AC/DC CONVERTER
First Claim
1. An AC/DC converter comprising:
- at least two phase legs connected in series between first and second DC connection terminals of the AC/DC converter, wherein each phase leg comprises;
an AC connection having first and second terminals arranged to connect the phase leg to a phase of an AC system;
a phase branch comprising at least one converter cell and having first and second branch end terminals (E); and
a capacitor;
whereinthe capacitor is connected the between the first branch end terminal and the first AC connection terminal, the capacitor forming a DC blocking capacitor;
the second AC terminal is connected to the second branch end terminal; and
whereinthe series connection of the phase legs between first and second DC connection terminal is such that a first series connection point in a phase leg is located between the first branch end terminal and the DC-blocking capacitor, while a second series connection point is located between the second branch end terminal and the second AC connection.
5 Assignments
0 Petitions
Accused Products
Abstract
The present invention relates to an AC/DC converter comprising at least two phase legs connected in series between first and second DC connection terminals of the AC/DC converter, wherein each phase leg comprises: an AC connection having first and second terminals arranged to connect the phase leg to a phase of an AC system; a phase branch comprising at least one converter cell and having first and second branch end terminals; and a capacitor. The capacitor is connected the between the first branch end terminal and the first AC connection terminal, so that the capacitor forms a DC blocking capacitor. The second AC terminal is connected to the second branch end terminal. The series connection of the phase legs between first and second DC connection terminal is such that a first series connection point in a phase leg is located between the first branch end terminal and the capacitor, while a second series connection point is located between the second branch end terminal and the second AC connection. The invention further relates to a method of operating such AC/DC converter.
18 Citations
20 Claims
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1. An AC/DC converter comprising:
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at least two phase legs connected in series between first and second DC connection terminals of the AC/DC converter, wherein each phase leg comprises; an AC connection having first and second terminals arranged to connect the phase leg to a phase of an AC system; a phase branch comprising at least one converter cell and having first and second branch end terminals (E); and a capacitor;
whereinthe capacitor is connected the between the first branch end terminal and the first AC connection terminal, the capacitor forming a DC blocking capacitor; the second AC terminal is connected to the second branch end terminal; and wherein the series connection of the phase legs between first and second DC connection terminal is such that a first series connection point in a phase leg is located between the first branch end terminal and the DC-blocking capacitor, while a second series connection point is located between the second branch end terminal and the second AC connection. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 20)
where k indicates the kth phase leg, k∈
[1, P], P being the number of phases of the AC/DC converter 300;
UkDC denotes a predetermined desired DC voltage between the first and second connection points, where Σ
k=1P UkDC=UDC, UDC being the voltage between the DC connection terminals;
Û
vAC is a desired peak AC voltage between the first and second connection points, t is time, ω
is the desired angular frequency at the AC output and Θ
k is the desired phase angle.
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5. The AC/DC converter of claim 1, comprising:
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a voltage measurement device arranged to measure at least one voltage from which the DC voltage across the DC-blocking capacitor of the phase leg may be obtained; and
whereinthe control system is responsively connected to the voltage measurement device and configured to receive a signal from the voltage measurement device from which the DC voltage across the DC-blocking capacitor may be obtained; and the control system is configured to perform the control of the switching of the converter cells of the phase branches in dependence of the received voltage measurement signals so that the DC voltage across the DC-blocking capacitor of a phase leg corresponds to a predetermined capacitor DC voltage.
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6. The AC/DC converter of claim 5, wherein
the voltage measurement device is configured to measure the voltage across the DC-blocking capacitor. -
7. The AC/DC converter of claim 5, wherein
the voltage measurement device is configured to measure: -
at least one voltage whereby the voltage across the phase branch of the phase leg may be obtained, and the voltage across the AC connection of the phase leg.
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8. The AC/DC converter of claim 4, wherein
the predetermined desired DC voltage corresponds to -
9. The AC/DC converter of claim 1, comprising
a control system configured to control the switching of the converter cells of the phase branch of a phase leg, wherein the control system is configured to: -
receive a signal indicative of a zero sequence component of the AC output voltage from the AC/DC converter; and control the switching of at least one converter cell of the AC/DC converter in dependence of said signal indicative of a zero sequence component so as to mitigate DC side harmonic common mode current components.
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10. The AC/DC converter of claim 9, wherein
the at least one converter cell which the control system is configured to control the switching to mitigate DC side harmonic common mode current components are the converter cells of the phase branches of the phase legs. -
11. The AC/DC converter of claim 10, wherein
the AC connection of each phase leg is connected to a first winding of a transformer; - and
the neutral of the second winding of the transformer is connected to a grounded arrester, the neutral thus being floating.
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12. The AC/DC converter of claim 9, wherein
the at least one converter cell which the control system is configured to control the switching to mitigate DC side harmonic common mode current components is part of an active filter connected in series with the phase legs between the terminals of the DC connection. -
13. The AC/DC converter of claim 1, wherein
a passive filter is connected, between the first and second series connection points of a phase leg, in series with the phase branch. -
14. The AC/DC converter of claim 1, wherein
a passive filter is connected, between the first and second series connection points of a phase leg, in series with the DC-blocking capacitor. -
20. The AC/DC converter of claim 2, comprising:
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a voltage measurement device arranged to measure at least one voltage from which the DC voltage across the DC-blocking capacitor of the phase leg may be obtained; and
whereinthe control system is responsively connected to the voltage measurement device and configured to receive a signal from the voltage measurement device from which the DC voltage across the DC-blocking capacitor may be obtained; and the control system is configured to perform the control of the switching of the converter cells of the phase branches in dependence of the received voltage measurement signals so that the DC voltage across the DC-blocking capacitor of a phase leg corresponds to a predetermined capacitor DC voltage.
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15. A method of operating an AC/DC converter having at least two phase legs connected in series, wherein each phase leg comprises:
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an AC connection having first and second terminals arranged to connect the phase leg to a phase of an AC system; a phase branch comprising at least one converter cell and having first and second branch end terminals (E); and a capacitor;
whereinthe capacitor is connected the between the first branch end terminal and the first AC connection terminal, the capacitor forming a DC blocking capacitor; the second AC terminal is connected to the second branch end terminal; and the series connection of the phase legs between first and second DC connection terminal is such that a first series connection point in a phase leg is located between the first branch end terminal and the DC-blocking capacitor, while a second series connection point is located between the second branch end terminal and the second AC connection;
the method comprising;controlling the switching of the converter cells of the phase branch of a phase leg to provide a voltage according to the following expression between the first and second series connections points of a phase leg;
Uk=UkDC+Û
vAC sin(ω
t+Θ
k),where k indicates the kth phase leg, k∈
[1, P], P being the number of phases of the AC/DC converter 300;
UkDC denotes a predetermined desired DC voltage between the first and second connection points, where Σ
k=1p UkDC=UDC, UDC being the voltage between the DC connection terminals;
Û
vAC is a desired peak AC voltage between the first and second connection points, t is time, ω
is the desired angular frequency at the AC output and Θ
k is the desired phase angle.- View Dependent Claims (16, 17, 18, 19)
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Specification