Photovoltaic assembly with battery and replacement power plant

The invention relates to a method and apparatus for operating a photovoltaic system with a plurality of photovoltaic modules and having a first and a second connected to the photovoltaic modules DC motor, which are coupled to a three-phase generator or coupled with the three-phase generator can be connected to a power grid, and the power supplied by the photovoltaic modules, electric power is selectable in the upper two DC motors.

Such a device is in the non-prepublished Appl. No.<patcit id="pcit0001" dnum="US12649536B"><text>12 / 649.536</text></patcit> (BECK-8; ad 16 / 08US) proposed.

In the construction of solar power plants, it is provided in the purchase agreements with the associated utilities partly to feed a contractually guaranteed minimum performance within a specified time in the supply network. So it can be called at a 2.4 megawatt solar plant that 11:00 to 17:00 is a power of at least 60 percent, feed about 1.5 megawatts. Depending on weather conditions, the minimum benefit is not always alone generated by the solar system.

The invention has for its object to modify a method and an apparatus of the aforementioned type so that a desired minimum performance at any time is available.

This object is achieved with respect to the method according to the invention that it is assumed that a first group of photovoltaic panels on the first DC motor and a second group of photovoltaic modules is connected to the second DC motor, that on one of two DC motors, a battery can be connected, and that a regulating and control unit causes, in a step the switching of the power supplied by the photovoltaic panels on one of the DC motors and in a further step takes such influence on the excitation of the direct current motor that the motor voltage is desired battery discharge below the battery open circuit voltage, so that the battery discharges in said DC motor.

Here, take the two steps can be interchanged with each other.

By this measure it is achieved that at drop of the photovoltaic system at the minimum power from the battery out of the loss can be fed.

Because the battery can compensate only for a limited period of a few minutes the loss of energy, it is useful to prepare a replacement power plant to feed, once it becomes clear that the present case of the photovoltaic system falls below the minimum power is not temporary in nature, such as a individual passing cloud. In this respect, the connection of the battery with the start up of a spare power plant or the connection process of an ongoing replacement power station should be connected. The replacement power plant is to supply direct current suitable and may be a conventional diesel generator with rectifier that can provide the additional power available in about 1 minute, or else may be a fuel cell. The time that passes to the DC motor between the request by the control unit to the actual switching, so is advantageously between 1 and 5 minutes, especially between 2 and 4 minutes.

A criterion which results in the requesting of the additional power plant output can be, for example, that the electric power generated by the photovoltaic modules is below a predeterminable period of time a minimum value. Another possible criterion may be that the product of the generated by the photovoltaic modules and electric power for a period (ie, the integral of the power) falls below a preselected minimum value. There are other criteria to imagine, consider the nature of the observed drop in performance of the photovoltaic system, such as harsh shadows - light - changing, fleecy clouds, stratus, etc.

In the actual connection of the battery to the DC motor, it is advantageous for the regulation and control unit, the motor voltage initially as exactly adjusted to the battery open circuit voltage, then the motor voltage descends further to set a desired discharge. This measure provides the advantage that the battery is almost dead connected to the DC motor, which keeps low wear of the associated switch.

Lowering can be done incrementally or continuously. It may be useful in reducing the motor voltage and the adjustment of a desired ratio of PV module feed power to battery power input.

The battery itself can consist of a variety of conventional car batteries, the respective short-term load is at least 500 amps, which are partially connected in series to give a battery voltage of 96 volts, and connected partially in parallel to increase the total output current. The battery voltage of 96 volts is considered a good compromise between the high, to transmit streams and the number of to be monitored battery cells. The battery can in principle take any voltage value between 80 and 150 volts, at a feed-in power of 400 KW, for example, is already a power of four thousand amperes for driving the DC motor at a voltage of 100 volts. An effective monitoring ability of the cells, the battery voltage can also be designed on the voltage of the photovoltaic system of, for example 400 volts.

The battery can be charged either via an external charger for the PV system itself by increasing the motor voltage to a value above the rated voltage of the battery or on the spare power plant. Several of these options can be simultaneously provided. The choice of the charge is then dependent on the nature of the current drain on the battery. Can be with shadows for example noon high PV capacity in the short-term changes, the use of rectifier charger offers itself, since it is often as short and without an elaborate docking event connected to the battery terminals.

It makes sense to keep the battery at a very high charge level and keep it there. This should be connected to each discharge of the battery immediately a load, possibly with the assistance of the aforementioned spare power plant. This is also important with regard to the use of lead-acid batteries as a battery, which should be loaded as possible always and should experience a deep discharge never, which can lead to damage to the cells.

To protect the DC machines, it is expediently provided that the control unit is supplied with the measured value of the temperature of that DC motor, which is driven by the photovoltaic system, and that at a predetermined temperature limit is exceeded, a change is made such that the connection of carried battery of the formerly supplied by photovoltaic system DC motor to the other DC motor, and that the other, previously driven by the battery DC motor is now driven by the photovoltaic system. it when both DC motors are provided with a means for temperature control, since both the direct current motor, which is supplied with the entire load of the photovoltaic system, can overheat, and the other DC motor, the high with is particularly advantageous battery current is fed at low voltage. Here, the control unit must provide compensation by possibly several times to switch between the energy sources that drive DC motors.

When approaching both DC motors a predetermined upper temperature, the activation of a spare power plant is practically mandatory. The replacement power plant can be operated at 400 volts or the PV system voltage of 700 volts as the output voltage, which again present currents close to the nominal current of the DC machines. Ideally, the output voltage of the replacement power plant is regulated to the voltage of the photovoltaic system. This makes it possible to substitute for the temporary use of the battery, this battery for an extended period of, for example 5 to 20 minutes by the spare power plant as a power supplier, and regulate the excitation of the dc motor back on the output voltage of the PV system. Then the previously operated on the battery DC motor can be simultaneously fed to both of the spare power plant, as well as of the photovoltaic system. Certain equalization currents are taken into account, or the output voltage of the replacement power plant is continuously adapted to the voltage of the PV system. In this procedure, a high minimum power, as are 80% of the rated power of the photovoltaic system, guaranteed.

Regarding the device, the inventive photovoltaic system is characterized by a large number of photovoltaic modules, with two switchable to the photovoltaic modules DC motors, the case can be switched from the photovoltaic modules supplied with a DC voltage and a DC current, by a Three-phase generator which is connectable to the first and / or second DC motor by means of a respective clutch, and which is connectable to the supply line of the AC voltage generated by it to a power supply network, and, through a switchable to at least one of the DC motors battery whose switching is controlled by a regulating and control unit, wherein an engagement criterion is a predetermined minimum output power of the AC generator.

This results in substantially the same advantages described above in connection with the embodiments of the method discussed, which are analogous also applicable to the device.

The possibility of switching the total power generated to a single DC motor is provided in that the photovoltaic modules are divided into a first and a second set that the first amount of its generated power at a first output and the second set the power generated by it provides at a second output is provided, wherein the first and the second output in each case by means of a switching element connected to the input of the first and second DC motor can be connected, and that a bridge switches in the closed state the first output with the second output connects. Here is intended primarily to a parallel circuit of the two outputs.

Further advantages and embodiments of the invention will be apparent from the description of exemplary embodiments with reference to FIGS. Show it:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>a schematic diagram of an electromechanical converter with two DC motors, an alternator and a battery; and</dd><dt>FIG. 2</dt><dd>a schematic diagram of an electromechanical converter with two DC motors, an alternator and a battery, and a spare power plant.</dd></dl>

In the <figref idrefs="f0001">figure 1</figref> is in a photovoltaic system A with Q1 a first set of photovoltaic modules 2 called the first power source having a first output terminal pair 1, in which a DC voltage U1 and a direct current I1 can be tapped. Via a first switch 3, the output terminal pair 1 can be connected to a first separately excited DC motor 5 to drive this.

Analogously, located on the right side shows a second quantity Q2 of photovoltaic modules 2 as a second power source having a second pair of output terminals 7, where a DC voltage U2 and a direct current I2 can be tapped. About a second switch 9, the output terminal pair 7 may be connected to a second separately excited DC motor 11, to drive it.

Between the two DC motors 5, 11 is a three-phase generator 13 is disposed, whose wave generator 15 is aligned with the two motor axes 17, 19 of the DC motors 5 bzw.11. The generator shaft 15 is led out left and right from the alternator 13 and is provided at each free end with a clutch 21 or 23rd By means of the clutches 21, 23 the axes 17, 19 of the DC motors 5, 11 separated by the alternator 13 are connected. It may alternatively be a rigid connection without couplings 21, 23 can be provided. The alternator 13 has an electrical connection or switching element 25 to join him for the purpose of passing on its AC voltage to a power grid 28th

There is a control and regulation unit 26 are provided, the switches 3 and 9 controls, which is indicated by dashed lines. You can split or join (via dashed lines lines) and the couplings 21, 23rd The control unit 26 is also equipped with a signal generator, the operation of a bridge switch 27 controls, with the output terminals can be 1 and 7 connected to each other. With a closed bridge switches 27, the two outputs 1 and 7 are connected in parallel. When starting operation of the first DC motor 5 of the bridge switch 27 is closed, and the output E2 of the second energy source of Q2 is in addition to the power of the first power source E1 Q1 also at the input of the first DC motor 5 is available. Reaches the power of the first DC motor 5 a predetermined value, in particular, for. Example, its nominal power, the bridge switch 27 is opened. The electrical energy generated by the energy source Q2 is then used to start and continued operation of the second DC motor eleventh If the speed of the axis 19 of the adapted to the shaft 15, 26 is given a signal to initiate the Einkupplungsvorgangs the clutch 23 from the control unit. After coupling form the axes 17, 19 together with the shaft 15 a common pivot composite.

On the second DC motor 11, a battery 31 is activated via a battery switch 29th The battery 31 is, in turn, optionally connected via a further, not shown switch, with a charger 33, in particular with a rectifier charger, the z. B. is fed from the power supply net 28.

In the event that on the connecting element 25 is no fixed minimum power can be fed into the grid 28, the control unit 26 is configured to initially open the switch 9, a change in the excitation of the second DC motor 11 whose motor voltage on the to regulate battery open-circuit voltage and then the battery switch to close 29 to feed in addition to the solar energy more energy in the system A. The feed-in is achieved in that after closing the battery switch 29, the motor voltage is reduced at the second DC motor 11, which causes a power flow from the battery 31 to the second DC motor 11 inside.

In normal mode the full system output is achieved. Then, the bridge switch 27 is opened, as is the battery switch 29 is open so that no power is fed from the battery 31 forth; the first power source Q1 then feeds the first motor 5, and the second energy source supplies the second motor Q2 eleventh

The control and regulation of DC motors 5 and 11 is expediently carried out by the MPP method. A preferred example here is in the<patcit id="pcit0002" dnum="US20070290636A1"><text>US-2007-0290636-A1</text></patcit>(= <patcit id="pcit0003" dnum="US7609019B"><text>US 7,609,019</text></patcit>) Described. This publication is incorporated by citation herein.

Only when the power E1 + E2 of the two energy sources Q1 and Q2 located along below the guaranteed minimum in the supply power, the bridge switch 27 is closed, the switch 9 is opened and the battery switch 29 is also closed. Then, the battery 31 is connected to the second motor eleventh The battery 31 thus increase the power supplied by the energy sources Q1, Q2 performance to the minimum assured power.

It is assumed that when considering the fact that the first motor 5 from the photovoltaic unit A (that is, from two energy sources Q1 and Q2 together) and that the second motor 11 is driven by the battery 31st The danger here is that the first motor 5 starts to overheat it.

Preferably, both the first DC motor 5, and the second DC motor 11 is connectable to the battery 31st It does not matter whether a changeover switch is provided, or whether - as indicated in broken lines - the battery 31 separate in two batteries 31a, 31b is divided, of which 31a is associated with the first DC motor 5 is a battery and the other battery 31b to the second DC motor 11. This measure is related to the following consideration for heating the direct current machines 5, 11 of importance.

To protect the DC machines 5, 11 means for monitoring the temperature is expediently provided. It is provided that the control and regulation unit 26 from a sensor 32 is supplied (via the dashed lines) with the measured value of the temperature of the first DC motor fifth Suppose the first motor 5 runs up to the Q1 and Q2, and the second motor 11 runs up to the battery 31. On the first motor 5 there is a risk of overheating. Now, a safety measure is effected in that at a predeterminable temperature limit is exceeded, a change is performed such that the feeding from the battery 31 to the previously supplied by Q1 and Q2, the first DC motor 5 is transferred to the other DC motor 11, and that the other, so far only of the battery 31 driven second DC motor 11 is now driven by Q1 and Q2. The driving conditions are thus reversed.

it when both DC motors 5, 11 are provided with a device for temperature control, since both, the DC motor, which is supplied with the entire load of the photovoltaic system, can overheat, and the other DC motor, the low to the high battery current is particularly advantageous voltage is fed. Here, the control unit 26 should provide compensation by possibly several times between the energy sources, namely solar energy (Q1 and Q2) on the one hand and the battery 31 (replacement source) on the other hand, changed.

The DC motors 5, 11 can be overloaded but separately despite their exposure to only a part of the total output. This is the case if the minimum output of eg 70% of nominal power (first and second power source Q1, Q2 taken together) is not reached when the PV system (Q1 and Q2 together) but at least it provides 60% of their rated power. Then, the redirection of the energy supplied from the second power source Q2 by means of closing of the switch 27 to the first bridge DC machine 5, which is then charged with 60% of the total energy. This means, based on half the total power is accounted for by this direct current motor 5, an overload of 20%.

This is demonstrated by a numerical example: There lies a solar system A with a total capacity of 2.4 megawatts in front, which is divided into equal parts of the plant, so that the power E1 of Q1 equal to the power E2 of Q2, ie respectively equal to 1.2 MW is. The respective associated DC motors 5, 11 are performed in accordance with each with a rated power of 1.2 MW. The current sunlight delivers an output of 1.44 MW, which corresponds to a power of 60% of the photovoltaic system (Q1 + Q2). For maintaining the delivery schedule with the utility but are 70% of rated power, to deliver corresponding 1.68 megawatts. It is missing 0.24 MW, to be fed through a backup source. After the switch 9 and closing the switch bridge 27 are open to the first direct-current motor 5 thus 1.44 megawatts, that is 0.24 megawatts (= 20% of the rated power of said one DC motor of 1.2 MW) more than the power for continuous operation at the ers is designed te DC motor. 5 The second DC motor 11 is supplied from the battery 31 with the missing 0.24 megawatts.

It is therefore useful to both DC motors 5, 11 to be provided with a means for monitoring the temperature, which helps prevent overheating. It is first one of the DC motors 5, 11 is operated with the higher current until it has reached a machine-related limit temperature. Then, the above-mentioned exchange is made. The higher power is the question warmer DC motor 5, 11 operated at reaching the temperature limit with the lower power, and the other, cooler DC motor 5, 11 will henceforth be operated with that source of energy (PV system or battery) outputs to the motor 5, the eleventh

Instead of regulating all alone on the magnitude of the current may also be a more detailed introduction of the bill and return change by analyzing the resulting respectively in the DC motor 5, 11 power dissipation to be made.

If the reduced power of the photovoltaic system (Q1 + Q2) could last for a longer period of several minutes, was to ensure the delivery of a minimum amount of energy into the grid 28 to the <figref idrefs="f0002">figure 2</figref> Embodiment shown recourse.

In the <figref idrefs="f0002">figure 2</figref> the same parts are provided with the same reference numerals as in <figref idrefs="f0001">Fig. 1</figref>, The<figref idrefs="f0002">figure 2</figref> equals to <figref idrefs="f0001">figure 1</figref>, It adds a DC replacement power plant 35, which is connected to the second DC motor 11 by means of an auxiliary switch 37th

The battery 31 can be used only for a short-term bridging of a bottleneck to providing the promised minimum performance of the PV system A. In an ongoing underperformance, it is provided 35 to connect the DC replacement power plant instead of the battery 31 to the second DC motor 11th Depending on the DC replacement power plant 35 different start-up times are required to make the spare power plant 35 zuschaltfertig. Thus, the preparation time is to Zuschaltzustand in a diesel generator with rectifier for about 1 minute, whereas it may take in a fuel cell up to several minutes. Accordingly, the control unit 26 is interpreted as meaning that the replacement power plant 35 is approached at an early stage, before the danger that the battery 31 no longer holds to the Connect time.

One criterion for initiating the Zuschaltvorgangs may be that the electric power generated by the photovoltaic modules 2 below over a predetermined period of time a minimum value. This means for example that the connection process is initiated when the photovoltaic system with Q1, Q2 remained within a period of 1 minute below the minimum power and the battery 31 during this had to be supplied switches a minute. Another criterion may provide that the connection process takes place when the product of the photovoltaic modules 2 electric power generation and a time period falls below a pre-selected minimum value. This means for example that the replacement power plant is switched 35, when over a period of 6 minutes away, an electric power is consumed by 20% of the battery capacity, because it has been used to supplement the reduced output in order to cover the contractually guaranteed power output.

Basically put, it is irrelevant whether the criteria are designed so that the replacement power plant is 35 prepared, or that the Connection time is the basis for the calculation. In the second case, then you have the required setup time of replacement power plant 35 excluded from the calculation.

The replacement power plant 35 serves firstly to charge the battery 31 quickly, and secondly, it serves to provide the minimum power for a relatively short duration, eg, 5 to 20 minutes.

But if it is foreseeable that the extra power from the battery 31 and the spare power plant 35 over a longer period of eg 20 minutes to several hours is required, an additional power plant is 39 additionally switched on the AC side by means of a switching element 38th This additional power plant 39 is also in<figref idrefs="f0002">FIG. 2</figref> registered. It can be arranged spatially separated at another location in the supply network 28th So it may be a gas power plant, which is available for feeding to a set-up time of about 4 minutes. The startup Allow and / or switching on the auxiliary power plant 39 is then also carried out by the control unit 26th

In summary, a method for operating a photovoltaic system (A) comprising a plurality of photovoltaic modules (2) and having a first and a second of the photovoltaic modules (2) connected DC motor (5 bzw.11) with a three-phase generator (13) connected or connectable with the three-phase generator (13) to a power supply network (28) is connectable, and wherein the from the photovoltaic modules (2) supplied electrical energy (E1 + E2) selectable on the two DC motors (5, 11) is distributed, <b>characterized in that</b> it is assumed that a first group (Q1) of the photovoltaic modules (2) at the first DC motor (5) and a second group (Q2) is connected to the photovoltaic modules (2) on the second DC motor (11) that a regulating and control unit (26) in one step, the switching of the photovoltaic modules (2) delivered energy (E1 + E2) to one (5) of the DC-motors (5, 11) and the terminal of a battery (31) so influences the other (11) of the two DC motors (5, 11) causes and in a further step on the excitation of the other DC motor (11) that the motor voltage is desired battery discharge below the battery open circuit voltage so that the battery (31) discharges into said other DC motor (11), stated.

LIST OF REFERENCE NUMBERS

<dl id="dl0002" compact="compact"><dt>A</dt><dd>Photovoltaic system</dd><dt>E1</dt><dd>electrical power</dd><dt>E2</dt><dd>electrical power</dd><dt>Q1</dt><dd>first power source</dd><dt>Q2</dt><dd>second power source</dd><dt>1</dt><dd>Output terminal pair of Q1</dd><dt>3</dt><dd>first switch</dd><dt>5</dt><dd>first direct current motor (DC motor)</dd><dt>7</dt><dd>Output terminal pair of Q2</dd><dt>9</dt><dd>second switch</dd><dt>11</dt><dd>second direct current motor (DC motor)</dd><dt>13</dt><dd>Alternator</dd><dt>15</dt><dd>wave</dd><dt>17</dt><dd>Motor axis of the first DC motor 5</dd><dt>19</dt><dd>Motor axis of the second DC motor 11</dd><dt>21</dt><dd>first clutch</dd><dt>23</dt><dd>second clutch</dd><dt>25</dt><dd>connecting element</dd><dt>26</dt><dd>Control unit</dd><dt>27</dt><dd>bridge switch</dd><dt>28</dt><dd>Power supply network</dd><dt>29</dt><dd>battery switch</dd><dt>31</dt><dd>battery</dd><dt>32</dt><dd>Sensor for temperature</dd><dt>33</dt><dd>charger</dd><dt>35</dt><dd>Replacement power plant</dd><dt>37</dt><dd>auxiliary switch</dd><dt>38</dt><dd>switching element</dd><dt>39</dt><dd>Additional power plant</dd></dl>