JP4705682B2 - Inverter for two direct current sources and driving method of the inverter - Google Patents

Description

The present invention provides a first direct current for converting electrical energy from a first direct current source and a second direct current source having a common reference potential to be supplied to a conductor and a neutral conductor of the alternating current source. The current source has a positive potential with respect to the reference potential, the second DC current source has a negative potential with respect to the reference potential, and the common reference potential of the two DC current sources is connected to the neutral conductor; The inverter relates to an inverter including a first down converter that connects a positive potential to the conductor of the alternating current source and a second down converter that connects a negative potential to the conductor of the alternating current source . The present invention further relates to a method for driving such an inverter.

  Inverters having various topologies for feeding power from a direct current source to an alternating current source are known. For example, direct current sources, such as cells of photovoltaic devices, fuel cells, batteries, etc., usually have a voltage characteristic curve related to the current drawn (derived current). Due to external influences, for example in the case of photovoltaic cells, the maximum output of the extracted current, the so-called max power point MPP, changes due to the variable light characteristics. This kind of dynamic operating state must be taken into account when controlling the inverter.

  In addition, the inverter is driven by a driver circuit of an AC power source so as to supply a sinusoidal current to an AC current source regardless of whether it is a joint network or a so-called isolated network.

  A simple means of controlling the inverter is given in US Pat. No. 6,914,418. This is called a so-called MPP tracking device, in which the continuously extracted current is slightly changed and multiplied by the measured voltage of the DC current source. The power thus obtained is compared with the power measured immediately before. The obtained voltage is also compared with the voltage measured immediately before. Depending on the power and voltage changes taken, a correspondingly increased current or a correspondingly reduced current is set in the next step.

  Instead, U.S. Pat. No. 4,390,940 describes an inverter that can drive a photovoltaic cell at maximum power.

  Known inverter topologies are selected based on the voltage level of the connected DC current source for a particular application. When the voltage level of the direct current source is below the peak voltage of the alternating current source to be fed, the inverter usually has an upconverter stage and an inverter stage. US application 2004/0165408 describes an inverter in which two DC current sources are connected to a common reference potential.

  Inverters having only an inverter stage are also known because the upconverter stage is not lossless and reduces the efficiency of the inverter stage. In that case, the voltage of the connected direct current source must always exceed the peak voltage of the alternating current source. According to the prior art, the direct current sources are grouped as so-called strings, and the output voltage of the strings is a multiple of the voltage of the individual direct current sources.

  In particular, alternative direct current sources such as photovoltaic cells or fuel cells require the high efficiency of the inverter to be used at an advantageous cost.

  Therefore, an object of the present invention is to provide an inverter that is more efficient than the prior art.

This problem is solved in the inverter that converts the electrical energy from the first DC current source and the second DC current source having a common reference potential and supplies them to the conductor and the neutral conductor of the AC current source. The current source has a positive potential with respect to the reference potential, the second DC current source has a negative potential with respect to the reference potential, and the common reference potential of the two DC current sources is connected to the neutral conductor; In the inverter driving method, the inverter includes a first down converter that connects a positive potential to the conductor of the alternating current source and a second down converter that connects a negative potential to the conductor of the alternating current source. After the reduction of the power supplied to the power converter is set, the energy of the potential connected to the down converter is transmitted to the other potential by the compensation converter, and the energy is transmitted from the compensation converter. The arrangement for setting the high supply power to more down-converter connected to a potential that is, Ru is resolved.

The potential to which the first down converter is connected corresponds to the positive terminal of the first DC current source. The potential to which the second down converter is connected corresponds to the negative terminal of the second DC current source. The current extracted by the down converter is set so that the maximum output is extracted from the direct current source .

Advantageously, the two downconverters are driven alternately to produce a supply current in the form of a complete sine wave. In this driving, a positive sine half wave is formed from the positive potential applied to the input side by the first down converter, and a negative sine half wave is formed from the negative potential applied to the input side by the second down converter. Is performed. Thereby, the energy from two direct current sources can be supplied to one alternating current source .

Also advantageously, the voltage of the first DC current source and the current drawn therefrom are continuously measured and the product of the voltage and current of the first DC current source is continuously driven by driving the first down converter. To the instantaneous maximum output of the first DC current source, and the voltage of the second DC current source and the current drawn therefrom are continuously measured, and the second DC is driven by driving the second down converter. The product of the voltage and current of the current source is continuously approximated to the instantaneous maximum output of the second DC current source. In this way, the maximum output is always taken from the two DC current sources, and the overall efficiency is optimized .

In order to prevent a DC component from being generated in the supply current, the DC component of the supply current is continuously measured, and when a positive DC component is present, a low supply power is set for the first down converter, When a negative DC component is present, a low supply power is set for the second down converter .

The present invention further includes a first direct current source for converting electrical energy from a first direct current source and a second direct current source having a common reference potential to be supplied to a conductor and a neutral conductor of the alternating current source. The DC current source has a positive potential with respect to the reference potential, the second DC current source has a negative potential with respect to the reference potential, and the common reference potential of the two DC current sources is connected to the neutral conductor. The inverter relates to an inverter including a first down converter that connects a positive potential to the conductor of the alternating current source and a second down converter that connects a negative potential to the conductor of the alternating current source. Here, the positive potential of the first DC current source and the negative potential of the second DC current source are connected to each other via the compensation converter. This is particularly important in the case where the current supplied to the alternating current source must not have a direct current. The difference between the maximum outputs of the two DC current sources is compensated by transmitting the excess power of one DC current source to the other DC current source via the compensation converter .

Furthermore, the inverter of this invention has a control unit provided with the suitable means which controls each down converter and compensation converter, This control unit is an inverter of any one of Claim 1 to 4 Each step of the driving method is configured to be executed. Since the control signal is formed in the inverter itself, the inverter can be integrated. The control unit sets a high supply power for the downconverter connected to the potential at which energy is transferred from the compensation converter .

The inverter of the present invention reduces the number of required elements and thus the power loss to a minimum, optimizing efficiency compared to known inverters. Here, the voltage of the direct current source is at least equal to or higher than the maximum peak voltage predicted by the alternating current source.

Advantageously, the first DC current source and the second DC current source are configured as so-called strings of photovoltaic devices. In this case, each string delivers a voltage that exceeds the peak voltage of the alternating current source. Since the photovoltaic device cell is usually mounted on the roof of a building, the reference potentials of the two strings are such that an AC electric field having a power frequency with respect to earth is generated in the building and does not cause a failure. Connected to neutral conductor.

  According to an advantageous embodiment of the invention, the first downconverter comprises a first capacitor, a first switching element, a first auxiliary switching element and a first diode and a choke circuit connected in series therewith. Including a positive potential and a reference potential of the first DC current source on the input side, and connected to a conductor of the AC current source via a filter capacitor on the output side, and the second down converter includes a second capacitor, A second switching element, a second auxiliary switching element, a second diode connected in series to the second switching element, and a choke circuit; the input side has a negative potential and a reference potential of the second DC current source; Is connected to the conductor of the AC current source via the filter capacitor, and the neutral conductor is connected to the common reference potential of the first DC current source and the second DC current source. It has been continued. With such a topology, two down converters that connect two DC current sources to one AC current source are particularly easily formed.

Advantageously, the choke circuit is divided into a first choke element and a second choke element, the first down converter comprising a first choke element, and the second down converter being a second choke element. including. The If such load switching elements Ru is significantly reduced.

Also advantageously, the compensation converter includes a third switching element and a fourth switching element connected in series with the third switching element, and the connection point between the third switching element and the fourth switching element is the third switching element. Are connected to a reference potential via a choke element and current measuring means. This realizes a simple topology of the compensation converter with a small number of elements and achieves high efficiency.

  Here, it is advantageous if the current measuring means has a shunt resistance. In this way, the current can be easily measured. However, it is also possible to use other types of current measuring means such as a magnetic transducer that compensates for direct current.

  More advantageously, a third diode is arranged antiparallel to the first switching element and a fourth diode is arranged antiparallel to the second switching element. Through these diodes, the energy stored in the choke circuit when the inverter is separated from the alternating current source can be reduced. Each diode also forms a protection element of the inverter protection circuit against a voltage peak in the alternating current source.

In order to protect the inverter element against voltage peaks in the alternating current source, the connection point between the second switching element and the second choke element is the fifth diode and the first resistor and third capacitor. And a connection point between the first switching element and the first choke element is connected to the parallel circuit consisting of the sixth diode and the second resistor and the fourth capacitor. To the reference potential. Each diode connected antiparallel to the first switching element and the second switching element forms a current path that leads to the capacitor even when a voltage peak from the AC current source occurs. Thereby, the short-time overvoltage is reduced by the choke circuit, and the switching element is not loaded. Therefore, it is not necessary to design the switching element to be large, and a complicated additional filter is not necessary .

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 shows a circuit diagram of a basic circuit. FIG. 2 shows a circuit diagram of a circuit having two choke elements. FIG. 3 shows a circuit diagram of a circuit having a compensation converter. FIG. 4 shows a circuit diagram of a circuit having a compensation converter and a protection circuit against voltage peaks.

  FIG. 1 shows a circuit diagram of an embodiment of an inverter having two down converters arranged in parallel according to the present invention. The input of the first down-converter comprising the first capacitor C1, the first switching element S1 (eg, transistor), the first diode D1, and the choke as the choke circuit L is connected to the positive terminal of the first DC current source. Terminal, that is, positive potential 1, and negative terminal, that is, reference potential 0 are connected. The positive terminal, that is, the reference potential 0 and the negative terminal, that is, the negative potential 2 of the second DC current source are connected to the second down converter. The second down converter includes a second capacitor C2, a second switching element S2 (for example, a transistor), a second diode D2, and a choke as a choke circuit L.

  Two auxiliary switching elements SH1 and SH2 are further arranged so that a short circuit of the power supply does not occur. Here, the first auxiliary switching element SH1 of the first down converter is arranged in series with the first diode D1. The first auxiliary switching element SH1 is cut off when the second down converter operates. The second auxiliary switching element SH2 of the second down converter is arranged in series with the second diode D2, and is cut off when the first down converter operates.

  In the circuit shown in FIG. 2, unlike the circuit shown in FIG. 1, two choke elements L1 and L2 are arranged as the choke circuit L. Here, the first down converter includes a first choke element L1, and the second down converter includes a second choke element L2. In this device, the load on the switching elements S1 and S2 can be reduced.

On the output side, the inverter is connected to an alternating current source. Here, the reference potential 0 is consistently connected to the neutral conductor N _Netz , and the output side of the choke circuit L is connected to the conductor _L1Netz of the alternating current source. On the output side, a filter capacitor CF is arranged between the neutral conductor N _Netz and the conductor L _{1 Netz} .

  A third diode D3 is arranged antiparallel to the first switching element S1, and a fourth diode D4 is arranged antiparallel to the second switching element S2. These diodes keep the current path open to return the magnetizing energy of the choke circuit L when the inverter is separated from the alternating current source.

  The two direct current sources are formed, for example, by two strings of photovoltaic devices. The inverter supplies the energy from the string to the connected AC current source if the string voltage is higher than the maximum peak value predicted by the AC voltage (eg 230V × 10% × 1.414 = 358V).

  The string is composed of panel surfaces of the same size, where the first panel surface supplies power only to the first down converter when energy is supplied by the positive power half wave, and the second panel surface is When energy is supplied by the negative half-power wave, only the second down converter is fed. In order to prevent the direct current component from being supplied to the alternating current source, the two panel surfaces assume the same amount of energy.

  The two capacitors C1 and C2 are designed to have a sufficient size. This is because each down converter supplies energy to the AC current source during the corresponding half of the power supply, and no energy is output during that time. Capacitors C1 and C2 are charged from a direct current source during periods when energy is not output, but must not reach a voltage limit set for switching.

  The inverter is driven as follows. That is, first, the direct current component of the current supplied to the alternating current source is measured. This is done, for example, by a current transducer with a Hall sensor. The residual DC current obtained in this way is used as an input quantity for controlling the two down converters.

  The down converter is closed-loop controlled by the current target value setting unit. The current supplied to the alternating current source by the alternating current source driver circuit must be sinusoidal, that is, free of harmonics of the current. To achieve this, there are two means of forming the basic current target value. That is, a) Deriving a sine half-wave from a power supply voltage by a voltage divider and using it as a model of current shape; b) Storing the sine half-wave as a table in a memory (for example, EPROM), and a period of 50 Hz The data is read and converted into an analog signal by a DA converter. In the latter means, it is necessary to form a synchronization pulse from the power supply voltage in order to indicate the start of each half wave and to start the reading process from the memory. This means is more complicated than the means a), but this current distortion can be compensated by adapting the table according to the current distortion caused by the circuit. In either of the two cases, a sinusoidal half-wave train occurs. Here, a basic current target value signal consisting of a positive sine half wave is formed for the first down converter, and a basic current target value signal consisting of a negative sine half wave for the second down converter. It is formed. A complete sine wave signal is obtained by adding the signals of the two basic current target values.

  In the next step, a load value for each of the two DC current sources is formed. When each DC current source delivers the maximum output, that is, when each DC current source operates at the maximum power point MPP, each load value is determined. For the panel surface of the photovoltaic device, the current characteristic curve is output based on the irradiation of sunlight, and the maximum output is supplied to the power source. In this case, the irradiation of sunlight is measured and a corresponding current value is set. However, obstacle factors such as partial shadows or dirt on the panel surface remain unconsidered.

  The so-called MPP tracking device thus measures the current continuously drawn from the string and the corresponding string voltage and multiplies them together. A slight change in the load detects whether the output tends to increase or whether the output has reached a maximum value.

  As an output of the MPP tracking device, an output signal describing the target current or target voltage from one string is generated. In setting the target voltage, the inverter must increase the current until the string voltage drops to the set value. In the embodiment of the present invention, the target voltage is used as a control set value. The target voltage does not change so quickly due to the connected capacitors C1 and C2, so that the closed loop control of the voltage value is performed more stably than the closed loop control of the current value.

  A target voltage is set as a target value for each of the two DC current sources by the MPP tracking device. Here, the voltage at one of the capacitors C1 and C2 is compared with the target value by the differential amplifier for each DC current source. The control characteristic requires an integral component, for example, a PI control circuit, to provide a slow response and to keep the control deviation small.

  In order to limit the output of each down converter and protect the components of the output stage, a maximum value is advantageously set for the output signal of each differential amplifier. Thereby, the target current is limited, and current distortion and harmonics in the alternating current are not generated.

  A target current for driving each down-converter is formed by multiplying the output signal of the differential amplifier by the signal of each basic current target value. Here, the output signal of the differential amplifier of the first down converter is multiplied by the signal of the basic current target value formed from the derived value of the positive sine half wave. The output signal of the differential amplifier of the second downconverter is multiplied by the basic current target value signal formed from the negative half sine wave derived value.

  Advantageously, the downconverter is driven in a so-called current mode. Here, the switching frequency of the switching elements S1 and S1, for example, 30 kHz, is determined by the clock generator.

  The individual switching processes follow the variant shown in FIG. Here, the first down converter is considered first. The first switching element S1 is switched on at the start of the period. As a result, a current flows through the choke element L1, and the current increases in accordance with the equation: current increase ΔI = [voltage U / inductance L1] × switch on time At.

  The comparator compares the current flowing through the first choke element L1 with the current target value. When the choke current reaches the current target value, the comparator cuts off the first switching element S1. As a result, the choke current is rectified by the first diode D1 and the auxiliary switching element SH1 connected in series therewith.

  In order to prevent an overcurrent that rises rapidly due to an impulse of the power supply voltage or an external failure of the electronic circuit, a fixed limit value is set for the comparator that measures current, and when the current exceeds the set value The switching elements S1 and S2 can be shut off immediately.

  The current is best measured by a shunt resistor or a direct current compensation type current sensor in the drain section of the first switching element S1. With one terminal leading to the first capacitor C1, the measured current signal is hardly disturbed.

  There is also means for measuring the current during the return period of the magnetization energy of the first choke element L1. An advantageous measuring point exists in the drain section of the first auxiliary switching element SH1. The current is out of phase with the current passing through the first switching element S1. Finally, the current flowing through the first switching element S1 is measured. Since the choke element L1 prevents an abrupt current change, the first switching element S1 is cut off and the choke current is rectified by the first diode D1 and the first auxiliary switching element SH1 for only a very short time. A current further flows through the first switching element S1. Based on the detected current value, an intervention is made in the switch-on time of the first switching element S1, and the clock generator is controlled.

  The first switching element S1 is no longer driven in the known current mode. This is because the first switching element S1 is not directly cut off by the rising choke current, but is cut off using a current value detected at a later time.

  The second down-converter including the second capacitor C2, the second switching element S2, the second choke element L2, the second diode D2, and the second auxiliary switching element SH2 is in a negative power supply half-wave. Works accordingly.

  Since the device of the present invention is an inverter for two DC current sources, it is meaningful to prevent the downconverter drive stage that is not in the drive mode. This is particularly important during the transition from a positive half-wave to a negative half-wave. Around the zero point of the power supply, the AC current source is likely to fail due to round control impulses and switching processing. If two down converters are operated at this time, a current flows between the two down converters, and a significant loss occurs.

  As described above, in the supply protocol by the driver circuit of the alternating current source, control is performed so that the direct current component of the current is not supplied to the alternating current source as much as possible. In order to satisfy this requirement, the following means are adopted. First, the alternating current supplied to the current sensor (converter or shunt resistor) of the power supply line of the inverter is measured. In a simple case, a direct current flowing into the power supply is detected via an integrator consisting of RC elements having a time constant far exceeding the power supply frequency of 50 Hz. Alternatively, the current of each half-sine wave may be digitized, integrated in the processor, and subtracted from each other.

  A correction signal is derived from the direct current signal. This correction signal is used as an additional signal in the current control by the down converter, and limits the output of the down converter that has supplied the direct current component to the alternating current source. Only the power supplied to one downconverter is always reduced. This is because a DC current source operating at the MPP operating point cannot deliver any more power to compensate for non-uniformities in the supply current.

  Taken from a DC current source providing higher power (eg, more efficient fuel cells, large photovoltaic cells with different panel area, power loss, or roof tilt for each tile, etc.) The current is reduced and no direct current is supplied. By doing so, the voltage of the direct current source increases and no longer operates at the optimum operating point. It is therefore important to use the same two DC current sources with equal maximum power.

  If the requirement to use two DC current sources with equal maximum power is not met, the circuit of the present invention includes a compensation converter AW for energy transfer between the first capacitor C1 and the second capacitor C2. To be replenished. In this way, the two direct current sources can deliver maximum power. When there is a surplus in the output of the first DC current source, a half of the surplus is transmitted from the first capacitor C1 to the second capacitor C2 of the second down converter. Similarly, when there is a surplus in the output of the second DC current source, a half of the surplus is transmitted from the second capacitor C2 to the first capacitor C1 of the first down converter.

FIG. 3 shows a choke inverter in which the following elements are added to the basic circuit shown in FIG. The choke inverter includes a third choke element L3. The first terminal of the third choke element L3 is connected to the neutral conductor N _Netz via the shunt resistor RS in order to measure current. The second terminal of the third choke element L3 is connected to the drain section of the first switching element S1 via the third switching element S3, and further to the second switching via the fourth switching element S4. It is connected to the drain section of the element S2. In some cases, a freewheel diode, for example a MOSFET or IGBT with a freewheel diode, is arranged antiparallel to the two switching elements S3, S4 of the inverter.

  Instead, a bidirectional converter, for example, a blocking converter, may be used as the compensation converter AW.

  Advantageously, the closed loop is not complicated because the control of the compensation converter AW operates independently of the rest of the control.

  For each down-converter, in addition to the differential amplifier that defines the supply current, a separate differential amplifier that determines the control deviation between the MPP target voltage and the actual voltage is arranged. When the control deviation reaches a settable maximum value, for example, 2% of the MPP target voltage, the compensation converter AW is started. The compensation converter AW transfers the surplus energy from one capacitor to the other. The difference signal is supplied as a target current set value to the compensation converter AW.

  The control of the compensation converter AW opposes the control of the direct current described above. When the direct current controller detects a direct current component in the supply current, the current drawn from the direct current source that is sending a strong output is first reduced. Thus, the higher DC current source moves away from the MPP operating point, and in response, control of the compensation converter is required, and current extraction is again increased. If the other down converter feeds power by the compensation converter AW and the outputs become equal, the direct current component in the supply current decreases.

  There are two means for increasing the power transmitted by the down converter that additionally supplies power. Control by the MPP tracking device takes place after a large time constant without additional intervention in the control unit. This is because MPP tracking devices generally have slow control dynamics.

  In order to quickly increase the supply current of the additionally supplied down converter, it is advantageous to form the target current of the down converter directly on the basis of the output of the compensation converter AW.

  Since the compensation converter AW can transmit energy in two directions, a photovoltaic device when the inverter is rotating at high speed or when the output of the DC current source fluctuates strongly (eg when the movement of the cloud is very fast) The panel should be tested for drive by applying different criteria. If there is a request to transfer energy from both downconverters to the other downconverter, the controller must block the compensation converter AW. In this case, a stable status does not occur and the feed power of the two down converters must be increased until the MPP operating point is reached.

  If devices with structural differences due to manufacturing techniques are used for the two DC current sources, the digital control can be used to improve the control dynamics. This is the case, for example, in the case of a photovoltaic device in which the direct current source formed by one string has only a small panel area. The digital controller detects the output difference between the two DC current sources over several hours and forms an average value. This average value sets the compensation output to be transmitted from the compensation converter AW immediately upon the next switch-on of the device. Even weighting of the control is achieved in a short time by this means.

  FIG. 4 shows a basic diagram of a circuit with additional circuit elements for escaping voltage peaks generated in the compensation converter and the alternating current source. The voltage peak is triggered, for example, by a switching process, but its pulse voltage level reaches several kilovolts on the 230V / 400V line. In order to protect the electronic circuit of the inverter from such a voltage peak, it is usually required to design a circuit element larger. Moreover, a complicated filter is also required.

  The circuit of the present invention is provided with an additional current path having two additional capacitors C3 and C4. Since the current is conducted to the four capacitors C1 to C4 via the choke elements L1 and L2, it is guaranteed that the voltage load on the circuit element hardly exceeds the maximum load corresponding to the operation mode. It should be noted here that the time constant of the LC circuit composed of the choke elements L1 and L2 and the capacitors C1 to C4 is larger than the maximum time constant expected for the overvoltage impulse of the power supply.

  The additional circuit element includes a parallel circuit in which the connection point between the second switching element S2 and the second choke element L2 is the fifth diode D5, and the first resistor R1 and the third capacitor C3. And is arranged to be connected to the reference potential 0 via Further, the reference potential 0 is between the first switching element S1 and the first choke element L1 via the parallel circuit including the fourth capacitor C4 and the second resistor R2 and the sixth diode. Connected to the connection point.

  At this time, it is necessary to provide a plurality of MOSFETs incorporating diodes D3 and D4, for example, diodes, in antiparallel to the switching elements S1 and S2 of the down converter.

  When a positive voltage impulse is generated from the AC current source, the circuit device operates as follows. At this time, the first capacitor C1 is charged to the peak value of the power supply voltage through the preceding power supply period. Since the first capacitor C1 has a high ohmic discharge resistance, almost no post-charging occurs in the normal operation mode, and no harmonic distortion of the sine wave current occurs. A positive voltage impulse causes a current to flow to the first capacitor C1 via the first choke element L1 and the third diode D3 disposed antiparallel to the first switching element S1. For this reason, the voltage at the connection point between the first switching element S1 and the first diode D1 is limited to a value obtained by adding the diode threshold value of the third diode D3 to the voltage of the first capacitor C1. At the same time, a current flows to the third capacitor C3 via the second choke element L2 and the fifth diode D5. As a result, the voltage at the connection point between the second switching element S2 and the second diode D2 is limited to a value obtained by adding the diode threshold value of the fifth diode D5 to the voltage of the third capacitor C3. When the voltage peak of the power supply is attenuated, the magnetizing energy of the two choke elements L1 and L2 is returned, and finally no current flows to the capacitors C1 and C3.

  When an impulse of negative voltage is generated from the AC current source, the characteristics through the fourth diode D4 and the second capacitor are equal to the characteristics through the sixth diode D6 and the fourth diode C4. Controlled.

  Capacitors C1-C4 are selected so that they are not charged to unacceptable heights even if the maximum overvoltage predicted by the power source continues for the maximum time expected. After the current due to the overvoltage is accommodated, the third capacitor C3 and the fourth capacitor C4 are discharged again via the first resistor R1 and the second resistor R2 connected in parallel.

  An important advantage of such a design is that the function of the protection circuit does not depend on the switching speed of the monitoring part and possibly the power switching element. This is because the choke elements L1 and L2 behave like a current source, and an arbitrary voltage can be increased in a very short time, for example, several tens of ns. Furthermore, after returning the magnetization energy, oscillation may occur due to a parasitic capacitance, for example, a coil capacitance, which may overload the control of the power switching element when the protection circuit is active. Therefore, only the diode is provided as the limiting element in the protection circuit of the present invention.

  Instead of the configuration of the protection circuit described above, a configuration in which a low ohmic discharge resistor is connected to the capacitors C1 to C4 via an additional switching element may be employed. In this way, the voltage applied to the capacitors C1 to C4 is monitored by the comparator, and the discharge resistor is turned on when the voltage reaches the upper limit value.

  As another configuration of the protection circuit, a varistor for limiting the voltage may be provided, and the choke elements L1 and L2 may be connected to the varistor via a diode. In this case, attention should be paid to the internal differential resistance of the varistor or suppressor diode. This is because a high current that significantly increases the limit voltage may be generated.

  The first switching element S1 and the second switching element S2 are positive or negative when an overvoltage occurs, that is, when the power supply voltage exceeds a predicted maximum peak voltage, for example, [240V + 10%] × peak coefficient = 373V. The switching elements S1 and S2 are controlled to be cut off for a predetermined time in both directions. As a result, a time for attenuating the pulse voltage and the current in the choke elements L1 and L2, for example, 500 ns can be obtained.

It is a circuit diagram of a basic circuit. It is a circuit diagram of a circuit having two choke elements. It is a circuit diagram of a circuit having a compensation converter. FIG. 3 is a circuit diagram of a circuit having a compensation converter and a protection circuit against voltage peaks.

Claims (12)

The electric energy from the first DC current source and the second DC current source having a common reference potential (0) is converted and supplied to the conductor (L1 _Netz ) and the neutral conductor (N _Netz ) of the AC current source. for,
The first DC current source has a positive potential (1) with respect to the reference potential (0), the second DC current source has a negative potential (2) with respect to the reference potential (0), and two DC currents The common reference potential (0) of the source is connected to the neutral conductor (N _Netz ),
The inverter includes a first down converter that connects a positive potential to the conductor of the alternating current source (L1 _Netz ) and a second down converter that connects a negative potential (2) to the conductor of the alternating current source (L1 _Netz ). Inverter driving method including:
Set the reduction of the power supply of one down converter by controlling the direct current,
After the reduction of the power supplied to one of the down converters is set, the energy of the potential (1; 2) to which the down converter is connected is transferred to the other potential (2; 1 ) by the compensation converter (AW). )
A driving method of an inverter, characterized in that a high supply power is set for a down converter connected to a potential (2; 1 ) to which energy is transmitted from an compensation converter (AW).   The two down converters are driven alternately to produce a supply current in the form of a complete sine wave, where a positive sine half wave is generated from the positive potential (1) applied to the input side by the first down converter. The method according to claim 1, wherein a negative sine half wave is formed from a negative potential (2) applied and applied to the input side by a second down converter.   The voltage of the first DC current source and the current extracted therefrom are continuously measured, and the first down converter is driven to continuously calculate the product of the voltage and current of the first DC current source. Approximate the instantaneous maximum output of the DC current source, continuously measure the voltage of the second DC current source and the current drawn from it, and drive the second down converter to obtain the voltage of the second DC current source 3. A method according to claim 1 or 2, wherein the product of current is continuously approximated to the instantaneous maximum output of the second direct current source.   The DC component of the supply current is continuously measured. When a positive DC component is present, a low supply power is set for the first down converter, and when a negative DC component is present, the second down converter is set. 4. The method of claim 3, wherein a low supply power is set. The electric energy from the first DC current source and the second DC current source having a common reference potential (0) is converted and supplied to the conductor (L1 _Netz ) and the neutral conductor (N _Netz ) of the AC current source. for,
The first DC current source has a positive potential (1) with respect to the reference potential (0), the second DC current source has a negative potential (2) with respect to the reference potential (0), and two DC currents The common reference potential (0) of the source is connected to the neutral conductor (N _Netz ),
The inverter includes a first down converter that connects a positive potential to the conductor of the alternating current source (L1 _Netz ) and a second down converter that connects a negative potential (2) to the conductor of the alternating current source (L1 _Netz ). Including,
In the inverter,
The positive potential (1) of the first direct current source and the negative potential (2) of the second direct current source are connected to each other via a compensation converter (AW),
The inverter has a control unit with suitable means to control each downconverter and compensation converter,
The control unit sets a reduction in the supply power of one down converter by controlling a direct current, and is connected to the down converter after the reduction in the supply power of the one down converter is set. The energy of the other potential (1; 2) is transmitted to the other potential (2; 1) by the compensation converter (AW) and connected to the potential (2; 1) to which energy is transmitted from the compensation converter (AW). An inverter characterized in that it is configured to set a high power supply to the downconverter that is being used.   6. The inverter according to claim 5, wherein the first direct current source and the second direct current source are configured as so-called strings of photovoltaic devices. The first down-converter includes a first capacitor (C1), a first switching element (S1), a first auxiliary switching element (SH1), a first diode (D1) connected in series to the first down-converter (SH1), and a choke circuit. (L), the positive potential (1) and reference potential (0) of the first DC current source on the input side, and the conductor (L1 _Netz ) of the AC current source via the filter capacitor (CF) on the output side The second down converter includes a second capacitor (C2), a second switching element (S2), a second auxiliary switching element (SH2), and a second diode connected in series to the second capacitor (C2). (D2) and a choke circuit (L), the negative potential (2) and reference potential (0) of the second DC current source on the input side, and the filter capacitor (CF) on the output side And it is connected to the AC current source conductor (L1 _Netz), a neutral (N _Netz) is connected to the common reference potential of the first direct current source and the second direct current source (0) The inverter according to claim 5 or 6.   The choke circuit (L) is divided into a first choke element (L1) and a second choke element (L2), and the first down converter includes a first choke element (L1), The inverter according to claim 7, wherein the down converter includes a second choke element (L2).   The compensation converter (AW) includes a third switching element (S3) and a fourth switching element (S4) connected in series to the third switching element (S3) and the fourth switching element (S4). 9. The inverter according to claim 5, wherein the connection point is connected to the reference potential (0) via the third choke element (L 3) and the current measuring means.   The inverter according to claim 9, wherein the current measuring means includes a shunt resistor (RS).   A third diode (D3) is disposed antiparallel to the first switching element (S1), and a fourth diode (D4) is disposed antiparallel to the second switching element (S2). The inverter according to any one of claims 5 to 10.   The connection point between the second switching element (S2) and the second choke element (L2) is a parallel composed of a fifth diode (D5), a first resistor (R1), and a third capacitor (C3). The connection point between the first switching element (S1) and the first choke element (L1) is connected to the reference potential (0) through the circuit, and the sixth diode (6) and the second 12. Inverter according to claim 11, connected to a reference potential (0) via a parallel circuit consisting of a resistor (R2) and a fourth capacitor (C4).

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