FI96467C - Method for defining the rotational speed, magnitude and momentum of a flow - Google Patents

Description

96467

The present invention relates to a method for determining the speed, magnitude and instantaneous direction of flux rotation -5 for use between a n-phase AC network and a DC link in both directions to synchronize electrical power via an inverter, which mains inverter comprises n branches with their respective controlled switches and their only parallel-connected components connected in parallel, which branches are connected via chokes to the phases of the AC network. The invention also relates to a situation in which the mains inverter is already loaded to operate in diode mode, i.e. current is already flowing through its components conducting in only one direction. The method can also be varied to cover situations where the direction of rotation and the frequency of the AC network are already known, as well as a voltage directly proportional to the flux when the frequency of the AC system is constant, in which case only the flux direction needs to be determined.

Accordingly, the invention relates to a method. . 25 to determine the initial value of the flux for use in synchronizing the AC inverter with the AC voltage network when the network inverter is connected between the AC voltage network and the DC link. Typically, this DC link supplies, in turn, supplies 30 inverters that supply one or more electric motors. In such an arrangement, the power is usually supplied from the electrical network to the motor, but when the motor is braked, for example, situations may arise in which it is necessary to transfer electrical energy also from the load via the DC link 35 to the electrical network. In these situations, the controlled switches of the mains inverter must be enabled and synchronized with the AC mains, and the mains inverter cannot be used in diode mode alone, where it acts exclusively as a rectifier-5 back-up bridge and does not allow power transfer from the DC link to the AC.

In order to synchronize the mains inverter with the AC mains, information on the rotational speed of the voltage or voltage-generating current in the mains, ie the frequency, magnitude and instantaneous direction, is required to properly synchronize the AC switches' branches with the AC mains voltages. After all, a voltage is known to be formed according to the formula U = -d £ / dt, in which case the voltage vector 15 U and the current vector Ψ are in a phase shift of 90 ° with respect to each other. The voltage of the AC mains is sinusoidal and varies according to the constant angular velocity, ie frequency. In this case, the voltage present in the alternating current system is directly proportional to the current when the magnitude of the angular velocity is a factor of 20. In addition, the following presentation assumes that the positive flow direction is defined as the direction from the AC mains to the intermediate circuit.

According to the invention, the rotational speed, magnitude and instantaneous direction of the flux when no current is still flowing through the mains inverter are determined by measuring the DC link voltage when the DC link is charged to the mains voltage and the DC link is loaded and energized from elsewhere, and determining the magnitude of the flux based on this measured DC voltage, short-circuiting the AC mains phases by switching the switches of each phase of the AC inverter to the same DC link potential, and measuring the short-circuit current , 5 determine the phase sequence of the AC voltage network, ie the direction of rotation, on the basis of the difference between the short-circuit current vectors and their measurement moments a and frequency, and the direction of the flux is determined by rotating the second short-circuit vector by 90 ° in the specified direction of rotation.

10 If, in a situation where no current is still flowing through the AC inverter, the direction and frequency of rotation of the AC network as well as the voltage directly proportional to the flux are known, the method according to the invention can be simplified to comprise only the steps of short-circuiting AC switches the phase of each phase to the same DC link potential and measures the short-circuit current vector during the short circuit and determines the flow direction by rotating the short-circuit current vector 90 ° in the direction of rotation of the network.

Often, the mains inverter is used only as a rectifier bridge and the inverter feature is activated only when necessary. As a rectifier bridge, the network switch- ''. . Current flows through the components in only one direction of the 25 rectifiers. In this situation, the method according to the invention comprises the steps of measuring the DC link voltage when no current is yet flowing through the mains inverter and no energy is supplied to the DC link from elsewhere and determining the flux based on this measured DC voltage, measuring the first peak current vector. measuring a second peak current vector at the next peak value of the current, 96467 4 determining the phase sequence of the AC voltage network, i.e. the direction of rotation and frequency, based on the difference between the peak current vectors and their measurement moments, and determining the flow direction based on the direction of either peak current vector.

The determination of the flux direction is then based on the dependence between the peak value of the current and the peak value of the voltage, in particular with respect to the direction, and on the other hand, the dependence between the voltage direction and the flux direction. However, from the point of view of Tah-10, the moment of peak current is not the most desirable precisely because of the magnitude of the current. In order for the synchronization to be based on the start time of the commutation, the method further comprises the steps of determining the start time of the commutation and determining the flow direction at the beginning of the commutation time by rotating the second peak current vector 360 ° / 2n forward in the direction of rotation.

If synchronization is to be based on the end of commutation, which is probably the most favorable moment for performing the synchronization itself, the method further comprises the steps of determining the commutation duration, determining the angle at which the flux shifts during commutation, the frequency and commutation duration: after summing the flux direction at the beginning of the commutation time by the angle that the flux shifts during commutation.

If, in the situation defined above, where only 30 unidirectional components are already flowing, the direction and frequency of rotation of the AC network as well as the voltage directly proportional to the flux are known, the method of the invention can be simplified to include only the steps of measuring the current at peak current. 1! 5 96467 vector and determining the flow direction based on the direction of the peak current vector. In this case, the synchronization is therefore based on the peak current moment. If it is desired to base the synchronization on the start time of the commutation 5, then the method further comprises the steps of determining the start time of the commutation and determining the flow direction at the beginning of the commutation time by rotating the peak vector by 360 ° / 2n in the forward rotation direction. If synchronization is to be established at the end of commutation, the method further comprises the steps of determining the commutation duration, determining the angle flowing during the commutation time as a product of frequency and commutation duration, and determining the flux direction after commutation by summing the flux at the beginning of the commutation time. .

The methods according to the invention will now be described in more detail with reference to the accompanying drawing, in which Fig. 1 shows the basic connection of a network inverter suitable for carrying out the methods according to the invention; Fig. 2 shows a vector representation of currents in a network inverter short circuit and based on them. to the network inverter as it acts as a rectifier bridge.

Figure 1 shows a schematic circuit in which the mains inverter WS is connected between a three-phase switching voltage network U with phase voltages U0, U1 and U2, 35 and a DC link 1. In this case, the network 6- a line choke L is connected between each branch of the rectifier WS and the phases of the AC voltage network. A capacitor C is connected to the DC voltage intermediate circuit 1 side of the mains inverter, over which the DC voltage Uc acts and 5 this DC voltage circuit 1 is loaded by a load Sdc. The mains inverter WS itself, in turn, comprises two controlled switches in each branch, switches S1 and S2 in the first branch, switches S3 and S4 in the second branch and switches S5 and S6 in the third branch. Alongside these controlled switches 10, only one-way conductive components, such as diodes, D1 ... D6, are connected. When the mains inverter acts as a rectifier bridge, current flows only through diodes D1 ... D6 and, respectively, when the mains inverter acts as an inverter and transfers 15 powers primarily from the DC link to the AC side of the AC network, controlled switches S1 ... S6 operate.

The object of the invention is to provide a method by means of which the switches S1 ... S6 of a mains inverter WS as described in Fig. 1 can be synchronized to the phases of the AC network U, i.e. primarily to determine the current flowing in the AC network at any given time. In a situation where no power is yet flowing through the mains inverter, this information can be accessed by the following steps.

In the first step, to determine the magnitude of the flux, the DC voltage of the DC link circuit is measured when the capacitor C is charged with the prevailing mains voltage to the DC voltage Uc. From this measured DC voltage, the phase voltage acting on the AC network U can be deduced directly. This voltage of the AC network is again directly proportional to the flux in this AC network.

Next, the phases of the AC voltage network are short-circuited for a limited time. In practice, this can be done by connecting 35 all the switches controlled by the lower branches, i.e. the switches

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7 96467 S2, S4 and S6, simultaneously conducting or alternatively by connecting all the switches of the upper branches, i.e. switches S1, S3 and S5, simultaneously conducting. In this situation, the phases of the AC voltage network supply a short-circuit current through the chokes L 5, which is measured. In practice, to determine the direction and magnitude of this short-circuit current, it is sufficient to measure the two-phase current in a three-phase network and to measure the direction and magnitude of the n-1 phase current in an n-phase network. This short circuit must, of course, be of relatively short duration, for example about 100 s. Next, a second similar short circuit is performed to determine the second current vector as described above. These two short-circuit current vectors, which can be considered significant, for example il 15 and i2, and the difference Δt of the measurement moments of these short-circuit current vectors can now be used to determine the phase sequence, ie direction of rotation and frequency, ) 20 where <il means the direction of the short-circuit current vector il, <i2 the direction of the second short-circuit current vector i2 and ws the electrical frequency of the electrical network. The sign of the value ws determines to represent the phase sequence of the network, i.e. the direction of rotation of the network.

25 Next, the direction of the flux is determined by rotating the second short-circuit current vector i2 90 ° in the specified direction of rotation. This is based on the fact that in the case of a short circuit, the flux is 90 ° above the current vector.

Accordingly, it is possible to determine all the necessary information, i.e. the current speed, magnitude and current direction, in order to obtain the starting information for controlling the controlled switches of the mains inverter so that their operation can be synchronized with phases U0, U1 and U2 of the alternating voltage network.

Fig. 2 schematically shows the short-circuit current 96467a vectors 111 and i2 as well as the current vector E at the time of measuring the short-circuit current vector i2.

The procedure described above can be significantly simplified if the direction of rotation and the frequency of the AC voltage network 5 are known in advance, as well as a voltage which, as before, is proportional to the magnitude of the flux. In this case, only one short-circuit has to be made and the short-circuit current vector generated in this situation has to be measured. Based on this short-circuit current vector, it is possible to determine the direction of the flow by rotating the short-circuit current vector 90 ° to the already known direction of rotation of the network. Thus, the method steps of determining the rotational speed and magnitude of the flux may be omitted.

As already shown above, the mains-15 inverter is quite often used in diode mode, i.e. in a state where only components conducting in one direction, such as diodes, D1 ... D6 conduct, i.e. act as a rectifier bridge, but where controlled components S1 ... S6 are not yet controlled. . In order for the controlled switches S1 ... S6 to be able to synchronize to the AC network in this situation, information on the rotational speed, magnitude and instantaneous direction of the AC network flux is required, as above. Now that current is already flowing through the mains inverter WS, this current can be used to determine the flow. As above, the magnitude of the flux is determined by measuring the DC voltage Uc of the DC link circuit 1 in a state where the capacitor C of the DC link circuit is charged with the prevailing mains voltage. On the basis of this direct voltage, as already stated above, it is possible to directly determine the magnitude of the mains voltage 30 and thus the magnitude of the flux.

Next, in the case of a three-phase network, the first current vector at the moment when the current reaches a peak value is measured by means of two-phase current measurements and in the case of an n-phase network by means of n-1-phase current measurements. 35 This measurement moment is marked in the flow circle in Figure 3

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9646? 9 with the notation Tl. Based on the measurement moment of this peak current vector alone, the direction of the flux could be determined based on the dependence between the current and the voltage and the voltage and the flux on the other hand. After time T1, it can be seen in Figure 3 that the current 5 drops rapidly until time T2, when the current begins to move to the next step. This start of commutation is denoted by T2 in Fig. 3. The commutation, the duration of which can be marked Atk, ends at the point marked T3 in Fig. 3. In the most preferred embodiment of the method 10 according to the invention, the aim is to determine the flow direction at the end of the commutation and for this purpose the start time T2 of the commutation and its end time T3 and the difference of the commutation duration Atk are determined. At the end of the commutation, the current increases to its next peak value, which is reached at time T4. In this case, measure the second peak current vector ± 2. As above, the phase sequence of the AC network, i.e. the direction of rotation and the frequency ws, can now be determined on the basis of the difference Δt of the peak current vectors 11 and i2 and their measurement moments according to the formula 1. The flow direction, in turn, is determined by first determining the flow direction at the beginning of the commutation time by rotating the second peak current vector i2 in the three-phase network 60 ° and in the n-phase network 360 ° / 2n in the specified direction of rotation. This is based on the fact that if the commutations are disregarded and the DC component is assumed to be continuous, it could be inferred from the zero of the current vector that the network flux and the flux generated by the DC link are equal and parallel, flowing from in an n-phase network 360 ° / 2n above the current vector). The flow vector thus obtained is illustrated in Fig. 3 by the vector ΨΤ2. In practice, however, commutation must be taken into account. As a result, the angle Δα whose flux shifts during the commutation time 35 Atk is determined by the frequency ws and the commutation duration Atk 10 9646? as input or Δα = wsAtk. (2)

The direction of the flux after commutation can now be determined by summing the angle Δα in the direction of the flux determined at the beginning of the commutation time, i.e. the angle whose flux approximately shifts during commutation. The flow vector thus obtained is illustrated in Fig. 3 by the vector ΨΤ4. It is clear that instead of the procedure described above, the location of the flux could also be determined according to, for example, the peak current vector or the initial moment of commutation, whereby the determination of the flux location bound to that moment would differ slightly from the described procedure. If it is desired to bind the synchronization routine to a specific flux location, it makes sense to select a specific diode-15 state (peak current, start or end of commutation) to determine the flux for synchronization. The above solution is thus suitable for situations in which it is desired to bypass the diode bridge commutation at the time of synchronization, but the current has not yet risen to its peak value.

20 If the direction and frequency of rotation of the AC voltage network as well as the voltage, i.e. the magnitude of the flux, are known and the network inverter operates in diode mode, quite a number of the steps described above can be omitted. In this case, it is not necessary to determine the magnitude of the flow or the rotation speed of the flow, but only information about the instantaneous direction of the flow is needed. For this purpose, as before, the start and end time of the commutation and, as a difference, the duration of the commutation are determined. Similarly, the peak current vector is measured at the peak value of the current following commutation. From these, the flow direction can be deduced at the beginning of the commutation time by rotating the peak current vector 60 ° forward in the direction of rotation in the case of a three-phase network. The angle Δα, the flux of which shifts during the commutation time according to formula 2, is then determined. As above, after the flux direction commutation has taken place, the angle Aa whose flux has shifted during the commutation is now summed in the flux direction at the beginning of the commutation time.

The method according to the invention has been described above mainly only in connection with a three-stage system.

On the other hand, as indicated, the method according to the invention is also suitable for implementation in connection with any phase or frequency AC voltage network by carrying out the necessary measures in accordance with the appended claims.

Claims (8)

9646? 12 A method for determining the rotational speed, magnitude and instantaneous direction of a flux for use in synchronizing a mains inverter (WS) adapted to transfer electrical power in both directions between an n-phase AC voltage network (U) and a DC link (1) when the current is not via a mains inverter, which mains inverter comprises n 10 branches with their respective controlled switches (S1 ... S2n) and their only one-way conducting components (D1 ... D2n) connected in parallel, which branches are connected via chokes (L) to the AC voltage network (U) phases (UO ... U (n-1)), characterized in that the method comprises the steps of measuring the voltage of the DC link when the DC link is charged to a level determined by the mains voltage and the DC link is not loaded or energized elsewhere, and the flux is determined on the basis of this measured DC-20 voltage, short-circuiting the AC mains phases by switching the switches of each phase of the mains inverter to the same DC link potential and measuring the first short-circuit current vector during the short-circuit, short-circuiting the alternating , 30 determine the phase sequence of the AC network, i.e., the direction of rotation and frequency (ws), based on the difference between the short-circuit current vectors (il, i2) and their measurement moments (Δt), and determine the direction of flux by rotating the second short-circuit current vector (i.2) 90 ° to the specified direction of rotation. 13 96467 2. A method for determining the instantaneous direction of flux for use between an n-phase AC voltage network (U) and a DC link (1) in both directions to synchronize a power inverter 5 (WS) adapted to transfer AC power with an AC network (U) and the frequency as well as the voltage, which is directly proportional to the magnitude of the flux, is known, which network inverter comprises n branches with their anomicable controlled switches (S1 ... S2n) and their one-way only components (D1 ... D2n) connected in parallel , the branches of which are connected via chokes (L) to the phases of the alternating voltage network (U) (U0 ... U (nl)), characterized in that the method comprises the steps of short-circuiting the phases of the alternating voltage network by connecting the switches of each phase of the AC inverter to the same DC link and the short-circuit current vector is measured during the short circuit and the flow direction is determined by rotating the short-circuit current vector 90 ° in the direction of rotation of the network. 3. A method for determining the rotational speed, magnitude and instantaneous direction of a current for use in synchronizing a mains inverter (WS) adapted to transfer electrical power in both directions between an n-phase AC network (U) and a DC link • 25 (1) in an AC converter (U) branch with its respective controlled switches (S1 ... S2n) and with their components (D1 ... D2n) connected in parallel in each direction only in one direction, which branches are connected via chokes (L) to the phases of the AC voltage network (U) (U0 .. .U (nl)), and when current flows through the components (D1 ... D2n) conducting the network inverter in only one direction, characterized in that the method 35 comprises the steps of 9646? 14 measure the DC link voltage when no current is passing through the AC inverter and no other energy is applied to the DC link, and determine the flux based on this measured DC voltage; 5 measure the first peak current vector (il) at the current peak value; measure the second peak current at the next peak value (i2) , determine the phase sequence of the AC network, i.e. the direction of rotation and the frequency (ws), based on the difference between the peak current vectors (il, i2) and the measurement moments (Δt) and determine the flow direction based on the direction of either peak current vector (il, i2). A method according to claim 3, characterized in that it further comprises the steps of determining the start time of the commutation and determining the flow direction at the beginning of the commutation time by rotating the second peak current vector (d.2) by an angle of 360 ° / 2n in the direction of rotation. The method of claim 4, further comprising the steps of determining the commutation duration (Atk), determining the angle (Δα) whose flux shifts during the commutation time (Atk) as a product of the frequency (ws) and the commutation duration, and determining the direction of the flux after commutation by summing the angle 30 (Δα) in the direction of flux at the beginning of the commutation period, which flux shifts during commutation. A method for determining the instantaneous direction of flux for use in synchronizing an AC converter 35 (WS) adapted to transfer electrical power in both directions between an n-phase AC voltage network (U) and a DC link (1) in a synchronous manner with an AC voltage network (U) ... S2n) and with their single-directional components (D1 ... D2n) connected in parallel, the branches of which are connected via chokes (L) 5 to the phases of the alternating voltage network (U) (UO ... U (nl)), and when the current passes through the components (D1 ... D2n) conducting the network inverter in only one direction and the direction and frequency of rotation of the AC voltage network as well as a voltage directly proportional to the flux is known, the method comprising the steps of measuring a peak current vector at peak current and determining the flow direction at peak current based on the direction of the ktor. The method of claim 6, further comprising the steps of determining the start time of the commutation and determining the flow direction at the beginning of the commutation time by rotating the peak current vector by an angle of 360 ° / 2n in the direction of rotation. The method of claim 7, further comprising the steps of determining the commutation duration (Atk), determining the angle (Δα) whose flux shifts during the commutation time as a product of frequency (ws) and commutation duration, and determining the flux direction for commutation. by summing the angle (Δα) in the direction of flux at the beginning of the commutation period, which flux shifts during commutation. 16 9646?