Converter system and method for operating a converter system

Abstract

A converter system and a method for operating a converter system having block-type energy feedback, in particular, includes: a power inverter that feeds energy back to an AC-voltage supply system, i.e. in particular a first power inverter; a DC/DC transformer having a control unit; and an electric motor, which is able to be fed by a second power inverter. The DC-voltage-side terminal of the second power inverter is connected to a first terminal of the DC/DC transformer 102, and a current-acquisition device for acquiring the current conveyed by the DC/DC transformer to the terminal of the regenerative power inverter on the DC-voltage side is connected to a control unit, e.g., such that the current values acquired by the current-acquisition device are supplied to the control unit. The control unit supplies to the DC/DC transformer control signals such that the voltage supplied by the DC/DC transformer to the regenerative power inverter, the acquired current is able to be controlled, in particular controls, to a setpoint-value characteristic.

Claims

1. A method for operating a converter system, comprising: controlling, with the aid of a DC/DC transformer, current supplied by a regenerative power rectifier to an AC-voltage supply system and/or current supplied to a power inverter feeding energy back to the AC-voltage supply system to a setpoint-value characteristic that (a) crosses a continuously differentiated zero point at each point of intersection of line voltages, (b) passes through a respective zero point at instants of zero crossing of a respective line voltage and/or at respective instants of a point of intersection of the line voltages in a continuously differentiable manner, and (c) has a smooth configuration and/or a continuously differentiable configuration in respective temporal ranges around the instants of the zero crossings of the line voltages of the AC-voltage supply system.

2. The method according to claim 1, wherein the setpoint-value characteristic has no positive values.

3. The method according to claim 1, wherein the setpoint-value characteristic in the regions of the zero crossings has a smooth configuration and/or a continuously differentiable configuration.

4. The method according to claim 1, wherein the setpoint-value characteristic in the respective temporal regions around the instants of the zero crossings has a smooth configuration and/or a continuously differentiable configuration.

5. The method according to claim 1, wherein the setpoint-value characteristic in the ranges of the zero crossings and/or in the respective temporal regions around the instants of the zero crossing, extends according to an even power of a system-synchronous sine function and/or according to a polynomial of an even order.

6. The method according to claim 1, wherein the setpoint-value characteristic has a constant characteristic between the regions.

7. The method according to claim 1, wherein each region includes precisely a single instant at which a zero crossing of one of the line voltages occurs.

8. The method according to claim 1, wherein a temporal extension of the respective regions around the respective instant is smaller than the temporal interval between this respective instant and the instant that temporally directly follows.

9. The method according to claim 1, wherein the converter system includes: the regenerative power rectifier adapted to feed energy back to the AC-voltage supply system; the DC/DC transformer including a control unit; an electric motor adapted to be supplied by a second power inverter, a DC-voltage-side terminal of the second power inverter being connected to a first terminal of the DC/DC transformer; and a current-acquisition device adapted to acquire current conveyed by the DC/DC transformer to a terminal of the regenerative power inverter on a DC-voltage side connected to a control unit, so that current values acquired by the current-acquisition device are suppliable to the control unit; wherein the control unit is adapted to convey control signals to the DC/DC transformer such that voltage supplied by the DC-DC transformer to the regenerative power inverter, and an acquired current is controllable to the setpoint-value characteristic so that at instants of zero crossing of a respective line voltage and/or at instants of a respective point of intersection of phase voltages, the setpoint-value characteristic crosses a zero point in a continuously differentiable manner.

10. A converter system, comprising: a regenerative power rectifier adapted to feed energy back to an AC-voltage supply system; a DC/DC transformer including a control unit; an electric motor adapted to be supplied by a second power inverter, a DC-voltage-side terminal of the second power inverter being connected to a first terminal of the DC/DC transformer; and a current-acquisition device adapted to acquire current conveyed by the DC/DC transformer to a terminal of the regenerative power inverter on a DC-voltage side connected to a control unit, so that current values acquired by the current-acquisition device are suppliable to the control unit; wherein the control unit is adapted to convey control signals to the DC/DC transformer such that voltage supplied by the DC-DC transformer to the regenerative power inverter, and an acquired current is controllable to a setpoint-value characteristic so that at instants of zero crossing of a respective line voltage and/or at instants of a respective point of intersection of phase voltages, the setpoint-value characteristic crosses a zero point in a continuously differentiable manner.

11. The converter system according to claim 10, wherein the converter system is adapted for block-type energy feedback.

12. The converter system according to claim 10, wherein the regenerative power rectifier includes a regenerative power inverter.

13. The converter system according to claim 10, wherein a device adapted to acquire phase voltages of the AC-voltage supply system are connected to the control unit, the control unit adapted to determine zero-crossing instants of the line voltages and to determine the setpoint-value characteristic, the setpoint-value characteristic vanishing and/or reaching a zero value at the zero-crossing instants, having a smooth configuration in regions of the zero crossings determined by the control unit, and/or having a continuously differentiable configuration.

14. The converter system according to claim 10, wherein the setpoint-value characteristic vanishes and/or has a zero value at the zero-crossing instants, has a smooth configuration in respective temporal regions around the zero-crossing instants and/or has a continuously differentiable configuration.

15. The converter system according to claim 10, wherein the setpoint-value characteristic in the regions of the zero crossings and/or in the temporal regions around the instants of the zero crossings has a configuration according to an even power of a system-synchronous sine function and/or according to a polynomial of an even order.

16. The converter system according to claim 10, wherein the setpoint-value characteristic between the regions has a constant characteristic.

17. The converter system according to claim 10, wherein each region encompasses precisely a single instant at which a zero crossing of one of the line voltages takes place.

18. The converter system according to claim 10, further comprising a power rectifier having a terminal on an DC-voltage side connected to the terminal of the second power inverter on the DC-voltage side and a terminal on an AC-voltage side connected to the AC-voltage supply system.

19. The converter system according to claim 10, further comprising a capacitor arranged at a respective terminal on the DC-voltage side adapted to smooth the voltage.

20. The converter system according to claim 10, wherein the converter system is adapted to perform a method that includes controlling, with the aid of the DC/DC transformer, current supplied by the regenerative power rectifier to the AC-voltage supply system and/or current supplied to a power inverter feeding energy back to the AC-voltage supply system to the setpoint-value characteristic that (a) crosses a continuously differentiated zero point at each point of intersection of line voltages, (b) passes through a respective zero point at instants of zero crossing of a respective line voltage and/or at respective instants of a point of intersection of the line voltages in a continuously differentiable manner, and (c) has a smooth configuration and/or a continuously differentiable configuration in respective temporal ranges around the instants of the zero crossings of the line voltages of the AC-voltage supply system.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a first converter according to an example embodiment of the present invention, which has a DC/DC transformer 102 disposed in the intermediate circuit.

(2) FIG. 2 shows temporal characteristics of currents and voltages.

(3) FIG. 3 illustrates an energy-feedback unit according to an example embodiment of the present invention connected to a converter.

DETAILED DESCRIPTION

(4) As illustrated in FIG. 1, a first power inverter 101 is supplied from an AC-voltage supply system 100; its terminal on the DC-voltage side feeds a second terminal of a DC/DC transformer 102 whose first terminal is connected to the DC-voltage-side terminal of a second power inverter 103, whose terminal on the AC-voltage side is connected to an electric motor M arranged as a three-phase motor. As a result, the rotational speed of motor M is controllable during a motor operation of motor M. No voltage conversion by DC/DC transformer 102 takes place in this case.

(5) A capacitance (C1, C2) is disposed at the terminals of DC/DC transformer 102 in each case, so that smoothing of the respectively applied voltage may take place.

(6) In a generator mode of motor M, the power generated in the process is rectified via second power inverter 103 and thus made available at its terminal on the DC-voltage side. Current it conveyed in the direction of first power inverter 101 is adjustable with the aid of the DC/DC transformer.

(7) Toward this end, the three system-side phase voltages (UL1, UL2, UL3) are acquired at the terminal of first power inverter 101 on the AC-voltage side, and instants (t1, t2, . . . , t6) of the zero crossings of the line voltages are determined. On that basis, future instants (t1, t2, . . . , t6) are calculated in advance.

(8) In order to achieve a system-synchronous block-type energy feedback, the controllable semiconductor switches S1, S2, . . . , S6 are appropriately controlled. As illustrated in FIG. 2, the control signals are controlled in a system-synchronized manner, thereby resulting in phase currents iL1, iL2, iL3.

(9) According to example embodiments of the present invention, a setpoint-value characteristic is predefined for current i1 for DC/DC transformer 102, which is not constant but vanishes at the instants of the determined zero crossings and exhibits a smooth characteristic, i.e. has a continuously differentiable characteristic, in the time ranges around the determined zero crossings.

(10) In other words, the setpoint-value characteristic of current i1 crosses its zero points in a continuously differentiable manner. It should be noted that the setpoint-value characteristic in FIG. 2 is substantially negative because the regenerative case is shown, i.e. the energy feedback. The horizontal line extending in the temporal direction represents the zero value and becomes tangential to the setpoint-value characteristic of current i1 at instants t1, t2, t3, t4, t5 and t6. At these instants, two of the three system-side phase voltages (UL1, UL2, UL3) are identical in each case. Put another way, one of the three line voltages, i.e. the line to line voltages, has a zero crossing at these instants.

(11) In particular, a characteristic that corresponds to an even power of a sine-shaped characteristic is considered to be especially advantageous. In other words, the characteristic in the ranges around the determined zero crossings is used, according to, for example:
a+b*(sin(n*t)){circumflex over ()}M
a, b being constant values in each case, n being proportional to the system frequency, and M being 6, for example. Embodiments featuring M=4 or 8 are also possible. Outside the mentioned regions, i1 is restricted so that a constant value will then be present.

(12) The control of DC/DC transformer 102 has a clock frequency that is much higher than the pulse-width modulation frequency of power inverter 103. A very high characteristic recovery-time constant in comparison with a control with the aid of power inverter 103 is therefore achievable.

(13) As illustrated in FIG. 3, the energy feedback is alternatively able to be added to a converter 105. For instance, a converter 105 is able to be retrofitted with an energy feedback system.

(14) The converter has a power rectifier 104, which is able to be supplied from AC-voltage supply system 100. The output of power rectifier 104 on the DC-voltage side feeds a capacitor C1 for smoothing the voltage, in particular the intermediate-circuit voltage, and the input of power inverter 103 on the DC-voltage side is connected to the output of power rectifier 104 on the DC-voltage side. Electric motor M arranged as a three-phase motor once again is able to be supplied by power inverter 103. As a result, the rotational speed of motor M is controllable with the aid of converter 105.

(15) In addition, the first terminal, in particular the DC/DC-voltage-side terminal, of DC/DC transformer 102 is connected to the terminal of power rectifier 104 on the DC-voltage side and/or of power inverter 103. The second terminal of DC/DC transformer 102 is connected to the terminal of power inverter 101 on the DC-voltage side, whose controllable semiconductor switches, which are once again arranged in half bridges, are controlled in a system-synchronous manner in the previously described manner.

(16) In a generator mode, electric power flows from motor M via power inverter 103 back into the intermediate circuit. From there, the regenerative first power inverter 101 is supplied via DC/DC transformer 102, the former controlling the power flow as a block-type energy feedback in a system-synchronous manner.

(17) In order to control the DC/DC transformer, DC-voltage-side current i1 of first power inverter 101 is acquired and controlled to a setpoint value by an appropriate setting of output voltage UC2. A capacitor C2 is situated at the second output of DC/DC transformer 102 for the smoothing.

(18) Power inverter 101 may be arranged as a regenerative power rectifier so that block-type control voltages are sufficient and no higher-frequency, pulse-width-modulated control voltages are required.

(19) A polynomial of degree 6 or degree 8 may be used instead of an even-numbered power of the sine.

LIST OF REFERENCE CHARACTERS

(20) 100 AC-voltage supply system

(21) 101 first power inverter

(22) 102 DC/DC transformer

(23) 103 second power inverter

(24) 104 power rectifier

(25) 105 converter

(26) UL1 first phase voltage of the AC-voltage supply system

(27) UL2 second phase voltage of the AC-voltage supply system

(28) UL3 third phase voltage of the AC-voltage supply system

(29) iL1 first line-current phase

(30) iL2 second line-current phase

(31) iL3 third line-current phase

(32) S1 controllable semiconductor switch

(33) S2 controllable semiconductor switch

(34) S3 controllable semiconductor switch

(35) S4 controllable semiconductor switch

(36) S5 controllable semiconductor switch

(37) S6 controllable semiconductor switch

(38) S7 controllable semiconductor switch

(39) I1 output current at the DC-voltage-side terminal of the first power inverter 101

(40) UC2 output voltage at the DC-voltage-side terminal of first power inverter 101

(41) C1 first capacitance

(42) C2 second capacitance

(43) M electric motor

(44) I2 output current at the DC-voltage-side terminal of the second power inverter 101

(45) UC1 output voltage at the DC-voltage-side terminal of the second power inverter 101

(46) t1 instant for the zero crossing

(47) t2 instant for the zero crossing

(48) t3 instant for the zero crossing

(49) t4 instant for the zero crossing

(50) t5 instant for the zero crossing

(51) t6 instant for the zero crossing