The disclosure relates to the field of power electronics, and in particular to a method for operating a converter circuit, and to an device for carrying out the method.
Conventional converter circuits have a converter unit with a multiplicity of controllable power semiconductor switches, which are switched in a known manner in order to switch at least two switching voltage levels. Furthermore, by way of example, an LCL-filter can be connected to each phase connection of the converter unit.
The method for operating a converter circuit described above is subject to the problem that the switching frequency of the power semiconductor switches varies to a very major extent as a result of the formation of the reference phase connection current ifi,i,ref from the reference power value Pref, from the reference wattless component value Qref and from the phase flux vector ψg,αβ. A switching frequency which is variable to such a major extent results in a significant increase in the harmonics in the phase connection currents ifg,i and in the phase connection voltages uinv,i on the converter circuit. In this context,
A method for operating a converter circuit is disclosed, by means of which the switching frequency of controllable power semiconductor switches in a converter unit in the converter circuit can be kept virtually constant. Also disclosed is a device by means of which the method can be carried out in a particularly simple manner.
A method for operating a converter circuit is disclosed, with the converter circuit having a converter unit with a multiplicity of controllable power semiconductor switches and having an energy storage circuit formed by two series-connected capacitors, in which the controllable power semiconductor switches are controlled by means of a control signal formed from a hysteresis signal vector (x), and the hysteresis signal vector (x) is formed from a difference-phase connection current vector (Δifi,i) by means of a hysteresis regulator, and the difference-phase connection current vector (Δifi,i) is formed from the subtraction of a phase connection current vector (ifi,i) from a reference phase connection current vector (ifi,i,ref), with the reference phase connection current vector (ifi,i,ref) being formed from a difference power value (Pdiff), a difference wattless-component value (Qdiff) and a phase flux vector (ψg,αβ), wherein a current correction value (i0) is additionally subtracted in order to form the difference-phase connection current vector (Δifi,i) in that the current correction value (i0) is formed by integration of a phase connection voltage mean value (uinv,A), and in that the phase connection voltage mean value (uinv,A) is formed by determining the arithmetic mean value of the phase connection voltages (uinv,iM) with the reference point of the connection point of the capacitors in the energy storage circuit.
A device for carrying out a method for operating a converter circuit is disclosed, with the converter circuit having a converter unit with a multiplicity of controllable power semiconductor switches and having an energy storage circuit formed by two series-connected capacitors, having a control device which is used to produce a hysteresis signal vector (x) and is connected via a control circuit for forming a control signal to the controllable power semiconductor switches, with the control device having a hysteresis regulator for forming the hysteresis signal vector (x) from a difference-phase connection current vector (Δifi,i), a first adder for forming the difference-phase connection current vector (Δifi,i) from the subtraction of a phase connection current vector (ifi,i) from a reference phase connection current vector (ifi,i,ref) and a first calculation unit for forming the reference phase connection current vector (ifi,i,ref) from a difference power value (Pdiff), a difference wattless component value (Qdiff) and a phase flux vector (ψg,αβ), wherein a current correction value (i0) is additionally supplied to the first adder in order to form the difference-phase connection current vector (Δifi,i), in order to form the difference-phase connection current vector (Δifi,i) from the subtraction of the phase connection current vector (ifi,i) and the current correction value (i0) from the reference phase connection current vector (ifi,i,ref), in that the control device comprises an integrator for forming the current correction value (i0) by integration of a phase connection voltage mean value (uinv,A), and an averager for forming the phase connection voltage mean value (uinv,A) by determining the arithmetic mean value of the phase connection voltages (uinv,iM) with the reference point of the connection point of the capacitors in the energy storage circuit.
These and further objects, advantages and features of the present disclosure will become obvious from the following detailed description of exemplary embodiments of the disclosure, and in conjunction with the drawing.
In the figures:
The reference symbols used in the drawing and their meanings are listed in a summarized 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 disclosure, and have no restrictive effect.
The converter circuit has a converter unit with a multiplicity of controllable power semiconductor switches, and an energy storage circuit formed by two series-connected capacitors. In the method according to the disclosure for operating the converter circuit, the controllable power semiconductor switches are now controlled by means of a control signal which is formed from a hysteresis signal vector, with the hysteresis signal vector being formed from a difference-phase connection current vector by means of a hysteresis regulator, and with the difference-phase connection current vector being formed from the subtraction of a phase connection current vector from a reference phase connection current vector. The reference phase connection current vector is furthermore formed from a reference power value, a reference wattless component value and a phase flux vector. According to the disclosure, a current correction value is additionally subtracted in order to form the difference-phase connection current vector, with the current correction value being formed by integration of a phase connection voltage mean value, with the phase connection voltage mean value being formed by determining the arithmetic mean value of the phase connection voltages with the reference point of the connection point of the capacitors in the energy storage circuit. The current correction value formed in this way allows the switching frequency of the controllable power semiconductor switches in the converter unit to be kept virtually constant. The very largely constant switching frequency also allows the harmonics in the phase connection currents and in the phase connection voltages of the converter unit to be kept low.
The device according to the disclosure for carrying out the method for operating the converter circuit has a control device which is used to produce a hysteresis signal vector and is connected to the controllable power semiconductor switches via a control circuit for forming the control signal, with the control device having a hysteresis regulator in order to form the hysteresis signal vector from the difference-phase connection current vector, a first adder in order to form the difference-phase connection current vector from the subtraction of the phase connection current vector from the reference phase correction current vector, and a first calculation unit in order to form the reference phase connection current vector from the reference power value, the reference wattless component value and the phase flux vector. Furthermore, the current correction value is also supplied to the first adder in order to form the difference-phase connection current vector, in order to form the difference-phase connection current vector from the subtraction of the phase connection current vector and the current correction value from the reference phase connection current vector. Furthermore, the control device has an integrator in order to form the current correction value by integration of a phase connection voltage mean value, and an averager in order to form the phase connection voltage mean value by determining the arithmetic mean value of the phase connection voltages with the reference point of the connection point of the capacitors in the energy storage circuit.
The device according to the disclosure for carrying out the method for operating a converter circuit can then be produced very easily and cost-effectively, 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 therefore be carried out particularly easily by means of this device.
In the method according to the disclosure for operating the converter circuit, the controllable power semiconductor switches in the converter unit 1 are now controlled by means of a control signal S formed from a hysteresis signal vector x. A look-up table is used in the normal manner to form the control signal, in which hysteresis signal vectors x are associated in a fixed form with corresponding control signals S, or a modulator which is based on pulse-width modulation. It should be noted that all the vectors with the index i have vector components corresponding to the total of i phases, that is to say if i=3 phases, the corresponding vectors also have i=3 vector components. The hysteresis signal vector x is also formed from a difference-phase connection current vector Δifi,i by means of a hysteresis regulator 6, and the difference-phase connection current vector Δifi,i is in turn formed from the subtraction of a phase connection current vector ifi,i from a reference phase connection current vector ifi,i,ref, with the reference phase connection current vector ifi,i,ref being formed from a difference power value Pdiff, a difference wattless component Qdiff and a phase flux vector ψg,αβ. The vector components of the phase connection current vector ifi,i are typically measured by means of current sensors at the appropriate phase connections of the converter unit 1. According to the disclosure, a current correction value i0 is additionally subtracted in order to form the difference-phase connection current vector Δifi,i, and the current correction value i0 is formed by integration of a phase connection voltage mean value uinv,A, with the phase connection voltage mean value uinv,A being formed by determining the arithmetic mean value of the phase connection voltages uinv,iM with the reference point of the connection point M of the capacitors in the energy storage circuit 2. The current correction value i0 means that the switching frequency of the controllable power semiconductor switches in the converter unit 1 can be kept virtually constant. The very largely constant switching frequency in turn allows the harmonics in the phase connection currents ifi,i and in the phase connection voltages uinv,i of the converter unit 1 to be kept low. In this context,
The phase flux vector ψg,αβ can be formed from the phase connection current vector ifi,i, from the control signal S and from an instantaneous DC voltage value uDC in the energy storage circuit 2. This will be described in detail in the foreign text. It should be noted that all the vectors with the index αβ as vector components have an α-component of the space vector transformation of the corresponding variable, and a β-component of the space vector transformation of the corresponding variables.
The space vector transformation is in general defined as follows:
where
The phase flux ψg is obtained in a general form, using complex notation as:
where
and Lg is a power supply system inductance and f1(S), f2(S) are predeterminable switching functions of the control signal S. The formulae mentioned above can therefore be used to form the phase flux vector ψg,αβ, that is to say in particular its components ψg,α, ψg,β, in a very simple form.
According to the exemplary embodiment shown in
In addition to the hysteresis regulator 6 which has been mentioned in order to form the hysteresis signal vector x from the difference-phase connection current vector Δifi,i, the control device 15 in the device shown in
As shown in
According to the method, in the exemplary embodiment shown in
The damping power value Pd is formed using the following formula:
Pd=kd·(iCfα·ifiα+iCfβ·ifiβ)
The reference power value Pref as shown in
The damping wattless component value Qd is formed using the following formula:
Qd=kd·(iCfβ·ifiα−iCfα·ifiβ)
The reference wattless component value Qref as shown in
It should be noted that the formation of the damping power value Pd and of the damping wattless component value Qd can be avoided by just calculating a damping current vector from the α-component of the space vector transformation of filter capacitance currents iCfα of the LCL-filter and from the β-component of the space vector transformation of filter capacitance currents iCfβ of the LCL-filter by suitable filtering, which damping current vector is then included directly in the formation of the reference phase connection current vector ifi,i,ref and therefore in the formation of the difference-phase connection current vector Δifi,i. This is associated with a saving of computation time, since there is no need to calculate the damping power value Pd and the damping wattless component value Qd.
The damping power value Pd and the damping wattless component value Qd make it possible to actively dampen distortion, that is to say undesirable oscillations, in the filter output currents ifg,i and filter output voltages, so that this distortion is greatly reduced and, best of all, is very largely suppressed. There is also no need to connect a discrete, space-consuming complex and therefore expensive damping resistance at the respective phase connection, in order to allow the undesirable distortion to be effectively damped. The addition or connection of at least one compensation harmonic power value Ph in order to form the difference power value Pdiff and of at least one compensation harmonic wattless component value Qh to form the difference wattless component value Qdiff can result in active reduction of harmonics, and therefore, overall, in a further improvement in the reduction of harmonics.
As shown in
According to
QCf=ω·(ψCfα·iCfα+ψCfβ·iCfβ)
In order to form the estimated filter capacitance wattless component QCf, the control device 15 has, as shown in
The estimated filter capacitance flux vector ψCf,αβ is formed, as shown in
The α-component of the space vector transformation ψCfα of the filter capacitance flux vector ψCf,αβ is therefore formed using the following formula:
ψCfα=∫uinv,αdt−Lf·ifiα
In a corresponding manner, the β-component of the space vector transformation ψCfβ of the filter capacitance flux vector ψCf,αβ is formed using the following formula:
ψCfβ=∫uinv,βdt−Lf·ifiβ
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, in particular as illustrated 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, in particular as illustrated by the following formula.
ψLβ=ψCfβ−Lfg·ifgβ
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 can be calculated, for example, in the second calculation unit 4 or can also be calculated in the fifth calculation unit 11, although this is not illustrated for the sake of clarity, in
The control device 15 has a fifth calculation unit 11 in order to form the compensation harmonic power value Ph and the compensation harmonic wattless component value Qh in each case from the α-component of the space vector transformation of filter output currents ifgα, from the β-component of the space vector transformation of filter output currents ifgβ, from the α-component of the space vector transformation of filter output fluxes ψLα, from the β-component of the space vector transformation of filter output fluxes ψLβ and from the fundamental frequency angle ωt with respect to the fundamental frequency of the filter output current vector ifg,i. The filter output current vector ifg,i is calculated very easily from the phase connection current vector ifi,i and from the filter capacitance current vector iCf,i, as shown in
The Park-Clarke-Transformation is in general defined as:
ā=(ad+jaq)ejωt
where ā is a complex variable, ad is the d-component of the Park-Clarke-Transformation of the variables ā and aq is the q-component of the Park-Clarke-Transformation of the variable ā. In the Park-Clarke-Transformation, not only is the fundamental frequency of the complex variable ā transformed, but also all of the harmonics that occur in the complex variable ā. As shown in
Ph=ω·(ψLα·i*hβ−ψLβ·i*hα)
Qh=ω·(ψLα·i*hα+ψLβ·i*hβ)
All the steps in the method according to the disclosure may be implemented as software, which can then be loaded and run, for example, on a computer system, in particular with a digital signal processor. The digital delay times that 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 in the Park-Clarke-Transformation. Furthermore, the device according to the disclosure as described in detail above may also be implemented in a computer system, in particular in a digital signal processor.
Overall, it has been possible to show that the device according to the disclosure, in particular as illustrated in
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
This is a continuation application under 35 U.S.C. §120 of PCT/CH2006/000648 filed as an International Application on Nov. 16, 2006 designating the U.S., which claims the benefit of U.S. Provisional Patent No. 60/738,065 filed on Nov. 21, 2005, under 35 U.S.C. 365(c), the entire contents of which are hereby incorporated by reference in their entireties.
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6166928 | Chandorkar | Dec 2000 | A |
6804130 | Morimoto | Oct 2004 | B2 |
7310253 | Fujii et al. | Dec 2007 | B2 |
20060215425 | Fu et al. | Sep 2006 | A1 |
Number | Date | Country | |
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20080278977 A1 | Nov 2008 | US |
Number | Date | Country | |
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60738065 | Nov 2005 | US |
Number | Date | Country | |
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Parent | PCT/CH2006/000648 | Nov 2006 | US |
Child | 12153514 | US |