EP3647553B1 - Supply of an electromechanical power converter with electrical energy from a thermodynamic cyclical process - Google Patents

Description

field of invention

The invention relates to a device for operating an electromechanical energy converter and a method for operating an electromechanical energy converter.

State of the art

A thermodynamic cycle device for obtaining electrical energy from thermal energy comprises the following main components: a feed pump, which conveys liquid working medium to an evaporator under pressure increase, the evaporator itself, in which the working medium is preheated with the supply of heat, evaporated and optionally additionally overheated, a Expansion machine, in which the high-pressure, vaporized working medium is expanded and mechanical energy is generated in the process, which can be converted into electrical energy, for example, via a generator, and a condenser, in which the low-pressure steam (expanded working medium) from the expansion machine is heated and liquefied . The liquid working medium returns from the condenser to the system's feed pump, which closes the thermodynamic cycle. If the working medium is an organic working medium, it is an Organic Rankine Cycle as a thermodynamic cycle (ORC process).

From the state of the art are so-called dry coolers (eg dry coolers in engine combined heat and power plants, BHKWs), through which air flows through electrically driven fans. In order to minimize the energy consumption, according to the applicant's internal state of the art, these fans should be supplied with electrical energy via a thermodynamic cycle process (eg an ORC process). At the same time, the heat dissipation of the cycle process should be realized via the fans of the dry cooler (normally the cycle or ORC process a separate fan to provide cooling of the condenser via an air flow). The cyclic process converts heat (eg unused exhaust heat from a combustion engine or part of the heat from the fluid to be cooled in the cooler) into electrical energy. The problem here is ensuring a stable supply of electrical energy to the fan so as not to impair the cooling function. Another disadvantage is that excess energy from the ORC process is fed back into the public power grid. Feeding energy into the power grid is associated with other requirements, such as compliance with feed-in guidelines, system certification, registration with the grid operator, and payment of the EEG surcharge in accordance with the law for the expansion of renewable energies (Renewable Energy Sources Act, EEG). .

document DE 10 2008 039449 A1 discloses, for example, a power plant with control of a compressor powered by two power sources.

Description of the invention

The object of the invention is to avoid or at least alleviate the disadvantages mentioned.

The circular or ORC process should always deliver exactly as much power as the fan consumes (quasi-island operation). Due to the joint use of the fan for the cooling process and the cycle process, the speed of the fan and thus its power consumption are only dependent on the cooling requirement of the cooling process. The dry cooler of the ORC process can therefore not be influenced in terms of control technology. In order to ensure a high level of operational reliability, it must be possible to draw additional power from the public power grid if the ORC process (e.g. due to high outside temperatures or too little process energy (waste heat)) cannot supply enough power to operate the fan.

A possibility must therefore be found to cover the fluctuating power requirement of the fan as precisely as possible with the ORC generator. If the cyclic process does not provide enough energy, there must be a way to supply the fan with energy from the public power grid or from another source and at the same time avoid feeding it into the grid.

The invention describes the solution of at least part of the above problems.

The solution according to the invention is defined by a device with the features according to claim 1.

The invention thus discloses a device for operating an electromechanical energy converter, such as a fan or a pump; the device comprising: a thermodynamic cycle device; an electric generator connected to a shaft of an expander of the thermodynamic cycle device and rotatable together with the shaft; wherein the generator is electrically connected to a first voltage converter, the first voltage converter is electrically connected to a DC voltage intermediate circuit and the DC voltage intermediate circuit can be electrically connected to the electromechanical energy converter in order to operate it; wherein the first voltage converter is designed to convert a first AC voltage of the electrical generator into a DC voltage; and wherein the intermediate DC circuit can be connected to an additional electrical energy supply, in particular a public power grid. The device further comprises a control device (60) for controlling the electrical energy supplied to the electromechanical energy converter, so that the electromechanical energy converter can be operated at a predetermined speed, the control device for controlling the electrical energy supplied to the electromechanical energy converter from the generator and, if the Electrical energy provided by the generator is not sufficient for regulating the electrical energy supplied to the electromechanical energy converter from the additional energy supply.

The device according to the invention has the advantages that energy is saved by supplying an electromechanical energy converter (e.g. fan or pump) via a cycle or ORC process that uses waste heat, that, for example, a separate cycle process or ORC fan is not required, that the operation of the fan is independent of the ORC process, thereby achieving high system reliability, and that grid feed-in is avoided, thereby bypassing the provision of feed-in requirements.

The device according to the invention can be further developed such that a second voltage converter is also provided for converting a DC voltage in the DC voltage intermediate circuit into a second AC voltage for operating an electromechanical energy converter without its own voltage converter, the second voltage converter being electrically connected to the DC voltage intermediate circuit.

Another development is that the additional energy supply is a public power grid, which is connected to the DC voltage intermediate circuit via a rectifier circuit or via a power factor correction stage, and the control device is also designed in particular to reduce the energy provided by the generator in order to avoid feeding in electrical To avoid energy in the public power grid, in particular by reducing the heat flow introduced into the thermodynamic cycle device and / or by reducing the efficiency of the thermodynamic cycle device.

As an alternative to this, the utility grid can be connected to the DC link via a bidirectional converter circuit in order to feed excess energy from the generator into the utility grid.

According to another development, the DC voltage intermediate circuit can include a first partial DC voltage intermediate circuit connected to the first voltage converter, a second partial DC voltage intermediate circuit that can be connected to the electromechanical energy converter or is connected to the second voltage converter, and a step-up converter arranged between the two partial circuits.

This can be further developed in such a way that a further electromechanical energy converter can be operated via a parallel circuit on the second partial DC voltage intermediate circuit, a third voltage converter for converting the DC voltage in the second partial DC voltage intermediate circuit into a third AC voltage for operating the further electromechanical energy converter being optionally provided the additional electromechanical energy converter is, for example, an additional pump, in particular a feed pump for pumping a working medium in the thermodynamic cycle device or an additional fan.

In this case, the electromechanical energy converter can comprise an intermediate circuit with an AC voltage connection, and the AC voltage connection can be connected directly to the second partial DC voltage intermediate circuit.

According to another development, a battery can be connected via a parallel connection to the second partial DC voltage intermediate circuit and a bidirectional DC voltage converter.

The invention also provides a system that includes the following: a heat-generating device with a cooling fluid for dissipating heat from the heat-generating device and a cooling device with an electrically operable fan for cooling the cooling fluid, in particular the speed of the fan and thus in particular its recorded power is predetermined by the cooling demand of the cooling device; and a thermodynamic cycle device, in particular an organic Rankine cycle device, which has an evaporator for evaporating a working medium, an expansion machine that can be operated by expanding the evaporated working medium with the evaporated working medium, an electrical generator that can be operated with the expansion machine, and a condenser for condensing the expanded Working medium includes; wherein the fan is further provided for cooling the working fluid in the condenser; and wherein the system further comprises a device according to the invention for operating the fan as an electromechanical energy converter or one of the developments described above.

The system can be further developed such that the speed of the fan is predetermined by a temperature of the cooling fluid to be achieved with the cooling device.

The above problems are at least partially solved by the method according to the invention as claimed in claim 10 .

The invention thus discloses a method for operating an electromechanical energy converter, for example a pump or a fan, at a predetermined speed, comprising the steps: converting a first AC voltage of a generator into a DC voltage in a DC intermediate circuit between the generator and the electromechanical energy converter, the electrical Generator is connected to a shaft of an expander of a thermodynamic cycle device, rotates together with the shaft and is driven by the shaft; Applying the DC voltage in the DC voltage intermediate circuit to the electromechanical energy converter; Application of a DC voltage to the DC voltage intermediate circuit from an additional electrical energy supply, in particular with electrical energy from a public power grid; Regulating the electrical energy supplied to the electromechanical energy converter from the generator in order to operate the electromechanical energy converter at the predetermined speed, and regulating the electrical energy supplied to the electromechanical energy converter from the auxiliary power supply if the electrical energy provided by the generator is required to operate the electromechanical energy converter at the predetermined speed is not sufficient.

Optionally, a second AC voltage can be generated from the DC voltage intermediate circuit and this (instead of the DC voltage in the DC voltage intermediate circuit) can be applied to the electromechanical energy converter (eg to a fan motor).

The advantages of the method according to the invention or its developments correspond to those of the device according to the invention or its developments and are therefore not repeated here.

The method according to the invention can be further developed in such a way that the additional energy supply is a public power grid, which is connected to the DC link via a rectifier circuit, and the method also includes the following step: avoiding the feeding of electrical energy into the public power grid by reducing the generator energy provided, in particular by reducing the heat flow introduced into the thermodynamic cycle device and/or by reducing the efficiency of the thermodynamic cycle device.

Alternatively, the method according to the invention can be further developed such that the additional energy supply is a public power grid, which is connected to the DC link via a bidirectional converter circuit, the method also includes the following step: feeding excess energy from the generator into the public power grid.

Another development is that the DC voltage intermediate circuit comprises a first partial DC voltage intermediate circuit connected to the generator and a second partial DC voltage intermediate circuit connected to the electromechanical energy converter, the method comprising the following additional step: converting the first DC voltage in the first partial DC voltage intermediate circuit into a higher second DC voltage introduced into the second partial DC voltage intermediate circuit.

This can be developed in such a way that the method comprises the further step: Setting the second DC voltage below a third DC voltage provided by the additional energy supply in the second partial DC voltage intermediate circuit if the electrical energy provided by the generator for operating the electromechanical energy converter at the predetermined speed is not sufficient is sufficient.

According to another development, the method can include the following additional step: converting the DC voltage in the DC voltage link into a third AC voltage to operate a further electromechanical energy converter, in particular a pump, for example a feed pump for pumping a working medium in the thermodynamic cycle device or for operating a further fan .

The developments mentioned can be used individually or, as claimed, can be suitably combined with one another.

Further features and exemplary embodiments as well as advantages of the present invention are explained in more detail below with reference to the drawings. It is understood that the embodiments do not exhaust the scope of the present invention. It is also understood that some or all of the features described below can also be combined with one another in other ways.

drawings

Figure 1A

shows a first embodiment of the device according to the invention.

Figure 1B

shows a system according to the invention with the first embodiment of the device according to the invention.

2

shows operating states of the fan or fans in the first embodiment of the device according to the invention.

3

shows a second embodiment of the device according to the invention.

4

shows a third embodiment of the device according to the invention.

figure 5

shows a fourth embodiment of the device according to the invention.

6

shows a fifth embodiment of the device according to the invention.

Figure 7

shows a sixth embodiment of the device according to the invention.

8

shows a seventh embodiment of the device according to the invention.

9

shows an eighth embodiment of the device according to the invention.

10

shows a ninth embodiment of the device according to the invention.

11

shows a tenth embodiment of the device according to the invention.

Like reference numbers in the drawings refer to identical or corresponding components. In some cases, only additional components are provided with reference symbols to simplify the representation in the drawings compared to previously described embodiments.

embodiments

The embodiments show one or more fans and/or one or more pumps, in particular for example a feed pump in the thermodynamic cycle device, as electromechanical energy converters, merely by way of example. Electromechanical energy converters convert electrical energy into mechanical kinetic energy, whereby the movement can be linear or rotary. Accordingly, a distinction is made between linear machines and rotating electrical machines. The embodiments relate to rotating electrical machines, but linear machines can also be used for the electromechanical energy converters in the embodiments in which speed control is not essential.

Furthermore, the electromechanical energy converters in the embodiments are predominantly constructed in such a way that the electromechanical energy converter itself has a Has intermediate circuit with an AC voltage connection. Each of these embodiments can be modified in such a way that a corresponding voltage converter is provided on the DC link for connection to the electromechanical energy converter.

Figure 1A shows a first embodiment 100 of the device according to the invention for operating a fan.

The device 100 comprises an electrically operable fan 80 with a motor 10 and a DC/AC voltage converter 44, an electric generator 20, which is connected to a shaft 35 of an expansion machine 30 of a thermodynamic cycle device, here an ORC device, and together with the Shaft 35 is rotatable. A first voltage converter 42 (input converter 42) and a DC voltage intermediate circuit 40 are provided between the generator 20 and the fan 80 . The first voltage converter 42 is designed to convert a first AC voltage of the electrical generator 20 into a DC voltage. The DC/AC voltage converter 44 (or output converter 44) is designed to convert a DC voltage in the DC voltage intermediate circuit 40 into a second AC voltage for operating the fan motor 10. The DC voltage intermediate circuit 40 is connected to an additional electrical energy supply 50, here a public power grid 51. The device 100 also includes a control device 60 for controlling the electrical energy supplied to the fan 80 so that the fan can be operated at a predetermined speed, the control device 60 being designed in such a way that it regulates the electrical energy supplied to the fan 80 from the generator 20 and, if the electrical energy provided by the generator 20 is not sufficient for this, the electrical energy supplied to the fan 80 by the additional energy supply 50 regulates.

The DC voltage intermediate circuit 40 includes a capacitor 41. The AC voltage from the public power grid 51 is rectified by a rectifier circuit 52 and applied to the DC voltage intermediate circuit 40. The control device 60 is also designed to reduce the energy provided by the generator 20 in order to meet the energy requirements of the/des To correspond to consumer(s), in particular by reducing the heat flow introduced into the thermodynamic cycle device and/or by reducing the efficiency of the thermodynamic cycle device.

The ORC device for obtaining electrical energy from thermal energy (e.g. waste heat) includes: a feed pump, which conveys liquid working medium under pressure increase to an evaporator, the evaporator itself, in which the working medium is preheated with the supply of heat, evaporated and optionally additionally overheated , the expansion machine 30, in which the high-pressure, vaporized working medium is expanded and mechanical energy is generated in the process, which can be converted into electrical energy via the generator 20, and a condenser, in which the low-pressure steam (expanded working medium) from the expansion machine 30 is heated and liquefied. The liquid working medium returns from the condenser to the system's feed pump, which closes the thermodynamic cycle.

Figure 1B shows a system according to the invention in combination with the first embodiment of the device according to the invention Figure 1A .

The system comprises a heat-generating device 110, an outlet 111 of the heat-generating device, the outlet 111 being provided for discharging process fluid to be cooled from the heat-generating device 110; an inlet 112 of the heat-generating device 110, the inlet 112 being provided for supplying cooled process fluid to the heat-generating device 110; and a thermodynamic cycle device, in particular an ORC device, wherein the thermodynamic cycle device comprises: an evaporator 120 with an inlet 121 for supplying the process fluid to be cooled from the outlet 111 of the heat-generating device 110 and with an outlet 122 for discharging the cooled process fluid to the inlet 112 the heat-generating device 110, wherein the evaporator 120 is designed for evaporating a working medium of the thermodynamic cycle device by means of heat from the process fluid; the expansion machine 30 for expanding the vaporized working medium and for generating electrical energy by means electric generator 20; an air-cooled condenser 150 for liquefying the expanded working fluid; and a pump 160 for pumping the liquefied working fluid to the evaporator.

In addition, an air cooler 170 is provided for cooling at least part of the process fluid to be cooled. The system includes a branch 171, which is provided, for example, in relation to a flow direction of the process fluid downstream of the outlet 111 and upstream of the inlet 121 for dividing the process fluid to be cooled into a first and a second partial flow of the process fluid. The system further includes a junction 172, which is provided with respect to a flow direction of the process fluid downstream of the outlet 122 and upstream of the inlet 112 for merging the second partial flow of the process fluid cooled by the cooler 170 and the first partial flow of the process fluid cooled by the evaporator 120 ; the branch 171 for supplying the first partial flow to the evaporator 120 and for supplying the second partial flow to the cooler 170 is designed. The flow of ambient air sequentially passes first through the radiator 170 and then through the condenser 150.

The specific design of the system is only an example.

2 shows the operating states of the fan(s) in the first embodiment 100 of the device according to the invention in a performance versus outside temperature diagram, which will be described in more detail below.

The fan 80 is connected to the generator 20 via the DC link (direct current) 40 (or via several DC links). The speed of the fan 80 is regulated as a function of a target flow temperature of a cooling system and is independent of the generator speed and energy supply from the ORC process.

If the ORC process generates less energy than is required at the intermediate circuit 40 (U_DC), the missing energy is drawn from the public grid 51 via the rectifier 52 . The rectifier 52 also provides operation of the fan 80 independent of the thermodynamic cycle process (e.g. in the event of failure, error). In the event of an error or failure of the cyclic process, the entire power required is drawn from the network 51 . Thus, the radiator driven by this fan 80 can continuously and independently provide sufficient cooling performance.

If the ORC process generates more energy than is required at intermediate circuit 40 (U_DC) (the system is designed for normal operation below a certain outside temperature for this purpose), appropriate measures must be taken.

The speed of the generator 20 is initially aligned with the optimal operating point of the ORC process and regulated by means of the input converter 42 (regulated operation). At this operating point, the amount of heat Q _zu transferred to the ORC is converted into electrical energy P _el with optimum efficiency η _ORC .

• Reduktion der zugeführten Wärme Q_zu durch Reduktion der Speisepumpendrehzahl
• Reduktion des Wirkungsgrads η_ORC=η_th•η_Gen•η_EW durch Verschlechterung von einzelnen Wirkungsgraden in der Wirkungsgradkette wie z.B. des thermischen Wirkungsgrads η_th, des Generatorwirkungsgrads η_Gen oder des Wirkungsgrads des Eingangswandlers η_EW

In principle, there are two different ways to reduce the converted electrical energy as desired:

• Reduction of the supplied heat Q _to by reducing the feed pump speed
• Reduction of the efficiency η _ORC =η _{th •} η _{Gen •} η _EW by deterioration of individual efficiencies in the efficiency chain such as the thermal efficiency η _th , the generator efficiency η _Gen or the efficiency of the input converter η _EW

In the real implementation, the measures will influence each other slightly, e.g. the reduction of the feed pump speed will lead to different steam parameters and thus also to a changed thermal efficiency.

In contrast to previous ORC controls, the voltage U_DC is now used as a control variable for the generator speed and/or the feed pump speed and the speed is reduced or increased again until sets a stable balance between ORC power generation and energy consumption. With constant consumption by the fan, the voltage U_DC behaves in such a way that it also increases with increasing ORC power. The voltage U_DC thus serves as a controlled variable.

According to the prior art, a brake chopper would be provided on the intermediate circuit 40, which limits the intermediate circuit voltage to a value that is not critical for the components. However, this has the disadvantage that sufficient heat dissipation of the braking resistor must be ensured and the material costs increase due to the additional component. This can be omitted here. Instead, according to the invention, more losses are generated in generator 20 via fast regulation of input converter 42 and activation of generator 20 in the suboptimal range, and the intermediate circuit voltage is thereby limited. That is, the input converter 42 is operated with a poorer efficiency as intended.

3 shows a second embodiment 200 of the device according to the invention for operating a fan.

Compared to the first embodiment 100 according to Figure 1A the DC voltage intermediate circuit 40 comprises a first partial DC voltage intermediate circuit 46 connected to the input converter 42, a second partial DC voltage intermediate circuit 48 connected to the output converter 44 and a step-up converter 45 arranged between the two partial circuits. The step-up converter 45 is also synonymously known as a boost converter or step-up converter designated.

In order to obtain generators with a rated voltage well below the required output voltage for the fans, the step-up converter 45 is interposed. The mains connection consists of a passive B6 rectifier 52 which is connected in 3 phases.

4 shows a third embodiment 300 of the device according to the invention for operating a fan.

As an alternative to the second embodiment 200 according to 3 the network coupling can also take place on the input side of the step-up converter 45. In addition, an active grid coupling via power factor correction stage 54 (active PFC, Power Factor Correction) is used, which always draws a small amount of power from the grid and thus creates leeway for controlling the power balance between ORC generator and consumer (fan). In contrast to the second embodiment, a 1-phase mains connection is sufficient. In contrast to the second embodiment, the current consumption is almost sinusoidal due to the active PFC (avoidance of harmonics).

figure 5 shows a fourth embodiment 400 of the device according to the invention.

In the fourth specific embodiment 400, in comparison to the second specific embodiment 200, a parallel circuit is provided on the second partial DC voltage intermediate circuit 48. In this way, a pump 81 can be connected via a further output converter 49 for converting the DC voltage in the second partial DC voltage link 48 into a third AC voltage for operating a motor 11 of the pump 81, for example a water pump and/or a feed pump for pumping a working medium in the thermodynamic Cyclic process device are driven.

In this case, in addition to the fan 80, the pump 81 is also supplied from the second intermediate circuit 48 (U_DC2). The advantage is a further increase in efficiency, since in normal operation the energy of the pump 81 also comes from the ORC process and does not have to be drawn from the grid 51 . To start the ORC process, the energy is drawn from the network 51 via the B6 bridge 52 . An auxiliary voltage supply (eg 24 VDC, not shown) can also be taken from the intermediate circuit 48 in the same way.

6 shows a fifth embodiment 500 of the device according to the invention.

Compared to the fourth embodiment 400, a further fan 82 is driven instead of the pump 81.

The fifth embodiment 500 shows a parallel connection of several fans 80, 82 on the common DC intermediate circuit. Depending on the performance of the fans, any number of fans can be connected in parallel. In practice, multiple fans and larger coolers are often used to improve quietness and efficiency through reduced air speeds.

7 shows a sixth embodiment 600 of the device according to the invention.

The sixth embodiment 600 includes the supply of a plurality of fans 80, 82 via a common converter, namely the output converter 44. The parallel connection is therefore on the AC side. A sine filter 13 connected downstream of the common converter 44 is required for this. This supplies a sinusoidal output current of variable frequency. The advantage over the fifth embodiment 500 results from simpler wiring (electrical strength, omission of shielded cable) and better EMC properties (electromagnetic compatibility). The wiring between the converter 44 and the fan motor can be 10 m and longer, for example.

8 shows a seventh embodiment 700 of the device according to the invention.

The seventh embodiment 700 shows the connection of a three-phase AC input of a fan 80 directly to the DC intermediate circuit 48. The converter 44 usually has input rectifier diodes (body diodes), which allow direct connection to a DC circuit. The intermediate circuit 48 (U_DC2) is thus connected directly to the intermediate circuit of the fan converter (converter 44). Commercially regulated EC fans (Electronically Commutated Motor) can be used directly. Any existing phase failure or AC voltage monitoring must be deactivated for this. In a modification, this embodiment also allows several fans to be connected in parallel.

9 shows an eighth embodiment 800 of the device according to the invention.

The eighth embodiment 800 shows an energy store, for example a battery 70 on the intermediate circuit 48. This is a step towards a completely currentless fan (all consumers such as pumps, fans, auxiliary voltage supply are connected to the intermediate circuit, at least there is no permanent connection to the electrical supply network required, and with appropriate dimensioning of the battery 70, the mains connection can be omitted) and also allows more freedom in the design of the control circuit of the ORC power.

10 shows a ninth embodiment 900 of the device according to the invention.

In the ninth embodiment 900, a topology with regenerative power converter 53 (bidirectional power converter circuit) is shown. Excess energy thus flows back into the grid 51 without limiting the performance of the ORC generator. The feed-in converter 53 must comply with the feed-in guidelines applicable in the respective country. The advantage of all the previous embodiments is that there is no need for increased effort to comply with all technical and regulatory feed-in guidelines.

11 shows a tenth embodiment 1000 of the device according to the invention.

The tenth embodiment 1000 represents the supply of a pump 83, for example a hot water pump of a heating circuit from the DC intermediate circuit 48. However, instead of the pump 83, a compressor or any other electrical consumer can also be connected.

In this application, pumps often have a higher power requirement than the fans. If the required pump power is permanently higher than the ORC power, a direct connection of the DC output of the ORC generator converter to the intermediate voltage circuit of a regulated pump is possible. The ORC will then generate maximum energy at its optimum operating point, which is then used to operate the pump. Additional energy is permanently drawn from the grid.

The illustrated embodiments are only exemplary. The full scope of the present invention is defined by the claims.

Claims (15)

1. An apparatus (100-1000) for operating an electromechanical energy converter (80, 81, 82, 83), e.g. a fan or a pump, comprising:

   a thermodynamic cycle apparatus (30, 120, 150, 160);

   an electrical generator (20) connected to a shaft (35) of an expansion machine (30) of the thermodynamic cycle apparatus and rotatable together with the shaft;

   wherein the generator (20) is electrically connected to a first voltage converter (42), the first voltage converter (42) is electrically connected to a DC intermediate circuit (40), and the DC intermediate circuit (40) is electrically connectable to the electromechanical energy converter (80, 81, 82, 83) for operating the same;

   wherein the first voltage converter (42) is configured for converting a first AC voltage of the electrical generator (20) into a DC voltage; and

   wherein the DC intermediate circuit (40) is connectable to an electrical auxiliary power supply (50), in particular a public power grid (51); and

   a control unit (60) for controlling the electrical energy supplied to the electromechanical energy converter (80, 81, 82, 83), so that the electromechanical energy converter can be operated at a predetermined speed,

   characterized in that

   the control unit (60) is configured for controlling the electrical energy supplied to the electromechanical energy converter (80, 81, 82, 83) from the generator (20) and, if the electrical energy provided by the generator (20) is not sufficient for this purpose, for controlling the electrical energy supplied to the electromechanical energy converter (80, 81, 82, 83) from the auxiliary power supply (60).
2. The apparatus according to claim 1, wherein a second voltage converter (44) is provided for converting a DC voltage in the DC intermediate circuit into a second AC voltage for operating the electromechanical energy converter, the second voltage converter being electrically connected to the DC intermediate circuit.
3. The apparatus according to claim 1 or 2, wherein the auxiliary power supply is a public power grid (51), which is connectable to the DC intermediate circuit via a rectifier circuit (52) or a power factor correction stage (54), and the control unit is, optionally, further configured to reduce the energy provided by the generator, so as to prevent electrical energy from being fed into the public power grid, in particular by reducing the heat flow introduced in the thermodynamic cycle apparatus and/or by reducing the efficiency of the thermodynamic cycle apparatus; or
   wherein the auxiliary power supply is a public power grid (51), which is connectable to the DC intermediate circuit via a bidirectional current rectifier circuit (53), and an excess energy from the generator is feedable into the public power grid.
4. The apparatus according to one of the claims to 3, wherein the DC intermediate circuit (40) comprises a first DC intermediate subcircuit (46) connected to the first voltage converter (42), a second DC intermediate subcircuit (48) connectable to the electromechanical energy converter or, in combination with claim 2, connected to the second voltage converter, and an up-converter (45) arranged between the two subcircuits.
5. The apparatus according to claim 4, wherein a further electromechanical energy converter can be operated via a parallel connection at the second DC intermediate subcircuit, wherein, optionally, in combination with claim 2, a third voltage converter is provided for converting the DC voltage in the second DC intermediate subcircuit into a third AC voltage for operating the further electromechanical energy converter, the further electromechanical energy converter being e.g. a further pump, in particular a feed pump for pumping a working medium in the thermodynamic cycle apparatus, or a further fan.
6. The apparatus according to one of the claims 4 or 5 in combination with claim 2, wherein the electromechanical energy converter comprises an intermediate circuit with an AC voltage connection and the AC voltage connection is directly connected to the second DC intermediate subcircuit.
7. The apparatus according to one of the claims 3 to 6, wherein a battery is connected via a parallel connection at the second DC intermediate subcircuit and a bidirectional DC converter.
8. A system, comprising:

   an apparatus (100-1000) for operating an electromechanical energy converter according to any one of claims 1 to 7;

   a heat generating unit (110) with a cooling fluid for dissipating heat from the heat generating unit (110) and a cooling device (150) with the electrically operable fan (80) for cooling the cooling fluid;

   wherein the thermodynamic cycle apparatus is in particular an organic Rankine cycle apparatus and wherein the thermodynamic cycle apparatus comprises an evaporator (120) for evaporating a working medium, the expansion machine (30) operable by means of the vaporized working medium through expansion of the vaporized working medium, and a condenser for condensing the expanded working medium; and

   wherein the fan (80) is further provided for cooling the working medium in the condenser (150).
9. The system according to claim 8, wherein the speed of the fan is predetermined by a cooling fluid temperature achievable by the cooling device.
10. A method for operating an electromechanical energy converter (80, 81, 82, 83), e.g. a pump or a fan, at a predetermined speed, the method comprising:

    converting a first AC voltage of a generator (20) into a DC voltage, which is supplied to a DC intermediate circuit (40) between the generator and the electromechanical energy converter, wherein the electrical generator is connected to a shaft (35) of an expansion machine (30) of a thermodynamic cycle apparatus (30, 120, 150, 160), rotates together with the shaft and is driven by the shaft;

    optionally, converting a DC voltage in the DC intermediate circuit (40) into a second AC voltage;

    applying the DC voltage in the DC intermediate circuit (40) or the second AC voltage to the electromechanical energy converter (80, 81, 82, 83);

    applying a DC voltage to the DC intermediate circuit (40) from an electrical auxiliary power supply (50), in particular with electrical energy from a public power grid (51); and

    controlling the electrical energy supplied to the electromechanical energy converter (80, 81, 82, 83) from the generator, so as to operate the electromechanical energy converter at the predetermined speed;

    characterized by

    controlling the electrical energy supplied to the electromechanical energy converter (80, 81, 82, 83) from the auxiliary power supply (50), if the electrical energy provided by the generator (20) for operating the electromechanical energy converter (80, 81, 82, 83) at the predetermined speed is not sufficient.
11. The method according to claim 10, wherein the auxiliary power supply is a public power grid (51), which is connected to the DC intermediate circuit via a rectifier circuit (52), and the method further comprises:
    preventing electrical energy from being fed into the public power grid by reducing the energy provided by the generator (20), in particular by reducing the heat flow introduced in the thermodynamic cycle apparatus and/or by reducing the efficiency of the thermodynamic cycle apparatus.
12. The method according to claim 10, wherein the auxiliary power supply is a public power grid (51), which is connected to the DC intermediate circuit (40) via a bidirectional current rectifier circuit, and the method further comprises:
    feeding excess energy from the generator (20) into the public power grid (51).
13. The method according to one of the claims 10 to 12, wherein the DC intermediate circuit comprises a first DC intermediate subcircuit (46) connected to the generator (20) and a second DC intermediate subcircuit (48) connected to the electromechanical energy converter, wherein the method further comprises:
    converting the first DC voltage in the first DC intermediate subcircuit into a higher second DC voltage, which is introduced in the second DC intermediate subcircuit.
14. The method according to claim 13, further comprising:
    adjusting the second DC voltage to a value below a third DC voltage, provided by the auxiliary power supply, in the second DC intermediate subcircuit, if the electrical energy provided by the generator for operating the electromechanical energy converter at the predetermined speed is not sufficient.
15. The method according to one of the claims 10 to 14, further comprising:
    converting the DC voltage in the DC intermediate circuit (40) into a third AC voltage for operating a further electromechanical energy converter, in particular a pump, e.g. a feed pump for pumping a working medium in the thermodynamic cycle apparatus, or for operating a further fan.

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