A grid connected pv system with a variable switching frequency hysteretic modulation

International Journal of Research in Advanced Technology - IJORAT Vol. 2, Issue 2, FEBRUARY 2016

All Rights Reserved © 2016 IJORAT 1

A Grid Connected PV System with a

Variable Switching Frequency Hysteretic

Modulation Using Sliding Mode

Controller

S.Jeya Pradeepa1

,M.Shunmugavidya2,S.Jeya Prakash

3

1PG scholar, Dept of EEE, Francis Xavier Engineering College

2PG scholar, Dept of EEE, Francis Xavier Engineering College

2UG scholar, Dept of EEE, Francis Xavier Engineering College

Abstract: This project presents a sliding mode controller with a variable switching frequency hysteretic

modulation technique. The PV system drives the PV voltage to follow a reference provided by an

external MPPT algorithm and mitigates the perturbation caused by irradiance and temperature

change. The proposed design of a sliding mode controller requires to fulfill three conditions:

transversality, equivalent control and reachability. These conditions are used to develop a design

procedure for the control system that ensures the desired performance criteria of the PV voltage.

Simulation results show the reduction in setting time and it was attained by using the improved design

of the sliding mode control with the MPPT algorithm. The overshoot is also reduced in the output

voltage of the boost converter. Finally, the PV system was connected to the grid through the boost

converter and inverter.

keywords: PV-photovoltaic, MPPT-maximum power point tracking, Sliding Mode Controller,

Hysteretic modulation technique.

I. INTRODUCTION

Photovoltaic (PV) systems are a suitable

option to produce clean electrical energy since

they can be dimensioned for a wide range of

power ratings in both standalone and grid-

connected applications. The disadvantages of

grid connected PV system:

• Grid-connected PV can cause issues

with voltage regulation. The traditional

grid operates under the assumption of one-

way, or radial, flow. But electricity

injected into the grid increases voltage,

and can drive levels outside the acceptable

bandwidth of ±5%.

• Grid-connected photovoltaic (PV) can

compromise power quality. PV’s

intermittent nature means rapid changes in

voltage. This not only wears out voltage

regulators due to frequent adjusting, but

also can result in voltage flicker.

• Connecting to the grid poses many

protection-related challenges. In addition

to islanding, as mentioned above, too high

levels of grid-connected PV result in

problems like relay desensitization,

nuisance tripping, interference with

automatic reclosers, and ferroresonance.

A typical PV system is composed by a PV

array, a dc/dc converter to transform the power

provided by the PV source, and an inverter. The PV

array is characterized by a non-linear behaviour

that changes significantly with the operating

conditions, e.g. irradiance level, shades,

temperature, among others, which makes difficult

to predict the voltage and current to guarantee the

maximum power production. The operation point

in which the PV array provides its maximum power

is named maximum power point (MPP) . Then, the

main objective of the control strategy in a PV

system is to ensure the system operation around its

MPP (Maximum Power Point Tracking - MPPT) in

whichever load and environmental conditions. In

the proposed system, the sliding mode controller is

used. The controller is used to improve the

behaviour of the PV system accounting for the

changes in the environmental condition.

Sliding Mode Controller is a non-linear

control method that alters the dynamics of a

non-linear system by application of a

https://en.wikipedia.org/wiki/Voltage_regulation

https://en.wikipedia.org/wiki/Power_quality

https://en.wikipedia.org/wiki/Intermittent_energy_source

https://en.wikipedia.org/wiki/Ferroresonance_in_electricity_networks



discontinuous control signal that forces the

system to "slide" along a cross section of the

system's normal behaviour. It can switch from

one continuous structure to another based on the

current position in the state space. The motion of

the system as it slides along the boundaries is

called sliding mode. SMC is the control of

electrical drives operated by switching power

converter. Because of the discontinuous

operating mode of those converters, SMC is

used by means of pulse width modulation. In

SMC, the hysteretic modulation technique is

used. It is used to limit the range of signal.

II. EXISTING SYSTEM

R.Khanna et al (2014) proposed an

adaptive control architecture for maximum

power point tracking (MPPT) in photovoltaic

systems. MPPT technologies have been used in

photovoltaic systems to deliver the maximum

available power to the load under changes of the

solar insolation and ambient temperature. To

improve the performance of MPPT, this paper

develops a two-level adaptive control

architecture that can reduce complexity in

system control and effectively handle the

uncertainties and perturbations in the

photovoltaic systems and the environment. The

first level of control is ripple correlation control

(RCC), and the second level is model reference

adaptive control (MRAC). By decoupling these

two control algorithms, the system achieves

MPPT with overall system stability. But

increase in irradiance level and temperature,

difficult to predict the voltage and current. The

MPPT is not guarantee to track the maximum

power production under these conditions [11].

E.Mararelis et al (2014) proposed the

procedure for designing a sliding mode

controller for maximum power point tracking

photovoltaic (PV) applications is proposed. It is

applied to a single-ended primary inductor

converter, thus to a fourth-order topology, but it

can be extended to a wide class of converters

suitable for PV applications. The reachability

and existence conditions give rise to a number

of design inequalities that add to the classical

steady-state conditions in order to have the

desired closed-loop converter’s performances.

Reachability, equivalent control and

transversality condition are solved in this paper.

The stability of the system is improved but

overshoots may occur in the increased

temperature[19].

N.Femia et al (2009) proposed the

double-stage grid-connected photovoltaic (PV)

inverters, the dynamic interactions among the

dc/dc and dc/ac stages and the maximum power

point tracking (MPPT) controller may reduce

the system performances. In this paper, the

detrimental effects, particularly in terms of

system efficiency and MPPT performances, of

the oscillations of the PV array voltage, taking

place at the second harmonic of the grid

frequency are evidenced. The use of a proper

compensation network acting on the error signal

between a reference signal provided by the

MPPT controller and a signal that is

proportional to the PV array voltage is proposed.

In this paper, the MPPT parameters are chosen

greater than the suitable threshold for avoiding

low frequency voltage oscillations from grid and

disturbance caused by irradiance. The filter is

inserted between the reference and the

controller. But it does not modify the settling

time and overshoot of the PV voltage in all

environmental condition [10].

E.Bianconi et al (2013) proposed a current-

based technique is proposed: the sensing of the

current in the capacitor placed in parallel with

the PV source is one of the innovative aspects of

the proposal. A dual control technique based on

an inner current loop plus an outer voltage loop

allows to take profit of the fast current tracking

capability of the inner current loop while the

voltage loop benefits from the logarithmic

dependency of the PV voltage on the irradiation

level. The SMC sense the capacitance current.

The capacitor current changes in order to reject

the perturbation on the bulk capacitor voltage

and to track the perturbation in the irradiance

level. This SMC design satisfies only the

equivalent control condition. But it has longer

setting time[1].

Y.Levron et al (2013) proposed a fast

and unconditionally stable maximum power

point tracking scheme with high tracking

efficiency is proposed for photovoltaic

generators. The fast dynamics and all range

stability are attained by a sliding mode control

and the high tracking efficiency by a maximum

power point algorithm with fine step. In

response to a sudden change in radiation, our

experiments show a typical convergence time of

15ms. Normally the PWM based MPPT has the

convergence time of 210min . The major

advantages of SMC based MPPT over PWM

based MPPT: Fast tracking in response to a

radiation change and stability across the entire

photovoltaic curve. The stability is maintained

when the PV source is current or voltage[15].

N.Femia et al (2005) proposed the

solutions based on SMC have been proposed to

provide a good performance in the mitigation of

the load voltage oscillations and to ensure the

tracking of the reference provided by the MPPT

algorithm [10]. However, in general, these

solutions do not guarantee the existence of the

sliding-mode in all the operation range.



Moreover, the reported design of the SMC

parameters is not necessarily related with the

requirements of the MPPT algorithm, hence it is

difficult to ensure the desired behaviour of the

complete PV system, e.g. an accurate settling

time of the PV voltage is required to ensure the

stability of a P&O algorithm at any operation

condition [8], [10].

N.Femia et al (2010) proposed a new

analog Maximum Power Point Tracking

(MPPT) technique is presented and discussed.

Such a technique is particularly suitable for

Distributed Maximum Power Point Tracking

Applications (DMPPT). Its main advantages are

simplicity of implementation, absence of

memory and multiplication operations and the

high MPPT efficiency obtainable under both

stationary and time-varying atmospheric

conditions. This technique is not worth for the

grid connected system[9].

R.Mastromauro et al (2012) proposed the photovoltaic Systems (PVS) can be easily integrated in residential buildings hence they will be the main responsible of making low-voltage grid power flow bidirectional. Control issues on both the PV side and on the grid side have received much attention fr

III. SLIDING MODE CONTROLLER

Transversality condition

The transversality condition is required

to modify the system dynamics. Then, the

transversality condition is satisfied by

maintaining k ≠0.

Equivalent control condition

The next step is to analyze the equivalent

control condition, which imposes the operation

range of that control variable. For the dc/dc

converter, the correct range is 0 < α < 1.

K must to exhibit the negative sign to

ensure the system stability Therefore, the k

values must be granted to fulfil the equivalent

control condition.

Reachability conditions

The reachability conditions analyze the

ability of the system to reach the desired state.

The work demonstrated in a system that fulfils

the equivalent control condition also fulfils the

reachability conditions. The constrained limit

within the dynamic limits for the equivalent

control also fulfils the reachability conditions.

IV. CIRCUIT DIAGRAM The circuit diagram of the proposed

system having the PV panel, boost converter,

inverter, grid, Sliding Mode Controller (SMC),

MPPT -P&O algorithm shown in figure.1. The

output of the PV system is connected to the

boost converter. The gate signal of the boost

converter is given through the SMC. The SMC

compares the PV voltage and 𝑉𝑟𝑒𝑓 from the

P&O-MPPT algorithm. The P&O get the input

power from the PV panel.

The SMC has a gain values. The gain

parameter is k. These values of k is chosen as

-0.5 for satisfying the three conditions of SMC.

The boost converter boost the DC voltage from

the PV system. The DC output from the boost is

converted into AC by the three phase inverter.

The inverted AC output is connected to the AC

grid.

Figure.1.Circuit diagram of the proposed

system

V. SIMULATION OF THE PROPOSED

SYSTEM

The simulation of the proposed system is shown

in figure.2. The improved design of the SMC is

implemented in the proposed system



Figure.2. Simulink model of the proposed system.

VI. SIMULATION RESULTS

The simulation result of the boost

converter is shown in figure.3. The settling time is

reduced as 0.6ms and no overshoots are occurred

in the output is shown in figure.3. This can be

achieved by the proposed design of the Sliding

Mode Controller.

Figure 3.Voltage across boost converter

The single phase AC output is shown in the

figure.4. This Ac output from the inverter is

connected to the AC grid.

Figure 4. Voltage and current across inverter.

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60

70

Time(sec)

voltage(V

)

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1-400

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voltage(V

)

curr

ent(

I)

Vac I ac



The output pulse of the sliding mode control is

shown in figure.5. This pulse is given to the

boost converter.

Figure 5.Output pulse of the sliding mode

control

VII. CONCLUSION

This project has proposed an improved

procedure for designing the sliding mode

controller of a boost converter in a grid

connected PV system. The PV voltage tracked

the reference provided by an external MPPT

with a reduced settling time as 0.6ms and no

overshoot while being insensitive to changes in

all environmental conditions, such as solar

irradiation or PV module temperature. The SMC

forces the PV voltage to satisfactorily track the

reference. Without using the SMC, the settling

time is longer and overshoots are also in the

waveform. The controllers is used in providing

the DC voltage across boost converter with no

overshoot and the specified settling times

required by MPPT. Simulation results showed

that the controller designed following the

improved procedure fulfilled correctly all these

requirements. In the simulations, a sliding mode

controller with a very simple variable-switching

frequency hysteretic-modulation was

considered. The design of SMC can be applied

in further developments to PV systems based on

other converter topologies such as buck (e.g.

battery charges), buck-boost (e.g. module

optimizers), inverters (e.g. PV micro-inverters),

among others

ACKNOWLEDGMENT

First of all we would like to thank the almighty

for giving me sound health throughout my paper

work. This research was supported/partially

supported by our college. We thank our staffs

from our department who provided insight and

expertise that greatly assisted the research,

although they may not agree with all of the

interpretations/conclusions of this paper.

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A grid connected pv system with a variable switching frequency hysteretic modulation

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