149 results about "Grid connected converter" patented technology

An LVRT control method for a grid-connected converter of distributed energy resources comprises steps of: obtain a positive sequence electrical component and a negative sequence electrical component during an LVRT period; outputting a compensation signal according to a power threshold withstood by a grid-connected converter to undertake reactive power compensation; and constraining the output power lower than the power threshold. The present invention uses the positive and negative sequence electrical components to undertake reactive power compensation, whereby to improve balance and stability of voltage during the LVRT period, avoid reverse torque and mechanical resonance, and prolong the service life of the power generator. Moreover, the present invention constrains the sum of the compensation currents below the power threshold to prevent the circuit of the power generator from being overloaded and damaged, whereby is prolonged the service life of the power system.

The invention relates to a precise phase locking method based on a cross decoupling self-adaptive complex filter, which comprises the following steps: firstly carrying out the Clarke coordinate transformation on three-phase voltage input signals of Ua, Ub and Uc for obtaining voltage signals of Ualpha and Ubeta under an alpha-beta coordinate system; then leading the voltage signals to pass throughthe cross decoupling self-adaptive complex filter for extracting positive sequence voltage components *alpha<plus> and *beta<plus> under the alpha-beta coordinate system; further carrying out the Clarke inverse transformation on the *alpha<plus> and the *beta<plus> for obtaining three-phase voltage positive sequence components of *a<plus>, *b<plus> and *c<plus> under an a-b-c coordinate system; carrying out the Park transformation on the *alpha<plus> and the *beta<plus> for obtaining a d-axis component *d<plus> and a q-axis component *q<plus> under a d-q coordinate system, wherein, the q-axiscomponent *q<plus> reflects the positive sequence amplitude; leading the d-axis component *d<plus> to pass through a PI regulator to obtaining the frequency estimated value *0; feeding the *0 back tothe cross decoupling self-adaptive complex filter for realizing the frequency self-adaption; and carrying out integration on the *0 for 1 / s for obtaining the positive sequence phase *<plus>. The precise phase locking method is characterized by simpleness, easy realization, high phase-locking precision and fast speed, thereby being particularly applicable to the precise phase locking of grid-connected converters under the extreme industrial field situations of power grid voltage distortion, three-phase voltage imbalance, large fluctuation range of voltage frequency and the like.

A method and an apparatus for controlling a grid-connected converter which includes a boost converter, a buck converter, and a current source inverter having an output CL filter. An input of the buck converter input is connected to an output of the boost converter, and an input of the current source inverter is connected to an output of the buck converter. The method includes controlling a boost converter input voltage, controlling a boost converter output voltage through control of a buck converter output voltage, and controlling the current source inverter to produce an AC current from the buck converter output voltage. The apparatus implements the method.

The invention provides a positive and negative sequence impedance measuring module, a positive and negative sequence impedance measuring system and a positive and negative sequence impedance measuringmethod for a new energy grid-connected converter. The positive and negative sequence impedance measuring module comprises a disturbance voltage injection unit, a grid-connected point voltage / currentacquisition unit, an impedance calculation unit and an impedance bode map generating unit. The positive and negative sequence impedance measuring system comprises a controller, I / O interface equipmentand a real-time simulation system which are sequentially connected, wherein the real-time simulation system comprises the positive and negative sequence impedance measuring module. Compared with theprior art, the positive and negative sequence impedance measuring module, the positive and negative sequence impedance measuring system and the positive and negative sequence impedance measuring method for the new energy grid-connected converter are provided by the invention, the positive and negative sequence impedance measuring module can control and disturb phases, amplitude values and waveforms of a voltage signal flexibly; the controller, the I / O interface equipment and the real-time simulation system in the positive and negative sequence impedance measuring system form a hardware-in-loopcontrol real-time simulation system, real-time simulation and positive and negative sequence impedance measurement can be carried out on the new energy grid-connected converter, and the precision ofimpedance measurement of the new energy grid-connected converter is improved.

The invention discloses an output phase-locked loop system of a grid-connected converter and a control method. The system comprises a Clark transform module for Clark transform of a three-phase voltage signal outputted by a grid-connected converter, a delay elimination module for carrying out delay elimination on two phases of voltages in an alpha-beta coordinate system, a Park transform module for Park transform of the two phases of voltages in the alpha-beta coordinate system after delay elimination according to an initial output phase, a PI regulator for PI adjustment on a q-axis signal, an integration module for integration processing on a grid voltage estimation value to obtain an initial output phase, an amplification module for amplification of a frequency adjustment error to obtain a phase compensation value, and a superimposition module for superimposition of the initial output phase and the phase compensation value to obtain a final output phase. With the output phase-locked loop system and the control method, the fundamental frequency and phase information of the output voltage of the grid-connected converter can be obtained accurately when the system voltage is not balanced or distorts.

A method of controlling the grid-side current of a single-phase grid-connected converter having an LCL filter connected between the output of the converter and the grid includes measuring a grid voltage and at least one signal in a group of signals consisting of a grid-side current, a converter-side current and a capacitor voltage, estimating the fundamental component of the grid voltage, forming a grid-side current reference, a converter-side current reference and a capacitor voltage reference for the grid-side current of the LCL filter, forming estimates for the non-measured signals in the group of signals, forming a grid-side current difference term, a converter-side current difference term and a capacitor voltage difference term, and controlling the output voltage of the converter based on the grid voltage, a formed injection term and a formed estimate of the harmonic distortion term to produce a grid side current corresponding to the current reference.

The invention discloses a decoupling and delayed compensation method for a complex vector PI controller of a grid-connected converter. The decoupling and delayed compensation method comprises the steps of directly arranging a zero point of the controller at a pole point of a controlled object by taking a vector model of the controlled object as a basis to obtain a complex coefficient current controller model; calculating to obtain a system delay transfer function with regard to single delay of digital control and inherent zero-order maintaining characteristic of the converter; and achieving delay compensation of a current ring after connecting a delay compensation item in series with the complex vector PI controller. A single and effective method is designed for the current ring of the grid-connected converter, the problem of d-axis current and q-axis current coupling is prevented to the greatest extent, the phase margin of the system is expanded by delay compensation, the stability of the current ring is improved, and the dynamic response performance is improved.

The invention discloses an optimized power allocation method applied to parallel operation of grid-connected converters. The input power and output power of each grid-connected converter in independent operation are detected, and the item coefficients of an efficiency model based on the load characteristics of the converter are determined based on the input power and the output power. A system efficiency expression of n grid-connected converters during parallel operation is built according to the efficiency model of each grid-connected converter. By calculating the output power of each grid-connected converter, optimized output power allocation is carried out in order to improve the system efficiency of a parallel system under the condition that grid-connected converters with different energy conversion efficiency are in parallel operation. Therefore, optimized control during parallel operation of grid-connected converters such as grid-connected inverters and PWM rectifiers is realized.

The invention discloses a current control system and method for the grid-connected converter of a DC micro-grid. The method comprises pre-estimating the power of the grid-connected converter by the change of DC bus voltage; calculating the steady-state value of the inductive current according to the change of the DC bus voltage; and establishing a linear control relationship between the DC bus voltage and the inductive current to predict directive current. The control strategy improves the current control accuracy of the grid-connected converter, increases response speed, and improves the dynamic and static performance of the grid-side current of the grid-connected converter, reduces the influence of system parameter changes on the grid-side current, and enhances the robustness of the DC micro-grid. The DC micro-grid grid-connected converter current control strategy and device include a bidirectional converter topology circuit and its control device, and solve the problem that the control of the grid-connected converter in the DC micro-grid in the prior art cannot realize bidirectional power flow and the grid-connected converter has line impedance.

The invention discloses a control method for improving grid-connected voltage source inverter system stability. The method comprises the steps of (1) generating a grid-connected converter modulating wave initial order; (2) calculating a power grid side current control circuit gain T, obtaining corresponding cut-off frequency omega 1 and cut-off frequency omega 2 when an amplitude-versus-frequency curve of the T passes through 0dB twice before a resonant frequency omega r of an LCL filter, and obtaining an s-domain transfer function of a lag compensation link according to the cut-off frequency omega 1 and the cut-off frequency omega 2; (3) performing discretization on the s-domain transfer function of the lag compensation link, and bringing the grid-connected converter modulating wave initial order obtained in the step (1) into an express form, in a digital controller, of the s-domain transfer function of the lag compensation link obtained through the discretization, so as to obtain a final modulating wave order value of the converter; (4) obtaining a modulating signal according to the final modulating wave order value of the converter obtained in the step (3), and controlling various switching elements of the converter according to the modulating signal; the control method provided by the invention can effectively improve the system stability.