DE102007014597A1 - Multistage voltage convertor has switching network for selective activation of direct current energy accumulators on voltage system, and control unit for controlling switching network - Google Patents

Abstract

The multistage voltage convertor (1) has a switching network (4) for selective activation of direct current energy accumulators (3) on a voltage system, and a control unit for controlling the switching network. The control unit is provided for determining the voltage level of the output voltage from the detected actual voltages of the direct current energy accumulator obtained by the switching network and for controlling the switching network depending on the detected accessible voltage level. An independent claim is also included for a method for controlling a multistage voltage convertor.

Description

The The invention relates to a multi-stage voltage converter with a Switching network for the selective connection of DC voltage energy storage to a voltage system and to a control unit for control of the switching network.

The The invention further relates to an arrangement of multistage voltage converter and DC energy storage and a method for driving such a multi-stage voltage converter.

to Transformation of electrical energy while controlling the Energy flow in power engineering will be particularly power electronic Circuits used. This will be different types of converters realized. There are AC-AC converters known to AC voltage a first frequency in an AC voltage of a changed second frequency to convert. Furthermore, AC-DC converters are known, by an AC voltage with an input frequency to a DC voltage to rectify to a predetermined voltage level. Vice versa DC-AC inverters are known to be a constant voltage DC Change voltage to an AC voltage with a defined frequency. Furthermore, DC-DC converters are known to have a DC voltage of a first voltage level to a DC voltage with a second To transfer voltage level.

In a voltage source inverter, an AC-DC rectifier and a DC-AC inverter are combined. Such a voltage source converter allows the conversion of an input frequency f ₁ in the output frequency f ₂ and an input amplitude to a desired output amplitude. For this purpose, the voltage applied to the voltage source inverter or the current applied there is rectified by a controlled or uncontrolled rectifier to a defined DC voltage. The energy is latched in a memory and finally reversed to the desired output voltage form at the frequency f ₂ .

alternative this is the execution of a power source inverter known, in which a throttle serves as an energy store.

The Input voltage is usually a three-phase three-phase system with 50 Hz fundamental. For other power grids in some parts of the world the fundamental frequency is 60 Hz. The output voltage of the inverter is also usually one Three-phase three-phase system with an adjustable output voltage and output frequency.

The Today's inverters are mostly as voltage source inverter and executed as a two- or three-point inverter. For this purpose, the terminals of a DC voltage source via switches optionally to each phase of a single- or multi-phase output side Voltage system can be connected. By switching on and off (reciprocal Blocking phases and conducting phases of the valves) by self-guided Valves can reduce the voltages between the connection points of the single- or multi-phase voltage system respectively the value of accept positive DC voltage or negative DC voltage (two-point inverter).

at Selection of a suitable modulation method, i. H. a rule for controlled switching on and off of the valves, can at the output of the inverter a fundamental wave with different pronounced harmonics be measured. Through optimized modulation methods, the Harmonic content minimized.

The Valves are mostly used as semiconductor valves (MOSFET, IGBT, thyristors etc.). Modern IGBTs (bipolar transistor with insulated gate electrode - Insulated Gate Bipolar Transistor) have reverse voltages up to a maximum of 6.5 kV. Should the performance of a Inverter must be increased, so either the electricity or the Voltage can be increased. Often the alternative the higher voltage chosen to the disadvantage of increased material usage, larger copper cross sections, Weight u. a. to meet at large currents. If the input voltage over the critical reverse voltage of a Semiconductor valve is to be increased, it requires a (multiple) series connection of valves or another Topology that sets the intermediate circuit voltage to be blocked to several Distributed valves. There are also combinations of the above Alternatives.

In multilevel inverters, the distribution of the intermediate circuit voltage to several valves is achieved. There are numerous topologies, of which the "Neutral Point Clamp (NPC)" topology, currently ge most common is. In this case, it is possible to apply the voltage value "zero" to the output of the converter in addition to the positive and negative DC voltage, whereby the harmonic content at the output can be considerably reduced by means of suitable modulation methods. Inverters (CC) "and" modular H-bridge inverters (MHB) ".

It There is a need for it, the number of possible output stages from multilevel inverters to further increase the output voltage and to further increase the influence of the harmonics at the output minimize. This leads to NPC and CC topology Commutation problems (low-inductive commutation branches) in the individual branches and voltage balance problems. modular H-bridge inverters do not have these disadvantages.

Multilevel inverter have the further advantage of being more readily available and cheaper low-voltage components used can be. Modular multilevel inverters consist of a plurality of each of a voltage source and a switch assembly formed modules, at the output of a positive or negative if necessary DC voltage or the voltage "zero" is applied.

When Voltage sources can be DC voltage sources, such as batteries, Solar cell assembly, fuel cells, etc. are used.

Out US 5,625,545 is also known to use a rectified from a single-phase or multi-phase AC voltage system and smoothed to a capacitor DC voltage.

DE 101 03 031 A1 discloses the use of a capacitor in conjunction with appropriate measures such. B. adapted modulation method, as a DC voltage source. Here, the control method must also regulate the charge balance of the capacitors.

at become the modular inverters disclosed in the cited document to realize the control the module voltages as constant considered. Especially with rectified AC or three-phase systems The module capacitors have a large capacity have to close to those expected by the control or regulation To achieve constant module voltages, since the power removed with double output frequency pulses.

US 6,005,788 discloses a modular inverter in which a maximum number of voltages at the output is also produced assuming constant module voltages. For this purpose, modules with extremely different dielectric strength are used. However, an asymmetry in the module voltages also causes an asymmetry in the energy extraction from the different modules. In addition, the different voltage distribution and thus also different energetic design of the switch assemblies and energy sources of disadvantage.

US 6,166,513 discloses a four-quadrant inverter for AC powering an electric drive from an AC power grid having a rectifier and an inverter and intermediate capacitors.

outgoing It is an object of the present invention to provide an improved to create multistage voltage converter, without big Material overhead improved quality of the output voltage having.

The Task becomes with the multilevel voltage converter of the beginning mentioned type achieved in that the control unit for Determining the detected currently provided voltages reach the DC energy storage with the switching network Voltage levels of the output voltage and to control the switching network depending on the determined achievable voltage levels is set up.

By this respectively currently carried out evaluation of by Combination of at least slightly varying over time Voltages of the DC energy storage achievable voltage levels and Selection of a switching state as a function of these currently achievable voltage levels, the variation of the voltage levels be used for the control, which is through the over the Time occurring voltage fluctuations of the DC energy storage results. In contrast to the previously known methods thus the different and time varying output voltages the modules (DC energy storage) as parameters of the controller used.

Instead of the theoretically possible, ideally assumed constant Voltage of the individual modules according to the invention actual output voltages of the modules in the modulation considered. For this purpose, the module voltages are recorded and processed to a desired setpoint voltage of multistage voltage converter the corresponding switching state to search.

There the operational voltage fluctuations can be used specifically, these can be present anyway Variations are greater than conventional Inverters without disturbing the operation of the inverter. This has the advantage that in particular the capacitors of the modules smaller can be dimensioned, which has advantages in volume, cost, Weight, error stress etc. brings with it.

Preferably is the multi-stage voltage converter for use in a single or multiphase voltage system, preferably in a three-phase Voltage system, set up. The switching network is designed in this way that it has a single or multi-phase AC voltage on the output side in the voltage system, z. B. an alternating voltage network, feed or can exchange energy with such.

Preferably is a plurality for each phase of the AC voltage network of DC voltage energy storage with associated switch arrangements connected in series. The switching arrangement of the individual modules form then together the switching network that is controlled by the control unit appropriate manner depending on the actual DC voltages of the DC energy storage is controlled.

In a preferred embodiment, the rated voltages the same amount of DC energy storage. The individual modules of the multistage voltage converter are thus in their design variables current and voltage equal. This offers advantages in the production and spare parts inventory.

One The multi-stage inverter described above forms together with the DC voltage energy store an arrangement. As DC voltage sources can in a conventional manner batteries, solar cell assemblies, Fuel cells, capacitors or the like used become.

The Arrangement also preferably has a connected to the control unit Voltage detection unit for detecting the DC voltage energy storage currently provided voltages.

• – Detektieren der von den mit dem Schaltnetzwerk verbundenen Gleichspannungsenergiespeichern jeweils aktuell bereitgestellten Spannungen,
• – Ermitteln der aus den detektierten aktuell bereitgestellten Spannungen mit dem Schaltnetzwerk erreichbaren Spannungsniveaus der Ausgangsspannung und
• – Ansteuern des Schaltnetzwerkes in Abhängigkeit von den ermittelten erreichbaren Spannungsniveaus.

The object is further achieved by the method of the type mentioned by the steps

• Detecting the DC voltage energy stores connected to the switching network, in each case currently provided voltages,
• Determining the voltage levels of the output voltage which can be reached from the detected currently provided voltages with the switching network;
• - Control of the switching network as a function of the determined achievable voltage levels.

The achievable as a measure for controlling the switching network achievable Voltage level can be selected by selecting one closest to a desired voltage level coming voltage value be determined from the achievable voltage levels. This can z. B. time-discrete. It is also conceivable, above and below a desired voltage level (adjacent or farther) to select attainable voltage levels, The control of the switching network is then taking into account the selected voltage levels one behind the other time-multiplexed to the desired voltage level to reach as accurately as possible.

advantageous Embodiments are described in the subclaims.

The The invention will be described below with reference to the accompanying drawings exemplified in more detail. Show it:

1 Block diagram of a three-phase modular multistage voltage converter;

2 - Circuit diagram of a switch arrangement for providing three possible output voltages after US 5,625,545 ;

3 - Diagram of an example of at a time t ₁ with the current DC voltages of the DC voltage sources realizable output voltages of a multi-stage voltage converter;

4 - Diagram of a time t ₂ with the current DC voltages of the DC voltage sources realizable output voltages U ₁ ;

5 - Block diagram of a three-phase modular voltage converter according to DE 101 03 031 A1

6 - Switch arrangement for providing two possible output voltages.

1 shows a block diagram of a three-phase, modular, multistage voltage converter 1 detect. The voltage converter 1 has a number n of DC modules for each phase A, B, C 2 , each a DC voltage source 3 and switch assembly 4 exhibit.

Each of the modules provides an output voltage U _A1 , U _A2 ..., U _An ; U _B1 , U _B2 , ... U _Bn ; U _C1 , U _C2 , ... U _Cn as a function of the respective position of the switches of the associated switch arrangements SA1, SA2 ... SAn _I ; SB1, SB2 ... SBn, SC1, SC2 ... SCn and the respective DC voltage of U _Ad1 , U _Ad2 ..., U _Adn ; U _BD1 , U _BD2 ..., U _BDn ; U _Cd1 , U _Cd2 ..., U _{Cdn of} the respective DC voltage source 3 to disposal.

2 shows a circuit diagram of a switch arrangement with three possible output voltages. Here are two blocks of two switches in series 5a . 5b ; 5c . 5d , each with anti-parallel diodes 6a . 6b . 6c . 6d are provided. The output voltage U _A is applied between the two connection points of the respective series circuits.

The state S _{modul of} the switch arrangement determines the output voltage U _{A of} the module. Each state S _module is assigned an internal switch state, which realizes the desired output voltage U _A in the terminals of the module. The possible switch states are as follows: S _module U _A 0 0 Module of FIGS. 2 and 6 +1 + U _d Module of FIGS. 2 and 6 -1 -U _d Module from FIG. 2

The output voltage U _{a of} the module is thus calculated from the current voltage U _{d of} the voltage source and the module state S _modul .

The respective phase voltage U ₁ , U ₂ , U ₃ can now from the sum of the individual module output voltages U _A1 , U _A2 ..., U _An ; U _B1 , U _B2 ..., U _Bn ; U _C1 , U _C2 ..., U _Cn are calculated as follows: U 1 = U A1 + U A2 + U A3 + ... + U At = S SA1 × U Ad1 + S SA2 × U Ad2 + ... + S SAn × U adn U 2 = U B1 + U B2 + U B3 + ... + U Bn = S SB1 × U Bd1 + S SB2 × U Bd2 + ... + S SBn × U vols U 3 = U C1 + U C2 + U C3 + ... + U cn = S SC1 × U Cd1 + S SC2 × U Cd2 + ... + S SCn × U Cdn

The module voltages U _Ydx need not be identical. The voltages are subject to a natural voltage fluctuation. On the other hand, it is also possible to selectively influence the individual module voltages in order to be able to realize a desired number and level of output voltage levels.

A single-phase structure with n-modules has a total of 3 ⁿ different switching states. Thus 27 switching states are available for three modules. With identical constant DC link voltages, a maximum of 2 * n + 1 different phase voltages U ₁ from the inverter 1 to be generated. Not every one of the 3 ⁿ switching states leads to a different output voltage. With variations in the module voltages, the number of possible output voltages can be increased in contrast.

The time profile of the DC voltage U _d (t) of the DC voltage source of a module is dependent on the realization of the voltage source, the load and other parameters. If, for example, the time profile of the output voltage U _d (t) of a battery is considered, this is usually over a short time tervall considered to be constant. Over a longer period of time, the battery voltage will be reduced by continuous energy extraction. In the event that a capacitor is used as the energy source, which is constantly fed via a rectified AC or three-phase voltage system, a voltage ripple of z. B. the double or six times feeding frequency to watch. Furthermore, a fluctuation with double output frequency can be observed because of the single-phase energy extraction. Considered over a long period of time, the module voltage will change depending on the feeding voltage and the load, e.g. B. at a fluctuation of the mains voltage. The amount of voltage ripple in this case, of course, depends on the size of the capacitor. Similar considerations may be made in the other energy sources such as fuel cell, solar cell, etc.

By evaluating the temporal fluctuations of the DC voltages U _Adi , U _Bdi , U _{Cdi of} the modules and using them as an influencing variable for driving the switching network, the actual possible output voltages are taken into account in the modulation and not only the theoretically possible with an idealized assumed constant voltage. The present at a time DC voltages U _Adi , U _Bdi , U _Cdi with i = 1, ..., n are detected and processed by means of known _{per se} optimization method to use these DC voltages to a desired setpoint voltage to the corresponding switching state of the switching network search.

It but also voltage differences of the same order of magnitude be adjusted specifically to an improved output voltage form or to allow a lower switching frequency.

3 allows a diagram of realizable at a time t ₁ output voltages U ₁ detect for each of 27 possible switching states. The diagram is based on a single-phase design with three modules and 27 different switching states. On the abscissa the 27 different switching states are plotted and on the ordinate a normalized output voltage is shown. The DC voltages U _Ad1 , U _Ad2 and U _Ad3 actually available at time t ₁ are: U Ad1 = 1.1 × U DC U Ad2 = 1 × U DC U Ad3 = 0.92 × U DC

The factors 1,1, 1 and 0, 92 are thus the deviations of the actual DC voltages from the defined nominal voltages U _{DC of} the DC voltage sources.

Due to the above-described effects, such as discharge of capacitors, batteries, etc. are at a different time t ₂ other DC voltages U _Adx DC _sources 3 available. Thus, the characteristic of the realizable output voltages U _{1 has} shifted. For example, at another time t ₂ , the stress distribution is as follows: U Ad1 = 1.2 × U DC U Ad2 = 1 × U DC U Ad3 = 0.8 × U DC

The Niveuas of the output voltage which can be scanned at time t ₂ are in 4 shown.

Depending on the desired output voltage, the desired switching state for each module and thus for each switch can now be determined at any instant t with the information of the actual DC voltages U _Ai , U _Bi , U _{Ci of} the modules.

The driving of the switching network can provide a constant switching state during a sampling interval. After the current DC voltages of the DC voltage sources have been measured and a realizable phase voltage vector has been formed, the phase voltage vector is combined or multiplied with all 3 ⁿ switching states in order to calculate all realizable output voltages of each phase of the voltage converter. The result is a vector for each phase containing all possible output voltages. In order to obtain the corresponding switching state for a given output voltage, the suitable switching state for each switch arrangement of the modules will be described by means of a table Right. To obtain the transistor states for the individual switch arrangements, another table is used.

in Abhängigkeit von der Schaltfrequenz f_C, den Spannungspegel V_ab, V_low und der Referenzspannung V_Ref berechnet werden.To control the switching network z. B. but it is also conceivable to use a pulse width modulation. For this purpose, two output voltage levels of the currently realizable output voltages are evaluated, which come closest to the reference voltage. The voltage levels are switched to the output. At the beginning of each switching cycle of length 1 / f _C , the output is switched to the upper voltage level V _off . Later, at a time t _PWM, the output voltage is switched to the lower voltage level V _low . The switching time t _pwm can be determined by the following equation

depending on the switching frequency f _C , the voltage level V _ab , V _low and the reference voltage V _{Ref are} calculated.

The control method presented here can also be applied to topologies DE 101 03 031 , please refer 5 , be applied. In this topology, the switch arrangements can after 2 or 6 will be realized.

6 shows a switch diagram of a switch arrangement with two possible output signals. It becomes clear that the DC voltage U _{d of} a module in two switches in series 5a . 5b with antiparallel diodes 6a . 6b connected. At the connection point of the switches connected in series 5a . 5b a connection for the output voltage U _{a is} provided.

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 patent literature

• US 5625545 [0014, 0034]
• - DE 10103031 A1 [0015, 0037]
• US Pat. No. 6005788 [0017]
• US 6166513 [0018]
• - DE 10103031 [0057]

Claims (15)

Multistage voltage converter ( 1 ) with a switching network ( 4 ) for the selective connection of DC voltage energy storage devices ( 3 ) to a voltage system and with a control unit for controlling the switching network ( 4 ), characterized in that the control unit for determining the currently provided voltages (U _Adi , U _Bdi , U _Cdi ) of the DC _{energy storage} ( 3 ) with the switching network (4) achievable voltage levels of the output voltage and for driving the switching network ( 4 ) is set up as a function of the ascertained achievable voltage levels. Multistage voltage converter ( 1 ) according to claim 1, characterized in that the switching network ( 4 ) on the output side for feeding a single- or multi-phase AC voltage (U ₁ , U ₂ , U ₃ ) is set up in an AC voltage network. Multistage voltage converter ( 1 ) according to claim 1 or 2, characterized in that the switching network ( 4 ) is set up on the output side for single or multi-phase energy exchange with the voltage system. Multistage voltage converter ( 1 ) according to claim 2 or 3, characterized in that for each phase of the AC voltage network a plurality of DC voltage energy storage ( 3 ) are connected in series via associated switch arrangements, the switch arrangements comprising the switching network ( 4 ) form. Multistage voltage converter ( 1 ) according to one of the preceding claims, characterized in that the DC voltage energy storage ( 3 ) have defined nominal voltages (U _D ). Multistage voltage converter ( 1 ) according to claim 5, characterized in that the nominal voltages (U _D ) of the plurality of DC voltage energy stores ( 3 ) are the same. Arrangement according to one of the preceding claims, characterized in that the DC voltage energy storage ( 3 ) Batteries, solar cell assemblies, fuel cells or capacitors are. Arrangement according to one of the preceding claims, characterized by a voltage detection unit for the detection of the DC voltage energy stores ( 3 ) currently provided voltages (U _Adi , U _Bdi , U _Cdi ). Arrangement of a multistage voltage converter ( 1 ) according to one of the preceding claims and a plurality of with the switching network ( 4 ) connected DC voltage energy storage ( 3 ). Method for controlling a multistage voltage converter ( 1 ) according to one of claims 1 to 8, characterized by - detecting the of the with the switching network ( 4 ) connected DC voltage energy storage ( 3 ) currently provided voltages (U _Adi , U _Bdi , U _Cdi ), - Determining the detected from the detected currently provided voltages (U _Adi , U _Bdi , U _Cdi ) with the switching network ( 4 ) achievable voltage levels of the output voltage and - driving the switching network ( 4 ) as a function of the determined achievable voltage levels. Method according to claim 10, characterized by feeding one by activation of the switching network ( 4 ) in response to the determined achievable voltage levels generated single- or multi-phase AC voltage (U ₁ , U ₂ , U ₃ ) in the designed as AC voltage system voltage system. Method according to one of Claims 10 to 11, characterized by selecting a voltage value coming closest to a desired voltage level from the achievable voltage levels as for driving the switching network ( 4 ) used measure. Method according to one of claims 10 to 12, characterized by selecting achievable voltage levels above and below a desired voltage level and driving the switching network ( 4 ) taking into account the selected voltage levels one behind the other in time multiplexer in time division in order to achieve the desired voltage level as accurately as possible. Method according to one of Claims 10 to 13, characterized by optimization of the activation of the switching network ( 4 ) with a vector of switching functions as a function of predetermined influencing parameters. A method according to claim 14, characterized in that influencing parameters, the charge balance, the voltage levels of the individual DC voltage energy storage ( 3 ), the energy loss of the individual DC energy storage ( 3 ), defined limit states and / or the future behavior of the voltage converter ( 1 ) are characteristic predictive parameters.