Electrical converter and method for operating an electrical converter

Patent metadata

Field	Value
Publication number	US-12107488-B2
Application number	US-201917616801-A
Country	US
Kind code	B2
Filing date	Jun 6, 2019
Priority date	Jun 6, 2019
Publication date	Oct 1, 2024
Grant date	Oct 1, 2024

Abstract

An electrical converter has an alternating-voltage side with at least two alternating-voltage terminals and a direct-voltage side. At least two series connections connected in parallel and each forming a converter arm of the converter assigned to one of the alternating-voltage terminals. Circular currents can flow between the series connections. According to the method, a load value describing the thermal load of the converter is calculated based on: an active power current value that indicates the active power current component of a phase current flowing across one of the alternating-voltage terminals; a reactive power current value that indicates the reactive power current component of the phase current flowing across the alternating-voltage terminal; and a circular current value that indicates the magnitude of the circular current(s) flowing between the series connections. The converter is controlled while also taking into account this load value.

First claim

The invention claimed is:

1. A method for operating an electrical converter which has an AC voltage side with at least two phases and a DC voltage side, the method comprising:
providing the electrical converter with at least two AC voltage connections on the AC voltage side and at least two parallel-connected series circuits, with each of the series circuits forming a respective converter arm of the converter and being assigned to one of the AC voltage connections on the AC voltage side of the converter;
wherein one or more circuit currents are able to flow between the at least two parallel-connected series circuits;
calculating a loading value describing a thermal loading of the converter on a basis of at least three current values, namely:
an active power current value that indicates an active power current component of a phase current flowing through one of the AC voltage connections;
a reactive power current value that indicates a reactive power current component of the phase current flowing through the one AC voltage connection; and
a circuit current value that indicates a magnitude of the one or more circuit currents flowing between the series circuits; and

controlling the converter while taking into consideration the loading value; and
calculating the series circuit-related circuit currents in accordance with
Iki ( t )=( Ipi ( t )+ Igi ( t ))/2+ Idc ( t )/ n−Iai ( t )

where:
Iki(t) denotes a series circuit-related circuit current, as a function of time t, in an ith series circuit or an ith converter arm;
Ipi(t) denotes the active power current, as a function of time t, flowing through the AC voltage connection connected to the ith series circuit or to the ith converter arm;
Iqi(t) denotes the reactive power current, as a function of time t, flowing through the AC voltage connection connected to the ith series circuit or to the ith converter arm;
Idc(t) denotes the DC current, as a function of time t, flowing on the DC voltage side;
lai(t) denotes an arm current, as a function of time t, flowing between a positive DC voltage connection of the DC voltage side and the AC voltage connection connected to the ith converter arm; and
n denotes a number of series circuits or converter arms.

2. The method according to claim 1 , which comprises ascertaining the circuit current value by ascertaining, for each of the series circuits, the circuit current flowing therein, by determining a greatest series circuit-related circuit current in terms of absolute value and by considering the absolute value (amplitude) of the greatest series circuit-related circuit current as the circuit current value.

3. The method according to claim 1 , which comprises controlling the converter to cause the loading value to fall below or to not to exceed a predefined loading limit value.

4. The method according to claim 1 , which comprises ascertaining a loading limit value for controlling the converter by applying an integral relating to the loading value, namely:
Ith max= f (∫ Ith ( r ) 2 dt )

wherein Ith (t) denotes the loading value over time t and f denotes a predefined function of the integral formed via the square of the loading value.

5. The method according to claim 4 , which comprises reducing the loading limit value when a temperature of the converter reaches or exceeds a predefined maximum temperature.

6. The method according to claim 4 , wherein the step of controlling the converter, in an event that the loading value reaches or exceeds the predefined loading limit value, includes a targeted reduction of the active power current.

7. The method according to claim 1 , which comprises controlling the converter, in an event that the loading value reaches or exceeds a predefined loading limit value, such that the active power current value does not exceed a predefined active power maximum current value, and ascertaining the active power maximum current value from the following conditional equation:

Ith
⁢

max

=

1
a

·

(

Ip

max
2

+

Iq
2

)

+

(

k
⁢

1
·
Ip

⁢

max
·

f
⁡
(

Vconv
Vdc

)

+

k
⁢

2
·
Ik

)

wherein:
Ithmax denotes the predefined loading limit value, Ipmax denotes the active power maximum current value;
Iq denotes the reactive power current value and is formed by an absolute value of or an amplitude of the reactive power current component of the phase current flowing through the AC voltage connection;
Vconv denotes an absolute value of or an amplitude of a voltage at the AC voltage connection;
Vdc denotes an absolute value of or an amplitude of the DC voltage on the DC voltage side;
Ik denotes the circuit current value and is formed by an absolute value of or an amplitude of a greatest series circuit-related circuit current; and
a, k 1 and k 2 are predefined constants.

8. The method according to claim 1 , which comprises controlling the converter, in an event that the loading value reaches or exceeds a predefined loading limit value, such that the active power current value does not exceed a predefined active power maximum current value;
wherein the active power maximum current value is ascertained in accordance with

Ip
⁢

max

=

2
⁢
Ith

max
2

-

Assignees

• Siemens Energy Global Gmbh & Co Kg

Inventors

• Delzenne Maxime
• Ebner Guenter

Classifications

• H02M1/0009

  Devices or circuits for detecting current in a converter · CPC title

• H02M7/4835

  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 title

• H02M1/327 Primary

  against abnormal temperatures · CPC title

• H02M1/32

  Means for protecting converters other than automatic disconnection · CPC title

• H02M7/483 Primary

  Converters with outputs that each can have more than two voltages levels · CPC title