CN103259287B - Bi-directional grid-connected inversion device and bi-directional grid-connected inversion method for distributed type new energy power generation system - Google Patents

Abstract

A bidirectional grid-connected inverter device and method for a distributed new energy power generation system, the device includes a signal acquisition unit, a main control unit, a rectification inverter unit and a power storage unit; the signal acquisition unit includes a first signal acquisition unit and a second In the signal acquisition unit, the input device of the first signal acquisition unit is connected to the DC input terminal of the rectification and inverter unit, and the input terminal of the second signal acquisition unit is connected to the grid end of the rectification and inversion unit; the rectification and inversion unit includes a bridge rectifier circuit, a bridge Type inverter circuit, Boost boost circuit and Cuk step-down circuit, the storage battery of the storage unit is connected to the distributed new energy generation system through the storage battery controller. The method of the invention first makes a quick judgment, and if it is in an island state, the system is quickly cut off from the power grid, and then the active detection is called to detect the result of the passive detection, which fully utilizes the advantages of high accuracy of active detection and overcomes the problem of detection If the time is long, the degree of harmonic pollution to the power grid is insufficient.

Description

A bidirectional grid-connected inverter device and method for a distributed new energy generation system

technical field

The invention belongs to the field of distributed new energy power generation and electrical technology, and specifically relates to a bidirectional grid-connected inverter device and method for a distributed new energy power generation system.

Background technique

Energy is the source of human economic and cultural activities. With many advantages such as convenience and cleanliness, electric energy is firmly in the position of energy currency. With the depletion of fossil energy all over the world, distributed power generation of new energy (such as wind energy, solar energy, etc.) has attracted more and more attention due to its unique characteristics. But the island effect has become the main factor restricting the development of distributed power generation technology. The main reason is that the distributed power generation technology is different from the traditional large-scale power plant power generation and large-scale power grid transmission power supply and distribution technology. A failure will make the grid-connected distributed generation system fall into an island state. In order to improve the reliability and controllability of the grid-connected distributed generation system and give full play to the advantages of the distributed generation system, all countries require the islanding effect detection function for the grid-connected distributed generation system.

At present, there are many methods of island detection, which are mainly divided into active detection, passive detection and communication-based island detection. However, these methods have their own shortcomings, such as active detection will cause disturbance to the power grid, the selection of passive detection threshold is difficult, and the blind area is large.

At the same time, due to the lack of distributed new energy grid-connected technology, in order to avoid the impact of distributed new energy on the power grid, the relevant regulations on user-side grid-connected are relatively strict, which seriously limits the development of distributed new energy.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a bidirectional grid-connected inverter device and method for a distributed new energy generation system.

Technical scheme of the present invention is:

A bidirectional grid-connected inverter device for a distributed new energy generation system, comprising a signal acquisition unit, a main control unit, a rectification and inverter unit, and an electric storage unit.

The signal acquisition unit includes a first signal acquisition unit and a second signal acquisition unit, the input of the first signal acquisition unit is connected to the DC input end of the rectification and inverter unit, and the input end of the second signal acquisition unit is connected to the rectification and inverter unit. The grid end, the output end of the first signal acquisition unit and the output end of the second signal acquisition unit are all connected to the main control unit.

The rectification and inverter unit includes a bridge rectifier circuit, a bridge inverter circuit, a Boost boost circuit and a Cuk step-down circuit, and the input end of the Cuk step-down circuit and the input end of the Boost step-up circuit are connected to distributed new energy power generation system, the output of the Cuk step-down circuit is connected to the input of the bridge rectifier circuit, the output of the Boost boost circuit is connected to the input of the bridge inverter circuit, the input of the bridge rectifier circuit, and the input of the bridge inverter circuit The terminals are respectively connected to the main control unit, and the output terminal of the bridge rectifier circuit and the output terminal of the bridge inverter circuit are connected to the power grid through a circuit breaker.

The power storage unit includes a battery and a battery controller, and the battery is connected to the distributed new energy generation system through the battery controller.

The side of the rectification and inverter unit connected to the distributed new energy system is connected with a supercapacitor.

Both the first signal acquisition unit and the second signal acquisition unit include a voltage sensor, a current sensor, a frequency tester, a band-pass filter circuit, a three-phase voltage sampling signal modulation circuit, a three-phase current sampling signal modulation circuit and a frequency sampling signal modulation circuit circuit.

The output end of the voltage sensor, the output end of the current sensor and the output end of the frequency tester are all connected to the input end of the band-pass filter circuit, and the output end of the band-pass filter circuit is respectively connected to the input end of the three-phase voltage sampling signal modulation circuit, the three-phase The input end of the phase current sampling signal modulation circuit and the input end of the frequency sampling signal modulation circuit, the output end of the three-phase voltage sampling signal modulation circuit, the output end of the three-phase current sampling signal modulation circuit and the output end of the frequency sampling signal modulation circuit are all Connect to the input of the main control unit.

The main control unit is connected with a power module, a communication module, a storage module and a display module.

The working mode of the rectification inverter unit includes inverter mode and rectification mode. When the distributed new energy power generation system generates enough power, the rectifier inverter unit works in the inverter mode. When the distributed new energy power generation system has abnormal power supply or needs power grid When charging the battery, the rectification and inverter unit works in the rectification mode.

The storage battery is a lead-acid storage battery, and the storage batteries are connected in parallel; the storage battery controller includes a voltage stabilizing chip, a power supply control chip and an output voltage regulating chip, the storage battery is connected to the input terminal of the voltage stabilizing chip, and the output terminal of the voltage stabilizing chip is connected to the power supply control chip. The input terminal of the chip, the input terminal of the output voltage regulating chip is connected to the output of the power supply control chip, and the output terminal of the output voltage regulating chip is connected to the distributed new energy power generation system.

The method of using the bidirectional grid-connected inverter device of the distributed new energy generation system includes the following steps:

Step 1: Collect the voltage, current, and frequency of the common coupling node PCC of the power grid and the voltage, current, and frequency of the DC side of the rectification and inverter unit in real time, and perform filtering, noise reduction, and voltage transformation processing;

Step 2: Normalize the data of voltage, current and frequency after filtering, noise reduction and voltage transformation, and transmit to the storage module of the main control unit for storage;

Step 3: Initialize the parameters of the distributed new energy power generation system, including the resistance value R, the inductance value L and the capacitance value C;

Step 4: According to the normalized data stored in the storage module, calculate the active power P and reactive power Q of the distributed new energy generation system and store them in the storage module for storage;

Step 5: Send the data in the storage module to the main control unit, and use the over-undervoltage/over-underfrequency detection method to perform passive island detection;

Step 5.1: Calculate the unbalance degree of active power and the unbalance degree of reactive power and store them in the storage module;

Step 5.2: using wavelet analysis method to detect the singular point of the voltage signal V _PCC of the public coupling point of the power grid;

Step 5.3: If it is detected that there is a singular point in V _PCC , and the unbalance of active power and reactive power exceeds the threshold, the distributed new energy power generation system is in an island state, and the main control unit sends out PWM waves to The distributed new energy power generation system performs inverter control to drive the circuit breaker to cut the distributed new energy power generation system from the grid, otherwise go to step 6;

Step 6: Active island detection by active frequency shift method;

Step 6.1: Calculate the phase angle of the voltage after the disturbance, the phase angle of the current and the angular frequency ω _Pcc at the PCC node after the disturbance according to the voltage and current values at the collected grid public coupling point;

Step 6.2: Calculate the impedance angle of the distributed new energy generation system;

Step 6.3: Calculate the maximum frequency shift ω _max and the minimum frequency shift ω _min ;

Step 6.4: Determine whether ω _min <ω _pcc <ω _max is true, if yes, the passive island detection result is accurate, otherwise the passive island detection result is inaccurate, at this time the main control unit sends out PWM waves to invert the distributed new energy generation system Control and drive the circuit breaker to cut off the distributed new energy generation system from the grid;

Step 7: The data stored in the storage module is displayed in real time through the display module, providing maintenance basis for the maintenance personnel.

Beneficial effect:

Compared with the traditional island detection device, the bidirectional grid-connected inverter device of the distributed new energy generation system of the present invention has the characteristics of small detection blind area, high detection accuracy, and strong applicability. The invention adopts the method of wavelet analysis based on pattern recognition to detect the island, and effectively eliminates the blind area caused by the setting of the threshold. Compared with the traditional island detection device that adopts traditional passive detection and active detection, it fully utilizes the advantages of rapid passive detection and less harmonic pollution to the power grid, and realizes that the detection device first quickly judges the system. If distributed If the power generation system is in an isolated state, the system will be removed from the power grid quickly, and then active detection will be called to detect the results of passive detection, which will give full play to the advantages of high accuracy of active detection and overcome the long detection time and harmonic pollution of the power grid. A large degree of insufficiency. Generally speaking, compared with the traditional island detection method, the detection blind area is reduced by 24%, the detection time is shortened by 38%, the detection accuracy is increased by 92%, and the harmonic pollution to the power grid is reduced by 93%. In the traditional grid-connected mode, the present invention can intelligently switch between the grid-connected mode and the island mode, which provides the possibility for the user end to generate electricity through random grid-connected.

Description of drawings

Fig. 1 is a schematic diagram of a working system of a bidirectional grid-connected inverter device in a power grid of a distributed new energy generation system according to a specific embodiment of the present invention;

Fig. 2 is a schematic structural diagram of a bidirectional grid-connected inverter device of a distributed new energy power generation system according to a specific embodiment of the present invention;

Fig. 3 is the circuit schematic diagram of the band-pass filter circuit of the specific embodiment of the present invention;

Fig. 4 is the circuit schematic diagram of the three-phase voltage sampling signal modulation circuit of the specific embodiment of the present invention;

Fig. 5 is the circuit schematic diagram of the three-phase current sampling signal modulation circuit of the specific embodiment of the present invention;

6 is a schematic circuit diagram of a frequency sampling signal modulation circuit according to a specific embodiment of the present invention;

Fig. 7 is the circuit schematic diagram of DSP and power supply module thereof of the embodiment of the present invention;

8 is a schematic circuit diagram of a memory module according to a specific embodiment of the present invention;

Fig. 9 is a schematic circuit diagram of a communication module according to a specific embodiment of the present invention;

Fig. 10 is a schematic circuit diagram of a display module according to a specific embodiment of the present invention;

Fig. 11 is a circuit schematic diagram of a rectification and inverter unit according to a specific embodiment of the present invention;

Fig. 12 is the SPWM control flowchart of the embodiment of the present invention;

Fig. 13 is a flowchart of a bidirectional grid-connected inverter method for a distributed new energy generation system according to a specific embodiment of the present invention.

Detailed ways

The specific implementation manners of the present invention will be described in detail below in conjunction with the accompanying drawings.

As shown in Figure 2, the bidirectional grid-connected inverter device of the distributed new energy power generation system includes a signal acquisition unit, a main control unit, a rectification inverter unit and a power storage unit.

The signal acquisition unit includes a first signal acquisition unit and a second signal acquisition unit, the input of the first signal acquisition unit is connected to the DC input end of the rectification and inverter unit, and the input end of the second signal acquisition unit is connected to the grid end of the rectification and inverter unit , the output end of the first signal acquisition unit and the output end of the second signal acquisition unit are both connected to the main control unit.

Both the first signal acquisition unit and the second signal acquisition unit include a voltage sensor VT, a current sensor CT, a frequency tester, a band-pass filter circuit, a three-phase voltage sampling signal modulation circuit, a three-phase current sampling signal modulation circuit and a frequency sampling signal modulation circuit. circuit. The model of the voltage sensor is HNV500T, the model of the current sensor is ACS712ELCTR-05A5ASOP-8, the voltage sensor is used to collect the voltage at the distributed new energy power generation system and the grid node (ie PCC node), and the current sensor is used to collect distributed new energy The voltage at the node of the power generation system and the power grid (PCC node) and the current of the distributed new energy output direct current, use a frequency tester model BT3C to collect the frequency and The frequency of the DC output terminal of the distributed new energy generation system.

The output end of the voltage sensor, the output end of the current sensor and the output end of the frequency tester are all connected to the input end of the band-pass filter circuit, and the output end of the band-pass filter circuit is respectively connected to the input end of the three-phase voltage sampling signal modulation circuit, the three-phase The input end of the phase current sampling signal modulation circuit and the input end of the frequency sampling signal modulation circuit, the output end of the three-phase voltage sampling signal modulation circuit, the output end of the three-phase current sampling signal modulation circuit and the output end of the frequency sampling signal modulation circuit are all Connect to the input of the main control unit.

The band-pass filter circuit of this embodiment is shown in Figure 3, the output pin u _o of the band-pass filter circuit outputs 7 signals, wherein the voltage signal is connected to the u _a interface of the three-phase voltage sampling signal modulation circuit, as shown in Figure 4 As shown, the output terminals OUT _a of the three-phase voltage sampling signal modulation circuit are respectively connected to the signal input terminals of the main control unit (such as the ADCINA0 and ADCINA2 terminals of the DSP); the three current signals output by the band-pass filter circuit are connected to the three-phase current sampling The i _a interface of the signal modulation circuit, as shown in Figure 5, the output terminal OUT _a1 of the three-phase current sampling signal modulation circuit is respectively connected to the signal input terminal of the main control unit (such as the ADCINA3 and ADCINA5 ends of DSP); the frequency signal is connected to the frequency The input terminal f _g of the sampling signal modulation circuit is shown in FIG. 6 , and the output terminal OUT _f of the frequency sampling signal modulation circuit is connected to the signal input terminal of the main control unit (such as the ADCINA6 terminal of DSP).

The rectification and inverter unit is shown in Figure 11, including bridge rectification circuit 2, bridge inverter circuit 4, Boost boost circuit 3 and Cuk step-down circuit 1, the input terminal of Cuk step-down circuit 1 and Boost boost circuit 3 The input ends of all are connected to the distributed new energy power generation system, the output end of the Cuk step-down circuit 1 is connected to the input end of the bridge rectifier circuit 2, the output end of the Boost boost circuit 3 is connected to the input end of the bridge inverter circuit 4, and the bridge The input end of the bridge rectifier circuit 2 and the input end of the bridge inverter circuit 4 are respectively connected to the main control unit, and the output end of the bridge rectifier circuit 2 and the output end of the bridge inverter circuit 4 are connected to the grid through a circuit breaker. Wherein, the Boost step-up circuit does not have an isolated connection bridge inverter circuit, and is connected in parallel with the Cuk step-down circuit isolation connection bridge rectifier circuit.

The bidirectional grid-connected inverter device of the distributed new energy generation system generates a PWM control wave signal through the I/O port of the DSP. After the control signal is amplified by the signal amplification circuit, it is connected to the relay at the PCC point (the The on-off state of the model is DW15 circuit breaker controller) and the thyristors in the rectification and inverter unit are controlled to realize the cut-off operation of the island operating state of the distributed new energy generation system and the reclosing operation of the distributed generation system in the island state.

The side where the rectification and inverter unit is connected to the distributed new energy system is connected with a supercapacitor.

The working mode of the rectification inverter unit includes inverter mode and rectification mode. When the distributed new energy power generation system generates enough power, the rectifier inverter unit works in the inverter mode. When charging, the rectification and inverter unit works in rectification mode.

In this embodiment, the DSP model TMS320F2812 is used as the main control unit, which is used for A/D conversion of the phase voltage, phase current and frequency of the PCC point collected by the signal acquisition unit, and the A/D converted signal Carry out island detection, trigger the corresponding trigger control signal according to the detection result, and drive the actuator (circuit breaker) at the PCC point to perform corresponding actions.

As shown in FIG. 7 , the DSP model TMS320F2812 in this embodiment is connected with a power module, a communication module, a storage module and a display module, and the power module provides a 3.3V voltage that meets the working requirements for the DSP.

The output signal of the DSP is sent to the storage module, communication module, display module and circuit breaker. The storage module and the display module respectively realize the storage and display of the key data of the operation status of the distributed new energy power generation system, so that the operator can understand the operation status of the system. And make correct processing operations according to the key data recorded.

In this embodiment, the model of the memory module is CY7C1041BV33, and its data input terminal DO-D15 pins are connected to the XD0-XD15 pins of the DSP, and the A0-A17 pins are connected to the XA0-XA17 pins of the DSP chip, as shown in Figure 8 shown.

The communication module is used to realize the network communication between the device and the upper computer, which is convenient for dispatchers to make reasonable arrangements for the distributed new energy power generation system and realize the maximum benefit operation of the distributed new energy power generation system. In this embodiment, the RS485 communication protocol and the MAX232 driver chip are used to realize the communication module. The circuit principle is shown in FIG.

The display module is implemented by a liquid crystal display, the model is LCM12864ZK, as shown in Figure 10, the RS pin of the liquid crystal display is connected to the IOPF4 pin of the TMS320LF2812 chip, the R/W pin of the liquid crystal display is connected to the IOPF5 pin of the DSP, and the liquid crystal display The E pin of the LCD is connected to the IOPF6 pin of the DSP, the D0-D7 pins are connected to the IOPB1-IDPB7 pins of the DSP, and the /RST pin of the liquid crystal display is connected to the IOPC1 pin of the DSP.

The power storage unit includes a battery and a battery controller, and the battery is connected to the distributed new energy power generation system through the battery controller.

The battery is lead-acid battery, and each battery is connected in parallel; the battery controller includes a voltage stabilizing chip, a power supply control chip and an output voltage regulating chip, the battery is connected to the input terminal of the voltage stabilizing chip, and the output terminal of the voltage stabilizing chip is connected to the power supply control chip. The input terminal, the input terminal of the output voltage regulating chip is connected to the output of the power supply control chip, and the output terminal of the output voltage regulating chip is connected to the distributed new energy power generation system.

As shown in Figure 1, in the working system of the bidirectional grid-connected inverter device of the distributed new energy power generation system in the power grid, the DC output of the distributed new energy power generation system is output by the bidirectional grid-connected inverter device and the frequency and amplitude of the grid voltage. An alternating current of the same value and phase supplies the local load, i.e. island mode operation. When the electric energy provided by the distributed new energy power generation system meets the grid-connection requirements, the circuit breaker is closed, and the distributed new energy power generation system operates in grid-connected mode to supply power to the public load of the grid. When the distributed new energy generation system is abnormal (such as a sudden change in light conditions in photovoltaic power generation), the circuit breaker will quickly cut off the distributed new energy generation system from the grid. The supercapacitor is used to provide or access the required electric energy to the grid during the operation time of the circuit breaker, so as to adjust the voltage frequency, amplitude and phase of the distributed new energy generation system to be consistent with the grid, thereby reducing the impact on the grid. When the distributed new energy power generation system restarts after a long-term power failure or the battery needs to be charged from the grid, the bidirectional grid-connected inverter works in reverse in the rectification state to provide power for the storage unit.

The process of using the above-mentioned bidirectional grid-connected inverter device of the distributed new energy power generation system is shown in Figure 13, including the following steps:

Step 1: Collect the voltage, current, and frequency of the common coupling node PCC of the grid in real time, and the voltage u, current i, and frequency of the DC side of the rectification and inverter unit, and perform filtering, noise reduction, and voltage transformation processing;

Step 2: Normalize the data of voltage, current and frequency after filtering, noise reduction and voltage transformation, and transmit to the storage module of the main control unit for storage;

Step 3: Initialize the parameters of the distributed new energy power generation system, including the resistance value R, the inductance value L and the capacitance value C;

Step 4: According to the normalized data stored in the storage module, calculate the active power P and reactive power Q of the distributed new energy generation system and store them in the storage module for storage;

in, is the power factor angle, Z is the total load of the grid system;

Step 5: Send the data in the storage module to the main control unit, and use the over-undervoltage/over-underfrequency detection method to perform passive island detection;

Step 5.1: Calculate the unbalance of active power and reactive power imbalance and stored in the storage module;

Calculation of Active Power Unbalance and reactive power The formula for unbalance is as follows:

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; ,</span>$

$\frac{\mathrm{<span\; class="notranslate">\; \&Delta;Q</span>}}{\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}\frac{\mathrm{<span\; class="notranslate">\; \&Delta;P</span>}}{\mathrm{<span\; class="notranslate">\; P</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\frac{{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; Z</span>}}}{\mathrm{<span\; class="notranslate">\; Q</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; P</span>}}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ,</span>$

Among them, ω _g is the grid angular frequency, and there is ω _g =2πf _g , f _g is the grid frequency; u _g is the grid voltage; Q _Z is the reactive power on the resonant capacitor, and there is

Step 5.2: Using wavelet analysis method based on pattern recognition to detect the voltage signal V _PCC of the public coupling point of the power grid, the voltage signal V _PCC of the public coupling point is the voltage signal at the grid-connected place of the circuit breaker;

Step 5.2.1: record V _PCC as u(t);

Step 5.2.2: Determine whether the sudden change ΔV _PCC of the voltage signal at the public coupling point at the island or the sudden change Δf _PCC of the frequency signal at the public coupling point at the island exceeds the threshold, and if it exceeds the threshold, detect the current distributed new The energy generation system is in an island state, otherwise go to step 5.2.3;

Step 5.2.3: Perform singular point detection;

The specific method is as follows; define u(t)∈-L ² (R), θ(t)∈-L ² (R) as a Gaussian smoothing function, and -L ² (R) represent a real two-dimensional space, and take Gaussian smoothing respectively first derivative of a function Second Derivative As the wavelet transform generating function, Then θ _s (t) represents the expansion and contraction under the scale factor s of θ(t), then perform wavelet transformation on u(t):

${\mathrm{<span\; class="notranslate">\; WT</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; *</span>\frac{\mathrm{<span\; class="notranslate">\; d</span>}}{\mathrm{<span\; class="notranslate">\; dt</span>}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

${\mathrm{<span\; class="notranslate">\; WT</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span>{\mathrm{<span\; class="notranslate">\; \&psi;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; *</span><span\; class="notranslate">\; [</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; dt</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span><span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; the\; s</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; *</span>\frac{{\mathrm{<span\; class="notranslate">\; d</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; dt</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; [</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; \&theta;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ]</span>$

in, Both are wavelet transform moduli of the signal u(t);

From the above formula, the wavelet transform modulus of signal u(t) The local maximum point of the signal u(t) has a singular point (or abrupt point); the wavelet transform modulus of the signal u(t) The local zero-crossing point of , the response signal u(t) has a singularity point (or a sudden change point). Therefore, for the original signal with singular points, the wavelet transform modulus maximum value is the singular point of the original signal;

Step 5.2.4: If it is detected that there is a singular point in _VPCC , then delay 50ms, wait for the _VPCC signal to be stable, perform Fourier transform on the signal u(t) and calculate the spectrum of _VPCC , the first 18 odd times in the spectrum The amplitude of the harmonic is used as a characteristic parameter, and each characteristic parameter constitutes a sample characteristic library;

Step 5.2.5 Use the neural network classification algorithm to perform pattern recognition on the current signal u(t), that is, perform feature parameter screening in the sample feature library for the characteristic parameters of the frequency spectrum of the current signal u(t) to identify whether the system is operating in an isolated manner Status: If the characteristic parameters of the frequency spectrum of the current signal u(t) exist in the sample feature library, it is recognized that the distributed new energy power generation system is currently operating in an isolated state, and step 5.3 is performed, otherwise the distributed new energy power generation system is currently Grid-connected operation status;

In this embodiment, the 18-36-1 BP neural network is used for classification to identify whether the system is in an island operation state;

Step 5.3: If the neural network recognizes that the distributed new energy power generation system is in an island operation state, and the unbalance degree of active power and reactive power exceeds the threshold, the distributed new energy power generation system is already in an island operation state. At this time The main control unit sends out PWM waves to perform inverter control on the distributed new energy generation system, and drives the circuit breaker to cut off the distributed new energy generation system from the power grid, otherwise go to step 6;

The process of inverter control for the distributed new energy generation system is shown in Figure 12, and the details are as follows:

The open-loop transfer function of the inner loop current can be expressed by the following formula:

G _I (S)=(G _P (S)*G _INV (S)-U _net )*G _L (S)*e ^-ωt

In the formula, G _P (S) is the PI adjustment function, G _INV (S) is the transfer function of the inverter link, and G _L (S) is the transfer function of the filter link.

The adjustment process of the current inner loop control can be described as: relative to the given reference current I _ref ^* , when the inverter output grid-connected current I _out is less than the reference current, the difference signal between the two is positive, after PI adjustment, plus the grid After the voltage feed-forward value, the amplitude of the sinusoidal modulation signal is increased, so the duty cycle of the inverter bridge is increased, so that the output grid-connected current increases; when the inverter output current I _out is greater than the reference current, both The difference signal is negative, and the grid voltage feed-forward value subtracts the PI-adjusted error signal, thereby reducing the amplitude of the sinusoidal pulse width modulation signal, reducing the duty cycle of the inverter bridge, and reducing the inverter output grid-connected current .

The voltage outer loop control is to control the DC bus voltage to be constant. The specific process is: when the bus voltage measurement value V _dclink is greater than the given reference value V _dcref , the capacitor stores energy at this time, and the grid-connected reference current I _ref can be increased through PI adjustment ^* , the current inner loop adjusts and controls the duty cycle of the inverter bridge to increase, the grid-connected power increases, and the capacitor voltage is reduced; when the bus side voltage measurement value V _dclink is less than the given reference value V _dcref , the capacitor releases energy, which can reduce The small reference current I _ref ^* reduces the grid-connected power, thereby increasing the capacitor voltage.

PI regulation is based on the difference between the inverter output grid-connected current I _out and the reference current I _ref ^* , and responds quickly to achieve I _out fast tracking I _ref ^* changes: the collected DC bus voltage V _dclink and the given Compared with V _dcref , the obtained error signal (the difference between V _dclink and V _dcref ) is output after PI adjustment and processing as the inner loop reference current amplitude I _ref , which is multiplied by the unit sine of the same frequency and phase of the grid voltage The wave is used as the inner loop current given signal I _ref ^* , the given current is compared with the instantaneous value I _out of the output grid-connected current, and the error signal is adjusted and processed by PI as a sinusoidal pulse modulation signal, and the signal pulse controls the power switch of the inverter bridge The tube is switched on and off, and after the output passes through the filter circuit, a sinusoidal current with the same frequency and phase as the grid voltage is fed into the grid.

Step 6: Active island detection by active frequency shift method;

Step 6.1: Change the output current of the rectifier and inverter unit by changing the frequency of the PWM wave output by the main control unit;

Step 6.2: Add a disturbance to change the angular frequency of the inverter output current PWM wave:

Step 6.2: Calculate the phase angle of the disturbed voltage according to the collected voltage and current values at the PCC node current phase angle and the angular frequency ω _Pcc at the PCC node after the disturbance, ω _pcc =2πf _pcc ;

Step 6.3: Calculate the impedance angle of the distributed new energy generation system, the formula is as follows:

If the distributed new energy generation system is in an island state, the phase angle of the voltage at the PCC node current phase angle The difference is equal to the load impedance angle That is:

Step 6.4: Calculate the maximum frequency shift ω _max and the minimum frequency shift ω _min ;

Calculate the maximum frequency shift ω _max and the minimum frequency shift ω _min , the formula is as follows:

In the formula, is the voltage phase angle; is the current phase angle;

Step 6.4: Determine whether ω _min <ω _pcc <ω _max is true, if yes, the passive island detection result is accurate, otherwise the passive island detection result is inaccurate, at this time the main control unit sends out PWM waves to invert the distributed new energy generation system Control and drive the circuit breaker to cut off the distributed new energy generation system from the grid;

Step 7: The data stored in the storage module is displayed in real time through the display module, providing maintenance basis for the maintenance personnel.

Claims (1)

1. A bidirectional grid-connected inverter method for a distributed new energy power generation system, the adopted bidirectional grid-connected inverter device for a distributed new energy power generation system includes a signal acquisition unit, a main control unit, a rectifier inverter unit and a storage electric unit; The signal acquisition unit includes a first signal acquisition unit and a second signal acquisition unit, the input of the first signal acquisition unit is connected to the DC input end of the rectification and inverter unit, and the input end of the second signal acquisition unit is connected to the rectification and inverter unit. At the power grid end, the output end of the first signal acquisition unit and the output end of the second signal acquisition unit are both connected to the main control unit; The rectification and inverter unit includes a bridge rectifier circuit, a bridge inverter circuit, a Boost boost circuit and a Cuk step-down circuit, and the input end of the Cuk step-down circuit and the input end of the Boost step-up circuit are connected to distributed new energy power generation system, the output of the Cuk step-down circuit is connected to the input of the bridge rectifier circuit, the output of the Boost boost circuit is connected to the input of the bridge inverter circuit, the input of the bridge rectifier circuit, and the input of the bridge inverter circuit The terminals are also respectively connected to the main control unit, and the output terminal of the bridge rectifier circuit and the output terminal of the bridge inverter circuit are connected to the power grid through a circuit breaker; The power storage unit includes a battery and a battery controller, and the battery is connected to the distributed new energy power generation system through the battery controller; It is characterized in that: the method comprises the following steps: Step 1: Collect the voltage, current, and frequency of the common coupling node PCC of the power grid and the voltage, current, and frequency of the DC side of the rectification and inverter unit in real time, and perform filtering, noise reduction, and voltage transformation processing; Step 2: Normalize the data of voltage, current and frequency after filtering, noise reduction and voltage transformation, and transmit to the storage module of the main control unit for storage; Step 3: Initialize the parameters of the distributed new energy power generation system, including the resistance value R, the inductance value L and the capacitance value C; Step 4: According to the normalized data stored in the storage module, calculate the active power P and reactive power Q of the distributed new energy power generation system and store them in the storage module for storage; Step 5: Send the data in the storage module to the main control unit, and use the over-undervoltage/over-underfrequency detection method to perform passive island detection; Step 5.1: Calculate the imbalance degree of active power and reactive power and store them to the storage module; Step 5.2: using wavelet analysis method to detect the singular point of the voltage signal V _PCC of the public coupling point of the power grid; Step 5.3: If it is detected that there is a singular point in V _PCC , and the unbalance of active power and reactive power exceeds the threshold, the distributed new energy power generation system is in an island state, and the main control unit sends out PWM waves to The distributed new energy power generation system performs inverter control to drive the circuit breaker to cut the distributed new energy power generation system from the grid, otherwise go to step 6; Step 6: Active island detection by active frequency shift method; Step 6.1: Calculate the phase angle of the voltage after the disturbance, the phase angle of the current and the angular frequency ω _Pcc at the PCC node after the disturbance according to the voltage and current values at the collected grid public coupling point; Step 6.2: Calculate the impedance angle of the distributed new energy generation system; Step 6.3: Calculate the maximum frequency shift ω _max and the minimum frequency shift ω _min ; Step 6.4: Determine whether ω _min <ω _pcc <ω _max is true, if yes, the passive island detection result is accurate, otherwise the passive island detection result is inaccurate, at this time the main control unit sends out PWM waves to invert the distributed new energy generation system Control and drive the circuit breaker to cut off the distributed new energy generation system from the grid; Step 7: The data stored in the storage module is displayed in real time through the display module, providing maintenance basis for the maintenance personnel.