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Switched Boost Inverter using Coupled Inductor for
Renewable Energy Sources
Wilma Sharon. F
PG student in Power Electronics and Drives, Kings College of Engineering, Punalkulam
N. Rajeswari M.E.,
Assistant Professor, Kings College of Engineering, Punalkulam
Abstract- Many recent industries require converters with large voltage conversion ratio. This requirement can be achieved by introducing Coupled Inductor instead of inductor in the Switched boost Inverter (SBI) circuit. Output from SBI is given to the grid so the grid synchronization is achieved by using SOGI Second Order Generalized Integrator(SOGI) based PLL(Phase Locked Loop) and the current is regulated by the Synchronous Reference Frame (SRF) technique. Control strategy is implemented by Microcontroller digital domain kit. This paper shows the increased output DC voltage from the SBI circuit.
Index terms- Coupled Inductor (CL), Switched Boost Inverter (SBI), SOGI, and SRF.
Distribution power generation system (DPGS) is based on renewable energy sources like PV panel, wind, fuel cell (FC), etc. They are free from emission, more reliable, efficient, and generate better quality power . A distributed power generation system using Switched Boost Inverter (SBI) as a power interface.These systems are used for residential power applications. The SBI can produce simultaneously dc and an ac output, from a single dc input as shown in fig.1.Unlike the traditional Voltage Source Inverter, the ac output voltage of SBI can be either higher or lower than the available dc input voltage . Also, as the SBI is tolerant to the shoot through in the inverter phase legs, it gives good immunity to EMI noise. Thus, the reliability of SBI increased in overall system. Now the need of more voltage is required and the conversion ratio has to be increased. The converters have to work on an extreme duty ratios but it is not possible as they have the latch up problem and creates severe switch stress along with the saturation problem. To produce few watts and few kilo watts, the following solutions are used but they have some drawbacks
i. Transformer-based converter: using transformers
produces many losses.
ii. A cascade of two boost converter: two energy
processing steps large element and decreases efficiency.
iii. Quadratic boost converter: two sets of passive
iv. Boost-converter with diode-capacitor multiplier.
So the introduction of the coupled inductor is done in this paper. It has a large conversion ratio like twice as compared to the previous methods. This makes the system more reliable, constant dc voltage can be maintained, applicable in electrical appliances etc.
Fig. 1 Schematic Block Diagram of Switched Boost Inverter based DPGS
II. REVIEW OF COUPLED INDUCTOR
Concept of using coupled inductor (CL)  in the converter has put forward in the recent years making the system more compact and efficient with the majority of achieving high voltage gain in the boost mode converter of SBI. Coupled inductor is basically similar to transformer but they have some difference in them such as follows power flow, current direction, leakage inductance etc. Controlling algorithm in transformers based topology is difficult.
When current flows through conductors, magnetic field is generated. Steady-state current will induce a steady magnetic field, and a time-varying current will induce a time varying magnetic field. Nearby conductors will generate a current as
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the varying magnetic flux permits the conductor, as stated by Faraday's law. Two inductors or coils that are linked by electromagnetic induction are said to be coupled inductors. When an alternating current flows through one coil, the coil sets up a magnetic field which is coupled to the second coil and induces a voltage in that coil. The phenomenon of one inductor inducing a voltage in another inductor is known as mutual inductance.Coupled coils can be used as a basic model for transformers. It is an important part of power distribution systems and electronic circuits.
Fig. 2 Circuit diagram of simple coupled inductor based boost converter.
The switching frequency is directly related to the inductance of windings so if this frequency gets varied then the windings of CL must also vary. The voltage gain is increased by using a CL. The copper usage with low number of winding helps in reducing the magnetic core losses.
Generally, the total energy stored in the inductor is given as,
W= (1/2) Li2.
L - Inductance.
i - Current through the inductor.
This CL that we use for boosting the DC voltage is modified in the SBI. Controlling of these energies in the device is done by the switches. ON and OFF of these switches stops the flow of electricity into inductor and allowed to store in magnetic field for brief time. Operation of the switches and the diodes are by soft switching techniques. The coupled inductor and the series diode, which are connected in parallel to the diode of basic converter, new large conversion ratio converters are derived as shown in the fig.3.
The inductors (L1 and L2) which are coupled here can only help in increasing the voltage conversion ration from the input DC voltage. As shown in the fig.3 the switches (s1, s2, s3 and s4) are there to control the DC conversion and the current passing through the circuit. As per the requirement of the DC voltage the number of switches can be added in the DC voltage or source side of the circuit. The output from the source side (i.e.) the DC output voltage can be connected to any dc load or it can be connected to the inverter which converters the DC to AC output voltage.
Fig. 3 Circuit Diagram of Coupled Inductor.
In the AC output side, the circuit operates normally by ON and OFF of the switches (Q1, Q2, Q3, and Q4) using the proper firing angle like the inverter circuit operates. Capacitor allows storing energy in every ON and OFF of the switch S(S ON discharges, S OFF charges). Diode helps in preventing the discharging of the capacitor through L1 and L2. The coupled inductor increases the magnetic field which helps in
transferring more amount of energy to gird as required
Fig. 4 Controller Block Diagram of SBI
The task of controllers in this block is that they help in generating the gate pulses for the switches in the Switched Boost Inverter circuit. The Vdc, P, Q injected into grid are regulated with respect to their reference values so to accomplish this the microcontroller kit is required. An inbuilt 12-bit analog to digitalconverter is there which receives the feed signals (AC and DC voltage and inductance current) from SBI. These feed back signal and the reference signal (Vdc*, Pg*, Qg*) are given as the input signal to the microcontroller based controller block. Here, reference DC
voltage Vdc*, ω, Vd, Vq, Pg*, Qg*, Id, Iq, Vdc are given as an
input to the controller and the modulation signal is the output
of the controller. This modulation signal (Mq and Md) are
Ca La S4 S3 S2 S1 R0 Co C2 L2 Db Q4 Q3 Q2 Q1 + -Vs Da L1 C1
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again send to the dq to 1ϕ block which changes it into the modulation index m. This ‘m’ and the Duty cycle ‘D’ is input to the ePWM.
Vdc*- reference dc output voltage. Pg*- reference active power Qg*- reference reactive power Vd, Vq- voltage in dq reference frame.
ω – frequency, θ- Phase Angle (∫ .
Id, Iq- curren in dq reference frame.
a. SOGI and QSG(Quadrature Signal Generator)
The phase, frequency, and amplitude of the grid voltage are critical information for the operation of the grid connected system. For such application, accuracy is needed and also fast detection of thephase angle, frequency and amplitude is essential to assure the correct generation of reference signals and to cooperate with new standards.This structure has a simple implementation;
i. The generated orthogonal system has filtered
without delay by the same structure due to its resonance in the fundamental frequency,
ii. The proposed structure is not sensitive to the
The actual grid code requirements include specific demands for the grid connected wind power generation facilities. The Transmission System Operators(TOS) are more concerned about the Low Voltage Ride Through (LVRT) requirements are becoming more restrictive in terms of the disconnection conditions, but also in the active and reactive power that wind farms should inject to the network under fault conditions to support the grid. Solutions based on the installation of compensators such as STATCOMs and DVRs, are on advanced control functionalities for the existing power converters of wind power plants, have contributed to enhance their response under faulty and distorted conditions because to fulfil these requirements. However, in order to achieve satisfied result with such systems it is necessary to count on accurate and fast grid voltage synchronization algorithms which can be able to work under unbalanced and distorted conditions. The PLL based on SOGI also separates and perfectly detects the phase angle of positive and negative sequence components but module that converters them into firing signals for the switches in the switched boost inverter (SBI). Fig.6 block diagram of PLLbased QSG involve Quadrature Signal Generation (QSG) with the use of SOGI. Two SOGI based QSGs are used to obtain the in phase and quadrature components of the α- axis and β- axis voltage. The α and β axis voltages of the positive and negative sequence components so obtained are fed to two separate conventional SRF PLLs which separately obtain the d and q axis voltages of the two sequence components and hence the corresponding
phase angles are properly detected. The block diagram of the algorithm is shown in fig.5.
Fig. 5 Block Diagram of SOGI Based PLL Technique
The quadrature signal generator consists of a quadrature signal generation block and a phase control loop to calibrate quadrature signals in respect with the real-time. The phase of a phase shifter is tuned by a current controller from the phase control loop. The two phase detector detects the error of quadrature signals. A charge pump generates a feedback voltage to control the phase of the phase shifter as shown in the fig.6.
Fig. 6 Block Diagram of QSG based PLL Technique
b. Voltage Controller
A voltage controller also called an AC voltage controller or AC regulator is an electronic module based on thyristors, TRIACs, SCRs or IGBTs, which converts a fixed voltage, fixed frequency alternating current (AC) input supply to obtain variable voltage in output delivered to aresistive load. This varied voltage output is used for dimming street lights, varying heating temperatures in homes, industries and many other applications. A voltage controller module always comes under the preview of power electronics.
There are essentially two types of voltage controllers: single-phase voltage controllers which control voltage of 230 rms, 50 Hz power supply, and three-phase voltage controllers which control 400 rms voltages, 50 Hz frequency (depending on the country).
The DC supply can be switched rapidly on and off, the load waveforms will be those shown. A continuously variable average voltage from (nearly) zero to (nearly) the full supply
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voltage is available by changing the duty cycle of the switching.
Fig. 7 Basic Pulse Width modulation (a) Simple circuit and (b) Pulses for each duty cycle.
The “nearly” has to be added, because switching devices in the real world have minimum on times that produce a small output and minimum off times that prevent them from reaching full output voltage in a controlled manner. They can be switched completely on or completely off, but small prohibited areas of control always exist near those extremes. Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique that controls the width (in time) of an electrical pulse usually the pulse's duration based on modulator signal information. Though the modulation technique used to encode information for transmission, it is mainly used is to allow the control of the power supplied to electrical devices, especially to the inertial loads such as motors. In addition, PWM is one of the two principal algorithms used in photovoltaic battery chargers and the other being MPPT.From these two DC signals in dq domain, the sinusoidal modulation signal(m) of SBI can be obtained using dq to 1Φ transformation given in the equation below.
The outputs of the controller (D and m) are given as inputs to the ePWM modules of microcontroller which is the key peripherals to generate the PWM signals of SBI .
d. Simulation of C oupled Induct or
Fig. 8 Simulation diagram of coupled inductor.
The simulation explains the operation of the coupled inductor as shown in the fig.8, need 4 switches and a coupled inductor with a diode which helps in controlling the reversing of the current.
Fig. 9 Simulation Output of Coupled Inductor
e. Simulation of Proposed System
Fig.10. Simulation Diagram of Proposed System
Discrete, Ts = 5e-005 s. powergui v +-v + -v + - v + -1 2 g m D S g m D S g m D S g m D S K*u Gain2 10 Gain1 0.3057 Display m a k m a k i + -i + -i + -Discrete, Ts = 5e-006 s. powergui power iref1 g A B + -inverter 1 i + -ic1 i + -iDC3 i + -iDC2 i* PID control1 v + -es1 p1 p2 p3 p4 coulped inductor v + -Vout1 v + -VM4 v + -VM3 out_Port1 out_Port 2 Pv system P\Q1 ic ic* pu ls e PWM1 ugrid iref PLL1 OUT_v/i/i* Mean Mean Value2 MPPT1 Load1 L4 L3 P2 Goto4 Udc1 Goto1 D1 From1 Divide5 Divide4 Divide2 600.3 Display2 -2410 Display1 Diode4 V I PQ Active & Reactive
Power1 110V 50Hz1
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Fig.11 Simualtion Output of Proposed System
By proposing a switched coupled inductor cell, inserting it to the classical DC-DC converters, new converters with high DC voltage gain is obtained. The energy of the leakage inductance was transferred to the load in a non-oscillatory way. Soft-switching of all switches was obtained: the transistor turns ON with ZCS and turn OFF with ZVS similarly for the diode ON and OFF respectively. In addition to coupled inductor, a single diode is added, and that was that only way of conducting without a switching losses. As a result, a good efficiency was obtained. Coupled inductor helps people in charging mobile, players, and small rechargeable devices. As it can transfer more energy they are used in high electricity required industries and fields. It can also be used in residential application such as fluorescent lamps, fans, bulbs etc.Single stage conversion is achieved through Switch Boost Inverter. Coupled Inductor provides high power output. Capacitor provides constant DC output voltage. Efficiency is increased.
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