EP1639691A2

EP1639691A2 - Rectifier/power converter for an ac power source having a connection for a back-up power source

Info

Publication number: EP1639691A2
Application number: EP04739838A
Authority: EP
Inventors: Ralf Briest
Original assignee: RWE Piller GmbH
Current assignee: Piller Group GmbH
Priority date: 2003-06-17
Filing date: 2004-06-11
Publication date: 2006-03-29
Also published as: WO2004112231A2; WO2004112231A3

Abstract

The invention relates to a rectifier/power converter for an AC power source (U1) which has one step-up chopper each for both current directions. Every step-up chopper has its own chopper coil (L1, L2), a disconnectible semiconductor valve (T1, T2), a freewheeling diode (D1, D2) and a capacitor (C1, C2). The step-up choppers are connected to a DC output having a center (M). Every chopper coil (L1, L2) can be optionally connected to the phase of the AC power source (U1) or to a back-up power source (U2) via a changeover switch (T11 and T21; T12 and T22) having a fixed current direction.

Description

RECTIFIER AND RECTIFIER FOR AN AC POWER SOURCE WITH A CONNECTION FOR A SPARE POWER SOURCE

The invention relates to a rectifier and converter for an AC source with the features of claim 1 and special uses of such a rectifier and converter.

STATE OF THE ART

In various practical applications, a rectifier and converter must be switched between an AC source, for example a three-phase three-phase network, and a consumer. The rectifier and converter can serve to supply an inverter following it with an input DC voltage, from which the subsequent inverter generates an AC voltage suitable for supplying the consumer. The consumer can also directly use the DC output voltage of the rectifier and converter. In the case of a subsequent inverter in particular, it is also desirable in the case of a rectifier and converter if the converter steps up the voltage. The step-up converters are provided for this purpose in a rectifier and converter according to the preamble of patent claim 1. With the semiconductor valves of the step-up converter, the desired current direction is carried out at the rectifier and converter in order to maintain a defined shape of the current curve. As a rule, a sinusoidal current curve of the alternating current source is desired.

In a system for uninterruptible power supply, ie a so-called UPS system, the consumer is in the event of failure of a primary AC power source, ie Rule of the power grid, supplied with the help of a backup power source. For this purpose, a substitute current source, which supplies direct current with the direct output voltage of the rectifier and converter, can alternatively be connected directly to the consumer or an inverter connected upstream of it. However, this is not possible if the backup power source does not deliver this output voltage.

From J.W. Kohler and F.C. Zach "A novell three phase three switch three level Unity Power Factor PWM Rectifier", Power Conversion * June 1994 proceedings, pages 125 ff., A rectifier and converter with the features of the preamble of claim 1 is known. An actuator choke for each phase of the alternating current source is arranged on the input side in front of diodes, with which the respective phase is branched to the separate components of the two step-up converters for the two current directions; a connection option for a substitute current source is not provided here.

OBJECT OF THE INVENTION

The invention has for its object to show a rectifier and converter with the features of the preamble of claim 1, which provides an additional connection option for a backup power source in an efficient and easily controllable manner.

SOLUTION

The object of the invention is achieved by a rectifier and converter with the features of patent claim 1. Preferred embodiments of the rectifier and converter are described in subclaims 2 to 7. Preferred uses of the rectifier and converter are described in the likewise dependent claims 8 to 10. DESCRIPTION OF THE INVENTION

In the invention, the step-up converters are used not only for rectifying and rectifying the alternating current source, but also in particular for rectifying the current for the substitute current source. In order to create the prerequisite for this, each step-up converter is assigned its own converter choke, which is thus arranged behind the branching of the respective phase of the AC power source in the two current directions. In the new rectifier and converter, each phase of the AC source is branched using the fixed current direction of the changeover switches, which are connected upstream of the converter chokes of the step-up converters. At the same time, these change-over switches allow the connection of each converter choke of each step-up converter with the same fixed current direction as when connecting to the AC power source and also to a backup power source. The current from the backup power source can be directed with the full functionality of the step-up converter and increased in terms of its voltage, without requiring additional equipment for all step-up converters in addition to the changeover switches and its own converter chokes. The changeover switches in front of the actuator choke of each step-up converter are preferably each made up of two electronic switches with a current direction, which have the same orientation to the respective actuator choke. In addition to simply switching between the AC power source and the backup power source, it is also possible to switch the two power sources on and off independently.

The electronic switches in front of each actuator choke of each step-up converter can be implemented, for example by means of thyristors. Transistors, e.g. IGBTs or Mosfets can be used, but their functionalities are not exhausted here. When using thyristors, it is generally sufficient for a switchover from a failing AC power source to the backup power sources to ignite the thyristors leading to the backup power source. The thyristors leading to the AC source are then of course commutated.

The new rectifier and converter can be used in conjunction with a wide variety of backup power sources. Examples are batteries, double layer capacitors, flywheel storage or diesel generators. The direction of the current is in any case effected by the semiconductor valves of the step-up converters. They are typically transistors that can be configured as IGBTs or Mosfets depending on the power to be switched. - A -

The construction of the new rectifier and converter is preferably such that each step-up converter has its own semiconductor valve which can be switched off. However, there are also embodiments of the new rectifier and converter, in which for each phase of the alternating current source only one semiconductor valve which can be switched off is provided for the step-up converter assigned to the two current directions and which interacts with an additional diode for each step-up converter. With a separate semiconductor valve that can be switched off for each step-up converter, there are special possible uses of the new rectifier and converter when switching from the backup power source back to the AC power source. This will be explained in more detail below.

However, it is unnecessary if the step-up converters have their own capacities for the same current direction of several phases of the AC power source. A total capacitance, which is connected in parallel to the output of the rectifier and converter, is advantageous here.

With the new rectifier and converter, it is possible, but not mandatory, that a center or star point of the alternating current source and / or the substitute current source is connected to the center of the direct current connection. In this way, a common center point can be established for all three positions, even if one of the center points is loaded. However, it is also possible to use one that has no center as the backup power source. Even then, the star or center of the alternating current source and the center of the output of the rectifier and converter can still be connected to one another.

Even if no center points are connected to one another in the new rectifier and converter, the semiconductor valves of the step-up converters can be controlled such that a direct voltage output at the direct voltage output is symmetrical with its center point.

In the basic use of the new rectifier and converter, the changeover switch permanently connects the converter choke of each step-up converter to the AC power source in a first operating mode and to the in a second operating mode Backup power source. If the AC power source fails, the first operating mode must be switched to the second operating mode.

If several step-up converters are provided for each current direction and if the backup power source is a direct current source, the changeover switches of the step-up converters for one current direction can connect the converter chokes in succession to the backup power source in pulsed mode for limited periods of time. If the actuator chokes are connected to the backup power source for the same period of time and an equal amount of energy is drawn from the backup power source via the respective actuator choke, the energy can be drawn from the backup power source with high uniformity, whereby the backup power source is minimally stressed.

It is particularly preferred if the step-up converters for one current direction connect the converter chokes in pulse mode to the backup power source for successive thirds of the period of the AC power source, i.e. if synchronization of the pulse mode with the energy withdrawal from the backup power source is obtained with the period of the AC power source.

Such synchronization enables a smooth transition when the power supply has to be switched from the backup power source to the AC power source by temporarily taking parallel power from both power sources. During the parallel power draw, the power share from one power source can be continuously reduced, while the power draw from the other power source is continuously ramped up. This avoids unfavorable jumps in the withdrawal of services. In addition, the parallel power withdrawal also enables a partial connection of the backup power source if the power supply via the AC power source only partially breaks down or is not sufficient for certain requirements. A prerequisite for parallel power consumption, which is also referred to here as quasi-parallel operation of the two current sources, because a step-up converter is only supplied with power from one of the two current sources at a time is that each step-up converter has its own semiconductor valve that can be switched off. Quasiparallel operation is not possible with only one semiconductor valve that can be switched off for each phase of the AC power source. In quasi-parallel operation, each semiconductor valve that can be switched off is switched by the respective step-up converter in alternate periods within the period of the AC power source alternately connected to the AC power source and the backup power source, so that energy is drawn from both the AC power source and the backup power source within the period of the AC power source. There is never a direct connection between the power sources. At any time, only one of the power sources is used. Quasi-parallel operation can be realized particularly advantageously if six step-up converters are provided for a three-phase alternating current source, because then 120 ° blocks in which the step-up converters are supplied with energy from the backup current source in one current direction are combined to form a full 36 ° ° period, via which constant power is drawn from the backup power source.

BRIEF DESCRIPTION OF THE FIGURES

The invention is further explained and described below with reference to preferred exemplary embodiments illustrated in the figures.

Fig. 1 shows a circuit diagram of a first embodiment of the new DC and

Power converter in connection with a single-phase alternating current source and a standby alternating current source.

Fig. 2 shows various plots of current profiles to explain the

Function of the first embodiment of the new rectifier and converter according to FIG. 1.

3 shows a circuit diagram of a second comprising additional thyristors

Embodiment of the new rectifier and converter in connection with a single-phase alternating current source and a standby alternating current source.

Fig. 4 shows different plots of current profiles to explain the

Function of the second exemplary embodiment of the new rectifier and converter according to FIG. 3. Fig. 5 shows a circuit diagram of a third embodiment of the new DC and

Converter, which differs from the embodiment shown in FIG. 3 by the absence of additional thyristors.

Fig. 6 shows different plots of current profiles to explain the

Function of the third exemplary embodiment of the new rectifier and converter according to FIG. 5.

Fig. 7 shows a circuit diagram of a fourth embodiment of the new DC and

Converter which differs from the exemplary embodiment according to FIG. 5 by only a single semiconductor valve which can be switched off for both current directions.

Fig. 8 shows a circuit diagram of a fifth embodiment of the new DC and

Power converter in connection with a three-phase alternating current source and a standby alternating current source.

FIG. 9 shows a circuit diagram of a sixth exemplary embodiment of the new rectifier and converter in connection with a three-phase alternating current source and a non-central substitute current source.

10 shows various plots of current profiles to explain the

Function of the fifth and sixth exemplary embodiment of the new rectifier and converter according to FIGS. 8 and 9.

Fig. 11 shows a circuit diagram of a seventh embodiment of the new DC and

Converter, which differs from the exemplary embodiment according to FIG. 9 by only a single semiconductor valve which can be switched off for each phase of the alternating current source. DESCRIPTION OF THE FIGURES

The rectifier and converter shown in FIG. 1 for an alternating current source U ₁ has two step-up converters, each with a converter choke L1 or L2, a semiconductor valve that can be switched off in the form of a transistor T1 or T2, a free-wheeling diode D1 or D2 and a capacitance in the form a capacitor C1 or C2. The two step-up converters are each provided for a current direction of one phase of the single-phase alternating current source U ₁ , which is branched toward the two step-up converters via two thyristors T11 and T12 provided in opposite orientations. The second connection of the single-phase alternating current source Ui is connected to a center point M of the output of the rectifier and converter, at which an output voltage U _{d is present} in two halves Ud, i and U _{d, 2} via the capacitors C1 and C2.

The structure described so far differs from a known rectifier and converter in that each individual step-up converter has its own converter choke L1 or L2 and that instead of the usual diodes, the comparatively complex thyristors T11 and T12 are used, around the one phase of the AC source To branch U ₁ to the two step-up converters. However, this also creates the possibility of using an equivalent current source U ₂ to provide the output voltage U _d . For this purpose, only two further thyristors T21 and T22 are provided in FIG. 1. These thyristors lead in the same current direction as the thyristors T11 and T12 to the actuator chokes L1 and L2. _If the alternating current source U _1iL i _{fails, the equivalent} current _source can be switched on by firing the thyristors T21 and T22, the thyristors T11 and T12 automatically commutating and with the aid of the actuation of the transistors T1 and T2 the required current is subsequently drawn from the equivalent current source U ₂ , At the same time, the two high seat actuators are also used to raise the output voltage of the backup power source U ₂ to the desired level of the output voltage U _{d of} the rectifier and converter. The two step-up converters can therefore perform this function for both current sources Ui and U ₂ . It is therefore only necessary to control these two step-up converters in order to provide a constant output voltage U _d . By regulating the duty cycle of the transistors T1 and T2, a symmetry of the components U _d , i and U _{dl2 of} the output voltage U _d can be achieved. In the exemplary embodiment of the rectifier and converter, which is shown in FIG. 1, an equivalent current source U _{2 is} provided which has a center point, ie which provides two partial output voltages U _{2 | 1} and U ₂ , ₂ . The center of the backup power source U ₂ is connected to the center M of the output of the rectifier and converter. This connection is also possible when the center M is loaded, for example by a downstream inverter.

In Fig. 2 different current profiles are plotted, namely for the alternating current source U ₁ , for the two parts U _2, i and U _{2ι2 of} the _{backup power} source U ₂ and for the actuator chokes L1 and L2. 2 a) is based on normal operation, in which the energy is supplied exclusively by the alternating current source U ₁ . Here, the current lu-i drawn by the AC source is sinusoidal. The currents Iu2, i and Iu2,2 from the equivalent current source U ₂ are zero; and the inductor currents I _L1 and I _L2 correspond to the two separate half-waves of Iu ₁ . In an alternative operation according to FIG. 2 b), in which, for example in the event of a failure of the alternating current source Ui, the power supply is provided by the alternative current source U ₂ , the current lui is zero. The equivalent currents Iu2, i and Iu2, ₂ are constant. The choke currents I _L1 and I _L2 correspond to the equivalent currents Iu2, i and Iu2, z. Fig. 2 c) outlines a quasi-parallel operation of both emergency power sources, ie a supply of the rectifier and converter during a period of the alternating current source U ₁ with both energy from the alternating current source U ₁ and the backup power source U ₂ . Here the current is sinusoidal but smaller than in normal operation according to FIG. 2a). The portions Iu2, i and Iu _{2.2 of} the equivalent current from the equivalent current source U ₂ supplement the inductor currents I _L1 and I _L2 in the periods of the period of Iu _{1 in} addition to the half-waves of lui. The entire power supply of L1 and L2 is thus composed of portions of both current sources U ₁ and U ₂ , the size of which can be varied. In this way, the energy supply can be gently transferred from one power source to the other without any jumps in power consumption from one of the power sources.

FIG. 3 shows an exemplary embodiment of the new rectifier and converter, in which an equivalent current source U _{2 is} provided compared to FIG. 1, which is also a direct current source but has no center. That is, it supplies only a single output voltage U ₂ and it is not connected to the center M of the output of the rectifier and converter. In order to nevertheless provide essentially the same functionalities as in the exemplary embodiment of the rectifier and converter according to FIG. 1, additional thyristors T211 and T222 are provided in the exemplary embodiment according to FIG. 3, which connect the backup current source U ₂ directly to the output of the rectifier and converter , The additional thyristors T211 and T222 are only for the _{Quasi-parallel operation} according to FIG. 4 c) is required in order to divide the _equivalent current l _ü2 between the two actuator chokes L1 and L2. For this purpose, the additional thyristor T222 is switched during the half-wave of lui, in which the step-up converter L1, T1, D1 is in operation, ie is supplied with lui, while the additional thyristor T211 is switched if, during the other half-wave of lui, the step-up converter L2, T2, D2 is in operation.

The embodiment of the rectifier and converter according to FIG. 5 differs from that according to FIG. 3 in that the additional thyristors are missing, or in comparison with FIG. 1 in that the equivalent current source U _{2 has} no center. As already indicated in connection with FIG. 3, this has effects on the quasi-parallel operation, which is outlined for the exemplary embodiment according to FIG. 5 in FIG. 6c. Here, the respective step-up converter with the thyristor ignited to the alternating current source Ui not only carries the current lui from the alternating current source Ui but also the current Iu ₂ from the substitute current source U ₂ . The other step-up converter determines the current of the backup power source. In other words, in the quasi-parallel operation of the exemplary embodiment of the rectifier and converter according to FIG. 5, the actuator chokes Li and L ₂ are simultaneously connected to the backup power source U ₂ while they are being supplied by the AC power source U ₁ . To avoid this, the additional thyristors are provided in the embodiment according to FIG. 3, which bypass the actuator chokes L1 and L2.

FIG. 7 shows an embodiment of the new rectifier and converter for a single-phase alternating current source U ₁ , in which the two step-up converters for the two current directions of the one phase of the alternating current sources do not each have their own transistor T1 or, in contrast to the exemplary embodiment according to FIG. 5. T2 as in Fig. 1 but have only a common transistor T1. For this purpose, an additional diode D11 or D12 is provided in each of the two step-up converters. Because only the single transistor T1 has to be controlled, the control of the new rectifier and converter is simplified in this exemplary embodiment, but quasi-parallel operation of the two current sources U1 and U2 is not possible. Rather, it is only possible to switch directly between normal operation and replacement operation, as is sketched in FIGS. 4 a) and b) or 6 a) and b).

The backup power source U ₂ can be a battery or generally a DC power source. But it can also be an AC power source. The step-up converter with the separate converter chokes L ₁ and L ₂ are flexible in this regard and do not depend on a specific type of backup power source U ₂ .

This also applies to the embodiments of the rectifier and converter for three-phase AC sources U ₁ described below. 8 shows a first _exemplary embodiment of the new rectifier and converter for an alternating current source Ui with three phases U _1iL i, U _{1L | 2} and U _1iL3 . Each of the phases is branched to two step-up converters via two thyristors T11 and T12 or T13 and T14 or T15 and T16. These step-up converters each have their own converter choke Li, their own free-wheeling diode Di and their own transistor Ti. The capacities additionally assigned to each step-up converter are in a capacitor C1 for the one current direction to which the step-up converters with the odd indices i are assigned, and in one Capacitor C2 for the other current direction, to which the step-up converters with the even indices i are assigned, are combined. The output voltage U _{d of} the rectifier and converter drops across these two capacitors C1 and C2. The star point of the alternating current source U ₁ can be connected to the center M of the output of the rectifier and converter. The backup power source U ₂ , which is preferably a battery or another DC power source, is connected via a total of six thyristors T21 to T26 to each of the six step-up converters in order to supply them with power as an alternative to the AC power source U1. The function of the rectifier and converter is in principle identical to that of the exemplary embodiment according to FIG. 1, the connection of the star point of the alternating current source Ui to the center M of the rectifier and converter not being mandatory in FIG. 8. Furthermore, it goes without saying that the DC voltage at the output of the rectifier and converter according to FIG. 8 will in principle be more constant due to the three-phase nature of the AC power source U ₁ than in the exemplary embodiments with a single-phase AC power source U ₁ according to FIGS. 1, 3, 5 and 7 ,

The exemplary embodiment of the rectifier and converter shown in FIG. 9 is modified from that according to FIG. 8 only in that the equivalent current source U ₂ according to FIG. 9 has no center that would be connected to the center M of the output of the rectifier and converter , This has no significant effect on the function of these two exemplary embodiments explained below due to the plurality of step-up converters in each current direction. In addition, could also at 9, the star point of the alternating current source U _{1 is} connected to the center M of the rectifier and converter.

10 shows the profile of the current IUI, _L .I of a phase of the alternating current source U ₁ , of the total equivalent current I _U2 from the equivalent current source and of the inductor currents Iu and I _L 2, which are assigned to the phase Ui, _L2 , for the exemplary embodiments according to 8 and 9. Again, a) normal operation, b) replacement operation and c) quasi-parallel operation are outlined separately. The normal operation, in which the actuator chokes L1 and L2 are supplied via the alternating current source U ₁ , does not differ from the normal operation in the single-phase alternating current source according to FIG. 2. The equivalent operation according to FIG. 10 b) differs in this respect from the equivalent operation according to FIG 2 b) that only a third of the equivalent current I _{U2 is} attributable to the inductor currents Iu and I _L2 , since here a total of three inductors L1 to L6 each carry the current. In the quasi-parallel operation according to FIG. 10 c), a difference to FIG. 2 c) can be seen in that the 120 ° blocks by which the inductor currents l _{u are added in} addition to the half-waves of the sinusoidal current IU _I , L _I add up a constant equivalent current Iu ₂ . The 120 ° blocks are 120 ° out of phase with each other in synchronism with the phases of the AC power source. 10 b) the substitute current Iu _{2 is divided} at any time onto the actuator choke assigned to each phase of the alternating current source U ₁ , each of the 120 ° blocks of the substitute current Iu ₂ , which are included in the choke currents Li, each have the full current of the backup current Iu ₂ .

In the exemplary embodiment of the rectifier and converter according to FIG. 11, the number of transistors in the step-up converters is halved compared to the exemplary embodiment according to FIG. 9 and analogously to the single-phase exemplary embodiment according to FIG. 7, and additional diodes D11 to D16 are provided instead, so that a pair of step-up converters, which are assigned to a phase of the alternating current source U1, manage with a transistor T1 or T3 or T5. Even with the three-phase exemplary embodiments of the new rectifier and converter, this has the consequence that quasi-parallel operation of the two current sources Ui and U ₂ according to FIG. 10 c) is not possible.

Claims

1. Rectifier and converter for an alternating current source, which has a step-up converter for each current direction, each step-up converter comprising a converter choke, a semiconductor valve which can be switched off, a freewheeling diode and a capacitor, and the step-up converters are connected to a DC voltage output having a center point that each step-up converter has its own converter choke (Li), which can be connected to the AC power source (UO and a backup power source (U ₂ ) via a changeover switch with a fixed current direction.

2. Rectifier and converter according to claim 1, characterized in that each changeover switch has two electronic switches with a current direction, which have the same orientation to the actuator choke (Li).

3. Rectifier and converter according to claim 2, characterized in that the electronic switches are thyristors (Tji).

4. Rectifier and converter according to one of claims 1 to 3, characterized in that the semiconductor valve which can be switched off of each step-up converter is a transistor (Ti).

5. Rectifier and converter according to one of claims 1 to 4, characterized in that each step-up converter has its own switchable semiconductor valve.

6. Rectifier and converter according to one of claims 1 to 5, characterized in that a center or star point of the AC power source (U ₁ ) and / or the backup power source (U ₂ ) is connected to the center point (M) of the DC connection.

7. rectifier and converter according to one of claims 1 to 5, characterized in that no center or star point of the AC power source (U ₁ ) or the backup power source (U ₂ ) is connected to the center of the DC voltage output.

8. Use of a rectifier and converter according to claim 5 or one of claims 6 and 7, which is dependent on claim 5, characterized in that the semiconductor valves of the step-up converters are controlled such that a direct voltage output at the direct voltage output is symmetrical to its center point (M) is.

9. Use of a rectifier and converter according to one of claims 1 to 7, characterized in that the changeover switch sets the choke (Li) of each step-up converter in a first operating mode permanently to the AC power source (U1) and in a second operating mode permanently to the backup power source ( U ₂ ) connects.

10. Use of a rectifier and converter according to claim 5 or according to one of claims 5 and 7, wherein six step-up converters are provided for a three-phase alternating current source and the substitute current source is a direct current source, characterized in that the changeover switch of the step-up converter for one direction of current connect the actuator chokes (Li) one after the other in pulsed mode for limited periods of time to the backup power source (U ₂ ).

11. Use according to claim 11, characterized in that the changeover switch of the step-up converter for one current direction connect the converter chokes (Li) in pulsed operation for successive thirds of the period of the alternating current source (Ui) to the substitute current source (U ₂ ), in each third of which Period an equal amount of energy is taken from the backup power source (U ₂ ).

12. Use of a rectifier and converter according to claim 5 or one of claims 6 and 7 or use according to claim 10 or 11, characterized in that the changeover switch of each step-up converter in quasi-parallel operation delimits the converter choke (Li) from one another Periods within a period of the AC power source (U ₁ ) alternately connects to the AC power source (Ui) and the backup power source (U ₂ ), so that within the period of the AC power source (U ₁ ) both the AC power source (U ₁ ) and the backup power source (U ₂ ) Energy is extracted.