Three-port DC-AC converter control method and device for photovoltaic power generation system

Abstract

The present invention discloses a three-port DC-AC converter control method and device for a photovoltaic power generation system, the method comprising: sampling the photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage #imgabs0# is obtained by the MPPT control algorithm, and #imgabs1# is combined with U PV The difference between the two is obtained by the PI regulator to obtain the duty cycle D; in the grid-connected mode, the output current of the AC port is sampled i o , the difference between it and the output current reference value #imgabs2# is obtained through the PI regulator to obtain the secondary side conduction angle #imgabs3#; S103, according to the soft switching condition and #imgabs4#, the primary side conduction angle #imgabs5# is obtained; the duty cycle D, #imgabs6# and #imgabs7# are input into the control signal generator to generate the control signal VG 1 , VG 2 , VG 3 , VG 4 , Q P , Q N According to VG 1 , VG 2 , VG 3 , VG 4 Control the primary side bridge arm switch tube VG1~4, according to Q P , Q N The P and N groups of switch tubes of the secondary side bridge arm are controlled so that the three-port DC-AC converter is in zero reactive working mode throughout the entire cycle.

Description

Technical Field

[0001] The present invention relates to the field of photovoltaics, and more specifically, to a three-port DC-AC converter control method and device for a photovoltaic power generation system. Background Art

[0002] The photovoltaic power generation system is a power generation system that combines photovoltaic equipment and energy storage equipment. It aims to solve the intermittent and instability problems of photovoltaic power generation and improve the efficiency and reliability of energy utilization. The three-port DC-AC converter used in the photovoltaic power generation system usually adopts a semi-isolated structure. Among them, the three-port DC-AC converter based on the dual active bridge (DAB) circuit is known for its high efficiency, high power density and good electromagnetic compatibility. It is particularly suitable for applications that require bidirectional power flow and electrical isolation. Figure 1 As shown, the three-port DC-AC converter based on the DAB circuit has the characteristics of output and input electrical isolation, single-stage conversion between ports, simple circuit, and broad application prospects. It has important theoretical and application value in the new energy power generation system.

[0003] like Figure 2 As shown, Figure 2 This is a circuit topology diagram of a grid-connected / off-grid photovoltaic power generation system (see Chinese invention patent CN117977699A), in which the circuit topology consists of a photovoltaic cell assembly, a battery energy storage unit, an AC load, a three-port DC-AC converter, an AC grid, an output filter inductor, and a power grid. L f , Photovoltaic port filter capacitor C PV , Battery port filter capacitor C BAT , output filter capacitor C f The primary side of the three-port DC-AC converter is integrated with the IBBC circuit and the inverter bridge, including 3 inductors. L 1. L 2. L p , four switch tubes VG1, VG2, VG3, VG4; the secondary side is composed of a cycloconverter, including eight switch tubes Q 1P , Q 1N , Q 2P , Q 2N , Q 3P , Q 3N , Q 4P , Q 4N (Here, the secondary side bridge arm switch tubes are divided into two groups, P and N. The P group includes Q 1P -Q 4P , N group includes Q1N -Q 4N ). The input port 1 of the three-port DC-AC converter is connected to the photovoltaic cell, and the input port 2 is connected to the battery; the output port of the three-port DC-AC converter is connected to the CL filter; the CL filter is connected to the AC load, and the AC load is connected to the AC load through the filter inductor. L 4 Connected to the AC power grid.

[0004] However, for Figure 2 The photovoltaic power generation system shown in the figure, since the three-port DC-AC converter based on DAB usually adopts pulse width modulation (Pulse Width Modulation, PWM) + extended phase shift (Extended Phase Shift, EPS) control, its control idea is to control the power flow between the photovoltaic port and the battery port by using the interleaved buck-boost converter (Interleaved Buck-Boost Converter, IBBC) to achieve the maximum power point tracking control (Maximum Power Point Tracking, MPPT) of the photovoltaic port; EPS and sinusoidal pulse width modulation (Sinusoidal Pulse Width Modulation, SPWM) are used to control the AC output, and the output power and waveform quality are controlled by adjusting the modulation parameters and phase shift; the power flow of the photovoltaic, battery and AC ports is controlled by adjusting the phase shift and modulation index in the EPS modulation. The final modulation waveform is as follows Figure 3 shown.

[0005] Figure 3 The control method shown can achieve soft switching operation in the full range, but has the following drawbacks:

[0006] 1) When this control method works in the two working modes shown in Figure 4 (a) and Figure 4 (b), there is a power reflux problem, which generates reactive power and reduces the conversion efficiency of the system;

[0007] 2) Under the working modes shown in Figure 4 (a) and Figure 4 (b), the average output power at the output port of the three-port DC-AC converter is:

[0008]

[0009] Output current obtained in grid-connected mode i o for:

[0010]

[0011] The output voltage obtained in off-grid mode is:

[0012]

[0013] The calculated theoretical output waveform and experimental waveform are shown in Figure 5 (a) and Figure 5 (b). Due to the poor quality of the output waveform, in order to achieve low total harmonic distortion (THD), a larger output filter is required, which increases the cost and volume of the system. Summary of the invention

[0014] The present invention provides a three-port DC-AC converter control method and device for a photovoltaic power generation system, which are used to overcome the above problems or at least partially solve the above problems.

[0015] The embodiment of the present invention provides a three-port DC-AC converter control method for a photovoltaic power generation system, which includes:

[0016] S101, sampling photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained by PI regulator to obtain the duty cycle D;

[0017] S102, in grid-connected mode, samples the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by the PI regulator to obtain the secondary side conduction angle of the grid-connected mode. ;

[0018] S103, based on the soft switching conditions and the secondary side conduction angle Get the primary side conduction angle ;

[0019] S104, the duty cycle D and the secondary side conduction angle and primary conduction angle The input control signal generator generates the required control signals VG1, VG2, VG3, VG 4、 Q P , Q N ;

[0020] S105, controlling the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals VG1, VG2, VG3, VG4, and controlling the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals Q P , Q NThe two groups of switch tubes P and N of the secondary side bridge arm of the three-port DC-AC converter are controlled so that the three-port DC-AC converter is in a zero reactive working mode throughout the entire cycle.

[0021] Preferably, in step S103, it also includes:

[0022] Primary side conduction angle Perform sinusoidal modulation.

[0023] Preferably, the duty cycle of the control signals VG1 and VG2 of the primary bridge arm is D, VG1 and VG3, VG2 and VG4 are complementary turned on to achieve voltage matching between the photovoltaic and battery ports, and the primary side conduction angle required for SDPS modulation is achieved by introducing a phase shift angle between VG1 and VG2. ;

[0024] The control signal Q of the secondary bridge arm P With Q N The duty cycle is 1-D, where Q N Synchronously turned on with VG4, at Q N With Q P A constant phase shift angle is introduced between the two sides to achieve the secondary side conduction angle .

[0025] Preferably, in step S103, the soft switching condition is ,in, u o is the output voltage obtained in off-grid mode.

[0026] Preferably, the three-port DC-AC converter has two working states: positive half cycle and negative half cycle; the P group of switch tubes of the secondary side bridge arm include Q 1P -Q 4P , N groups of switch tubes include Q 1N -Q 4N ; Control signal Q P , Q N In the positive half cycle, Q is controlled separately 1P , Q 2P , respectively control Q in the negative half cycle 2N , Q 1N ;Q 3P , Q 4P With Q 1P , Q 2P Complementary conduction; Q 3N , Q 4N With Q 1N , Q 2N Complementary conduction.

[0027] Preferably, for the positive and negative half cycles, Q P , QN The corresponding secondary side switch status is shown in the following table:

[0028]

[0029] Among them, 0 represents a low-level signal and 1 represents a high-level signal.

[0030] Preferably, the battery port has two working states: charging and discharging. Assuming that the three-port DC-AC converter is in the positive half cycle and the battery port is in the discharging state, the high-frequency switching process of the three-port DC-AC converter is divided into the following 6 intervals:

[0031] During the t0-t1 period: the primary-side bridge arm switch tubes VG2 and VG3 are turned off, while VG1 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 2P The remaining switches are turned on; at this time, the primary side is forward-conducting, which is the inductor L p Charging, the secondary side enters the freewheeling mode; L 1 for C PV Charge, L 2 Enter charging state;

[0032] During the interval t1-t2: the primary-side bridge arm switch tubes VG3 and VG4 are turned off, while VG1 and VG2 are turned on; the secondary-side bridge arm switch tube Q 2P , Q 3P The remaining switches are turned on. At this time, the primary side IBBC circuit and the inductor L p The circuit shares VG1 and VG2 paths, but not between the photovoltaic port and the inductor. L p The secondary side conducts forward, L p The energy is fully transferred to the secondary side; L 1. L 2 is also C PV Charge;

[0033] During the t2-t3 period: the primary-side bridge arm switch tubes VG3 and VG4 are turned off, while VG1 and VG2 are turned on; the secondary-side bridge arm switch tube Q 3P , Q 4P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG1 and VG2 paths, but not between the photovoltaic port and the inductor. L p Energy is transferred between the two sides; the secondary side enters the freewheeling mode; L 1. L 2 is also C PVCharge;

[0034] During the t3-t4 period: the primary-side bridge arm switch tubes VG1 and VG4 are turned off, while VG2 and VG3 are turned on; the secondary-side bridge arm switch tube Q 3P , Q 4P The remaining switches are turned on; at this time, the primary side is reversely conducting, which is the inductor L p Charging, the secondary side enters the freewheeling mode; L 2 for C PV Charge, L 1 Enter charging state;

[0035] During the t4-t5 period: the primary-side bridge arm switch tubes VG1 and VG2 are turned off, while VG3 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 4P The remaining switches are turned on. At this time, the primary side IBBC circuit and the inductor L p The circuit shares VG3 and VG4 paths, but not between the photovoltaic port and the inductor L p The secondary side conducts in the reverse direction, L p The energy is fully transferred to the secondary side; L 1. L 2 Enter charging state at the same time;

[0036] During the t5-t6 period: the primary-side bridge arm switch tubes VG1 and VG2 are turned off, while VG3 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 2P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG3 and VG4 paths, but not between the photovoltaic port and the inductor L p Energy is transferred between the two sides; the secondary side enters the freewheeling mode; L 1. L 2 Enter charging state at the same time.

[0037] Preferably, it also includes:

[0038] Sampling battery terminal current I BAT , the battery SOC is obtained by the ampere-hour integration method, combined with the input and output current limits, and the secondary side conduction angle is seized when it exceeds the normal range. Control priority to protect the battery.

[0039] Preferably, in full cycle operation mode, the output voltage u o, output current i o The primary conduction angle Into a linear relationship.

[0040] The embodiment of the present invention further provides a three-port DC-AC converter control device for a photovoltaic power generation system, which includes:

[0041] Duty cycle calculation unit, used to sample the photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained by PI regulator to obtain the duty cycle D;

[0042] Secondary side conduction angle acquisition unit, used to sample the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by the PI regulator to obtain the secondary side conduction angle of the grid-connected mode. ;

[0043] The primary side conduction angle acquisition unit is used to obtain the conduction angle of the secondary side according to the soft switching conditions and the Get the primary side conduction angle ;

[0044] A control signal generating unit is used to convert the duty cycle D and the secondary side conduction angle and primary conduction angle The input control signal generator generates the required control signals VG1, VG2, VG3, VG 4、 Q P , Q N ;

[0045] A control unit is used to control the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals VG1, VG2, VG3, VG4, and control the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals Q P , Q N The two groups of switch tubes P and N of the secondary side bridge arm of the three-port DC-AC converter are controlled so that the three-port DC-AC converter is in a zero reactive working mode throughout the entire cycle.

[0046] In summary, the control method proposed in the embodiment of the present invention has the following advantages:

[0047] (1) The three-port DC-AC converter control method proposed in the embodiment of the present invention does not have reactive power in the full-cycle working mode, which solves the power return problem of the inverter based on the DAB principle, realizes zero reactive power in the power transmission process of the DAB circuit, and improves the conversion efficiency of the system;

[0048] (2) The control method of the three-port DC-AC converter proposed in the embodiment of the present invention has an effect on the primary side conduction angle Using sinusoidal modulation, in full cycle working mode, the input current, voltage amplitude and primary side conduction angle This is a linear relationship, thus greatly reducing the filters required to achieve low THD. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 This is a structural diagram of the photovoltaic power generation system.

[0050] Figure 2 This is a circuit topology diagram of an on-grid / off-grid photovoltaic power generation system.

[0051] Figure 3 It is the EPS modulation waveform of the three-port DC-AC converter based on DAB.

[0052] Figure 4 (a)-Figure 4 (b) are diagrams of two working modes of EPS.

[0053] Figure 5 (a) - Figure 5 (b) are the calculated theoretical output waveform and experimental waveform; Figure 5 (a) is the theoretical output current at different Φ values; Figure 5 (b) is the output voltage after filtering.

[0054] Figure 6 A schematic flow chart of a control method for a three-port DC-AC converter for a photovoltaic power generation system provided in the first embodiment of the present invention.

[0055] Figure 7 A control strategy block diagram provided for an embodiment of the present invention.

[0056] Figure 8 It is the steady-state principle waveform of the control signal generator.

[0057] Fig. 9 It is a schematic diagram of the control method of the P and N groups of switch tubes in the secondary side bridge arm.

[0058] Fig.10 This is the high-frequency switching waveform of the three-port DC-AC converter.

[0059] Figure 11-Figure 16 This is the equivalent circuit diagram of the high-frequency switch in 6 intervals.

[0060] Fig.17This is the full cycle working mode diagram of the inverter.

[0061] Fig.18 The following are the simulation waveforms of the transformer primary side input power and secondary side output power.

[0062] Fig.19 The following are the simulation waveforms of the transformer primary and secondary voltages and primary current.

[0063] Fig. 20 This is the inverter output current and control quantity simulation waveform.

[0064] Fig.21 A schematic structural diagram of a three-port DC-AC converter control device for a photovoltaic power generation system provided in the second embodiment of the present invention. DETAILED DESCRIPTION

[0065] The specific implementation of the present invention is further described in detail below in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0066] The first embodiment of the present invention provides a three-port DC-AC converter control method for a photovoltaic power generation system, aiming to achieve the following control objectives:

[0067] (1) Load voltage control: ensure that the AC load port voltage is consistent with the grid voltage;

[0068] (2) Grid-connected current control: In the grid-connected operation mode, the grid-connected current is controlled to be consistent with the grid voltage phase and the amplitude meets the power demand;

[0069] (3) PV port MPPT control: The PV port is always in MPPT mode when connected to the grid, and is kept in MPPT mode as much as possible when off the grid;

[0070] (4) Battery charge and discharge control: Ensure that the power input and output of the battery does not exceed the limit, and manage the battery state of charge (SOC) to protect the battery and extend its service life.

[0071] See also Figure 6 To achieve the above control objectives, the three-port DC-AC converter control method for a photovoltaic power generation system according to an embodiment of the present invention comprises the following steps:

[0072] S101, sampling photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained through the PI regulator to obtain the duty cycle D.

[0073] S102, in grid-connected mode, samples the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by the PI regulator to obtain the secondary side conduction angle of the grid-connected mode. .

[0074] S103, based on the soft switching conditions and the secondary side conduction angle Get the primary side conduction angle .

[0075] S104, the duty cycle D and the secondary side conduction angle and primary conduction angle The input control signal generator generates the required control signals VG1, VG2, VG3, VG 4、 Q P , Q N .

[0076] S105, controlling the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals VG1, VG2, VG3, VG4, and controlling the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals Q P , Q N The two groups of switch tubes P and N of the secondary side bridge arm of the three-port DC-AC converter are controlled so that the three-port DC-AC converter is in a zero reactive working mode throughout the entire cycle.

[0077] In this embodiment, the three-port DC-AC converter adopts PWM+synchronous dual phase shift (Sync Dual-Phase-Shift, SDPS) control mode. Among them, the duty cycle of the control signals VG1 and VG2 of the primary side bridge arm is D, VG1 and VG3, VG2 and VG4 are complementary to each other to achieve voltage matching between the photovoltaic and battery ports, and the primary side conduction angle required for SDPS modulation is achieved by introducing a phase shift angle between VG1 and VG2. The control signal Q of the secondary bridge arm P With Q N The duty cycle is 1-D, where Q N Synchronously turned on with VG4, at Q N With Q P A constant phase shift angle is introduced between the two sides to achieve the secondary side conduction angle .

[0078] In this embodiment, by controlling the duty cycle D, the conduction angles of the primary and secondary sides are , The control freedom of the system can be improved. Specifically, by adjusting the duty cycle D to meet the voltage balance between the primary photovoltaic port and the battery port; controlling the secondary conduction angle Used to control the effective value of the inverter AC port output power. , sinusoidal modulation is performed in a way that meets the soft switching conditions to achieve sinusoidal control of the grid current and load voltage.

[0079] To implement this control scheme, the control strategy block diagram is as follows: Figure 7 As shown:

[0080] The MPPT control of the photovoltaic port uses the perturbation observation method. Through the PI regulator, the PWM control quantity duty cycle D is given. According to the voltage matching relationship of the IBBC circuit U BAT =DU PV , the PV voltage is controlled by the duty cycle D to achieve maximum power. That is, D is controlled by the PV and the battery to achieve the matching of the primary side voltage. The battery charge and discharge management and the energy management strategy work together. When the battery SOC and charge and discharge power are normal, the energy management strategy is used to control the reference value selection; when the SOC exceeds the normal working range or the battery charge and discharge power exceeds the working range, the battery charge and discharge management intervenes to protect the battery. The two work together to give the final reference value.

[0081] In this embodiment, according to the given reference value, the secondary side conduction angle is obtained. , and according to the soft switching conditions , the primary side conduction angle can be obtained , then the duty cycle D, the secondary side conduction angle and primary conduction angle Input control signal generator The control signal generator generates the required control signals VG1, VG2, VG3, VG4, Q P , Q N , the working principle of the control signal generator is as follows Figure 7 As shown, the steady-state principle waveform is as follows Figure 8 As shown. Figure 7 In the case of primary side conduction angle After passing through the sawtooth wave generator, a corresponding sawtooth wave signal is generated, which is then sent to each comparator. The sawtooth wave signal and the duty cycle D are input into the first comparator to generate a control signal VG1, and the sawtooth wave signal and the duty cycle D are input into the first comparator to generate a control signal VG3 through a NOT gate circuit; the duty cycle D and the primary side conduction angle After the addition operation, the operation result and the sawtooth wave signal are generated by the second comparator to generate the second result. The sawtooth wave signal and the primary side conduction angle The third result is generated by the third comparator, and the second result and the third result are connected to the AND gate circuit to generate the control signal VG2; the second result and the third result are connected to the AND gate circuit and the NOT gate circuit to generate the control signals VG4 and Q N The secondary side conduction angle The primary conduction angle After the addition operation, a fourth result is generated. The fourth result and the sawtooth wave signal are input into the fourth comparator to generate a fifth result. The fourth result and the duty cycle D are added to generate a sixth result. The sixth result and the sawtooth wave signal are input into the fifth comparator to generate a seventh result. The fifth result and the seventh result are input into the OR gate circuit to generate a control signal Q. P ; Among them, each of the above comparators is used to compare the amplitudes of the two input signals, and outputs a high level 1 when the first signal is greater than the second signal, otherwise it outputs a low level 0.

[0082] In this embodiment, when generating control signals VG1, VG2, VG3, VG4, Q P , Q N After that, the switch tubes in the converter can be controlled. As mentioned above, the three-port DC-AC converter has two working states: positive half cycle and negative half cycle; the P group of switch tubes on the secondary side bridge arm include Q 1P -Q 4P , N groups of switch tubes include Q 1N -Q 4N ; Control signal Q P , Q N In the positive half cycle, Q is controlled separately 1P , Q 2P , respectively control Q in the negative half cycle 2N , Q 1N ;Q 3P , Q 4P With Q 1P , Q 2P Complementary conduction; Q 3N , Q 4N With Q 1N , Q 2N Complementary conduction. For the positive and negative half cycles, Q P , Q N The corresponding secondary side switch states are shown in Table 1 and Fig. 9 As shown:

[0083] Table 1

[0084]

[0085] Among them, 0 represents a low-level signal and 1 represents a high-level signal.

[0086] In this embodiment, based on the control method, the three-port DC-AC converter can ensure that it is in the same working mode throughout the entire cycle, and through SDPS control, the power reflux problem existing in the DAB-based inverter is solved, and the power transmission process of the DAB circuit is achieved in a zero reactive working mode, that is, there is no reactive work.

[0087] Specifically, the following takes the three-port DC-AC converter working in the positive half cycle and the battery port in the discharge state as an example to analyze the high-frequency switching process of the inverter. In an ideal situation, the high-frequency switching waveform of the three-port DC-AC converter is as follows: Fig.10 Inductance L p The charging and discharging process can be divided into 6 intervals, such as Figure 11-16 The equivalent circuit analysis of the six high-frequency switching intervals in the positive half cycle of the inverter is as follows:

[0088] During the t0-t1 period: the primary-side bridge arm switch tubes VG2 and VG3 are turned off, while VG1 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 2P The remaining switches are turned on; at this time, the primary side is forward-conducting, which is the inductor L p Charging, the secondary side enters the freewheeling mode; L 1 for C PV Charge, L 2 Enter charging state;

[0089] During the interval t1-t2: the primary-side bridge arm switch tubes VG3 and VG4 are turned off, while VG1 and VG2 are turned on; the secondary-side bridge arm switch tube Q 2P , Q 3P The remaining switches are turned on. At this time, the primary side IBBC circuit and the inductor L p The circuit shares VG1 and VG2 paths, but not between the photovoltaic port and the inductor. L p The secondary side conducts forward, L p The energy is fully transferred to the secondary side; L 1. L 2 is also C PV Charge;

[0090] During the t2-t3 period: the primary-side bridge arm switch tubes VG3 and VG4 are turned off, while VG1 and VG2 are turned on; the secondary-side bridge arm switch tube Q 3P , Q 4P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L pThe circuit shares VG1 and VG2 paths, but not between the photovoltaic port and the inductor. L p Energy is transferred between the two sides; the secondary side enters the freewheeling mode; L 1. L 2 is also C PV Charge;

[0091] During the t3-t4 period: the primary-side bridge arm switch tubes VG1 and VG4 are turned off, while VG2 and VG3 are turned on; the secondary-side bridge arm switch tube Q 3P , Q 4P The remaining switches are turned on; at this time, the primary side is reversely conducting, which is the inductor L p Charging, the secondary side enters the freewheeling mode; L 2 for C PV Charge, L 1 Enter charging state;

[0092] During the t4-t5 period: the primary-side bridge arm switch tubes VG1 and VG2 are turned off, while VG3 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 4P The remaining switches are turned on. At this time, the primary side IBBC circuit and the inductor L p The circuit shares VG3 and VG4 paths, but not between the photovoltaic port and the inductor L p The secondary side conducts in the reverse direction, L p The energy is fully transferred to the secondary side; L 1. L 2 Enter charging state at the same time;

[0093] During the t5-t6 period: the primary-side bridge arm switch tubes VG1 and VG2 are turned off, while VG3 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 2P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG3 and VG4 paths, but not between the photovoltaic port and the inductor L p Energy is transferred between the two sides; the secondary side enters the freewheeling mode; L 1. L 2 Enter charging state at the same time.

[0094] like Fig.17 ,It can be seen that under this control method, the inverter is in the same working mode throughout the entire cycle. ,Through SDPS control, the power reflux problem of the DAB-based inverter is ,solved, and the DAB circuit is in a zero reactive working mode during ,the power transmission process.

[0095] Further, in Fig.17 In the working mode shown, the average output power of the output port of the three-port DC-AC converter is:

[0096]

[0097] Output current obtained in grid-connected mode i o for:

[0098]

[0099] The output voltage obtained in off-grid mode is

[0100]

[0101] therefore, It is linearly related to the output current / voltage amplitude. In particular, when the primary side conduction angle When sinusoidally modulated, the output current / voltage THD is low.

[0102] In order to more intuitively reflect the effect of the control method proposed in the embodiment of the present invention, Figure 2 The circuit structure shown in the figure takes the grid-connected mode and the output power of 1000W as an example. Figure 7 The proposed control method is explained and simulation results are given.

[0103] Sample photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained by PI regulator to obtain the duty cycle D; the battery port current is sampled I BAT , the battery SOC is obtained by the ampere-hour integration method, combined with the input and output current limits, and the secondary side conduction angle is seized when it exceeds the normal range. Control priority to protect the battery; take the grid-connected mode as an example: sample the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by PI to obtain the secondary side conduction angle of the grid-connected mode ; According to the soft switching condition, enter the secondary side conduction angle , for the primary side conduction angle Perform sinusoidal modulation. Finally, the duty cycle D and secondary conduction angle , primary side conduction angle The required control signal is obtained through the control signal generator. The simulation waveform obtained is as follows Figure 18-20 As shown, Fig.18 is the inductor current i L p and transformer primary voltage U AB , secondary voltage U CD The product of Fig.19 is the transformer primary voltage U AB , secondary voltage U CD With the inductor current i Lp High frequency expansion diagram; Fig. 20 is the AC port output current i o The primary conduction angle of the control signal .

[0104] Depend on Figure 18-20 It can be seen that:

[0105] 1. In the full-cycle working mode, the control method provided in this embodiment has the following characteristics: during the DAB process, the primary input power and the secondary output power of the transformer are always greater than 0. Fig.19 , it can be obtained that there is no reflux power in the power transmission process of the DAB circuit;

[0106] 2. AC port output current amplitude and primary side conduction angle It forms a linear relationship, with high waveform quality, low THD, and no clipping.

[0107] In summary, the control method proposed in the embodiment of the present invention has the following advantages:

[0108] (1) The three-port DC-AC converter control method proposed in the embodiment of the present invention does not have reactive power in the full-cycle working mode, which solves the power return problem of the inverter based on the DAB principle, realizes zero reactive power in the power transmission process of the DAB circuit, and improves the conversion efficiency of the system;

[0109] (2) The control method of the three-port DC-AC converter proposed in the embodiment of the present invention has an effect on the primary side conduction angle Using sinusoidal modulation, in full cycle working mode, the input current, voltage amplitude and primary side conduction angle This is a linear relationship, thus greatly reducing the filters required to achieve low THD.

[0110] See also Fig.21The second embodiment of the present invention further provides a three-port DC-AC converter control device for a photovoltaic power generation system, comprising:

[0111] The duty cycle calculation unit 210 is used to sample the photovoltaic port output voltage. U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained by PI regulator to obtain the duty cycle D;

[0112] The secondary side conduction angle acquisition unit 220 is used to sample the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by the PI regulator to obtain the secondary side conduction angle of the grid-connected mode. ;

[0113] The primary side conduction angle acquisition unit 230 is used to obtain the primary side conduction angle according to the soft switching condition and the secondary side conduction angle. Get the primary side conduction angle ;

[0114] The control signal generating unit 240 is used to convert the duty cycle D, the secondary side conduction angle and primary conduction angle The input control signal generator generates the required control signals VG1, VG2, VG3, VG 4、 Q P , Q N ;

[0115] The control unit 250 is used to control the primary-side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals VG1, VG2, VG3, VG4, and control the primary-side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals Q P , Q N The two groups of switch tubes P and N of the secondary side bridge arm of the three-port DC-AC converter are controlled so that the three-port DC-AC converter is in a zero reactive working mode throughout the entire cycle.

[0116] The above implementation modes are only suitable for illustrating the present invention, but not for limiting the present invention. Ordinary technicians in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, all equivalent technical solutions also belong to the scope of the present invention. The patent protection scope of the present invention should be defined by the claims.

Claims

1. A three-port DC-AC converter control method for a photovoltaic power generation system, characterized in that: include: S101, sampling photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained by PI regulator to obtain the duty cycle D; S102, in grid-connected mode, samples the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by the PI regulator to obtain the secondary side conduction angle of the grid-connected mode. ; S103, based on the soft switching conditions and the secondary side conduction angle Get the primary side conduction angle ; The soft switching condition is ,in, u o is the output voltage obtained in off-grid mode; S104, the duty cycle D and the secondary side conduction angle and primary conduction angle The input control signal generator generates the required control signals VG1, VG2, VG3, VG4, Q P , Q N ; S105, controlling the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals VG1, VG2, VG3, VG4, and controlling the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals Q P , Q N The two groups of switch tubes P and N of the secondary side bridge arm of the three-port DC-AC converter are controlled so that the three-port DC-AC converter is in a zero reactive working mode throughout the entire cycle.

2. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 1, characterized in that: In step S103, it also includes: Primary side conduction angle Perform sinusoidal modulation.

3. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 2, characterized in that: The duty cycle of the control signals VG1 and VG2 of the primary bridge arm is D. VG1 and VG3, VG2 and VG4 are complementary turned on to achieve voltage matching between the photovoltaic and battery ports. The primary side conduction angle required for SDPS modulation is achieved by introducing a phase shift angle between VG1 and VG2. ; The control signal Q of the secondary bridge arm P With Q N The duty cycle is 1-D, where Q N Synchronously turned on with VG4, at Q N With Q P A constant phase shift angle is introduced between the two sides to achieve the secondary side conduction angle .

4. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 3, characterized in that: The three-port DC-AC converter has two working states: positive half cycle and negative half cycle; the P group of switch tubes on the secondary side bridge arm include Q 1P -Q 4P , N groups of switch tubes include Q 1N -Q 4N ; Control signal Q P , Q N In the positive half cycle, Q is controlled separately 1P , Q 2P , respectively control Q in the negative half cycle 2N , Q 1N ;Q 3P , Q 4P With Q 1P , Q 2P Complementary conduction; Q 3N , Q 4N With Q 1N , Q 2N Complementary conduction.

5. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 4, characterized in that: For positive and negative half cycles, Q P , Q N The corresponding secondary side switch status is shown in the following table: Among them, 0 represents a low-level signal and 1 represents a high-level signal.

6. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 4, characterized in that: The battery port has two working states: charging and discharging. Assuming that the three-port DC-AC converter is in the positive half cycle and the battery port is in the discharging state, the high-frequency switching process of the three-port DC-AC converter is divided into the following 6 intervals: During the t0-t1 period: the primary-side bridge arm switch tubes VG2 and VG3 are turned off, while VG1 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 2P The remaining switches are turned on; at this time, the primary side is forward-conducting, which is the inductor L p Charging, the secondary side enters the freewheeling mode; L 1 for C PV Charge, L 2 Enter charging state; During the interval t1-t2: the primary-side bridge arm switch tubes VG3 and VG4 are turned off, while VG1 and VG2 are turned on; the secondary-side bridge arm switch tube Q 2P , Q 3P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG1 and VG2 paths, but not between the photovoltaic port and the inductor. L p The secondary side conducts forward, L p The energy is fully transferred to the secondary side; L 1. L 2 is also C PV Charge; During the t2-t3 period: the primary-side bridge arm switch tubes VG3 and VG4 are turned off, while VG1 and VG2 are turned on; the secondary-side bridge arm switch tube Q 3P , Q 4P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG1 and VG2 paths, but not between the photovoltaic port and the inductor. L p Energy is transferred between the two sides; the secondary side enters the freewheeling mode; L 1. L 2 is also C PV Charge; During the t3-t4 period: the primary-side bridge arm switch tubes VG1 and VG4 are turned off, while VG2 and VG3 are turned on; the secondary-side bridge arm switch tube Q 3P , Q 4P The remaining switches are turned on; at this time, the primary side is reversely conducting, which is the inductor L p Charging, the secondary side enters the freewheeling mode; L 2 for C PV Charge, L 1 Enter charging state; During the t4-t5 period: the primary-side bridge arm switch tubes VG1 and VG2 are turned off, while VG3 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 4P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG3 and VG4 paths, but not between the photovoltaic port and the inductor L p The secondary side conducts in the reverse direction, L p The energy is fully transferred to the secondary side; L 1. L 2 Enter charging state at the same time; During the t5-t6 period: the primary-side bridge arm switch tubes VG1 and VG2 are turned off, while VG3 and VG4 are turned on; the secondary-side bridge arm switch tube Q 1P , Q 2P The remaining switches are turned on; at this time, the primary side IBBC circuit and the inductor L p The circuit shares VG3 and VG4 paths, but not between the photovoltaic port and the inductor L p Energy is transferred between the two sides; the secondary side enters the freewheeling mode; L 1. L 2 Enter charging state at the same time.

7. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 1, characterized in that: Also includes: Sampling battery port current I BAT , the battery SOC is obtained by the ampere-hour integration method, combined with the input and output current limits, and the secondary side conduction angle is seized when it exceeds the normal range. Control priority to protect the battery.

8. The three-port DC-AC converter control method for a photovoltaic power generation system according to claim 1, characterized in that: In full cycle operation mode, the output voltage u o , output current i o The primary conduction angle Into a linear relationship.

9. A three-port DC-AC converter control device for a photovoltaic power generation system, characterized in that: include: Duty cycle calculation unit, used to sample the photovoltaic port output voltage U PV and output current I PV , the maximum power point voltage is obtained through the MPPT control algorithm ,Will and U PV The difference is obtained by PI regulator to obtain the duty cycle D; Secondary side conduction angle acquisition unit, used to sample the output current of the AC port i o , and compare it with the output current reference value The difference is obtained by the PI regulator to obtain the secondary side conduction angle of the grid-connected mode. ; The primary side conduction angle acquisition unit is used to obtain the conduction angle of the secondary side according to the soft switching conditions and the Get the primary side conduction angle ; The soft switching condition is ,in, u o is the output voltage obtained in off-grid mode; A control signal generating unit is used to convert the duty cycle D and the secondary side conduction angle and primary conduction angle The input control signal generator generates the required control signals VG1, VG2, VG3, VG 4、 Q P , Q N ; A control unit is used to control the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals VG1, VG2, VG3, VG4, and control the primary side bridge arm switch tubes VG1, VG2, VG3, VG4 according to the control signals Q P , Q N The two groups of switch tubes P and N of the secondary side bridge arm of the three-port DC-AC converter are controlled so that the three-port DC-AC converter is in a zero reactive working mode throughout the entire cycle.

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