341 results about "Grid-tie inverter" patented technology

An expert system manages a power grid wherein charging stations are connected to the power grid, with electric vehicles connected to the charging stations, whereby the expert system selectively backfills power from connected electric vehicles to the power grid through a grid tie inverter (if present) within the charging stations. In more traditional usage, the expert system allows for electric vehicle charging, coupled with user preferences as to charge time, charge cost, and charging station capabilities, without exceeding the power grid capacity at any point. A robust yet accurate state of charge (SOC) calculation method is also presented, whereby initially an open circuit voltage (OCV) based on sampled battery voltages and currents is calculated, and then the SOC is obtained based on a mapping between a previously measured reference OCV (ROCV) and SOC. The OCV-SOC calculation method accommodates likely any battery type with any current profile.

The invention provides a microgrid and microsource control method based on a virtual synchronous electric generator. The method comprises the following steps of building a mechanical equation and an electromagnetic equation of the virtual synchronous electric generator, carrying out microsource active control through active adjustment of the virtual synchronous electric generator, carrying out microsource reactive control through reactive adjustment of the virtual synchronous electric generator and achieving seamless switching between different operating modes of a microgrid. The microgrid and microsource control method based on the virtual synchronous electric generator has the active and reactive adjustment capacity similar to that of the synchronous electric generator, can simulate the inertia and the damping characteristic of the synchronous electric generator, can overcome the impact on a power grid from inertialessness of a traditional grid-connected inverter, and can effectively improve the capacity of the power grid to accept the renewable energy sources.

The invention provides a bidirectional power converter, that can be connected directly to an AC system without interposing a transformer, that is small in size, light in weight, inexpensive to manufacture, and capable of regenerative operation, and also provides a motor drive equipped with such a power converter and a BTB system and a grid-linking inverter system each comprising such a power converter. The power converter comprises converter cells each comprising: a first AC/DC converter which performs bidirectional power conversion between single-phase AC power and DC power; a second AC/DC converter whose DC side is connected to the DC side of the first AC/DC converter, and which performs bidirectional power conversion between single-phase AC power and DC power; a third AC/DC converter which performs bidirectional power conversion between single-phase AC power and DC power; and a high-frequency transformer which is connected between the AC side of the second AC/DC converter and the AC side of the third AC/DC converter. If the power converter 1 is an AC-input/AC-output type, the power converter further comprises a fourth AC/DC converter which is connected to the DC side of the third AC/DC converter, and which performs bidirectional power conversion between single-phase AC power and DC power.

The invention relates to an off-grid grid-connected hybrid photovoltaic power generation control system and an economical operation optimization method of the off-grid grid-connected hybrid photovoltaic power generation control system. The control system is composed of a photovoltaic array, a grid-connected inverter, a storage battery pack, a bi-directional inverter, a load, a power meter, a public grid, a demand response control system and a switch set. The photovoltaic array is connected into an alternating-current side through the grid-connected inverter, and the storage battery pack is connected into the alternating-current side through the bi-directional inverter. The grid-connected inverter is connected with the bi-directional inverter through a switch, and the public grid and the load are connected through the switch set (S1-S4). The whole off-grid grid-connected hybrid photovoltaic power generation control system is uniformly managed and controlled by the demand response control system. Through the turn-on and turn-off combination of the switch set, the system supports eight different operation modes to achieve the optimization of economic benefits and peak shifting of the grid, and the service life of the system is prolonged through the method of limiting the discharging depth and charging and discharging power of storage batteries.

A device and method for detecting islanding of a grid connected inverter makes use of an injected white noise as a perturbing force on the output voltage of the inverter. The white noise is injected at least once in every cycle and can be generated at different rates in implementation. On loss of the grid, a frequency drift of the output voltage is detected and a positive feedback is activated that accelerates the drift.

The invention discloses a power compensation method for unbalanced direct power control of a voltage controlled grid-connected inverter, which is suitable for direct power control (the conventional direct power control) without synchronous speed rotational coordinate transformation. The method comprises the following steps of extracting negative sequence voltage signals and positive sequence current signals by collecting voltage and current signals of a three-phase electric network; and computing compensation items of active and reactive power according to selected control targets. In the method of the invention, the compensation items of active and reactive power are injected in the power reference signals of the conventional direct power control according to required control targets so as to respectively eliminate negative sequence current, double frequency fluctuation of the active power and double frequency fluctuation of the reactive power in the electric network, caused by unbalanced voltage in the electric network, and fit different application situations. The invention has the advantages of enhancing the capabilities of control and uninterrupted operation of the voltage controlled grid-connected inverter when the electric network is in an unbalanced fault.

The invention discloses a networking method for a micro grid. The method is characterized in that: an AC generation source is connected with a DC bus through an AC/DC converter; a DC generation source is connected with the DC bus through a DC/DC converter; the DC bus is connected with a large power grid through a grid-connected inverter; the DC bus is connected with a power accumulator; and the AC/DC converter, the DC/DC converter and the grid-connected inverter are controlled by a system controller. The micro grid of the invention can be connected with a plurality of generation sources with different power generation properties and promote the development of micro grids. A networking structure of the DC bus can reduce the control difficulty of the micro grid and improve the power supply quality of the micro grid. The networking structure of the DC bus has a great advantage in connection of the micro grid to the large power grid and can adjust the grid-connection output active power and inactive power of the micro grid through the grid-connected inverter during grid connection in favor of the large power grid.

The invention discloses a photovoltaic microgrid power equalization control method based on three-end cooperative control, and the method comprises the steps: A) judging the current operation mode of a photovoltaic microgrid according to a DC bus voltage value of hte photovoltaic microgrid, a DC bus rated voltage value, an energy storage unit SOC, a photovoltaic power supply output power, and AC load power; B) carrying out the cooperative control of the working conditions of a photovoltaic power supply, an energy storage device and a grid-connected inverter in the photovoltaic microgrid according to the current operation model of the photovoltaic microgrid; C) controlling the current operation mode of the photovoltaic microgrid to be switched to an adjacent operation mode when the corresponding operation conditions are met; D) and enabling the converted operation mode to be updated to the current operation mode of the photovoltaic microgrid; and then switching to the step B). The method can enable the photovoltaic microgrid to be quickly switched to the corresponding operation mode in a seamless manner, thereby quickly eliminating the operation deviation, balancing the flow of an internal energy of the microgrid, reducing impact on the operation of the microgrid from power fluctuation, maintaining the stability of the voltage of a DC bus of the microgrid, and achieving the dynamic balance of the internal power of the microgrid.

The invention discloses a grid-connected inverter capable of reducing electrolytic capacitance, belonging to the field of inverters in power electronic converters. The inverter comprises a direct current (DC) power source, a DC/DC converter, a DC/AC converter, a bidirectional DC/DC converter, a DC-link capacitor and an energy storage capacitor. The output end of the DC power source is connected with the DC/DC converter in series, then is connected with the DC-link capacitor in parallel and finally is connected with the bidirectional input end of the bidirectional DC/DC converter and the input end of the DC/AC converter respectively. The bidirectional output end of the bidirectional DC/DC converter is connected with the two ends of the energy storage capacitor and the output end of the DC/AC converter is connected into the grid. When the instantaneous output power of the DC/AC converter is greater than or smaller than that of the DC power source, the energy storage capacitor correspondingly outputs or absorbs power. The grid-connected inverter uses less electrolytic capacitance as far as possible or does not use electrolytic capacitance and the service life of the whole inverter is lengthened.

The invention discloses a photovoltaic grid-connected power generation system and a direct current bus voltage control method thereof. The photovoltaic grid-connected power generation system comprises N photovoltaic direct-current modules, N diodes, a direct current bus capacitor and a grid-connected inverter. The photovoltaic direct-current module comprises a photovoltaic assembly and a direct-current converter. Each photovoltaic direct current module output is connected in parallel with one diode and the photovoltaic direct current modules are connected in series with each other so as to form a direct current bus. The direct current bus voltage control method is characterized in that: the grid-connected inverter automatically adjusts a direct current bus voltage according to changes of system output power so that the direct current bus voltage is reduced with the reduction of the system output power. The photovoltaic grid-connected power generation system of the invention has the following advantages that: generating efficiency is high; system reliability is high; maintenance is easy; hot plug of the photovoltaic direct current module can be supported and so on. By using the direct current bus voltage control method, the system generating efficiency can be effectively increased and a system redundancy operation capability can be improved too.

The invention provides a method for controlling direct power of a grid-connected inverter without any non-AC voltage sensor and belongs to the field of electric energy transformation. The invention aims to solve the problem that because an initial value of an integrator in a virtual flux observer of a voltage vector on the network side is improperly selected, the grid-connected inverter cannot normally operate. The method comprises the following steps of: by transformation, obtaining components i alpha and i beta of the three-phase current value in a two-phase stationary coordinate system; by calculation, obtaining components us alpha and us beta of the inversion voltage value of the current grid-connected inverter in the two-phase stationary coordinate system; after the integration of the integrator, calculating components psi alpha and psi beta of the magnetic flux linkage of the voltage on the network side in the two-phase stationary coordinate system; calculating the instantaneous output active power p and reactive power q of the grid-connected inverter, and obtaining components usp * and usq * of the control voltage set value of the new grid-connected inverter in a two-phase rotary coordinate system; and finally obtaining the control signal of all power devices of the grid-connected inverter. The method can be used for direct power control of the grid-connected inverter.

The invention discloses an inverter grid-connected control method based on the virtual synchronous generator technology and belongs to the field of distributed power generation system grid-connected researches. According to the technical scheme, the method includes the steps that a grid-connected inverter phase voltage phase value is obtained through calculation by simulating a conventional synchronous generator unit active power control method; a grid-connected inverter phase voltage amplitude value is obtained through calculation by simulating a conventional synchronous generator unit reactive power control method; a three-phase voltage reference value is worked out according to the inverter phase voltage phase value and the inverter phase voltage amplitude value, a three-phase modulated wave is figured out according to direct current side voltage obtained through detection, and the three-phase modulated wave is compared with a carrier wave to obtain six switching signals to control turn-off and turn-on of switching devices in a main circuit. System damping and active power-frequency droop control are achieved by means of control link signals, and power grid frequency does not need to be detected. The method simplifies a control structure and avoids the problems caused by a frequency detection link. Effectiveness of the method is verified through simulation and experiment results.

The invention discloses a grid-connected inverter for low-frequency current ripple output restraining of a fuel cell and a control device. The grid-connected inverter comprises the fuel cell FC, a boosting converter, a full bridge inverter and an LCL filter. The control device comprises a voltage sensor, a current sensor and a DSP digital controller. The boosting converter comprises an inverse-current-preventing diode, an input filtering capacitor Cin, a filtering inductor LB, an electric MOSFET and an output capacitor CDC. The full bridge inverter comprises four electric MOSFETs. The LCL filter comprises a capacitor C1 and two inductors L1 and L2. The DSP digital controller comprises a proportioner, a phase-locked loop, a subtracter, a PI adjuster, a multiplying unit, a summator, a signal generator, a comparer and a phase inverter. By establishing the boosting converter, energy decoupling on an input side and an output side is achieved, the fact that currents on the input side do not contain low-frequency ripples is guaranteed, the manufacturing cost of the grid-connected inverter is lowered, power conversion efficiency is improved, and an electric energy converting device suitable for fuel battery power generation is achieved.

The invention discloses a reactive phase modulation method for a photovoltaic power station. Active power is emitted while own reaction output capacity of a grid-connected inverter is fully utilized as a supplement or a substitute of reaction compensation equipment, and configuration capacity of an SVG (static var generator) in an original photovoltaic power station is reduced to greatest extent or even without configuring the SVG, so that cost of the photovoltaic power station is greatly lowered; a reactive phase modulation subsystem uses a multi-target dynamic optimization algorithm to dynamically calculate a reactive target value of each power generating node, large occupied area of the photovoltaic power station and position dispersion of a photovoltaic array are taken into consideration, reactive in-place balance is realized, and flowing of reactive power is reduced; factors like geographical position of the photovoltaic array, type of the inverter and optimal working interval are taken into consideration, so that realization of reactive balance is guaranteed while maximization of active power output by the whole station is realized, whole-station optimal adjusting and economical running of the photovoltaic power station are realized, and the reactive phase modulation method has higher engineering application value.

The invention relates to a grid connected inverter control method based on hysteresis modulation under the unbalanced grid voltage condition. The control method comprises that the voltage of a dc bus is detected, and a reference active power value is calculated via a PI (Proportion Integration) regulator; the positive sequence components and the negative sequence components of the grid voltage under a two-phase rotating coordinate system are obtained by processing three phases of detected grid voltages via coordinate conversion and positive/negative sequence component decomposition; three phases of instantaneous reference-current values are obtained from the reference active power value and the positive and negative sequence components of the grid voltage via calculation, coordinate conversion and the like; and finally, the three phases of instantaneous reference-current values are compared with three phases of practical current values, a certain hysteresis width is set, and driving pulses are emitted in a hysteresis control principle. The control method requires no parameters of grid connected filtering reactors, and only includes the PI regulator, thereby providing convenience for construction realization; and under the unbalanced grid voltage condition, the stability of instantaneous grid power can be effectively ensured, the voltage fluctuation of the dc bus can be lowered, and the stability of the grid connected inverters is improved.

The invention discloses a reactive power and voltage control method for grid-connected inverters of a large photovoltaic power station. The method comprises steps as follows: a voltage reference unit gives reference voltage uref to a voltage control point; a reactive power setting unit is used for comparing actual voltage of the voltage control point with the reference voltage to obtain voltage deviation, and reactive power reference quantity Qref required by maintaining voltage of the voltage control point is automatically acquired through a PID (proportional-integral-derivative) controller; a reactive power distribution unit automatically performs reactive power distribution between SVG (scalable vector graphics) and each photovoltaic power generation unit; the grid-connected inverters in the photovoltaic power generation units adopts distribution in equal proportion of reactive capacity. According to the method, coordinated control of a reactive power compensation device of the photovoltaic power station and the photovoltaic inverters is sufficiently utilized, grid-connected point voltage fluctuation of the photovoltaic power station is reduced, reactive power support is provided for a power grid, and voltage stability of a weak grid is improved; meanwhile, reactive power is distributed according to line loss of the photovoltaic power generation units, and active loss of the photovoltaic power station is reduced; therefore, the reactive power and voltage control method facilitates safe, economic and stable operation of the large photovoltaic power station accessing the weak grid.

The invention discloses a method for realizing a network access current of a unity power factor of a grid-connected inverter and internal anti-islanding, which belongs to control technology of inverters. The method comprises the following steps: phase difference detection, frequency droop calculation, reference current generation, grid voltage feed-forward and a proportional integral controller. A frequency droop algorithm comprises the following steps: performing real-time calculation on a phase difference between the network access current and a grid voltage; multiplying the phase difference by a droop coefficient to obtain a frequency variable quantity; and subtracting the frequency variable quantity from a previous frequency output quantity of the last frequency droop algorithm so as to obtain an output quantity of a new frequency droop algorithm. The method realizes phase control of the network access current of the grid-connected inverter, realizes the network access current of the unity power factor, and internally realizes an anti-islanding measure of frequency drift positive feedback of the grid-connected inverter at the same time. Therefore, the method is of a simple and effective realizing mode.

A system includes an uninterruptible power supply and a grid-tie inverter, connected to batteries via double conversion of high quality DC power sources. A Grid Interactive Double Conversion unit includes DC source with MPPT control and power modulation; a Bi-directional DC battery port; a Bi-direction AC grid port; a Pure Sine wave AC output; a Generator AC input, and DC contacts to prevent the inverter from back feeding generator during a power failure.

The invention discloses a harmonic wave damping control method for a one-phase LCL type grid-connected inverter. The harmonic wave damping control method for the one-phase LCL type grid-connected inverter mainly comprises a fundamental wave control loop, a harmonic wave damping loop and a capacitance current inner loop. The fundamental wave control loop enables fundamental wave components in non-error follow current command signals of network-entry currents to change, and grid connection with a high power factor is achieved. The harmonic wave damping loop can inhibit background harmonic voltage of a power grid and the influence on the network-entry currents of the grid-connected inverter from the harmonic wave components of the current command signals at the same time, and provide the network-entry currents with high quality. The capacitance current inner loop is used for improving system damping, inhibits the LCL resonance peak and improves the system stability. The harmonic wave damping control method is easy to achieve, and can improve the ability of the grid-connected inverter to inhibit the harmonic wave components in the background harmonic voltage of the power grid and the current command signals, and the quality of the network-entry currents of the grid-connected inverter is improved. The harmonic wave damping control method is suitable for a grid-connected photovoltaic power generation system, a fuel battery and a wind power generation grid-connected system of an LCL type filter.

The invention provides a voltage type control method for a novel photovoltaic grid-connected inverter and relates to a voltage type control method for the grid-connected inverter. The method aims to solve the problems that grid-connected power of the voltage control type inverter is prone to being influenced by power grid fluctuation, and direct-current bus voltage can not be stabilized. The method comprises the following steps that 1, a closed-loop feedback control method is introduced into droop control, power rings are increased, and a translation quantity delta U0 of a droop curve U0 and a translation quantity delta f0 of rated output frequency f0 of the inverter are obtained after laplace transformation of the power rings is carried out; 2, the translation quantity delta U0 of the droop curve U0 and the translation quantity delta f0 of the rated output frequency f0 of the inverter are respectively superposed to a grid-connected droop equation of the voltage type of the novel photovoltaic grid-connected inverter, the grid-connected droop equation is simplified to obtain an equation, the power rings in the equation obtained after simplification are replaced by direct-current bus voltage rings, and the novel photovoltaic grid-connected inverter can control the direct-current bus voltage. The method is mainly applied to the grid-connected inverter.

The invention relates to coupling inductance type double-Boost inverter circuits in a photovoltaic system, which comprises two coupling inductance type Boost circuits sharing a direct current power supply, and alternate current output is taken from two coupling inductance type Boost output capacitors. The invention solves the defects of large power loss of a power switching tube, large power loss of a transformer, low conversion efficiency, low utilization rate of photovoltaic generation and the like in a method in which a single-stage inversion circuit is combined to the grid through an industrial frequency transformer boost mode, a DC-DC boosted circuit is at the front stage and an inverter is at the back stage. The invention comprises two coupling inductance type Boost circuits and uses a full-control type device switching tube, so the inversion circuit can realize four-quadrant operation of energy; and under the conditions that the coupled inductance has lower input voltage and smaller duty ratio, the Boost circuits can also output higher voltage, thus the grid-combined inverter of the invention does not need a booster transformer and can realize primary grid-combined generation.

The invention discloses a photovoltaic charge station, comprising a photovoltaic component array used for converting solar energy to electric energy, a current-converging lightning protection box connected to the photovoltaic component array and used for converging the currents from the photovoltaic component array and performing lightning protection, a grid-connected inverter connected to the current-converging lightning protection box and used for performing current conversion, an energy storage battery used for storing the electric energy, an energy manager connected to the grid-connected inverter and the energy storage battery and used for being connected with a mains supply power grid so as to transmit the electric energy in different directions according to the different states of the electric energy and an electrical load connected to the grid-connected inverter. The photovoltaic charge station disclosed by the invention only comprises one set of current conversion system; the control system of the photovoltaic charge station is simple and convenient to implement; and the photovoltaic charge station is reasonable in design, capable of meeting the needs of different charge devices and decreasing manufacturing cost, capable of operating no matter whether the mains supply power grid exists, strong in adaptability, and convenient in market promotion.

The disclosed grid-tie inverter is provided with: a single-phase or three-phase inverter (1) which changes a DC voltage supplied from a DC power supply (5) to a pulse-width modulated voltage; a first capacitor circuit (41) which is connected so as to form a neutral point (c) on the input side of the inverter (1); a second capacitor circuit (42) which is connected so as to form a neutral point (f) on the output side of the inverter (1); a common mode current bypass channel (g) which is formed by connecting the neutral point (c) on the first capacitor circuit (41) and the neutral point (f) on the second capacitor circuit (42); a grounded capacitor (11) which is provided between the bypass channel (g) and the earth; a first common mode choke coil unit which is provided with common mode choke coils (31, 32) in at least one location between the first capacitor circuit (41) and the inverter (1) or the inverter (1) and the second capacitor circuit (42), and which uses the inverter (1) to suppress generated common mode current; and an output filter (2) which converts the pulse-width modulated voltage waveform output from the inverter (1) to a sinusoidal single-phase or three-phase AC voltage.

The invention discloses an output impedance correcting method suitable for an LCL type grid-connected inverter. The output impedance correcting method suitable for LCL type grid-connected inverter includes: step (1), detecting capacitance current iC, grid-connected current ig, grid-connected point voltage vpcc and voltage VL2 of a filter inductor L2, and obtaining feedback signals iC-of, ig-of, vpcc-of and vL2-of thereof; (2) inputting the feedback signals iC-of, ig-of and vpcc-of to a current controller, and processing to output vr1; (3) inputting the signals vpcc-of and vL2-of to an impedance regulator, and processing to output vr2; (4) adding vr1 and vr2 together to obtain a modulating signal vm, inputting to a PWM generator to generate a PWM signal to control a switching tube of an inverter bridge. The output impedance correcting method suitable for the LCL type grid-connected inverter corrects the output impedance of the grid-connected inverter through the impedance regulator and is capable of effectively improving the closed loop stability and the interference rejection of the grid-connected inverter.