Electric power conversion systems – Phase conversion without intermediate conversion to d.c. – With automatic voltage magnitude or phase angle control
Reexamination Certificate
2003-05-22
2004-06-01
Riley, Shawn (Department: 2838)
Electric power conversion systems
Phase conversion without intermediate conversion to d.c.
With automatic voltage magnitude or phase angle control
C363S148000
Reexamination Certificate
active
06744650
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling a matrix converter, in particular a matrix converter with nine bidirectional power switches arranged in a 3×3 switch matrix.
A matrix converter is a self-commutated direct converter. It enables the conversion of a constant three-phase system into a system with variable voltage and frequency. Through the arrangement of the bidirectional power switches in a 3×3 switch matrix, each of the three output phases of the matrix converter can be electrically connected to any one input phase. One phase of the matrix converter includes an arrangement of three bidirectional power switches wherein each switch is connected, on the one hand, to an input phase and, on the other hand, to an output phase. An arrangement of this type is also referred to as a 3×1 switch matrix. The matrix converter does not require an intermediate circuit. Due to its topology, the self-commutated direct converter advantageously has a recovery capability and achieves sinusoidal mains currents through a suitably designed control.
Each of the bidirectional power switches of the matrix converter has two anti-serially connected semiconductor switches. Insulated Gate Bipolar Transistors (IGBT) are preferably used as semiconductor switches, which each include an antiparallel diode. Bidirectional power switches designed in this way are preferably used in converters for small and medium power. Through the control of these semiconductor switches of the bidirectional power switches, a continuous current path is established in a direction determined by the arrangement of the semi-conductor switches. If both semiconductor switches of a bidirectional power switch are controlled, the latter is bidirectionally activated and a current can flow in both directions. This creates a safe electrical connection between an input phase and an output phase of the matrix converter. If only one semiconductor switch of a bidirectional power switch is controlled, the latter is unidirectionally activated, creating an electrical connection between an input phase and an output phase of the matrix converter only for a preferred current direction.
Any desired time-averaged output voltage can be obtained—within certain limits—by a controlled temporal sequence of combinations of switch positions within a modulation period. A matrix converter includes a controller capable of computing a suitable switch combination based on information about the input voltage space vector and a desired value for the output voltage space vector.
Conventional control methods operate either according to a phase-oriented or a vector-oriented method.
The phase-oriented control method is described in the publication “Analysis and Design of Optimum-Amplitude Nine-Switch Direct AC-AC Converters”, by Alberto Alesina and Marco G. B. Venturini, IEEE Transactions on Power Electronics, Vol. 4, No. 1, January 1989, pp. 101-112. The space vector control method is described in “Space Vector Modulated Three-Phase to Three-Phase Matrix Converter with Input Power Factor Correction”, by Lászó Huber and Du{haeck over (s)}an Borejević, IEEE Transactions on Industrial Applications, Vol. 31, No. 6, November/December 1995, pp. 1234-1245.
To prevent an open circuit of the load current it or a short circuit of two input phases A, B of a matrix converter from occurring at any time, a defined switching sequence has to be observed. The publication “A Matrix Converter without Diode Clamped Over-Voltage Protection”, J. Mahlein and M. Braun, Conf. Proceed. “IPEMC”, 2000, Beijing, China, in particular Chapter 3, describes possible commutation sequences for an output phase of a matrix converter. The commutation from the state semiconductor switches S
1
and S
2
conducting and semiconductor switches S
3
and S
4
blocking into the state semiconductor switches S
1
and S
2
blocking and semiconductor switches S
3
and S
4
conducting will, now be described based on the figures in the reference, which are reproduced herein as
FIGS. 1 and 2
.
As seen in
FIG. 1
, an output phase of a matrix converter
2
has three bidirectional power switches
4
which are arranged in a 3×3 switch matrix. As also seen in
FIG. 1
, each bidirectional power switch
4
includes two antiserially connected power switches S
1
, S
2
and/or S
3
, S
4
and/or S
5
, S
6
, which each include an antiparallel connected diode. The illustrated semiconductor switches S
1
, S
2
, S
3
, S
4
, S
5
, and S
6
are implemented as Insulated-Gate-Bipolar-Transistors (IGBT). Each of the antiparallel connected diodes forms a component of the associated IGBT module. Each semiconductor switch S
1
, S
2
, S
3
, S
4
, S
5
, S
6
of the bidirectional power switches
4
of this phase of the matrix converter
2
can be controlled separately and independently. A switch is regarded as being switched on bidirectionally, if both semiconductor switches S
1
, S
2
and/or S
3
, S
4
and/or S
5
, S
6
of a bidirectional power switch
4
are driven. If only one of the semiconductor switches S
1
, S
2
and/or S
3
, S
4
and/or S
5
, S
6
of a bidirectional power switch
4
are driven, then the switch is called a unidirectionally switched-on switch.
FIG. 2
shows all possible commutation sequences for commutating from the state semiconductor switches S
1
and S
2
conducting and semiconductor switches S
3
and S
4
blocking into the state semiconductor switches S
1
and S
2
blocking and semiconductor switches S
3
and S
4
. These possible commutation sequences depend on information about the polarity of the voltage and/or current and can be divided into three groups. The switching sequences that are not marked can be performed only when the polarity of both the voltage and the current are known and are not of technical interest because two pieces of information are required. A second group surrounded by a dashed line is independent of the voltage polarity and only requires information about the polarity of the current. The third group surrounded by a dash-dotted line is independent of the current polarity and only requires information about the polarity of the voltage. These switching sequences are also referred to as voltage-controlled commutation.
The following discussion is limited to voltage-controlled commutation.
If an erroneous measurement of the voltage polarity with voltage-controlled commutation results in a selection of the wrong switching sequence, then a short circuit occurs in the linked input voltage. This does not cause any technical problems as long as the amplitude of the input voltage is smaller than the turn-on voltage of the semiconductor valves in the short current path, which is approximately 10 V when implemented using IGBT's. The voltage-controlled commutation hence requires a precise measurement technique for measuring the voltage polarity. Typically employed analog measurements of the input voltage which are required for controlling the matrix converter are not adequate, so that additional electronic components are required. The required high precision is also vulnerable and does not lend itself to a desired robust solution of the commutation problem.
The publication “A New Two Steps Commutation Policy For Low Cost Matrix Converters”, M. Ziegler and W. Hofmann, Conf. Proc. “PCIM 200 Europe”, Nürnberg, September 2000, proposes a control method with relaxed requirements for determining the voltage polarity. The control method described in this reference will now be described based on a time-dependent diagram of an output phase with pulse-width modulation as depicted in FIG.
3
.
The three-phase matrix converter
2
has nine bidirectional power switches
4
, which are arranged in a 3×3 switch matrix
6
. The arrangement of the nine bidirectional power switches
4
in a 3×3 switch matrix
6
allows each output phase X, Y, Z to be switched to any desired input phase U, V, W. An inductive load
8
is connected to the output phases X, Y, Z of the matrix switch
2
. The input phases U, V and W are connected with
Mahlein Jochen
Simon Olaf
Feiereisen Henry M.
Riley Shawn
Siemens AG
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