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WO1991011847A1 - Procede de commande d'un convertisseur commute en frequence fondamentale et a tension constante, et appareil convertisseur possedant un dispositif de mise en ×uvre du procede - Google Patents

Procede de commande d'un convertisseur commute en frequence fondamentale et a tension constante, et appareil convertisseur possedant un dispositif de mise en ×uvre du procede Download PDF

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Publication number
WO1991011847A1
WO1991011847A1 PCT/SE1991/000070 SE9100070W WO9111847A1 WO 1991011847 A1 WO1991011847 A1 WO 1991011847A1 SE 9100070 W SE9100070 W SE 9100070W WO 9111847 A1 WO9111847 A1 WO 9111847A1
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WO
WIPO (PCT)
Prior art keywords
convertor
flux
path
vector
voltage
Prior art date
Application number
PCT/SE1991/000070
Other languages
English (en)
Inventor
Lennart Ängquist
Original Assignee
Asea Brown Boveri Ab
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by Asea Brown Boveri Ab filed Critical Asea Brown Boveri Ab
Publication of WO1991011847A1 publication Critical patent/WO1991011847A1/fr

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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
    • H02M7/00—Conversion of AC power input into DC power output; Conversion of DC power input into AC power output
    • H02M7/42—Conversion of DC power input into AC power output without possibility of reversal
    • H02M7/44—Conversion of DC power input into AC power output without possibility of reversal by static converters
    • H02M7/48—Conversion of DC power input into AC power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/505—Conversion of DC power input into AC power output without possibility of reversal 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
    • H02M7/515—Conversion of DC power input into AC power output without possibility of reversal 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
    • H02M7/521—Conversion of DC power input into AC power output without possibility of reversal 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 in a bridge configuration

Definitions

  • the present invention relates to a method for control of a voltage stiff fundamental-frequency commutated convertor with alternating voltage terminals for connection to an alternating voltage network via inductive elements and with direct voltage terminals for connection to a direct voltage source, in which the flux vector of the convertor is formed and utilized for control of the commutation instants of the converter.
  • the invention also relates to convertor equipment comprising a voltage stiff fundamental-frequency commutated convertor with alternating voltage ⁇ terminals for connection to an alternating voltage network via inductive elements, with, direct voltage terminals for connection to a direct voltage source and with means for forming the flux vector of the convertor.
  • a voltage stiff self-commutated convertor may generate an alternating voltage with a frequency and a phase position which are determined by the control equipment of the conver ⁇ tor.
  • the fact that the convertor is voltage stiff means that it is intended for connection to a direct voltage net ⁇ work or a direct voltage source with low internal impedance .
  • the magnitude of the direct voltage then determines the amplitude of the generated alternating voltage.
  • pulse width modulation is used for con ⁇ trol of the amplitude of the alternating voltage and poss ⁇ ibly also of its curve shape. In such a convertor a large number of commutations per alternating voltage period are made, and the commutating losses therefore become high.
  • this category of convertors are the so-called fundamental-frequency commutated convertors .
  • each valve in the convertor has only one single uninterrupted conduction interval per alternating voltage cycle. The number of commutations therefore becomes the lowest possible and the commutating losses low, which makes this type of convertor especially suited for use at high power ratings.
  • the amplitude of the alternating voltage is, in principle, completely determined by the direct voltage amplitude and cannot therefore be affected by the control means of the convertor.
  • fundamental-frequency commutated convertors occasional extra commutations per conduc ⁇ tion interval of the valves of the convertor occur for the purpose of reducing the harmonic content of the alternating voltage. However, this does not affect the characteristic properties of this type of convertors .
  • a conventional connection for the main circuits of such a convertor is shown in Figure 2. It has direct voltage connections DT+ and DT- for connection to a stiff direct voltage source, that is, a direct voltage source with low internal impedance. It has three phases a, b, c. Each phase, for example phase a, comprises two series-connected controllable semiconductor valves Tau and Tan. Of these, one of the valves is conducting during 180° of each alter ⁇ nating voltage period and the other valve during the remai ⁇ ning 180° of the period. Each valve is antiparallel- connected to a diode Dau and Dan, respectively. The three phase units operate mutually 120° offset in phase .
  • valves of the convertor may consist of gate turn-off thyristors but they may alternatively consist of conventional thyristors which are provided with turn-off means, or of transistors.
  • a thyristor and its antiparallel-connected diode may be integrated into a common device.
  • Figure 1 shows such a convertor SR with its direct voltage terminals connected to a direct voltage network DP, DN.
  • a capacitor C is connected between the direct voltage connec ⁇ tions of the convertor to achieve the necessary low internal impedance.
  • the alternating voltage terminals AT of the convertor are connected to an alternating voltage network N via inductive elements with the resistance r and the reactance x ⁇ _. These elements may consist of separate inductors or of the reactance of a convertor transformer.
  • the network N typically consists of a three-phase power network or of a rotating three-phase machine. The main part of the difference between the instantaneous values of the line voltage, which in principle is sinusoidal, and the square-wave voltage of the convertor is taken up by the reactance x*_, (the voltage drop across the resistor r is normally of minor importance) .
  • a sinusoidal alternating voltage may be described using a vector which rotates in the complex plane.
  • a corresponding flux defined as the time integral of the voltage, will then be a vector which in the same complex plane, assuming a constant frequency and amplitude of the alternating voltage, moves in such a way that its tip follows a circular orbit at a constant peripheral velocity.
  • the alternating voltage and the corresponding flux of a self-commutated convertor may in a corresponding way be described using vectors in a complex plane. This is known, for example, from
  • a motor drive which comprises a convertor of the kind described above.
  • a torque controller With the aid of a torque controller, a reference value for the amplitude of the motor flux is obtained.
  • the flux amplitude reference in turn affects the frequency of the convertor voltage and hence eventually also the phase position of this voltage.
  • a method is proposed for changing, as quickly as possible, the flux amplitude from one value to another.
  • the path of the flux vector may for various reasons deviate from the desired path, which for a six-pulse convertor consists of an equilateral ' hexagon with its centre at the origin of the complex plane.
  • Reasons for such disturbances in the path of the flux vector may, for example, be the following:
  • a disturbance of the path of the flux vector means that the path will no longer be centered in the origin of the complex plane.
  • the alternating currents of the convertor form an unsymmetrical three-phase system with a risk of overload of certain valves and of interruption of the operation because of missing commutation.
  • a disturbance of the above-mentioned kind generally gives rise to a phase change of the alternating voltage of the convertor.
  • Such a phase change will entail a change of' the active power flux between the network and the convertor and hence a rapid charge or discharge of the capacitor on the direct voltage side of the convertor, which in turn entails a rapid and undesired change of the direct voltage of the convertor.
  • the invention aims to provide a method and convertor equip ⁇ ment of the kind described in the preamble to the specification, which provides:
  • the above advantageous properties are obtained by generating, according to the invention, a flux reference vector in dependence on the line voltage, determining the flux vector of the convertor, and controlling the commutations of the convertor such that the flux vector of the convertor, in the fastest possible way after a disturbance, is brought to pass to a new symmetrical path, while at the same time restoring the desired phase position of the convertor voltage relative to the line voltage. Since in this way undesired deviations of the phase position of the convertor voltage will be restored in the fastest possible way, undesired charges and discharges of the capacitor of the direct voltage side will be maintained at a minimum.
  • Figure 1 shows a convertor of the relevant kind connected to an alternating voltage network.
  • Figure 2 which has been described above, shows an example of the configuration of the main circuits of the convertor.
  • Figure 3 shows the path in the complex plane for the flux vector of the convertor.
  • Figure 4 shows the- paths of the flux vectors in the complex plane and illustrates how the determination of the instant of the next commutation is done according to the invention.
  • Figure 5 shows an example of the configuration of the circuit which is used for forming the flux vector of the convertor in the equipment shown in Figure 1.
  • Figure 6 shows the mode of operation of the calculating member in the equipment according to Figure 1, which is used for determining the instant of the next commutation.
  • Figure 1 the main circuits of which have been described above, shows a convertor which is voltage stiff, self- com utated and fundamental-frequency commutated.
  • the convertor is connected to a three-phase alternating voltage network N.
  • This may consist of a three-phase power network and the convertor, for example, be intended for static reactive power compensation.
  • the direct voltage network connected to the direct voltage terminal of the convertor consists only of the busbars DP and DN and the capacitor bank C.
  • signals - bus which depict the network alternating voltage, are generated.
  • a three-phase signal i is generated which depicts the alternating currents flowing between the network and the convertor.
  • a calculating circuit MC the function of which will be described with reference to Figure 5. From the calculating circuit a signal ⁇ conv s obtained, which indicates the position in the complex plane of the flux vector of the convertor. Further, the calculating circuit generates a signal ffc > us which is a measure of the frequency of the network alternating voltage. The calculating circuit also supplies a signal arg( ⁇ bUS ) which is a measure of the argument of that flux vector which corresponds to the network voltage.
  • a direct voltage measuring device DM for example a voltage divider connection, generates a measured signal UD which is a measure of the direct voltage of the convertor. This signal is supplied to a summator S2 as well as to a -control circuit FCC.
  • the circuit FCC supplies control signals SS to the convertor, which trigger commutations in the convertor.
  • a reference voltage generator RS which in its simplest form may consist of a potentiometer, delivers a voltage reference signal o ref , which is a measure a of the desired direct voltage of the direct voltage side of the convertor. This reference is compared in the summator S2 with the measured voltage UD, and the difference is supplied to a voltage regulator UR, which has a PI characteristic.
  • the output signal ⁇ ref of the regulator is in steady-state operation that phase angle between the flux vectors of the network and the convertor which is required for the capacitor voltage to be maintained constant at the reference value given by the reference generator RS.
  • the output signal of the regulator is added in a summator SI to the signal arg( ⁇ _- >us ) , and the sum of these two signals constitutes the argument arg( ⁇ ref ) for a reference flux vector.
  • Figure 3 shows the flux vector ⁇ conv and its path in the complex plane.
  • the path of the tip of the flux vector consists of a symmetrical hexagon.
  • the flux vector ⁇ conv is formally defined by the following equation:
  • u conv is the voltage vector of the convertor and ⁇ n is the angular frequency of the network voltage.
  • ⁇ conv of the side of the hexagon is determined by the condition that the circumference of the hexagon is to be traversed during one of the network alternating voltage cycles at a peripheral speed determined by the amplitude of the alternating voltage of the convertor, that is, by its direct voltage UD.
  • the side length is obtained from the following equation:
  • Figure 4 illustrates the principle of the invention.
  • the flux vector ⁇ conv of the convertor is continuously determined, the tip of the vector at a certain time being assumed to be at point A.
  • an estimation is made of the direct voltage value which will prevail up to the commutation which succeeds the immediately following commutation.
  • This estimation is made in accordance with a suitable algorithm.
  • the estimation consists of the assumption that the direct voltage will be constantly equal to the measured value.
  • an estimation is made of the value of the network frequency b us which will prevail for two commutations onwards in time.
  • this estimation consists of the assumption that the frequency will be constantly equal to the value measured at that particular instant.
  • the side length ⁇ ex of an equilateral hexagon centered at the origin of coordinates, is determined, which hexagon constitutes the path of a reference flux vector ⁇ ref , which at the current values of direct voltage and network frequency and in case of undisturbed steady-state operation, would follow this path.
  • the upper half HDEK is shown in Figure .
  • the circumference of the path is parameterized with a parameter 0 to 2 ⁇ for one revolution, and the magnitude of the vector is obtained by finding that point on the path whose parameter value corresponds to the argument arg( ⁇ ref ) according to Figure 1.
  • the reference flux vector assumes the shown position with its tip at the point 3 while at the same time the flux vector of the convertor has its tip at the point A.
  • the reference vector and the flux vector of the convertor will move in parallel in a direction towards the points D and i, respectively, and at the same velocity, which is determined by the currently measured value of the direct voltage of the convertor.
  • the next commutation is assumed to take place when the flux vector of the convertor is at point Ai.
  • the flux vector will thereafter move along the path AiGC, whereas the reference flux vector moves along the path BiDEC.
  • the instant of the commutation is selected such that the length of the path AiGC equals the length of the path BiDEC.
  • the distance betwen the tip B of the vector and the next corner D of the polygon namely (l- ⁇ ) ⁇ h ex
  • the simul ⁇ taneous distance between the tip A of the convertor flux vector and the polygon side HD in a direction which is parallel to the next polygon side DE (this distance becomes the same as A*_F in Figure 4) are determined continuously one or several times .
  • the distance in the flux plane from the position of the reference flux vector at the time of measurement and its position at the time of commutation are given by the difference between the measured values calculated above.
  • the distance in the flux plane may be converted into distance in time since the velocity of travel in the flux plane is known by the estimation uoestim-
  • the calculated commutating time t CO m can now be calculated if the time for the measurement has been recorded. This will make it possible to set, in-a running clock, the time when triggering of the commutation is to take place. If the distance to the commutation is sufficiently great, there will be time to carry out several calculations, and the time set for commutation can thus be adjusted several times upon passage of a hexagon side.
  • Figure 5 shows the configuration of the calculating circuit MC in Figure 1. From the measuring devices IM and UM the circuit is supplied with the instantaneous values of the three phase currents i a r i__ , i c and the phase voltages u a , b , u c .
  • the reference axis for phase a is assumed to coincide with the positive direction of the real axis of the complex plane. According to known relationships, the real part i RE and the imaginary part im of the complex vector, which corresponds to the current flowing from the convertor to the network, are now formed. This is done by addition of the instantaneous values of the phase currents in the operational amplifiers Fl and F2 with the proportionality constants indicated in the operational amplifier symbols.
  • the output signals from these summators constitute the real part ⁇ convRE and the imaginary part ⁇ convi M /- respectively, of the flux vector of the convertor.
  • These signals are supplied to the control circuit FCC in the manner shown in Figure 1.
  • the network alternating voltage is supplied to a frequency measuring device FM, which delivers a signal f us which is a measure of the frequency of the network alternating voltage.
  • a calculating circuit AB forms the argument for the flux vector of the network according to the relationship
  • Figure 6 illustates the mode of operation of the control circuit FCC in Figure 1.
  • the circuit may, for example, consist of a fast processor adapted to operate according to the flow chart shown in Figure 6.
  • the time remaining till commutation, ⁇ t CO m, is obtained by division of the latter quantity by the velocity of the flux vectors along the path.
  • the remaining time is added to the time t m t at the time of measurement and a calculated commutating time t C om is obtained, which may be loaded in a register in a system clock (Load t C om) •
  • the system clock (t) passes the loaded-in time
  • the commutation (COM) which is next in turn is triggered.
  • the calculations and the updating of the commutating time may be made one time or several times per polygon side, depending on the need of calculating time.
  • a method and a convertor according to the invention have been described above for the case where the convertor is used as a reactive power compensator.
  • the described control will then have to be supplemented, in conventional manner, with control members which control the amplitude of the alternating voltage of the convertor such that the desired reactive power flow between the convertor and the network is obtained. This can be made by influencing the direct vol ⁇ tage reference u re f n Figure 1.
  • the method and the convertor equipment according to the invention may be used for other purposes than for power factor correction.
  • the convertor consists of a six-pulse convertor.
  • the invention may be applied to other pulse numbers as well, for example to twelve-pulse convertor connections, in which the path of the flux reference vector in steady state becomes an equilateral twelve-sided polygon.
  • the invention can also be applied when six-pulse bridges according to the invention are adapted to cooperate relative to a common network.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)
  • Ac-Ac Conversion (AREA)
  • Control Of Ac Motors In General (AREA)

Abstract

Appareil convertisseur comportant un convertisseur (SR) à tension constante commuté en fréquence fondamentale et autocommuté, devant se raccorder à un réseau à tension alternative (N) et à un réseau à tension continue (DP, DN, C). L'appareil comporte des éléments (FCC) de détermination de parcours qui sont aptes, en fonction de la tension continue (uD) mesurée du convertisseur et d'une référence de fréquence (fbus), à déterminer les données caractéristiques (γhex) d'un parcours polygonal estimé (HDEK) pour un vecteur de référence de flux (γref), des éléments de formation d'un vecteur de référence (FCC) qui sont aptes, en fonction d'une référence d'angle de phase arg (γref) suivant ce parcours, ainsi que des éléments de commande de la commutation (FCC) aptes à déclencher la prochaine commutation à un instant tel que le vecteur de référence de flux et le vecteur de flux du convertisseur coïncident au point d'intersection (C) entre le parcours (A1, GC) du vecteur de flux et un côté (EK) dudit parcours polygonal, ledit côté ayant une direction qui dévie de celle du côté du polygone (HD) le long duquel se déplace le vecteur de référence de flux juste avant la commutation.
PCT/SE1991/000070 1990-02-02 1991-01-31 Procede de commande d'un convertisseur commute en frequence fondamentale et a tension constante, et appareil convertisseur possedant un dispositif de mise en ×uvre du procede WO1991011847A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
SE9000374-0 1990-02-02
SE9000374A SE465546B (sv) 1990-02-02 1990-02-02 Foerfarande och stroemriktarutrustning foer styrning av en spaenningsstyv grundfrekvenskommuterad stroemriktare

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WO1991011847A1 true WO1991011847A1 (fr) 1991-08-08

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SE (1) SE465546B (fr)
WO (1) WO1991011847A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2639955A3 (fr) * 2011-12-19 2017-04-05 RWE Deutschland AG Procédé de réglage d'un convertisseur de courant à commutation automatique

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4678248A (en) * 1984-10-20 1987-07-07 Brown, Boveri & Cie Ag Direct self-control of the flux and rotary moment of a rotary-field machine
EP0316804A1 (fr) * 1987-11-12 1989-05-24 Kabushiki Kaisha Toshiba Régulateur de puissance réactive

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4678248A (en) * 1984-10-20 1987-07-07 Brown, Boveri & Cie Ag Direct self-control of the flux and rotary moment of a rotary-field machine
EP0316804A1 (fr) * 1987-11-12 1989-05-24 Kabushiki Kaisha Toshiba Régulateur de puissance réactive

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2639955A3 (fr) * 2011-12-19 2017-04-05 RWE Deutschland AG Procédé de réglage d'un convertisseur de courant à commutation automatique

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Publication number Publication date
SE465546B (sv) 1991-09-23
SE9000374L (sv) 1991-08-03
SE9000374D0 (sv) 1990-02-02
AU7229891A (en) 1991-08-21

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