hysteretic controlled buck boost fed pv inverter … s.dhanasekaran and r.s.sivakumar.,...

ADVANCES in NATURAL and APPLIED SCIENCES

ISSN: 1995-0772 Published BYAENSI Publication EISSN: 1998-1090 http://www.aensiweb.com/ANAS

2017 May 11(7): pages 176-183 Open Access Journal

To Cite This Article: S.Dhanasekaran and R.S.Sivakumar, Hysteretic Controlled Buck Boost Fed PV Inverter System with LCLC Filter. Advances in Natural and Applied Sciences. 11(7); Pages: 176-183

Hysteretic Controlled Buck Boost Fed PV Inverter System with LCLC Filter

1S. Dhanasekaran and 2R. S. Sivakumar

1PG Scholar, Department of EEE, Sathyabama University, Chennai, India. 2Assistant Professor, Department of EEE, Sathyabama University, Chennai, India. Received 12 February 2017; Accepted 20 April 2017; Published 25 May 2017

Address For Correspondence: S.Dhanasekaran, PG Scholar, Department of EEE, Sathyabama University, Chennai, India. E-mail: [email protected]

Copyright © 2017 by authors and American-Eurasian Network for Scientific Information (AENSI Publication). This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

ABSTRACT This paper deals with comparison of responses of Buck Boost Fed PV and Inverter System (BBPVIS) with PI and hysteretic controllers. The output of PV array is stepped up using Buck Boost converter and its output is converted to fifty hertz AC using an inverter. LCLC filter is proposed at the output of the inverter to reduce the harmonics. Closed loop PI & HC based BBPVIS system are modeled, simulated and the corresponding results are presented. The studies indicate that the response with HC is superior to PI controlled BBPVI system. KEYWORDS: Hysteritic Controller, Buck Boost fed FV, Inverter System, PI Controller, LCLC Filter

INTRODUCTION

Due to the global energy challenge, grid-tied inverters for the renewable energy sources are becoming

widely used today’s [1]–[3]. They can be divided into voltage-source inverters (VSI) and current-source

inverters (CSI), where the VSI is the dominant converter. One of the reasons is that the VSI does not need a

large inductor as the energy storage element, while the CSI should adopt a larger inductor in order to keep the dc

current constant for a proper modulation. The research related to CSI mainly focus on the control [4]–[7]. So far,

how to decrease the total dc-link inductance for CSI is a challenge, especially in the low voltage and three-phase

application area. Since the VSI is a step-down inverter and the CSI is a kind of step-up inverter, the Z-source

inverters (ZSI) was proposed in [8] in order to fully utilize the basic character of VSI and CSI and the minimum

semiconductors were used with the combined characters of the step-down and the step-up converters. However,

compared to the CSI or the VSI, the ZSI has two extra inductors in the power loop, which may sacrifice the

efficiency [9], [10]. The control difficulty is also a demerit in the Z-source impedance.

In the renewable power generation system, the input dc voltage of the converter may vary greatly. For

example, the output dc voltage of a solar panel will change a lot under different temperature conditions. To

transfer this kind of dc energy into the grid, a two- or three-stage inverter may be required as the power

interface, especially for the VSI-based system. If all power stages work at high frequency, the efficiency of the

inverter will be inevitable affected. In order to decrease the switching frequency, many interesting inverters have

been proposed [11]–[13] and the basic idea is to ensure that only one of the power stages of the system works at

high frequency.

177 S.Dhanasekaran and R.S.Sivakumar., 2017/Advances in Natural and Applied Sciences. 11(7) May 2017, Pages: 176-183

Nevertheless, the main output filter of these inverters should be designed to satisfy the harmonic

requirements [14] in the “buck” mode, especially when the dc input voltage is higher than the amplitude of the

grid voltage. Thus, when they work in the “boost” mode, an over filtering may take place due to that the output

filter is a CL–CL filter. Since the excessive inductance is in the power loop, extra conduction losses will be

present and the grid current is not easy to control as well. A consensus has been reached that the power

electronics will take a main role in the future energy area [15]. But which favorite type of grid-tied inverters for

the future is still discussed. Dependent on the efficiency evaluation, the smaller inductance in the power loop

will cause a higher efficiency, due to the fact that the power loss caused by power device has become smaller

and smaller. Thus, it may be a good way to achieve high efficiency through decreasing the total inductance in

the power loop. It should be pointed out that aiming to minimize the inductance of output filter of VSI, a

recently new type of power filter named as the LLCL-filter was proposed and analyzed for the grid-tied VSI

[16]–[18].

Theoretically, compared with an LCL-filter, an LLCL-filter can save the total inductance. Due to the reason

of familiarity, the conventional LCL-filter is still used as the output filter benchmark for the comparison between

several classical inverters. In this paper, typical full-bridge single-phase grid-tied inverters with the different

power sources are introduced. Next, a new type of “buck in buck, boost in boost” grid-tied inverter is proposed

and the operating principle is illustrated through a half-bridge inverter with the equivalent circuits in the

different working stages. Then, the modeling is carried out with a small signal model method. Based on this, an

indirect current control method is introduced, when the inverter is working in the “boost” stage. Finally,

simulations and experiments are given to verify the theoretical analysis and the principle of operation.

Fig. 1: Single-phase grid-tied VSI.

Fig. 2: Single-phase grid-tied CSI.


Fig. 3: Single-phase grid-tied ZSI

Typical Full-Bridge Single-Phase Grid-Tied Inverter With The Different Power Source:

A. Single-Stage Inverters:

1) Inverters With the Single Function of Step-Down or Step- Up: Figs. 1 and 2 show the typical VSI with

LCL-filter and the typical CSI with CL-filter, respectively. The VSI is bucktype (step-down) inverter, which

means its dc voltage should be higher than the amplitude of the grid voltage. The CSI is a boost-type (step-up)

inverter, which means that its dc voltage should be lower than the amplitude of the grid voltage [19]. Generally,

the output dc voltage of the renewable power source (for example, a PV panel) may vary in a large range, then

the VSIs or the CSIs have their own limitations as a renewable power conditioner connected to the grid directly,

and after an additional dc/dc converter is used.

2) Inverters With the Function of Both Step-Down and Step-Up:

a) ZSI:

Combined with the voltage characters of the VSI and the CSI, a Z-source type inverter was proposed [8]. In

theory, ZSI (as shown in Fig. 3) can work in the step-down and the step-up states as required and its reliability

can be improved a

Fig. 4: Single-phase grid-tied natural soft-switching inverter

lot, owing to its immunity to the electromagnetic interference. However, due to the two additional inductors

in the power loop, the conduction power loss is high and over filtering may also take place, especially when the

input dc voltage is high. It is basically a boost–buck type converter and it is difficult to realize the overall

parameter optimization, when the input dc voltage varies in a large range. The efficiency of the ZSI seems not as

high as that of the other conventional two-stage inverters [9], [10].

b) Natural Soft-Switching Inverter (NSSI):

For a VSI, the reverse recovery power loss and the power losses caused by the tail current of insulated-gate

bipolar transistor (IGBT) limit the switching frequency of the VSI [20.For the CSI, the high conduction power


losses of the devices and the high power losses caused by the dc-link inductor are the main drawbacks related to

the efficiency. Nevertheless, the CSI has no reverse recovery power losses.

Using the merit of VSI and CSI and avoiding the demerit of them, a high efficiency inverter was proposed

[21] as shown in Fig. 4 (For a single-phase application), named as the NSSI. When the additional switch of S5 is

ON, the inverter works as a pure VSI with an LC-type dc input filter and an LCL type of ac output filter. While

S5 is OFF, it works like a CSI with a clamped voltage and an LCL filter. Thus, this inverter can fit for a wide

variation of input dc voltage, especially for the permanent magnet synchronous wind generator with a front-end

diode rectifier. An improved NSSI was proposed to increase the efficiency when it is used for the three-phase

photovoltaic inverter application [22], whereas an additional boost dc/dc circuit had been inserted. Note that the

NSSI may have a higher efficiency than the traditional two-stage VSI, since more switches can work in the soft-

switching or quasi-soft-switching state. More efficiency analysis about this inverter is introduced in [23].

However, the inductance in the power loop still seems large. The above literature does not deal with comparison

of PI & HC based BBPVI system. This work proposes HC for BBPVI system.

III Simulation Results:

Closed loop system with PI controller is shown in Fig 5.1. The output voltage of solar system is shown in

Fig 5.2 and its value is increases from 10 to 15 V. The output voltage of Buck Boost converter is shown in Fig

5.3 and its value is 250 V. The output voltage of inverter is shown in Fig 5.4. The output current of inverter is

shown in Fig 5.5. The spectrum for output current is shown in Fig 5.6 and THD is 6.8 %.

Fig. 5.1: Closed loop system with PI controller

Fig. 5.2: Output voltage of solar

Fig. 5.3: Output voltage of buck boost converter

VPV

V

Time

V0

Time


Fig. 5.4: Output voltage of inverter

Fig. 5.5: Output current of inverter

Fig. 5.6: Frequency spectrum for Output current

Closed loop system with hysteretic controller is shown in Fig 6.1. The output voltage of solar system is

shown in Fig 6.2 and its value is increases from 10 to 15 V. The output voltage of Buck Boost converter is

shown in Fig 6.3 and its value is 220 V. The output voltage is shown in Fig 6.4 and its peak value is 190 V.

Fig. 6.1: Closed loop system with hysteretic controller

V0

Time

I0

Time

F

[I]


Fig. 6.2: Output voltage of solar system

Fig. 6.3: Output voltage of buck boost converter

Fig. 6.4: Output voltage of Inverter

The output current is shown in Fig 6.5 and its peak value is 0.2 A. The frequency spectrum for output

current is shown in Fig 6.6. The comparison of time domain parameters is shown in Table-1. The comparison of

current harmonics is shown in Table-2. The time response with HC is better than that of PI corbelled system.

The THD with HC is less than that of PI controlled BBPVI system.

Fig. 6.5: Output current of Inverter

Fig. 6.5: Frequency spectrum for Output current

Time

VPV

V0

Time

Voi

Time

iI

Time

[I]

F


Table 1: Comparison of Time Domain Parameters

Controller Tr Ts Tp Ess

PI controller 2.2 4 2.3 5.2

Hysteresis 2.1 3 2.1 4.6

Table 2: Comparison of Current Harmonics

Controller THD

PI controller 6.83%

hysteresis controller 4.70%

Conclusion:

PI & hysteretic Controlled BBPVI systems are successfully designed and simulated using Matlab and the

results are presented. The settling time with HC is 3 sces and steady state error in voltage is 4.6 V. The THD in

the output current with HC is 4.7 %. Therefore the response with HC is better than that of PI controlled BBPVI

system. The advantages of proposed system are high gain, low THD and reduced steady state error. The

disadvantage of this system is that it is suitable for low power levels.

The present work deals with comparison of responses with PI & HC. The comparison of responses with PI

& FLC based BBPVI system will be done at a later date.

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hysteretic controlled buck boost fed pv inverter … s.dhanasekaran and r.s.sivakumar.,...

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