phase shifted carrier.
III. SIMULATION RESULTS
A total of 231 ALOs are involved with the switching
scheme. Although three times more switching devices are
used in the 43-level converter, the semiconductor cost is about
41% lower than that of the 15-level converter, due to the
cheap cost of low voltage rated devices. The line peak to peak
voltage consists of 84 voltage levels and each level contributes
1156 V to the peak to peak line voltage. Due to small step
size, the line voltage waveforms are found to be very
consistent with the reference sine waveforms. Fig. 10 plots the
line voltage waveforms. The output power quality of a 43-
level converter is good enough to feed into the grid. The line
voltage THD is about 3.61%, which satisfies well the 5% limit
by IEEE1547 and IEC61727 standards. The frequency
spectrum of line voltage is shown in Fig. 11. Compared with
the 15-level converter, the 43-level converter provides 44%
better quality output power. As the number of active switching
devices has increased three times, the complexity of the
Citations
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Journal Article•DOI•
Future Power Distribution Grids: Integration of Renewable Energy, Energy Storage, Electric Vehicles, Superconductor, and Magnetic Bus

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Kashem M. Muttaqi1, Md. Rabiul Islam1, Danny Sutanto1•
University of Wollongong1
30 Jan 2019-IEEE Transactions on Applied Superconductivity
TL;DR: This paper focuses on a review of the state of the art of future power grids, where new and modern technologies will be integrated into the power distribution grid, and will become the future key players for electricity generation, transmission, and distribution.
Abstract: This paper focuses on a review of the state of the art of future power grids, where new and modern technologies will be integrated into the power distribution grid, and will become the future key players for electricity generation, transmission, and distribution. The current power grids are undergoing an unprecedented transformation from the original design, changing the way how energy has been produced, delivered, and consumed over the past century. This new energy era includes the integration of renewable sources such as wind and solar, supported by the distributed or community energy storage, to power distribution grids through innovative high-frequency magnetic links and power-electronic converters. The use of emission free transportation, such as electric vehicles, and energy efficient technologies, such as superconducting generators and storage systems, are also rapidly emerging and will be integrated into the power grids in the foreseeable future. However, it is necessary to reconsider the current paradigms of system analysis and plan with a focus on how to achieve the most flexible, efficient, and reliable power grid for the future - the one that enables operation in a domain which is very different than the current one to deliver the services to consumers at an affordable cost.

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  • ...In order to reduce the size and weight of the energy conversion system, a step-up transformer-less direct grid integration technology has been proposed in recent years [7]....

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Proceedings Article•DOI•
Modeling of magnetic flux in multi-winding toroidal core high frequency transformers using 3D reluctance network model

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Mohammad Jafari1, Zahra Malekjamshidi1, Md. Rabiul Islam1, Jianguo Zhu1•
University of Technology, Sydney1
09 Jun 2015
TL;DR: In this paper, a 3D reluctance network is introduced for modelling of magnetic flux distribution and estimation of self and leakage inductances of multi-winding toroidal core high frequency transformer, and the effective factors on accuracy of model and computation time are studied and the results are compared with experimentally measured parameters to verify the accuracy.
Abstract: Multi-winding transformers as main part of multiport phase shift converters play an important role in integration of renewable energy sources, storage device and loads. The range of power transfer in multi-port phase shift converters particularly depends on the leakage inductance of multi-winding transformer. Numerical analysis such as 2D and 3D finite element methods have been widely used in analysis of magnetic structures and estimation of leakage inductance although their computation time is the main issue especially in online and iterative design processes. In this paper, a 3D reluctance network is introduced for modelling of magnetic flux distribution and estimation of self and leakage inductances of multi-winding toroidal core high frequency transformer. The proposed network is formed in cylindrical coordination, according to the geometrical shape of toroidal core. The effective factors on accuracy of model and computation time are studied and the results are compared with experimentally measured parameters to verify the accuracy of model.

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  • ...The toroidal transformer was already designed as a part of project on integration of renewable energy sources into the grid using multi-level inverters [2], [2]....

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Structure and the space vector modulation for a medium-voltage power-electronic-transformer based on two seven-level cascade H-bridge inverters

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01 Oct 2019-Iet Electric Power Applications
TL;DR: This study presents the structure and the space vector pulse-width modulation (SVPWM) for power electronic transformer (PET) based on two seven-level cascade H-bridge (CHB) inverters and proposes the optimal management of the DC-link voltage distribution.
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  • ...They are commonly used in Static Synchronous Compensator (STATCOM) [3], [4], Energy Storage Systems [5], [6], [28], for the integration of Renewable Generation Systems [7], [8], [29] as well as in electric drive applications [30], [31]....

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Book Chapter•DOI•
Power Converter Topologies for Grid-Integrated Medium-Voltage Applications

[...]

Md. Rabiul Islam1, Youguang Guo1, Jianguo Zhu1•
University of Technology, Sydney1
01 Jan 2014
TL;DR: Different multilevel converter topologies, such as neutral point clamped (NPC), flying capacitor (FC), and modular multilesvel cascaded (MMC), have been considered and compared for the design of an 11 kV converter system and the performance is analyzed and compared in the MATLAB/Simulink environment.
Abstract: Although several converter topologies have been used in low-voltage applications, most of the topologies are not suitable in medium-voltage applications. The selection of converter topology in medium-voltage applications is really a critical problem and highly affects the converter performance and cost. The main aim of this chapter was to find out a suitable converter topology, which can interconnect the renewable generation units directly to the medium-voltage grid with mature semiconductor devices. Different multilevel converter topologies, such as neutral point clamped (NPC), flying capacitor (FC), and modular multilevel cascaded (MMC), have been considered and compared for the design of an 11 kV converter system. The comparison is made in terms of the number of semiconductors, semiconductor cost and availability, total harmonic distortions (THDs), filter size, and control complexity of the converters. The performance is analyzed and compared in the MATLAB/Simulink environment. To ensure quality performance, a level-shifted carrier-based switching scheme is used for the NPC topologies and a phase-shifted carrier-based switching scheme is used for the FC and MMC converter topologies with a carrier frequency of 1–2 kHz and modulation index of 0.8–0.9.

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Journal Article•DOI•
Power electronic transformer based on cascaded H-bridge converter

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Gdańsk University of Technology1
01 Oct 2017-Bulletin of The Polish Academy of Sciences-technical Sciences
TL;DR: In this article, the authors proposed a control strategy of power electronic transformer (PET) using two seven-level cascaded H-bridge rectifiers, which allowed for controlling the active and reactive power with a low level of harmonic distortions.
Abstract: In this paper the control strategy of power electronic transformer (PET) is proposed. The analyzed structure of PET uses two seven-level cascaded H-bridge (CHB) rectifiers. The electrical power of PET is transferred between DC-links of CHB converters using dual-active-bridges (DABs) and low voltage high frequency transformers. The roposed solution allows for controlling the active and reactive power with a low level of harmonic distortions. The DC-link voltages and the load of the utilized H-bridges are controlled using appropriate modulation strategy. The theoretical issues are confirmed by simulation and experimental results.

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Cites background from "A 43-level 33 kV 3-phase modular mu..."

  • ...They can be used in active filter applications for total harmonic distortion (THD) improvement and reactive power compensation, in energy storage systems, as well as for the integration of renewable generation systems [1, 2]....

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References
More filters
Journal Article•DOI•
Multicell converters: basic concepts and industry applications

[...]

Thierry Meynard1, Henri Foch1, P. Thomas2, J. Courault2, R. Jakob2, M. Nahrstaedt2 •
Centre national de la recherche scientifique1, Alstom2
07 Nov 2002-IEEE Transactions on Industrial Electronics
TL;DR: The main results obtained through the research done on these converters over this period are topology and derivation of multicell choppers and voltage-source inverters; harmonics cancellation; open-loop modulation techniques; self-balancing understanding; and optimization.
Abstract: Multicell power converters were introduced ten years ago. This paper summarizes the main results obtained through the research done on these converters over this period: topology and derivation of multicell choppers and voltage-source inverters; harmonics cancellation; open-loop modulation techniques; self-balancing understanding; and optimization. During this same period, industrial products using this technique have been developed and the corresponding know-how has contributed to the field in various ways, such as modular design, low inductance busbars, specific drivers, etc.

540 citations

"A 43-level 33 kV 3-phase modular mu..." refers background in this paper

  • ...For the flying capacitor (FC) multilevel converter, the advantage of the even power distribution is that once the flying capacitors are properly charged (initialized to their corresponding values) no imbalance will be produced due to the self balancing property of this topology [21], [22] and as a result there is no need to control the dc-link voltages....

    [...]

Journal Article•DOI•
A High-Frequency Link Multilevel Cascaded Medium-Voltage Converter for Direct Grid Integration of Renewable Energy Systems

[...]

Rabiul Islam1, Youguang Guo1, Jianguo Zhu1•
University of Technology, Sydney1
01 Jan 2014-IEEE Transactions on Power Electronics
TL;DR: In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed, which generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues.
Abstract: Recent advances in solid-state semiconductors have led to the development of medium-voltage power converters (e.g., 6-36 kV) which could obviate the need for the step-up transformers of renewable power generation systems. The modular multilevel cascaded converters have been deemed as strong contenders for the development of medium-voltage converters, but the converters require multiple isolated and balanced dc supplies. In this paper, a high-frequency link multilevel cascaded medium-voltage converter is proposed. The common high-frequency link generates multiple isolated and balanced dc supplies for the converter, which inherently minimizes the voltage imbalance and common mode issues. An 11-kV system is designed and analyzed taking into account the specified system performance, control complexity, cost, and market availability of the power semiconductors. To verify the feasibility of the proposed system, a scaled down 1.73-kVA laboratory prototype test platform with a modular five-level cascaded converter is developed and explored in this paper, which converts a 210 V dc (rectified generator voltage) into three-phase 1 kV rms 50 Hz ac. The experimental results are analyzed and discussed. It is expected that the proposed new technology will have great potential for future renewable generation systems and smart grid applications.

262 citations

Journal Article•DOI•
Natural Balance of Multicell Converters: The General Case

[...]

Richardt H. Wilkinson1, Thierry Meynard2, H. du T. Mouton3•
Cape Peninsula University of Technology1, Centre national de la recherche scientifique2, Stellenbosch University3
13 Nov 2006-IEEE Transactions on Power Electronics
TL;DR: In this article, the authors developed a model for p-cell multicell converters based on the same principles that were used to develop the two-cell model in, except that the mathematics is much more involved.
Abstract: This paper focuses on the development of the natural balancing theory for the p-cell case. It describes the relationship between the models for different numbers of cells in a generic model for a p-cell multicell converter. The model discussed is based on the same principles that were used to develop the two-cell model in , except that the mathematics is much more involved. The same conclusions that were found to be true for the two-cell case was also found to be true for the general case of p cells. These conclusions include that the natural balancing mechanism of multicell converters depends on the overlap of the groups of harmonics of the switching function as well as on the load impedance. It will also be shown that the self-balancing mechanism ensures safe operation under most operating conditions where a high enough switching frequency is chosen and the load is not purely reactive. Two new aspects of the balancing theory were identified in the p-cell case: 1) for fixed duty-cycle modulation there exists certain values of the duty-cycle that causes the natural balancing mechanism to fail and 2) for p-cell converters the balance booster concept can be extended to a number of balance boosters tuned to multiples of the switching frequency. A "DesignTool" based on the balancing theory was developed to aid practicing engineers in designing multicell converters

254 citations

"A 43-level 33 kV 3-phase modular mu..." refers background in this paper

  • ...For the flying capacitor (FC) multilevel converter, the advantage of the even power distribution is that once the flying capacitors are properly charged (initialized to their corresponding values) no imbalance will be produced due to the self balancing property of this topology [21], [22] and as a result there is no need to control the dc-link voltages....

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Journal Article•DOI•
Natural Balance of Multicell Converters: The Two-Cell Case

[...]

Richardt H. Wilkinson, Thierry Meynard1, H. du T. Mouton2•
National Polytechnic Institute of Toulouse1, Stellenbosch University2
13 Nov 2006-IEEE Transactions on Power Electronics
TL;DR: In this paper, a two-cell multicell converter topology is modelled for the general case of p-cells and the switching functions used in switching these converters are derived and presented.
Abstract: The multicell converter topology is said to possess a natural voltage balancing property. This paper is the first of a two-part series in which multicell converters are modelled for the general case of p-cells. This paper focuses on the development of the natural balancing theory for the two-cell case. An understanding of the two-cell case is fundamental to understanding the general balancing theory. The switching functions used in switching these converters are mathematically analyzed. Equivalent circuits are derived and presented. The switching and balancing properties of these converters are mathematically analyzed. The main conclusion of the analysis is that the natural balancing of these converters are influenced by three factors namely, the harmonic content of the reference waveform, the switching frequency and the load impedance. Mathematical tools are presented that can help designers to predict if balancing problems would occur for a particular set of operating conditions. As a result of the detailed understanding of the balancing mechanism that is gained through this theory it is shown that by adding a balance booster, the load impedance can be manipulated to improve the natural balancing of the converter. Simulation results are included to verify the presented balance theory and properties

249 citations

Journal Article•DOI•
A Multilevel Modular Converter for a Large, Light Weight Wind Turbine Generator

[...]

Chong Ng1, Martin A. Parker1, Li Ran1, Peter Tavner1, J.R. Bumby1, E. Spooner1 •
Durham University1
02 May 2008-IEEE Transactions on Power Electronics
TL;DR: In this article, a power electronic solution based on a permanent magnet generator design is presented, where a multilevel cascaded voltage source converter is developed to synthesize a high sinusoidal output voltage.
Abstract: In an onshore horizontal axis wind turbine, generator and converter are usually in the nacelle on the top of the tower, while the grid step-up transformer is placed at the bottom. Electric power is transmitted down through flexible cables of high current rating which are expensive and can suffer from large I2 R loss. An offshore wind turbine usually has to include the step-up transformer in the nacelle. This adds significantly to the mechanical loading of the tower even new designs aim to reduce the transformer size and weight. In either case, a transformer-less, high voltage, high reliability generating unit for nacelle installation would be an attractive technology for large wind turbines. This study presents a power electronic solution based on a permanent magnet generator design. A multilevel cascaded voltage source converter is developed to synthesize a high sinusoidal output voltage. The dc link voltages of inverter modules are balanced by rectifiers fed from isolated generator coils while the inverter switching strategy equalizes the power sharing between the modules. The switching strategy also reduces the low order harmonics to constrain the sizing of the dc link capacitors. The modulating effect between the ac and dc sides of the inverter is taken into account. This paper describes the generator-converter arrangement, analyzes the inverter switching effects and derives the switching strategy which is verified by simulation and laboratory experiment.

197 citations

"A 43-level 33 kV 3-phase modular mu..." refers background in this paper

  • ...These remarkable features enable the connection of renewable energy systems directly to the grid without using large, heavy and costly power transformers and also minimize the input and output filter requirements [8]–[14]....

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Frequently Asked Questions (1)
Q1. What have the authors contributed in "A 43-level 33 kv 3-phase modular multilevel cascaded converter for direct grid integration of renewable generation systems" ?

This paper proposed a 43-level 3-phase 33 kV modular multilevel cascaded ( MMC ) converter for direct grid integration of renewable generation systems. It is expected that the proposed new technology will have great potential for future renewable power plants and smart grid applications.