2397 results about "Grid connected inverter" patented technology

The invention provides a compensation method of direct current (DC) voltage fluctuation of a photovoltaic grid-connected inverter, and the method can be used for improving the quality of the grid-connected current through compensating an input DC side secondary pulse voltage by adding a DC voltage pulse compensation module in a DC / AC (direction current / alternating current) high-frequency link, and eliminating a grid-connected current harmonic wave caused by the DC voltage pulse. The control performance of the system can be improved without adding a filter device and adding any extra appliance.

The invention relates to a control method which can be applied to an active-clamp flyback miniature photovoltaic grid-connected inverter device. The active-clamp flyback miniature photovoltaic grid-connected inverter device comprises a flyback converter and a power frequency polarity conversion circuit. In the device, a current reference is used for controlling a flyback primary-side current peak value so that the device can output a half-wave sinusoidal current, and the output voltage is clamped by a grid voltage. When the instantaneous power is lower, a constant frequency current discontinuous mode in combined with a variable frequency current critical continuous mode is adopted in the flyback control method. When the flyback converter works in a variable frequency current critical discontinuous mode, an auxiliary switching tube can be conducted for a period of time when the secondary-side current of the flyback converter reaches zero, the conduction time can be accurately controlled by a digital chip, thus realizing the leakage inductance energy feedback and the soft switch of a master switching tube under the condition of wide-range output voltages and different instantaneous powers and greatly improving the efficiency under the condition of full loads.

The invention discloses a parallel structure and a control method for a photovoltaic power generation grid-connected inverter and belongs to the technical field of renewable energy sources. A topological circuit structure of the photovoltaic power generation grid-connected inverter is divided into a parallel structure of single-phase voltage type pulse-width modulation (PWM) inverters and a parallel structure of three-phase voltage type PWM inverters; and in the control method, an outer ring regulator of a control circuit of the parallel voltage type PWM inverters is independent based on a power grid voltage-oriented vector control technology in a control mode of voltage outer ring and current inner ring so as to form a common unified outer ring regulator; control strategies of various inverters are simplified into single closed loop current control so as to achieve the consistency of energy flow directions of the parallel voltage type PWM inverters and avoid ring current; and the parallel current sharing of the voltage type PWM inverters is realized. Therefore, multiple modules of the voltage type PWM inverters are connected in parallel to realize high-power modularized large-scale application.

The invention provides an intelligent energy storage machine and an operating method thereof. The intelligent energy storage machine is used in a large scale, so that the electrical load of a power grid is relatively stable, the electrical load for the daytime and night is balanced, and the peak load shifting function is realized; and the energy storage machine comprises a miniature wind power and photovoltaic power generation input interface, and a new energy access power system is easily realized. The intelligent energy storage machine comprises a cabinet shell, a control system, an energy device and an energy storage device, wherein the energy device is used for providing energy for the load and comprises a solar energy device, a wind energy device and a mains supply; the electric energy generated by the solar energy device and the wind energy device is stored in the energy storage device; the energy storage device is an energy storage battery pack; the energy storage battery pack is used for storing the energy generated by the solar energy device and the wind energy device and the energy charged by the mains supply; and the control system comprises a wind and photovoltaic complementary controller, a grid-connected inverter, an off-grid inverter, a programmable logic controller (PLC), a battery management system and a bidirectional intelligent electric meter.

The invention discloses a robust dicyclic photovoltaic grid-connected control method based on power feedforward, which mainly comprises three parts: proportion integration (PI) control of exocyclic voltage, dead-beat control of endocyclic robust predictive current and power feedforward control, wherein the exocyclic PI control of the voltage is used for stabilizing the capacitive voltage of a direct-current side; the dead-beat control of the endocyclic robust predictive current is used for carrying out linear prediction on the voltage of a power grid at a next control period and carrying out non-linear prediction on grid-connected current by advanced control so as to obtain the command value of the grid-connected current at the next period; and then, PWM (pulse-width modulation) and grid-connected control are realized by the dead-beat control. According to the robust dicyclic photovoltaic grid-connected control method based on the power feedforward, a photovoltaic grid-connected inverter has higher robustness, wider stability margin and quicker dynamic response, and the requirement of grid-connected running of an inverter is better met.

The invention relates to a virtual synchronous generator control method based on self-adapting moment inertia. The output of a grid-connected inverter in distributed generation is connected with an AC bus of a filter capacitor Cf which is in parallel connection with the grid-connected inverter through a filter inductor Lf; sampling is performed to obtain the output power, the voltage and the current of an output interface of an inverter; the output power, the voltage and the current are transmitted to a VSG (virtual synchronous generator) algorithm; the calculated terminal voltage of a VSG stator is sent to be controlled by a voltage external loop; the voltage external loop adopts a PI controller to stably load the voltage; the current of the filter capacitor is sent to be controlled by a voltage internal loop; the voltage internal loop adopts a PI controller to increase the response speed; a control signal is outputted by a voltage-current dual-closed loop to the grid-connected inverter; the moment inertia in the virtual synchronous generator in the control method can be changed in a self-adapted manner according to the change capacity of the system frequency. Through the adoption of the virtual synchronous generator control method disclosed by the invention, the transient state process of the system is reduced; a great deal of harmonic waves in the system is offset; the stability of frequency and the stability of voltage can be improved; the adaptability and the power supply quality of a micro-electrical network are improved; the problem that in a conventional method, the output frequency is reduced, is solved.

A purpose of the present invention is disclosing a flyback type miniature photovoltaic grid connected inverter with a power decoupling circuit and a control method thereof. The inverter comprises a flyback converter and a power frequency polarity conversion circuit. The flyback converter is provided with a power decoupling circuit, a decoupling capacitance voltage grade is higher than output voltage of a solar energy photovoltaic array, decoupling capacitance voltage is allowed to fluctuate in a large range, thus decoupling capacitance capacity is decreased, power decoupling can be realized by only using a non-electrolytic capacitor, using an electrolytic capacitor is avoided, a service life of the miniature photovoltaic grid connected inverter is prolonged, and reliability is raised. Through the control method, not only is decoupling of miniature photovoltaic grid connected inverter output power and solar energy photovoltaic array output power realized, but also direct current voltage and current waveform outputted by the solar energy photovoltaic array can maintain smooth, a service life of the solar energy photovoltaic array is guaranteed, and realization of maximum power point tracking (MPPT) is facilitated.

The invention relates to a three-phase four-wire three-level photovoltaic grid-connected inverter and a control method thereof. In the inverter, voltage input from a solar panel is filtered by a filter capacitor; the input voltage is boosted by a boosting circuit to form direct-current bus voltage serving as input voltage of a post inversion circuit; the bus voltage is inverted by a three-phase four-wire inversion circuit to form three-phase voltage; after being filtered by a filtering circuit, the three-phase voltage is output to a power grid; a controller detects the voltage and output current of the solar panel, the three-phase voltage of the power grid and three-phase current output by the three-phase four-wire inversion circuit; a boosting converter and an inversion controller in thecontroller 101 respectively generate driving pulses of the boosting circuit and the three-phase four-wire inversion circuit to control the operation of the integral inverter. A three-phase four-wire power supply system is formed by the addition of a neutral line, so the inverter can be connected with symmetrically-balanced three-phase loads, and also can be connected with single-phase loads. The application field of the photovoltaic inverter is broadened while the safety of the power supply system is improved.

The invention belongs to the technical field for testing photovoltaic grid-connected inverters, in particular to a test bench for testing various performance indexes of a photovoltaic grid-connected inverter. The test bench uses a photovoltaic battery array simulating power supply as the input source of the inverter so to displace the original real photovoltaic battery array, and uses a grid characteristic stimulating power supply to displace a large-power resistor load. The photovoltaic battery array simulating power supply can set the needed weather conditions like illumination, environment temperature, wind speed and the like conveniently, output a V-I (voltage-current) curve conforming to the requirements, and overcome the shortages that the real photovoltaic battery array has multiple uncontrollable factors and the installation and maintenance are not convenient. The grid characteristic stimulating power supply can simulate the characteristics like a grid voltage, a frequency, background harmonic waves and the like, can detect the working performances of the inverter under different grid states, and can feed back the output electric energy of the inverter to a public grid, so that the electric energy loss is reduced.

The invention relates to a capacitance current feedforward control method for a grid-connected inverter with an LCL filter and belongs to the field of electric energy conversion. The capacitance current feedforward control method for the grid-connected inverter with the LCL filter solves the problem of low stability of the grid-connected inverter with the LCL filter in the prior art and the problem of reduced efficiency of a system due to phase difference between grid side voltage and current. The method comprises the following steps of: 1, acquiring three-phase power grid voltage and acquiring a vector angle theta of the power grid voltage; 2, acquiring three-phase output current of the inverter and acquiring direct current components ild and ilq of the inverter side current; 3, acquiring three-phase filter capacitance current and acquiring direct current components icd and icq of the filter capacitance current; 4, setting set values of the inverter output current to perform proportional integral (PI) adjustment on a processed signal, outputting uq, performing PI adjustment on the processed signal, and output ud; and 5, inversely converting the ud and the uq into u(alpha) and u(beta) and performing pulse width modulation on the u(alpha) and the u(beta) to acquire six paths of switching signals which are used for controlling six switching tubes of the three-phase inverter so as to perform capacitance current feedforward control on the grid-connected inverter.

The invention belongs to the field of electrical engineering, distributed power generation and power quality control, and aims to provide a multi-functional grid-connected inverter and a grid-connected inverter control method. The grid-connected inverter comprises a direct-current bus bar with a capacitor and three sets of single-phase full-bridge inverter circuits sharing the direct-current bus bar, the direct-current output ends of a distributed power supply or a grid-connected energy-storing generating set are connected to both ends of the capacitor of the direct-current bus bar, the output of each set of single-phase full-bridge inverter circuit is connected to a filter, and the output ends of each filter are connected with a distribution network of the 380V voltage class through a single-phase step-up isolation transformer. According to the invention, the grid-connected inverter equipment is effectively utilized to carry out effective control on the power quality of points of interconnection, so that the grid-connected inverter is multi-purpose and multi-functional, the cost performance of the grid-connected inverter is enhanced, the investment, operation and maintenance cost of a system can be reduced, and the reliability of the system can be enhanced. The principle of the provided control scheme is clear, and the control scheme is highly operable and reliable in operation.

The invention relates to an active damping method of an LCL grid-connected inverter system. The active damping method is realized through the following steps of: setting conjugated zero points or independent zero points to set off conjugated resonance limit points generated by an LCL filter in the grid-connected inverter system or to draw the conjugated resonance limit points to a stable area, and adopting grid-side inductive current to feed back and introduce a state variable in the LCL filter to conduct feedback compensation. By conducting feedback compensation on grid-side inductive voltage, the resonance damping of the LCL filter is controlled, the waveform and the amplitude of grid current of the grid-connected inverter system are controlled and the influence of grid voltage harmonic wave on the grid current can be effectively suppressed. The active damping method is a simple and effective realization method. A realization circuit comprises parallel and series active damping circuits.

The invention discloses a control method of a three-phase grid-connected inverter based on a modified proportional resonant regulator. The method comprises the following steps of: firstly, computing according to given active and reactive powers of the inverter and a voltage of a power grid to obtain required d-axis and q-axis currents under a synchronous coordinate system, and performing coordinate transformation by combining with phase information which is measured by a phase locking loop and a measured three-phase voltage signal of the power grid to obtain a current reference signal under a stationary alpha-beta coordinate system; secondly, performing coordinate transformation on an output current signal of the inverter to the alpha-beta coordinate system, controlling and tracking the current reference signal by the modified proportional resonant regulator with a harmonic compensator; and finally, returning to an abc coordinate system by coordinate transformation to generate a pulse-width modulation (PWM) pulse-control three-phase full-bridge inverter output, so as to make a distributed generation system grid-connected for power generation. By the method, a large number of complicated computation processes are eliminated, and a control structure is simplified. The control method of the three-phase grid-connected inverter based on the modified proportional resonant regulator is an accurate and high-efficiency novel inverter control method and has a bright development future.

The invention discloses a generalized impedance criterion calculation method for stability analysis of a grid-connected inverter and an application. The method comprises the following steps of building a small signal impedance model of an inverter side network port and a small signal impedance model of a power grid side network port under polar coordinates; and calculating generalized impedances of the inverter side network port and the power grid side network port according to the built small signal impedance model of the inverter side network port and small signal impedance model of the power grid side network port under the polar coordinates, and dividing the two generalized impedances obtained in the second step to obtain the ratio of the generalized impedances of the inverter side network port and the power grid side network port as a generalized impedance criterion. The obtained generalized impedance criterion can be used for small signal stability analysis of a grid-connected inverter system, the problem that the analysis accuracy is affected by a traditional impedance method due to the presence of coupling is solved, a foundation is laid for clearing power grid oscillation generated when new energy is connected to a power grid on a large scale, and the method disclosed by the invention is an important method for designing an inverter controller to improve the stability.

The invention discloses a grid-connection control method for solar photovoltaic power generation and belongs to the field of solar photovoltaic power generation. The method is characterized in that: constant voltage control of a direct-current bus is taken as a basic starting point and the output voltage and current of a photovoltaic cell are adjusted by adjusting the pulse-width modulation (PWM) duty ratio of a DC / DC converter so as to realize the tracking control of the maximum output power point of the photovoltaic cell; and in addition, stable and grid-connection running of a photovoltaic generating system is realized and the constant voltage of the direct-current bus is maintained by adjusting the output current of a DC / AC grid-connected inverter. The tracking control of the maximum power point of the photovoltaic cell is characterized in that: the variation track of a power-voltage vector is obtained by sampling the output voltage and current of the photovoltaic cell at three or more points and is matched with a preset variation mode so as to determine the adjusting direction of the output current. During grid-connection running, the PWM duty ratio of the inverter is adjusted by using the measured voltage amplitude, phase position and frequency information of a power grid so as to synchronize the voltage generated by the system and the power grid. Moreover, the voltage of the direct-current bus is kept constant by using high-speed feedback of the output current of the inverter, so that the power of the system fed in the power grid is close to the power generated by a solar cell to the maximum.

The invention provides a cascade megawatt photovoltaic grid-connected inverter, wherein a topology structure of the cascade megawatt photovoltaic grid-connected inverter is composed of two levels, namely a DC / DC (direct current / direct current) isolation level and a DC / AC (direct current / alternating current) output level; the structures of three phases of circuits are the same; the output ends of a power inverter group of each single-phase of DC / DC output level are connected in a star shape; the input sides of power units of each single-phase level are provided with independent PV (photovoltaic) modules of the same structure; the DC / DC isolation level comprises high-frequency DC / AC, a high-frequency transformer and high-frequency AC / DC nodes of each single-phase for realizing isolation and boosting, and reducing the consumption of a switch tube via action of a resonant soft switch; the output level power transformer set adopts a bridge type inverter circuit; and the single-phase output level power units are connected with each other in a cascade mode. Based output cascade, the device can realize megawatt grid connection; as a high-frequency chain technology is used, the traditional low frequency transformer is omitted, and the power density is high; and compared with the existing photovoltaic grid-connected inverter structure, the device provided by the invention has the advantages of high energy conversion efficiency, excellent output energy quality, certain fault-tolerant capability and the like.

The invention relates to a current forecasting dead-beat control method of a Z source type interconnected inverter and a control device thereof, which belongs to the field of electrical energy conversion and is used for interconnected power generation. The current forecasting dead-beat control method overcomes the defect of sampling delay of the conventional control method. In each sampling period, a robust prediction algorithm is adopted to forecast interconnected current of the next period, and the needed inverted voltage is calculated according to a voltage equation of the inverter to realize the deadbeat control of the interconnected current. A single-voltage space vector modulating method with a through zero vector is used for generating a through-state pulse-width modulation wave shapes of the inverted voltage to control the DC capacitance voltage and the interconnected inverted voltage. The control device comprises a central processing unit, a synchronous signal generating circuit, a voltage and current testing circuit and an isolated driving circuit. The current forecasting dead-beat control method of the Z source type interconnected inverter has high control precision, is easy to digitally realize, has stronger inverted-side inductance parameter variation robustness, and the like.

The invention provides a non-isolated grid-connected inverter and a switch control time sequence thereof. The non-isolated grid-connected inverter comprises a voltage dividing capacitor branch (1), a clamping branch (2) and a full-bridge basic unit (3), wherein the voltage dividing capacitor branch (1) consists of a first voltage dividing capacitor (Cdc1) and a second voltage dividing capacitor (Cdc2), the clamping branch (2) consists of a first power switch pipe (S1) and a second power switch pipe (S2), and the full-bridge basic unit (3) consists of a third power switch pipe (S3), a fourth power switch pipe (S4), a fifth power switch pipe (S5) and a six power switch pipe (S6). The invention adds two controllable switch pipes and voltage dividing capacitors on the basis of a full-bridge circuit for forming a bidirectional clamping branch, is matched with the switch time sequence, and can realize the battery voltage at a half of the follow current loop potential in the follow current stage, so the leakage current of the non-isolated grid-connected inverter is eliminated, the output current only passes through three switch pipes in the power transmission stage is ensured, and the conduction consumption is effectively reduced.

The invention provides a photovoltaic grid connected inverter island detection method based on negative sequence current injection, belonging to the technical field of power system relay protection and automatic control. According to the method, an inverter is started to inject negative sequence current when a voltage harmonic distortion rate is larger than a fixed value, common connection point voltage unbalanced degree and voltage harmonic distortion rate are detected, when both the common connection point voltage unbalanced degree and the voltage harmonic distortion rate are larger than the respective fixed value and the duration time exceeds a set time, the generation of island is determined, and the rapid detection of the island is realized. According to the method, the setting difficulty of a criterion is reduced, the improvement of the detection speed is facilitated, the interference on a power grid is reduced as much as possible in the condition that the normal operation is ensured, the influence of a power grid asymmetrical fault is avoided, and there is no detection blind area. The simulation verification is carried out in the condition that the island detection is most not facilitated, and an island operation state still can be rapidly and accurately detected according to the method. A good method is provided for the operation withdrawal of a distributed power supply in the island or the turning of power grid connected operation into island operation control mode power system safe operation and the detection.

The invention discloses a centralized-type photovoltaic power generation system capable of achieving distributed MPPT, and the system comprises photovoltaic modules, photovoltaic optimizers, a voltage compensator, and a grid connected inverter. The output end of each photovoltaic module in the system is connected with one Buck type photovoltaic optimizer, so as to achieve the tracking of the maximum power of each photovoltaic module. The output ends of the photovoltaic optimizers are connected in series to form strings. Each string is connected with one isolated-type DC / DC converter, i.e., the voltage compensator, wherein the input end is connected with a DC bus, and the output end is connected to the string in a series manner. The plurality of strings are connected in parallel to form a photovoltaic array, and are connected with the grid connected inverter for grid connected power generation. The photovoltaic optimizers, the voltage compensator and the grid connected inverter communicate with each other in a mode of power signal recombination modulation communication. The system enables the power of the photovoltaic array to be maximum, and solves a problem of module-level mismatching and string-level mismatching. The proposed communication does not need additional wires and communication modules, so the communication cost is low, and the maintenance is simple.

The invention aims to disclose a photovoltaic grid-connected inverter for active energy decoupling, which comprises a first flyback converter, a second flyback converter, a voltage regulating converter, an output filter circuit and an inverter circuit. The decoupling of the output power of the photovoltaic grid-connected inverter and the output power of a solar photovoltaic array is realized, pulsation of the output power of the solar photovoltaic array is greatly reduced, the fluctuation loss caused by maximum power point tracking (MPPT) is reduced, and the conversion efficiency of the photovoltaic array is improved; only a non-electrolyte capacitor with small capacity and high reliability is adopted, the defects that the service life of the photovoltaic grid-connected inverter is shortened and the reliability is reduced caused by adopting an electrolytic capacitor are overcome, the service life and the reliability of the photovoltaic grid-connected inverter are improved; and the peak power of a transformer in the flyback converter is reduced, the volume of the transformer is reduced, the loss is effectively reduced, and the conversion efficiency is improved, so that the aim of the invention is realized.

The invention belongs to the field of photovoltaic power generation, applies a power decoupling circuit to reduce the capacity of a capacitor at the side of a DC (Direct Current) bus for prolonging the service life and improving the reliability of the inverter, replaces an electrolytic capacitor with high capacity and a short service life with a thin film capacitor with low capacity and a long service life and designs a miniature photovoltaic grid-connected inverter. To fulfill the aims, the invention adopts the technical scheme that the miniature photovoltaic grid-connected inverter with an optimized DC bus capacitor comprises a main circuit and a control and driving circuit, wherein the main circuit is formed by a photovoltaic cell panel, a phase-shift full-bridge circuit, a high frequency transformer, a full-bridge rectifying circuit, the DC bus capacitor, the power decoupling circuit and an inverter circuit which are sequentially connected; the control and driving circuit comprises a photovoltaic output current sampling circuit, a photovoltaic output voltage sampling circuit, a power MOSFET (Metal Oxide Semiconductor Field Effect Transistor) driving circuit, a capacitor voltage sampling circuit, a grid-connected current sampling circuit, a phase-locked loop circuit and a DSP (Digital Signal Processor) controller. The miniature photovoltaic grid-connected inverter is mainly applied to photovoltaic power generation.

The invention relates to the technical field of detection, in particular to a relay failure detection device and a relay failure detection method for a grid-connected inverter. The device comprises a relay module 1, a driving module 2, a control module 3, a first signal acquisition module 41 and a second signal acquisition module 42, wherein one end of the relay module 1 is connected with an output end of an inverter 5, and the other end of the relay module 1 is connected with a power grid 6; the driving module 2 is connected with the relay module 1; one end of the first signal acquisition module 41 is connected with the output end of the inverter, and the other end of the first signal acquisition module 41 is connected with the control module 3; one end of the second signal acquisition module 42 is connected with the power grid 6, and the other end of the second signal acquisition module 42 is connected with the control module 3; and the other end of the driving module 2 is connected with the control module 3. By the invention, turn-off or turn-on failure of any one or more relays in the relay module 1 can be detected, a detection result is fed back to a user through a display module, and the reliability in relay redundancy design of an output stage of the inverter 5 is improved.

The present invention relates to the technical field of electrical engineering and discloses a PRBS disturbance injection-based power grid impedance online identification device. The device is mainly composed of a grid-connected inverter, a current loop controller, a sampling device and an impedance identification unit. The device is characterized in that the grid-connected inverter is connected with the current loop controller. When the grid-connected state is stable, the grid-connected inverter injects the PRBS disturbance into the power grid. During the injection process of a PRBS signal, a built-in output voltage THD is fed back to the controller, so that the THD value of the output voltage of the inverter is ensured to be smaller than 5%. The sampling device is connected with the PCC part of the power grid and is used for sampling and recording the voltage and the current at the PCC part of the power grid. The impedance identification unit is used for subjecting the sampled data of the sampling device to DFT analysis, and taking the average value of the amplitude and the average value of the phase of each harmonic component of the voltage and the current during the current sampling period. The method of the invention is high in precision, high in speed, strong in real-time property, wide in frequency range, lower in measuring cost and difficulty, and better in stability.

The invention relates to the technical field of photovoltaic grid-connected inverters, particularly to a method for detecting the failure of relays and protecting filter capacitors of photovoltaic grid-connected inverters. The method comprises the following steps: before the relays are closed, if the difference of the absolute values of the effective value (Vinv) of one-phase or multi-phase inversion voltage and the effective value (Vgrid) of the same-phase grid voltage is detected to be smaller than the failure voltage threshold (delta V) of the relays, namely the absolute value of(Vinv-Vgrid)is smaller than delta v, judging that the relays in the phase are adhered, otherwise, judging that the relays are normal; similarly, after the detection of the relays on closed inversion sides, the detection of the relays on closed grid sides, and the closed detection of the relays on both sides are successively performed by the same method, if the relays have no failures in every step, grid connection is allowed, if any relay has a failure, machines are stopped, and grid connection is denied. According to the method disclosed by the invention, when every relay is accurately detected to have a failure or not, the filter capacitor voltage output by the inverters is processed, so that the possibility that at the moment of grid connection of the inverters, the grids generate current impact on the filter capacitors is eliminated, the system stability of the inverters is improved, and the service life of the filter capacitors is prolonged.

The invention discloses a method for preventing a grid-connected island effect of a distributed power source. A distribution network terminal is arranged at a distribution network terminal and is respectively connected with a distribution network and a distributed power source through feeder wires. The method for preventing the grid-connected island effect of the distributed power source comprises the following steps of: (a) acquiring the running state quantity of a distribution feeder wire and a distributed power source grid-connected feeder wire by using the distribution network terminal; (b) processing the acquired state quantity in the distribution network terminal to obtain the running conditions of the distribution network and the distributed power source; and (c) processing the grid-connected state of the distributed power source according to the running conditions of the distribution network and the distributed power source. The invention solves the problem of the detection of the side island effect of a grid-connected inverter in the grid-connected running process of the distributed power source and effectively prevents the island effect of the distributed power source caused by grid connection.

The invention relates to a distributed photovoltaic energy storage system and an energy management method. The system comprises a photovoltaic cell array and an energy storage cell component; a converter device comprises a photovoltaic cell direct current conversion module, an energy storage cell direct current conversion module, a rectification conversion module, a grid-connected inverter module and an off-grid inverter module; the energy management system is connected with each module; a layered control strategy is applied to optimize operation of the distributed photovoltaic energy storage system; a central decision-making level makes an operating strategy of the whole system according to current energy conditions and feeding characteristics of each power supply; a centralized control level monitors states of distributed power supplies in real time and takes corresponding control measures under different energy conditions; and a local executing level selectively cuts a part of loads or stores surplus electricity into an energy storage cell according to the load requirement of an actual system and the energy conditions. Photovoltaic power generation and energy storage technologies are sufficiently combined, so that the photovoltaic and the energy storage are intelligently controlled, and the energy management efficiency, the power supply reliability, power quality and the like of the system are effectively improved.

The invention discloses a pulse width modulation (PWM) control method for a single-phase grid-connected inverter, which is implemented according to the steps of: calculating to obtain single-polarity PWM wave; comparing network voltage detection with a zero crossing comparator to obtain a synchronous square wave signal, and then performing two divided-frequency on the synchronous square wave signal to obtain a synchronous square wave two divided-frequency signal; keeping only one of four power switch tubes of a single-phase full-bridge inverter in a high-frequency PWM action state, the power switch tube, which is on the diagonal of the power switch tube, of another bridge arm in a power frequency action state, and the other two power switch tubes in a shutoff state; making the four power switch tubes alternately act in a high-frequency PWM mode according to certain phase sequence; and adopting a principle that the power switch tube which conducts shuts off in advance to add dead zone time only during the zero crossing of network voltage at the same time. The method is applicable to single-phase grid-connected power generation systems, and has the characteristics of reducing the loss of switches, eliminating dead zone effect and optimizing heat dissipation.

The invention discloses a photovoltaic power-generating maximal power tracking controlling device which is on the basis of digital signal processing device, the device comprises a direct current converter, a voltage and electric current detecting module, a controlling module and a driving and protecting module, wherein the input end of the direct current converter is connected with the output end of a solar battery array, the output end is connected with the input end of a grid-connected inverter through a direct current generatrix, the grid-connected inverter is connected with an electric net, the input end of the voltage and electric current detecting module is connected with the output end of the voltage and electric current detecting module, the output end of the voltage and electric current detecting module is connected with the input end of the controlling module, the output end the controlling module is connected with the input end of the driving and protecting module, and the output end of the driving and protecting module is connected with a grid electrode G of a isolated-gate bipolar field effect transistor of the direct current converter. The invention has the advantages of low cost, which is easy to popularize and use, reduces the difficulty of the system controlling realization, and increases controlling effect. The installation of the invention is flexible, maintenance is convenient, and the influence of a single branch road fault can be reduced in maximum limit.

The invention discloses a method for detecting an island of a photovoltaic grid-connected inverter. The method comprises the following steps of: 1), detecting a voltage frequency at a common coupling point of the inverter and a power grid, wherein when the voltage frequency is between f11 and f12, a phase position of output current of the inverter is the same to that of voltage at the coupling point; and, by modifying the phase position between the output current of the inverter and the voltage at the coupling point, compared with the voltage at the coupling point, the output current is ahead of time in theta degrees (when fgrid is more than f12 and less than f22) or lags in theta degrees (when fgrid is more than f21 and less than f11); and 2), to compensate a dead zone appeared in frequency detection, judging whether an island effect exists by modifying an amplitude value of the output current of the inverter within one power frequency period after every four power frequency periods and recovering the amplitude value of the output current into an original value after the period. According to the method, harmonic waves output by the inverter to the power grid can be effectively reduced; the detection time is short; the calculation method is simple; and the computing resource of a control chip can be saved.