Electric power conversion systems – Frequency conversion without intermediate conversion to d.c. – By semiconductor converter
Reexamination Certificate
2002-03-19
2004-11-30
Berhane, Adolf (Department: 2838)
Electric power conversion systems
Frequency conversion without intermediate conversion to d.c.
By semiconductor converter
C363S163000
Reexamination Certificate
active
06826065
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of electrical engineering in general and more particularly to conversion technique and to methods of current commutation by bi-directional switches of matrix converters, for instance to three phase-to three phase matrix converters with a space vector modulation.
The invention can be used in induction motor drives, special power supplies, etc. More particularly this invention can be used in power supplies on a base of AC-AC converters with control and stabilization of output frequency.
BACKGROUND OF THE INVENTION
There are well-known methods of current commutation by bi-directional switches which consist of two separately controlled halves having the opposite direction conductivity, that are based on information about polarity of load current (I
L
) of matrix converters (MC) [P. Wheeler, D. Grant, “Optimized input filter design and low-loss switching techniques for a practical matrix converter”, in
IEE Proc
.-
Electr. Power Applicat
., vol.144, no.1, pp.53-60, January 1997; L. Empringham., P. W. Wheeler, J. C. Clare, “Matrix converter bi-directional switch commutation using intelligent gate drives”, IEE Power Electronics and Variable Speed Drives Conference, No.456, London, September, 1998], or on information about relation of mains voltages [M. Ziegler, W. Hofmann, “Semi natural two steps commutation strategy for matrix converter”, in
Rec.
29
th
Annual IEEE meeting, PESC'
98, 1998, vol.1, pp. 727-731; H. Youw, B. H. Kwon, “Switching technique for current controlled AC-to-AC converters”,
IEEE Trans. Ind. Electron
., vol. 46, no. 2, pp. 309-318, April 1999].
In case of tracking the I
L
polarity, halves of switches are being controlled separately for every current polarity. It allows to provide a correct commutation (without short circuit currents and overvoltages under breaking current in the load inductance), if the polarity of I
L
is single-valued. If current I
L
≈0 or changes its polarity repeatedly during the period of the output voltage, a method proposed in [P. W. Wheeler, D. Grant, “Optimized input filter design and low-loss switching techniques for a practical matrix converter”, in
IEE Proc
.-
Electr. Power Applicat
., vol.144, no.1, pp 53-60, January 1997], does not allow to get any exact determination of step-by-step commutations order of switches halves under every changing of current I
L
polarity. According to [L. Empringham, P. W. Wheeler, J. C. Clare, “Matrix converter bi-directional switch commutation using intelligent gate drives”, IEE Power Electronics and Variable Speed Drives Conference, No.456, London, September, 1998], the polarity of I
L
is being defined on the difference of voltage across switches halves at every moment of time. It allows to define enough exactly the moment when current falls to zero. But this method requires a considerable increasing of intellectual potential of power switches drivers and the further complication of logical part of control system due to multiple cross connections between drivers of all the switches of every output MC phase. Besides, after the fixing of zero current it appears an uncertainty in subsequent choice of the necessary order of switching the switches halves, and this also complicates a realization of the commutation method.
Under the real conditions, when the output current curve is a high frequency ripple and crosses zero line repeatedly, a method realization of how to transfer current from one switch to another with using mentioned method will be complicated.
Under using methods being based on information of the relation of mains voltages, the voltages period is being divided into intervals with said relation being constant, and it is turned constantly on those halves of all switches which are connected to a load phase and which do not produce paths for short circuit currents during current interval of the mains voltage [M. Ziegler, W. Hofmann, “Semi natural two steps commutation strategy for matrix converter”, in
Rec.
29
th
Annual IEEE meeting, PESC'
98, 1998, vol.1, pp. 727-731 ], or halves of only two switches being connected to input phases with maximal and minimal voltages within the interval given [H. Youw, B. H. Kwon, “Switching technique for current controlled AC-to-AC converters”,
IEEE Trans. Ind. Electron
., vol. 46, no. 2, pp. 309-318, April 1999].
Such approach allows to provide for a MC phase constant being of conditional freewheeling diodes on the analogy with voltage source inverters and gives a possibility to make switches commutation with dead time, because there always is a way for current of both polarity. But in the moments of approximate equality of phase voltages, especially if they are distorted (for instance, as a result of flowing the modulated current being supplied from the mains through filter inductance) and repeatedly are being compared under intervals changing, it appears an uncertainty when fixing boundaries of mains voltage intervals.
The uncertainty in the choice of switches halves which are to be constantly turned on during the interval results in short circuit currents through the switches in case of overlap time, or in current breaking under commutations, if the half of the switch which is necessary for current conducting during dead time appears to be turned off. In the case of significant distortions of input voltages methods mentioned above can not be used.
The prior art of the proposed invention is a method of commutation of current by bi-directional switches of matrix converters with at least three input phases, the switches consisting of two separately controlled halves with the opposite directions conductivity, which implies that under transferring current from the switch being turned on in both directions and connected to one input phase to the switch being connected to another input phase, it is being turned on the half of the switch that does not make a way for flowing short circuit current between the first and the second of mentioned phases for current relation of phases voltages on the first stage of commutation, on the second stage it is being turned off the half of the switch that is unidirected with the turned on half of the switch at the first stage of commutation that is being turned off, it is being turned on the second half of the switch that is being turned on at the third stage, and it is being turned off the second half of the switch that is being turned off [L. Mazet, H. Boulant, J-J. Huselstein, C. Glaize, “Switching control in three phase matrix converters by discrimination of command orders”, in Proc. PEMC'98, vol 2, Prague, Czech Republic, 1998, pp.2-64-2-67]. During time intervals where it exists the complete certainty of the relation of voltages for those phases with switches being switched the step-by-step algorithm described provides the correct current commutation.
A disadvantage of this and above mentioned methods is lack of conditions for realization of a safe step-by-step algorithm of switches commutation on intervals where it is impossible to define exactly the relation between input phase voltages, especially under distortions of curves of mains phase voltages with connected switches which take part in commutation.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a method of current commutation by bi-directional switches of matrix converters with at least three input phases, which allows to avoid short circuits current through the switches and overvoltages on circuit elements due to eliminating commutations between switches being connected to those mains phases for which it is impossible to determine exactly the voltages relation between them for a given moment of time.
It is another object of the present invention to provide a method of current commutation by bi-directional switches of a three phase—to three phase MC with a space vector modulation (SVM), which provides the withdrawal of commutations between switches being connected to t
Chekhet Eduard Mikhaylovich
Mikhalsky Valeriy Michaylovich
Sobolev Vladimir Nikolaevich
Berhane Adolf
Zborovsky I.
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