WO2012089361A2 - System comprising an electric machine - Google Patents

Abstract

The invention relates to a system comprising an n-phase electric machine (1), which can be controlled with the aid of a controllable first energy store (2) and is supplied with electric power. Said controllable energy store (2) comprises n parallel power supply branches (3-1, 3-2, 3-3) which can be connected to a reference bus (T-) and to one respective phase (U, V, W) of the electric machine (1). An intermediate circuit (10) can be coupled to a neutral point (S) of the electric machine (1) and to the reference bus (T-). According to an operational method, the supply of power from electric consumers (12;13) connected directly or indirectly to the intermediate circuit (10) is carried out by increasing or decreasing the voltages on the power supply branches (3-1, 3-2, 3-3) respectively to a value higher or lower than an actual voltage value required for supplying power to the electric machine (1).

Description

 Description title

 System with an electric machine

The invention relates to a system with an electrical machine, which is controlled by means of a controllable first energy storage and supplied with electrical energy, and a method for operating the system according to the invention.

State of the art

It is becoming apparent that in the future both stationary applications, e.g.

Wind turbines, as well as in vehicles such as hybrid or electric vehicles, increasingly electronic systems are used that combine new energy storage technologies with electric drive technology. In conventional applications, an electric machine, e.g. is designed as a rotating field machine, controlled by a converter in the form of an inverter. Characteristic of such systems is a so-called DC voltage intermediate circuit, via which an energy store, usually a battery, is connected to the DC side of the inverter. In order to meet the power and energy requirements of each application, multiple battery cells are connected in series. Since the power provided by such an energy store must flow through all the battery cells and a battery cell can only conduct a limited current, battery cells are often additionally connected in parallel in order to increase the maximum current.

The series connection of several battery cells in addition to a high total voltage involves the problem that the entire energy storage fails if a single battery cell fails, because then no battery power can flow. Such a failure of the energy storage can lead to a failure of the entire system. In a vehicle, failure of the traction battery can result in the vehicle "stalling". For other applications, such as the rotor blade adjustment of

Wind turbines, it may in unfavorable conditions, such as strong Wnd, even come to safety-threatening situations. Therefore, it is always high Reliability of the energy storage, where "reliability" is the ability of a system to work for a given time error-free.

In the older applications DE 10 2010 027857 and DE 10 2010 027861 batteries are described with multiple battery module strands, which directly to an electrical

Machine can be connected. The battery module strands in this case have a plurality of battery modules connected in series, each battery module having at least one battery cell and an associated controllable coupling unit, which allows depending on control signals to interrupt the respective battery module strand or to bridge the respectively associated at least one battery cell or each assigned to switch at least one battery cell in the respective battery module string. By suitable activation of the coupling units, e.g. with the help of pulse width modulation, suitable phase signals for controlling the electrical machine can be provided, so that on a separate

Pulse inverter can be dispensed with. The required for controlling the electrical machine pulse inverter is so to speak integrated into the battery. For purposes of disclosure, these two earlier applications are fully incorporated into the present application. In contrast to conventional systems in which an electrical machine is controlled by an inverter and is supplied with electrical energy by a separate electrical energy store, the batteries described in the earlier applications DE 10 2010 027857 and DE 10 2010 027861 do not have a constant DC voltage available, so that such batteries are not readily available in conventional power grids, such as Bordnetze an electric or hybrid vehicle, can be integrated.

If such batteries are to be used e.g. in electric vehicles, it should also be noted that battery technologies available today

Significantly limit electric vehicles.

Disclosure of the invention

The present invention provides a system with an n-phase electric machine, with n> 1, which is controlled by means of a controllable first energy storage and supplied with electrical energy, wherein the controllable first energy storage having n parallel power supply branches. The energy supply branches are on the one hand with a reference rail and on the other hand connected to a respective phase of the electrical machine. An intermediate circuit can be coupled on the one hand with a neutral point of the electric machine and on the other hand with the reference rail. The present invention also provides a method of operating a

According to the invention, the voltages at the power supply branches are respectively increased to a value which is above a voltage value currently required for the power supply of the electrical machine for the purpose of supplying energy directly or indirectly to the intermediate circuit connected electrical loads (10, 10 ').

Advantages of the invention

The invention is based on the basic idea of coupling to the neutral point of the electric machine a DC link via which electrical consumers, e.g. Consumers in a vehicle electrical system, either directly or indirectly, e.g. can be supplied via a DC-DC converter, with a DC voltage, which on the other hand, however, can also be used to connect additional energy sources with the system, which can support the controllable first energy storage in the supply of electrical energy and / or

 Load energy storage cells of the controllable first energy storage. The system according to the invention is characterized in particular by an easily realizable and therefore cost-effective circuit topology. In conventional control of the controllable first energy storage is located on the

Star point of the electric machine on an average potential equal to the potential of the reference rail on. However, it is possible to shift this potential by the voltages at the power supply branches of the controllable first

Energy storage can be increased or decreased respectively to a value which above or below a currently required for the power supply of the electric machine

Voltage value is.

Due to the control of the controllable first energy storage with

Pulse width modulation result at the star point positive and negative, rectangular voltage blocks with the drive frequency, for example 3-6 kHz. These can, however simply with the help of a filter, which between the electrical machine and the

Reference rail on the one hand and the DC link on the other hand is connected

be smoothed so that an at least approximately constant

DC link voltage results. The filter has to be designed with a correspondingly low corner frequency.

According to one embodiment of the invention, the intermediate circuit is a first

Downstream of DC voltage converter, which adapts a first voltage level of the intermediate circuit to a second voltage level of a second energy storage. From the second energy storage then electrical consumers with a DC voltage at the second voltage level can be supplied. In this way, a two-voltage power supply network can be realized.

If the second energy storage is designed as a low-voltage energy storage, this must typically for safety reasons galvanically from the high or

Medium voltage to be separated on the DC link. In this case, the first

DC-DC converter designed as a DC-DC converter with galvanic isolation. Between the electric machine and the reference rail on the one hand and the

 On the other hand, a second DC-DC converter, which adapts a third voltage level at the neutral point of the electric machine and the first voltage level of the DC link to one another, can also be connected. Thus, the DC-DC converter can e.g. be configured as a boost converter, which the

Increased voltage level of the DC link, which also consumers with higher

Voltage level can be supplied from the DC link.

If the second DC-DC converter is bidirectional, it can be used in the reverse direction as a buck converter for charging the controllable first energy store.

According to a further embodiment, the intermediate circuit can be connected directly or indirectly with at least one additional direct current source. By coupling an additional energy source, it is possible to provide additional electrical energy available and in this way, for example, the range of

Considerably extend the life of electric vehicles. The energy provided can be Depending on the current operating state of the controllable energy storage and the electrical machine either for charging energy storage cells of the controllable energy source or to support the controllable energy source in the

Power supply of the electric machine can be used.

In this case, the DC link can be coupled to the star point of the electric machine, for example via a boost converter directed from the DC link to the electric machine. The injected current can then over the

Duty cycle of the boost converter can be adjusted. The regulation of the controllable first energy storage device sets the correct voltages at each point in time

Stages of the electric machine safely. Depending on the current instantaneous value of the phase current of the electric machine, current thereby flows from the step-up converter to support the controllable first energy store in the electric machine or for charging into the controllable first energy store. The topology of

Step-up converter is also advantageous since the intermediate circuit voltage can be below the maximum phase voltage here. A diode of the boost converter prevents a reverse current in the DC link. In this arrangement, the supply of all energy supply branches of the controllable first energy storage takes place simultaneously. A particularly efficient high-input power supply can be achieved when the DC source includes a range extender with a generator driven by an internal combustion engine

Generator can be designed as a DC generator or as an alternator with downstream rectifier.

Alternatively or additionally, however, any other direct current sources, such as e.g. Fuel cells, photovoltaic modules or wind turbines, are used. Basically, any number of DC sources in any

Embodiments be provided.

For charging the controllable first energy storage device, however, it is also possible to connect a charging device to the intermediate circuit, which connects the intermediate circuit to an external energy supply network, in particular a public electricity network. A further embodiment of the invention provides that the

Energieversorgungszweige the controllable energy storage in each case at least two in Have row connected energy storage modules, which each comprise at least one electrical energy storage cell with an associated controllable coupling unit, which in response to control signals each associated

Energy storage cells bridged or switches the respective associated energy storage cells in the respective power supply branch. By such a configuration, the dual function of the controllable energy storage, namely control and power supply of the electric machine can be realized in a particularly simple and efficient way. The increase or decrease of the voltages at the energy supply branches provided for shifting the voltage potential at the neutral point can be achieved in such an embodiment of the controllable first energy store in that the energy storage cells each have one or more

Energy storage modules of each power supply branch by appropriate control of the associated coupling units permanently or clocked with positive or negative polarity in the respective power supply branch are switched. The actual power supply and control function for the electrical machine can be ensured by the other energy storage modules. However, this reduces the usable for the motorized operation of the electric machine

Voltage swing. This can be circumvented by adding one or more additional modules per power supply branch for the purpose of feeding energy into the system

DC bus be kept.

The connected energy storage modules of a power supply branch can also be changed during operation to ensure a uniform load. As soon as a load current is drawn from the star point, the sinusoidal currents in the power supply branches shift upwards by one third of the magnitude of this load current. It is also possible to directly use the voltage at the star point of the electric machine, without extra energy storage modules in the

To add energy supply branches. If the coupling unit of the controllable first energy store is configured as a full bridge, positive and negative, rectangular voltage blocks with the drive frequency occur at the star point. In

Operating areas with only one clocked energy storage module, these have an amplitude of one third of the module voltage. When using several Energy storage modules, the voltage can also be higher, which depends in particular on the driving method used. If now between the electric machine and the reference rail on the one hand and the DC link on the other hand a

Rectifier unit, in particular a one- or full-wave rectification is connected, so the resulting positive potential can be used directly. The possibility of connecting a DC-DC converter, e.g. in the form of a boost converter, remains unaffected. If the coupling units are configured as half bridges, only positive potentials occur at the neutral point, so that the rectification can be dispensed with.

Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

Brief description of the drawings

Show it:

Fig. 1 is a schematic representation of a first embodiment of a

 system according to the invention,

Fig. 2 is a schematic representation of a second embodiment of a

 system according to the invention,

Fig. 3 is a schematic representation of a third embodiment of a

 system according to the invention,

Fig. 4 is a schematic representation of a fourth embodiment of a

 inventive system and

Fig. 5 is a schematic representation of a fifth embodiment of a

 inventive system.

Figures 1 to 5 show schematic representations of embodiments of a system according to the invention. To a three-phase electric machine 1, a controllable first energy storage 2 is connected. The controllable first

Energy storage 2 comprises three power supply branches 3-1, 3-2 and 3-3, which on the one hand with a reference potential T- (reference rail), which in the illustrated Embodiments with respect to phases U, V, W of the electric machine performs an average potential, and on the other hand in each case with the individual phases U, V, W of the electric machine 1 are connected. Each of the power supply branches 3-1, 3-2 and 3-3 has m series-connected energy storage modules 4-1 1 to 4-1m and 4-21 to 4-2m and 4-31 to 4-3m, respectively 2. The energy storage modules 4, in turn, each comprise a plurality of series-connected electrical energy storage cells which, for reasons of clarity, are provided only in the energy supply branch 3-3 connected to the phase W of the electric machine 1 with reference numerals 5-31 to 5-3m. The energy storage modules 4 further comprise one each

Coupling unit, which is associated with the energy storage cells 5 of the respective energy storage module 4. For reasons of clarity, the coupling units are also provided only in the power supply branch 3-3 with reference numerals 6-31 to 6-3m. In the illustrated embodiments, the coupling units 6 are each formed by four controllable switching elements 7-31 1, 7-312, 7-313 and 7-314 to 7-3m1, 7- 3m2, 7-3m3 and 7-3m4, which in shape a full bridge are connected. The switching elements may be used as power semiconductor switches, e.g. in the form of IGBTs (Insulated Gate Bipolar Transistors) or as MOSFETs (Metal Oxide Semiconductor Field-Effect Transistors). The coupling units 6 make it possible to interrupt the respective power supply branch 3 by opening all switching elements 7 of a coupling unit 6.

Alternatively, the energy storage cells 5 can either be bridged by closing two of the switching elements 7 of a coupling unit 6, e.g.

Close the switches 7-312 and 7-314 or in the respective

Power supply branch 3 are switched, for. Close the switches 7-312 and 7-313.

The total output voltages of the power supply branches 3-1 to 3-3

are determined by the respective switching state of the controllable

Switching elements 7 of the coupling units 6 and can be adjusted in stages. The

Staging results depending on the voltage of the individual

Energy storage modules 4. Starting from the preferred embodiment

from similarly designed energy storage modules 4, the result is a maximum possible total output voltage from the voltage of a single

Energy storage module 4 times the number m of per energy supply branch 3 in series energy storage modules. 4 The coupling units 6 thus allow the phases U, V, W of the electric machine 1 either against a high reference potential or a low

Switching reference potential and can thus fulfill the function of a known inverter. Thus, the power and operating mode of the electric machine 1 can be controlled by the controllable first energy store 2 with suitable control of the coupling units 6. The controllable first energy storage 2 thus fulfills a dual function insofar as on the one hand it serves, on the other hand, the electric power supply but also the control of the electric machine 1.

The electric machine 1 has stator windings 8-U, 8-V and 8-W, which are connected in a known manner in star connection with each other.

The electric machine 1 is designed as a three-phase three-phase machine in the illustrated embodiments, but may also have fewer or more than three phases. Of course, the number of power supply branches 3 in the controllable first energy store 2 also depends on the number of phases of the electrical machine. In the exemplary embodiments illustrated, each energy storage module 4 has a plurality of energy storage cells 5 connected in series. The

Energy storage modules 4 may alternatively have only a single energy storage cell or parallel energy storage cells.

In the illustrated embodiments, the coupling units 6 are each formed by four controllable switching elements 7 in the form of a full bridge, which also offers the possibility of a voltage reversal at the output of the energy storage module .. The coupling units 6 can also be realized by more or less controllable switching elements, as long as the necessary functions

(Bridging the power supply cells and switching the

Energy supply cells in the power supply branch) can be realized. In particular, the coupling units can also be designed in the form of Hall bridges. Such embodiments are shown by way of example in the older applications DE 10 2010 027857 and DE 10 2010 027861. To a star point S of the electric machine 1 on the one hand and the reference rail T- on the other hand, a DC link (DC intermediate circuit) 10 in the form of a DC link capacitor 10 ', connected (Figure 1). In conventional control of the controllable first energy storage 2 is located at the neutral point S, an average potential of T-. However, this potential can be shifted by the energy storage cells 5 each having one or more energy storage modules 4 of each energy supply branch 3

corresponding control of the associated coupling units 6 permanently or clocked with positive or negative polarity in the respective power supply branch 3 are switched. The voltages at the power supply branches 3 are thus respectively increased or decreased to a value which is above or below a voltage value currently required for the power supply of the electric machine 1. The actual function of the controllable first energy store 2 can be ensured by the remaining energy storage modules 4. In order to avoid a reduction of the usable for the motorized operation of the electric machine voltage swing, at least one additional energy storage module 4 can be provided per energy supply branch, which serves specifically for the purpose of energy supply to the intermediate circuit 10. In Figure 1 are such

"Additional modules" indicated by the block 9.

The connected to the power supply to the DC link 10

Energy storage modules 4 of a power supply branch 3 can also be changed during operation in order to ensure a uniform loading of the energy storage cells 4. As soon as a load current is drawn from the neutral point S, the sinusoidal currents in the power supply branches 3 are shifted upwards by in each case one third of the magnitude of this load current. Due to the control of the controllable first energy storage device 2 with pulse width modulation arise at the neutral point S positive and negative, rectangular voltage blocks with the drive frequency. These can be easily smoothed by a filter 11 with a low corner frequency, which is connected between the electric machine 1 and the reference rail T- on the one hand and the DC link 10 on the other.

To the DC link 10 can directly medium voltage consumers 12th

are coupled, which are then supplied from the DC link 10 with electrical energy. In order also to supply energy to low-voltage consumers 13 to enable the DC link 10, a first DC-DC converter 14 is connected downstream, which adjusts a first medium voltage level of the DC link 10 to a second low-voltage level of a second energy storage device 15. Low-voltage consumers 12 which can be supplied with electrical energy from this can then be directly coupled to the second energy store 15.

Is, e.g. For safety reasons, galvanic isolation of the low-voltage network from the intermediate circuit 10 is required, the first DC-DC converter can also be designed with galvanic isolation.

FIG. 2 shows schematically a second embodiment of a system according to the invention. This differs from the first embodiment in that the filter 1 1 is replaced by a second DC-DC converter 20, which is formed in the illustrated embodiment as a boost converter. This offers the

Possibility to provide a higher voltage level at the DC link 10 than at

Star point S, so that from the intermediate circuit 10, for. directly high-voltage consumers 12 'can be powered.

If a diode 21 of the boost converter 20 of Figure 2 by a controllable

Substitutes switching element, a bidirectional converter 30 is realized, which can be shared in the reverse direction as a buck converter for charging the energy storage cells 5 of the controllable first energy storage device 2 (see Figure 3). In this case, for charging e.g. a charger 31 are connected to the intermediate circuit 10, which connects the intermediate circuit 10 with an external power supply network 32, in particular a public power grid. The charger has e.g. a line filter 33, a downstream power factor correction 34 - often referred to as Power Factor Correction or Power Factor Compensation (PFC) - and optionally also a further DC-DC converter 35 on. The

Power factor correction 34 regulates the recorded mains current by means of a circuit breaker to a sinusoidal course and thereby minimizes its

Harmonic content. Furthermore, mains voltage fluctuations can also occur

be compensated. A typical implementation of a PFC circuit includes a bridge rectifier and a subsequent boost converter stage. Alternatively to an increase in the setting at the star point S.

Voltage potential by active connection of energy storage cells 5 additional Energy storage modules 4, the voltage potential can also be used directly, that is, without switching additional energy storage cells 5 are used. If the coupling units 6 are designed as full bridges, so positive and negative, rectangular voltage blocks occur at the star point S with the drive frequency. In operating areas with only one clocked energy storage module 4, these have an amplitude of one third of the module voltage. When using several

Energy storage modules can also be subject to higher voltages depending on the particular driving method. Figure 4 shows schematically a fourth embodiment of the invention, which allows the mentioned immediate use of the voltage potential at the neutral point S. This embodiment differs from the first embodiment shown in Figure 1 only in that between the filter 11 and the

electric machine 1, a rectifier unit 40 is connected. In the illustrated embodiment, the rectifier unit 40 is a full-wave rectifier

designed. However, a design as a disposable rectifier is conceivable. The possibility of connecting a further DC-DC converter, e.g. in the form of a jack-up, remains unaffected. Are the coupling units 6 configured as half bridges, occur at the neutral point S only positive potentials, so that on the

Rectifier unit can be dispensed with.

FIG. 5 shows a further embodiment of the invention. In this case, on the one hand between the neutral point S of the electric machine 1 and the DC link 10 a

Boost converter 50 switched. On the other hand, the intermediate circuit 10 with a

DC power source 51 connected. The DC power source 51 comprises a range extender 52 known per se with an AC generator 54 driven by an internal combustion engine 53, to which a rectifier 55 is connected downstream. As an alternative to an alternator 54 with downstream rectifier 55, a DC generator may also be provided. Alternatively, or in addition to range extender 52, any other DC sources, such as those shown in FIG.

Fuel cells and / or photovoltaic modules are connected to the intermediate circuit 10.

The current fed into the star point S can be controlled by the duty cycle of the

Hochsetzstellers 50 are set. The scheme of the taxable first

Energy storage 2 sets at each time the correct voltages at the phases U, V, W of the electric machine 1 safely. Depending on the current instantaneous value of the phase current of the electric machine 1, current flows from the boost converter 50 to support the controllable first energy store 2 in the electric machine 1 or for charging in the controllable first energy store 2. The boost converter 50 also allows the DC link voltage below a maximum

 Phase voltage can be. A diode 56 of the boost converter 50 prevents a reverse current in the intermediate circuit 10. In this arrangement, the supply of all energy supply branches of the controllable first energy storage takes place simultaneously.

Claims

claims 5 1. System with  - an n-phase electric machine (1), with n> 1, which by means of a  controllable first energy storage (2) is controlled and supplied with electrical energy, wherein the controllable first energy storage (2) n parallel  Having power supply branches (3-1, 3-2, 3-3) which 0 ^■ on the one hand with a reference rail (T) are connectable and ^■ On the other hand, each having a phase (U, V, W) of the electrical machine (1) are connectable, and  - A DC link (10), which on the one hand with a neutral point (S) of the  electric machine (1) and on the other hand with the reference rail (T) is coupled  2. System according to claim 1, wherein between the electric machine (1) and the reference rail (T) on the one hand and the intermediate circuit (10) on the other hand, a filter (1 1) is connected for smoothing an intermediate circuit voltage. 0 3. System according to one of claims 1 or 2, wherein from the intermediate circuit (10)  electrical consumers (12; 13) can be supplied directly or indirectly with DC voltage. 4. System according to claim 3, wherein the intermediate circuit (10) has a first 5 DC-DC converter (14) is connected downstream of which a first voltage level of the intermediate circuit (10) to a second voltage level of a second  Energy storage (15) adapts. 5. System according to claim 4, wherein the first DC-DC converter (14) as o DC-DC converter with galvanic isolation is executed. 6. System according to any one of the preceding claims, wherein between the electric machine (1) and the reference rail (T) on the one hand and the intermediate circuit (10) on the other hand, a second DC-DC converter (20; 30) is connected, which ein5 a third voltage level at the neutral point ( S) of the electric machine (1) and the first voltage level of the intermediate circuit (10) adapts to one another. 7. System according to claim 6, wherein the second DC-DC converter (20; 30) is designed as a bidirectional converter (30). 8. System according to any one of the preceding claims, wherein the intermediate circuit (10) with an additional DC power source (31, 32, 51) is connectable, which of the  Power supply of the electric machine (1) and / or for charging the controllable first energy storage (2) is used. 9. System according to claim 8, wherein with the intermediate circuit (10), a charger (31) is connectable, which the intermediate circuit (10) with an external  Energy supply network (32), in particular a public grid, connects. 10. The system of claim 8, wherein the DC power source (51) as Range extender (52) with a by an internal combustion engine (53) driven generator (54) is configured. A system according to claim 8, wherein the DC power source (51) comprises at least one Fuel cell and / or a photovoltaic module comprises. 12. System according to any one of the preceding claims, wherein the  Energy supply branches (3-1, 3-2, 3-3) of the controllable first energy storage device (2) each have at least two series-connected energy storage modules (4), each having at least one electrical energy storage cell (5) with a comprise associated controllable coupling unit (6), which bridges depending on control signals, the respective associated energy storage cells (5) or the respective associated energy storage cells (5) in the respective Power supply branch (3-1, 3-2, 3-3) switches. 13. System according to claim 12, wherein the coupling units (6) are designed as full bridges and between the electric machine (1) and the reference rail (T) on the one hand and the intermediate circuit (10) on the other hand, a rectifier unit (40) is connected. 14. A method for operating a system according to one of claims 1 to 13, wherein for the power supply of indirectly or directly to the intermediate circuit (10) connected electrical loads (12; 13), the voltages to the Power supply branches (3-1, 3-2, 3-3) each increased or decreased to a value be, which is above or below a current to the power supply of the electric machine (1) required voltage value.