The invention relates to the field of power electronics, based on a method for operating a converter circuit, and an apparatus for carrying out the method.
Conventional converter circuits have a converter unit with a multiplicity of drivable power semiconductor switches, which are connected in a known manner in order to switch at least two switching voltage levels. An LCL filter is connected to each phase connection of the converter unit. A capacitive energy store is also connected to the converter unit and is normally formed by one or more capacitors. An apparatus is provided for operating the converter circuit, which has a control device for producing a hysteresis power value, a hysteresis wattless component value and a selected flux sector, which control device is connected to the drivable power semiconductor switches via a drive circuit in order to form a drive signal from the hysteresis power value, the hysteresis wattless component value and the selected flux sector. The power semiconductor switches are therefore driven by means of the drive signal.
A converter circuit as mentioned above is subject to the problem that the LCL filters can cause permanent distortion, that is to say undesirable oscillations, in the filter output currents and filter output voltages as a result of resonant oscillations of the LCL filters, as shown in the normal waveform of filter output currents shown in
One object of the invention is therefore to specify a method for operating a converter circuit, by means of which it is possible to actively damp distortion, caused by LCL filters connected to the converter circuit, in the filter output currents and filter output voltages. A further object of the invention is to specify an apparatus by means of which the method can be carried out in a particularly simple manner.
The converter circuit has a converter unit with a multiplicity of drivable power semiconductor switches, and an LCL filter connected to each phase connection of the converter unit. In the method according to the invention for operating the converter circuit, the drivable power semiconductor switches are now driven by means of a drive signal formed from a hysteresis power value, from a hysteresis wattless component value and from a selected flux sector. According to the invention, the hysteresis power value is formed from a difference power value by means of a first hysteresis regulator and the difference power value is formed from the subtraction of an estimated power value and of a damping power value from a reference power value, with the damping power value being formed from a sum, weighted by a variable damping factor, of a multiplication of the α component of the space vector transformation of filter capacitance currents of the LCL filters by an α component of the space vector transformation of phase connection currents and a multiplication of a β component of the space vector transformation of filter capacitance currents of the LCL filters by a β component of the space vector transformation of phase connection currents. Furthermore, the hysteresis wattless component value is formed from a difference wattless component value by means of a second hysteresis regulator, and the difference wattless component value is formed from the subtraction of an estimated wattless component value and of a damping wattless component value from a reference wattless component value with the damping wattless component value being formed from a difference, weighted by the variable damping factor of a multiplication of the β component of the space vector transformation of the filter capacitance currents of the LCL filters by the α component of the space vector transformation of phase connection currents and a multiplication of the α component of the space vector transformation of filter capacitance currents of the LCL filters by the β component of the space vector transformation of the phase connection currents.
The damping power value and the damping wattless component value advantageously make it possible to actively damp distortion, that is to say undesirable harmonics, in the filter output currents and filter output voltages, so that distortion is greatly reduced and, in the ideal case is very largely suppressed. A further advantage of the method according to the invention is that there is no need to connect any discrete, space-consuming, complex and therefore expensive damping resistor to the respective phase connection, in order to allow undesirable distortion to be effectively damped.
The apparatus according to the invention for carrying out the method for operating the converter circuit has a control device which is used to produce a hysteresis power value, a hysteresis wattless component value and a selected flux sector and is connected via a drive circuit to the drivable power semiconductor switches in order to form a drive signal.
According to the invention, the control device has a first calculation unit for forming the hysteresis power value, the hysteresis wattless component value and the selected flux sector, with the first calculation unit having a first hysteresis regulator for forming the hysteresis power value from a difference power value, a second hysteresis regulator for forming the hysteresis wattless component value from a difference wattless component value and a vector allocator for forming the selected flux sector. Furthermore, the control device has a first adder for forming the difference power value from the subtraction of an estimated power value and of a damping power value from a reference power value and a second adder for forming the difference wattless component value from the subtraction of an estimated wattless component value and of a damping wattless component value from a reference wattless component value. Moreover, the control device has a second calculation unit for forming the damping power value and the damping wattless component value, with the damping power value being formed from a sum, weighted by a variable damping factor, of a multiplication of an α component of the space vector transformation of filter capacitance currents of the LCL filters by an α component of the space vector transformation of phase connection currents, and a multiplication of a β component of the space vector transformation of filter capacitance currents of the LCL filter by a β component of the space vector transformation of phase connection currents. Furthermore, the damping wattless component value is formed from a difference, weighted by the variable damping factor, of a multiplication of the β component of the space vector transformation of filter capacitance currents of the LCL filters by the α component of the space vector transformation of phase connection currents and a multiplication of the α component of the space vector transformation of filter capacitance currents of the LCL filters by the β component of the space vector transformation of phase connection currents.
The apparatus according to the invention for carrying out the method for operating the converter circuit can thus be produced very easily and at low cost, since the circuit complexity can be kept extremely low and, furthermore, only a small number of components are required to construct it. The method according to the invention can be carried out particularly easily by means of this apparatus.
These and further objects, advantages and features of the present invention will become clear from the following detailed description of preferred embodiments of the invention and in conjunction with the drawing.
In the drawings:
The reference symbols used in the drawing and their meanings, are listed in summary form in the list of reference symbols. In principle, identical parts are provided with the same reference symbols in the figures. The described embodiments represent examples of the subject matter of the invention and have no restrictive effect.
Accordingly, each LCL filter 3 has a first filter inductance Lfi, a second filter inductance Lfg and a filter capacitance Cf with the first filter inductance Lfi being connected to the associated phase connection 2 of the converter unit 1, to the second filter inductance Lfg and to the filter capacitance Cf. Furthermore, the filter capacitances Cf of the individual LCL filters 3 are connected to one another. By way of example,
In the method according to the invention for operating the converter circuit, the drivable power semiconductor switches of the converter unit 1 are now driven by means of a drive signal S formed from a hysteresis power value dP, from a hysteresis wattless component value dQ and from a selected flux sector θn. The drive signal is normally formed using a look-up table, in which hysteresis power values dP, hysteresis wattless component values dQ and selected flux sectors θn are permanently associated with corresponding drive signals S, or a modulator, which is based on pulse-width modulation. According to the invention, the hysteresis power value dP is formed from a difference power value Pdiff by means of a first hysteresis regulator 16 as shown in
Pd=kd·(iCfα·ifiα+iCfβ·ifiβ)
The reference power value Pref is freely variable and is the nominal value of the power which is intended to be produced at the output of the LCL filters 3. Furthermore, the hysteresis wattless component value dQ is formed from a difference wattless component value Qdiff by means of a second hysteresis regulator 17 and the difference wattless component value Qdiff is formed from the subtraction of an estimated wattless component value Q and a damping wattless component value Qd from a reference wattless component value Qref, with the damping wattless component value Qd being formed from a difference, weighted by the variable damping factor kd, of a multiplication of the β component of the space vector transformation of filter capacitance currents iCfβ of the LCL filters 3 by the α component of the space vector transformation of phase connection currents ifiα and a multiplication of the α component of the space vector transformation of filter capacitance currents iCfα of the LCL filters 3 by the β component of the space vector transformation of phase connection currents ifiβ as illustrated in particular by the following formula.
Qd=kd·(iCfβ·ifiα−iCfα·ifiβ)
The reference wattless component value Qref is freely variable and is the nominal value of the wattless component which is intended to be produced at the output of the LCL filters 3.
It should be mentioned that the space vector transformation is defined as follows:
where
The damping power value Pd and the damping wattless component value Qd can advantageously be used for active damping of distortion, that is to say undesirable oscillation, in the filter output currents ifg1, ifg2, ifg3 and filter output voltages, so that this distortion is very greatly reduced and, ideally is very largely suppressed. A further advantage of the method according to the invention is that there is no need to connect any discrete space-consuming, complex and thus expensive damping resistor to the respective phase connection 2, in order to allow effective damping of the undesirable distortion.
According to
The estimated power value P and the estimated wattless component value Q are in each case formed from an α component of the space vector transformation of filter output currents ifgα, from a β component of the space vector transformation of filter output currents ifgβ, from an α component of the space vector transformation of filter output fluxes ψLα and from a β component of the space vector transformation of filter output fluxes ψLβ, as is illustrated in particular by the following formulae:
P=ω·(ψLα·ifgβ−ψLβ·ifgα)
Q=ω·(ωLα·ifgα−ψLβ·ifgβ)
In order to form the estimated power value P and the estimated wattless component value Q, the control device 4 as shown in
The α component of the space vector transformation of filter output fluxes ψLα is formed from an α component of the space vector transformation of estimated filter capacitance fluxes ψCfα and from the α component of the space vector transformation of filter output currents ifgα, as illustrated in particular by the following formula:
ψLα=ψCfα−Lfg·ifgα
Furthermore, the β component of the space vector transformation of filter output fluxes ψLβ is formed from a β component of the space vector transformation of estimated filter capacitance fluxes ψCfβ and from the β component of the space vector transformation of filter output currents ifgβ, as indicated in particular by the following formula:
ψLβ=ψCfβ−Lfg·ifgβ.
In order to form the α component of the space vector transformation of filter output fluxes ψLα and the β component of the space vector transformation of filter output fluxes ψLβ, the control device 4 as shown in
The α component of the space vector transformation of filter output currents ifgα is formed from the α component of the space vector transformation of phase connection currents ifiα, which is formed by space vector transformation of the phase connection currents ifi1, ifi2, ifi3 as shown in
The α component of the space vector transformation of estimated filter capacitance fluxes ψCfα is once again formed from an instantaneous DC voltage value udc of the capacitive energy store 19 connected to the converter unit 1, from the drive signal S and from the α component of the space vector transformation of phase connection currents ifiα, as indicated in particular by the following formula, with uCα being the α component of the phase connection voltage of the converter unit 1, formed from the instantaneous DC voltage value udc and from the drive signal.
ψCfα=∫uCαdt−Lfi·ifiα
In a corresponding manner, the β component of the space vector transformation of estimated filter capacitance fluxes ψCfβ is formed from the instantaneous DC voltage value udc of the capacitive energy store 19 connected to the converter unit 1, from the drive signal S and from the β component of the space vector transformation of phase connection currents ifiβ, uCβα being the β component of the phase connection voltage of the converter unit 1, formed from the instantaneous DC voltage value udc and from the drive signal.
ψCfβ=∫uCβdt−Lfi·ifiβ
In order to form the α component of the space vector transformation of estimated filter capacitance fluxes ψCfα and the β component of the space vector transformation of estimated filter capacitance fluxes ψCfβ, the control device 4 as shown in
In order to form the already mentioned difference wattless component value Qdiff, a compensation wattless component value Qcomp is additionally added, with the compensation wattless component value Qcomp being formed by low-pass filtering of an estimated filter capacitance wattless component value Qcf by means of a low-pass filter 15. This therefore advantageously avoids undesirable wattless components of the LCL filters 3, in particular of the filter capacitances Cf of the LCL filters 3, being produced at the output of the LCL filters 3, thus making it possible to ensure that only a wattless component value corresponding to the selected reference wattless component value Qref is produced at the output of the LCL filters 3. As shown in
QCf=ψ·(ψCfα·iCfα+ψCfβ·iCfβ)
In order to form the estimated filter capacitance wattless component value QCf as shown in
In order to form the already mentioned difference power values Pdiff, at least one compensation harmonic power value Ph relating to the fundamental of the filter output currents ifg1, ifg2, ifg3 is additionally added. Furthermore, in order to form the already mentioned difference wattless component value Qdiff, at least one compensation harmonic wattless component value Qh relating to the fundamental of the filter output currents ifg1, ifg2, ifg3 is additionally added. As shown in
As shown in
In general, the Park-Clarke transformation is defined as
where
Ph=ω·(ψLα·i*hβ−ψLβ·i*hα)
Qh=ω·(ψLα·i*hα−ψLβ·i*hβ)
All of the steps in the method according to the invention may be implemented as software, in which case this software can then be loaded in and run on a computer system, in particular using a digital signal processor. The digital delay times which occur in a system such as this, in particular for the calculations, may, for example be taken into account in a general form by addition of an additional term to the fundamental frequency ωt for the Park-Clarke transformation. Furthermore, the apparatus according to the invention, as described in detail above, can also be implemented in a computer system, in particular in a digital signal processor.
Overall, it has been possible to show that the apparatus according to the invention, in particular as shown in
This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Application 60/646,504 filed in US on Jan. 25, 2005, and as a continuation application under 35 U.S.C. §120 to PCT/CH2005/000292 filed as an International Application on May 24, 2005, designating the U.S., the entire contents of which are hereby incorporated by reference in their entireties.
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Number | Date | Country | |
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20080007974 A1 | Jan 2008 | US |
Number | Date | Country | |
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60646504 | Jan 2005 | US |
Number | Date | Country | |
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Parent | PCT/CH2005/000292 | May 2005 | US |
Child | 11878418 | US |