GB2506121A

GB2506121A - Vector controlled three-phase voltage stabilizer

Info

Publication number: GB2506121A
Application number: GB1216752.4A
Authority: GB
Inventors: Martin Xavier
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-09-20
Filing date: 2012-09-20
Publication date: 2014-03-26
Anticipated expiration: 2032-09-20
Also published as: GB201216752D0; GB2506121B

Abstract

A three phase, three wire voltage stabilizer regulates an unregulated 3 phase AC source to a regulated three phase AC output. The regulator consists of a buck-boost transformer primary PR, PY, PB, connected in delta format and three isolated secondary windings SR, SY, SB, each connected in series with each phase of the input R1, Y1, B1, to provide a regulated output R2, Y2, B2. An IGBT based power stage consists of half bridge IGBT modules Q1-Q12 in anti-series connection from each input phase. The output of the IGBT half bridge modules feeds the primary of the buck-boost transformer through high frequency inductors L1-L6. Across each primary winding capacitors C4, C5, C6, and metal oxide varistors (MOV) M1, M2, M3, are connected. A control circuit is provided to sense the input voltages, output voltages and output current and give the required PWM drive signals to the switches. The half-bridge modules may be replaced with full-bridge modules.

Description

3 PHASE 3-WIRE STATIC VOLTAGE STABILIZER, VECTOR CONTROLLED, PWM TYPE, DIFFERENCE POWER MODE. POWER TOPOLOGIES AND PWM METHODS FOR AC VOLTAGE STABILIZING.

The commercially available 3 phase power supply is having variation. All electrical and electronic equipments are designed to operate in certain voltage range. Excess voltage will lead to energy loss and damage of the product. Lower working voltage will lead to higher energy loss for loads like 3 phase induction motor.

This invention relates to a 3 phase 3 wire electronic solid state voltage regu'ator which regulates the unregulated 3 phase AC source to a regulated 3 Phase AC output. h addition to that the system will correct the voltage imbalances in the incoming 3 phases. The system will work without the requirement of a neutral connection and hence is the most efficient power transmission method and more economical than 3-phase 4-wire system, single-phase and two-phase systems at the same voltage because it uses less conductor material to transmit same electric power. The regulated output is not isolated from the input and hence the existing neutral wire can be used to single phase loads or 3-Phase 4-wire loads.

The incoming unregulated phase to phase voltage is processed by a power stage consisting of IGBT or MOSFET using AC to AC P\VM (Pulse Width Modulation) where PWM is made directly in AC-to-AC switching, without any haimonic distortion. In this topology there is no need to convert the AC input to DC and again convert it back to regulated AC output, This simplifies the design and reduces the component count. Another specialty of this design is, only the difference power is processed through the power stage which reduces the size, improves the efficiency and reliability.

The key features of this invention is a unique power topology and PWM method which can regulate alternating voltage to any desired value and polarity. This voltage can be added or subtracted to the available unregulated AC source to get a tightly regulated output. A 400V 3-Phase AC stabilizer made with this method achieves an output regulation better than +1-0.5%. In this method offly the difference power is processed through the power stage. If available voltage is more than the required voltage, for example if the required output is 400V 3-Phase AC and the available AC input is 440V 3-Phase AC then only 46.9 V AC vector in 150 degree angle is generated with the power stage and added to the available 440V AC to get an output of 400V AC. In other case if the available voltage is 380V AC then 23V AC vector in degree angle is generated with the power stage and added to the available 380V AC to get an output of 400V AC.

Drawbacks of existing methods The existing method for a voltage stabilizer which can achieve a comparatively tight regulation is Servo Controlled \Toltage Stabilizer. It is an Electro Mechanical type voltage stabilizer. In this a continuously variable auto transformer (dimmerstat) is connected with a motor. The motor is rotated clock-wise or anti-clockwise for increasing or decreasing the voltage. The disadvantages of this method are: > Wear and tear due to the mechanical movement, requires periodic replacement of brushes > Due to low correction speed there will be voltage overshoot and voltage dip during correction of sudden input vanation.

> Heavy and bulky. Oil cooHng required for higher KVA.

> No inrush current limiting for surge loads.

Another existing method for a voltage stabilizer is Auto Transformer Tap changing using relay or semiconductor device like SCR connected in back-back or Triac.

The Relay based method has the following drawbacks: > Poor regulation (only step variation is possible) > Periodic maintenance due to relay failure > Interrupts load culTent during step change > Unsuitable for higher KVA operation > No inrush current limiting for surge loads Method based on SCR connected th back-back or Triac have the following drawbacks > Poor regulation (only step variation is possible) > Wide range input requires more number of steps, which require more number of Triac/SCR. This in turn results higher cost and complicated wiring.

> Disturbance in load current during step change > No inrush current limiting for surge loads

Brief description of the new method

The main advantages of the new invention are: * Fully solid state, no moving parts thus less maintenance * Due to specialty of the power topology 3 Phase 3 wire system is possible. Can use 4 wire also if needed by simply connecting the incoming neutral to the load.

* PWM type voltage regulation results smooth variation of the voltage and no need of voltage tapings.

* Tight regulated output +1-0.5% or better.

* Very high correction speed.

* Low cost in higher KVA.

* Only the difference power is processed through the system resulting higher efficiency.

* Inrush current limiting for surge loads.

The specialty of the invention is the unique power topology and PWM methods. Two types of power topologies are possible with this invention. They are: Buck only or boost only topology, buck and boost topology. In both topologies interleaved PWM or non irnerleaved PWM is possible. The power topology for interleaved buck only or boost only is shown in figure 1. The power topology for non-interleaved buck and boost is shown in figure 2. In these figures IGBT is shown as the Power Switching Devices. Equivalently MOSFETs can be used instead of IGBTs. Recommended PWM switching frequency is around 20 Khz because there will not be any audible noise. The PWM drives to these IGBTs/MOSFETs is given from a control circuit based on microcontroller, DSP or discrete PWM circuits. The contr6l circuit will sense the output voltage, output current, input voltage etc and will vary the PWM for maintaining the output at a constant voltage and do the current limiting for overload and surge loads.

Interleaved Buck only or boost only Power Topology This method is illustrated in figure (1). Three phase input R. Y and B are marked as Ri, Y 1 and B 1. In this RI is connected to collector of the IGBTs Q9 and QI 1 and starting of the secondary winding SR. The starting of windings are marked with a DOT. The input Yl is connected to collector of the IGBTs Q5 and Q7 and starting of the secondary winding SY. The input B I is connected to collector of the IGBTs QI and Q3 and staring of the secondary winding SB. The three phase outputs R2, Y2 and B2 are taken from the finishing of the secondary windings SR. SY and SB respectively.

The circuit uses 6 Nos of half bridge TGBT modules. Or it can be 3 Nos of full bndge IGBT modules. Half bridge IGBT modules as well as full bridge IGBT modules are very popular and easily available. Ql and Q2 forms one half bridge IGBT module.

Sinñlarly Q3 and Q4 forms the next half bridge IGBT module. Or it can be one full bridge IGBT module formed by Ql, Q2, Q3 and Q4. This full bridge IGBT module is for Phase B. Similarly Q5, Q6, Q7 and Q8 forms the full bndge IGBT module for Phase Y. Q9. Ql0, QI 1 and Q12 forms the full bridge IGBT module for Phase R. In each full bridge IGBT modules both the half bridge limbs are operating in 180 degree out-of-phase PWM.

The snubber capacitors Cl, C2 and C3 are connected across the three IGBT full bridge modules. The emitters of all the full bridge IGBT modules are connected together.

This forms an anti-series connection between any two phases and make it possible to withstand AC voltage across this anti-series combination. With this direct AC-AC PWM is possible instead of the usual way of converting AC to DC and back to AC.

Primary windings of the transformer PR, PY and PB are connected in Delta. The three connections to this are coming from the center points (collector-emitter joint) of each TGBT half bridge modules through six sepal-ate high frequency inductors Li through L6. Across each primary windings capacitors C4, C5 and C6 and Metal Oxide Varistors (MOV) Mi, M2 and M3 are connected. Inductors and capacitors are for high frequency filtering and MOVs are for surge protection during heavy loads and short circuits.

PWNI method of Interleaved Buck only or Boost only Power Topology The topology of the power section and the PWM method are in such a way that the flyback voltage will be damped to the AC input. This has a veiy important role in the working of the system. The control circuit will sense the fly back voltage direction as well as the incoming phase sequence and will periodically and cyclically disable the PWM and turn on the IGBTs to clamp the flyback voltage back to the incoming 3 phase line itself. Due to this efficiency will increase and IGBT will never operate in unclamped inductive switching. This timing and PWM generation task is done by embedded controller software using DSP (Digital Signal Processor) in the control circuit. The software is copy protected and I am not revealing it.

The interleaved switching waveform is shown in figure 3. WI. W2 and W3 shown in figure 3 are incoming 3 Phase voltage waveforms which are connected to RI, 11 and BI shown in figure 1. The PWM waveform W4. W5, W6 and W7 shown in figure 3 are the PWM drives given to IGBTs Q9, QI 1, Q12 and Ql0 shown in figure 1. W4 and W5 are operated in I 80 degree out of phase. W6 and W7 are complimentary waveforms of W5 and W4 respectively. These complimentary waveforms are inserted with dead band to avoid shoot-through conduction of IGBTs, When the duty cycle of the PWM W4 and W5 increases the primary voltage of the buck-boost transformer will increase so the secondary voltage also increase. So by adjusting the PWM duty cycle the voltage correction factor can be varied.

Similarly, as per figure 1, the PWM duty cycle of IGBTs Q5, Q7, Q8 and Q6 in Y phase and Qi, Q3. Q4 and Q2 in B Phase can be varied for adjusting the voltage.

More than that the PWM duty cycle of any phase can be varied independent of the other 2 phases so that the voltage imbalance of the three incoming phases can be corrected.

Since the IGBTs connected between any two phases is in anti-series form, direct AC to AC PWM is achieved. The PWM output waveform between the center points of half-bridge IGBT module of any two phases and the corresponding tiltered output across the primary winding is shown in figure 4. Figure 4(a) shows around 70% PWM duty cycle and filtered output having around 70% amplitude and figure 4(b) shows around 30% PWM duty cycle and filtered output having around 30% amplitude.

Sinñlarly the power stage in figure 1 can be used for non-interleaved operation in buck only or boost only mode. For this only three half bridge modules and three high frequency inductors are required. IGBT modules Ql. Q2, Q5, Q6. Q9 and Ql0 along with high frequency inductors Ll, L3 and L5 can be used. QI and Q2 are operated in complimentary mode driven by waveforms W4 and W7 shown in figure 3.

Figure 5 and 6 illustrate vector voltage addition in buck mode operation. Vi in figure and 6 is the input voltage between RI and Bi shown in figure 1. In other words it is input R-B. V4 is output R-B, between R2 and B2 in figure 1. V2 and V3 figure 5 and 6 are the secondary voltages generated in secondary windings SR and SB respectively in figure 1. The voltage in SR will be 180 degree out of phase with the input voltage R-B. The voltage in SB will be in 120 degree out of phase with the input voltage R-B.

So the resultant vector of SR and SB (that is V2 and V3) shown as VS will be 150 degree out of phase to input voltage R-B. The output voltage across R2 and B2 is the resultant vector V4. The formula for this is: vi V -3V12 -40/12 -V42) V4= 2 Buck and boost topology This method is illustrated in figure (2), Three phase input R, Y and B are marked as R3, Y3 and B3. In this R3 is connected to collector of the IOBTs Q21 and Q23 and starting of the secondary winding SRI. The starting of windings are marked with a DOT. The input Y3 is connected to collector of the IGBTs Q17 and Qi9 and starting of the secondary winding SY1. The input B3 is connected to collector of the ICBTs Q13 and Q15 and starting of the secondary winding SB1. The three phase outputs R4, Y4 and B4 are taken from the finishing of the secondaiy windings SR I, SY I and SB I respectively.

The circuit uses 6 Nos of half bridge IGBT modules. Or it can be 3 Nos of full bridge IGBT modules. Half bridge IGBT modules as well as full bridge IGBT modules are very popular and easily available. Q13 and Q14 forms one half bridge IGBT module.

Similarly QiS and Q16 forms the next half brdge IGBT module. Or it can be one full bndge IGBT module formed by Q13, Q14, Q15 and Q16. This full bridge IGBT module is for Phase B. Similarly Q17, Q18. Q19 and Q20 forms the full bridge IGBT module for Phase Y, Q21, Q22, Q23 and Q24 forms the full bridge IGBT modde for Phase R. Tn each full bridge IGBT modules one half bridge limb is meant for the buck operation and the half bridge limb is meant for the boost operation. That is, Q13 and Q14 are for buck operation and Qi5 and Q16 are for boost operation. Similarly Ql7 and Qi8 are for buck operation and Q19 and Q20 are for boost operation. Similarly Q21 and Q22 are for buck operation and Q23 and Q24 are for boost operation.

The snubber capacitors C7, C8 and C9 are connected across the three IOBT full bridge modules. The emitters of all the full bridge IGBT modWes are connected together.

There are two sets primary windings for the buck boost transformer. One set of primary windings PR1, FYi and PB 1 are connected in Delta and meant for the boost operation. The three connections to this are coming from the center points (collector-emitter joint) of each IGBT half bridge modules Q15-Q16, Q19-Q20 and Q23-Q24 through three separate high frequency inductors L8. L10 and L12. Across each primary windings capacitors Cl 0, CI and C 12 and Metal Oxide Varistors (MOV) M4. M5 and M6 are connected. Inductors and capacitors are for high frequency filtering and MOYs are for surge protection during heavy thads and short circuits.

The next set of primary windings PR2, PY2 and PB2 are connected in Delta in 180 degree out of phase compared to PR 1. PYI and PB 1 and meant for the buck operation.

The three connections to this are coming from the center points (collector-emitter joint) of each IGBT half bridge modules Ql3-Ql4, Q17-Ql8 and Q21-Q22 through three separate high frequency inductors L7, L9 and Ll 1. Across each primary windings capacitors Cl3, C14 and C15 and Metal Oxide Varistors (MOY) M7, M8 and M9 are connected. Inductors and capacitors are for high frequency filtering and MOVs are for surge protection during heavy loads and short circuits.

PWNI method of Buck Boost Topology The topology of the power section and the PWM method are in such a way that the flyback voltage will be clamped to the AC input. This has a very important role in the working of the system. The control circuit will sense the fly back voltage direction as well as the incoming phase sequence and will periodically and cyclically disable the PWIM and turn on the IGBTs to clamp the flyback voltage back to the incoming 3 phase line itself Due to this efficiency will increase and IGBT will never operate in unclamped inductive switching. This timing and PWM generation task is done by embedded controller software using DSP (Digital Signal Processor) in the control circuit. The software is copy protected and I am not revealing it.

The switching waveform for this topology is similar to interleaved switching waveform is shown in figure 3. WI, W2 and W3 shown in figure 3 are incoming 3 Phase voltage waveforms which are connected to R3, Y3 and B3 shown in figure 2.

The PWM waveform W5 and W6 shown in figure 3 are the PWM drives given to TGBTs Q21 and Q22 (in figure 2) during buck operation or Q23 and Q24 (in figure 2) during boost operation. W5 and W6 are complimentary waveforms inserted with dead band to avoid shoot-through conduction of IGBTs, Similar drives are given to IGBTs in Phase B andY.

During the buck operation the PWM is given to IGBTs meant for buck operation and no PWM drives are given to IGBTs meant for boost operation. Similarly during the boost operation the PWM is given to IGBTs meant for boost operation and no PWM drives are given to lGBTs meant for buck operation. But in buck as well as boost mode acdve clamping drives are given to all buck as well as boost IGBTs.

When the duty cycle of the PWM V/S increases the primary voltage of the buck-boost transformer will increase so the secondary voltage also increase. So by adjusting the PWM duty cycle the voltage correction factor can be varied.

More than that the PWM duty cycle of any phase can be varied independent of the other 2 phases so that the voltage imbalance of the three incoming phases can be corrected provided that all the three phases are either in buck mode or in boost mode.

Generally in Interleaved Buck only or Boost only Power Topology or Buck Boost Topology, since the secondary is connected between the phase input and load, the load is not isolated from the input. Due to this single phase loads and 3 phase 4 wire loads can be connected by simply connecting the incoming neutral to the load neutral as shown in figure 7 (b). In this figure LS is a single phase load connected simultaneously with L which is a 3 phase 3-wire load. Figure 7 (a) shows the connection of 3-phase 3-wire load.

Figure 8 shows the block diagram of the static voltage stabilizer. R5, Y5 and B5 are the 3 phase inputs and R6, Y6 and B6 are the 3 phase outputs. A contactor SW is connected at the input and it is controlled by BLI which is the DSP based control circuit. BLI senses the input and output voltages shown as FB3 and FBI, output current shown as FB2. The control circuit work from the power supply shown as BLS.

The IGBT gate drives from the control circuit are shown as DRY and given to the TGBT based power stage shown as BL2. The 3 phase inputs are given to BL2 and the PWIM outputs from BL2 is given to a low pass filter BL3 and output of the low pass filter is connected to the primary of the buclc-boost transformer BL4. The secondary of the buck-boost transformer is connected in between input and output. The current sensors for sensing the load current are shown as CT.

Claims

Claims 1. 3 PHASE 3-WIRE VECTOR CONTROLLED DIFFERENCE POWER MODE PWM TYPE STATIC VOLTAGE STABILIZER comprising a. Buck -Boost transformer primary of which is connected in Delta format and three secondary windings each connected in series with each phase of the input to provide a 3-Phase 3-wire regulated output.b. IGBT based power stage consists of half bridge IGBT modules in anti-series connection from each input phases and output of the IGBT half bridge modules feeding the primary of the buck-boost transformer through high frequency inductors.c. Capacitor and MOV (Metal Oxide Varistor) connected across each primary winding.d. A control circuit which senses the input voltages, output voltages and output current and giving the required PWM drives to the IGBTs in order to keep the output voltage at the desired level.
2, The static voltage stabilizer according to claim i, wherein IGBT based AC to AC PWM type correction is implemented for correcting variation in input voltage.
3. The static voltage stabilizer according to claim 2, since the PWM duty cycle is continuous'y variable, continuous variation of the output voltage is achieved.
4. The static voltage stabilizer according to daims I and 3, control circuit will sense the output voltage and vary the PWM duty cycle to keep the output at the desired voltage.
5. The static voltage stabilizer according to claim 2, since the PWM duty cycle is suddenly variable sudden correction of the output voltage is achieved.
6. The static voltage stabilizer according to claim 5, PWM duty cycle is varied at any desired portion of the input wave to change the wave shape to correct a distorted input wave.
7. The static voltage stabilizer according to claim 5, suddenly change the PWM duty cyde to limit the inrush load current.
8. The static voltage stabilizer according to claim 1, 3 Phase 3 wire system is achieved.
9. The static voltage stabilizer according to claim 8, is the most efficient power transmission method and more economical than 3-phase 4-wire system, single-phase and two-phase systems at the same voltage because it uses tess conductor material to transmit same electric power.
10. The static voltage stabilizer according to claim 1, since the buck-boost transformer secondary windings are connected in series with the input 3 phases, the output will be non-isolated from the input.
11. The static voltage stabilizer according to claim 10. is compatible to 3-Phase 4-wire system by connecting an input neutra' wire to output load.
12. The static voltage stabilizer according to cbim 1, since the buck-boost transfoimer secondary windings are connected in series with the input 3 phases, the TGBT power stage and the transformer processes only the difference power which makes rating of the buck-boost transformer and the IGBT power stage lesser compared to full power processing system.
13. The static voltage stabilizer according to claim 1, PWM duty cycle of each phase is varied independently to correct the voltage imbalance in the three phases.
14. The static voltage stabilizer according to claim 1, PW1VI is done in forward and reverse directions to achieve buck and boost mode operation.
15. The static voltage stabilizer according to claim I, the control circuit will sense the tly back voltage direction as well as the incoming phase sequence and will periodicafly and cyclically disable the PWM and turn on the lGBTs to clamp the flyback voltage back to the incoming 3 phase line itself so that efficiency will increase and the IGBT will never operate in unclamped inductive switching.
16. The static voltage stabilizer according to claim 1, since primary of the buck-boost transformer is connected in Delta and secondary connected in between input and output a vector addition of voltage occur.
17. The static voltage stabilizer according to claim I 6, in buck mode operation to get an output voltage of Vo from an input voltage of Vi, a vector of K = ViV_3Vi2_4(Vi2_VO2) . . 2 in an angle of 150 degree with \ us added.
18. The static voltage stabilizer according to claim 1, IGBTs in each phases are switched in interleaved and 180 degree out of phase.
19. The static voltage stabilizer according to claim 18. input and output ripple currents are less compared to a switching method where both the IGBTs in a phase are switched simultaneously.
20. The static voltage stabilizer according to cbim IS, output voltage distortion is less compared to a switching method where both the IGBTs in a phase are switched simultaneously.
21. The static voltage stabilizer according to claim 8, a 3 phase power stage of 3 wire input and 3 wire output is achieved.
22. The static voltage stabilizer according to claim 21. the number of IGBTs are less compared to a 3 phase 4 wire power stage topology having same performance.
23. The static voltage stabilizer according to claim 14. the buck to boost and boost to buck transition is continuous.
24. The static voltage stabilizer according to claim 3, operate without any interruption in the output.
25. The static voltage stabilizer according to claim 3, operate with no tapping required in the primary or secondary of the buck boost transformer.
26. The static voltage stabilizer according to claim 3, operate without any sudden variation in the output.
27. The static voltage stabilizer according to claim I, operate with PWM switching in primary of the buck boost transformer,
28. The static voltage stabilizer according to claim 27, current through the IGBT is much less than the load current.
29. The static voltage stabilizer according to claim 27, the transformer size is less compared to a system doing voltage conection in the secondary.
30. The static voltage stabilizer according to claim 8, primary voltage is more than a 3 phase 4 wire system with same features.
3 I. The static voltage stabilizer according to daim i, the power stage operate in more voltage compared to an equivalent 3 phase 4 wire system, hence IGBT current is reduced in addition to the reduction as per claim 28.
32. The static voltage stabilizer according to c'aim i, IGBTs forms an anti-series connection between any two phases and make it possible to withstand AC voltage across this anti-series combination.
33. The static voltage stabilizer according to claim 32, direct AC-AC PWM is achieved which is efficient compared to the usual way of converting AC to DC arid back to AC.
34. The static voltage stabilizer according to claim 33. require less switching components and eBminate bulky high voltage electrolytic filter capacitor, which reduces the product life, compared to the usual way of converting AC to DC and back to AC.
35. The static voltage stabilizer according to claim 3, achieve voltage optimization energy saving for reducing carbon emission with higher accuracy compared to SCR tap changing type and fixed ratio transformer based voltage optimization energy saving methods.
36. The static voltage stabilizer according to claim i8. the resultant switching frequency at the buck-boost transformer primary is double of the TGBT switching frequency.
37. The static voltage stabilizer according to claim 36, require less low pass filter compared to a non-intefleaved PWM method.
38. The static voltage stabilizer according to claim 36. achieves less switchiig loss in IGBTs since the IGBT switching frequency is half of the resultant switching frequency at the buck-boost transfoimer primary.