Electrical energy conversion device
The device with a current and voltage inverter maintains efficient energy conversion and system operation during voltage drops by adjusting voltage and current, ensuring continuous power delivery and preventing short-circuit conditions.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Applications
- Current Assignee / Owner
- COMMISSARIAT A LENERGIE ATOMIQUE ET AUX ENERGIES ALTERNATIVES
- Filing Date
- 2024-12-02
- Publication Date
- 2026-06-05
AI Technical Summary
Existing energy conversion systems fail to maintain efficient operation when there is a voltage drop in the alternating current voltage source, particularly in photovoltaic systems, leading to a decrease in the voltage of the direct current voltage source and preventing power injection into the grid.
A device comprising a current inverter and a voltage inverter, where the current inverter adjusts the voltage and current between a direct current and alternating current source, and the voltage inverter maintains minimum energy conversion during voltage drops, ensuring continuous operation through a capacitor and maintaining the minimum operating voltage.
Ensures continuous energy conversion and operation of electrical systems during voltage drops, preventing a shift to short-circuit current and maintaining system functionality by using a current inverter and a voltage inverter with a minimum operating voltage.
Smart Images
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Abstract
Description
Title of the invention: Electrical energy conversion device
[0001] The present invention relates to a device for converting electrical energy between a direct current voltage source and an alternating current voltage source. The present invention also relates to an associated electrical assembly.
[0002] Conventionally, the conversion of energy from a direct current (DC) voltage source to an alternating current (AC) voltage source is carried out using a two-level voltage or three-level voltage inverter.
[0003] In the photovoltaic (PV) field, two types of energy conversion chains are commonly used:
[0004] - one comprising a single DC / AC conversion stage, and
[0005] - the other comprising a chopper stage, called "boost", at the input (DC / DC) which performs the The search for the maximum power point (MPPT) that allows for the extraction of the maximum power (MPP) from the photovoltaic generator is performed independently of the bus voltage of the DC / AC conversion stage.
[0006] A current inverter can also be used to convert the energy from a PV generator. This is a structure where the current source is at the input (PV generator side) and the voltage source at the output (grid side). Such a current inverter allows for direct current / voltage boosting to voltage conversion, thus eliminating a conversion stage and removing the capacitors from the DC bus.
[0007] However, when the voltage source is on the grid side (as in the case of current inverters), and the grid experiences a voltage drop, the voltage of the PV generator will decrease since it is imposed by the output, and the PV generator will then operate close to its short-circuit current. This makes it impossible to inject power into the grid.
[0008] The aim of the invention is then to propose an energy conversion device between a direct voltage source and an alternating voltage source comprising a current inverter and capable of operating even in the event of a voltage drop in the alternating voltage source.
[0009] To this end, the invention relates to a device for converting electrical energy between a direct current voltage source and an alternating current voltage source, the direct current voltage source operating over a voltage range having a minimum voltage, the device comprising:
[0010] - a current inverter suitable for connection between the DC voltage source and the alternating voltage source, the current inverter being designed to adjust the voltage across the terminals of the direct voltage source and to convert a portion of the electrical energy between the direct voltage source and the alternating voltage source, and
[0011] - a voltage inverter suitable for connection between the DC voltage source and the alternating voltage source, the voltage inverter being connected in series with the current inverter, the voltage inverter being suitable for converting the other part of the electrical energy between the direct voltage source and the alternating voltage source, the voltage inverter having an operating voltage equal to the minimum voltage so as to ensure a minimum energy conversion even in the event of a voltage drop in the alternating voltage source.
[0012] According to other advantageous aspects of the invention, the device comprises one or more of the following features, taken individually or in all technically possible combinations:
[0013] - the current inverter is configured to convert electrical energy from unidirectional between the DC voltage source and the AC voltage source;
[0014] - the current inverter is configured to convert electrical energy in a way bidirectional between the DC voltage source and the AC voltage source;
[0015] - the DC voltage source has an optimal voltage range having a lower voltage limit, the minimum voltage being less than or equal to the lower voltage limit of the optimal voltage range;
[0016] - the minimum voltage is equal to the lower voltage limit of the optimal domain of tension ;
[0017] - the DC voltage source is a power generation system photovoltaic, the lower voltage limit of the optimal voltage range being equal to the lower limit of the voltage range possible for operation at the maximum power point of the photovoltaic power generation system;
[0018] - the current inverter is a three-phase current inverter;
[0019] - the voltage inverter is a three-phase voltage inverter.
[0020] The invention also relates to an electrical assembly comprising:
[0021] - a DC voltage source, the DC voltage source operating on a voltage range having a minimum voltage,
[0022] - an alternating voltage source, and
[0023] - an electrical energy conversion device between the direct voltage source and the alternating voltage source, the device being as described previously.
[0024] According to other advantageous aspects of the invention, the electrical assembly comprises one or more of the following features, taken individually or in all technically possible combinations:
[0025] - the DC voltage source comprises one or more electrical modules connected in series and / or parallel, the electrical module(s) being chosen including: photovoltaic modules, batteries, electrolyzers and fuel cells.
[0026] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:
[0027] [Fig-1] [Fig.1] is a schematic view of an example of an electrical assembly comprising a direct current voltage source, an alternating current voltage source, and a device for converting energy between the direct current voltage source and the alternating current voltage source,
[0028] [Fig.2] [Fig.2] is a schematic view of an example of an embodiment of an electrical assembly, the electrical assembly allowing unidirectional energy transfer from a direct voltage source (power generator) to an alternating voltage source,
[0029] [Fig.3] [Fig.3] is a schematic view of an example of a current-voltage characteristic for the electrical assembly of [Fig.2],
[0030] [Fig.4] [Fig.4] is a schematic view of an example of the operation of the electrical assembly of [Fig.2] symbolizing the case of a voltage drop from the alternating voltage source,
[0031] [Fig.5] [Fig.5] is a schematic view of an example of the current-voltage characteristic of the electrical assembly of [Fig.2] during a voltage drop from the AC voltage source,
[0032] [Fig. 6] [Fig. 6] is a schematic view of an example of another embodiment of an electrical assembly, the electrical assembly enabling bidirectional energy conversion (towards a load consuming or supplying energy) from an alternating voltage source to a direct voltage source, and
[0033] [Fig.7] The [Fig.7] is a schematic view of an example of yet another embodiment of an electrical assembly, the electrical assembly allowing a unidirectional energy transfer (towards an energy-consuming load) from an alternating voltage source to a direct voltage source.
[0034] An electrical assembly 10 is schematically illustrated in [Fig.1].
[0035] The electrical assembly 10 includes a direct voltage source 12 (or DC source), an alternating voltage source 14 (or AC source) and a device 16 for converting electrical energy between the direct voltage source 12 and the alternating voltage source 14.
[0036] The DC voltage source 12 may comprise at least one electrical module, a DC voltage source. It may also consist of a set of electrical modules in series, forming a DC voltage source, for example, photovoltaic modules in series.
[0037] A minimum operating voltage Vmin is defined for this voltage source, which ensures acceptable operation, i.e. maintaining electricity production and / or absorption at a level compatible with the operation of the system.
[0038] Preferably, this minimum operating voltage Vmin can be chosen to be less than or equal to the voltage VMPPmin which corresponds to the lower limit of the optimal voltage range of the DC voltage source 12. In the case of a photovoltaic installation, this optimal voltage range corresponds for example to the possible voltage range for operation at the maximum power point of the installation given the environmental conditions (e.g. the possible temperature range of the photovoltaic modules).
[0039] Even more preferably, Vmin can be chosen to be equal to VMPPmin, which corresponds to the examples of embodiments illustrated in the rest of the application and for which reference will therefore be made only to VMPPmin.
[0040] The alternating voltage source 14 is formed from one or more alternating voltage sub-sources. In the example of Figures 2, 4, 6 and 7, the alternating voltage sub-sources originate from a transformer with two secondary windings, for example a three-phase delta-connected transformer and a three-phase wye-connected transformer. Alternatively, they may be two independent transformers.
[0041] In addition or alternatively, the alternating voltage sub-source(s) are, for example, an electrical network or energy-consuming devices, such as a computer device or a household appliance.
[0042] As illustrated by [Fig.1], the conversion device 16 comprises a current inverter 20 and a voltage inverter 22.
[0043] The current inverter 20 is suitable for connection between the DC voltage source 12 and the AC voltage source 14.
[0044] The current inverter 20 is suitable for adjusting the current flowing in the DC voltage source 12, and the associated voltage, and is suitable for transferring a portion of the power from the DC voltage source 12 to the AC voltage source 14. In particular, in the case of a DC voltage source based on photovoltaic modules, the current inverter 20 is suitable for operating the DC voltage source 12 at the maximum power point (MPP). For this purpose, the current inverter 20 is, for example, controlled by a disturbance and observation (P&O) type MPPT algorithm.
[0045] In one embodiment, the current inverter 20 is configured to convert electrical energy unidirectionally between the DC voltage source 12 and the AC voltage source 14. In particular, in the examples In Figures 2 and 4, the conversion takes place from the DC voltage source 12 to the AC voltage source 14 (which could be photovoltaic modules, batteries in discharge mode, and fuel cells). In the example in [Fig. 7], the conversion takes place from the AC voltage source 14 to the DC voltage source 12 (which could be batteries being charged or electrolyzers).
[0046] In another example of implementation, as illustrated by [Fig.6], the current inverter 20 is constructed to convert electrical energy bidirectionally between the DC voltage source 12 and the AC voltage source 14. This configuration is mainly of interest for batteries which can then be charged or discharged, and possibly for heterogeneous systems comprising both photovoltaic modules, and / or batteries and / or fuel cells and / or electrolyzers.
[0047] The current inverter 20 can be constructed from a wide variety of three-phase current inverters. In particular, in the examples in Figures 2, 4, 6 and 7, the current inverter 20 is a three-phase current inverter.
[0048] Preferably, the current inverter 20 includes at least one power semiconductor component.
[0049] In particular, in the examples of Figures 2, 4, and 7, the current inverter 20 comprises three parallel branches. Each branch is formed by two switches. Each switch comprises a transistor (for example, an IGBT: insulated-gate bipolar transistor) and a diode connected in series with the transistor. The midpoint between the switches of each branch is connected to the AC voltage source 14. In the examples of Figures 2 and 4, each switch (position of the diode and the transistor) is configured so that current flows only from the DC voltage source 12 to the AC voltage source 14. In the example of [Fig. 7], each switch is configured so that current flows only from the AC voltage source 14 to the DC voltage source 12.
[0050] In the example of [Fig. 6], the current inverter 20 comprises three parallel branches. Each branch consists of two switches. Each switch comprises two transistors connected in anti-series (e.g., IGBT: insulated-gate bipolar transistor) with a diode connected in anti-parallel across each transistor. Each switch (position of the diodes and transistors) is configured so that current flows bidirectionally from the DC voltage source 12 to the AC voltage source 14. The midpoint between the switches of each branch is connected to the AC voltage source 14.
[0051] In these examples, the current inverter 20 is connected to the DC voltage source 12 via an inductor, which allows the input waveform of the current inverter 20 to be smoothed.
[0052] The voltage inverter 22 is suitable for connection between the DC voltage source 12 and the AC voltage source 14. The voltage inverter 22 is connected in series with the current inverter 20. In the examples in Figures 2, 4, 6, and 7, the voltage inverter 22 is connected to the current inverter 20 via an inductor, which smooths the current. Furthermore, a capacitor Cl is also connected to the input of the voltage inverter 22, ensuring a nearly DC voltage source, particularly in the event of a voltage drop in the AC voltage source 14 (see the operation of the device described later).
[0053] The voltage inverter 22 is suitable for converting the other part of the electrical energy between the direct voltage source 12 and the alternating voltage source 14.
[0054] The voltage inverter 22 has an operating voltage equal to the minimum voltage VMPpmin (or in the more general case to the minimum operating voltage Vmin, which is here taken to be equal to VMppmm) so as to ensure a minimum energy transfer even in the event of a voltage drop in the AC voltage source 14. This prevents a shift towards zero power from the operating point of the DC voltage source 12 (towards the short-circuit current) during a voltage drop on the AC voltage source side 14. This function is called "Low voltage ride through" (LVRT) and corresponds to the ability of PV systems to remain operational during an accidental collapse of the grid injection point voltage.
[0055] In particular, the voltage inverter 22 is connected between a voltage reference terminal and a potential terminal equal to the minimum voltage VMpPmin.
[0056] Preferably, the voltage inverter 22 is selected from a three-phase voltage inverter technology. For example, with two voltage levels, or with multiple output voltage levels.
[0057] In particular, in the examples in Figures 2, 4, 6 and 7, the voltage inverter 22 is a three-phase voltage inverter.
[0058] Preferably, the voltage inverter 22 includes at least one power semiconductor component.
[0059] In particular, in the examples of Figures 2, 4, 6, and 7, the voltage inverter 22 comprises three parallel branches. Each branch has two switches in series. Each switch consists of a transistor (e.g., IGBT) and a diode connected in antiparallel. The midpoint between the switches of each branch is connected to the AC voltage source 14.
[0060] Alternatively, the voltage inverter 22 and the current inverter 20 can be single-phase inverters.
[0061] An example of the operation of the electrical assembly 10 will now be described.
[0062] In normal operation (no voltage drop from the AC voltage source 14), the current inverter 20 adapts the current, and the associated voltage, of the DC voltage source 12 over a voltage range. The current inverter 20 also converts a portion of the electrical energy between the DC voltage source 12 and the AC voltage source 14. The voltage inverter 22 converts the remaining electrical energy between the DC voltage source 12 and the AC voltage source 14.
[0063] In particular, in the example illustrated by [Fig. 2], the conversion of electrical energy is carried out unidirectionally from the DC voltage source 12 to the AC voltage source 14. In the example illustrated by [Fig. 6], the conversion of electrical energy is carried out bidirectionally between the DC voltage source 12 and the AC voltage source 14 depending on the nature of the DC voltage source 12. In the example illustrated by [Fig. 7], the conversion of electrical energy is carried out unidirectionally from the AC voltage source 14 to the DC voltage source 12.
[0064] Figure 3 illustrates, on the thin-lined curve, an example of the current-voltage characteristic of a series of PV modules. The bold curve illustrates the power as a function of the voltage. At 1200 V, the power produced is at its maximum on this characteristic.
[0065] In the event of a sudden drop in the voltage of the AC voltage source 14 (mains), the voltage delivered on the DC side by the current inverter 20 drops immediately since, by principle, it is always lower than the voltage on the AC side. The voltage delivered on the DC side by the voltage inverter 22, on the other hand, is always, by principle, higher than the voltage present on its AC side; its drop can therefore be delayed, which is made possible by the presence of the capacitor CL. If the voltage drop of the AC voltage source 14 is partial, the voltage inverter 22 can permanently compensate for or limit the voltage drop on the DC side. If the voltage of the AC voltage source 14 drops to zero, only the capacitor Cl maintains the voltage on the DC side, and it can only do so for a limited time proportional to its capacitance.Most network outages are brief, and it is therefore possible to size Cl so that service continuity is maintained in 90% of failure cases, for example by operating at the minimum voltage VMpPmin. This degraded operation is shown in the example in [Fig.4].
[0066] Figure 5 illustrates an example of a shift in the operating voltage of the DC voltage source 12 from 1200 V to 800 V following a voltage drop on the AC voltage source side 14. The energy produced by the voltage source The voltage at DC 12 is reduced (because the 800 V voltage is lower than the voltage at the maximum power operating point). However, continuity in energy conversion remains ensured. Furthermore, electronic equipment, such as auxiliary devices, connected to the DC voltage source 12 remain operational and can resume normal operation once the fault on the AC voltage source 14 side is resolved. These auxiliary devices are, in fact, normally powered by the DC voltage source. Without the invention, the voltage drop on the DC voltage source side would cause them to malfunction, and the system could potentially be unable to restart once the disturbance on the AC voltage source side has passed.
[0067] Thus, the electrical energy conversion device 16, through the use of a current inverter 20, eliminates the need for a chopper and therefore increases conversion efficiency. Furthermore, the voltage inverter 22 connected in series with the current inverter 20 enables electrical energy conversion even in the event of a voltage drop in the AC voltage source 14 (and therefore a malfunction of the current inverter 20).
[0068] Furthermore, even if the current inverter 20 is short-circuited in the event of a fault between the output terminals of the inductors L1 and L2 by any external electronic or electromechanical contactor, the voltage inverter will ensure continuity of service.
[0069] Such a conversion device 16 is particularly suitable for medium to high power and low to medium voltage applications, especially photovoltaic applications. Such a conversion device 16 is also suitable for other types of electrical modules, such as batteries, electrolyzers, or fuel cells.
[0070] A person skilled in the art will understand that the embodiments and variants described above can be combined to form new embodiments provided that they are technically compatible.
Claims
Demands
1. Device (16) for converting electrical energy between a direct current voltage source (12) and an alternating current voltage source (14), the direct current voltage source (12) operating over a voltage range having a minimum voltage (Vmin), the device (16) comprising: - a current inverter (20) suitable for being connected between the direct current voltage source (12) and the alternating current voltage source (14), the current inverter (20) being suitable for adjusting the voltage across the terminals of the direct current voltage source (12) and for converting a portion of the electrical energy between the direct current voltage source (12) and the alternating current voltage source (14), and - a voltage inverter (22) suitable for being connected between the direct current voltage source (12) and the alternating current voltage source (14), the voltage inverter (22) being connected in series with the current inverter (20),the voltage inverter (22) being suitable for converting the other part of the electrical energy between the direct current voltage source (12) and the alternating current voltage source (14), the voltage inverter (22) having an operating voltage equal to the minimum voltage (Vmin) so as to ensure a minimum energy conversion even in the event of a voltage drop in the alternating current voltage source (14).
2. Device (16) according to claim 1, wherein the current inverter (20) is configured to convert electrical energy unidirectionally between the DC voltage source (12) and the AC voltage source (14).
3. Device (16) according to claim 1, wherein the current inverter (20) is configured to convert electrical energy bidirectionally between the DC voltage source (12) and the AC voltage source (14).
4. Device (16) according to any one of claims 1 to 3, wherein the DC voltage source (12) has an optimal voltage range having a lower voltage limit (VMPPmin), the minimum voltage (Vmin) being less than or equal to the lower voltage limit (VMPPmin) of the optimal voltage range.
5. Device (16) according to claim 4, wherein the minimum voltage (Vmin) is equal to the lower voltage limit (VMpPmin) of the optimal voltage range.
6. Device (16) according to claim 4 or 5, wherein the DC voltage source (12) is a photovoltaic power generation system, the lower voltage limit (VMppmm) of the optimal voltage range being equal to the lower limit of the voltage range possible for operation at the maximum power point of the photovoltaic power generation system.
7. Device (16) according to any one of claims 1 to 6, wherein the current inverter (20) is a three-phase current inverter.
8. Device (16) according to any one of claims 1 to 7, wherein the voltage inverter (22) is a three-phase voltage inverter.
9. Electrical assembly (10) comprising: - a DC voltage source (12), the DC voltage source (12) operating over a voltage range having a minimum voltage (Vmin), - an AC voltage source (14), and - a device (16) for converting electrical energy between the DC voltage source (12) and the AC voltage source (14), the device (16) being according to any one of claims 1 to 8.
10. Electrical assembly (10) according to claim 9, wherein the DC voltage source 12 comprises one or more electrical modules connected in series and / or in parallel, the electrical module(s) being selected from: photovoltaic modules, batteries, electrolyzers and fuel cells.