Design of Single-Phase AC DC AC Bidirectional Three-Arm

Converter with Reduced Switches

Sonali N Borkade

1 a

And M. S. Aspalli

1 b

Department of Electrical and Electronics Engineering, Poojya Doddappa Appa College of Engineering, Kalaburagi

(affiliated to VTU Belgaum), Karnataka, India

Keywords: Three-Level Unidirectional MLI, AC DC AC Conversion, Bidirectional Power Flow Capability, Reduced

Components, and T-Type Inverter.

Abstract: The paper proposes a 1ф unidirectional five-level three arm inverter. It is comprised of a T-Type arm in the

output side with bidirectional capability. The proposed inverter provides the voltage with regulation of

magnitude and frequency. It also provides better power quality in terms of Total Harmonic Distortion and

power factor, and also reduces the number of components as we are using shared arms or leg. The space-

vector PWM strategy was designed in order to increase the performance and also to get 5 level output at both

ends and also eliminates the unbalance caused in the DC-link due to the DC capacitance with midpoint

connection. The simulation is carried out in MATLAB/Simulink 2018b version software.

1 INTRODUCTION

Due to applications like Active Power Filters (APF),

and Uninterruptible Power Supply (UPS), Unified

Power Quality Conditioners (UPQC), fascinate in 1ϕ

AC-AC converters have considerably expanded

recently. These converters supply steady ac voltage to

serve essential loads including computers,

telecommunication systems, and biomedical

instruments. They also deliver sinusoidal source

currents with unity power factor (N. B. de Freitas

2018). The three-leg six-switch converters have been

employed as a less expensive option to a four-leg

arrangement in the aforementioned applications. This

structure offers identical voltage capacity as its four-

leg equivalent when the input and output voltages are

at the same frequency (N. Rocha 2018). Numerous

three-leg configurations are being suggested in the

literature as a result of these properties. It was

suggested to use a unidirectional, single-phase, three-

leg AC-DC-AC converter (Wang 2020).

Comparing this design to a three-leg converter, it

is more effective and less expensive (referred to as a

3L2D converter)

(Sandeep 2019)

. The rise in

https://orcid.org/0009-0000-8084-3937

https://orcid.org/0000-0002-5483-6415

harmonic distortion is its lone flaw. Three-legged

converters have also been used with multilevel

topologies. These topologies combine the shared leg's

ability to minimise switch count with the key

advantages of multilevel systems, including reduced

voltage strain across the power components,

minimum switching losses, and less harmonic

distortion. For unidirectional applications, the

multilevel three-leg topologies cascaded, and parallel

3L2D converters are all appropriate (K. Yadav

2019). Due to its simplicity, the suggested topology—

referred to here as converter 3LNPC2D—is of

particular importance. Based on the unidirectional

leg, it is more efficient and retains all the benefits of

its bidirectional form despite having just 10 active

switches. The 3LNPC2D converter's primary

drawback is the more number of components in the

current path, which maximizes the conduction losses

(Lopez 2017). The application of this finding to the

3L2D and 3LNPC2D converter is possible.

Therefore, the ordinary 3L2D converter is

unquestionably the best option when performance is

the primary criterion for selection. T-type inverters

are often used in industrial settings, including

automated and renewable energy systems. There are

just four switches in a 3-level T-type leg, which

combines the satisfaction of minimal conduction

losses with excellent output voltage quality. T-type

inverters have therefore been the subject of extensive

N Borkade, S. and Aspalli, M.

Design Of Single-Phase AC DC AC Bidirectional Three-Arm Converter With Reduced Switches.

DOI: 10.5220/0012507300003808

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 1st International Conference on Intelligent and Sustainable Power and Energy Systems (ISPES 2023), pages 67-73

ISBN: 978-989-758-689-7

investigation in the literature. The T-type inverter

evolved from having four levels to having n levels.

These were known as nested multilevel converters

because the central points of the limbs are connected

to the same spot. T-type inverters are being used with

different multilevel topologies to enhance the number

of levels. For instance, a T-type leg can be used to

create a nine-level inverter. A T-type inverter may be

used to combine a wide range of hybrid topologies.

There hasn't been much research done on using a T-

type converter for single-phase ACDC-AC

conversion.

Determining a single-phase T-type unilateral AC-

DC-AC converter is the goal of this work. A

unidirectional T-type arm and 2 bidirectional T-type

arms make up the suggested converter. A typical two-

level leg forms the T-type leg, which is connected to

the DC-link midway by an active bidirectional

switch. The bidirectional switch can be implemented

in several ways.

In this paper, two switches are connected with

common source or emitter and create a bidirectional

switch which is used in proposed 3 leg 5 level

inverter. The new inverter possesses minimized

number of switches compared to other traditional

multilevel inverters of same levels with bidirectional

capability. Due to this and improved performance

based on power quality, it can be utilized in

uninterruptible power supplies and active filters.

2 SYSTEM IMPLEMENTATION

Figure 1: Modified system block diagram.

The block diagram of the new inverter is given below

in Figure 1. AC voltage source is provided to the

proposed AC-AC converter which operates based on

the reference voltage provided to the controller. The

output voltage and DC-link voltage is given back to

controller and based on the modulation signal,

SVPWM pulse generator provides the pulses to the

converter. It is also possess bidirectional capability so

that the path of power flow can be reversed. The

modified converter consists of five-level

unidirectional and bidirectional voltage arms, DC-

link capacitor bank (C

and C

) and filters.

The unidirectional leg is composed of q

and q

and

by the bidirectional switch q

. By this, we can able to

achieve power flow from grid to load and load to grid.

The proposed 5 level 3 leg T-type inverter is given

below in Figure 2:

Figure 2: Proposed 5-level Inverter.

Modes 1, 2 and 3 are for positive half cycle of

voltage supply and modes 4, 5 and 6 are for negative

half cycle.

Mode 1:

In this mode, the inductor L

gets charged as the

switches q

and q

is turned ON. The load is supplied

from the energy stored in C

. The operational circuit

for mode 1 operation is given below in Figure 2 (a):

Figure 2(a): Mode 1 circuit of 5-level T-type inverter.

Mode 2:

In this mode, q

and q

are turned ON. The inductor

discharges and charges the capacitor C

along

with supplying the load. The load voltage is around

ind

-V

co1

. The operational circuit for mode 2

operation is given below in Figure 2(b):

ISPES 2023 - International Conference on Intelligent and Sustainable Power and Energy Systems

Figure 2(b): Mode 2 circuit of 5-level T-type inverter.

Mode 3:

In this mode, q

and q

are turned ON. The inductor

discharges and supplies the load. The load voltage

is around V

ind

. The operational circuit for mode 3

operation is given below in Figure 2(c):

Figure 2(c): Mode 3 circuit of 5-level T-type inverter.

Mode 4:

In this mode, the inductor L

gets charged as the

switches q

and q

is turned ON. The load is supplied

from the energy stored in C

. The operational circuit

for mode 4 operation is given below in Figure 2(d):

Figure 2(d): Mode 4 circuit of 5-level T-type inverter.

Mode 5:

In this mode, q

’ and q

’ are turned ON. The inductor

discharges and charges the capacitor C

along

with supplying the load. The load voltage is around –

ind

-V

co2

). The operational circuit for mode 5

operation is given below in Figure 2(e):

Figure 2(e): Mode 5 circuit of 5-level T-type inverter.

Mode 6:

In this mode, q

’ and q

’ are turned ON. The inductor

discharges and supplies the load. The load voltage

is around –(V

ind

). The operational circuit for

mode 6 operation is given below in Figure 2(f):

Figure 2(f): Mode 6 circuit of 5-level T-type inverter.

3 PROPOSED CONTROL

STRATEGIES

To synchronise the grid side and load side, a control

circuit is suggested for regulating the capacitor

voltages. The control scheme has a series framework,

with an exterior loop in charge of adjusting the

electrical grid current reference i

and an inner loop

in charge of adjusting the voltage at the DC link V

C01

+ V

C02

. A PI regulator controls the reference grid

current's amplitude and modifies V

to match its

reference value. Since the converter's power flow is

unidirectional in nature the control method should be

able to eliminate the distortion caused by the input

current zero-crossing.

This issue is resolved by using a PLL (Phase Lock

Loop Technique) to synchronise the grid current i

relative to the rectifier voltage v

. The topology can

nevertheless function using a power factor that is near

to unity because the shift angle among e

and v

is so

tiny. With respect to Ig* and g, the block Gig specifies

the grid current reference as i

= I

sin g. Resonant

control (R

) was utilised to modify ig to match its

reference. The block G v

, i.e., v

= Vl sin g,

establishes a reference voltage using v

and g.

Design Of Single-Phase AC DC AC Bidirectional Three-Arm Converter With Reduced Switches

It only operates when the load voltage is in phase

with grid voltage with reduced magnitude and also by

balancing the dc capacitor voltages v

C01

and v

C02

Figure 3: Proposed control strategy for three-leg five-level

T-type inverter.

The reference load voltage and grid voltage can be

incorporated using SVM strategy. The space-vector

plane for the proposed inverter is given below in

Figure 4.

Figure 4: Switching states of proposed inverter.

From above figure, there are nine active switching

vectors (V

→ V

), eight sectors in additional with a

null vector (V

). The vectors are provided in the

equation shown below:

= v

+ jv

Where, the inconsistencies can be expressed as V

, k

, where k

, k

, and k

represent the switching

phases of arms g, l, and s, respectively. The grid and

load voltages correspond towards the real (Re) and

imaginary (Im) axes, respectively. There are

opportunities to create the model vector V since there

are duplicate switching states. The switching patterns

are intended to balance the imbalance brought on

through the DC-link mid-point interconnection and

minimise the loss of power (conduction and switching

losses).

The reference vector must be incorporated as:

= V

𝑡1

𝑇𝑠

+ V

𝑡2

𝑇𝑠

+ V

𝑡3

𝑇𝑠

In the above equation, t

, t

and t

are time weights

for the vectors V

, V

and V

, respectively, and the

switching cycle time is defined by Ts = t

. The

time weights are determined using the following

relation:

4 SIMULATION FRAMEWORK &

OUTCOME

The simulation parameters for the modified inverter

are provided below in Table 2:

Table 2: Simulation Parameters.

Input Voltage

110 Volt

Output Voltage

210 Volt

Frequency

50 HZ

Output power

100 Watt

Load Resistance

100 Ohm

The simulation circuit is given below in Figure 5.

Figure 5: Simulation circuit of 3-leg 5-level inverter.

Here, the input AC voltage of 110 Volt is connected to

the modified inverter which boosts up to 210V and

provided to the resistive load of 100Ω. It consists of 8

ISPES 2023 - International Conference on Intelligent and Sustainable Power and Energy Systems

switches including a bidirectional switch. The pulses

generated from the s pulse generator are provided below in

Figure 6.

Figure 6: Switching Pulses of proposed inverter.

The output voltage and current along with power is given

below in Figure 7.

Figure 7: Output voltage, current and power waveforms of

3-leg 5-level inverter.

The peak output voltage is around 210V and the

current is around 0.6 A with power is around 106VA.

The %THD of the load current is given below in

Figure 8.

Figure 8: %THD of modified inverter.

The %THD of the load current is around 4.7%.

The power factor measured at the input side is given

below in Figure 9.

Figure 9: Power Factor of proposed system.

The power factor is around 0.964.

A hardware prototype of modified inverter with

input voltage of 12V, 50 Hz is developed with 24V as

load voltage with load resistance of 100 ohm. The

hardware parameters are given below in the following

Table 3.

Table 3: Hardware Parameters.

IRF 250N MOSFET

200Volt, 30A

U1560-Diode

200-400-600Volt, 15A

Capacitor

1000μF, 25Volt

1000μF,100Volt

Transformer

12Volt, 1A

TLP-250 Driver IC

12Volt, 1.5A

CD 4050 Buffer IC

3-18Volt, 0.32mA

12V Regulator 7812

12Volt, 1A

IN 4007 Diode

700Volt, 1A

Arduino UNO

controller

7-12Volt, 20mA

The load voltage division setting is 20V/div for

the above voltage waveforms.

Arduino UNO control is used to produce the

pulses for the modified inverter and it is given to

driver circuit (TLP 250) in order to navigate the

MOSFETs IRF 250. The five-level three-leg inverter

voltage is given below in Figure 10.

Design Of Single-Phase AC DC AC Bidirectional Three-Arm Converter With Reduced Switches

Figure 10: Five-level three-leg inverter voltage.

Figure 11: Load voltage with Capacitor filter.

In the above waveform, in positive cycle, two

levels (one level is Vdc-Vc1 and second level is Vdc)

and in negative cycle two levels and with zero level

we get five-levels.

The load voltage with C filter is given below in

Figure 12.

Figure 12: Hardware framework of modified system.

5 CONCLUSIONS

Here, a 5-level 3 leg T-type inverter with bidirectional

power conduction capability is designed and the

modes of operation of the modified inverter was

explored. A control structure is formulated to reduce

the voltage distortions caused by DC-link capacitors.

A space vector modulation based switching stategy is

followed to reduce the unbalances and therby reduce

the harmonics as well as system losses. In this, the

power factor is measured as 0.964 and the %THD is

around 4.7% for the R load of 100 ohm. A hardware

model is designed and the output voltage waveforms

with and without filter is verified. The main

advantage and applications of proposed AC-DC-AC

converter are it possesses minimum number of

switches and hence the losses will be low. In

reference paper [1] total number of switches is ten,

and here in this work it is reduced to eight. It is

capable of bidirectional power flow; it can be used in

AC drives with regenerative braking capability. It

also possesses voltage boosting capability.

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Design Of Single-Phase AC DC AC Bidirectional Three-Arm Converter With Reduced Switches