GB2403855A - Burst firing control for switching elements in a three phase power supply - Google Patents
Burst firing control for switching elements in a three phase power supply Download PDFInfo
- Publication number
- GB2403855A GB2403855A GB0414710A GB0414710A GB2403855A GB 2403855 A GB2403855 A GB 2403855A GB 0414710 A GB0414710 A GB 0414710A GB 0414710 A GB0414710 A GB 0414710A GB 2403855 A GB2403855 A GB 2403855A
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- Prior art keywords
- cycle
- controlled
- phases
- conducting
- power
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M5/25—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M5/257—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M5/2573—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit
- H02M5/2576—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only with control circuit with digital control
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/22—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M5/275—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M5/293—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M5/2932—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage, current or power
- H02M5/2937—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage, current or power using whole cycle control, i.e. switching an integer number of whole or half cycles of the AC input voltage
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Electrical Variables (AREA)
Abstract
A method of controlling power supplied to a 3-phase load by a 3-phase 3-line AC supply in which at least two phases are controlled by solid state switching devices in a burst control manner; and in which the firing angle of the switching devices is cyclically varied in successive bursts to produce a load current averaged over a number of bursts which has substantially no DC component and in which the RMS values of the currents in the three lines are substantially equal.
Description
1 "Thyristor Control" 3 This invention relates to methods and devices for
4 the control of solid-state controlled switching devices. The invention will be described with 6 particular reference to the control of back-to-back 7 thyristor pairs, but it will be understood that it 8 may be applied to other controlled switching devices 9 such as triacs.
11 In the control of AC loads using thyristors or 12 triacs the two main approaches are phase angle 13 control and burst fire control. For many 14 applications, for example heating loads, burst fire control is preferred because of the reduced harmonic 16 distortion and conducted radio frequency emissions.
17 However, known forms of burst fire control for 3 18 phase loads are subject to deficiencies, as 19 discussed below.
21 The present invention provides a method of 22 controlling power supplied to a 3-phase load by a 3 1 phase 3-line AC supply in which at least two phases 2 are controlled by solid state switching devices in a 3 burst control manner; in which the firing angle of 4 the switching devices is cyclically varied in successive bursts to produce a load current averaged 6 over a number of bursts which has substantially no 7 DC component and in which the RMS values of the 8 currents in the three lines are substantially equal.
Preferably, the solid state switching devices 11 operate in a single cycle burst control manner.
13 Typically, the solid state switching devices will be 14 thyristor pairs or triacs.
16 In one form of the invention the supply has 3-line 17 control and the order in which the phases are 18 triggered into conduction is changed in a cyclical 19 manner so as to rotate the current waveforms around the phases.
22 In another form of the invention, the supply has 23 two-line control and the angle at which the 24 controlled phases are triggered into conduction is changed in an alternating manner so as to invert the 26 current waveform of each of the controlled phases in 27 successive bursts.
29 The invention also provides a control system adapted to apply the foregoing method to a 3-phase 3-line AC 31 power supply system, and further provides a power 32 supply system including such a control system.
2 Embodiments of the invention will now be described, 3 by way of example, with reference to the drawings, 4 in which: 6 Figure 1 illustrates a known single phase 7 thyristor control arrangement and associated load 8 waveforms; 9 Figure 2 shows a known 3-phase 4-wire system and associated waveforms; 11 Figure 3 shows a first embodiment of the 12 present invention in the form of a 3-phase 3-line 13 system, with a typical waveform; 14 Figure 4 shows a sequence of waveforms used in the embodiment of Figure 3; 16 Figure 5 shows a second embodiment of the 17 present invention in the form of a 3-phase system 18 with 2-line control; 19 Figure 6 illustrates single waveforms obtained in the system of Figure 5; 21 Figure 7 shows a sequence of waveforms in the 22 system of Figure 5; and 23 Figure 8 is a key to symbols used in Figures 3, 24 4 and 7.
26 Figure 1 illustrates a "single cycle burst fire" 27 technique in a single phase system, and the 28 associated waveforms for 50% power, 25% power and 29 75% power. This technique is commonly used with fast response loads such as radiant or near infrared 31 heaters, being the fastest form of burst fire 32 control. A load of 50% is attained by switching one 1 cycle on, followed by one cycle off (or in some 2 cases one half cycle on followed by one half cycle 3 off). Three cycles on followed by one cycle off 4 gives 75% power, while one cycle on followed by three cycles off gives 25\ power, and so on.
7 In single phase systems this concept is simple to 8 arrange and works well. When it is sought to apply 9 the technique to 3-phase systems, however, it becomes more complex.
12 Figure 2 shows a 3-phase 4-wire system and 13 associated waveforms showing current in each limb of 14 the load. This is the simplest 3-phase system, and may be considered as three single phase loads which 16 do not interfere with each other. The single on 17 period now occupies a period of 480 degrees.
18 Although the load current is composed of complete 19 sinusoids, the neutral current is non-sinusoidal.
21 Figure 3 shows a 3-phase 3-wire system and 22 associated waveforms. In fig. 3 there is no neutral 23 current, but current flowing into one line must flow 24 out via one or both of the other lines. The conduction period now covers 420 degrees, and the 26 current waveforms are no longer sinusoidal and are 27 not the same on all the lines. The RMS value 28 associated with the different waveforms is not the 29 same, and in addition a DC component is associated with some of the waveforms.
1 One preferred form of the present invention 2 overcomes these problems, as illustrated in Figure 4 3 which shows a sequence of on-off periods which 4 rotates the current waveforms around the phases.
The thyristor pairs in each line are fired in a 6 special sequence (by adjusting the time at which 7 they are switched on) to rotate the waveshapes 8 around the three lines in sequence. Each line thus 9 sees the same overall sequence, but this is displaced in time between the lines. This ensures 11 that the load power is shared equally over the three 12 limbs of the load, and that there is no DC 13 component in any limb.
It should be noted that in Figures 3 and 5 the load 16 could equally be delta connected, in which case the 17 waveform illustrations would represent the line 18 currents.
Several such sequences are possible, each producing 21 a different harmonic and sub-harmonic content in the 22 ensuing wave train. For example, the second and 23 third bursts could be interchanged relative to the 24 start points shown.
26 It should be noted that this "one cycle on and one 27 cycle off" no longer corresponds to exactly 50% 28 power and it may be desired to compensate for this 29 in the cycle switching algorithm.
31 One scheme for controlling the system of Figure 4 32 will now be described. Other schemes capable of 1 producing similar results will be apparent to those 2 skilled in the art.
4 The controller accepts a power demand signal which can assume values between 0% and 100%, where 0% 6 corresponds to no conduction and 100% corresponds to 7 continuous conduction. For intermediate values the 8 mean square voltage (or current) delivered to the 9 load is 11 [Power Demand (%) x Mean Square Voltage (or 12 Current) at full conduction/100 14 A sequence of conducting/non-conducting cycles which meets this requirement may be achieved by an 16 algorithm as follows: 18 Compute, after each cycle, a running mean of the 19 squared value of the conducting and non-conducting cycles fed to the load, compare this value with the 21 power demand value, and use the result of the 22 compare to determine whether the next cycle should 23 be conducting or non-conducting.
There is a value of the power demand which 26 corresponds to one cycle on followed by one cycle 27 off, and this value may be predetermined (see 2 8 below).
Above this value only one cycle off is allowed 31 at a time, but there may be any number of 32 consecutive on cycles.
2 Below this value only one cycle on is allowed 3 at a time, but there may be any number of 4 consecutive off cycles.
6 Except as disallowed by the above two rules, if the 7 running mean is greater than the demand signal then 8 the next cycle is off, and if the running mean is 9 less than the demand signal then the next cycle is on.
12 In computing the running mean one full conducting 13 cycle may be assumed to have a mean square value of 14 100%, and one full non-conducting cycle a mean square value of 0. Each time there is a transition 16 from the non-conducting to the conducting state, an 17 additional, predetermined (see below) quantity is 18 incorporated into the calculation of the running 19 mean to account for the mean square values of the conducting burst at the start and finish of the 21 burst, and the fact that the off period is not an 22 exact number of whole cycles. The waveform is also 23 rotated as shown for example in Figure 4, and also 24 in Figure 7 below.
26 The predetermined values referred to above (of that 27 value of power demand which corresponds to one cycle 28 on followed by one cycle off, and the quantity 29 incorporated at each transition to conducting) may be predetermined for a given type of single cycle 31 ' on' burst and sequence of rotations.
1 Figure 5 shows a 3-phase 3-wire system with 2-line 2 control. This method is often used in burst fire 3 applications, as it is cheaper (two thyristor pairs 4 rather than three), more compact, and dissipates less heat. However, as previously used this method 6 has severe load imbalance, and significant DC 7 components and harmonics.
9 It is not possible to follow the approach of Figure 4 by rotating the waveshape sequences around the 11 three limbs, as one of these is uncontrolled.
13 Intuitively, it would seem that it is not possible 14 to balance the load, because line 3 starts conducting when line 1 is switched on and continues 16 conducting until line 2 switches off, i.e. line 3 is 17 conducting for longer than either line 1 or line 2.
18 We have determined, however, that such balancing is 19 possible.
21 Figure 6 shows two waveforms. We have established 22 that the RMS values of forms a and b in Figure 6 are 23 closely balanced (within 0. 5%) and that, by correct 24 phasing of the switch-on of the two pairs of thyristors, waveshape b and its inverse on the two 26 controlled lines will correspond with waveshape a on 27 the uncontrolled line. The conduction period is 480 28 degrees. All of these waveshapes have a DC component 29 associated with them, and a sequence must then be generated as shown in Figure 7 such that each line 31 conducts a waveshape followed by its inverse 32 (rotated through 180 degrees) in the next period.
2 The foregoing discussion has been restricted to the 3 case of one cycle on followed by one cycle off, 4 which is the worst case from the point of view of load imbalance and DC components. The effects can 6 be corrected for all cases (N cycles on followed by 7 one cycle off, or one cycle on followed by N cycles 8 off, where N is any number) by rotating the sequence 9 each time the thyristors are switched to an 'on cycle' which follows an 'off cycle'.
12 Similar waveshapes are generated for either phase 13 rotation, but the order in which the thyristors 14 switch on is altered.
16 The length of an off period does not alter the 17 balance of the line currents, provided that each on 18 period has waveforms of the correct form. It simply 19 alters the RMS value of the whole wavetrain.
21 Any suitable method may be used to fire the 22 thyristors, so long as the following fundamentals 23 are observed.
A thyristor (or triac) may be triggered to switch 26 from non-conducting to conducting at any point in 27 the AC cycle provided that (in the case of a 28 thyristor) its anode is positive with respect to its 29 cathode. The thyristor (or triac) will automatically change from the conducting to the non 31 conducting state whenever the current flowing 32 through it falls to zero; in the case of AC 1 waveforms this occurs each time a current cycle 2 passes through zero. For standard phase control 3 thyristors, and for trials, this is the only way in 4 which the device can be switched from conducting to non-conducting.
7 To generate the required waveforms the following 8 actions must therefore be performed: 1. At the start of a burst, the thyristors must be 11 triggered in sequence to ensure initial switch on at 12 the correct time.
14 2. To ensure continuous conduction of the AC current, the correct thyristor must be triggered to 16 continue the conduction after each reversal of the 17 current waveform.
19 3. At the end of the conduction period the thyristors are allowed to switch off naturally when 21 the current next falls to zero.
23 In the above waveform diagrams, the symbols detailed 24 in Figure 8 are provided to aid understanding of the timing. The time base is graduated with major 26 divisions of 60 degrees and minor divisions of 10 27 degrees.
29 It will be noted that in the foregoing 3-phase 3-line systems the single cycles are not true 31 sinusoidal single cycles, but are as shown in the 32 waveform diagrams.
2 The principles of the invention may be applied to 3 controlled switching devices other than thyristors 4 and triacs, such as power transistors, and to loads y other than resistive loads.
Claims (1)
1 CLAIMS e 3 1. A method of controlling power supplied to a 3 4 phase load
by a 3-phase 3-line AC supply in which at least two phases are controlled by solid state 6 switching devices in a burst control manner; and in 7 which the firing angle of the switching devices is 8 cyclically varied in successive bursts to produce a 9 load current averaged over a number of bursts which has substantially no DC component and in which the 11 RMS values of the currents in the three lines are - 12 substantially equal.
14 2 The method of claim 1, wherein the solid state switching devices operate in a single cycle burst 16 control manner.
18 3. The method of claim 1 or claim 2 wherein the 19 solid state switching devices are thyristor pairs or triacs.
22 4. The method of any of claims 1- 3 wherein the 23 supply has 3 -line control, the method further 24 comprising the step of changing the order in which the phases are triggered into conduction in a 26 cyclical manner so as to rotate the current 2 7 waveforms around the phases.
29 5 The method of claim 4 wherein power is controlled in response to a power demand signal 31 according to the function: 1 [Power Demand (%) x Mean Square Voltage 2 (or Current) at full conduction]/100 4 6. The method of claim 5, wherein power is controlled in a sequence of conducting/non 6 conducting cycles in accordance with the algorithm: 8 (a) compute after each cycle a running means 9 of the squared value of the conducting and non-conducting cycles fed to the load, 11 (b) compare this value with the power demand 12 value, and 13 (c) use the result to determine whether the 14 next cycle is to be conducting or non conducting. I 17 7. The method of claim 6, wherein, if the running 18 mean is greater than the demand signal, then the 19 next cycle is off, and if the running mean is less than the demand signal then the next cycle is on.
22 8. The method of claim 7, wherein the selection of - 23 next cycle on/off is subject to (a) when the 24 power demand is above a reference value only one cycle off is allowed at a time but there 26 may be any number of consecutive on cycles, (b) 27 when the power demand is below the reference 28 value only one cycle on is allowed at a time 29 but there may be any number of consecutive off cycles, (c) said reference value corresponding 31 to the power supplied by alternate off and on 32 cycles.
2 9. The method of any of claims 1-3, wherein the 3 supply has two-line control, the method further 4 comprising changing the angle at which the controlled phases are controlled to have 6 waveforms which are equal in magnitude, 7 opposite in sign and displaced in time such 8 that the uncontrolled phase substantially 9 balances the RMS values of the controlled phases.
12 10. The method of claim 9, in which the controlled 13 phases are triggered into conduction in an 14 alternating manner so as to invert the waveform of each of the controlled phases in successive 16 bursts.
18 11. The method of claim 9 or claim 10, in which the 19 controlled phases are triggered 90 degrees apart and the conduction cycle lasts for 480 21 degrees..
23 12. A control system adapted to apply the method of 24 any of claims 1-11 to a 3-phase 3-line AC power supply system.
27 13. A power supply system including the control 28 system of claim 12.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB0315463A GB0315463D0 (en) | 2003-07-02 | 2003-07-02 | Thyristor control |
| GB0319704A GB0319704D0 (en) | 2003-08-22 | 2003-08-22 | Thyristor control |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB0414710D0 GB0414710D0 (en) | 2004-08-04 |
| GB2403855A true GB2403855A (en) | 2005-01-12 |
| GB2403855B GB2403855B (en) | 2005-12-21 |
Family
ID=32852425
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB0414710A Expired - Lifetime GB2403855B (en) | 2003-07-02 | 2004-07-01 | Thyristor control |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2403855B (en) |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007123458A1 (en) * | 2006-04-24 | 2007-11-01 | Abb Ab | Motor control |
| WO2008033088A1 (en) * | 2006-09-11 | 2008-03-20 | Abb Ab | Method and device for reducing the influence of a dc component in a load current of an asynchronous three-phase motor |
| WO2015022691A1 (en) * | 2013-08-15 | 2015-02-19 | Solcon Industries Ltd. | Medium voltage power controller |
| RU2622890C1 (en) * | 2016-07-27 | 2017-06-21 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Комсомольский-на-Амуре государственный технический университет" (ФГБОУ ВО "КнАГТУ") | Method for switching-on, switching-off and regulating voltage of transformer substation |
| EP3211782A1 (en) * | 2016-02-24 | 2017-08-30 | Hydrogenics Europe NV | Configurable ac dc converter |
| RU2667095C1 (en) * | 2017-12-29 | 2018-09-14 | Владимир Степанович Климаш | Method of control starting transformer for power transformer |
| RU2667481C1 (en) * | 2017-12-14 | 2018-09-20 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Комсомольский-на-Амуре государственный университет" (ФГБОУ ВО "КнАГУ") | Device for switching on, switching off and adjusting voltage of transformer substation |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5128604A (en) * | 1989-04-21 | 1992-07-07 | Claude Caen | Two phase power control of a three-phase load circuit |
-
2004
- 2004-07-01 GB GB0414710A patent/GB2403855B/en not_active Expired - Lifetime
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5128604A (en) * | 1989-04-21 | 1992-07-07 | Claude Caen | Two phase power control of a three-phase load circuit |
Cited By (12)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2007123458A1 (en) * | 2006-04-24 | 2007-11-01 | Abb Ab | Motor control |
| US8072171B2 (en) | 2006-04-24 | 2011-12-06 | Abb Ab | Motor control |
| CN101427458B (en) * | 2006-04-24 | 2012-08-15 | Abb公司 | Method and device for controlling tri-phase motor current by tri-phase controller |
| EP2011225A4 (en) * | 2006-04-24 | 2017-07-05 | ABB Schweiz AG | Motor control |
| WO2008033088A1 (en) * | 2006-09-11 | 2008-03-20 | Abb Ab | Method and device for reducing the influence of a dc component in a load current of an asynchronous three-phase motor |
| US8030870B2 (en) | 2006-09-11 | 2011-10-04 | Abb Ab | Method and device for reducing the influence of a DC component in a load current of an asynchronous three-phase motor |
| CN101512887B (en) * | 2006-09-11 | 2011-11-30 | Abb公司 | Method and device for reducing the influence of a DC component in a load current of an asynchronous three-phase motor |
| WO2015022691A1 (en) * | 2013-08-15 | 2015-02-19 | Solcon Industries Ltd. | Medium voltage power controller |
| EP3211782A1 (en) * | 2016-02-24 | 2017-08-30 | Hydrogenics Europe NV | Configurable ac dc converter |
| RU2622890C1 (en) * | 2016-07-27 | 2017-06-21 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Комсомольский-на-Амуре государственный технический университет" (ФГБОУ ВО "КнАГТУ") | Method for switching-on, switching-off and regulating voltage of transformer substation |
| RU2667481C1 (en) * | 2017-12-14 | 2018-09-20 | Федеральное государственное бюджетное образовательное учреждение высшего образования "Комсомольский-на-Амуре государственный университет" (ФГБОУ ВО "КнАГУ") | Device for switching on, switching off and adjusting voltage of transformer substation |
| RU2667095C1 (en) * | 2017-12-29 | 2018-09-14 | Владимир Степанович Климаш | Method of control starting transformer for power transformer |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0414710D0 (en) | 2004-08-04 |
| GB2403855B (en) | 2005-12-21 |
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