Power Quality Improvement using PV Coupled Non-Isolated Quasi Z

Source Inverter

R. ARTHI1, G. RAMYA2, P. SURESH3, K. MURUGESAN4, T. RAMYA1

1Department of ECE, SRM Institute of Science and Technology University, Ramapuram Campus,

INDIA

2Department of EEE, SRM Institute of Science and Technology University, Ramapuram Campus,

INDIA

3Department of EEE, St. Joseph College of Engineering, Sriperumbudur, INDIA

4Department of ECE, Eswari Engineering College, Ramapuram, INDIA

5Department of ECE, SRM Institute of Science and Technology University, Ramapuram Campus,

INDIA

Abstract: - Z source inverter is a DC to AC converter, but it can be operated as buck boost converter without

employing separate bridge converter. The proposed work presents the new Quasi- Z Source Inverter to improve

the effectiveness by drop in conduction loss of the system. High boost capability with smaller capacitance and

inductance makes the system output stable, which is also suitable for Photovoltaic and Fuel cell based

renewable energy systems. The existing DC link in the converter system has been replaced by X shape

connected capacitors and inductors in Z source network with common ground connection. the new Quasi- Z

Source Inverter increases the output voltage range with improved power factor, reduced harmonics and has

good ride through capability. Photovoltaic fed quasi-Z source inverter is employed nowadays for its high

potential to integrate with power systems. The proposed converter reduces the damping of the grid connected

grid connected system to reduce the transient interactions. Unipolar PWM technique is employed to reduce the

THD of the system. MATLAB simulink has been employed to simulate the proposed method and the prototype

has been developed to verify the simulink.

Key-Words: - Quasi Z Source Inverter (QZSI), Photovoltaic (PV), Total Harmonic Distortion (THD).

Received: March 26, 2021. Revised: January 15, 2022. Accepted: February 23, 2022. Published: March 26, 2022.

1 Introduction

Z Source Inverter is a single stage buck boost

converter with good voltage gain. The wind and

voltage control can be improved by injection of

wind power using QZSI with battery assistance [1]-

[2]. The THD and voltage gain are analysed and

compared for different levels of QZSI [3]. The

settling time and overshoot for frequency regulation

and stabilization issues in power system can be

reduced by Nonlinear Sliding Mode Controller [4] -

[6]. The Proposed Resonance and Sliding Mode

Controllers characteristics has been applied to UPS

[7]. Model Predictive Control (MPC) scheme was

employed in chemical industries in earlier days. The

new and wide ranges of control schemes are

described as MPC, do not imply any particular one

controller. Nowadays, MPC application schemes

plays a vital role in Power Electronics Drives

System. Development of Pulse Width Modulation

technique has replaced the existing controller

techniques with demonstration of MPC system [8]-

[11]. Auto Adaptive Discrete-time Model Predictive

Control (ADMPC) compares the real speed with

reference speed with acceleration of IM drive

system [12]. In [13] Digital Predictive Current

control design and implementation in Integrated

Renewable Energy based system is discussed. Finite

control Set MPC is a new alternative to constant

switching.

Higher voltage boosting using shoot through

state helps to improve the impedance networks

using coupled magnetics. Many Industries employ

traditional voltage source and current source

inverters. Higher voltage boosting using shoot

through state helps to improve the impedance

networks using coupled magnetics. In [15] Existing

DC link in the converter system are replaced by X

shape connected capacitors and inductors in Z

source network with common ground connection is

depicted in Figure 1.

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10.37394/232016.2022.17.7

R. Arthi, G. Ramya, P. Suresh, K. Murugesan, T. Ramya

E-ISSN: 2224-350X

Volume 17, 2022

Fig. 1: ZSI circuit diagram

Fig. 2: ZSI with Switched Inductor

Shoot through duty cycle helps to achieve the

desired AC voltage using singular LC Z source

network. It has advantages as improved voltage

range, improved power factor with reduced

harmonics. Combining the continuous and

discontinuous diode and capacitor assisted quasi-Z

source Inverter to get the extended Z Source boost

inverter [16]. ZSI with Switched Inductor cells are

proposed in Figure 2. Quasi Z source with switched

inverter is obtained by replacing network with two

SL cells in QZSI and one SL cells. Enhanced Boost

QZSI circuit diagram is depicted in Figure 3 and the

Figure 4 depicts the Enhanced Boost Quasi Z

Source Inverter to obtain the AC output [17].

Photovoltaic fed quasi-Z source inverter is

employed nowadays for its high potential to

integrate with power systems. To improve the

voltage gain, L. Pan introduced a new Z-source

inverter based on switched inductor network [18]-

[20]. The above literature does not deal with the

proposed quasi–Z Source inverter. Section II

describes the proposed system and operating modes

of the proposed system is explained in section III.

Section IV describes the simulation results and

concluded in section V.

Fig. 3: Enhanced Boost Z Source Inverter

Fig. 4: Enhanced Boost Quasi Z Source Inverter

2 Proposed Method

The proposed system consists of two inductors, two

capacitors with one diode to produce improved AC

output voltage. Figure 5 depicts the QZSI circuit

diagram.

Fig. 5: Proposed QZSI circuit diagram

Block diagram of the QZSI is depicted in Figure 6.

Renewable DC source has been generated by the PV

system, processed through the proposed QZSI and

applied to the inverter to get AC output waveform.

An electronically commutated AC motor is

employed and the AC power from the motor has

been applied to it. The advantages such as less

maintenance, high efficiency makes the system to

employ BLDC motor.

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R. Arthi, G. Ramya, P. Suresh, K. Murugesan, T. Ramya

E-ISSN: 2224-350X

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Fig. 6: Proposed QZSI block diagram

3 Operating Modes of Proposed QZSI

The boost capacity of the proposed QZSI is obtained

by combining the two different quasi-Z source

inverter using diodes D2 and D5. Each quasi-Z

source network are with the combination of

inductors and capacitors and each complement each

other to produce the increased boosted output

voltage.

Fig. 7: Proposed Z Source Inverter with combined

quasi network circuit diagram

Simplified analysis is done by considering the

inverter bridge with Solid State Switch (SST). Each

QZSI has two inductors, two capacitors with diode

to have a boosted output voltage. SST is used to

perform the active and shoot through modes of

operations. During this mode, switches S1, S3 in

first leg or switches S2, S4 in second leg will be

turned, makes the inductors to store energy without

short circuiting the DC capacitors is one of the

added advantages of the network. The ramp up of

inductor current takes place in this interval

disconnect the output from input. The proposed

method operation is similar to the classical QZSIs

with two zero states, six active states and one

additional shoot through zero state. Figure 8a

depicts the QZSI shoot through mode.

Fig. 8a: Shoot through mode of proposed QZSI.

Figure 8b represents the Proposed QZSI Non shoot

mode with reverse biasing of diodes D1, D3 & D4

and forward biasing of diodes D2 & D5. There are

four loops during this state: loop 1 consists of input

voltage source Vdc, inductor L1, and capacitor C1.

The input voltage source Vdc is in series with

capacitor C1 to charge inductor L1; loop 2 consists

of input voltage Vdc, diode D2, inductor L2, and

capacitor C2. The supply voltage Vdc and capacitor

C2 discharge the energy to inductor L2; loop 3

consists of supply voltage Vdc, capacitor C3,

inductor L3 and diode D5. The supply voltage Vdc

and capacitor C3 charge inductor L3 in series; loop

4 consists of the supply voltage Vdc, capacitor C4,

inductor L4. The supply voltage Vdc and capacitor

C4 discharge the energy to inductor L4. To have a

linear increase of current in inductors, Capacitor

voltages are kept constant. Inductors are connected

to the DC source with each capacitor is in series

with it.

In Figure 7, Open switch represents the equivalent

circuit of working state with two zero states and six

active states. Diodes D1, D3 and D4 will be

activated during this state with diodes D2 and D5

are turned off to the reverse voltage of the inductors

L1 and L4.

Fig. 8b: Proposed Quasi Z Source Inverter Non

shoot mode

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R. Arthi, G. Ramya, P. Suresh, K. Murugesan, T. Ramya

E-ISSN: 2224-350X

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Operating state consists of five loops: loop 1

consists of inductor L1, L2, diodes D1, D3 and

capacitor C3, Inductors L1 and L2 discharge the

energy to capacitor C3; loop 2 consists of inductors

L1, L2, L3, diodes D1, D3, D4 and capacitor C4.

Inductors L1, L2 and L3 discharge the energy to

capacitor C4; loop 3 consists of diodes D3, D4,

inductors L3, L4 and capacitor C2. Inductors L3 and

L4 charge capacitor C2 in series; loop 4 consists of

diodes D1, D3, D4, inductors L2, L3, L4 and

capacitor C1. Inductors L2, L3 and L4 discharge the

energy to capacitorC1; loop 5 consists of supply

voltage Vdc, inductors L1, L2, L3, L4, diodes D1,

D3, D4, and therefore the inverter bridge.

Table 1. Switching states of Synchronous Rectifier

4 Simulation Results

The proposed system simulation results are

described in this section. L filter is employed in line

with frequency to reduce the THD. The requirement

of high inductance value results in increased cost in

order of several Kilowatts. Low pass filter is

employed to replace the small values of inductors

and capacitors. Weight, height, size, costs are

different, depending upon the type of the filter.

Figures 9 and 10 depict the output voltage of QZSI

without and with filter respectively. After

employing the filter, the harmonics present in the

filter has been reduced.

Fig. 9: Output voltage of QZSI without filter.

Simulations are done using the MATLAB simulink

to boost the quasi-Z source inverter with the below

parameters. All the components are assumed to be

ideal in the simulation part. The simulation

parameters of the proposed system are given in

Table 2.

Fig. 10: Output voltage of QZSI with filter.

Table 2. Simulation parameters of proposed system.

Fig. 11: Z Source Inverter output torque.

Fig. 12: Hardware prototype of Proposed QZSI

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R. Arthi, G. Ramya, P. Suresh, K. Murugesan, T. Ramya

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Figure 11 depicts the QZSI output torque. Hardware

prototype has been developed for the proposed

Quasi Z Source Inverter. The proposed hardware

prototype has been developed with the same

specification of the simulation parameters is shown

in Figure 12.

5 Conclusion

A new Quasi Z source boost inverter, which

combines the different Z Source networks has been

presented in the proposed work. It also increases the

output voltage range with improved power factor,

reduced harmonics and has good ride through

capability. The block diagram of the proposed

system with its operating principles has been

discussed. PV system has been employed as DC

source to the proposed quasi-Z source inverter. An

electronically commutated AC motor has been

employed and the AC power from the motor has

been applied to it. The advantages for the proposed

work can be notified as less maintenance, high

efficiency that makes the system to employ BLDC

motor. Simulated output shows that the proposed

system has better output voltage and torque. The

proposed system has been simulated using

MATLAB simulink and the hardware prototype has

been developed to verify the simulation results of

the proposed system.

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R. Arthi, G. Ramya, P. Suresh, K. Murugesan, T. Ramya

E-ISSN: 2224-350X

Volume 17, 2022