CN103208939A - Photovoltaic micro-inverter based on secondary-side reference current reconstruction, control system and control method - Google Patents
Photovoltaic micro-inverter based on secondary-side reference current reconstruction, control system and control method Download PDFInfo
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Abstract
The invention discloses a photovoltaic micro-inverter based on secondary-side reference current reconstruction, a control system and a control method. A topological structure of a staggered flyback laser photovoltaic micro-inverter based on the secondary-side reference current reconstruction is adopted. The control system comprises the staggered flyback laser photovoltaic micro-inverter based on the secondary-side reference current reconstruction, a direct current voltage and current sampling module, a driving circuit, a secondary-side pulse current sampling module, an alternating current sampling and phase locking module and a signal processing unit. The control method is an indirect control method approximate to grid-connected current direct control, primary-side reference current based on the secondary-side reference current reconstruction is adopted to control connection and disconnection of a primary-side switching tube of a flyback converter, and the control method effectively avoids the problem of slow control response, low tracking accuracy and the like in a direct control method, can guarantee same frequency and same phase of output current and public power grid voltage, reduces total harmonic distortion of grid-connected current substantially, and improves output power quality.
Description
Technical Field
The invention relates to a photovoltaic micro-inverter based on secondary reference current reconstruction, a control system and a method.
Background
The increasing world demand for energy makes the use of renewable energy, particularly photovoltaic power, increasingly favored. In recent years, the widespread acceptance and intensive research of photovoltaic building integrated systems and micro-grid systems has further enhanced the utility of photovoltaic power generation systems, and at the same time, has attracted people's attention to micro-inverters, i.e., single photovoltaic modules and inverters are integrated together to directly feed alternating current to a utility grid. Compared with the traditional centralized photovoltaic grid-connected inverter, the micro-inverter has the advantages of single-block assembly maximum power point tracking, low direct-current voltage, flexible expansion, plug and play and the like. The goal pursued by the photovoltaic micro-inverter is to inject high-quality same-frequency same-phase sine alternating current into the power grid, perform high-efficiency maximum power point tracking on the photovoltaic component and realize high efficiency, high cost performance and high reliability.
At present, topologies built based on flyback converters and converter bridges are considered as the most suitable solution for micro-inverters. On one hand, when the flyback converter works in a current continuous conduction mode, the peak current borne by the switching tube is lower, so that a power device with lower current rating is allowed to be used, and on the other hand, the transformer is not completely demagnetized, so that hysteresis loss is reduced, and the overall efficiency of the system is higher. Meanwhile, a high-frequency modulation technology can be adopted, and the influence of the volume of the high-frequency transformer can be reduced to a certain extent.
In the prior art, in order to ensure that an alternating current module injects high-quality in-phase sinusoidal alternating current into a power grid, two control methods of direct control and indirect control of grid-connected current are mainly adopted. In the direct control mode of the grid-connected current, the maximum power point tracker calculates the amplitude of the grid-connected current according to the state of a photovoltaic component, calculates the phase of a power grid by using a single-phase-locked loop method, multiplies the phase of the power grid and the phase of the photovoltaic component to serve as a reference value of the grid-connected current, samples the grid-connected current to perform feedback control, and realizes that the grid-connected current tracks the reference value with certain. However, the flyback converter controls the right half s-plane zero point existing in the transfer function of the output current in the continuous conduction mode, so that not only is the system bandwidth limited, but also the tracking performance of the controller on the output grid-connected current is influenced. In the scheme of indirectly controlling the primary current, the primary current is controlled to output grid-connected current by open loop control, and the grid-connected current is controlled by controlling the primary current, so that the defect of directly controlling the grid-connected current is fundamentally eliminated, but the control structure of the double inner loops not only increases the complexity of a control system, consumes more controller resources, but also is not beneficial to the stability of the system.
Disclosure of Invention
The invention provides a photovoltaic micro-inverter based on secondary reference current reconstruction, a control system and a method, and aims to reduce total harmonic distortion to a certain extent and improve the power quality by reconstructing a primary reference current based on a secondary reference current and taking the secondary current as a control target.
The photovoltaic micro inverter based on secondary reference current reconstruction comprises a direct current side capacitor CPV(301) The converter comprises an interleaved parallel flyback circuit (302), an H converter bridge (303) and an output filter (304);
DC side capacitor CPVConnected in parallel with the photovoltaic cell; the device is used for buffering the secondary ripple power on the direct current side;
the interleaving parallel flyback circuit comprises a first transformer T1, a second transformer T2, a power MOSFET tube SPV1、SPV2And a power diode Drect1And Drect2(ii) a The photovoltaic grid-connected micro-inverter is used for realizing output current waveform control and photovoltaic cell maximum power point tracking;
the output filter comprises a filter capacitor CgridAnd a filter inductance Lgrid；
The H converter bridge comprises a thyristor Sac1、Sac2And MOSFET Qac1、Qac2，Sac1And Qac1Form a forward converter arm, Sac1Negative pole and filter inductance LgridOne end is connected with a filter inductor LgridAnother end and Qac1The D pole of the grid is connected with a power grid; sac2And Qac2Forming a negative current conversion bridge arm, Qac2D pole and filter inductor LgridIs connected to one end of a filter inductor LgridThe other end and Sac2The negative electrode of the anode is connected with a power grid; sac1And Sac2Positive electrode of (2) and (D)rect1Is connected to the negative electrode of Qac1And Qac2The S poles of the first transformer T1 and the second transformer T2 are connected with the second ends of the secondary windings;
Sac1and Qac1D pole of (2) is connected to the input side of the output filter, Sac2And Qac2D pole of the filter is connected with the input of the output filterSide, output side of output filter and grid GgridConnecting;
first reverse blocking type power switch SPV1The S pole of the first reverse blocking type power switch S is connected with the negative pole of the photovoltaic cellPV1The D pole of the transformer is connected with the positive pole of the photovoltaic cell through the primary side of a first transformer T1; second reverse blocking type power switch SPV2The S pole of the second reverse blocking type power switch S is connected with the negative pole of the photovoltaic cellPV2The D pole of the second transformer T2 is connected with the positive pole of the photovoltaic cell through the primary side of the second transformer T2;
first termination D of the secondary winding of the first transformer T1rect1Positive electrode of (2), Drect1Negative pole of (2) is connected with Sac1And Sac2The positive electrode of (1); first termination D of the secondary winding of the second transformer T2rect2Positive electrode of (2), Drect2And Drect1The negative electrodes are connected;
MOSFET Qac1And Qac2And second ends of the secondary windings of the first transformer T1 and the second transformer T2 are shorted together;
Cgridis connected to Sac1And Sac2Between the negative electrodes of (1);
Lgridis connected with Sac1Negative electrode of (1), LgridAnother end of (1) and Sac2The negative pole of the grid is connected into the power grid.
The photovoltaic micro-inverter control system based on secondary reference current reconstruction comprises the photovoltaic micro-inverter based on secondary reference current reconstruction, a direct-current voltage and current sampling module, a driving circuit, a secondary pulse current sampling module, an alternating-current sampling and phase locking module and a signal processing unit;
the input end of the direct-current voltage sampling module is respectively connected with the anode and the cathode of the photovoltaic cell, and the output end of the direct-current voltage sampling module is connected with the signal processing unit; the photovoltaic power generation device is used for collecting the voltage of the photovoltaic cell;
the alternating current sampling and phase locking module is connected with the power grid;
for detecting the amplitude of the utility voltage, calculating the utility phase angle, where VgridThe voltage amplitude is processed by the alternating current sampling and phase locking module;
the primary side pulse current sampling module is connected with the first ends of primary side windings of the first transformer and the second transformer;
the device is used for detecting the primary side current of the high-frequency transformer;
2 output ends of the driving circuit are respectively connected with the power switch tube SPV1And SPV2G pole of the silicon substrate is connected;
the primary winding switching tube is used for providing a switching-on or switching-off driving signal for the primary winding switching tube;
the signal processing unit comprises an MPPT controller, a primary reference current reconstructor, a state machine, a current sharing controller and a grid-connected current controller;
the primary reference current reconstructor is connected with the direct current voltage and current sampling module and the alternating current sampling and phase locking module;
the method is used for reconstructing the primary reference current according to the output voltage of the photovoltaic module, the voltage amplitude and the phase angle of the public power grid and the amplitude of the secondary reference current provided by the maximum power point tracker.
A photovoltaic micro-inverter control method based on secondary side reference current reconstruction is adopted, a photovoltaic micro-inverter control system based on secondary side current reconstruction is adopted, a photovoltaic micro-inverter control method based on secondary side current reconstruction is adopted, secondary side current amplitude is taken as a control target, primary side reference current is reconstructed by using the secondary side reference current, high-frequency control is carried out on a primary side switch tube, namely, a main control quantity D of the duty ratio of the switch tube is obtained through grid-connected current peak value calculation, and an additional control quantity delta D obtained through a current sharing controller is superposed and then a pulse signal is output through a modulator to control SPV1And SPV2So that the secondary side current is maintained at
And the control on the grid-connected current in the staggered flyback photovoltaic grid-connected micro-inverter is realized.
The control method comprises the following specific steps:
step 1: detecting the output voltage V of the photovoltaic cell by using a direct current voltage and current sampling module in each control periodpvDetecting the voltage amplitude v of the public power grid by using an alternating current sampling and phase locking moduleg；
Step 2: calculating the current power grid voltage phase angle theta by adopting a single-phase-locked loop;
the phase-locked loop PLL of the photovoltaic grid-connected micro-inverter detects the current grid voltage phase angle theta (theta = ω t) by adopting zero-crossing detection of the grid voltage;
and step 3: initializing a counter A to be 0, adding 1 to the MPPT counter A, then judging the MPPT counter A, if the MPPT counter A reaches a set value M, then the MPPT execution period is up, carrying out MPPT control, and executing a step 4 if the MPPT, namely Maximum Power Point Tracking, is Maximum Power Point Tracking, otherwise, executing a step 5;
in the step 3, the execution frequency of the MPPT controller is 1-10 Hz, a selected controller main frequency is combined, the controller main frequency is divided by the operation execution frequency of the MPPT controller to obtain a value P, and the count value M of the MPPT counter is set, wherein M = 1/P;
and 4, step 4: calculating secondary reference current amplitude by maximum power point tracking method
Maximum power point tracking method: the average output voltage and the average output current of the photovoltaic cell are used as input, and the reference grid-connected current peak value is used as output of the photovoltaic cell;
and 5: primary side reference current reconstructor based on secondary side reference current to reconstruct primary side reference current
Wherein,
secondary reference current amplitude, v, calculated for maximum power point trackergFor the amplitude of the voltage of the public network, VpvIs the photovoltaic module output voltage, omega is the angular frequency of the utility grid voltage,
the turn ratio of a secondary winding of a first transformer to a primary winding of a second transformer is set, T = k.T is time corresponding to a kth control period, T =1/f, and f is frequency of grid-connected current closed-loop control;
step 6: the primary reference current reconstructor reconstructs the primary reference current according to the method
Primary side current detection value i of first transformer and second transformer obtained by combining sampling of primary side pulse current sampling modulepv1And ipv2Closed-loop negative feedback control is carried out to obtain a main control quantity D of the duty ratio of the switching tube, and the superposed current-sharing additional control quantity delta D is modulated to control the MOSFETSPV1And SPV2Make-and-break;
and 7: judging the direction of grid-connected current according to the phase angle ω t of the power grid so as to control the thyristor S in the positive and negative current conversion bridge armsac1And Sac2And MOSFET Qac1And Qac2Make-and-break;
when ω t is within 0o,180 DEG, S is turned onac1、Qac1Closing Sac2、Qac2(ii) a When ω t belongs to [180 °,360 °), S is turned onac2、Qac2Closing Sac1、Qac1。
The grid-connected current direction judgment and control step in the step 7 is as follows:
step 1: if the phase angle theta of the power grid enters a zero-crossing interval alpha, beta]Closing the power switch SPV1And SPV2And the driving signal of the thyristor in the current conversion bridge arm is switched on at present, and the current conversion bridge arm is switched to the state of switching to the other bridge arm for conduction;
step 2: detecting whether a voltage zero-crossing signal exists in a power grid, and if the voltage zero-crossing signal exists, closing an MOSFET (metal oxide semiconductor field effect transistor) tube in a current conversion bridge arm which is switched on currently;
and step 3: if the phase angle of the power grid leaves the zero-crossing interval [ alpha, beta ], entering a step 4; otherwise, directly quitting the grid-connected current direction control;
and 4, step 4: judging whether the grid-connected current state is in a first quadrant or a second quadrant, if so, switching the current grid-connected current to a third quadrant or a fourth quadrant; otherwise, switching the grid-connected current to the first quadrant and the second quadrant.
The zero-crossing interval [ alpha, beta ] is set according to the switching performance of the selected converter thyristor, wherein alpha depends on the reduction time of grid-connected current and the turn-off delay of the selected thyristor, the set alpha ensures that the thyristor of the current-switched converter bridge arm can be reliably turned off before the zero crossing of the power grid after the grid-connected current is reduced to zero, and the turn-off delay is set by 5-10% on the standard of the turn-off delay of the thyristor by referring to the turn-off delay in the selected thyristor data manual; beta depends on the reverse blocking recovery time delay of the selected thyristor and the sensitivity of hardware zero-crossing detection, the set beta ensures that a converter bridge arm to be switched on can be switched on safely after the power grid passes zero reliably, and the forward blocking recovery time setting in the selected thyristor data manual is referred to, so that the forward blocking recovery time standard of the thyristor is prolonged by 5-10%.
The power of the photovoltaic micro-inverter is 100-200W.
Advantageous effects
The invention provides a photovoltaic micro-inverter based on secondary reference current reconstruction, a control system and a method, wherein the topological structure of the photovoltaic micro-inverter based on the secondary reference current reconstruction is adopted, the control system comprises the photovoltaic micro-inverter based on the secondary reference current reconstruction, a direct current voltage and current sampling module, a driving circuit, a secondary pulse current sampling module, an alternating current sampling and phase locking module and a signal processing unit, the control method provided by the invention is an indirect control method which is closer to direct control of grid-connected current, the switching on and off of a primary side switching tube of a flyback converter is controlled by adopting the primary side reference current based on the secondary reference current reconstruction, the problems of slow control response, low tracking precision and the like in the direct control method are effectively avoided, the output current and the voltage of a public power grid are ensured to be in the same frequency, and the total harmonic distortion of the grid-connected current is greatly reduced, and the quality of output electric energy is improved.
Drawings
FIG. 1 is a block diagram of the control system of the present invention;
FIG. 2 is a control block diagram of the control method of the present invention;
FIG. 3 is a flow chart of a control method of the present invention;
FIG. 4 is a diagram illustrating a waveform of a primary current sampled and conditioned by a sampling circuit according to an embodiment of the present invention;
FIG. 5 is a graph of measured grid voltage, grid-tied current, and output instantaneous power waveforms in accordance with an embodiment of the present invention;
Detailed Description
The invention will be further described with reference to the accompanying drawings.
As shown in fig. 1, a structural diagram of a photovoltaic micro-inverter control system based on secondary reference current reconstruction according to the present invention includes a photovoltaic micro-inverter (300) based on secondary reference current reconstruction, a dc voltage and current sampling module, a driving circuit, a secondary pulse current sampling module, an ac sampling and phase locking module, and a signal processing unit;
a photovoltaic micro-inverter (300) based on secondary reference current reconstruction comprises a direct current side capacitor CPV(301) An interleaved parallel flyback circuit (302), an H converter bridge (303) and an output filter (304):
DC side capacitor CPV(301) Connected in parallel with the photovoltaic cell; the device is used for buffering the secondary ripple power on the direct current side;
an interleaved flyback circuit (302) includes a first transformer T1, a second transformer T2, and a power MOSFET SPV1、SPV2And a power diode Drect1And Drect2(ii) a The photovoltaic grid-connected micro-inverter is used for realizing output current waveform control and photovoltaic cell maximum power point tracking;
an output filter (304) comprising a filter capacitor CgridAnd a filter inductance Lgrid；
The H converter bridge comprises a thyristor Sac1、Sac2And MOSFET Qac1、Qac2，Sac1And Qac1Form a forward converter arm, Sac1Negative electrode of (2) and filterFeeling LgridOne end is connected with a filter inductor LgridAnother end and Qac1The D pole of the grid is connected with a power grid; sac2And Qac2Forming a negative current conversion bridge arm, Qac2D pole and filter inductor LgridIs connected to one end of a filter inductor LgridThe other end and Sac2The negative electrode of the anode is connected with a power grid; sac1And Sac2Positive electrode of (2) and (D)rect1Is connected to the negative electrode of Qac1And Qac2The S poles of the first transformer T1 and the second transformer T2 are connected with the second ends of the secondary windings;
first reverse blocking type power switch SPV1The S pole of the first reverse blocking type power switch S is connected with the negative pole of the photovoltaic cellPV1The D pole of the transformer is connected with the positive pole of the photovoltaic cell through the primary side of a first transformer T1; second reverse blocking type power switch SPV2The S pole of the second reverse blocking type power switch S is connected with the negative pole of the photovoltaic cellPV2The D pole of the second transformer T2 is connected with the positive pole of the photovoltaic cell through the primary side of the second transformer T2;
first termination D of the secondary winding of the first transformer T1rect1Positive electrode of (2), Drect1Negative pole of (2) is connected with Sac1And Sac2The positive electrode of (1); first termination D of the secondary winding of the second transformer T2rect2Positive electrode of (2), Drect2And Drect1The negative electrodes are connected;
MOSFET Qac1And Qac2And second ends of the secondary windings of the first transformer T1 and the second transformer T2 are shorted together;
Cgridis connected to Sac1And Sac2Between the negative electrodes of (1);
Lgridis connected with Sac1Negative electrode of (1), LgridAnother end of (1) and Sac2The negative pole of the grid is connected into the power grid.
The input end of the direct-current voltage sampling module is respectively connected with the anode and the cathode of the photovoltaic cell and used for collecting the voltage of the photovoltaic cell, and the output end of the direct-current voltage sampling module is connected with the signal processing unit;
the alternating current sampling and phase locking module is connected with the power grid; detecting the amplitude of the utility grid voltage and calculating the utility grid phase angle, wherein VgThe voltage amplitude is processed by the alternating current sampling and phase locking module;
the primary side pulse current sampling module is connected with the first ends of primary side windings of the first transformer and the second transformer; detecting primary side current of the high-frequency transformer;
two output ends of the driving circuit are respectively connected with the power switch tube SPV1And SPV2G pole of the silicon substrate is connected; the primary winding switching tube is used for providing a switching-on or switching-off driving signal for the primary winding switching tube;
the signal processing unit comprises an MPPT controller, a primary reference current reconstructor, a state machine, a current sharing controller and a grid-connected current controller.
The primary reference current reconstructor is connected with the direct current voltage and current sampling module and the alternating current sampling and phase locking module; the method is used for reconstructing the primary reference current according to the output voltage of the photovoltaic module, the voltage amplitude and the phase angle of the public power grid and the amplitude of the secondary reference current provided by the maximum power point tracker.
As shown in fig. 2 and fig. 3, a block diagram and a flowchart of the control method of the present invention are shown.
A photovoltaic micro-inverter control method based on secondary reference current reconstruction adopts a control system of a photovoltaic micro-inverter based on secondary reference current reconstruction and a photovoltaic micro-inverter control method based on secondary reference current reconstruction, uses secondary reference current as a control target, reconstructs primary reference current by using secondary reference current, obtains main control quantity D of the duty ratio of a switching tube by high-frequency control of a primary switching tube, namely calculating by grid-connected current peak value, superposes additional control quantity delta D obtained by a current sharing controller and outputs pulse signals to control S through a modulatorPV1And SPV2So that the secondary side current is kept at
And the control on the grid-connected current in the staggered flyback photovoltaic grid-connected micro-inverter is realized.
The control method comprises the following specific steps:
step 1: detecting the output voltage V of the photovoltaic cell by using a direct current voltage and current sampling module in each control periodpvDetecting the voltage amplitude v of the public power grid by using an alternating current sampling and phase locking moduleg；
Step 2: calculating the current power grid voltage phase angle theta by adopting a single-phase-locked loop;
the phase-locked loop PLL of the photovoltaic grid-connected micro inverter detects the current grid voltage phase angle theta (theta = ω t) by adopting zero-crossing detection of the grid voltage;
and step 3: initializing a counter A to be 0, adding 1 to the MPPT counter A, then judging the MPPT counter A, if the MPPT counter A reaches a set value M, then the MPPT execution period is up, carrying out MPPT control, and executing a step 4 if the MPPT, namely Maximum Power Point Tracking, is Maximum Power Point Tracking, otherwise, executing a step 5;
in the step 3, the execution frequency of the MPPT controller is 1-10 Hz, a selected controller main frequency is combined, the controller main frequency is divided by the operation execution frequency of the MPPT controller to obtain a value P, and the count value M of the MPPT counter is set, wherein M = 1/P;
and 4, step 4: calculating secondary reference current amplitude by maximum power point tracking method
Maximum power point tracking method: the average output voltage and the average output current of the photovoltaic cell are used as input, the peak value of the grid-connected current is referred to as the output of the photovoltaic cell, and the photovoltaic cell has the function of tracking the maximum power point of the photovoltaic cell;
and 5: primary side reference current reconstructor based on secondary side reference current weightReference current of primary side
Wherein,
secondary reference current amplitude, v, calculated for maximum power point trackergFor the amplitude of the voltage of the public network, VpvIs the photovoltaic module output voltage, omega is the angular frequency of the utility grid voltage,
the turn ratio of a secondary winding of a first transformer to a primary winding of a second transformer is set, T = k.T is time corresponding to a kth control period, T =1/f, and f is frequency of grid-connected current closed-loop control;
step 6: the primary reference current reconstructor reconstructs the primary reference current according to the method
First transformation voltage obtained by combining sampling of primary side pulse current sampling modulePrimary side current detection value i of transformer and second transformationpv1And ipv2Closed-loop negative feedback control is carried out to obtain a main control quantity D of the duty ratio of the switching tube, and the superposed current-sharing additional control quantity delta D is modulated to control the MOSFETSPV1And SPV2Make-and-break;
and 7: judging the direction of grid-connected current according to the phase angle ω t of the power grid so as to control the thyristor S in the positive and negative current conversion bridge armsac1And Sac2And MOSFET Qac1And Qac2Make and break of (2).
When ω t belongs to [0 °,180 °), S is turned onac1、Qac1Closing Sac2、Qac2(ii) a When ω t belongs to [180 °,360 °), S is turned onac2、Qac2Closing Sac1、Qac1. E.g. grid-connected current is positive, Sac1At 110 DEG is off, Qac1And is turned off at 170 deg..
The grid-connected current direction judgment and control step in the step 7 is as follows:
step 1: if the phase angle theta of the power grid enters a zero-crossing interval alpha, beta]Closing the power switch SPV1And SPV2And the driving signal of the thyristor in the current conversion bridge arm is switched on at present, and the current conversion bridge arm is switched to the state of switching to the other bridge arm for conduction;
step 2: detecting whether a voltage zero-crossing signal exists in a power grid, and if the voltage zero-crossing signal exists, closing an MOSFET (metal oxide semiconductor field effect transistor) in a current conversion bridge arm which is switched on currently;
and step 3: if the phase angle of the power grid leaves the zero-crossing interval [ alpha, beta ], entering a step 4; otherwise, directly quitting the grid-connected current direction control;
and 4, step 4: judging whether the grid-connected current state is in a first quadrant or a second quadrant, if so, switching the current grid-connected current to a third quadrant or a fourth quadrant; otherwise, switching the grid-connected current to the first quadrant and the second quadrant.
The zero-crossing interval [ alpha, beta ] is set according to the switching performance of the selected converter thyristor, wherein alpha depends on the reduction time of grid-connected current and the turn-off delay of the selected thyristor, the set alpha ensures that the thyristor of the current-switched converter bridge arm can be reliably turned off before the zero crossing of the power grid after the grid-connected current is reduced to zero, and the turn-off delay is set by 5-10% on the standard of the turn-off delay of the thyristor by referring to the turn-off delay in the selected thyristor data manual; beta depends on the reverse blocking recovery time delay of the selected thyristor and the sensitivity of hardware zero-crossing detection, the set beta ensures that a converter bridge arm to be switched on can be switched on safely after the power grid passes zero reliably, and the forward blocking recovery time setting in the selected thyristor data manual is referred to, so that the forward blocking recovery time standard of the thyristor is prolonged by 5-10%.
As shown in fig. 4, the method is used for actually measuring the primary current waveform conditioned by the sampling circuit based on the control system model established by the invention. The first part of the graph is an overall waveform diagram of the upper part of the graph, the second part of the graph is a partial enlarged view of the lower part of the graph, which is the position of the cursor in the first part of the graph, the enlargement is 400 times, the abscissa is time (ms), the ordinate is voltage (V), 10.0us in the second part of the graph refers to 10us per large cell on the horizontal scale, so that 4.00ms per large cell in the first part of the graph, namely the second part of the graph is used for displaying the signals of 40ms in total in the first part of the graph in detail by cutting 100 us. The upper graph and the lower graph are displays of the same signal under different time scales; 500mV means that the signal of channel 3 represents 500mV per grid on the vertical scale (so the signal in the figure is about 1.6V). 125M times/sec represents the current sampling rate of the oscilloscope, 5M: data points which represent that the oscilloscope samples 5M in total at a rate of 125M/s on the current time scale are obtained, and in a control system model, a flyback converter is designed to operate in a current continuous mode so as to reduce the peak value of primary current and reduce the current stress of a switching tube; the incomplete demagnetization of the high-frequency transformer is beneficial to reducing the hysteresis loss and improving the overall efficiency of the system. The envelope curve of the primary side current waveform in the graph is consistent with the primary side reference current obtained by reconstructing the secondary side reference current, and the adopted control method is proved to be correct and effective.
As shown in fig. 5, the control system according to the present invention measures the grid voltage, grid-connected current and output instantaneous power. In the figure, 100V indicates that the utility grid of the oscilloscope channel 1 is displayed in 100V/grid, and- "indicates AC; 500mA indicates that the grid-connected current of the oscilloscope channel 4 is displayed in 500 mA/grid, and- "indicates that the grid-connected current is alternating current; pac = vgrid × igrid, shown as M = channel 1 × channel 4 on the figure, 100W indicating that instantaneous power pac is shown at 100W/grid; m average 165W: the instantaneous power pac is averaged, and the current grid-connected output power is 165W. The effective value of the voltage of the actual power grid is 231V, the peak value of the reference current of the given secondary side current is 1A, and the output instantaneous power fluctuates by twice the frequency of the voltage of the power grid and twice the output average power. As can be seen from the figure, the grid-connected current and the grid voltage are basically in the same frequency and phase, the actually measured power factor reaches 0.998, the current waveform is a sine waveform overall, the harmonic distortion rate is 3.66%, the related technical indexes are met, and the effectiveness of the control method used by the invention is fully explained.
In the embodiment of the invention, the converter bridge consisting of the two thyristors and the two MOSFETs is beneficial to the convenient realization of the hardware overcurrent protection. And a grid-connected current hardware sampling and protecting circuit is used as an auxiliary circuit, when the grid-connected current exceeds a certain value, the hardware overcurrent protecting circuit is triggered, two MOSFETs in a bridge arm of the H converter bridge are turned off, the disconnection of the inverter and the public power grid is realized, a hardware overcurrent signal is sent, and a controller is informed to take other corresponding measures.
The present invention is disclosed above by way of preferred examples, but is not limited thereto. The protection scope of the present invention is subject to the scope defined by the claims of the present invention. Any person skilled in the art can make appropriate variations and modifications without departing from the spirit of the invention.
Claims (6)
1. The photovoltaic micro-inverter based on secondary reference current reconstruction is characterized by comprising a direct current side capacitor CPV(301) The converter comprises an interleaved parallel flyback circuit (302), an H converter bridge (303) and an output filter (304);
DC side capacitor CPVConnected in parallel with the photovoltaic cell; the device is used for buffering the secondary ripple power on the direct current side; written description
The interleaving parallel flyback circuit comprises a first transformer T1, a second transformer T2, a power MOSFET tube SPV1、SPV2And a power diode Drect1And Drect2；
The output filter comprises a filter capacitor CgridAnd a filter inductance Lgrid；
The H converter bridge comprises a thyristor Sac1、Sac2And MOSFET Qac1、Qac2，Sac1And Qac1Form a forward converter arm, Sac1Negative pole and filter inductance LgridOne end is connected with a filter inductor LgridAnother end and Qac1The D pole of the grid is connected with a power grid; sac2And Qac2Forming a negative current conversion bridge arm, Qac2D pole and filter inductor LgridIs connected to one end of a filter inductor LgridThe other end and Sac2The negative electrode of the anode is connected with a power grid; sac1And Sac2Positive electrode of (2) and (D)rect1Is connected to the negative electrode of Qac1And Qac2The S poles of the first transformer T1 and the second transformer T2 are connected with the second ends of the secondary windings;
Sac1and Qac1D pole of (2) is connected to the input side of the output filter, Sac2And Qac2D pole of the output filter is connected with the input side of the output filter, the output side of the output filter is connected with the power grid GgridConnecting;
first reverse blocking type power switch SPV1The S pole of the first reverse blocking type power switch S is connected with the negative pole of the photovoltaic cellPV1The D pole of the transformer is connected with the positive pole of the photovoltaic cell through the primary side of a first transformer T1; second reverse blocking type power switch SPV2The S pole of the second reverse blocking type power switch S is connected with the negative pole of the photovoltaic cellPV2The D pole of the second transformer T2 is connected with the positive pole of the photovoltaic cell through the primary side of the second transformer T2;
first termination D of the secondary winding of the first transformer T1rect1Positive electrode of (2), Drect1Negative pole of (2) is connected with Sac1And Sac2The positive electrode of (1); first termination D of the secondary winding of the second transformer T2rect2Positive electrode of (2), Drect2And Drect1The negative electrodes are connected;
MOSFET Qac1And Qac2And the secondary windings of the first transformer T1 and the second transformer T2Are shorted together;
Cgridis connected to Sac1And Sac2Between the negative electrodes of (1);
Lgridis connected with Sac1Negative electrode of (1), LgridAnother end of (1) and Sac2The negative pole of the grid is connected into the power grid.
2. The photovoltaic micro-inverter control system based on secondary reference current reconstruction is characterized by comprising the micro-inverter based on secondary reference current reconstruction as claimed in claim 1, a direct current voltage and current sampling module, a driving circuit, a secondary pulse current sampling module, an alternating current sampling and phase locking module and a signal processing unit;
the input end of the direct-current voltage sampling module is respectively connected with the anode and the cathode of the photovoltaic cell, and the output end of the direct-current voltage sampling module is connected with the signal processing unit;
the alternating current sampling and phase locking module is connected with the power grid;
the primary side pulse current sampling module is connected with the first ends of primary side windings of the first transformer and the second transformer;
2 output ends of the driving circuit are respectively connected with the power switch tube SPV1And SPV2G pole of the silicon substrate is connected;
the signal processing unit comprises an MPPT controller, a primary reference current reconstructor, a state machine, a current sharing controller and a grid-connected current controller;
and the primary reference current reconstructor is connected with the direct current voltage and current sampling module and the alternating current sampling and phase locking module.
3. The method for controlling the photovoltaic micro-inverter based on secondary reference current reconstruction is characterized in that the photovoltaic micro-inverter control system based on secondary current reconstruction and the method for controlling the interleaved flyback photovoltaic grid-connected micro-inverter based on secondary current reconstruction are adopted, the amplitude of the secondary current is taken as a control target, the primary reference current is reconstructed by using the secondary reference current, and the duty ratio of a switching tube is obtained through high-frequency control on the primary switching tube, namely through grid-connected current peak value calculationThe main control quantity D is superposed with the additional control quantity delta D obtained by the current-sharing controller and then is output by the modulator to output a pulse signal to control SPV1And SPV2So that the secondary side current is maintained at
And the control of the grid-connected current in the staggered flyback photovoltaic grid-connected micro-inverter is realized.
4. The photovoltaic micro-inverter control method based on secondary side reference current reconstruction as claimed in claim 3, characterized in that the control method comprises the following specific steps:
step 1: detecting the output voltage V of the photovoltaic cell by using a direct current voltage and current sampling module in each control periodpvDetecting the voltage amplitude v of the public power grid by using an alternating current sampling and phase locking moduleg；
Step 2: calculating the current power grid voltage phase angle theta by adopting a single-phase-locked loop;
and step 3: initializing a counter A to be 0, adding 1 to the MPPT counter A, then judging the MPPT counter A, if the MPPT counter A reaches a set value M, then the MPPT execution period is up, carrying out MPPT control, and executing a step 4 if the MPPT, namely Maximum Power Point Tracking, is Maximum Power Point Tracking, otherwise, executing a step 5;
in the step 3, the execution frequency of the MPPT controller is 1-10 Hz, a selected controller main frequency is combined, the controller main frequency is divided by the operation execution frequency of the MPPT controller to obtain a value P, and the count value M of the MPPT counter is set, wherein M = 1/P;
and 4, step 4: calculating secondary reference current amplitude by maximum power point tracking method
Maximum power point tracking method: the average output voltage and the average output current of the photovoltaic cell are used as input, and the reference grid-connected current peak value is used as output of the photovoltaic cell;
and 5: primary side reference current reconstructor based on secondary side reference currentReconstructing a primary reference current
Wherein,secondary reference current amplitude, v, calculated for maximum power point trackergFor the amplitude of the voltage of the public network, VpvIs the photovoltaic module output voltage, omega is the angular frequency of the utility grid voltage,
the turn ratio of a secondary winding of a first transformer to a primary winding of a second transformer is set, T = k.T is time corresponding to a kth control period, T =1/f, and f is frequency of grid-connected current closed-loop control;
step 6: the primary reference current reconstructor reconstructs the primary reference current according to the method
The first transformer and the second transformer are obtained by combining sampling of the primary side pulse current sampling modulePrimary side current detection value ipv1And ipv2Closed-loop negative feedback control is carried out to obtain a main control quantity D of the duty ratio of the switching tube, and the superposed current-sharing additional control quantity delta D is modulated to control the MOSFETSPV1And SPV2Make-and-break;
and 7: judging the direction of grid-connected current according to the phase angle ω t of the power grid so as to control the thyristor S in the positive and negative current conversion bridge armsac1And Sac2And MOSFET Qac1And Qac2Make-and-break;
when ω t belongs to [0 °,180 °), S is turned onac1、Qac1Closing Sac2、Qac2(ii) a When ω t belongs to [180 °,360 °), S is turned onac2、Qac2Closing Sac1、Qac1。
5. The photovoltaic micro-inverter control method based on secondary reference current reconstruction as claimed in claim 4, wherein the grid-connected current direction discriminating and controlling step in the step 7 is as follows:
step 1: if the phase angle theta of the power grid enters a zero-crossing interval alpha, beta]Closing the power switch SPV1And SPV2And the driving signal of the thyristor in the current conversion bridge arm is switched on at present, and the current conversion bridge arm is switched to the state of switching to the other bridge arm for conduction;
step 2: detecting whether a voltage zero-crossing signal exists in a power grid, and if the voltage zero-crossing signal exists, closing an MOSFET (metal oxide semiconductor field effect transistor) tube in a current conversion bridge arm which is switched on currently;
and step 3: if the phase angle of the power grid leaves the zero-crossing interval [ alpha, beta ], entering a step 4; otherwise, directly quitting the grid-connected current direction control;
and 4, step 4: judging whether the grid-connected current state is in a first quadrant or a second quadrant, if so, switching the current grid-connected current to a third quadrant or a fourth quadrant; otherwise, switching the grid-connected current to the first quadrant and the second quadrant.
6. The photovoltaic micro-inverter control method based on secondary reference current reconstruction as claimed in claim 5, characterized in that the zero-crossing interval [ α, β ] is set according to the switching performance of the selected converter thyristor, wherein α depends on the grid-connected current falling time and the turn-off delay of the selected thyristor, and the set α ensures that the thyristor of the currently-turned-on converter arm can be reliably turned off after the grid-connected current falls to zero before the zero-crossing of the grid, and is extended by 5% -10% of the thyristor turn-off delay standard with reference to the turn-off delay setting in the selected thyristor data manual; beta depends on the reverse blocking recovery time delay of the selected thyristor and the sensitivity of hardware zero-crossing detection, the set beta ensures that a converter bridge arm to be switched on can be switched on safely after the power grid passes zero reliably, and the forward blocking recovery time setting in the selected thyristor data manual is referred to, so that the forward blocking recovery time standard of the thyristor is prolonged by 5-10%.
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Address after: 338000 No. 8, science and Technology City, eco economic zone, Xinyu, Jiangxi Patentee after: JIANGXI Z-ENERGY ELECTRIC TECHNOLOGY CO., LTD. Address before: 338000 No. 8, science and Technology City, eco economic zone, Xinyu, Jiangxi Patentee before: Jiangxi Zhongneng Electrical Science & Technology Co., Ltd. |
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| CF01 | Termination of patent right due to non-payment of annual fee |
Granted publication date: 20150610 Termination date: 20170419 |