GB2091500A - Method of operation of a frequency changer - Google Patents
Method of operation of a frequency changer Download PDFInfo
- Publication number
- GB2091500A GB2091500A GB8200147A GB8200147A GB2091500A GB 2091500 A GB2091500 A GB 2091500A GB 8200147 A GB8200147 A GB 8200147A GB 8200147 A GB8200147 A GB 8200147A GB 2091500 A GB2091500 A GB 2091500A
- Authority
- GB
- United Kingdom
- Prior art keywords
- rectifier
- frequency changer
- inverter
- heating apparatus
- direct current
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
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
- H02M5/40—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 with intermediate conversion into dc
- H02M5/42—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 with intermediate conversion into dc by static converters
- H02M5/44—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac
- H02M5/443—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means
- H02M5/45—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M5/4505—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 with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only having a rectifier with controlled elements
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Inverter Devices (AREA)
- General Induction Heating (AREA)
Abstract
The frequency changer comprises a controllable rectifier and an inverter connected after the rectifier, and is operated such that direct current from the rectifier to the inverter is periodically chopped by control of the rectifier in an adjustable duty factor between a maximum and a minimum value. The frequency changer may for example be connected to an electrical heating apparatus, particularly an inductive heating apparatus. <IMAGE>
Description
SPECIFICATION
Method of operation of a frequency changer
This invention relates to a method of operation of a frequency changer which can be connected to an a.c. network from which large amounts of power are to be taken, for example for supplying a load to electrical heating apparatus in particular inductive heating means, which frequency changer comprises a controllable rectifier followed by an inverter connected thereto.
For the inductive heating of metal for example rods and melts in induction furnaces, the practice is known of converting, in a frequency changer of the type referred to, a low frequency electric current in an a.c. supply network to a medium or high frequency for heating the metal load.
However problems arise in the a.c. supply network due to the power factor and the imposition on the network of undesirable harmonics. To mitigate such problems it has been the practice to effect choking of the frequency changer by associated capacitances and/or inductances with respect to the supply network, or to provide series-tuned wave traps which damp undesirable harmonics.
The use of multipulse, e.g, twelve-pulse frequency changers is also known for the damping of the reactions in the network.
Such expedients are however elaborate, and the cost outlay can easily exceed the cost of the normal current source so that measures of the kind referred to are only justified in special circumstances.
The present invention is directed to the operation of a frequency changer in which the reaction upon the a.c. supply network is kept low and the outlay on the filter choke with respect to the network is avoided.
The invention provides a method of operation of a frequency changer which comprises a controllable rectifier and an inverter connected after the rectifier, characterized in that the direct current from the rectifier to the inverter is periodically chopped by control of the rectifier in an adjustable duty factor between a maximum and a minimum value.
The invention avoids the substantial worsening of the power factor which arises through the adjustment of the direct current in the intermediate d.c. circuit of the frequency changer by control of the rectifier, and reduces the backscatter of harmonic waves into the supply network down to that extent which is provided by the uncontrolled rectifier, e.g. in the region of full load.
In the method of the invention the rectifier feeding the inverter is operated for the supply of the load through the inverter during a predetermined switching period as an uncontrolled rectifier, and after that during a further period by controlling the rectifier down to a lower value of its output current or its output voltage is switched off.
During the flow of direct current in the intermediate circuit of the frequency changer, which is chosen to correspond with the required nominal power of the frequency changer, the frequency changer behaves in the same way as a frequency changer having an uncontrolled rectifier. The power factor is favourable and the remaining reactions upon the supply network are minimal.
The power required at the output from the frequency changer follows from the setting of the duty factor of the chopped direct current at the output from the rectifier. This duty factor is in the method of the invention settable or adjustable.
One embodiment of the invention is hereinafter described in more detail in the accompanying drawing, of which
Figure 1 is a circuit diagram of a frequency changer in accordance with the invention, and
Figure 2 is a graphical representation of the direct current fed into the intermediate direct current circuit of the frequency changer.
In Figure 1 a 50Hz three-phase network 1 is connected to a controllable rectifier 2. The rectifier 2 consists in known manner of a controllable three-phase bridge circuit the thyristor switching valves of which can be controlled in a settable manner by control device 3. The output voltage from the rectifier 2 fed to the intermediate direct current circuit 4 of the frequency changer can be controlled between a maximum value Mo and a minimum value M1 at the said control device 3. In the intermediate direct current circuit 4 a direct current choke 5 is arranged in the usual way. The intermediate circuit 4 is connected to an inverter bridge circuit 6 each of the four arms of which contains thyristor switching valves which can be controlled by control device 7.The feed-points of the bridge circuit are by control of the semiconductor switching valves of the inverter 6 in known manner, connected alternately to the output terminals 8 of the inverter 6 so that the load circuit 9 which has the form of a parallel resonant circuit, becomes fed with an alternating voltage of which the clock frequency is determined by the control frequency of the control signals from the control device 7.
The inductance 10 of the load resonant circuit 9 is formed in conventional manner as a heating coil for an induction furnace, an inductive heating apparatus.
In a method in accordance with the invention, the control device 3 of the rectifier 2 is actuated in such a way that the output voltage from the rectifier 2 corresponds during a time t, (Figure 2) with a maximum voltage value and during a time t2 with a minimum voltage value. The minimum voltage value must in that case be so chosen that "gappy" operation of the inverter 6 is avoided.
Thus it will in general differ from zero.
By setting the duty factor t1/t2 at the control device 3 the power required in the heating coil 10, which is dependent upon the load, can be set at the output from the inverter.
The method in accordance with the invention has the advantage that the reactions on the a.c.
supply network 1 may be kept small without the cost of the frequency changer being substantially increased.
The method in accordance with the invention is useful in all circumstances where large amounts of power have to be taken from a supply network, for example heating apparatus, particularly plants for the inductive heating of metal.
Claims (4)
1. A method of operation of a frequency changer which comprises a controllable rectifier and an inverter connected after the rectifier, characterised in that direct current from the rectifier to the inverter is periodically chopped by control of the rectifier in an adjustable duty factor between a maximum and a minimum value.
2. A method according to Claim 1, wherein the said frequency changer is connected to an a.c.
network to an electrical heating apparatus.
3. A method according to Claim 2, wherein the said heating apparatus is an inductive heating apparatus.
4. A method according to Claim 1, substantially as hereinbefore described and illustrated in the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19813101573 DE3101573A1 (en) | 1981-01-20 | 1981-01-20 | METHOD FOR OPERATING A CONVERTER |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2091500A true GB2091500A (en) | 1982-07-28 |
| GB2091500B GB2091500B (en) | 1984-04-18 |
Family
ID=6122921
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8200147A Expired GB2091500B (en) | 1981-01-20 | 1982-01-05 | Method of operation of a frequency changer |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS57138874A (en) |
| DE (1) | DE3101573A1 (en) |
| GB (1) | GB2091500B (en) |
| IT (1) | IT1147664B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4209644A1 (en) * | 1992-03-25 | 1993-09-30 | Abb Patent Gmbh | Method for controlling the converter valves of a load-guided parallel resonant circuit inverter of an induction furnace |
| DE4209645A1 (en) * | 1992-03-25 | 1993-09-30 | Abb Patent Gmbh | Method for controlling the converter valves of two or more parallel resonant circuit inverters fed from a common direct current source, each with an induction furnace, and system for carrying out the method |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5953673B2 (en) * | 1977-08-09 | 1984-12-26 | ソニー株式会社 | power circuit |
-
1981
- 1981-01-20 DE DE19813101573 patent/DE3101573A1/en not_active Ceased
-
1982
- 1982-01-05 GB GB8200147A patent/GB2091500B/en not_active Expired
- 1982-01-18 JP JP57005087A patent/JPS57138874A/en active Pending
- 1982-01-18 IT IT47597/82A patent/IT1147664B/en active
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4209644A1 (en) * | 1992-03-25 | 1993-09-30 | Abb Patent Gmbh | Method for controlling the converter valves of a load-guided parallel resonant circuit inverter of an induction furnace |
| DE4209645A1 (en) * | 1992-03-25 | 1993-09-30 | Abb Patent Gmbh | Method for controlling the converter valves of two or more parallel resonant circuit inverters fed from a common direct current source, each with an induction furnace, and system for carrying out the method |
| US5475582A (en) * | 1992-03-25 | 1995-12-12 | Abb Patent Gmbh | Stepless control of a load guided parallel resonant inverter |
Also Published As
| Publication number | Publication date |
|---|---|
| IT8247597A0 (en) | 1982-01-18 |
| DE3101573A1 (en) | 1982-07-29 |
| GB2091500B (en) | 1984-04-18 |
| JPS57138874A (en) | 1982-08-27 |
| IT1147664B (en) | 1986-11-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |