CA1188367A - Method and circuitry for sine wave reconstruction - Google Patents
Method and circuitry for sine wave reconstructionInfo
- Publication number
- CA1188367A CA1188367A CA000420511A CA420511A CA1188367A CA 1188367 A CA1188367 A CA 1188367A CA 000420511 A CA000420511 A CA 000420511A CA 420511 A CA420511 A CA 420511A CA 1188367 A CA1188367 A CA 1188367A
- Authority
- CA
- Canada
- Prior art keywords
- signal
- sine wave
- accordance
- voltage
- source voltage
- 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.)
- Expired
Links
Landscapes
- Transmission And Conversion Of Sensor Element Output (AREA)
Abstract
METHOD AND CIRCUITRY FOR SINE
WAVE RECONSTRUCTION
ABSTRACT OF THE DISCLOSURE
A scheme for providing an output signal approximating a true sine wave representative of a sine wave source voltage from corrupted line voltages connecting the source to a load includes the development of a first signal representative of the corrupted lines line voltage. The first signal is then filtered to reject all but higher frequency components andthis filtered output is then combined with the first signal to provide a combined signal which is further filtered to provide a final output signal.
WAVE RECONSTRUCTION
ABSTRACT OF THE DISCLOSURE
A scheme for providing an output signal approximating a true sine wave representative of a sine wave source voltage from corrupted line voltages connecting the source to a load includes the development of a first signal representative of the corrupted lines line voltage. The first signal is then filtered to reject all but higher frequency components andthis filtered output is then combined with the first signal to provide a combined signal which is further filtered to provide a final output signal.
Description
6~
METH~D AND CIRCUITRY FO-R SINE
WAVE RECONSTRUCTION
.~ .
BACKGROUND_OF: T~E I-N~ENTION
The present invention reIates generally to sine wave reconstruction techniques and more particularly to a method and circuitry for providing an outpu-t signal, representative of a sine wave source voltage, from, corrupted voltages which'appear on the lines connecting the source to a load.
There are a number of instances in which it is desirable'to have an accurate representation of a sine wave source ~oltage. One of the more common of these is in the power conversion/motor control art where semiconductor (e.g., thyristor) converter bridges are used to power and control an electric motor. In these applications it is necessary to have an accurate representation of the source voltage in order to properly synchronize the rendering of the bridge semiconductors conductive with'respect to the source voltage. This is normally done by detecting when the ~, voltage crosses the zero axis.
If no disturbances occur on the lines, such detection poses no problems~ Such,' however, is seldom the case. This is particularly true where semiconductor power bridges are used and the transfer of current from one bridge thyristor to anothér causes periodic short circuits across the power lines' which in turn causes rather sevexe disturbances' on those lines. These 3~7 21-DSO~2598 disturbances become even more pronounced when plural converters are connected to the lines with the attendant increase in the number of disturbances. ~ number of systems are known and have been employed to reconstruct the sine wave representation of the source voltage. In U.S. Patent No. 3,976~68 "~oltage Synthesization" by L.J. Lane, issued August 24, 1976, signals proportional to the instantaneous values of the voltage at the terminals of the voltage supply and to the rate of change, with respect to the time, of the current supplied to a load are developed and utilized to synthesize the voltage. An eLaboration of this scheme involves providing the output of the 3,876,~6~ patent to an overdriven ampli~ier, the output of which is then furnishecL to a self-tuning filter such as that described in U.S. Patent No. 3,978,420 'ISelf-Tuning Filter" by L.~. I.ane, issued August 31, 1976.
These known methods are very satisfactory and properly employed furnish excellent results. They are, however, fairly complex and hence expensive and in those applications requiring a high degree of precision can be Eully justified. There are, however, a number of situations in which this hiyh degree of accuracy is not necessary and in which it is difficult to justify the expense of these systems.
S`UMMARY OF T~E INVENTION
_ _ .
It is, therefore, an object of the present invention to provide a method and circuitry for reconstructing a representation of a sine wave source voltage from corrupted line voltages.
It is a further object to provide a sine wave reconstruction technique which requires the sensing of only line to line voltages.
It is still a ~urther object to provide a sine wa~e reconstruction technique which is relatively simple and inexpensive and ye~ sufficiently accurate ~or many applications.
It is an additional object to provide a sine wave recQnstruction technique which can be implemented in a relatively simple manner using relatively in-expensive components.
The foregoing and other objects are achieved in accordance with the present invention by first developing a signal which is representative of the line-to-line voltage between two phases of the line voltayes. In response to the thusly developed signal, there is developed a second signal which is representative of only the high frequency components o~ the first signal.
These two signals are then combin~d and this combined signal is filtered to provide an output signal which is representative of the sine wave source voltage.
BRIEF DESCR;IPTION OF THE D~AWING
While the present invention is described in particularity in the claims annexed to and :Eorming a part of this specification, a better unders-tanding of the invention can be had by reference to the following description taken into conjunct:Lon with the accompanying drawing in which:
Figure 1 is a schemat~c drawing illustrating the circuitry of the present invention in its preferred embodiment; and Figure 2 illustrates wave shapes helpful in understanding the present invention.
DETAILED~DESCRIPTION
Referring now to Figure 1, which shows the circuitry of the present invention in its preferred embodiment, it is seen that a source voltage represented y terminalS Tl! T2 and T3 is connected to a load 10 by way of lines Ll, L2 and L3. The nature of load 10 is not important to the present invention but it would, typically, comprise one or more power converters each supplying one or more eIectric motors. In accordance with the depiction of Figure l, the vol~ages on lines ~ 3~7 21-DS0-2598 Ll and L3 (which designation will also be used for the voltage) serve as inputs to a differential amplifier 12 which includes an operational amplifier 14 having its non-inverting input connected to ground by way of a suitable resistor 16 and a feedback resistor 18 connected between its output and its inverting input.
In order to properly scale the voltage levels, the phase voltage L3 is furnished to the inverting input of the operational amplifier 1~ by way of a vol~age divider comprised of serie~ connected resistors 20 and 22. Similarly, th~ phase voltage Ll is applied as the non-inverting input to operational amplifier 14 by way of the voltage divider comprised of resistors 24 and 26. Reference is now made to the upper trace of Figure 2 which shows the line to neutral voltages as they might appear on lines ~1' L2 and L3, including disturbances caused by a single converter supplying a motor load. The illustrated distortions shown of the sine wave are what are commonly known as commutation notches. The wave shapes shown in this trace are those which occur when the firing angle of the thyristors plus one-half of the commutation angle equals 90.
The second trace of Figure 2 illustrates the output of the differential amplifier circuit 12 and it is seen that it is essentially 30 electrical degrees lagging with respect to the Ll to neutral voltage and that the commutation notches are essentially in time alignment of that phase to neutral voltage.
Referring again to Figure 1, the output of the differential amplifier 12 serves as the input to a high pass filter network 28. The high pass filter 23 consists of a pair of series connected input capacitors 30 and 36 through which the signal from the amplifier 12 isapplied to the inverting input of an operational amplifier 37. The juncture of capacitors 30 and 36 (point 32) is connected to ground by way of a resistor 3~7 2l-Ds~-2598 34 and this same point i5 also connected by way of capacitor 40 to the output of the operational amplifier 37. A feedback resistor 38 is connected between the inverting input and the output of operational amplifier 37 and the non-inverting input of amplifier 37 is connected to ground by way of a resistor 39. The high pass filter within block 28 is essentially that which is shown and described in greater detail in the publication "Handbook of Operational Amplifier Active RC Networks" by Burr-Brown, copyright 1966 (Reference clrcuit number five on page 76). The frequencies to be passed by the high pass filter network28 are somewhat arbitrary but it is believed that satisfactory results can be obtained when the filter network 28 is designed to pass frequencies greater than approximately two and one-half times the fundamental fre~uency of the source voltage. Assuming this voltage were 60 hertz, the high pass filter 28 would, therefore, be designed and its component values appropriate to passing frequencies greater than 150 hertæ.
Referencing once again Figure 2, the output o:E ~ilter 28 is shown b~ the third trace from the top and it is seen that the filter output is a series o~
spikes or narrow pulses which a:re in time synchronization with the disturbances o~ the Ll-L3 voltage, equal the magnitude and inverted with respect thereto.
The outputs of the differential amplifier 12 and the fiLter 28 are summed within a suitable summing circuit represented within dashed line block 42. As shown, the summing circuit includes an operational amplifier ~6 having its non-inverting input connected to ground by way of a resistor 47 and the two signals from the circuits 12 and 28 are connected by respective resistors 48 and 44 to the inverting input. A feedback resistor 50 is connected between the output and the inverting input of the operational amplifier 46. The ~ 3~ 21-DS0-2598 ~ 6--The output of the summing circuit ~2 is supplied to a filter circuit 52 which provides as its output on line 62, a signal which is a representation of the sine wave source voltage. In the presently illustrated embodiment of the invention, the filter network 52 takes on the basic form of an integrating network which provides a fixed amount of the phase shift with resepect to its input. To this end the filter 52 includes an operational amplifier 54 having its non-inverting input connected to ground via resistor 55. The inverting input of the operational amplifier receives the output of circuit 42 by way of an input resistor 56. A parallel connection of a capacitor 58 and a resistor 60 is connected between the output and inverting input of the amplifier 54. Those familiar with operational amplifier integrators will recognize that the existence of the resistor 60 precludes this circuit from being a pure integrator and that, therefore,the phase displacement will not be exactly ~ 90. The need or desirability for the resistor ~ is apparent when it is recognized that a certain amount of dc components will be present in the signal applied to the integrator and were it not for the resistor 60 the integrating circuit (filter) would have a tendency to go to satur~tion and thus preclude the efficient use of the present invention.
The bottom trace of Figure 2 illustrates the improvement of the present invention ov~r a simple integration of the line voltages. As shown by the solid line in Figure 2, the integral of the Ll to L3 voltage, it is seen that, for example, at times tl and t2 there is a substantial flat spot within the wave shape. When this i~ compared to the upper trace Figure 1, it is seen that, in this instance, these flat spots correspond, in time, to the zero crossings of the L2 line voltage.
Thus t these flat spots would render a pure integration of the line voltages unsuitable since there are periods ~ 3~ 21-DSO-2598 ~7--of time in which the zero crossing is not well defined.
~y supplying, in accordance with the present invention, the combina~ion of the voltage Ll-L3 with the inverted high frequency components of that voltage the dashed line depiction of Figure 2 is achieved and it is seen that this more closely approximates a sine wave and does not exhibit the flat spot characteristics of the solid line depiction.
Thus, by the design o~ the integrator filter circuit 52, the phase displacement of the output signal with respect to the line voltages is known and by the use of any of the appropriate known zero crossing detectors~ the present invention may be utilized to provide synchronization with respect to the line voltages regardless o~ the number or type of disturbances on the lines.
While there has been shown and descrihed what is at present considered to be the preferred embodiment of the present invention, modifications thereto will readily occur to those skilled in the ar~. It is not desired, therefore, that the invention be limited to this specific circuit and scheme shown and described and it is i.ntended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.
METH~D AND CIRCUITRY FO-R SINE
WAVE RECONSTRUCTION
.~ .
BACKGROUND_OF: T~E I-N~ENTION
The present invention reIates generally to sine wave reconstruction techniques and more particularly to a method and circuitry for providing an outpu-t signal, representative of a sine wave source voltage, from, corrupted voltages which'appear on the lines connecting the source to a load.
There are a number of instances in which it is desirable'to have an accurate representation of a sine wave source ~oltage. One of the more common of these is in the power conversion/motor control art where semiconductor (e.g., thyristor) converter bridges are used to power and control an electric motor. In these applications it is necessary to have an accurate representation of the source voltage in order to properly synchronize the rendering of the bridge semiconductors conductive with'respect to the source voltage. This is normally done by detecting when the ~, voltage crosses the zero axis.
If no disturbances occur on the lines, such detection poses no problems~ Such,' however, is seldom the case. This is particularly true where semiconductor power bridges are used and the transfer of current from one bridge thyristor to anothér causes periodic short circuits across the power lines' which in turn causes rather sevexe disturbances' on those lines. These 3~7 21-DSO~2598 disturbances become even more pronounced when plural converters are connected to the lines with the attendant increase in the number of disturbances. ~ number of systems are known and have been employed to reconstruct the sine wave representation of the source voltage. In U.S. Patent No. 3,976~68 "~oltage Synthesization" by L.J. Lane, issued August 24, 1976, signals proportional to the instantaneous values of the voltage at the terminals of the voltage supply and to the rate of change, with respect to the time, of the current supplied to a load are developed and utilized to synthesize the voltage. An eLaboration of this scheme involves providing the output of the 3,876,~6~ patent to an overdriven ampli~ier, the output of which is then furnishecL to a self-tuning filter such as that described in U.S. Patent No. 3,978,420 'ISelf-Tuning Filter" by L.~. I.ane, issued August 31, 1976.
These known methods are very satisfactory and properly employed furnish excellent results. They are, however, fairly complex and hence expensive and in those applications requiring a high degree of precision can be Eully justified. There are, however, a number of situations in which this hiyh degree of accuracy is not necessary and in which it is difficult to justify the expense of these systems.
S`UMMARY OF T~E INVENTION
_ _ .
It is, therefore, an object of the present invention to provide a method and circuitry for reconstructing a representation of a sine wave source voltage from corrupted line voltages.
It is a further object to provide a sine wave reconstruction technique which requires the sensing of only line to line voltages.
It is still a ~urther object to provide a sine wa~e reconstruction technique which is relatively simple and inexpensive and ye~ sufficiently accurate ~or many applications.
It is an additional object to provide a sine wave recQnstruction technique which can be implemented in a relatively simple manner using relatively in-expensive components.
The foregoing and other objects are achieved in accordance with the present invention by first developing a signal which is representative of the line-to-line voltage between two phases of the line voltayes. In response to the thusly developed signal, there is developed a second signal which is representative of only the high frequency components o~ the first signal.
These two signals are then combin~d and this combined signal is filtered to provide an output signal which is representative of the sine wave source voltage.
BRIEF DESCR;IPTION OF THE D~AWING
While the present invention is described in particularity in the claims annexed to and :Eorming a part of this specification, a better unders-tanding of the invention can be had by reference to the following description taken into conjunct:Lon with the accompanying drawing in which:
Figure 1 is a schemat~c drawing illustrating the circuitry of the present invention in its preferred embodiment; and Figure 2 illustrates wave shapes helpful in understanding the present invention.
DETAILED~DESCRIPTION
Referring now to Figure 1, which shows the circuitry of the present invention in its preferred embodiment, it is seen that a source voltage represented y terminalS Tl! T2 and T3 is connected to a load 10 by way of lines Ll, L2 and L3. The nature of load 10 is not important to the present invention but it would, typically, comprise one or more power converters each supplying one or more eIectric motors. In accordance with the depiction of Figure l, the vol~ages on lines ~ 3~7 21-DS0-2598 Ll and L3 (which designation will also be used for the voltage) serve as inputs to a differential amplifier 12 which includes an operational amplifier 14 having its non-inverting input connected to ground by way of a suitable resistor 16 and a feedback resistor 18 connected between its output and its inverting input.
In order to properly scale the voltage levels, the phase voltage L3 is furnished to the inverting input of the operational amplifier 1~ by way of a vol~age divider comprised of serie~ connected resistors 20 and 22. Similarly, th~ phase voltage Ll is applied as the non-inverting input to operational amplifier 14 by way of the voltage divider comprised of resistors 24 and 26. Reference is now made to the upper trace of Figure 2 which shows the line to neutral voltages as they might appear on lines ~1' L2 and L3, including disturbances caused by a single converter supplying a motor load. The illustrated distortions shown of the sine wave are what are commonly known as commutation notches. The wave shapes shown in this trace are those which occur when the firing angle of the thyristors plus one-half of the commutation angle equals 90.
The second trace of Figure 2 illustrates the output of the differential amplifier circuit 12 and it is seen that it is essentially 30 electrical degrees lagging with respect to the Ll to neutral voltage and that the commutation notches are essentially in time alignment of that phase to neutral voltage.
Referring again to Figure 1, the output of the differential amplifier 12 serves as the input to a high pass filter network 28. The high pass filter 23 consists of a pair of series connected input capacitors 30 and 36 through which the signal from the amplifier 12 isapplied to the inverting input of an operational amplifier 37. The juncture of capacitors 30 and 36 (point 32) is connected to ground by way of a resistor 3~7 2l-Ds~-2598 34 and this same point i5 also connected by way of capacitor 40 to the output of the operational amplifier 37. A feedback resistor 38 is connected between the inverting input and the output of operational amplifier 37 and the non-inverting input of amplifier 37 is connected to ground by way of a resistor 39. The high pass filter within block 28 is essentially that which is shown and described in greater detail in the publication "Handbook of Operational Amplifier Active RC Networks" by Burr-Brown, copyright 1966 (Reference clrcuit number five on page 76). The frequencies to be passed by the high pass filter network28 are somewhat arbitrary but it is believed that satisfactory results can be obtained when the filter network 28 is designed to pass frequencies greater than approximately two and one-half times the fundamental fre~uency of the source voltage. Assuming this voltage were 60 hertz, the high pass filter 28 would, therefore, be designed and its component values appropriate to passing frequencies greater than 150 hertæ.
Referencing once again Figure 2, the output o:E ~ilter 28 is shown b~ the third trace from the top and it is seen that the filter output is a series o~
spikes or narrow pulses which a:re in time synchronization with the disturbances o~ the Ll-L3 voltage, equal the magnitude and inverted with respect thereto.
The outputs of the differential amplifier 12 and the fiLter 28 are summed within a suitable summing circuit represented within dashed line block 42. As shown, the summing circuit includes an operational amplifier ~6 having its non-inverting input connected to ground by way of a resistor 47 and the two signals from the circuits 12 and 28 are connected by respective resistors 48 and 44 to the inverting input. A feedback resistor 50 is connected between the output and the inverting input of the operational amplifier 46. The ~ 3~ 21-DS0-2598 ~ 6--The output of the summing circuit ~2 is supplied to a filter circuit 52 which provides as its output on line 62, a signal which is a representation of the sine wave source voltage. In the presently illustrated embodiment of the invention, the filter network 52 takes on the basic form of an integrating network which provides a fixed amount of the phase shift with resepect to its input. To this end the filter 52 includes an operational amplifier 54 having its non-inverting input connected to ground via resistor 55. The inverting input of the operational amplifier receives the output of circuit 42 by way of an input resistor 56. A parallel connection of a capacitor 58 and a resistor 60 is connected between the output and inverting input of the amplifier 54. Those familiar with operational amplifier integrators will recognize that the existence of the resistor 60 precludes this circuit from being a pure integrator and that, therefore,the phase displacement will not be exactly ~ 90. The need or desirability for the resistor ~ is apparent when it is recognized that a certain amount of dc components will be present in the signal applied to the integrator and were it not for the resistor 60 the integrating circuit (filter) would have a tendency to go to satur~tion and thus preclude the efficient use of the present invention.
The bottom trace of Figure 2 illustrates the improvement of the present invention ov~r a simple integration of the line voltages. As shown by the solid line in Figure 2, the integral of the Ll to L3 voltage, it is seen that, for example, at times tl and t2 there is a substantial flat spot within the wave shape. When this i~ compared to the upper trace Figure 1, it is seen that, in this instance, these flat spots correspond, in time, to the zero crossings of the L2 line voltage.
Thus t these flat spots would render a pure integration of the line voltages unsuitable since there are periods ~ 3~ 21-DSO-2598 ~7--of time in which the zero crossing is not well defined.
~y supplying, in accordance with the present invention, the combina~ion of the voltage Ll-L3 with the inverted high frequency components of that voltage the dashed line depiction of Figure 2 is achieved and it is seen that this more closely approximates a sine wave and does not exhibit the flat spot characteristics of the solid line depiction.
Thus, by the design o~ the integrator filter circuit 52, the phase displacement of the output signal with respect to the line voltages is known and by the use of any of the appropriate known zero crossing detectors~ the present invention may be utilized to provide synchronization with respect to the line voltages regardless o~ the number or type of disturbances on the lines.
While there has been shown and descrihed what is at present considered to be the preferred embodiment of the present invention, modifications thereto will readily occur to those skilled in the ar~. It is not desired, therefore, that the invention be limited to this specific circuit and scheme shown and described and it is i.ntended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.
Claims (8)
1. Circuitry for producing a sine wave output signal representative of a polyphase sine wave source voltage from signals representing line voltages taken from lines connecting the source to a load comprising:
(a) differential amplifier means to provide a first signal representing an actual voltage existing between two phases of the line voltages;
(b) means including an operational amplifier responsive to said first signal to provide a second signal representing only higher frequency components of said first signal;
(c) operational amplifier means to combine said first and second signals to develop a combined signal; and, (d) means to filter said combined signal to provide said sine wave output signal.
(a) differential amplifier means to provide a first signal representing an actual voltage existing between two phases of the line voltages;
(b) means including an operational amplifier responsive to said first signal to provide a second signal representing only higher frequency components of said first signal;
(c) operational amplifier means to combine said first and second signals to develop a combined signal; and, (d) means to filter said combined signal to provide said sine wave output signal.
2. The invention in accordance with claim 1 wherein said means to provide said second signal comprises a high pass filter.
3. The invention in accordance with claim 2 wherein said polyphase sine wave source voltage has a fundamental frequency and wherein said high pass filter rejects frequencies less than approximately two and one-half times the fundamental frequency of said source voltage.
4. The invention in accordance with claim 1 wherein said means to filter includes means to integrate said combined signal.
5. A method for reconstructing a sine wave signal representative of a polyphase source voltage having a predetermined frequency from line voltages appearing on lines connecting the source to a load comprising:
(a) developing a first signal representative of the line-to-line voltages of two phases of said line voltage, said first signal including lower frequency components and higher frequency components;
(b) developing, in response to said first signal, a second signal representative of only the higher frequency components of said first signal;
(c) combining said first and second signal to provide a combined signal; and, (d) filtering said combined signal to provide said sine wave signal.
(a) developing a first signal representative of the line-to-line voltages of two phases of said line voltage, said first signal including lower frequency components and higher frequency components;
(b) developing, in response to said first signal, a second signal representative of only the higher frequency components of said first signal;
(c) combining said first and second signal to provide a combined signal; and, (d) filtering said combined signal to provide said sine wave signal.
6. The method in accordance with claim 5 wherein the step of developing said second signal includes the step of filtering said first signal.
7. The method in accordance with claim 6 wherein said filtering acts to reject signal frequencies less than approximately two and one-half times said predetermined frequency of the source voltage.
8. The method in accordance with claim 5 wherein the step of filtering said combined signal includes integrating said combined signal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000420511A CA1188367A (en) | 1983-01-28 | 1983-01-28 | Method and circuitry for sine wave reconstruction |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000420511A CA1188367A (en) | 1983-01-28 | 1983-01-28 | Method and circuitry for sine wave reconstruction |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1188367A true CA1188367A (en) | 1985-06-04 |
Family
ID=4124446
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000420511A Expired CA1188367A (en) | 1983-01-28 | 1983-01-28 | Method and circuitry for sine wave reconstruction |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1188367A (en) |
-
1983
- 1983-01-28 CA CA000420511A patent/CA1188367A/en not_active Expired
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| Hanselman | Resolver signal requirements for high accuracy resolver-to-digital conversion | |
| US4669024A (en) | Multiphase frequency selective phase locked loop with multiphase sinusoidal and digital outputs | |
| US4099227A (en) | Sensor circuit | |
| US3875509A (en) | Electronic metering of active electrical energy | |
| US4469997A (en) | Self generative PWM voltage source inverter induction motor drive | |
| US3959720A (en) | Voltage control system for high frequency link cycloconverter | |
| US4906860A (en) | Control device for active filter | |
| CH647601A5 (en) | Phase detector circuit. | |
| KR910002055B1 (en) | Digital protect relay | |
| US3849719A (en) | Power rectifier having phase control angle of firing signals independent of supply frequency variation | |
| US4446512A (en) | Circuitry for sine wave reconstruction | |
| US4577154A (en) | Pulse width modulation circuit and integration circuit of analog product using said modulation circuit | |
| EP0371192B1 (en) | Electric quantity detecting method | |
| CA1188367A (en) | Method and circuitry for sine wave reconstruction | |
| US4479160A (en) | Band-pass sequence filters for symmetrical components of multiphase AC power systems | |
| US3564389A (en) | Ac to dc converter | |
| US4156275A (en) | Power conversion unit | |
| US4527116A (en) | Process and device for system characterization by spectral analysis | |
| US4138717A (en) | Constant-gain regulated-phase standard-phase converter | |
| US5047915A (en) | Unrestricted frequency converter for unbalanced loads | |
| US4021658A (en) | Angular rate deriving apparatus | |
| KR0139780B1 (en) | Compensating current detection circuit & its detection of positive power filter | |
| Richman et al. | A new fast computing RMS-to-DC conversion | |
| SU1598096A1 (en) | Shaper of multiphase sine voltage for frequency-controlled electric drive | |
| SU1374364A1 (en) | A.c. to d.c. voltage converter with compensation for higher harmonics of current consumed from the mains |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEC | Expiry (correction) | ||
| MKEX | Expiry |