Control of a modular converter having distributed energy stores with the aid of an observer for the currents and an estimating unit for the intermediate circuit energy

• US 8,837,185 B2
• Filed: 02/11/2010
• Issued: 09/16/2014
• Est. Priority Date: 02/11/2010
• Status: Active Grant

• Current Assignee: Siemens Energy Global GmbH & Co. KG (Siemens AG)
• Original Assignee: Siemens AG
• Inventors: Goerges, Daniel, Izak, Michal, Liu, Steven, Muench, Philipp
• Primary Examiner(s): Dole, Timothy J
• Assistant Examiner(s): AHMED, YUSEF A
• Application Number:
  US13/578,664
• Publication Number:
  US 20120314466A1
• Time in Patent Office: 1,678 Days
• Field of Search: 363/78, 363/125, 363/127, 363/132, 307/105, 307/151
• US Class Current: 363/127
• CPC Class Codes: H02M 1/0012 Control circuits using digital or numerical techniques in DC/DC converters H02M3/157, H02M3/33515; in DC-AC converters H02M7/53873
• CPC Class Codes: H02M 1/0025 Arrangements for modifying reference values, feedback values or error values in the control loop of a converter
• CPC Class Codes: H02M 7/4835 comprising two or more cells, each including a switchable capacitor, the capacitors having a nominal charge voltage which corresponds to a given fraction of the input voltage, and the capacitors being selectively connected in series to determine the instantaneous output voltage
• CPC Class Codes: H02M 7/53873 with digital control

Abstract

Methods and configurations controlling a converter having controllable power semiconductors, compare actual and target state values to obtain control difference values for a control unit producing setting voltage values. Control electronics provide control signals according to setting voltage values and transmit them to power semiconductors. The control unit generates voltage values so control difference values become small. Current and converter energy controls and energy balancing are performed jointly, actual state values are calculated by an observing unit based on setting voltage values considering measured current values and actual state intermediate-circuit energy values are calculated by an estimating unit considering measured intermediate-circuit energy values of positive and negative voltage sources. The observing and estimating units model the converter so actual state current and intermediate-circuit steady-state energy values correspond to error-free current and intermediate-circuit energy values. A periodic time-variant gain controller receives error-free values.

Claims

1. A method for controlling a converter having controllable power semiconductors, the method comprising the following steps:

comparing actual state values describing a state of the converter with desired state values to obtain control difference values;

feeding the control difference values to a control unit constructed as a periodic controller having a periodically time-variant gain and generating actuating voltage values at its output;

providing control signals with control electronics depending on the actuating voltage values and transmitting the control signals to the power semiconductors of the converter;

generating actuating voltage values with the control unit to make the control difference values as small as possible;

calculating the actual state values with an observer unit proceeding from the actuating voltage values and taking measured current values into account;

calculating actual state intermediate circuit energy values with an estimator unit taking measured intermediate circuit energy values of a positive-side and a negative-side three-phase voltage source of the converter into account;

modeling the converter with the observer unit and the estimator unit, causing the calculated actual state current values and actual state intermediate circuit energy values in the steady state to correspond to fault-free current and intermediate circuit energy values; and

feeding the fault-free current and intermediate circuit energy values to the control unit.

2. The method according to claim 1, which further comprises:

providing the observer unit with a periodically time-variant system model proceeding from a general state equation

{dot over (x)}=A·

x+B·

u

with x as a state variable, {dot over (x)} as a time derivative of the state variable, A as a system matrix, B as an input matrix and u as an input variable, having a time-invariant system matrix A_PLTV and a time-variant input matrix B_PLTV(t) with

3. The method according to claim 1, wherein the desired state values are desired current values and desired intermediate circuit energy values.

4. The method according to claim 1, which further comprises forming the desired state values from predefined desired values with a periodically operating feedforward control unit.

5. The method according to claim 1, which further comprises implementing the periodically time-variant gain in the periodic controller by a periodic changeover of controller matrices.

6. The method according to claim 1, wherein the observer unit takes disturbance effects into account, causing the actual state current values in the steady state to correspond to the current measurement values freed of disturbance effects.

7. The method according to claim 6, which further comprises:

providing, with the observer unit, besides the actual state current values being fault-free in the steady state, disturbed state model measurement values corresponding to measurable state measurement values;

comparing the state model measurement values with state measurement values obtained by measurements and obtaining a model measurement value deviation;

feeding the model measurement value deviation to a model unit on the input side; and

carrying out the modeling to make the model measurement value deviation as small as possible.

8. The method according to claim 7, which further comprises feeding the model measurement value deviation to the model unit through a feedback unit amplifying the model measurement value deviation.

9. The method according to claim 6, which further comprises taking disturbance effects into account by taking faults originating from an electrical power supply system connected to the converter into account and taking faults caused by the converter into account.

10. The method according to claim 6, which further comprises:

modeling the observer unit with the aid of a state space model in accordance with

{circumflex over (x)}′

_ρ

(k+1)=Φ

_ρ

·

{circumflex over (x)}′

_ρ

(k)+Γ

u_ρ

(k)

ŷ

_d(k)=H_ρ

·

{circumflex over (x)}′

_ρ

(k)

wherein {circumflex over (x)}′

_ρ

(k) corresponds to a state vector of the converter including disturbed states, u_ρ

(k) corresponds to a vector of actuating voltages, Φ

, Γ and

H correspond to model matrices, and ŷ

_d(k) corresponds to a vector of state model measurement values beset by disturbances.

11. The method according to claim 1, which further comprises taking delay effects into account with the observer unit, causing the actual state current values to correspond to undelayed and undisturbed current measurement values freed of disturbance and delay effects.

12. The method according to claim 11, which further comprises:

providing, with the observer unit, besides the undelayed actual state values, delayed state model measurement values corresponding to measurable state measurement values;

comparing the state model measurement values with state measurement values obtained by measurements;

obtaining a model measurement value deviation;

feeding the model measurement value deviation to the model unit on the input side; and

carrying out the modeling to make the model measurement value deviation as small as possible.

13. The method according to claim 11, which further comprises feeding the model measurement value deviation to a model unit through a feedback unit amplifying the model measurement value deviation.

14. The method according to claim 11, which further comprises taking delay effects into account by taking measurement delays arising during a digital detection of the state variables of the converter into account and taking actuating delays caused by the control electronics into account.

15. The method according to claim 11, which further comprises during the detection of the state measurement values, measuring the state variable of the converter, continuously sampling measurement signals being obtained in sampling steps to obtain samples, subsequently digitizing the samples, and effecting the modeling of the measurement delays being established under an assumption that the measurement delays correspond to a time duration of a plurality of sampling steps.

16. The method according to claim 15, which further comprises taking a measurement delay of four sampling steps into account.

17. The method according to claim 11, which further comprises modeling an actuating delay T in accordance with

τ

=(l−

1)·

T+τ

′

wherein l corresponds to a number of sampling steps having a sum less than the actuating delay τ

, and τ

′

as a remainder is shorter than a time duration T between two sampling steps k.

18. The method according to claim 17, which further comprises taking two sampling steps into account during the modeling of the actuating delay.

19. The method according to claim 11, which further comprises:

modeling the converter with the aid of a state space model in accordance with

{circumflex over (x)}′

(k+1)=Φ

{circumflex over (x)}′

(k)+Γ

u(k)

ŷ

_d(k)=H{circumflex over (x)}′

(k)

wherein {circumflex over (x)}′

(k) corresponds to a state vector of the converter including delayed states, u(k) corresponds to a vector of the actuating voltages, Φ

, Γ and

H correspond to model matrices, and ŷ

_d(k) corresponds to a vector of state model measurement values beset by delays.

20. The method according to claim 1, which further comprises:

determining state intermediate circuit energy values from measured intermediate circuit energy values with an estimator unit having recourse to a signal model of the intermediate circuit energy values;

calculating parameters of the signal model of the intermediate circuit energy values with the estimator unit while determining in each case a DC variable representing state intermediate circuit energy values of the positive-side and of the negative-side three-phase voltage source of the converter; and

feeding state intermediate circuit energy values to the control unit in addition to the state current values.

21. The method according to claim 20, which further comprises:

respectively individually detecting the state intermediate circuit energy values of positive-side and of negative-side power semiconductor valve branches of the converter;

calculating the parameters of the signal model of the intermediate energy values with a respective parameter estimator of the estimator unit; and

respectively individually adding the parameters of the positive-side and the negative-side power semiconductor valve branches that respectively describe a DC component, to form the intermediate circuit energy DC variables.

22. The method according to claim 21, which further comprises using parameter estimators with a recursive algorithm.

23. The method according to claim 22, which further comprises:

using a parameter estimator with an oscillation model w(t) for the intermediate circuit energy values w(t)=A₀+A_k1*cos(kω

t)+A_k2*sin(kω

t) for k=1 to n, as the estimator;

in which A₀ indicates the DC component of the intermediate circuit energy values and A_k1 and A_k2 indicate further parameters of the oscillation model and ω

indicates the angular frequency of an AC voltage power supply system connected to the converter.

24. The method according to claim 23, which further comprises providing an oscillation model with time-dependent parameters A₀(t) to A_k2(t).

25. The method according to claim 24, which further comprises predefining a time dependence of the parameters by a linear function or an exponential function.

26. The method according to claim 23, which further comprises providing an oscillation model with temporally constant parameters A₀ to A_k2.

27. The configuration according to claim 26, which further comprises:

a cut-out unit having an output;

a summing circuit having an output, one input connected to the output of the converter and a further input connected to said output of said cut-out unit;

a feedback unit having an output and being connected to said output of said summing circuit;

said observer unit having a model unit simulating the converter and having an input connected to said output of said control unit, another input connected to said output of said feedback unit and an output connected to said cut-out unit; and

a further cut-out unit connected between said output of said model unit and said input of said control unit.

28. The method according to claim 1, wherein the converter is a multilevel converter having power semiconductor valve branches connected to one another to form a bridge circuit, each power semiconductor valve branch is formed of a series circuit formed by submodules and each submodule includes a circuit formed by power semiconductors and a capacitor unit disposed in parallel therewith.

29. A configuration for carrying out the method according to claim 1 for controlling a converter having a bridge circuit formed by phase module branches each including a series circuit formed by submodules each having a semiconductor circuit with a connected capacitor, positive-side and negative-side three-phase voltage sources, power semiconductors, and a measurement value output, the configuration comprising:

a control unit having an input connected to the measurement value output of the converter and an output supplying generated actuating voltage values;

control electronics disposed downstream of said control unit, said control electronics providing control signals dependent on the actuating voltage values and transmitting said control signals to the power semiconductors of the converter;

an observer unit disposed between the measurement value output of the converter and said input of said control unit, said observer unit calculating actual state values, proceeding from the actuating voltage values u(k) and taking measured current values into account;

an estimator unit disposed between the measurement value output of the converter and said input of said control unit, said estimator unit calculating actual state intermediate circuit energy values, taking measured intermediate circuit energy values of the positive-side and of the negative-side three-phase voltage sources of the converter into account;

said observer unit and said estimator unit modeling the converter to cause the calculated actual state current values and actual state intermediate circuit energy values in the steady state to correspond to fault-free current and intermediate circuit energy values; and

said control unit receiving the fault-free current and intermediate circuit energy values and being constructed as a periodic controller having a periodically time-variant gain.

30. The configuration according to claim 29, wherein said observer unit has a periodically time-variant system model, and said system model proceeds from a general state equation

{dot over (x)}=A·

x+B·

u

with x as a state variable, {dot over (x)} as a time derivative of the state variable, A as a system matrix, B as an input matrix and u as input variable, has a time-invariant system matrix A_PLTV and a time-variant input matrix B_PLTV(t) with

31. The configuration according to claim 29, which further comprises a summing circuit disposed upstream of said periodic controller, and a periodic feedforward control unit having an output side connected to said summing circuit and a period corresponding to a period of an AC current.

32. The configuration according to claim 29, wherein said periodic controller is configured to have its periodically time-variant gain effected by a periodic changeover of its controller matrices.

33. The configuration according to claim 29, wherein said observer unit is configured to calculate actual state values proceeding from the actuating voltage values and state measurement values taking disturbance effects and/or delay effects into account to cause the actual state values to correspond to current measurement values being freed of disturbance effects and/or undisturbed in the steady state.

34. The configuration according to claim 29, wherein:

said estimator unit connected to the output of the converter simulates a signal model of intermediate circuit energy values; and

said observer unit and said estimator unit have an output side connected to actual inputs of said control unit.

35. The configuration according to claim 34, wherein:

the converter has six power semiconductor valve branches including three positive-side power semiconductor valve branches and three negative-side power semiconductor valve branches; and

said estimator unit has a respective estimator for each of the three positive-side power semiconductor valve branches and a respective further estimator for each of the three negative-side power semiconductor valve branches.

36. The configuration according to claim 29, wherein the converter is a multilevel converter having power semiconductor valve branches connected to one another to form a bridge circuit, each power semiconductor valve branch is formed of a series circuit formed by submodules and each submodule includes a circuit formed by power semiconductors and a capacitor unit connected in parallel therewith.

37. A method for controlling a converter having controllable power semiconductors, the method comprising the following steps:

comparing actual state values describing a state of the converter with desired state values and obtaining control difference values;

feeding the control difference values to a control unit constructed as a periodic controller having a periodically time-variant gain and generating actuating voltage values at its output;

providing control signals with control electronics depending on the actuating voltage values and transmitting the control signals to the power semiconductors of the converter;

generating actuating voltage values with the control unit to make the control difference values as small as possible;

calculating the actual state values with an observer unit proceeding from the actuating voltage values and taking measured current values into account;

calculating actual state intermediate circuit energy values with an estimator unit taking measured intermediate circuit energy values of a positive-side and of a negative-side three-phase voltage source of the converter into account;

modeling the converter with the observer unit and the estimator unit causing the calculated actual state current values and state intermediate circuit energy values of a total energy of the converter and a difference in the intermediate circuit energy values of the positive-side and of the negative-side three-phase voltage source of the converter in the steady state to correspond to fault-free current and intermediate circuit energy values; and

feeding the fault-free current and intermediate circuit energy values to the control unit.

38. The method according to claim 37, wherein the desired state values are desired current values and desired intermediate circuit energy values.

39. A configuration for carrying out the method according to claim 37 for controlling a converter including a bridge circuit formed by phase module branches each having a series circuit formed by submodules each having a semiconductor circuit with a connected capacitor, positive-side and negative-side three-phase voltage sources, power semiconductors, and a measurement value output, the configuration comprising:

a control unit having an input connected to the measurement value output of the converter and an output supplying generated actuating voltage values;

control electronics disposed downstream of said control unit, said control electronics providing control signals dependent on the actuating voltage values and transmitting said control signals to the power semiconductors of the converter;

an observer unit disposed between the measurement value output of the converter and said input of said control unit, said observer unit calculating actual state values, proceeding from the actuating voltage values and taking measured current values into account;

an estimator unit disposed between the measurement value output of the converter and said input of said control unit, said estimator unit calculating actual state intermediate circuit energy values, taking measured intermediate circuit energy values of the positive-side and the negative-side three-phase voltage sources of the converter into account;

said observer unit and said estimator unit modeling the converter to cause the calculated actual state current values and state intermediate circuit energy values of a total energy of the converter and a difference in intermediate circuit energy values of the positive-side and the negative-side three-phase voltage sources of the converter in a steady state to correspond to fault-free current and intermediate circuit energy values; and

said control unit receiving the fault-free current and intermediate circuit energy values and being constructed as a periodic controller having a periodically time-variant gain.