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Welcome to Boost's website, which contains useful advice and information about high performance phase converters.
Phase converters (also spelt three phase convertors or misnamed 3 phase transformers) provide single to 3-phase conversion. Boost's range of phase converters will supply a number and variety of loads at full performance. On this site you will find a complete list of standard rotary converters supplied as a complete unit for installation by a user, a competent industrial electrician or electrical engineer.
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In this paper the output of the single phase wind generator, common for low power application, is converted efficiently into a three phase power. The (e,2e) spectrometer vacuum chamber (figure 1) is manufactured from 304 grade stainless steel, the construction being carried out by Vacuum Generators using a design of Jones, Read and Cvejanovic, full details of which may be found in T.
3mm thick mu-metal magnetic shielding is placed both internally and externally to decrease extraneous external magnetic fields to less than 5mG at the interaction region.
All inputs and outputs to the spectrometer pass through the vacuum chamber via feedthroughs on the top flange.
The top flange of the vacuum system is a 25mm stainless steel flange with 11 conflat CF70 flanges arranged around a central 200mm flange designed for locating a hydrogen source. Two flanges are used for the high voltage channeltron and photomultiplier tube inputs and pulse outputs.
Three rotary motion feedthroughs allow the analysers and electron gun angles to be changed externally via stepper motors for both analysers and for the electron gun. The ionisation gauge is placed at right angles to the main flange to prevent light from the thoriated iridium filament entering the vacuum system, which would increase noise on the photomultiplier tube. The ionisation gauge feedthrough is sooted, and a loose cover is placed over the entrance in the chamber flange to prevent stray light from the ion gauge entering the vacuum system. The target gas enters the system via a CF70 flange which has two 6mm stainless steel tubes welded into the flange. The other gas feed is connected to a hypodermic needle set at 90A° to the incident beam for measurements in other geometries.
The gas jet which is not currently used in the interaction region can be used to non-locally fill the chamber with gas for background counting measurements.
The final CF70 flange is used when the photomultiplier tube is cooled, usually during baking of the system following exposure to atmosphere. The tube is cooled by passing vapour from a liquid nitrogen source through expansion coils wrapped around the photomultiplier tube housing. The electron gun is a two stage non-selected gun designed by Woolf (Ph.D thesis, University of Manchester) (see figure 3). The gun consists of a filament, grid and anode source which is focussed using a triple aperture lens through two 1mm defining apertures in the centre of the gun. The apertures define the electron beam pencil and beam angles, and are focussed onto the interaction region using a second triple aperture lens located between the apertures and interaction region. The electron gun is shielded using advance (constantin) sheet which is grounded to the body of the gun mounting.
The gun is mounted onto an x-y translation table to allow placement of the electron beam as accurately as possible to the centre of rotation of the analysers and electron gun rotation axis.
The gas jet is mounted from the electron gun using a narrow support of 310 stainless steel, and the Faraday cup can be attached to this support. The original unselected electron gun built by Woolf was completely rewired and a custom built PTFE 25 way inline wire-wrap plug and socket was placed between the 52 way vacuum electrical feedthrough and the electron gun. The wiring from the 52 way feedthrough to the inline plug is shielded colour coded 30 awg PTFE coated advance wire, and the inline plug and socket connectors are non-magnetic gold plated wire wrap pins.
The electron analysers are constructed from molybdenum and are mounted from two rotating gear plates controlled externally via the rotation feedthroughs on the top flange (see figure 2).
The input electrostatic lenses for each analyser are three element cylindrical lenses as shown in figure 4. The interaction region is focussed onto the entrance aperture of the hemispherical energy analysers with a beam angle of around zero degrees, the image of the analyser entrance aperture being larger than the size of the interaction region. Field gradients around the input and exit apertures are corrected using standard Jost correctors.
The energy selected electrons passing through the exit apertures are finally collected by Mullard X919BL channel electron multipliers which amplify the single electron to produce a current pulse at their output. A principle source of noise on the signal pulses arises from the turbo-molecular pump motor. The noise from the turbo pump is reduced to ~ 5mV using these techniques, and as the average pulse height from the saturated multiplier is around 20-40 mV, this allows adequate discrimination following amplification. The pre-amplifiers located external to the vacuum system are commercial 100X preamplifiers with 400pS rise-times, manufactured by Phillips Scientific. The NIM signals produced by the discriminators drive two ORTEC 437 Time to Amplitude Converter's via appropriate delay cables and an ORTEC pulse delay unit. The main TAC output feeds an ORTEC Multichannel Analyser card located in the PC controlling the experiment, whereas the second monitor TAC drives an external MCA, allowing convenient monitoring of the coincidence signal as the experiment progresses. The high voltage supplies to the electron multipliers are two Brandenberg 5kV supplies controlled by the main PC via serial DAC's. Principally the filter is used to reduce pickup noise from entering via the HT cable onto the multiplier output. Secondly, the filter has a slow response time for high voltage spikes, and reduces the probability of damage to the pulse electronics should the EHT supply suddenly turn on or off. Capacitor C2 decouples the 1kW load resistor to earth for high frequency pulses from the CEM's, and the voltage appearing across this load is connected via the capacitor C3 to the input of the 6954 preamplifier. Since the input impedance of the preamplifier is 50W and the CEM is effectively an ideal constant current supply, most of the current passes through to the preamplifier. Finally, the 10M resistor prevents the output to the preamp from rising above ground when the preamp is disconnected from the circuit and is therefore a safety device for the preamplifier when initially connected. The original design placed the atomic beam nozzle and Faraday cup on the same support structure fixed to the body of the electron gun, with the atomic beam direction being in the detection plane when the perpendicular plane geometry is chosen (see figure 2). A second configuration is adopted for exclusively perpendicular plane coincidence experiments, the atomic beam nozzle being oriented at an angle of 45A° to the detection plane so that the gas effusing from the nozzle does not fill the analysers when they oppose the nozzle (see figure 6).
In this configuration the support strut for the atomic beam nozzle is terminated lower than the detection plane, as is the nozzle itself. For non-perpendicular plane measurements the Faraday cup is once mounted from the support strut and the gas effuses perpendicular to the electron beam direction. One difficulty when aligning an (e,2e) coincidence experiment lies in the focussing the incident electron beam and analysers onto the interaction region. The throughput of electron current as detected by the Faraday cup is insensitive to both position and focusing of the electron beam, since the cup opening is usually made quite large (in this case 6 - 10mm) and the bias voltage applied to the cup to prevent electrons returning to the interaction region allows all electron trajectories within this opening to be detected. Conventionally, following maximisation of the Faraday cup current, the beam is steered and focussed onto the gas jet as detected by counts in the analysers. This has the disadvantage that the overlap volume is maximised for both atomic and electron beam density, which tends to place the interaction volume as close as possible to the output of the atomic beam nozzle, which is almost certainly not in the centre of the detection plane.
To eliminate the need for time consuming iterative techniques and the associated errors due to detection geometry, a separate method for tuning the electron gun is adopted that does not depend upon the analysers. The interaction between the target and the electron beam not only produces ionisation, but the valence states of the target also are excited with various probabilities depending upon the incident energy of the electron beam. These photons are detected by the photomultiplier tube, by placing a 450nm A± 50nm optical filter in front of the photocathode. The interaction region is therefore defined where an aperture in front of the photocathode is focused by the lens.
The plano-convex focussing glass lens is covered by a grounded fine tungsten mesh to eliminate surface charging. The photomultiplier tube may be cooled by circulating nitrogen gas boiled off LN2 through copper coils encircling the photomultiplier tube housing. The photomultiplier tube used in the experiment is a 9789QB EMI photomultiplier tube with a bi-alkali photocathode peaking in the blue region of the optical spectrum. As with the electron multiplier circuitry, it is important to optimise the load of the photomultiplier tube so that reflections along the feeder line to the counting electronics are minimised. The 1nF 6kV capacitors across the dynodes close to the output stage are used as charge storage pumps that quickly refurbish the surface charge on the dynodes, allowing increased counting rates. The dynode resistors are 1% tolerance metal film resistors as these are more stable with temperature. The EHT supply to the photomultiplier tube is a Brandenberg 2kV supply operating at 1500V for this tube. The negative going output pulses from the tube measure typically 200-500mV in height, and therefore are able to directly drive an ORTEC 473A constant fraction discriminator located in one of the NIM crates. All resistors and capacitors for the dynode chain are soldered to the photomultiplier tube base internal to the vacuum system, using standard 5-core solder.
Typical pulse heights from the electron multipliers in saturation mode are 25-40mV, whereas the typical height of the photomultiplier tube pulses is of the order of 250mV. The electron multiplier pulses are obtained from the multiplier supply circuitry as explained above.
The amplified pulses from the 6954 amplifiers pass along doubly shielded RG-58 cable to the input of the ORTEC 473A discriminators. The two analyser discriminators are located in separate NIM crates to increase isolation and reduce common mode pickup.
The slow rise-time positive outputs from the 473A discriminators pass to three ORTEC 441 rate-meters which allow counting and monitoring of the pulses.
The fast NIM pulses from the analyser 473A CFD's pass through appropriate delay lines to two 437 TAC's. This second multichannel analyser allows the operator to monitor the total accumulated coincidence signal during operation. The lens supplies that control the voltages impressed onto the lens elements and deflectors in the experiment were developed over a number of years, and therefore take different forms. Three of these supplies feed the deflectors in the electron gun, the other two supply the input deflectors in the analysers. In a second 19" crate is located the gun lens high voltage supplies together with the high voltage supplies for the Faraday cup. In a third 19" crate is located the analyser voltage supplies together with a set of serial loading supplies that control the electron multiplier EHT supplies.
A further supply controls the current boost circuitry located in the filament constant current supply unit (see below).
The outputs of each computer controlled supply that drives an individual lens element or deflector are connected to a 70 relay switching board. The Digital voltmeter is in turn accessed via an IEEE-488 interface which is addressed by an 8086 slave PC which converses with the central PC which controls the experiment. The outputs from the relay board connect to the spectrometer via shielded multicore cables which take the gun voltages to the 52 way feedthrough and the analyser voltages to the two 19 way feedthroughs located on the vacuum flange.
The gun supply multicore also carries the filament supply current to the 52 way feedthrough. The Faraday cup current is measured by the Keithley Digital voltmeter when under computer control but this can also be measured by an external pico-ammeter.
In addition to the analyser electrostatic lens and deflector voltage connections, the 19 way CF70 feedthroughs are used to control signals from internal sensing opto-isolators which control the stepper motor interlocks.


The stepper motors that drive the analysers and electron gun around the detection plane are five phase motors with integral 10X reduction gearboxes driving the rotary motion feedthroughs. The intelligent stepper motor drivers are addressed via a serial port located on the controlling PC bus. An additional interference problem was traced to the RS232 serial line from the controlling PC. The PC bus was found to be poorly earthed due to very little copper being used for the bus earth.
This was cured by decoupling the 0V RS232 line from the main 0V line for the stepper motors, as is shown in figure 10. The analyser stepper motor supplies have a facility for halting the motors using limit switches which are optically coupled to the internal 68000 logic circuits driving the supplies. The SD5443-3 phototransistor normally illuminated by the TEMT88PD photodiode during operation ensured a fail-safe mechanism should any of these components fail (this automatically prevent the motors from running). Should the analysers move into a position as defined by the four criteria (a) - (d) above, a shutter located on the analyser turntables moves between the appropriate photodiode and phototransistor, shutting off the light and thereby shutting down the stepper motor current.
Only motion in the opposite direction is allowed by controlling logic, allowing the analyser to move away from the point of imminent collision but no closer. The six pairs of optocouplers that prevent the analysers moving into the Faraday cup, electron gun and gas jet support are located on the mounting struts supporting the main body of the spectrometer.
Two optocouplers are located on the side of analyser 2, and two shutters are located on the sides of analyser 1 to prevent the analysers colliding with each other. Finally a ninth optocoupler is located over the electron gun counterweight which monitors when the gun is at an angle less than 65A°, where the sweep angle around the detection plane is reduced. The current boost circuit operates from a serial driven supply card as detailed previously. The main filament drive is through six power diodes that feed the current from the constant current supply to the filament. The Darlington transistor T1 feeds additional current to the filament via three parallel 10 turn 100W trim resistors through a 1N4007 diode. As the constant current supply acts as an infinite resistance source, the boost circuit supplies additional current only when the voltage at the anode of the feed 1N4007 exceeds the output voltage of the constant current supply. Finally, the filament bias voltage (and hence energy of the electrons) is set to the midpoint of the filament by two 100W balancing resistors located across the terminals. In addition to the ADC buffer card, three independent isolated regulated supplies drive REF01 voltage reference sources for measurement of the positions of 10 turn potentiometers located on the analyser and electron gun rotary drive shafts.
The angular position of the electron gun and analysers is calibrated when the system is opened using visible laser diodes that define these angles to an accuracy of A±0.2A°.
Figure 13 shows an overall block diagram detailing the computer control and high speed pulse interfacing to the spectrometer. You are also encouraged to contact us to discuss your particular circumstances so that we may advise and assist you in your selection. A control system for impedance(z)-source inverter is designed for this wind power conversion. IntroductionSingle phase wind generator seems attractive because of its simple construction and low cost. One of these is internally connected to a gas jet which can be set at 45A° to the incident electron beam and is used in the perpendicular plane experiments. These stainless steel feeder tubes are connected to the nozzle using grounded shielded PTFE hose.
One follows the anode, another corrects the beam direction between the apertures and a third steers the beam onto the interaction region. This shield is coated with aerodag colloidal graphite to reduce patch fields on the surface of the metal, and is made as small as possible to allow the analysers to approach the gun as close as is feasible when non-perpendicular plane geometries are selected (see figure 2). The XY translation table is mounted from the rotating yoke, to which is attached the photomultiplier tube.
This allows the gun to be dismounted from the system without the need for rewiring of the feedthrough when the need arises (filament changes, cleaning etc). The wiring between the gun and inline socket is also shielded colour coded PTFE coated advance wire facilitating spot welding to the electrostatic lens elements of the gun. The analysers are mounted onto x-z translation tables that allow them to view the interaction region accurately over the full range of angles accessible.
These lenses have a capability for energy zooming of around 10 : 1, and have a maximum entrance acceptance angle of A±3A° as defined by the entrance apertures. This ensures that the overlap volume accepted by each analyser encompasses the interaction volume for all detection angles as the analysers move in the detection plane. These devices use an activated lead glass internal surface which has a high coefficient of secondary electron emission when a high voltage (around 3000V) is applied across the multiplier. This noise may be picked up by the channel electron multiplier and the high voltage feed to the multiplier, and is generated internally in the vacuum system. The CFD's are operated in NaI mode as this has a 2ms dead time following the initial pulse, thus reducing the possibility of false triggering due to any mismatching impedance reflections along the delay cable.
These EHT supplies are connected via VERO 200 high voltage couplings to high voltage cable connecting to the pickoff circuitry located on the high voltage feedthroughs. This allowed the analysers to roam the detection plane over a complete 360A° angular range.
The configuration of the target source hypodermic when perpendicular plane measurements are conducted. The common procedure is to initially maximise the current from the gun onto the Faraday cup, then onto analyser counts as the electron beam is moved through the gas jet.
Maximising the Faraday cup current is therefore only a crude preliminary alignment of the incident electron gun beam. This therefore assumes that the analysers are initially focused onto the interaction region, and a slow iterative technique must be adopted where the analysers and electron gun are tuned so as to maximise the signal from both analysers. In this case a true differential cross section is not obtained, since the scattered and ejected electron trajectories lie in a different plane than defined in the initial experimental alignment.
An EMI 9789QB reduced photocathode photomultiplier tube is installed in the vacuum system together with optical focussing and defining elements (figure 2).
A group of these excited states decay back to lower valence states with the emission of visible photons at wavelengths around 450nm for both helium and argon targets. Tuning of the electron gun to PMT counts therefore guarantees that the electron gun is steered and focussed to the point at the centre of the detection plane independent of the analysers or gas beam density. This is mainly used when the vacuum system is baked at temperatures above 55A°C, since the photocathode is rapidly damaged by temperatures exceeding this. The tube is a venetian blind dynode construction, and has a reduced photocathode to decrease the noise on the output of the tube to less than 20Hz. The photomultiplier tube base was thoroughly cleaned in an ultrasound following location of these components, to displace any flux residue from the solder joints.
It is therefore necessary to amplify the channeltron pulses prior to transmission to the discriminators, whereas the photomultiplier tube pulses are sufficiently large to not require further amplification. These pulses are amplified by Phillips Scientific 6954 100X amplifiers located external to the EHT feedthroughs connected by 10cm lengths of RG-58 cable.
These crates are further decoupled from the AC mains supply using filter circuitry on each supply line. Internal to these rate-meters buffer 7400 TTL chips have been added to send to 32 bit counters located in the main PC via RG-58 cable.
These supplies are fully floating, their mid-point voltage being equal to the lens element voltage in which the deflectors are housed. All these supplies are fully computer controlled isolated units with low output impedance to reduce noise and eliminate current loops. This relay switching unit allows either the voltage or the current on each lens element to be measured by a Keithley Digital voltmeter. This drive is further reduced internally by 10X reduction gears, resulting in a reduction ratio of 100:1. This led to the ground line of the RS232 serial line moving around with respect to the 0V stepper motor reference as drive current to the motors returned along the ground line. The optocoupler logic circuit circuit that controls the stepper motors and avoids collisions between the analysers, the electron gun, the Faraday cup and the hypodermic support. Added to this filament supply is a computer controlled current boost circuit that can be used to increase the filament current during electron gun tuning.
The additional current then returns to the 12V DC regulated supply via a second 1N4007 diode. This therefore depends upon both the current driving the filament, as well as the resistance of the filament when hot (typically 4W - 6W).
This supply feeds current to the filament without changing the characteristics of the main constant current supply used while operating the spectrometer.
These high stability reference sources ensure that the analyser and electron gun positions are accurately measured with time. A datalogger internal to the controlling PC establishes a cubic spline relationship between the measured angles and the corresponding ADC conversion from the potentiometers. This PC also controls the selection of the relay motherboard for measurement of the required lens element either in voltage or current mode when a request is sent from the controlling computer via an RS232 serial line. Remember that at Boost we pride ourselves on the quality of our pre and post sales service and support.
The variable single phase ac output of wind generator due to unpredictable variation in wind speed is suitably controlled through a closed loop system employing the buck-boost capability of z-source inverter. For rural energy supply the development of wind power especially as smaller machines in the 5 - 100 kW range is becoming popular. The spectrometer is shown configured in the perpendicular plane, the electron gun being placed in the vertical position with respect to the analysers which span the horizontal detection plane. The electron source is a heated tungsten hairpin filament heated by passing around 2A of DC current through the filament.
The saturated gain of these devices yields around 1E8 electrons in the output current pulse for a single electron which enters the input cone. This allows the analyser to roam over a complete 360 degrees of the detection plane when in this geometry (apart from the position where the analysers would clash wth each other). The analysers are then adjusted for maximum signal count and the procedure is iterated until a maximum is found. The dark noise count is also reduced when cooled, however since the reduced cathode PMT only produces dark counts of less than 20Hz at room temperature, this is not necessary during routine operations.
The 1.82M resistor was chosen to optimise the single photon counting efficiency of the tube. It is not found that these solder connections significantly affect the ultimate vacuum pressure in the system. Isolated DC supplies to these amplifiers is obtained from a standard +15V supply, the circuit diagram being given in figure 8.
The power supply to these TTL buffers is derived from the rate-meter supplies via 7805 5V regulators located internally. This supply boosts the current without changing the main supply, thus ensuring supply stability before and after the electron gun is tuned. The z-source PWM inverter replacing the conventional PWM inverter provides the unique output voltage regulation by making an appropriate choice of boost factor under both variable generator voltage and variable load conditions. Wind power is used to provide electricity to individual homes or other facilities on a self-reliant basis.


The electron gun is a two stage non-energy selected gun that produces an incident electron beam current of up to 4 microamps at an incident energy from around 30eV to 300eV.
The 470k resistors bias the dynodes to achieve saturation of the current pulse at the output of the tube, hence biasing the tube for single photon counting applications. This was found to be necessary to eliminate problems associated with current loops from the 20A peak motor current feeding the common point of the logic circuitry. The closed loop controller carefully monitors the wind generator voltage and controls the shoot-through and non-shoot through duty cycles of the inverter to develop a three phase steady boosting voltage, which is not possible by conventional PWM control. The power generated in the wind depends on air density, swept area of rotor and of course on upwind free wind speed. The analysers are identical, and consist of a 3-element electrostatic lens focussing the interaction region onto the entrance of a hemispherical electrostatic energy analyser. The Anode deflector pair corrects for any misalignment of the filament emission point with respect to the axis of the electron gun.
But actual power output depends on several other factors like type of machine or rotor, the sophistication of blade design and the various losses like friction loss, loss in pump and loss in the other equipment connected to it. The Chamber is lined internally with 3mm thick mu-metal, and a mu-metal cylinder encloses the chamber externally as shown.
The electrons selected in angle and energy are amplified using Mullard 919BL channel electron multipliers. The defining apertures limit the pencil and beam angles of the electron beam following focussing by lens 2 onto the interaction region. The load is set by the 50W resistor across the anode to the HT feed, the pulse being decoupled to ground via the 1nF capacitor.
The system is simulated under arbitrary generator output condition both in surge and sag states and results steady three phase voltage across load. This reduces the magnetic field at the interaction region to less than 5mG, an acceptable level for the electron energies used in this experiment. The interaction region defined by the interaction of the gas target beam and the electron beam is focussed onto the photocathode of an EMI 9789QB photomultiplier tube via a lens, 450nmA±50nm optical filter and defining aperture. Placement of the apertures ensures that the beam angle is close to zero degrees at the interaction region over a wide range of energies, whereas the aperture opening reduces the pencil angle to around A±2 degrees over this energy range. They are:· Squirrel-cage induction generator· Doubly-fed (wound rotor) induction generator· Direct-drive synchronous generatorThe first one is the simplest and oldest system where the rotor speed variation is small and hence this is normally referred to a constant speed turbine.
The target gas effuses from a 0.6mm ID hypodermic needle constructed from platinum iridium alloy.
The 10MW safety resistor prevents the output charging up to a high voltage if the feed is disconnected. The deflectors between the apertures correct for space and surface charge beam variations inside the field free region, whereas the final deflectors allow the beam to be steered onto the interaction region defined by focussing a 1mm aperture in front of the photomultiplier tube onto the gas target beam. The proposed closed loop system, therefore, can be used for smooth and effective dynamic and steady state control maintaining the level of three phase output at a desired level. The main operating characteristic of the squirrel cage induction generator is that this always consumes reactive power. The electrons passing through the interaction region which are not scattered are collected in a Faraday cup opposite the electron gun. Also, this type ofgenerator tends to slow down voltage restoration after a fault and this can lead to voltage and rotor-speed instability.
The gun, photomultiplier tube, gas hypodermic and Faraday cup all rotate on a common yoke with an axis through the centre of the horizontal detection plane, allowing all geometries from the perpendicular plane to the coplanar geometry to be accessed.
When the voltage does not return quickly enough, the generator continues to accelerate and consumes even larger amount of reactive power. To prevent these types of instabilities, active voltage regulators like the Static VAR compensator (SVC or STATCOM) are included in the system as detailed in[2]. The self-excited induction generator (SEIG) has been proved to be a better replacement due to several advantages such as ruggedness, brushless, maintenance-free features, off-the shelf availability, reduced unit cost, no required synchronization system and no need for DC excitation[3]. However, they must deliver power to the consumer with acceptable form and so, this requires suitable controllers.
The critical function of those controllers would be to provide a required variable capacitive reactive power (VAR) to maintain a constant voltage across the variable load at varying prime mover speed[4]-[6]. Gupta, “ Analysis and design of STATCOM-based voltage regulator for self-excited induction generators”, IEEE Trans.
In[7], the voltage and frequency control are investigated by varying the effective rotor resistance of a self-excited slip-ring induction generator.
A study is done for SEIG employing a STATCOM through a sine PWM inverter working in synchronous mode[8].The other two generating systems are variable-speed systems.
In the doubly-fed induction generator (DFIG), a back-to-back voltage source converter feeds the three-phase rotor winding that results the mechanical and electrical rotor frequency decoupling and the electrical stator and rotor frequency matching, independently of the rotor speed[9].
A dynamic model with reduced-order double cage representation for the DFIG and its associated control and protection circuits has been developed and stability study is presented in[10]. A grid-connected wind driven doubly fed induction machine with stator-flux-oriented vector control approach is also presented in[11] for optimum active power control. Shilpakar, “Analysis of a novel solid state voltage regulator for a self-excited induction generator”, IEE Proc.
In the direct-drive synchronous generator, the generator is completely decoupled from the grid by two converters- one is connected to the stator winding and another is connected to the grid.
For the variable speed operation, this acts as a frequency converter that can limit the current to rated values during dips, and continue to deliver real power and reactive power at reduced voltage levels. Therefore, in the event of a fault, these turbines could stay connected to the grid and may help the conventional power stations rebuild the voltage after grid failures[12]. A mechanical interface consists of step up gear and a suitable coupling transmitter, which is connected between wind turbine and Synchronous Generator (most of the cases, permanent magnet Synchronous Generator (PMSG) are used). Since the wind is an intermittent source of energy, the output voltage and frequency from generator vary according to wind velocities.
Traditionally, this variable AC power from this generator is rectified first into DC and then is regulated for constant voltage by using dc to dc converter.
Abdel- Halim, “Solid-State control of wind driven self excited induction generator”, Electric Mach. The constant DC output then is fed to the load at the required level of voltage and frequency employing a PWM inverter.
The major requirement in this wind energy system is to realize and maintain consistently a constant voltage at the load terminal using minimum amount of circuitry. One recent application for permanent magnet generator with ac series regulator is proposed in[13], but the control circuit is complex in nature. In[14] a new topology of general voltage regulator is described based on the ac-ac buck-boost converter.
The controller used, provides good dynamic response for large input voltage variations, but not suitably tuned for wind power application.The focus in this paper is to employ impedance source inverter in place of conventional system and converting the single phase supply to a three phase regulated supply through a simple closed loop control. The buck-boost capabilities of impedance source inverter are expected to take care both the generator output voltage and load variations. A number of switching methods have been proposed so far to control Z-source inverter shoot-through and non-shoot through states[15].
Lai, “Voltage and frequency control of self excited slip-ring induction generators”, IEEE Trans. The methods include the sinusoidal PWM (simple boost control[16], maximum boost control[17] and modified space vector modulation based PWM[18]). Different applications of Z –Source inverter are also proposed, which includes motor drives[16], fuel cell[19] and renewable energy sources like solar system[20]. In line with the recent advancements of z-source inverter applications in different alternative source of power, this work deals with a proposed solution where z-source inverter is used with wind generator to provide a stable uninterrupted constant voltage power source employing simple control system.2. Operation of Impedance Source InverterAn Impedance (z) source inverters has been already proposed and proven as an alternative power conversion system because of its steady state voltage buck and boost characteristics using a unique impedance network. Bhadra, “A Study on STATCOM Excited Variable Speed Squirrel Cage Induction Generator”, in Proceedings of Int. It contains two-port network that consists of a split-inductor and capacitors which are connected in ‘X’ shape to provide an impedance source or z-source. 1” represents the circuit model of the z-source inverter where two switches S1 & S2 are arranged to show the shoot through switching and non shoot through switching. The switching can be performed in three states, the first state when S1 is turned on and S2 is turned off, which is the shoot through state. During this state, the input diode is reversely biased, the capacitors charge the inductors, and the output current is freewheeling through the diode.
The second state is when both switches are turned off, which is the traditional zero state. During this state, the capacitors are charged by the inductors, and output current is freewheeling through the diode. The third state is when S1 is turned off and S2 is turned on, which is the active state having duty ratio m (m+d ? 1) and the inverter applies voltage to the load.From the symmetry and the equivalent circuits, the output peak phase voltage from the z-source inverter can be expressed as whereas the output peak ac phase voltage of the traditional PWM inverter is given by Here V0 is the dc source voltage, M is the modulation index. B ?1 is the boost factor taken from the shoot-through zero state, which is further expressed as Figure 1. A wind turbine with single phase permanent magnet synchronous generator (PMSG) is selected here. The single phase output voltage which is normally variable in nature is rectified to a DC and is connected with the inverter through the z-source network. The development of the control system for the z-source inverter using the closed loop mechanism is the main focus of this work. This controller is used to regulate and boost the generator voltage to deliver quality stable power to the load or utility grid.
The control loop compares the voltage of capacitor of the z-network to a reference value and the error is fed to the P controller to create a reference signal.
This reference signal is then compared with a triangular pulse and generates shoot-through pulse.
The lower the reference signal amplitude the higher the shoot-through duty cycle as well as the boost factor.
Same triangular pulse is used to generate the sinewave PWM signals conventionally used for bridge inverter. The closed loop system has been found to be stable with only a proportional controller in the feed-forward path.
The transfer function of the closed loop system has been obtained from matlab simulink control design linear analysis tool having the operating point as the simulation snapshot. The obtained transfer function is (2)All the poles of the transfer function (2) lie in the left half of the s-plane, so the closed loop system is a stable system.
The transient stability analysis of the system by observing the step response shown in “ Figure 3” also supports that.Figure 3. Qian, “Maximum boost control of the Z-source inverter”, IEEE Transactions on power electronics,vol.
Holland, “Application of Z-source Inverter for Traction Drive of Fuel Cell”, IEEE Transactions Power Electronics,vol.



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