SELF-COMMUTATED INVERTER AND OPERATION OF SAME

Abstract

The invention relates to a method for operating a self-commutated inverter (1), which is supplied from a direct voltage circuit (3) and comprises electronic switches (S1, S2, S3) for producing a three-phase output voltage and a three-phase output filter (5) which is connected downstream of the electronic switches (S1, S2, S3) and is coupled to the direct voltage circuit (3). The electronic switches (S1, S2, S3) are controlled in an open-loop manner by space-vector modulation, in which a zero-phase-sequence system voltage is controlled in a closed-loop manner by filter-input voltages of the output filter (5) on the basis of a target-voltage space vector (uα, β_s) of the space-vector modulation and filter input currents (i1_in, 12_in, i3_in) of the output filter (5) such that oscillations in a zero-phase-sequence system of the filter input currents (i1_in, i2_in, i3_in) are suppressed.

Claims

1. A method for operating a self-commutated inverter (1), which is supplied from a direct voltage circuit (3) and electronic switches (S1, S2, S3) for generating a three-phase output voltage and a three-phase output filter (5) arranged downstream of the electronic switches (S1, S2, S3) and coupled to the direct voltage circuit (3), so that common mode portions of filter input currents (i1_in, i2_in, i3_in) of the output filter (5) can flow into the direct voltage circuit (3), wherein the electronic switches (S1, S2, S3) are controlled in an open-loop manner by space vector modulation, in which filter output currents (i1_out, i2_out, i3_out) of the output filter (5) are controlled in a closed-loop manner and a zero-phase-sequence system voltage of filter input voltages of the output filter (5) is controlled in a closed loop manner as a function of a target voltage space vector (u.sub.α,β_s) of the space vector modulation and the filter input currents (i1_in, i2_in, i3_in) of the output filter (5) so that oscillations in a zero-phase-sequence system of the filter input currents (i1_in, i2_in, i3_in) are suppressed.

2. The method as claimed in claim 1, wherein the zero-phase-sequence system voltage of the filter input voltages is controlled in a closed-loop manner by a zero-phase-sequence system shift (μ), which defines a duration ratio of durations, in which one of the zero-phase-sequence voltage space vectors is applied in each case during a clock period of the space vector modulation.

3. The method as claimed in claim 2, wherein the zero-phase-sequence system shift (μ) has two shift portions (μ.sub.1, μ.sub.2), wherein a first shift portion (μ.sub.1) is determined as a function of the target voltage space vector (μ.sub.α,β_s) of the space vector modulation and the second shift portion (μ.sub.2) is formed as a function of the filter input currents (i1_in, i2_in, i3_in) of the output filter (5).

4. The method as claimed in claim 3, wherein the zero-phase-sequence system shift (μ) is formed by adding the two shift portions (μ.sub.1, μ.sub.2).

5. The method as claimed in claim 3 or 4, wherein the first shift portion (μ.sub.1) defines a duration ratio, with which the target voltage space vector (u.sub.α,β_s) can be realized free of a zero-phase-sequence system.

6. The method as claimed in one of claims 3 to 5, wherein a zero-phase-sequence system voltage of the filter input voltages is effected by the second shift portion (μ.sub.2) and dampens oscillations in the zero-phase-sequence system of the filter input currents (i1_in, i2_in, i3_in).

7. The method as claimed in one of claims 3 to 6, wherein the second shift portion is formed by means of a P controller (25) as a function of a total current (i0_in), which is formed from the filter input currents (i1_in, i2_in, i3_in) of the output filter (5).

8. The method as claimed in claim 7, wherein the filter input currents (i1_in, i2_in, i3_in) of the output filter (5) are measured and the total current (i0_in) is formed by adding the measured filter input currents (i1_in, i2_in, i3_in).

9. The method as claimed in one of the preceding claims, wherein the target voltage space vector (μ.sub.α,β_s) of the space vector modulation is formed as a function of filter output currents (i1_out, i2_out, i3_out) of the output filter (5).

10. A self-commutated inverter (1), which is supplied from a direct voltage circuit (3), the inverter (1) comprising electronic switches (S1, S2, S3) for generating a three-phase output voltage, a three-phase output filter (5) arranged downstream of the electronic switches (S1, S2, S3) and coupled to the direct voltage circuit (3), so that common mode portions of filter input currents (i1_in, i2_in, i3_in) of the output filter (5) can flow into the direct voltage circuit (3), and a control unit (7) which is designed to activate the electronic switches (S1, S2, S3) with a space vector modulation, with which filter output currents (i1_out, i2_out, i3_out) of the output filter (5) are controlled in a closed-loop manner and a zero-phase-sequence system voltage of filter input voltages of the output filter (5) is controlled in a closed-loop manner as a function of a target voltage space vector (μ.sub.α,β_s) of the space vector modulation and the filter input currents (i1_in, i2_in, i3_in) of the output filter (5) so that oscillations in a zero-phase-sequence system of the filter input currents (i1_in, i2_in, i3_in) are suppressed.

11. An inverter (1) as claimed in claim 10, wherein the control unit (7) is designed to control in a closed-loop manner the zero-phase-sequence system voltage of the filter input voltages by means of a zero-phase-sequence system shift (μ), which defines a duration ratio of durations, in which one of the zero-phase-sequence voltage space vectors is applied in each case during a clock period of the space vector modulation.

12. The inverter (1) as claimed in claim 11, wherein the control unit (7) has a space vector modulator (29), which is designed to determine a first shift portion (μ.sub.i) of the zero-phase-sequence system shift (μ) as a function of the target voltage space vector (μ.sub.α,β_s) of the space vector modulation.

13. The inverter (1) as claimed in claim 11 or 12, wherein the control unit (7) has a P controller (25), which is designed to form a second shift portion (μ.sub.2) of the zero-phase-sequence system shift (μ) as a function of a total current (i0_in), which is formed from the filter input currents (i1_in, i2_in, i3_in) of the output filter (5).

14. The inverter (1) as claimed in one of claims 10 to 13, wherein the control unit (7) is embodied to form the target voltage space vector (μ.sub.α,β_s) of the space vector modulation as a function of the filter output currents (i1_out, i2_out, i3_out) of the output filter (5).

15. The inverter (1) as claimed in one of claims 10 to 14 with a first measuring apparatus (17) for measuring the filter input currents (i1_in, i2_in, i3_in) and/or a second measuring apparatus (19) for measuring the filter output currents (i1_out, i2_out, i3_out) of the output filter (5).

Description

[0024] The above-described characteristics, features and advantages of this invention, as well as the manner in which these are realized will become more clearly and easily intelligible in connection with the following description of exemplary embodiments which are explained in more detail with reference to the drawings, in which:

[0025] FIG. 1 shows a circuit diagram of a self-commutated inverter,

[0026] FIG. 2 shows a block diagram of a self-commutated inverter.

[0027] Parts which correspond to one another are provided with the same reference characters in the figures.

[0028] FIG. 1 shows a circuit diagram of a self-commutated inverter 1. The inverter 1 is supplied from a direct voltage circuit 3. The inverter 1 has electronic switches S1, S2, S3 for generating a three-phase output voltage, a three-phase output filter 5 and a control unit 7 for closed-loop current control. The inverter 1 and the direct voltage circuit 3 can be components of a converter, which also has a rectifier, which is connected to the inverter 1 by way of the direct voltage circuit 3.

[0029] Each electronic switch S1, S2, S3 switches a phase of the output voltage of the inverter 1 and has a first switching state, in which it sets the phase onto a first direct voltage potential Z+ of the direct voltage circuit 3, and a second switching state, in which the phase is set onto a second direct voltage potential Z− of the direct voltage circuit 3. The potential difference between the direct voltage potentials Z+, Z− is a direct voltage U.sub.z of the direct voltage circuit 3. The electronic switches S1, S2, S3 are only shown schematically in FIG. 1 and formed in each case for instance as a half-bridge with two semiconductor switches 9. Each semiconductor switch 9 is embodied for instance as an IGBT (bipolar transistor with insulated gate electrode) or as a MOSFET (metal oxide semiconductor field effect transistor).

[0030] The output filter 5 is arranged downstream of the electronic switches S1, S2, S3 and has a filter inductor 11 and two filter capacitors 13, 15 for each phase of the output voltage. The filter inductor 11 of a phase is connected to the electronic switch S1, S2, S3 of this phase. The output filter 5 is connected to the direct voltage circuit 3 by way of the filter capacitors 13, 15. A first filter capacitor 13 of each phase is connected with the first direct voltage potential Z+ of the direct voltage circuit 3 and the second filter capacitor 15 of each phase is connected to the second direct voltage potential Z− of the direct voltage circuit 3.

[0031] A filter input current i1_in, i2_in, i1_in of this phase flows between the electronic switch S1, S2, S3 of one phase and the output filter 5. Filter output currents i1_out, i2_out, i3_out which form an output current of the inverter 1 for one phase in each case, flow behind the output filter 5, in other words on the output side. Common mode currents of the output filter 5 can flow by way of the filter capacitors 13, 15.

[0032] The control unit 7 controls the electronic switches S1, S2, S3 with activation signals C1, C2, C3. The activation signals C1, C2, C3 are formed by the control unit 7 with a space vector modulation, in which, in a manner described in more detail below, a zero-phase-sequence system voltage of filter input voltages of the output filter 5 is controlled in a closed-loop manner as a function of a target voltage space vector μ.sub.α,β_s of the space vector modulation and the filter input currents i2_in, i3_in so that oscillations in a zero-phase-sequence system of the filter input currents i1_in, i2_in, i3_in are suppressed, wherein the target voltage space vector μ.sub.α,β_s is formed as a function of the filter output currents i1_out, i2_out, i3_out. The filter input currents i2_in, i3_in are detected by means of a first measuring apparatus 17. The filter output currents i1_out, i2_out, i3_out are detected by means of a second measuring apparatus 19.

[0033] FIG. 2 shows a block diagram of the inverter 1 shown in FIG. 1, wherein the output of the inverter 1 is connected to a three-phase electric motor 21, so that the filter output currents i1_out, i2_out, i3_out of the inverter 1 are the motor currents of the electric motor 21. The electric motor 21 is embodied as a rotating electric machine with a rotor and a stator and has an angular position sensor, which detects a rotor angle φ, which specifies a position of the rotor in relation to the stator. Alternatively, the electric motor 21 can also be embodied as a linear motor with a stator and a rotor which can be moved linearly in relation to the stator, and have a position sensor, which specifies a rotor position of the rotor in relation to the stator. The rotor position then appears at the position of the rotor angle φ.

[0034] The control unit 7 is designed to carry out the inventive method described below. To this end, the control unit 7 has an adder 23, a P controller 25, a PI controller 27, a space vector modulator 29 and two transformers 31, 33.

[0035] The actual values of the filter output currents i1_out, i2_out, i3_out detected by the second measuring apparatus 19 and the actual value of the rotor angle φ are supplied to a first transformer 31. The first transformer 31 determines an actual current space vector i.sub.d,q_out of the filter output currents i1_out, i2_out, i3_out in a dq coordinate system rotating with the rotor from these actual values by means of a dq transformation.

[0036] A differential current space vector i.sub.d,q_delta is formed from the actual current space vector i.sub.d,q_out and a target current space vector i.sub.d,q_s, by the actual current space vector i.sub.d,q_out being subtracted from the target current space vector i.sub.d,q_s. The differential current space vector i.sub.d,q_delta is the control deviation of the closed-loop current control of the filter output currents i1_out, i2_out, i3_out.

[0037] A dq target voltage space vector u.sub.d,q_s is formed by the PI controller 27 from the differential space vector i.sub.d,q_delta, and describes a target voltage of the inverter 1, in a dq coordinate system, which counteracts the control deviation.

[0038] A target voltage space vector u.sub.α,β_s for the space vector modulation is formed by the second transformer 33 from the dq target voltage space vector u.sub.d,q_s, by the dq target voltage space vector u.sub.d,q_s being transformed into a stator-fixed αβ coordinate system by using the rotor angle φ.

[0039] The space vector modulator 29 generates the activation signals C1, C2, C3, with which the electronic switches S1, S2, S3 are activated, from the target voltage space vector u.sub.α,β_s and a zero-phase-sequence system shift μ. The zero-phase-sequence system shift p defines a duration ratio of durations, in which one of the zero-phase-sequence voltage space vectors is applied during a clock period of the space vector modulation in each case. In the case of two zero-phase-sequence voltage space vectors, the zero-phase-sequence system shift μ therefore defines the quotients of a first duration, for instance, in which a first zero-phase-sequence voltage space vector is applied during a clock period, and a second duration, in which the second zero-phase-sequence voltage space vector is applied during the clock period.

[0040] The zero-phase-sequence system shift p is additionally formed according to μ=μ.sub.1+μ.sub.2 from two shift portions μ.sub.1, μ.sub.2. A first shift portion μ.sub.1 is formed by the space vector modulator 29 as a function of the target voltage space vector μ.sub.α,β_s, defines a duration ratio, with which the target voltage space vector μ.sub.α,β_s can be realized free of a zero-phase-sequence system.

[0041] The second shift part μ.sub.2 is formed by the adder 23 and the P controller 25 as a function of the filter input currents i1_in, i2_in, i3_in so that it effects a zero-phase-sequence system voltage of the filter input voltages, dampens the oscillations in the zero-phase-sequence system of the filter input currents i3_in. To this end, the actual values of the filter input currents i1_in, i2_in, i3 detected by the first measuring apparatus 17 are added by the adder 23 to form a total current i0_in. The second shift portion μ.sub.2 is determined from the total current i0_in by the P controller 25.

[0042] Instead of measuring the filter input currents i1_in, i2_in, i3_in and the filter output currents i1_out, i2_out, i3_out with measuring apparatuses 17 and 19, provision can also be made to measure only the filter input currents i1_in, i2_in, i3_in and to calculate the filter output currents i1_out, i2_out, i3_out. Alternatively, provision can be made to measure only the filter output currents i1_out, i2_out, i3_out and to calculate the filter input currents i1_in, i2_in, i3_in.

[0043] Although the invention has been illustrated and described in detail based on preferred exemplary embodiments, the invention is not restricted by the examples given and other variations can be derived therefrom by a person skilled in the art without departing from the protective scope of the invention.