Method for controlling and managing an inverter in a hybrid solar-diesel generator system, and associated system

Abstract

The present invention relates to a method for controlling and managing an inverter in a hybrid solar-diesel generator system. The proposed method is capable of absorbing and supplying active and reactive power during load transients and solar generation, guaranteeing system stability. The system includes an electronic converter connected in parallel to an isolated micro-grid, an inverter that measures the output voltage and current to determine the actuation signals of the semiconductor switches, a bank of capacitors for storing energy during transients, and a power meter for the Generator Motor Group (GMG), wherein the power measurement is sent to a control and management unit, ensuring a minimum power output of 30% of generation in the diesel GMG in order to prolong the service life thereof. The method also interacts with the solar inverter, limiting the power generated at certain times to stabilize the micro-grid by sending a reference power signal. Applicable in remote areas that use GMGs powered by diesel or other fuels such as gasoline, biodiesel, ethanol, methanol, CNG, biogas, hydrogen, etc., as well as in areas with no access to electrical energy or where the quality and power of the energy are inadequate, this solution offers a commercially viable approach for integrating solar energy into hybrid solar-diesel systems.

Description

“METHOD OF CONTROL AND MANAGEMENT OF INVERTER IN PHOTOVOLTAIC-DIESEL HYBRID GENERATOR SYSTEM AND ASSOCIATED SYSTEM” FIELD OF THE INVENTION

[0001] The present invention falls within the field of electrical engineering, specifically in the areas of energy conservation, electrical energy storage and electrical power supply circuits.

[0002] In more detail, the invention relates to the electricity generation sector, addressing an off-grid hybrid system that combines photovoltaic and diesel generators without the use of batteries. This system was developed to enable high penetration of solar energy in photovoltaic-diesel hybrid systems, promoting an efficient and sustainable solution for electricity generation in isolated regions.

[0003] Diesel-powered engine-generator sets (EMGs) remain the primary source of power in isolated systems in northern Brazil. However, increasing solar energy in these hybrid systems can result in significant generator fuel savings, reducing operating costs and the environmental impact associated with the use of fossil fuels. Thus, the present invention not only optimizes the use of renewable sources but also improves the efficiency and sustainability of power generation systems in remote areas. DESCRIPTION OF THE PRIOR ART

[0004] With the increasing penetration of renewable energy into the power system, grid inertia has been steadily decreasing, resulting in large variations in frequency and making the system more susceptible to instability during disturbances. The intermittent nature of these renewable sources and the fact that they are operated as non-dispatchable resources make the problem especially relevant.

[0005] In isolated microgrids, without connection to the utility's external grid, diesel engine-generator sets (GMGs) are typically used to power the loads. In some situations, solar generation is used in conjunction with GMGs to reduce fuel consumption and diesel-related costs.

[0006] However, when the proportion of solar energy generated exceeds 30% of the microgrid's total capacity, instabilities arise due to rapid load variations, uncertainty in solar generation, and slow response from GMGs. Isolated microgrids with these characteristics are especially sensitive to these disturbances, as they typically have low-inertia solar inverters that are unable to absorb large power differences between load demand and generation. Under these circumstances, an isolated microgrid with renewable energy faces one of the greatest technical challenges for frequency regulation, due to its greater sensitivity to imbalances between load and generation.

[0007] Several solutions have been proposed for this problem, such as adding extra rotating masses to power systems by connecting generators in synchronous compensation mode.

[0008] Another option is to complement the system with Energy Storage (ES), adding inertia virtually to the system (van Wesenbeeck et al., 2009). These AE units provide the necessary support for Dynamic Frequency Control (DFC), virtually adding inertia during large disturbances. However, these AEs typically utilize battery banks, which pose environmental challenges due to battery disposal every 2–5 years.

[0009] Another popular technique for providing DFC is to allow energy storage to emulate the behavior of traditional synchronous generators (Visscher et al., 2008), known as Virtual Synchronous Generators (VSG).

[0010] Regarding prior art documents, most patents address the management and sharing of power between the different generation sources of an isolated microgrid. Many address the same problem through different solutions, with Droop control being the most widely used, often in conjunction with other minor improvements.

[0011] In most cases where energy storage devices are used, patents also tend to be very broad, typically involving battery banks. No patents are found that use capacitor banks in the way proposed here. The control and management method proposed here is based on Droop control, with improvements that will be detailed later.

[0012] Document BR 102023012542-5 describes a control system for a microgrid containing diesel and solar generation, where the control acts directly on the solar inverter. Four arrays (sets) of solar panels are used, where one array always operates at maximum power and the others These arrays operate at reduced power, meaning they operate with a reserve of available power that can be used during transients. Energy storage, capacitor banks, and batteries are not used. The system's objective is to inject "controlled" power into the microgrid to contribute to frequency regulation.

[0013] The present invention presents a method in which capacitors are used for energy storage, and the control operates on a specific inverter that is connected in parallel with the microgrid to stabilize the frequency and voltage. In this method, it is possible to harness all the solar power generated. SUMMARY OF THE INVENTION

[0014] The present invention is presented and characterized in the independent claims, while the dependent claims describe other features of the invention or embodiments related to the main inventive idea.

[0015] The present invention develops a method of control and management of an electronic converter connected in parallel with an isolated microgrid, capable of absorbing and supplying active and reactive power during load transients and solar generation.

[0016] The system includes an inverter that measures output voltage and current so that control and management can determine the drive signals for the inverter's semiconductor switches. A capacitor bank is used for energy storage during transients, with voltage and current variables being monitored. Additionally, the system incorporates a Motor Generator Set (MGG) power meter, with power measured. being sent to an inverter control and management unit, ensuring a minimum power generation of 30% in the GMG Diesel to extend its useful life.

[0017] The system also interacts with the solar inverter, limiting its generated power at certain times to stabilize the microgrid by sending a reference power signal to the solar inverter. OBJECTIVES OF THE INVENTION

[0018] The objective of the invention is to develop a control and management method for an electronic converter that can be applied in remote regions that use Diesel Engine Generator Sets (GMG) or other fossil or non-fossil fuels (Gasoline, Biodiesel, Ethanol, Methanol, CNG, Biogas, Hydrogen, etc.), as well as in areas without access to electricity or where the quality and power of the energy are deficient.

[0019] The invention aims to offer a commercially viable solution for any location or activity that uses GMGs and has the possibility of installing solar energy, covering a global market. In Brazil, these regions are primarily in the Amazon, and other countries such as Canada, Africa, Central Asia, India, the Russian Federation, Indonesia, Malaysia, Colombia, Bolivia, Venezuela, and the Guianas also have significant commercial potential. REFERENCES

[0020] MPN van Wesenbeeck, SWH de Haan, P. Varela and K. Visscher, "Grid tied converter with virtual kinetic storage," 2009 IEEE Bucharest PowerTech, Bucharest, Romania, 2009, pp. 1-7, doi: 10.1109 / PTC.2009.5282048.

[0021] Visscher, K.; De Haan, SWH: “Virtual synchronous machines (VSG's) for frequency stabilization in future grids with a significant share of decentralized generation", IET Conference Proceedings, pp. 82-82, DOI: 10.1049 / ic:20080487. BRIEF DESCRIPTION OF FIGURES

[0022] Figure 1 presents the microgrid system with the proposed inverter. The system includes solar panels (100) and a solar inverter (101), an electronic converter (105) connected in parallel to the isolated microgrid (102), a capacitor bank (106), an inverter control and management unit (110), a Diesel GMG (112), and a GMG power meter (113).

[0023] Figure 2 shows the proposed inverter system, with its internal elements, measured signals, and actuation signals. The proposed inverter consists of three parts: the Boost converter (105a), Crowbar converter (105b), and output inverter (105c), all connected to the same DC bus capacitor.

[0024] Figure 3 shows the Bode plots of: a) Plant (in continuous line in gray scale), b) Pre-compensated Plant (dashed), c) Open loop plant with PR controller (continuous line in black).

[0025] Figure 4 illustrates the Inverter Current Control.

[0026] Figure 5 illustrates Inverter Modulation.

[0027] Figure 6 illustrates the microgrid voltage frequency / amplitude estimator and synchronization algorithm.

[0028] Figure 7 shows the DC Bus Balance Control.

[0029] Figure 8 shows the Group Power Measurement Motor Generator (GMG).

[0030] Figure 9 illustrates the Crowbar Control.

[0031] Figure 10 illustrates the Crowbar converter control and modulation.

[0032] Figure 11 shows the Power / Current Control of the Boost Converter.

[0033] Figure 12 shows the Modulation of the Boost converter and activation of the semiconductor switches.

[0034] Figure 13 illustrates the Control of the DC Bus voltage and the Energy Store voltage.

[0035] Figure 14 shows the structure of the Modified Droop controller. Left: Frequency droop (P / f); and Right: Voltage droop (Q / v).

[0036] Figure 15 illustrates the Inverter Power Management Strategy.

[0037] Figure 16 shows the GMG Minimum Power Control.

[0038] Figure 17 shows the Inverter Control and Management Scheme.

[0039] For ease of understanding, the same reference numerals have been used, wherever possible, to identify identical common elements in the drawings. It is understood that elements and features of one embodiment may be conveniently incorporated into other embodiments without further clarification. DETAILED DESCRIPTION OF THE INVENTION

[0040] In a microgrid without connection to the utility's external power grid (isolated), Diesel Engine Generator Sets (GMG) are generally used to power the loads. In some situations, use solar generation in conjunction with GMGs to reduce fuel consumption and reduce costs associated with diesel consumption.

[0041] When the proportion of solar energy generated exceeds 30% of the microgrid's total capacity, instabilities arise due to rapid load variations, uncertainty regarding solar generation, and slow GMG response. This instability manifests itself in poor power quality and even protective activation due to large voltage and frequency variations.

[0042] The present invention aims to increase the percentage of solar generation in the microgrid from the current 30% to 70% while maintaining the stability of the microgrid's generation.

[0043] The present invention presents a method for controlling and managing an electronic converter that will be connected in parallel with the isolated microgrid and will be capable of absorbing / supplying active power to the microgrid during both load and solar generation transients. The system will utilize a capacitor bank for energy storage during transients. The system will also guarantee a minimum power output of 30% of the diesel generator's generation (for lifespan reasons). The system will also interact with the solar inverter, limiting its generated power at certain times to stabilize the microgrid.

[0044] The control and management method of an electronic converter (105), shown in Figure 1, is connected in parallel with the isolated microgrid (102) and is capable of absorbing / supplying active and reactive power from the microgrid during both load (103) and load (104) transients. solar generation (100 and 101).

[0045] The inverter performs output voltage and current measurements (107) so that the inverter control and management (110) defines the actuation signals for the inverter semiconductor switches (109).

[0046] The system uses a capacitor bank (106) for Energy Storage (EA) during transients. The voltage / current variables of the capacitor bank are measured at (108). The system also uses a power meter (113) of the Motor Generator Set (GMG) and the measured power is sent through a communication link (111) to the inverter control and management unit (110), which, in turn, guarantees a minimum power of 30% generation in the Diesel GMG (112) (for lifespan reasons).

[0047] The system also interacts with the solar inverter (101) by limiting its generated power at certain times to stabilize the microgrid. This limitation is achieved by sending a reference power signal to the solar inverter through a communication link (114).

[0048] The proposed inverter, with its internal elements, its measured signals and actuation signals are shown in Figure 2.

[0049] To date, the present invention describes a control system for a microgrid containing Diesel and Solar (hybrid) generation, without the use of batteries, with a system that acts on the solar inverter and with the purpose of regulating the frequency of the microgrid.

[0050] In another modality, the inverter connected in parallel with the microgrid is dispensed with, with the system basically consisting of GMG Diesel and a solar inverter.

[0051] In this other modality, the actuation (control and management) is performed directly on the solar inverter. This requires intervention on the solar inverter, which must be more complex and must meet specific standards.

[0052] In this mode, not all solar panel arrangements (sets) operate at maximum power, as some operate with reduced power, or power reserve, to be used in transients.

[0053] Thus, in this mode, capacitors are not used to store energy for transients, as the energy is stored in the form of a power reserve. However, if solar intensity decreases, this reserve also decreases, or even ceases.

[0054] Therefore, this modality comprises a diesel photovoltaic hybrid generator system that maintains a photovoltaic array (PV1) always at its maximum power point, preferably in accordance with the P&O MPPT algorithm, and serves as a reference for other PV2, PV3 and PV4 arrays that are subsequently reduced preferably by the LPPT algorithm.

[0055] The power of the PV1 array is provided as a reference for the control input signal to pass through a proportional type controller, and the response of this signal is reduced to be sent to the saturation block as an upper limit, indicating the maximum power available from the photovoltaic system.

[0056] The frequency control loop is a proportional type control that receives the reference frequency signal with the error calculated by the sum operator that receives the filtered signal from the bus. The response of this control represents a power that is added to the operator that receives the power value of the PV system.

[0057] In this system, two inputs to the control loop are the signals that inform the generation of the PV system and the GMG, both signals added in a sum operator and resulting in the maximum power that the PV system can provide.

[0058] Optionally, the power of PV array 1 and the maximum generation of the PV system minus the power of PV array 1 are also used as input signal in the grid to result in the generation that PV arrays 2, PV 3 and PV 4 will have.

[0059] The control method mitigates frequency deviations by receiving the frequency reference signal at the first input of the mesh, while the second input signal is the frequency measured at the microgrid bus, treated with a passive second-order low-pass filter.

[0060] The control method also controls the input voltage of the inductor through the input voltage on the capacitor and controls the power of the PV array.

[0061] For proper inverter operation, the following steps are presented: modeling, obtaining the dynamic equations, and the proposed controllers. Next, the control and management strategy for the system as a whole is presented. Output Inverter Modeling and Control

[0062] The output inverter modeling is performed by raising the equations that describe the behavior of the electrical quantities involved in the inverter circuit. They are nine state variables modeled, namely: the three inductor currents inverter side [ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ], the three inductor currents ^^ ^^ network side [ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ] and the three filter capacitor voltages ^^ ^^ [ ^^ ^^ ^^ ^^^^ ^^ ^^ ^^ ^^ ]. These equations are obtained using Kirchhof's Laws of electrical circuits and rewritten in matrix form, according to the equation below:

[0063] [ 064] Where: state vector, is the vector of the voltage ^^ produced by the inverter, ^^ ^^ ^^ ^^ = [ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ] is the grid voltage vector which is considered as a disturbance, the variable ^^ is the output variable which can be any of the states according to the need, and chosen according to the matrix ^^ ^^ .

[0065] The matrices ^^ ^^ , ^^ ^^ and ^^ ^^ are shown below:

[0066] The dynamic system presented above describes the behavior of circuit currents and voltages for different values ​​of control action and network voltage.

[0067] A disadvantage of parameterizing the system as presented is that the inputs and outputs are coupled together. For example, a disturbance ^^ ^^ ^^ in ^^ ^^ ^^ causes a disturbance in ^^ ^^ ^^ , which ends up limiting the applicability of the model.

[0068] To get around this problem you can use the so-called ^^ ^^ ^^ transform or Clarke transformation. This transformation converts a three-phase system in coupled ^^ ^^ ^^ coordinates into a mutually orthogonal system in uncoupled ^^ ^^ ^^ coordinates. The transformation from ^^ ^^ ^^ coordinates to ^^ ^^ ^^ coordinates is performed using the Transformation matrix given in Equation (1):

[0069]

[0070] For systems with 9 states like the LCL filter, a transform matrix can be used as shown in Equation (3):

[0071]

[0072] Applying the transformation ^^ ^^ ^^ ^^3above on the state variables of the dynamical system of the Equation Error! Reference source not found., performing simplifications and multiplying both sides of the equality by ^^ ^^ ^^ ^^3 , we have:

[0073] −1

[0074] Where: ^^ ^^ ^^ ^^ = ^^ ^^ ^^ ^^3 ^^ ^^ ^^ ^^ ^^ ^^3 , is chosen according to the ^^ need, ^^ ^^ ^^ ^^ = [ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ] is the vector of ^^ states in ^^ ^^ ^^, ^^ ^^ ^^ ^^ = [ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ] is the vector of the voltage produced ^^ by the inverter at ^^ ^^ ^^ and ^^ ^^ ^^ ^^ = [ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ ]is the grid voltage at ^^ ^^ ^^.

[0075] Since the dynamic system shown above is controlled by a microcontroller, a discrete model of the system must be developed. This can be achieved using ZOH (Zero Order Holder) discretization, which best describes the effect of PWM modulation. Furthermore, here we can consider the grid voltage as a disturbance that will be compensated for later. As shown below:

[0076] ^^ ^^ ^^ ^^ [ ^^] = ^^ ^^ ^^ ^^ ^^ ^^ ^^ ^^ [ ^^]

[0077] Where: ^^ is the sample index and ^^ ^^ ^^ ^^ , ^^ ^^ ^^ ^^ and ^^ ^^ ^^ ^^ are the matrices obtained through discretization by ZOH.

[0078] When implementing digital signals in a microcontroller, it is also necessary to consider the delay of the digital signal. This can be done by defining an auxiliary variable ^^ that represents the delayed control action in a sample:

[0079]

[0080] This auxiliary variable corresponds to a new state of the dynamic system, which can be included in the discrete system as shown below:

[0081] ^^^^ ^^ ^^ ^^[ ^^] = ^^^^ ^^ ^^ ^^^^^^ ^^ ^^ ^^[ ^^]

[0082] Where: is the vector that can be chosen according to need and the discrete matrices of the system

[0083] The dynamic system above describes the discrete-time dynamic behavior of the LCL filter, which has a very strong resonance due to the inductive and capacitive elements.

[0084] There are two common ways to dampen this resonance. The first is passive damping, in which resistors are used in series or parallel with the filter elements. This technique generally involves high losses in the passive components. Another is active damping, in which some control technique is applied to alter the position of the poles in the closed-loop system, providing damping. The technique used here is state feedback with pole allocation. The following control technique is used:

[0085]

[0086] Where ^^ corresponds to the variable to be controlled, in this case the currents on the grid side.

[0087] The feedback gain ^^ ^^ ^^ is chosen so that the system is damped and has a fast response. Poles with a frequency one decade below the switching frequency are generally chosen. The reference gain is chosen so that the gain between input and output is unity.

[0088] By substituting the State Feedback Control Law (7) in (6) and applying the Laplace transform to the system ^^ ^^ ^^ above, it is possible to obtain a transfer function that relates the inverter output current at ^^ ^^ ^^ with the voltage at ^^ ^^ ^^ produced by the inverter.

[0089]

[0090] Furthermore, due to the symmetry of the transform ^^ ^^ ^^, and choosing the output variable ^^ as the output currents ^^ ^^, we have that the transfer functions of the current ( ^^ ^^ ^^ ) both axis ^^ ^^ ^^ are equal to each other, so the same current controller structure can be used for both axes.

[0091] [ 092] Where: ^^ ^ ∗ ∗ ^ ^^ and ^^ ^^ ^^ are the auxiliary reference currents of shaft ^^ and ^^, respectively.

[0093] The plant ^^ ^^ ^^It can also be considered a precompensated plant, as it has unity gain but does not offer rejection of power grid disturbances. Therefore, Proportional-Resonant (PR) controllers are used for this purpose. PR controllers consist of a proportional gain plus resonant controllers tuned to the harmonics of the grid voltage disturbances. Generally, the harmonic frequencies of the grid, in addition to the fundamental, are the odd harmonics.

[0094] The structure of a PR controller is shown below:

[0095] Where: The first term ^^ ^^ corresponds to the proportional gain, and the second and third terms correspond to the resonant frequencies tuned to 60Hz and 180Hz, respectively. These gains must be chosen to ensure system stability and good dynamic performance.

[0096] Figure 3 presents an example of a Bode plot for a plant with an LCL filter, for the proposed Precompensated Plant with state feedback, and for the Precompensated Plant with the open-loop PR Controller. It can be seen that the plant resonance is eliminated by the state feedback, and the PR controller provides a high open-loop gain, ensuring tracking at the fundamental frequency and rejection of disturbances at 180 Hz.

[0097] For the "o" axis, there is no need to insert a PR controller; state feedback control is sufficient. This approach makes the system simpler since the microgrid voltage generally has a common-mode voltage equal to zero ( ^^ ^^ ^^ ≈ 0 ^^), and thus there are no disturbances to be rejected. Furthermore, the inverter will inject only balanced currents into the microgrid, so the common mode current will be close to zero ( ^^ ^^ ^^≈ 0 ^^). The current from the “o” axis is used to balance the DC bus voltages, since it is divided in two and its central point is grounded. Figure 4 shows the implementation of the current control.

[0098] The reference currents are defined by the external loops that will be described in the following paragraphs. The output voltages [ ^^ ^^ , ^^ ^^ , ^^ ^^ ] must be transformed back to the reference frame ^^ ^^ ^^ to be modulated into PWM signals for driving the semiconductor switches. The transformation ^^ ^^ ^^ → ^^ ^^ ^^ is performed by the inverse transformation matrix ^^ −1 ^ ^ ^^ ^^ shown in the form of a transformation block in Error! Reference source not found.. This Figure also shows a way to perform PWM modulation, where the constant ^^ ^^ ^^ ^^ corresponds to the maximum value of the triangular voltage ^^ ^^ . Inverter Synchronization

[0099] For an inverter connected to the power grid to be able to inject current in phase with the grid voltage, the current reference must be purely sinusoidal and in phase with this voltage.

[0100] To obtain a quality current reference, a synchronization technique was used. In this technique, two second-order generalized integrators (SOGI) are used to generate four signals, two for the ^^ axis and one in-phase ^^′ ^^ and another in quadrature ^^ ^^′ ^^ , and two for the ^^ axis, one in phase ^^′ ^^ and another in quadrature ^^ ^^′ ^^ .

[0101] These signals are combined to extract the positive sequence component of the grid voltage ( ^^′ + ^^ ^^ ^^′ ^ + ^), as shown in Figure 6, which will be used to generate the inverter reference currents. The gain ^^ is used as a filter adjustment factor, and a value of ^^ =√ 2 provides a good compromise between selectivity and dynamic response of the filter.

[0102] This synchronization method requires the grid frequency in rad / s as a parameter ( ^^′). Therefore, a microgrid frequency estimator is included through the estimator also shown in Figure 6, where the gain ^^ ^^ is used to define the estimation speed. This estimated frequency is divided by (2 ^^) to generate the frequency signal ( ^^) in Hz, which will be used in the frequency / active power droop control. In the lower part of Figure 6, the grid voltage amplitude estimator ( ^^) is presented, which is calculated by the norm of the voltage signals ( ^^′ + ^^ ^^ ^^′ ^ + ^). This estimated voltage is used in the amplitude / reactive power droop control. Inverter Reference Current Generator

[0103] By estimating the grid voltages in positive sequence αβ obtained by the synchronization technique, it is possible to calculate the inverter reference currents using the equations below:

[0104]

[0105] The reference powers generated from the external power grids, as will be discussed in the following sections. The reference current for the "o" axis is calculated to balance the DC bus voltages, as shown below. DC Bus Balancing

[0106] Since the central point of the DC bus is grounded, if any level of direct current were to flow through this point, the DC bus voltages could become unbalanced. This phenomenon is undesirable and can cause distortions in the currents injected into the microgrid.

[0107] To solve this problem a Proportional Integral controller can be used ( ^^ ^^ ^^ ^^ ^^2 ), which receives as a reference half of the total DC bus voltage, and compares this value with the lower DC bus voltage, as can be seen in Figure 7.

[0108] How ^^ ^^ ^^ = 1 / 2 ( ^^ ^^ ^^1 + ^^ ^^ ^^2 ) , through the controller we have that ^^ ^^ ^^1 = ^^ ^^ ^^2 , balancing the DC bus. Measuring the power of the GMG

[0109] Figure 8 shows block (113) which corresponds to a simple scheme for measuring the generator's active power. The voltage ( ^^ ^^ ^^ , ^^ ^^ ^^ , ^^ ^^ ^^ ) of each phase is read through an isolated voltage sensor and the current ( ^^ ^^ ^^ , ^^ ^^ ^^ , ^^ ^^ ^^ ) of each phase is read by an isolated current sensor.

[0110] The signals from each phase are multiplied by the multiplier (113a) and added together in (113b). This signal is then applied to a second-order low-pass filter (113c) with a cutoff frequency of 30Hz and a damping factor of 0.7. This filter aims to remove power oscillations due to small power imbalances between the phases.

[0111] The power signal ^^ ^^ ^^ ^^ (111) is sent via digital communication (e.g. CANbus, Ethernet, RS485, etc.) to the control unit (110). Crowbar Converter Modeling and Control

[0112] A Crowbar circuit is a type of circuit used to prevent a circuit from being damaged by overvoltage. In the proposed inverter, this circuit corresponds to element (105b).

[0113] This circuit is activated only when the DC bus voltage ( ^^ ^^ ^^) becomes greater than a certain value, called threshold 1 ( ^^^^ ^^_ ^^ ^^ ^^1), a typical value for this value would be 5% above the DC bus reference voltage. If the voltage continues to rise and reaches a value called threshold 2 ( ^^^^ ^^_ ^^ ^^ ^^2), a typical value for this voltage would be 10% above the reference voltage, then the Crowbar will consume the maximum power of the converter on the DC bus.

[0114] Voltage limits are used in the form of squared error of the variables, which is related to the power. For negative voltage error values, there is an overvoltage on the DC bus, which requires Crowbar action, so the limit errors are ^^ ^^_ ^^ ^^ ^^1 ^^ ^ ^ ^ ^ ^^ ^ 2 2 calculated as ^^ = ^^ ^ − (1.05 ∙ ^^ ^^ ^ ^ ^ ^ ^^ ^^ ) 2 and ^^^^ ^^_ ^^ ^^ ^^2= ​​^^ ^^ ^ ^ ^ ^ ^^ ^^ − (1.1 ∙ ^^ ^^^ ^ ^ ^ ^^ ^^ ) 2 . This voltage error is applied to a proportional controller with gain ^^ ^^_ ^^ ^^ , the output of this controller ^^ ^^ ^^ provides the power that the Crowbar must dissipate ( ^^ ^^ ^^ ). This is shown in Figure 9. ^^ ^^ ^^

[0115] The reference power ( ^^ ^^ ^^ ) is transformed into the average voltage ( ^^ ^^ ^^ ) over a “Dissipation” resistor ^^ ^^ ^^ and then transformed into a PWM signal to be applied to the converter's semiconductors. Figure 10 shows the modulation strategy used. The last block on the right of Figure 10 inserts the dead time between the switches and adapts the voltage levels to those of the switches (Gate Driver). Modeling and Control of the Bidirectional Boost Converter

[0116] The Boost converter has the function of charging and discharging the energy storage element, in this case the capacitor bank ( ^^ ^^ ^^). By using the Boost converter it is possible to impose a greater voltage variation on the capacitor ^^ ^^ ^^ thus making better use of the energy on it.

[0117] An alternative version could be realized by connecting the capacitor bank ^^ ^^ ^^ directly to the inverter's DC bus without the Boost converter, but in this case the voltage variation will be much less due to the limitations of the output inverter, consequently the capacitance and cost of the capacitor bank would be much higher, exceeding the cost of the Boost converter.

[0118] The Power / Current Control of the Boost converter is performed through a Proportional Integral (PI) controller, as shown in Figure 11. The converter reference current is calculated by dividing the reference power ^^ ^^ ^^ ( ^^^^ ^^ ^^ ^^ ^^) by the measured capacitor bank voltage. This reference current is limited to prevent the converter current from exceeding the safe converter operating current ( ^^^^_ ^^ ^^ ^^), and this is accomplished by the limiter block of Figure 11.

[0119] The output voltage of this block is applied to the modulation and drive block of the boost converter, which produces the drive signals for the converter switches. Inverter Power Controllers

[0120] The proposed inverter according to Error! Reference source not found. is composed of 3 parts, the Boost converter (105a), Crowbar converter (105b) and output inverter (105c), all connected to the same DC bus capacitor ( ^^^^ = ^^ ^^1 / 2 The converter connected to the Crowbar will only operate in specific cases where the DC bus voltage exceeds a critical value. In steady state, only the Boost converter and the inverter are operating.

[0121] Controlling the DC bus voltage is of fundamental importance, since all the energy processed by the inverter passes through the DC bus. The DC bus reference voltage ( ^^ ^^ ^^ ^^ ^^ ) is generally kept constant, being greater than the maximum voltage that the inverter must synthesize at its output, thus preventing the inverter from entering over-modulation. Over-modulation introduces non-linearities into the modulation and, consequently, distortions in the variables to be controlled, and should be avoided.

[0122] To make the DC bus control analysis linear, it is performed based on the sum of the powers involved in the DC bus charging / discharging process. ^^ 1 ( ^^ ^^ ^^ 2 ^^ ^^ ^ 2 ^ ^^ ) = ^^ ^^ ^^ ^^ ^^ ^^ − ^^ ^^ ^^ ^^ (13)

[0124] By analyzing the equation above, we can see that an increase in the boost converter's power causes an increase in the capacitor voltage. An increase in the inverter's power causes a decrease in the DC link voltage. This same analysis can also be performed on the energy storage capacitor:

[0125]

[0126] In the energy storage capacitor, an increase in Boost power causes a decrease in capacitor voltage.

[0127] For analysis and obtaining the model for DC bus control, the power ^^^^ ^^ ^^ ^^ ^^, from the point of view of DC bus voltage control, is a disturbance and is disregarded when obtaining the transfer function. Furthermore, using the ZOH discretization, we have the discrete transfer function of Equation (15).

[0128]

[0129] Where: ^^ ^^ is the sampling period.

[0130] And to control the voltage of the energy storage, also using ZOH discretization, we have:

[0131]

[0132] The voltage control strategy of the The DC bus and energy storage capacitor voltage are shown in Figure 13. Two cascaded control loops are used; the outer loop controls the energy storage voltage. This loop receives the energy storage reference voltage squared ( ^^ ^ ^ ^^ 2 re ^ ^ ^ ^ ^^ ) subtracts this value from the squared measured voltage , and applies the result to a Proportional-Integral controller ( ^^ ^^ ^^ ^^ ) which will provide the inverter auxiliary reference power ( ^^ ^^ ∗ ^ ^ ^^ ). This power is added to the compensation power ( ^^ ^^ ) that will be used for frequency regulation and will be shown next. This sum provides the inverter's reference power . This power in turn, together with the Boost power, performs the charge / discharge of the DC bus, providing the voltage ( ^^ ^ 2 ^ ^^ ).

[0133] The internal loop controls the DC bus voltage. This control loop receives the voltage from the ^ ^ ^^ ^^2 squared reference bus ( ^^ ^^ ^^ ) and subtract it from the squared voltage ( ^^ ^ 2^ ^^ ). This subtraction is applied to a Proportional-Integral controller ( ^^ ^^ ^^ ^^ ^^ ) that will provide the power of the reference Boost converter, responsible for charging / discharging the Energy Store.

[0134] In the power control shown in Figure 13, two signals are also inserted that are used to enable (turn on) the controllers. The signal ( ^^ ℎ ^^ ) enables the controller ^^ ^^ ^^ ^^ , and the sign ( ^^ ℎ ^^ ) enables the controller ^^ ^^ ^^ ^^ . A value of 1 in these signals enables the controllers for normal operation, and a zero signal disables the controllers and their output is zeroed and the controller integrator is held at zero.

[0135] The definition of signs ^^ ℎ ^^ , ^^ ℎ ^^ , and ^^ ^^ is performed through Power Management Logic. Power Management Logic

[0136] The management of the active and reactive power control loops is carried out through the Power Management Logic block, as shown in Figure 17. In this block, decisions are made regarding the amount of active and reactive power the inverter supplies or consumes.

[0137] The strategy for defining the powers is based on the Droop control with some modifications. The injected active power is used to support the microgrid frequency and is calculated by Equation (17). For frequencies lower than the lower limit 2 ( ^^ ^^ ^^2 ) the inverter injects maximum active power into the microgrid. For frequencies greater than the upper limit 2 ( ^^ ^^ ^^2 ) the inverter absorbs the maximum active power. For frequencies between the lower limit 2 ( ^^ ^^ ^^2 ) and the lower bound 1 ( ^^ ^^ ^^1 ), and between the upper limit 1 ( ^^ ^^ ^^1 ) and the upper limit 2 the injected active power is proportional to the frequency, where ^^ ^^ ^^ is the proportionality gain. There is a frequency range ( ^^ ^^ ^^1 < ^^ < ^^ ^^ ^^1 ), or dead zone, where the controller does not inject active power.

[0138]

[0139] The injected reactive power is used to provide voltage support to the microgrid and is calculated by Equation (17). For voltages lower than the lower limit 2 ( ^^ ^^ ^^2 ) the inverter injects maximum reactive power into the microgrid. For voltages greater than the upper limit 2 ( ^^ ^^ ^^2 ) the inverter absorbs maximum reactive power. For voltages between the lower limit 2 ( ^^ ^^ ^^2 ) and the lower bound 1 ( ^^ ^^ ^^1 ), and between the upper limit 1 ( ^^ ^^ ^^1 ) and the upper bound 2 ( ^^ ^^ ^^2 ) the injected reactive power is proportional to the voltage, where ^^ ^^ ^^ is the proportionality gain. There is a frequency range < ^^ < ^^ ^^ ^^1 ), or dead zone, where the controller does not inject active power.

[0140]

[0141] The inverter has a maximum apparent power limitation ( ^^ ^^ ^^ ^^ ) that cannot be exceeded. And since the stored active power is limited, priority is given to frequency control. This is done first by executing Equation (17), and if there is excess power capacity, it is used to control the voltage.

[0142]

[0143] Figure 14 shows the modified Droop controller presented in Equations (17) and (18) in graphical form.

[0144] Equations (17) and (18) are executed in conjunction with the management logic, which turns off some control loops with the intention of making power available for frequency / voltage compensation more effective. This logic is organized in the form of the flowchart shown in Figure 15.

[0145] Initially, readings are taken of the microgrid frequency and voltage, DC bus and energy storage voltage, and auxiliary reference power. . Then the frequency ( ^^) is compared with the lower frequency limit 1 ( ^^ ^^ ^^1 ). If the frequency is higher, the Droop control works normally and the DC bus voltage controllers and energy storage work normally. If the frequency is ^^ > ^^ ^^ ^^1 the inverter will absorb energy and if the bus voltage rises above ^^^^ ^^_ ^^ ^^ ^^1 the Crowbar will dissipate this energy until generation decreases.

[0146] If the frequency is less than the lower limit 1 ( ^^ ^^ ^^1) the inverter must inject active power into the microgrid. At this moment the Energy Store voltage control is turned off ( ^^ ℎ ^^ = 0). This is done to avoid competition between control loops. Since the Droop control will inject power into the grid to compensate for the frequency disturbance, discharging the AE, the AE's voltage control loop will consume power from the microgrid to recharge the AE. Thus, the inverter's priority is to inject active power until the frequency disturbance is compensated or the AE's energy runs out.

[0147] If the AE voltage reaches critical values ​​( ^^ ^^ ^^ < ^^^^ ^^_ ^^ ^^ ^^) DC bus control is turned off ( ^^ ℎ ^^ = 0), the inverter then injects the remainder of the energy now available from the DC bus. When this energy is depleted and frequency has not yet returned, the inverter remains connected to the microgrid but does not process energy, waiting for the grid to stabilize via load and generation power balancing, shown below. This last case is critical and should be avoided by appropriately sizing the AE for the worst case.

[0148] The reference active power is then calculated using the auxiliary reference power ( ^^ ^^ ∗ ^ ^ ^^ ) plus the compensation power ( ^^ ^^ ).

[0149] Next, the voltage droop controller (Q / v) calculation is performed, which defines the amount of reactive power that the inverter must inject into the grid. If the voltage is within the lower limits 1 and above 1 ( ^^ ^^ ^^1 ), so there is no need to inject reactive power = 0. If the voltage is out of limits then ^^ ^^ ^^ ^^ ^ ^ ^^ ^^ = ^^^^ ^^ ^^ ^^ ^^. Then, check the available reactive power capacity ( ^^ ^^ ^^ ^^ ) that the inverter has to inject into the grid, calculated by Equation (19). If the reference reactive power is greater than the maximum, then it will be limited. GMG Minimum Power Control

[0150] Due to the use of a capacitor bank as an AE, the proposed inverter has a limited capacity to inject power into the microgrid. Therefore, in steady state, the load power must be delivered by the GMG and the solar inverter. Furthermore, diesel engines used in GMG should avoid operation at low loads. typically less than 30%.

[0151] Operating a Diesel engine under these conditions can cause two main types of damage: a) mirroring of the liners, where the rings mirror the honing of the cylinders, causing increased consumption of lubricating oil and loss of engine compression, b) locking of the rings caused by carbonization of the chamber, which can lead to the passage of lubricant into the combustion chamber.

[0152] In this way, it must be guaranteed, as long as the load power allows, a minimum power in the GMG of 30% of its nominal capacity. This must be done by adjusting the ^^ ^^ ^^ reference active power of the Solar Inverter ( ^^ ^^ ^^ ). This adjustment is made by setting a minimum generator reference power, in this case ^^^^ ^^ ^^_ ^^ ^^ ^^= 0.3 × ^^^^ ^^ ^^_ ^^ ^^ ^^ ^^ ^^ ^^ ^^, and subtracting the measured power of the GMG, generating an error signal that is applied to a controller ^^ ^^ ^^ ^^ ( ^^), which in turn produces the power of the auxiliary solar inverter ( ^^ ^∗ ^ ^^ ).

[0153] If the power injected by the solar inverter, plus the energy produced by the GMG, is greater than the load, the microgrid frequency will increase, and in this case, the proposed inverter will absorb active power and dissipate it in the Crowbar resistor. The controller will eventually correct the power. ^^ ^^ through the controller ^^ ^^ ^^ ^^ ( ^^). To speed up this correction, a feedforward portion of the power being dissipated in the inverter can be added to the reference power of the solar inverter.

[0154] This addition only occurs when ^^ ^^ ^^ ^^ ^ ^ ^^ ^^ < 0, as shown in Figure 16. At the controller output a saturator is added ^^ ^^ ^^ that maintains ^^ ^^ ^^ between zero and maximum power set for solar inverter ^^^^ ^^_ ^^ ^^ ^^= × ^^^^ ^^ ^^_ ^^ ^^ ^^ ^^ ^^ ^^ ^^. If the power signal saturates, it is detected and reported to the controller ^^ ^^ ^^ ^^ ( ^^) to prevent its internal states from exploding (Anti-windup).

[0155] Adjusting the controller gains ^^ ^^ ^^ ^^ ( ^^) must be such that it takes into account the communication dynamics between the management system and the Solar Inverter and between the management system and the GMG power measurement, in addition to the dynamics of the microgrid itself. Control and Management (110)

[0156] All the blocks described above are condensed in Figure 17, which shows the Control and Management block (110) of the Error! Reference source not found.

[0157] In the claims presented in this document, the sole purpose of the references in parentheses is to facilitate reading: they cannot be considered as restrictive factors with regard to the field of protection claimed in the specific claims.

[0158] As a differential of this invention, the following aspects can be mentioned: - it does not use batteries; - in one embodiment, use of a capacitor bank instead of batteries, which has a much longer useful life than batteries; - it allows to increase the capacity of solar energy installed in a microgrid from the current 30% to 70%; - reduction in the fuel consumption of GMG Diesel; - allows the GMG Diesel to maintain its minimum generating power at 30% to avoid problems with the diesel engine's lifespan; - the system does not process all of the system's energy, only transient energy. - In one version, the system is plug-and-play, meaning it is connected in parallel with the existing system. In other words, it is possible to use a conventional GMG and a conventional solar inverter, both already installed, requiring only an increase in the installed solar capacity to reach 70%. The only limitation regarding the solar inverter is the need for a digital communication input to limit the generated power, which is present in most solar inverters.

Claims

1 / 5 CLAIMS 1. A method for controlling and managing an inverter in a photovoltaic-diesel hybrid generator system, comprising: - an inverter (101) that performs output voltage and current measurements to define the actuation signals for the inverter's semiconductor switches; - a power meter (113) of the Motor Generator Set (GMG) with the measured power being sent to an inverter control and management unit, ensuring a minimum power of 30% generation in the Diesel GMG to extend its useful life; - and an interaction with the solar inverter, limiting its generated power at certain times to stabilize the microgrid by sending a reference power signal to the solar inverter.

2. A method according to claim 1, characterized in that the control and management is performed directly on the solar inverter (101). 3.Method according to claims 1 and 2, characterized in that it comprises a diesel photovoltaic hybrid generator system that maintains a photovoltaic array PV1 always at its maximum power point according to the P&O type MPPT algorithm and serves as a reference for other arrays PV2, PV3 and PV4 that are subsequently reduced by the LPPT algorithm.

4. Method according to claims 1 to 3, characterized in that the power of the PV1 array is supplied. 2 / 5 as a reference for the control input signal to pass through a proportional type controller, and the response of this signal is reduced to be sent to the saturation block as an upper limit, indicating the maximum power available of the photovoltaic system.

5. Method, according to claims 1 to 4, characterized in that the frequency control loop is a proportional type control that receives the reference frequency signal with the error calculated by the sum operator that receives the filtered signal from the bar, in which the response of this control represents a power that is added in the operator that receives the power value of the PV system. 6.Inverter control and management method according to claim 1, characterized by further comprising: - an electronic converter (105) connected in parallel with an isolated microgrid (102), capable of absorbing and providing active and reactive power during load transients and solar generation; - and a capacitor bank (106) used for energy storage during transients.

7. Inverter control and management method according to claim 6, characterized by adopting a strategy for controlling the DC link voltage and the energy storage capacitor voltage using two cascaded control loops, in which the outer loop controls the energy storage voltage by receiving the squared energy storage reference voltage and subtracting it. this value of the measured voltage squared, applying the result to a Proportional-Integral controller. 8.Inverter control and management method according to claims 6 and 7, characterized by adopting a strategy of disconnecting the voltage control loops of the energy storage and the DC bus to supply the compensation demand during a frequency dip event, in which the strategy is based on Droop control with modifications comprising: - the injected active power is used to support the frequency of the microgrid; - for frequencies lower than a lower limit, the inverter injects the maximum active power into the microgrid; - for frequencies higher than an upper limit, the inverter absorbs the maximum active power; - for frequencies between the lower limit and the lower limit, the injected active power is proportional to the frequency; - and there is a frequency band, or dead zone, where the controller does not inject active power. 9.Inverter control and management method according to any one of claims 6 to 8, characterized in that it includes the use of a transformation from abc coordinates to αβo coordinates to decouple the inputs and outputs of the system.

10. Inverter control and management method according to any one of claims 6 to 8, characterized in that it uses a discrete model of the system. 4 / 5 through discretization by ZOH (Zero Order Holder).

11. Inverter control and management method according to any one of claims 6 to 8, characterized by including a dynamic system controlled through a microcontroller that considers the delay of the digital implementation.

12. Inverter control and management method according to any one of claims 6 to 8, characterized by including state feedback with pole allocation to dampen the resonance of the LCL filter.

13. Inverter control and management method according to any one of claims 6 to 8, characterized by using Proportional-Resonant (PR) controllers to ensure tracking at the fundamental frequency and rejection of harmonic disturbances of the grid voltage. 14.Inverter control and management method according to any one of claims 6 to 8, characterized by including the implementation of a PR controller for the axes α and β, ensuring a stable and dynamic response.

15. Inverter control and management method according to any one of claims 6 to 8, characterized by not requiring a PR controller for the "o" axis, using only state feedback control to balance the bus voltages.

16. Photovoltaic-diesel hybrid generator system as described in claims 6 to 15, characterized by integrating. 5 / 5 solar panels (100), solar inverter (101), electronic converter (105), capacitor bank (106), inverter control and management unit (110), GMG Diesel (112) and GMG power meter (113).

17. Photovoltaic-diesel hybrid generator system, according to claim 16, characterized by being applicable in remote regions that use GMG diesel, gasoline, biodiesel, ethanol, methanol, CNG, biogas, hydrogen, or any other fossil fuels, as well as in areas without access to electricity or where the quality and power of the energy are deficient.

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