11-08-2012, 02:48 PM
A SINGLE PHASE TO THREE PHASE CONVERTER USING QUASI Z SOURCE NETWORK
QUASI Z SOURCE INVERTER.pptx (Size: 537.66 KB / Downloads: 130)
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.
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.
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.
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.
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
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
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.
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.
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.
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.