DE102007018720A1 - Multipoint-rectifier and multipoint power inverter circuit, has unsymmetrical intermediate circuit for increasing number of potential stages, and series connection of switches inserted in three point power converter between switches - Google Patents

Abstract

The circuit has an unsymmetrical intermediate circuit for increasing number of potential stages. A series connection of switches is inserted in a three point power converter between switches (S1-S4), where the converter is implemented in a neutral-point-clamped topology. One of the series-connected switches is arranged in series with the switches of the converter. Capacitors (C1, C2) with different capacitances are charged with different voltages.

Description

Field of use:

The The invention relates to the field of power electronics. When Examples of applications here are rectifiers, inverters, converters and called DC-DC. Application areas are for example the power supply of electrical systems and the drive technology. It helps to reduce the voltage and current harmonics at the same time the lowest possible circuit complexity.

State of the art:

• • Umrichter für frequenzgesteuerte Drehzahlstellung für Asynchron- und Synchronmaschinen
• • Versorgung von Gleichstromantrieben aus dem Wechsel-/Drehstromnetz mit Gleichrichtern oder aus Batterieen mit fester Spannung über Gleichstromsteller
• • Stromversorgung – von elektronischen Systemen, wie PC's – von Bahnanlagen (Bahnumrichter) – FACTS (Flexible AC Transmission Systems) – Einsatz aktiver Filter

The power electronics are used in the field of power supply and drive technology, for example in the following applications:

• • Frequency-controlled speed control inverter for asynchronous and synchronous machines
• • Supply of DC drives from the AC / DC network with rectifiers or from fixed-voltage batteries via DC-DC controllers
• • Power supply - of electronic systems, such as PC's - of railway systems (railway converters) - FACTS (Flexible AC Transmission Systems) - Use of active filters

The Inverters are needed in their different variants from the fixed network sizes voltage, frequency and phasing variable quantities at the load to generate. Here, both voltage and frequency, Phase angle and number of phases are each controlled separately. applications for this are the regulation of drive systems, where the Terminal voltage and frequency must be regulated, the power supply complex equipment, the supply of DC applications the AC mains, as well as the supply of networks with one other frequency (railway network with a frequency of 16.7 Hz).

The Benefits of using power electronics in this area lie in the flexible position of frequency, voltage and current, and the lower costs, losses, the smaller volume, freedom from maintenance, etc. The disadvantage here by the Switching generated voltage and current harmonics.

The Considering the harmonics is both on the part of the electric Network as well as on the part of consumption necessary. On the part of the electrical network must be the RU (power company) to ensure the quality. Thus there are restrictions on the part of the RU for the customers in terms of the maximum permissible supply of harmonics. On the website of the consumer, it is in particular the drive systems that are sensitive respond to harmonics. These are, for example, pendulum moments, resulting in noise pollution and signs of wear represent. To the burden on man and the costs to keep low for maintenance is one possible Harmonics-free energy supply necessary.

The classic two-point converters provide two potentials. Starting from a constant voltage on the intermediate circuit capacitor C _p , the switching elements T ₁ to T _{4 are driven} according to the pattern shown in Table 1 to generate a load voltage. If, for example, the elements T ₁ and T ₄ are activated, then the current flows from the positive pole via T ₁ , the motor, the inductance L and T ₄ to the negative pole. The voltage is therefore positive to the load (motor and inductance). On the other hand, if T ₂ and T ₃ are activated, then the current flows via T ₃ , the inductance, the motor and T ₂ . In this switching state, the voltage U _{d is} negative to the load. The switching states of the valves are shown with 1 (switched on) and 0 (switched off). The harmonics caused by the power electronics can be reduced by the following measures:

1. increase the switching frequency

2. Use of multi-point converters

With an increase in the switching frequency of the components is accompanied at the same time an increase in switching losses. In addition, the permissible switching frequency is limited. When the switching frequency is increased Also, the computing capacity of the controller / control must be increased, since the sampling intervals must be reduced.

One Multi-point inverter can be either one Combination of two-point converters in conjunction with potential separation or by complex power electronic circuits. at the transformer circuits for potential separation is the Material and volume required by the necessary multi-winding transformer very large. Another possibility of potential separation is inherent in regenerative systems (eg photovoltaic) given. In [5] are different topologies of an inverter for isolated power sources (using the example of the regenerative energy sources). This is an unbalanced DC link used to increase the number of potential levels. In [6] a possibility is shown that by means of a Multi-winding transformers generate potential-separated voltage sources to combine. Due to the very expensive potential separation by a multi-winding transformer is disclosed in the hereby incorporated Patent presents a topology that is not based on potential Power sources is dependent. In [7] is based on a topology a cell-based power converter with cells connected in series in the form of H-bridges and intermediate circuit capacitors lying parallel to them describe that by different voltages in the intermediate circuits avoid redundant states. With the same there already shown approach, according to a neutral point topology In contrast, it will be a first step towards elimination the disadvantage that the valves on the entire DC link voltage have to be designed with regard to their stress load, demonstrated.

In [8] is also a multi-point inverter with unbalanced DC link presented. This is a preliminary to the presented here Inverter. By further improvement could be achieved that the diodes provided in [8] are omitted in the extension branches. In addition, a placement of the extension branches is possible on both sides, so that the voltage load of the additional valves further reduced can be.

The Number of points of the inverter refers in this document to the positive (incl. zero) controllable potentials.

With the two-point inverter, the potentials 0 and + U _{d can be} controlled in the positive range. The first stage of the multi-point inverter is the three-point inverter ( 1 ).

und U_d. Die Erhöhung der Anzahl der Punkte ist somit mit einer Erhöhung der Anzahl der Schaltelemente verbunden. In 2 sind zwei Konzepte für Mehr-Punkt-Umrichter mit mehr als drei ansteuerbaren Potentialen dargestellt. Diese Konzepte sind jedoch mit einem erheblichen Aufwand an Bauelementen verbunden.For the three-point inverter, the potentials are 0,

and U _d . The increase in the number of points is thus associated with an increase in the number of switching elements. In 2 Two concepts for multi-point converters with more than three controllable potentials are shown. However, these concepts are associated with a considerable amount of components.

Description of the invention:

In the previous circuits, a balanced DC link with equal voltages and capacitances is used. This is in 1 for the three-point inverter with two identical capacitors. This is abandoned in this invention. Here is an unbalanced DC link application. These capacitors are used with different capacities, which are charged to different voltages. In the higher power range, the DC links are no longer realized with one (or two) single capacitors, but capacitor groups are used. This is due on the one hand by the voltage load as well as by the energy to be stored. The asymmetrical design can be achieved by changing the interconnection of the existing capacitors in such a way that the capacitors are no longer connected in the same number but in a specific ratio to one another (eg 1: 2 for the four-point converter) , The number of capacitors can be kept constant.

Starting from a three-point converter as already described in [2] and [4] ( 1 ), an unbalanced DC link supplies a four-point converter ( 3 ).

By The unbalanced DC link is possible from one Three-point inverter a four-point inverter without additional Generate material costs for the power electronics. In this way, without an increase in the switching frequency the valves achieved an improvement of the harmonic behavior become. A comparison of the achievable grading (symmetrical DC link) with the now accessible (unbalanced DC link) is shown in Table 2.

ausgeführt werden.With regard to the voltage load on the valves, there are switching states in which several blocking elements form a voltage divider which is undefined due to the component properties (manufacturing tolerances, temperature and time dependency). One such case is in 4 shown. In this case, the elements S _1- and S _{2- are} off 3 in the conductive state and are thus shown as a short circuit. The voltage divider D ₂ , S ₃ and S ₄ is defined here only by the parasitic properties of the components. By using high-resistance but defined resistors analogous to 5 can the voltage divider defined in proportion

be executed.

To compensate for the voltage stress of the components, a protective circuit can be used. This is in 5 for the four-point inverter example ohmic executed. For the four-point inverter results in a necessary _{combination of} resistance R _S₄ = 2 · R _S₃ , according to the voltage _load to be set. For the elements S ₁ and S ₂ as well as the elements of the negative half-wave also undefined voltage dividers, which can be determined by this method. With a nominal voltage load of U _S1 = 1 / 3U _ZK and U _S2 = 2 / 3U _ZK , the resistance ratio also becomes 1: 2. The resistors can be designed with high resistance (eg> 100 kΩ) and thus cause negligible power loss. If the reverse current flowing through the diode can no longer be neglected compared to the current flowing through the resistors, the voltage divider must be redetermined.

is the voltage reserve of the components big enough, must also nothing is changed in the arrangement of the valves. is the voltage reserve too low, the components in the species be amended or rearranged that either additional modules are connected in series or the existing series connection by a shift of the connection point is split again. In summary, the stress load remains identical. The resulting stress loads are included in Table 3.

. Die Spannungsbelastungen beim Vier-Punkt-Umrichter teilen sich hingegen in einem Verhältnis von 1 / 3 zu 2 / 3 auf. Ist die Spannungsreserve der Schaltelemente groß genug um auch die 2 / 3U_ZK sicher zu schalten, kann die Schaltung ohne Modifikationen in den Schaltelementen weiter verwendet werden. Anderenfalls kann die Spannungsbelastbarkeit durch ein zusätzliches Schaltelement vergrößert werden. Sind die Zweige S₁, S₃ bzw. D₁ als Reihenschaltung von Schaltelementen ausgeführt, so kann deren Anzahl gegebenenfalls reduziert werden um die auf diese Weise frei werdenden Schaltelemente in den Zweigen S₂, S₄ bzw. D₂ zur Erhöhung der Spannungsbelastbarkeit verwenden zu können.The voltage load of the switching elements is in three-point inverter respectively

, The voltage loads in the four-point inverter, however, split in a ratio of 1/3 to 2/3. If the voltage reserve of the switching elements is large enough to safely switch the 2 / 3U _ZK , the circuit can continue to be used without modifications in the switching elements. Otherwise, the voltage capacity can be increased by an additional switching element. If the branches S ₁ , S ₃ and D _{1 are designed} as a series connection of switching elements, then their number can be reduced if necessary to use the thus released switching elements in the branches S ₂ , S ₄ and D ₂ to increase the voltage rating to be able to.

A Increasing the number of valves goes with an increase the overall performance.

The ratio of the power of the inverter to the number of valves remains constant. In 3 is the first stage of the invention shown. The intermediate circuit voltage is applied to the terminals + or -. This is the connection of DC and inverter. At the terminals AC + or AC- the AC voltage is applied or tapped. Table 4 shows the valves to be controlled for the respective potential stage. This results in a simulated course according to 6 (measured courses in the 7 to 9 ). Since the DC and inverter are identical, only one component is shown at a time.

Become with the four-point inverter, all valves are switchable, so there is the possibility of power supply change in order to distribute the power loss. in this connection However, the problem arises of the voltage load of the valves. This is also above the already mentioned Resistors detachable.

To use additional intermediate stages, a further branch of switching elements is integrated into the circuit. This principle can be extended as desired. In 10 a configuration example for a seven-point converter is shown. The modules used for the extension are circled. Each extension is connected to an additional switching element assembly corresponding to the circled extension. Configuration examples for designing the graduation of the DC link capacitors are included in Table 5 for further expansion stages. In the fifth drive stage, a capacitor division of C ₁ = 2C _x , C ₂ = 6C _x , C ₃ = C _x , C ₄ = 3C _x and C ₅ = C _x , where C _{x represents} the reference capacitance, would make sense. The arrangement of the capacitors is mirror-symmetrical, so that a configuration in the reverse order is possible (C ₅ = 2C _x , C ₄ = 6C _x , C ₃ = C _x , C ₂ = 3C _x and C ₁ = C _x ).

The simulation of the seven-point converter ( 10 ) using the control according to Table 6 11 , A further stage of development results if analogous to the extension of 3 to 10 a further combination of three switching elements per half-bridge are inserted.

The Invention makes it possible with a low cost of materials To design multi-point converters of almost any order. With this invention, it is thus possible the harmonic content significantly reduce.

To compensate for the voltage stress of the components by resistors, as it was already done with the four-point inverter is also possible with the multi-point converters. For this purpose, the valves S ₃ and S _{4 are} considered to be conductive and interpret the voltage stress of the valves by a similar voltage divider. With a setpoint voltage load at the seven-point converter of U _S1 = 2 / 6U _ZK , U _S5 = 3 / 6U _ZK and U _S2 = 1 / 6U _ZK , the voltage divider becomes 2R _S1 = 3R _S5 = R _S2 . For the elements S ₃ and S _{4 there} is a voltage load of 1 / 6U _ZK or 5 / 6U _ZK , which is why the resistors for determining the voltage divider have this ratio (1: 5).

With Help of a unbalanced capacitive DC link There are also possible applications outside the (high) energy technology. At this point let's exemplify the Power supply from PC's mentioned so far by their Switching power supplies a significant burden on the electrical networks of office buildings (and beyond) represent. The DC link can be adjusted so that it provides the different internal voltages according to the grading. The multi-point rectifier ensures that out taken from the electrical network, a sinusoidal current becomes.

• 1. Spannungsbelastung der Ventile; gelöst über Ausgleichswiderstände (5)
• 2. Haltung der unsymmetrischen Zwischenkreisspannung; gelöst über • Steuerung eines Mehr-Punkt-Gleichrichters

The following problems have occurred and been solved:

• 1. voltage load of the valves; solved via balancing resistances ( 5 )
• 2. attitude of the unbalanced DC link voltage; solved via • Control of a multi-point rectifier

By it is the use of a controlled multi-point rectifier possible to control each capacitor group individually. On this way it is possible the voltages of the capacitor groups to maintain their target value. Simultaneously with the multi-point rectifier the current regulation. There is a combination of power (power) - and tension control according to classic model.

bibliography

• [1] Veenstra, M., Investigation and control of a hybrid asymmetric multi-level inverter for mediumvoltage applications, Ecole polytechnique federale de lausanne, 2003
• [2] Jenni, F .; Wüest, D., Control method for self-commutated power converters, Zurich: vdf, university publisher at the ETH, 1995
• [3] Lappe, R .; Conrad, C .; Kronberg, M., power electronics, Berlin: Verlag Technik GmbH, 1991
• [4] Schröder, D., Electric Drives 4, Power Electronic Circuits, Berlin: Springer Verlag Berlin, 1998
• [5] Valderrama-Blavi, H. et al., Grid connected asymmetric full-bridge multilevel inverter, EPE 2003, Toulouse
• [6] Kou, X. et al., Full binary combination scheme for floating voltage source multi-level inverters, Industry Applications Conference, 2002, 37th IAS Annual Meeting, Conference Record, Volume 4, 13-18. 2002
• [7] Abdul Kadir, MN .; Hussein, ZF, Asymmetrical multilevel inverter using ratio-based sources, Power and Energy Conference 2004, PECon 2004 Proceedings National, 29-30 November 2004
• [8th] Frank Grundmann; Jian Xie, circuit for a multi-point converter for the reduction of harmonics, patent application 10 2005 062 374.2-32

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited non-patent literature

• - Veenstra, M., Investigation and control of a hybrid asymmetric multi-level inverter for mediumvoltage applications, Ecole polytechnique federale de lausanne, 2003 [0029]
• - Jenni, F .; Wüest, D., Control method for self-commutated power converters, Zurich: vdf, university publisher at the ETH, 1995 [0029]
• - Lappe, R .; Conrad, C .; Kronberg, M., Power Electronics, Berlin: Verlag Technik GmbH, 1991 [0029]
• - Schröder, D., Electric Drives 4, Power Electronic Circuits, Berlin: Springer Verlag Berlin, 1998 [0029]
• Valderrama-Blavi, H. et al., Grid connected asymmetric full-bridge multilevel inverter, EPE 2003, Toulouse [0029]
• - Kou, X. et al., Full binary combination scheme for floating voltage source multi-level inverters, Industry Applications Conference, 2002, 37th IAS Annual Meeting, Conference Record, Volume 4, 13-18 Oct. 2002 [0029]
• Abdul Kadir, MN .; Hussein, ZF, Asymmetrical multilevel inverter using ratio-based sources, Power and Energy Conference 2004, Pecon 2004 Proceedings National, 29-30 November 2004 [0029]
• - Frank Grundmann; Jian Xie, Circuit for a Multi-Point Inverter for Harmonic Reduction, Patent Application 10 2005 062 374.2-32 [0029]

Claims (4)

Circuit for a multi-point equalization and inverters in which to increase the number of potential levels the voltages in the subcircuits are not all the same size are in one in the NPC (neutral point clamped) topology executed three-point converter between the switches (S1, S1, S2, S2, S3, S3, S4, S4-) is a series circuit of two Switches (S5, S5, S6, S6-) is inserted, where one this switch (S5, S5-) in series with the switches (S1, S1-, S2, S2-, S3, S3-, S4, S4-) of the three-phase converter is located. Circuit according to Claim 1, characterized in that the intermediate circuit voltages are distributed as follows. expansion stage Number of potentials 7 22 + 1 6 17 + 1 5 13 + 1 4 9 + 1 3 6 + 1 2 3 + 1 Circuit according to Claim 1, characterized in that the DC link capacitances are distributed as follows. expansion stage Configuration example for capacitors 7 2, 2, 2, 7, 3, 5, 1 6 1, 4, 4, 4, 2, 1 5 2, 6, 1, 3, 1 4 2, 3, 3, 1 3 2, 3, 1 2 2, 1 Circuit according to Claim 1, characterized in that correspondingly high-impedance resistors are used to compensate for the voltage load on the valves 5 be used.