1. A SINGLE PHASE TO THREE PHASE CONVERTER USING QUASI Z SOURCE NETWORK
DONE BY:
P. Govindan –
M. Mohammed Abdul Raheem –
S. Muthukumar –
PROJECT GUIDE:
Mr. Y. Chiranjeevi
Lecturer – EEE Department

2. ABSTRACT
This project presents an impedance-source power inverter and its control method for implementing dc-to-ac power conversion.
The quasi impedance source inverter employs a unique impedance network to couple the inverter main circuit to the power source.
Providing unique features that cannot be obtained in the traditional voltage-source and current-source inverters where a capacitor, diode and inductor are used, respectively.
The quasi impedance source inverter overcomes the conceptual, theoretical barriers and the limitations of the traditional VSI & CSI.

3. OBJECTIVE
Objective of this project is to implement an qausi Impedance Source network to Three phase Inverter for AC conversion.
Control of the three phase is through the simple boost PWM technique.
This inverter can boost the input voltage, minimize the component count, increase the efficiency and reduce cost.
To reduce the harmonics and high voltage gain.

4. VOLTAGE SOURCE INVERTER
In voltage source inverter the input voltage remains constant
When the power requirement is high, VSI are used in three phase inverters.
The gating signals for the three inverters have a phase difference of 120o.
The voltage source inverter is only buck (step down) inverter operation for DC to AC power conversion.
VSI has various problems like low voltage gain and less efficiency.

5. CURRENT SOURCE INVERTER
A current source inverter is fed from a constant current source. Therefore load current remains constant irrespective of the load on the inverter.
When a voltage source has a large inductance in series with it, it behaves as a current source.
The current source inverter is only boost (step up) inverter operation for DC to AC power conversion.
It consists of six switches and with anti parallel diodes. These diode provides bidirectional current flow and unidirectional voltage blocking capability.

6. IMPEDANCE SOURCE INVERTER
This Impedance source inverter is used to overcome the problems in the voltage and current source inverters.
This impedance source inverter employs a unique impedance network coupled with the inverter main circuit to the power source.
This inverter has unique features compared with the traditional sources as
Both buck and boost operation
Main circuits are interchangeable
Reduced harmonic interference to main circuit

7. QUASI IMPEDANCE SOURCE NETWORK
Impedance network is a two port network. A two port network has only two pairs of accessible terminals.
Usually one pair represents the input and other represents the output.
This network has impedance, capacitance and diodes in the network.
L1, L2 are series arms inductances and C1, C2 are the parallel capacitances.
This network is coupled with the main circuits and the source

8. BASIC QUASI IMPEDANCE SOURCE NETWORK

9. PRINCIPLE OF OPERATION
The three phase impedance source inverter bridge has nine permissible switching states unlike the traditional voltage source inverter that has eight switching states.
The impedance source inverter bridge has one extra zero state. When the load terminals are shorted through both upper and lower devices of any one phase leg or all three phase legs. This shoot through zero state is forbidden in the VSI, because it would cause a shoot- through.

10. PRINCIPLE OF OPERATION
This network makes the shoot through zero state possible. This states provides the unique buck-boost feature to the inverter.
The inverter bridge is equivalent to a short circuit when the inverter bridge is in the shoot-through zero state. The equivalent switching frequency from the Impedance source network is six times the switching frequency of the main inverter , which greatly reduces the required inductance of the Impedance source network.

11. PRINCIPLE OF OPERATION
There are two topologies used and they are
Shoot Through
Non Shoot Through
SHOOT THROUGH:
This state is introduced by turning on the two switches from a phase leg of the inverter bridge.
The inductors in the quasi network are connected In shunt for charging by the Z source capacitors and the common voltage expression is written as V1 = Vc

12. PRINCIPLE OF OPERATION
NON SHOOT THROUGH:
It is represented by one of the traditional active and including the null states.
In this states the diodes conduct and causing all the inductors to series discharge their energy to external load.
The common inductive voltage expression is V1 = (Vc-Vdc)/n
The boost factor increases as the number of cascaded cells increases and the gain also increases.

13. ADVANTAGES OF QUASI IMPEDANCE SOURCE NETWROK
The impedance source inverter concept can be applied in all ac-ac, dc-dc, ac-dc, dc-ac power conversion.
The output voltage range not limited.
The impedance source inverter does not affected by the electromagnetic interference noise.
The impedance source inverter cost is low .
The impedance source inverter has low current compare the traditional sources.

14. BLOCK DIAGRAM OF THREE PHASE CONVERTER

15. CIRCUIT DIAGRAM

16. PIC 16F877A MICRO CONTROLLER
We are using PIC 16F877A for producing switching pulses to multilevel inverter.
A carrier frequency of 2Khz is generated within the controller and PWM is got at the output ports.
The microcontroller drives the driver circuit so as to boost the voltage triggering signal to 12V.
To avoid any damage to micro controller due to direct passing of 230V supply to it we provide an isolator in the form of relay circuit before the same driver circuit.

17. PIC 16F877A PIN DIAGRAM

18. CONTROL STRATEGY SIMPLE BOOST CONTROL
Control methods for the Quasi Z-source inverter and their relationships of voltage boost versus modulation index.
Two control methods to obtain maximum voltage gain of the Z-source inverter.
The method has the shoot through period without effecting the active states by turning all zero states into the shoot through zero state, thus maximum output voltage can be obtained for a given modulation index.

19. CONTROL STRATEGY SIMPLE BOOST CONTROL
The simple boost control method, which has three 120 deg phase shifted sinusoidal compare signals.
Two straight compare values (Vp, Vn) whose level equals to or is greater than the peak value of sinusoidal compare signals
It is quite similar to the traditional carrier-based PWM control method. The point is: this control method maintains the six active states unchanged and turns all zero states into shoot-through zero states.

20. WAVE FORM FOR SIMPLE BOOST CONTROL

21. SIMULATION

22. SIMULATION OUTPUT

23. APPLICATIONS
The application of adjustable-speed drives in commercial and industrial facilities is increasing due to improved efficiency, energy savings, and process control.
Back to back converters for variable speed wind turbines
DC to DC converters for short term energy storage systems
Battery discharge to Grid Applications

24. MERITS OVER THE OTHER INVERTER
The boost factor, B is increased from 1 / (1 -2D) of the impedance network to (1+D) / (1–2D-D2) of the quasi impedance source network, where D is the duty cycle.
The output voltage is V = B . Vdc
The voltage gain of the simple boost control is, G = ma.B
The Z-source inverter system can produce an output voltage greater than the ac input voltage by controlling the boost factor.
Reduced harmonics due to the storage capacitors at the quasi network

25. CONCLUSION
The Quasi impedance source inverter employs a unique impedance network to couple the inverter main circuit to the power source, thus providing unique features that cannot be observed in the traditional inverters, where diodes, capacitors and inductors are used, respectively using PWM control.
The Impedance source technology can be applied to the entire spectrum of power conversion.
Unique features include buck-boost inversion by single power-conversion stage, improved reliability, strong EMI immunity, and low EMI.

26. FUTURE WORKS
The Boost factor of the inverter can be improved further by using Maximum Boost control.
The efficiency and the harmonics can be reduced by introducing Space vector model of PWM.
Cascading more number of inductors, capacitors and diodes can reduce the voltage stress across the capacitors during the starting condition.

27. REFERENCES
European journal Of Scientific Research “ Switched Quasi Z source Inverters with Extended Boost Capabilities”
International Conference on Renewable Energies and Power quality “ Experimental Verification of Novel Bi Directional qZSI Based DC/DC converter for short term Energy Storage System”
10th International Symposium “ Comparison of PWM methods for a quasi Impedance Source Inverters”
Z-Source Inverter Fang Zheng Peng, Senior Member, IEEE
Comptun.K.T(1947) ‘Design of impedance(lattice) network in Electronics devices and circuit theory’, prentice-Hall of India,New Delhi.

28. THANK YOU