Direct current (DC) bus control system and method for photovoltaics

Abstract

Solar power generation system and method for DC power transmission and centralized power inversion. The solar power generation system includes a photovoltaic (PV) bus system and a fixed bus system. The PV system utilizes a control mode switching control method, which includes determining to enable local maximum power point tracking (MPPT) control; in response to determining that the local MPPT control is enabled, starting an MPPT mode timer; performing local MPPT; determining whether the MPPT mode timer is greater than a predetermined period; and, in response to determining that the MPPT mode timer is greater than a predetermined period, switching the MPPT control to the next MPPT controller. Distributed MPPT control methods include sequential MPPT control, adaptive ΔV MPPT control and / or power limit control. The fixed bus system includes a PV string MPPT controller and a fixed DC input central inverter or multiple fixed DC modular inverters.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS:

[0002] This application claims priority to U.S. Patent Application No. 62 / 842,798 filed on May 3, 2019. Technical Field

[0003] The present invention relates to the technical field of solar power generation systems, and in particular to a solar power generation system and method for DC power transmission and centralized power inversion. Background Art

[0004] Solar and wind power are increasingly important renewable, non-polluting energy sources for consumers and businesses around the world. For solar power, photovoltaic (PV) panels arranged in arrays or strings typically provide the means for converting solar energy into electrical energy. When operating a PV array, maximum power point tracking (MPPT) is typically used to automatically determine the voltage or current at which the PV array should operate to produce the maximum power output for a specific temperature and solar irradiance. Although MPPT allows for the generation of maximum output power, the transmission and storage of the power generated by the PV array can be inefficient and costly. Summary of the invention

[0005] The present technology generally relates to PV bus and fixed DC bus power systems, and methods of controlling PV bus and fixed DC bus power systems. Among other advantages, the present technology provides redundancy between networks of DC / DC controllers in the event that a subset of the DC / DC controllers fails or is unable to perform MPPT functions.

[0006] In general, the invention provides a method for controlling a PV bus power system, the method comprising determining at a current DC / DC controller to enable local maximum power point tracking (MPPT) control; in response to determining that local MPPT control is enabled, starting an MPPT mode timer; performing MPPT; determining that the MPPT mode timer is greater than a predetermined period; and, in response to determining that the MPPT mode timer is greater than the predetermined period, switching the MPPT control mode to a next DC / DC controller. Other aspects include corresponding computer systems, apparatuses, and computer programs recorded on one or more computer storage devices, each of which is configured to perform the actions of the method.

[0007] Implementing the above functions may include one or more of the following features. The method may include determining that local MPPT control is not enabled; and in response to determining that local MPPT control is not enabled, maintaining the last duty cycle at the last known MPPT set point of the current MPPT controller. The method may include measuring local voltage and current; and determining the maximum power point voltage search direction ΔV based on the measured local power disturbance. The method may include determining to enable power limiting; and in response to determining that power limiting is enabled, determining the output power based on the measured local voltage and current, and determining that the output power is greater than a power threshold; and in response to determining that the output power is greater than the power threshold, performing MPPT in the direction of negative ΔV. The method may include determining that the output power is not greater than the power threshold; and, in response to determining that the output power is not greater than the power threshold, performing MPPT in the direction of positive ΔV, also referred to herein as reverse MPPT.

[0008] The method may include determining that power limiting is not enabled; and, in response to determining that power limiting is not enabled, performing MPPT. The method may include determining that an MPPT mode timer is not greater than a predetermined period; in response to determining that the MPPT mode timer is not greater than a predetermined period, further determining to enable MPPT control; and, in response to further determining that MPPT control is enabled, starting the MPPT mode timer. The method may include determining that an MPPT mode timer is not greater than a predetermined period; in response to determining that the MPPT mode timer is not greater than a predetermined period, further determining not to enable MPPT control; and, in response to further determining that MPPT control is not enabled, further maintaining a previous duty cycle at a last known MPPT set point of a current MPPT controller.

[0009] The method may include, in response to determining that the MPPT mode timer is greater than a predetermined period, allowing a voltage disturbance of the distributed energy source before switching the MPPT control mode to a next MPPT controller. The method may include scaling the magnitude of the voltage disturbance. The method may include scaling the magnitude of the voltage disturbance based on a local device metric. The local device metric may be output power or battery charge state. Implementations of the described techniques may include hardware, methods or processes, or computer software on a computer accessible medium.

[0010] Another general aspect is characterized by a PV bus system. The PV bus system includes a central inverter unit, a PV bus coupled to the central inverter unit, PV strings respectively coupled to the central inverter unit through the PV bus, batteries respectively coupled to the PV bus, and DC / DC controllers respectively coupled between the batteries and the PV bus. Each DC / DC controller includes a processor and a memory. Instructions are stored on the memory, and when the processor executes these instructions, the DC / DC controller determines to enable maximum power point tracking (MPPT) control; in response to determining that local MPPT control is enabled, starts an MPPT mode timer; performs MPPT; determines that the MPPT mode timer is greater than a predetermined period; and in response to determining that the MPPT mode timer is greater than the predetermined period, switches the MPPT control mode to the next DC / DC controller.

[0011] Implementations of the PV bus system may include one or more of the following features. Each DC / DC controller may include an MPPT controller and a DC / DC converter. Each DC / DC controller may include a proportional integral derivative (PID) control stage and a step-down stage coupled to the PID control stage. Each photovoltaic string may include at least one photovoltaic panel. The instructions, when executed by the processor, may also cause the DC / DC controller to determine that MPPT control is not enabled; and, in response to determining that MPPT control is not enabled, maintain the previous duty cycle at the last known MPPT set point of the current MPPT controller. The instructions, when executed by the processor, may also cause the DC / DC controller to measure local voltage and current; determine MPPTΔV based on the measured local voltage; determine that power limiting is enabled; and, in response to determining that power limiting is enabled, determine output power based on the measured local voltage and current; and determine that the output power is greater than a power threshold; and, in response to determining that the output power is greater than the power threshold, perform MPPT. The instructions, when executed by the processor, may also cause the DC / DC controller to determine that the output power is not greater than the power threshold; and, in response to determining that the output power is not greater than the power threshold, perform reverse MPPT.

[0012] Another general aspect features a fixed DC bus system. The fixed DC bus system includes a modular inverter; a fixed DC bus coupled to the modular inverter; a photovoltaic string coupled to the modular inverter via the fixed DC bus; a battery connected to the fixed DC bus; and a DC / DC controller coupled between the battery and the fixed DC bus. Each PV string includes an MPPT controller. The MPPT controller includes a PID control stage and a step-down stage with a step-down gain.

[0013] An implementation of a fixed DC bus system may include one or more of the following features. The PID control stage may include a first voltage gain block and a first proportional integral (PI) controller coupled to the output of the first voltage gain block. The step-down stage may include a step-down gain block configured to apply a step-down gain to an input voltage to obtain a step-down gain voltage; and a first subtraction block coupled to the output of the step-down gain block and subtracting the step-down gain voltage from the output of the first PI controller to obtain an adjusted PI controller output. The step-down stage may include an addition block coupled to the output of the first subtraction block and adding the adjusted PI controller output to a reference power to obtain a further adjusted PI controller output. The step-down stage may include a second subtraction block coupled to the addition block and subtracting the input voltage from the further adjusted PI controller output. The step-down stage may include a second voltage gain block coupled to the output of the second subtraction block, and a second PI controller coupled to the output of the second voltage gain block.

[0014] The details of one or more aspects of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this invention will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Various aspects of the present invention are described below with reference to the accompanying drawings, which are incorporated into and constitute a part of this specification, in which:

[0016] Figure 1 is a schematic diagram illustrating a photovoltaic bus system;

[0017] Figure 2 It is a flow chart illustrating the switching of the MPPT control mode of the photovoltaic bus system;

[0018] Figure 3 is a schematic diagram of a fixed DC bus system architecture according to one aspect of the present disclosure;

[0019] Figure 4 is a schematic diagram illustrating the PV bus model;

[0020] Figure 5 is a schematic diagram illustrating a fixed DC bus model;

[0021] Figure 6 is a graphical diagram illustrating the solar spectrum variation, which can be used to determine the speed at which MPPT control switches between two MPPT units of a network of MPPT units;

[0022] Figure 7 It is a diagram illustrating the MPPT performance of the PV bus;

[0023] Figure 8is a diagram illustrating the PV bus MPPT and power output limiting performance;

[0024] Fig. 9 is a diagram illustrating the fixed DC bus MPPT and voltage drop power sharing performance;

[0025] Fig.10 is a graphical diagram illustrating fixed DC bus power output limitations with MPPT performance;

[0026] Fig.11 is a schematic diagram illustrating a hybrid power limit descent controller;

[0027] Fig.12 is a schematic diagram of an example of a DC / DC controller according to the present invention;

[0028] Fig.13 is a schematic diagram of a fixed DC bus system architecture according to another aspect of the present invention. DETAILED DESCRIPTION

[0029] The fixed DC bus system architecture provided by the present invention (for example, Figure 3 The fixed direct current (DC) system 300 shown includes a fixed DC bus that serves as a standard power interconnect for photovoltaic (PV) power generation and storage devices (e.g., PV arrays, batteries, controllers, drives, alternating current (AC) systems, etc.) In some aspects, a common fixed bus system can solve some of the problems associated with PV and battery bus systems and accelerate deployment and increase cost savings of the entire PV / energy storage system.

[0030] In order to connect the PV array to a fixed DC bus, a distributed maximum power point tracking (MPPT) controller is required at the string level, sub-string level or module level to maximize the PV power generation. The added cost of a distributed MPPT controller can be fully offset by the savings in wiring costs and the increase in total energy production.

[0031] Central inverter PV bus system (e.g. Figure 1 The PV bus system 100 shown in FIG. 1 ) wherein a central inverter can drive the MPPT voltage of all PV strings connected to the central inverter can reflect the features inherent in a fixed DC bus system, including synchronous MPPT tracking, power sharing, and power limiting, while using a variable voltage DC bus. The present invention proposes control techniques that provide such feature and performance comparisons between a fixed DC bus system and a PV bus system.

[0032] Photovoltaic bus central inverter power supply system

[0033] Reference Figure 1, utility-scale solar projects include many photovoltaic panels 102a-102n connected to a grid-connected central inverter unit 110, which is equipped with an integrated maximum power point tracking (MPPT) function. Typically, multiple solar modules (e.g., 30 solar modules) are connected in series to form a photovoltaic string, and the photovoltaic strings (e.g., 10-24 photovoltaic strings) are connected in parallel to a combiner box (not shown). The combiner box is then connected to the central inverter unit 110. The photovoltaic bus system 100 of the present invention includes a photovoltaic panel group 102a-102n, an energy storage device 104a-104n and a central inverter unit 110 with grid-connected or islanded capabilities.

[0034] The photovoltaic panel groups 102a-102n are connected to a common fixed DC bus 108a-108n, respectively. Unlike the fixed DC bus structure, a distributed MPPT controller connected to the photovoltaic panel groups 102a-102n may not be used in the photovoltaic bus system. Instead, the MPPT is implemented in a central inverter unit 110 or a distributed DC / DC controller 106a-106n, each of which includes a DC / DC converter.

[0035] The energy storage devices 104a-104n (which may be vanadium flow batteries or lithium-ion batteries) are connected to a common fixed DC bus 108a-108n through battery controllers 106a-106n, respectively. A central inverter unit 110 with grid-connected or islanding capabilities converts DC power into AC power. The central inverter unit 110 includes a DC / DC controller 116 that implements the MPPT function. The DC / DC controller 116 may include a step-up or step-down DC / DC converter. The central inverter unit 110 also includes an inverter 118 connected to the output of the DC / DC controller 116. Alternatively, the DC / DC controller 116 and the inverter 118 may be mixed into a single unit.

[0036] Photovoltaic bus control method

[0037] Energy storage systems are difficult to integrate into these systems at the bus level due to performance and stability issues that arise when multiple DC / DC controllers with MPPT capabilities simultaneously attempt to track the maximum power point from a common PV bus. In some cases, DC / DC controllers with MPPT capabilities that rely on voltage perturbation methods, such as perturb and observe and incremental conductance MPPT methods, may inadvertently track the maximum power point based on voltage perturbations of neighboring DC / DC controllers with MPPT capabilities, resulting in poor performance and / or system instability. To address this issue, several new distributed multi-agent maximum power tracking methods that operate under low-bandwidth or no-bandwidth communication can be used for the PV bus system 100.

[0038] Control mode switching

[0039] Control mode switching is a distributed MPPT method that designates one of the DC / DC controllers 106a-106n as a PV bus agent with dedicated MPPT control authority. After a pre-specified duration (e.g., 5-15 seconds) or certain operating conditions are met (e.g., the lowest state of charge of the DC / DC controller 106a-106n associated with the battery or battery pack 104a-104n), the MPPT control authority will be "switched" to the adjacent DC / DC controller with MPPT functionality. The DC / DC controller that is not currently operating in MPPT mode operates at a fixed duty cycle. The duty cycle can be set at the last known MPPT set point of each DC / DC controller 106a-106n.

[0040] Figure 2 is a flow chart illustrating an example of a method 200 for controlling mode switching.

[0041] At block 201, the PV bus system is started. At block 202, the method 200 includes determining whether MPPT control is enabled at the current DC / DC controller. If MPPT control is enabled, an MPPT mode timer, which may also be referred to as an MPPT mode switching timer or an MPPT mode conversion timer, is started at block 204. Then, at block 206, a local voltage and current are measured, for example, a voltage and current at the output of a PV string are measured, and a maximum power point voltage search direction ΔV is calculated based on the measured local power disturbance.

[0042] At block 208, method 200 includes determining whether power limiting is enabled. If power limiting is enabled, the method includes determining at block 210 whether the output power is greater than the power limit. Block 210 may include determining the output power based on measured local voltage and current. If the output power is greater than the power limit, MPPT is performed in the direction of negative ΔV at block 212. If the output power is not greater than the power limit, MPPT is performed in the direction of positive ΔV (also referred to herein as reverse MPPT) at block 214. If it is determined at block 208 that power limiting is not enabled, MPPT is performed at block 212.

[0043] After performing MPPT at block 212 or performing reverse MPPT at block 214, method 200 includes determining whether the MPPT mode timer is greater than the time limit. If it is determined that the MPPT mode timer is greater than the time limit, the MPPT control mode is switched to the next unit at block 218. If the MPPT mode timer is not greater than the time limit at block 216, method 200 returns to block 202 to determine whether MPPT control is enabled. If MPPT control is not enabled, the previous duty cycle of the last known MPPT set point on the current device is maintained. Then, method 200 repeats block 216 to determine whether the MPPT mode timer is greater than the time limit.

[0044] Sequential MPPT control

[0045] Sequential MPPT control is a modification of control mode switching in which each distributed energy resource (DER) unit is allowed one voltage disturbance before passing MPPT control authority to the next DC / DC controller.

[0046] Adaptive ΔV MPPT control

[0047] Adaptive ΔV MPPT control operates by adjusting the magnitude of voltage or power disturbances based on local device metrics, such as current device power output or battery state of charge. In this mode, communication between DC / DC controllers may not be required.

[0048] Power limit control

[0049] While using control mode switching and adaptive delta-V techniques, power output reduction can be achieved by making a small modification to the basic MPPT method. This modification involves reversing the direction of the MPPT controller duty cycle adjustment during the voltage perturbation step when the output power exceeds the set limit. The power limit control applied to the perturbation, observation, and incremental conductance methods is similar.

[0050] Fixed DC Bus Power Systems

[0051] The fixed DC bus power system 300 utilizes a single fixed DC bus 308 to transmit power between all connected devices. MPPT and voltage matching can be provided by string MPPT controllers 103a-103n and a central inverter 310 with MPPT functionality. Multiple wiring to the central inverter 310 can be eliminated.

[0052] The fixed DC bus power supply system 300 includes multiple groups of PV panels 102a-102n, energy storage devices 104a-104n, DC / DC controllers 306a-306n, which include DC / DC converters, and a central inverter unit 310 with grid-connected and / or islanding capabilities. The PV panel groups 102a-102n are coupled to a common fixed DC bus 308 via distributed MPPT controllers 103a-103n. Each MPPT controller 103a-103n is coupled between a corresponding PV panel 102a-102n and a common fixed DC bus 308. The energy storage devices 104a-104n (which may be vanadium flow or lithium-ion batteries) are connected to the common fixed DC bus 308 through bidirectional DC / DC battery controllers 106a-106n, respectively. The central inverter unit 310 with grid-connected and / or islanding capabilities converts DC power to AC power and can operate with a fixed DC input.

[0053] Fixed DC bus control method

[0054] Providing a common voltage standard on all devices simplifies the control design of the fixed DC bus power system 300. Power sharing, power output limitation, and battery charging / discharging can be achieved by operating a single device (e.g., MPPT controllers 103a-103n) in voltage / power drop mode, current limiting mode, and current tracking mode, respectively. DC bus voltage stability is ensured by limiting voltage tracking to a single device of each fixed DC bus system using a power / voltage drop control method. Voltage regulation can be assigned to a central inverter 315 for outputting maximum utility power with limited battery charging / discharging, or to a battery system that outputs limited grid power with maximum battery charging. Voltage regulation allocation can be achieved through the same low-bandwidth communication path used in PV bus control mode switching. Table 1 illustrates the photovoltaic MPPT, inverter, and battery control modes of the PV bus and fixed DC bus power systems in various system operating modes.

[0055] Table 1. Examples of PV bus and fixed DC bus device control modes

[0056]

[0057] 1. Control switching is enabled; 2. Voltage / power reduction is enabled.

[0058] simulation

[0059] The above control method can be implemented and applied to 3:2:1 and 1.6:0.6:1 (PV:Battery:AC) PV bus and fixed DC bus power system models. Figure 4 and Figure 5Model examples for a PV bus and a fixed DC bus system are shown, respectively. In these models, solar data 402 is filtered by a low pass filter 404, and random noise 406 is added to the filtered solar data via an addition block 408. The processed solar data, e.g., irradiance applied to a PV panel, is applied to the input of a PV array model 415 via a saturation limit block 410. Temperature is also applied to the input of a PV array model 415 via a temperature model block 412.

[0060] exist Figure 4 In the PV bus system model of FIG. 4 , the measurement block 432 measures the voltage output from the PV array model 415 . Figure 5 In the fixed DC bus system model of FIG. 4 , a measurement block 432 measures the voltage output from the MPPT controller 525, which is coupled to the output of the PV array model 415. A measurement block 434 measures the voltage of the battery 422, a measurement block 436 measures the voltage at the combiner box location, and a measurement block 438 measures the voltage at the inverter 424. The PV bus system model also includes a display block 418 coupled to the measurement output of the PV array model 415. The display block 418 may display one or more measurement values ​​associated with the PV array model 415, such as voltage and current.

[0061] result

[0062] Simulation results comparing a photovoltaic bus power system and a fixed DC bus system are given below.The PV bus control method described above can be utilized to provide a PV bus power system that is functionally similar to a PV bus power system inherent in a fixed DC bus power system.

[0063] MPPT tracking time.

[0064] When applied to typical insolation distributions, the time tracking settings for centralized and distributed MPPT may not have a significant impact on performance. A survey of various MPPT methods shown in Table 2 below indicates that the tracking times of current MPPT methods may be sufficient to account for typical insolation time variations. Figure 6 Compared to the frequency of solar variations shown in , the current MPPT tracking speed is sufficient to track most of the time insolation variations, and a time-accelerated direct normal irradiance (DNI) profile is used in all simulations.

[0065] Example Tracking Method Sample tracking time (seconds) Differential Particle Swarm Optimization Algorithm 0.5 Duty Cycle 1.96 Adjusting the duty cycle 1.2 Traditional perturbation and observation method 0.2 Drift-free perturbation and observation method 0.15 Hybrid Ant Colony Algorithm / P&O 2.41 Particle Swarm Optimization 12.41 Ant Colony Algorithm 9.47

[0066] PV bus control mode switching performance

[0067] The PV bus MPPT tracking and power output limiting performance achieved with control mode switching can be evaluated by simulating an accelerated time insolation distribution with a PV+battery PV bus system. A digital twin PV observer model with a real MPPT can also be simulated to provide a performance baseline. The results of control mode switching with MPPT are shown in Figure 7 As shown. Figure 7 As shown, inverter power 702 and battery power 704 increase from about 1000 W to about 5000 W and then decrease back to about 1000 W. Total power curve 706 tracks MPPT power curve 708. In this simulation, power sharing is optional and is automatically determined by the ratio of the line impedance between the battery and the central inverter and the PV bus, but can be adjusted by using, for example Fig.12 The total energy extracted from the PV panel matches the baseline performance.

[0068] The control mode switching results using MPPT and 3000W inverter power output limit are as follows Figure 8 As shown. Figure 8 As shown, the battery power 704 increases from about 1000w to more than 6000w, and then decreases to the power output limit 801; the inverter power 702 increases from about 1000w to the power output limit 801, and then decreases to 0w; and the total power curve 706 tracks the MPPT power curve 708. In this case, the active PV bus device operates in a non-forced power sharing mode, which is a system operating in a static duty cycle mode and may correspond to Figure 2 Status 220, similar to Figure 7 When the power output limit is reached, for example, Figure 8 As shown in power output limit 801, the central inverter switches to reverse MPPT control to maintain a fixed power output, and the battery absorbs excess PV power. The control mode switching can automatically adjust the power distribution ratio to extract maximum photovoltaic energy while limiting the central inverter power output.

[0069] In both cases, the overall system MPPT is comparable to the baseline performance and the power output tracking performance is consistent with expectations. Slight tracking overshoot / undershoot is shown, but this is attributed to the aggressive simulation time acceleration factor and large ΔV. Improved performance is expected with real-time conditions and smaller voltage perturbation step sizes.

[0070] Fixed DC bus performance

[0071] The results of fixed DC bus MPPT power sharing and MPPT power sharing with inverter power output limitation are as follows Fig. 9 and 10 As shown. Fig. 9 The results shown are related to the non-export restriction case, where a 2:1 inverter to battery step-down ratio was established to demonstrate controlled power sharing. Fig. 9 As shown in FIG. 7 , the battery power 704 increases from about 700 W to more than 3000 W, and then decreases to about 700 W; the inverter power 702 increases from about 1300 W to more than 6000 W, and then decreases to about 1300 W; and the total power curve 706 tracks the MPPT power curve 708 .

[0072] In with Fig.10 The results shown are related to the power limit case, where a 3000W power output limit is imposed. Fig.10 As shown, the battery power 704 increases from 0 watts to more than 6000 watts and then decreases to 0 watts; the inverter power 702 mainly tracks the 3000W power output limit; and the total power curve 706 tracks the MPPT power curve 708. The hybrid power reduction / power limit controller allows seamless and automatic transitions between reduction control and power limiting, and can be applied to any bus-connected components. In some aspects, the hybrid power reduction / power limit controller can be incorporated into the central inverter unit, inverter, MPPT controller and / or DC / DC controller of the present invention. Fig.11 An example of a hybrid power reduction / power limit controller 1100 is shown in FIG. The hybrid power reduction / power limit controller 1100 includes a proportional integral (PI) control stage 1110 and a reduction stage 1120. Alternatively, the PI control stage 1110 may be replaced with a proportional integral derivative (PID) control stage. Alternatively, the differential gain of the PID control stage may be set to zero.

[0073] The hybrid power reduction / power limit controller 1100 includes a voltage input terminal 1102 and a current input terminal 1104 applied to a multiplication block 1111, which determines the multiplication of the voltage value applied to the voltage input terminal 1102 and the current value applied to the current input terminal 1104 and outputs the resulting power value. The power value is then subtracted from the bias value output by the bias block 1112 using a subtraction block 1113. The output of the subtraction block 1113 is applied to a voltage gain block 1114. The output of the voltage gain block 1114 is applied to a digital proportional integral (PI) block 1116. The voltage input 1102 is also applied to a reduction gain block 1121.

[0074] The output from the reduced gain block 1121 is then subtracted from the output of the digital proportional integral block 1116 by a subtraction block 1122. The output from the subtraction block 1122 and the offset value (e.g., 1500) output from the offset block 1119 are then added by an addition block 1123. The voltage input 1102 is then subtracted from the output of the addition block 1123 by a subtraction block 1124, and the output of the subtraction block 1124 is applied to a voltage gain block 1126. The output from the voltage gain block 1126 is then applied to a digital PI block 1128, which applies PI control to the output from the voltage gain block 1126. The output of the digital PI block 1128 is then provided to the DC / DC converter via an output terminal 1130.

[0075] System-level power output limiting can be implemented when the battery is idle until the inverter output limit is reached, at which point the hybrid controller automatically switches the DC / DC controller to voltage regulation mode, absorbing the excess available PV power.

[0076] System efficiency

[0077] Conductor and converter losses Inverter:battery power capacity ratios were evaluated for PV bus and fixed DC bus systems with varying single daily insolation curves (set to a combination of inverter and battery capacity). Examples of device and conductor resistance values ​​are listed in Table 3. Switching and other related DC / DC converter losses are omitted.

[0078] Fig.12 An example of a DC / DC controller 1200 is shown, which can implement Figure 1 In addition, the DC / DC controller 1200 or a modified version of the DC / DC controller 1200 may implement the central inverter unit 110, Figure 3 MPPT controller 103a-103n or Figure 3 The DC / DC controller 1200 includes a wireless antenna 1205 and a communication interface 1217, which is configured to communicate with other devices of the power system (e.g., other DC / DC controllers in the PV bus system). The DC / DC controller 1200 also includes a microcontroller 1210 and a power converter 1220. The microcontroller 1210 includes a processor 1211, such as a central processing unit (CPU), a random access memory (RAM) 1212 coupled to the processor 1211, a program memory 1213 coupled to the processor 1211, a data interface 1215 coupled to the processor 1211, a drive circuit 1216 coupled to the processor 1211 and the power converter 1220, and a communication interface 1217 coupled to the processor 1211.

[0079] The data interface 1215 may be coupled to sensors to receive measurement data about aspects of the power system. For example, the data interface 1215 may be coupled to a battery fuel gauge that may measure and / or determine voltage, current, state of charge, or other information related to the state of a battery or battery pack to which the DC / DC controller 1200 is connected. The program memory may store instructions for the MPPT control method 1214 that may be loaded into the RAM 1212 and executed by the processor 1211. In other aspects, the drive circuit 1216 is incorporated into the power converter 1220, or resides in a DC / DC controller 1200 that is separate from the microcontroller 1210 and the power converter 1220.

[0080] Example Equipment / Conductors Example Average DC Resistance DC bus – 1500V Inverter 0.005Ω DC Bus MPPT Converter 0.005Ω Total PV series resistance 0.485Ω Battery DC / DC Converter 0.005Ω Battery to DC bus segment 0.00025Ω Photovoltaic to DC bus line segment 0.00025Ω Total DC bus segment 0.00525Ω PV bus (1200–2000V) Inverter 0.005Ω Total PV series resistance 0.97Ω Battery DC / DC Converter 0.005Ω Battery to PV bus segment 0.00025Ω PV to PV bus segment 0.00025Ω Total PV bus segment 0.00525Ω

[0081] The power converter 1220 may include a DC / DC converter, such as a DC / DC buck converter, which steps down the DC voltage received from the PV string and outputs the lower DC voltage to a fixed DC bus. Figure 3 In the case of a central inverter 315, the power converter 1220 may include a DC / AC inverter that converts the DC voltage on the DC bus into an AC voltage suitable for feeding the grid. The DC / AC converter can convert the DC voltage at the DC bus into an AC voltage with an appropriate frequency and voltage amplitude to feed the grid. The power converter 1220 can be controlled by the microcontroller 1210 via the drive circuit 1216 to provide AC power regulation and maximum power extraction. As used herein, "AC power regulation" refers to regulating the active power or reactive power output of the power converter according to the active power or active power command signal, and "maximum power extraction" refers to dynamically moving the operating point of the solar power source to the highest point on the power curve (which may change due to environmental changes, such as radiation and temperature changes) to obtain the maximum power output of the photovoltaic panel.

[0082] In the case of the hybrid central inverter unit 110 or the central inverter 315, the microcontroller 1210 is configured to send control signals to the power converter 1220 to adjust the PV power output from the PV string according to various command signals and feedback signals. In the case of the hybrid central inverter unit 110 or the central inverter 315, the microcontroller 1210 is configured to send control signals to the power converter 1220 to adjust the active power or reactive power output from the power converter 1220 according to various command signals and feedback signals. The power converter 1220 may include any type of converter topology, such as a half-bridge converter, a full-bridge converter, or a push-pull converter. In the case of the hybrid central inverter unit 110 or the central inverter 315, the power converter 1220 may include any type of DC to AC inverter topology, such as a two-level converter or a three-level converter. The power converter 1220 may include semiconductor switching devices (not shown), including but not limited to integrated gate-commutated thyristors (IGCTs) and insulated gate bipolar transistors (IGBTs).

[0083] Fig.13 An example of a fixed DC bus system architecture 1300 according to another aspect of the present invention is depicted. The fixed DC bus system architecture 1300 includes at least one PV panel or PV string 1302, a flow battery 1312, and a lithium-ion battery 1322, electrically coupled to a fixed DC bus 1301 via DC / DC controllers 1304, 1314, 1324, respectively. Each DC / DC controller 1304, 1314, 1324 includes MPPT functionality. The fixed DC bus system architecture 1300 also includes two or more inverters 1332a-1332n coupled to the fixed DC bus 1301. The inverters 1332a-1332n may be configured as modular inverters that may be selectively added to or removed from the fixed DC bus system architecture 1300 so that the fixed DC bus system architecture 1300 may be expanded or contracted as needed.

[0084] It should be understood that the various aspects disclosed herein may be combined in combinations other than those specifically presented in the specification and drawings. It should also be understood that, by way of example, certain actions or events of any process or method described herein may be performed in a different order, may be added, combined, or omitted entirely (e.g., all described actions or events may not be necessary to perform the technique). In addition, while certain aspects of the invention are described as being performed by a single module or unit for clarity, it should be understood that the techniques of the invention may be performed by a combination of units or modules associated with, for example, a photovoltaic panel, a photovoltaic string, or a battery.

[0085] In one or more examples, the described techniques may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or codes on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include non-transitory computer-readable media corresponding to tangible media such as data storage media (e.g., RAM, read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and can be accessed by a computer).

[0086] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application-specific integrated circuits (ASICs), field-programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Thus, the term "processor" as used herein may refer to any of the foregoing structures or any other physical structure suitable for implementing the described techniques. Furthermore, these techniques may be fully implemented in one or more circuits or logic elements.

Claims

1. A method, characterized in that include: At a current DC / DC controller connected to the common bus, determining to enable maximum power point tracking control for one or more photovoltaic panels connected to the common bus; In response to determining that MPPT control is enabled, starting an MPPT mode timer; Implement MPPT; Determining that the MPPT mode timer is greater than a predetermined period; And in response to determining that the MPPT mode timer is greater than a predetermined period, switching the MPPT control mode to a next DC / DC controller connected to the common bus.

2. The method according to claim 1, characterized in that Also includes: Make sure MPPT control is not enabled; And in response to determining that MPPT control is not enabled, maintaining the last duty cycle at the last known MPPT set point of the current DC / DC controller.

3. The method according to claim 1, characterized in that Also includes: measuring a local voltage and a current; and determining an MPPT ΔV based on the measured local voltage.

4. The method according to claim 3, characterized in that Also includes: Determine if power limiting is enabled; And in response to determining that power limiting is enabled: Determine output power based on measured local voltage and current; and determining that the output power is greater than a power threshold; And in response to determining that the output power is greater than the power threshold, performing MPPT.

5. The method according to claim 4, characterized in that Also includes: Determining that the output power is not greater than a power threshold; as well as In response to determining that the output power is not greater than the power threshold, reverse MPPT is performed.

6. The method according to claim 1, characterized in that Also includes: Make sure power limiting is not enabled; And in response to determining that power limiting is not enabled, performing MPPT.

7. The method according to claim 1, characterized in that Also includes: Determining that the MPPT mode timer is not greater than a predetermined period; in response to determining that the MPPT mode timer is not greater than the predetermined period, further determining to enable MPPT control; And in response to further determining that MPPT control is not enabled, starting an MPPT mode timer.

8. The method according to claim 1, characterized in that Also includes: Determining that the MPPT mode timer is not greater than a predetermined period; in response to determining that the MPPT mode timer is not greater than the predetermined period, further determining not to enable MPPT control; and In response to further determining that MPPT control is not enabled, the previous duty cycle is further maintained at the last known MPPT set point of the current DC / DC controller.

9. The method according to claim 1, characterized in that The method also includes allowing voltage disturbance of the distributed energy before switching the MPPT control mode to a next DC / DC controller in response to determining that the MPPT mode timer is greater than a predetermined period.

10. The method according to claim 9, characterized in that It also includes scaling the amplitude of the voltage disturbance.

11. The method according to claim 10, characterized in that Also included is scaling the magnitude of the voltage disturbance based on local device metrics.

12. The method according to claim 11, characterized in that Where the local device metric is output power or battery state of charge.

13. A PV bus system, characterized in that: include: Central inverter unit; a plurality of PV buses coupled to a central inverter unit; a plurality of PV strings coupled to the central inverter unit via the plurality of PV buses, respectively; a plurality of batteries respectively coupled to the plurality of PV buses; and a plurality of DC / DC controllers respectively coupled between the plurality of batteries and the plurality of PV buses, Each of the multiple DC / DC controllers includes: a processor and a memory, the memory storing instructions, which, when the processor executes the instructions, causes the DC / DC controller to determine to enable maximum power point tracking control; in response to determining that local MPPT control is enabled, start an MPPT mode timer; perform MPPT; determine that the MPPT mode timer is greater than a predetermined period; and in response to determining that the MPPT mode timer is greater than the predetermined period, switch the MPPT control mode to the next DC / DC controller.

14. The PV bus system according to claim 13, characterized in that: Each of the plurality of DC / DC controllers includes an MPPT controller and a DC / DC converter.

15. The PV bus system according to claim 13, characterized in that: Wherein each of the plurality of PV strings comprises at least one PV panel.

16. The PV bus system according to claim 13, characterized in that: The instructions, when executed by the processor, further cause the DC / DC controller to: determine that MPPT control is not enabled; and when determining that MPPT control is not enabled, maintain the previous duty cycle at the last known MPPT set point of the current DC / DC controller.

17. The PV bus system according to claim 13, characterized in that: in, When the instructions are executed by the processor, the DC / DC controller further causes: measuring a local voltage and a current; determining an MPPTΔV according to the measured local voltage; determining that power limiting is enabled; and in response to determining that power limiting is enabled: Determining output power based on the measured local voltage and current; and determining that the output power is greater than a power threshold; and performing MPPT in response to determining that the output power is greater than the power threshold.

18. The PV bus system according to claim 13, characterized in that: in, The instructions, when executed by the processor, further cause the DC / DC controller to: determine that the output power is not greater than a power threshold; and in response to determining that the output power is not greater than the power threshold, perform reverse MPPT.

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