Control method of single-stage bidirectional high-frequency isolation inverter, inverter and storage medium

Abstract

The invention relates to a control method of a single-stage bidirectional high-frequency isolation inverter, the inverter and a storage medium. The method comprises the following steps: acquiring the voltage polarity of the secondary side circuit and the power transmission direction of the inverter; determining a current working quadrant of the inverter based on the voltage polarity and the power transmission direction; determining a modulation strategy corresponding to the current working quadrant based on the sinusoidal modulation signal and the triangular wave signal; and controlling the working state of a switching tube in the inverter based on the modulation strategy. A full-bridge module is arranged in a primary side circuit, a chopper module is arranged in a secondary side circuit, then the working quadrant of the inverter is determined according to the voltage polarity of the secondary side circuit and the power transmission direction of the inverter, and a corresponding modulation strategy is determined according to the working quadrant so as to control the working state of a switching tube in the inverter. Therefore, normal operation of the inverter under the non-unity power factor condition is completed.

Description

Technical Field

[0001] The present application relates to the field of inverter control technology, and in particular to a control method, an inverter and a storage medium of a single-stage bidirectional high-frequency isolation inverter. Background Art

[0002] Due to the high switching frequency of Power Electronic Transformers (PET), it has the advantages of small size, light weight, compact structure, flexible power flow control, etc. At the same time, with the rapid development of power electronics technology, PET is widely used in scenarios that require electrical isolation, voltage transformation, power flow control and other functions. A scenario that has attracted much attention is the bidirectional AC / DC isolation system. PET in this field can be further subdivided into single-stage or multi-stage topologies according to the different energy transmission levels. Among them, the single-stage topology has a more compact structure, higher energy transmission efficiency and longer service life, so it has received widespread attention.

[0003] In traditional technology, there is a dual active bridge applied to the AC / DC isolation system, which transforms the secondary side into a matrix converter and implements a single-stage double-frequency phase-shift SPWM (Sine Pulse Width Modulation) modulation strategy for bidirectional energy flow on this basis. However, this topology does not have the ability to operate at non-unit power factor. Summary of the invention

[0004] Based on this, it is necessary to provide a control method, an inverter and a storage medium for a single-stage bidirectional high-frequency isolation inverter capable of non-unit power factor operation in order to address the above technical problems.

[0005] In a first aspect, the present application provides a control method for a single-stage bidirectional high-frequency isolation inverter, which is applied to the control of an inverter, wherein the inverter comprises: a primary side circuit, a high-frequency isolation transformer, a secondary side circuit and a filter circuit, wherein the primary side circuit comprises: a full-bridge module composed of a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, and the secondary side circuit comprises: a chopper module composed of a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube;

[0006] The method includes: obtaining the voltage polarity of the secondary side circuit and the power transmission direction of the inverter; determining the current working quadrant of the inverter based on the voltage polarity and the power transmission direction; determining the modulation strategy corresponding to the current working quadrant based on a sinusoidal modulation signal and a triangular wave signal; and controlling the working state of the switch tube in the inverter based on the modulation strategy.

[0007] In one embodiment, the current working quadrant is one of the first quadrant, the second quadrant, the third quadrant, and the fourth quadrant, and the modulation strategy is one of the first modulation strategy corresponding to the first quadrant, the second modulation strategy corresponding to the second quadrant, the third modulation strategy corresponding to the third quadrant, and the fourth modulation strategy corresponding to the fourth quadrant.

[0008] In one of the embodiments, determining the modulation strategy corresponding to the current working quadrant based on the sinusoidal modulation signal and the triangular wave signal includes: taking the absolute value of the sinusoidal modulation signal to obtain a target modulation signal; and determining the modulation strategy corresponding to the current working quadrant based on the target modulation signal and the triangular wave signal.

[0009] In one embodiment, the first modulation strategy is: during the working cycle of the first quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the first switch tube and the fourth switch tube are controlled to be turned on, and the seventh switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube and the fourth switch tube are controlled to be turned off, and the seventh switch tube is controlled to be turned on; during the working cycle of the first quadrant of the inverter, the second switch tube, the third switch tube and the sixth switch tube are controlled to be turned off, and the fifth switch tube and the eighth switch tube are controlled to be turned on.

[0010] In one embodiment, the second modulation strategy is: within the working cycle of the second quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the first switch tube and the fourth switch tube are controlled to be turned on after a first preset time delay, and the second switch tube and the third switch tube are controlled to be turned on for the first preset time, and the seventh switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube, the fourth switch, the second switch tube and the third switch tube are controlled to be turned off, and the seventh switch tube is controlled to be turned on; within the working cycle of the second quadrant of the inverter, the fifth switch tube is controlled to be turned off, and the sixth switch tube and the eighth switch tube are controlled to be turned on.

[0011] In one embodiment, the third modulation strategy is: during the working cycle of the third quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the second switch tube and the third switch tube are controlled to be turned on, and the eighth switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the second switch tube and the third switch tube are controlled to be turned off, and the eighth switch tube is controlled to be turned on; during the working cycle of the third quadrant of the inverter, the first switch tube, the fourth switch tube and the fifth switch tube are controlled to be turned off, and the sixth switch tube and the seventh switch tube are controlled to be turned on.

[0012] In one embodiment, the fourth modulation strategy is: within the working cycle of the fourth quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the second switch tube and the third switch tube are controlled to be turned on after a first preset time delay, and the first switch tube and the fourth switch tube are controlled to be turned on for the first preset time, and the eighth switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube, the fourth switch, the second switch tube and the third switch tube are controlled to be turned off, and the eighth switch tube is controlled to be turned on; within the working cycle of the fourth quadrant of the inverter, the sixth switch tube is controlled to be turned off, and the fifth switch tube and the seventh switch tube are controlled to be turned on.

[0013] In one embodiment, the first preset time is the time when the current flowing through the fifth switch tube or the sixth switch tube changes from zero to the maximum AC current.

[0014] In a second aspect, the present application further provides an inverter. The inverter includes a memory and a processor, the memory stores a computer program, and the processor implements the steps of the above method when executing the computer program.

[0015] In a third aspect, the present application further provides a computer-readable storage medium having a computer program stored thereon, and the computer program implements the steps of the above method when executed by a processor.

[0016] The control method, inverter and storage medium of the above-mentioned single-stage bidirectional high-frequency isolation inverter are configured by setting a full-bridge module in the primary side circuit and a chopper module in the secondary side circuit, and then determining the working quadrant of the inverter according to the voltage polarity of the secondary side circuit and the power transmission direction of the inverter, and determining the corresponding modulation strategy according to the working quadrant to control the working state of the switch tube in the inverter, thereby completing the normal operation of the inverter under non-unit power factor conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] FIG1 is a circuit diagram of an inverter in one embodiment;

[0018] FIG2 is a schematic flow chart of a control method in one embodiment;

[0019] FIG3 is a schematic flow chart of a control method in another embodiment;

[0020] FIG4 is a waveform diagram of a first modulation strategy and a third modulation strategy in one embodiment;

[0021] FIG5 is a waveform diagram of the first modulation strategy under the switching cycle scale in FIG4;

[0022] FIG6 is a schematic diagram of the circuit from time t0 to time t1 in FIG5 ;

[0023] FIG7 is a schematic diagram of a circuit from time t1 to time t2 in FIG5 ;

[0024] FIG8 is a schematic diagram of a circuit from time t2 to time t3 in FIG5 ;

[0025] FIG9 is a schematic diagram of a circuit from time t3 to time t4 in FIG5 ;

[0026] FIG10 is a waveform diagram of the second modulation strategy and the fourth modulation strategy in one embodiment;

[0027] FIG11 is a waveform diagram of the second modulation strategy at the switching cycle scale in FIG10;

[0028] FIG12 is a schematic diagram of the circuit from time t0 to time t1 in FIG11;

[0029] FIG13 is a schematic diagram of a circuit from time t1 to time t2 in FIG11 ;

[0030] FIG14 is a schematic diagram of a circuit from time t2 to time t3 in FIG11;

[0031] FIG15 is a schematic diagram of a circuit from time t3 to time t4 in FIG11;

[0032] FIG16 is a schematic diagram of the circuit from time t4 to time t5 in FIG11;

[0033] FIG17 is a schematic diagram of a circuit at time t5 to t6 in FIG11 ;

[0034] Fig.18 is a simulation waveform diagram of energy transmission from the DC side to the AC side at a unity power factor in one embodiment;

[0035] FIG19 is a simulation waveform diagram of energy transmission from the AC side to the DC side at unity power factor in one embodiment;

[0036] FIG20 is a simulation waveform diagram when current leads voltage in one embodiment;

[0037] FIG. 21 is a simulation waveform diagram when current lags voltage in one embodiment. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0039] The control method of the single-stage bidirectional high-frequency isolation inverter provided in the embodiment of the present application can be applied to the inverter shown in Figure 1. The inverter includes: a primary side circuit, a high-frequency isolation transformer, a secondary side circuit and a filter circuit. The primary side circuit is connected to one end of the high-frequency isolation transformer. The primary side circuit is used to convert direct current into high-frequency pulsating direct current, and the polarity of the high-frequency pulsating direct current is switched at the industrial frequency according to the polarity of the grid voltage. The high-frequency isolation transformer is used for electrical isolation and voltage conversion, and is used to boost the high-frequency pulsating direct current to obtain high-voltage and high-frequency pulsating direct current. The secondary side circuit is connected to the other end of the high-frequency isolation transformer. The filter circuit is connected to the chopper module in the secondary side circuit, which is used to filter the industrial frequency alternating current with high frequency pulsation output by the chopper module to filter out the high-order harmonic components, thereby obtaining the industrial frequency alternating current used by the power supply network or AC load.

[0040] The primary side circuit includes: a full-bridge module composed of a first switch tube S1, a second switch tube S2, a third switch tube S3 and a fourth switch tube S4. Each switch tube is provided with a reverse parallel diode (respectively denoted as D1 to D4) and a capacitor. The left side of the full-bridge module is connected to the DC side power supply U dc The right side of the full-bridge module is connected to the high-frequency isolation transformer. The leakage inductance of the primary and secondary sides of the high-frequency isolation transformer is equivalent to L δ The secondary circuit includes a chopper module composed of a fifth switch tube S5, a sixth switch tube S6, a seventh switch tube S7 and an eighth switch tube S8, and each switch tube is also provided with a reverse parallel diode (respectively denoted as D5 to D8).

[0041] The switch tube can be an IGBT (Insulate-Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor). In the chopper module, the emitters of two IGBTs (or the sources of MOSFETs) are interconnected to form a four-quadrant switch tube, and one end of the two four-quadrant switch tubes is connected, finally forming a chopper circuit with an inverse "Γ" structure. According to the different functions of the switch tube in the energy transfer process, it can be divided into an energy transmission path (the fifth switch tube S5 and the sixth switch tube S6) and a freewheeling path (the seventh switch tube S7 and the eighth switch tube S8), wherein the different switching states of the fifth switch tube S5 and the sixth switch tube S6 correspond to power conduction paths of different flow directions, and the seventh switch tube S7 and the eighth switch tube S8 are mainly responsible for providing a freewheeling channel for the filter inductor and isolating the power frequency environment.

[0042] The filter circuit may be an LCL filter, and the filter circuit includes: a first inductor L1, a second inductor L2 and a filter capacitor C1, and the filter circuit is connected to an AC load or a power grid. The inverter of the present application is a single-stage structure, and does not require the participation of additional energy storage elements in the middle, and does not require the use of electrolytic capacitors, which is conducive to the high efficiency and miniaturization of the device, and has a longer service life, while also having the ability to bidirectionally flow energy and operate at non-unit power.

[0043] When energy is transferred from the DC side to the AC side, according to the voltage U ac and current i ac The polarity is different (the direction of current flowing into the AC power supply is taken as the positive direction of current, and the direction of current injected into the AC power supply is taken as the positive direction of voltage), which can be divided into U ac is positive, i ac is positive, U ac is negative, i ac is negative, which corresponds to the flow of power in the first quadrant and the third quadrant respectively. Correspondingly, when energy is transferred from the AC side to the DC side, there is U ac is positive, i ac is negative, U ac is negative, i ac The inverter of the present application can realize the four-quadrant power flow, but due to the asymmetric structure of the topology, the modulation strategies for different power flows are also different.

[0044] In one embodiment, as shown in FIG2 , a control method for a single-stage bidirectional high-frequency isolation inverter is provided, which is described by taking the method applied to the inverter in FIG1 as an example, and includes the following steps:

[0045] Step S110, obtaining the voltage polarity of the secondary side circuit and the power transmission direction of the inverter.

[0046] Specifically, when determining the specific modulation strategy of the inverter, the present application first obtains the voltage polarity of the secondary side circuit and the power transmission direction of the inverter. In some embodiments, the direction in which the current in the secondary side circuit is injected into the AC power supply is taken as the positive direction of the voltage. The power transmission direction of the inverter includes: power is transmitted from the DC side to the AC side, or power is transmitted from the AC side to the DC side.

[0047] Step S120: determining the current working quadrant of the inverter based on the voltage polarity and the power transmission direction.

[0048] Specifically, after obtaining the voltage polarity and the power transmission direction, the working quadrant of the inverter can be determined according to them, and the working quadrant is one of the first quadrant, the second quadrant, the third quadrant and the fourth quadrant. In some embodiments, when the voltage polarity is positive, the inverter will work in the first quadrant or the second quadrant; when the voltage polarity is negative, the inverter will work in the third quadrant or the fourth quadrant. When the power transmission direction is from the DC side to the AC side, the inverter will work in the first quadrant or the third quadrant; when the power transmission direction is from the AC side to the DC side, the inverter will work in the second quadrant or the fourth quadrant. By combining the voltage polarity and the power transmission direction, the current working quadrant of the inverter can be determined.

[0049] Step S130, determining a modulation strategy corresponding to the current working quadrant based on the sinusoidal modulation signal and the triangle wave signal.

[0050] Specifically, after determining the current working quadrant of the inverter, the corresponding modulation strategy can be determined according to the current working quadrant of the inverter. The modulation strategy is determined according to the sinusoidal modulation signal and the triangular wave signal, and in the modulation strategy, the first quadrant corresponds to the first modulation strategy, the second quadrant corresponds to the second modulation strategy, the third quadrant corresponds to the third modulation strategy, and the fourth quadrant corresponds to the fourth modulation strategy.

[0051] Step S140, controlling the working state of the switch tube in the inverter based on the modulation strategy.

[0052] Specifically, after determining the corresponding modulation strategy, the working state of the switch tube in the inverter can be controlled according to the modulation strategy, so as to control the switch tube accordingly according to the different working quadrants of the inverter, so that the inverter can invert DC power into AC power, or rectify AC power into DC power.

[0053] The control method of the above-mentioned single-stage bidirectional high-frequency isolated inverter is to set a full-bridge module in the primary side circuit and a chopper module in the secondary side circuit, and then determine the working quadrant of the inverter according to the voltage polarity of the secondary side circuit and the power transmission direction of the inverter, and determine the corresponding modulation strategy according to the working quadrant to control the working state of the switch tube in the inverter, thereby completing the normal operation of the inverter under non-unit power factor conditions.

[0054] In one embodiment, as shown in FIG3 , in step S130, determining a modulation strategy corresponding to the current working quadrant based on the sinusoidal modulation signal and the triangular wave signal includes:

[0055] Step S131, taking the absolute value of the sinusoidal modulation signal to obtain a target modulation signal;

[0056] Step S132, determining a modulation strategy corresponding to the current working quadrant based on the target modulation signal and the triangular wave signal.

[0057] Specifically, in this embodiment, when controlling the switch tube in the inverter, first obtain a sinusoidal modulation signal that changes in a sinusoidal wave and a triangular wave signal that changes in a triangular wave, then take the absolute value of the sinusoidal modulation signal, so that the signal amplitude in the negative half cycle of the sinusoidal modulation signal is positive, and use it as the target modulation signal, and finally compare the target modulation signal and the triangular wave signal, and use the cross-modulation strategy based on the comparison result to determine the corresponding modulation strategy, and thereby control the working state of the switch tube, that is, use the intersection of the target modulation signal and the triangular wave signal to control the on and off of the switch tube in the inverter. In some other embodiments, the corresponding modulation strategy can also be determined directly based on the intersection of the sinusoidal modulation signal and the triangular wave signal.

[0058] In the four-quadrant modulation strategy of the embodiment of the present application, the full-bridge module on the DC side adopts the unipolar SPWM modulation idea, and compares the sinusoidal modulation signal after taking the absolute value with the triangular wave signal, so as to obtain the trigger pulse of the corresponding switch tube to control the on and off of the switch tube. However, unlike conventional modulation, in half of the power frequency cycle, only a pair of diagonal switch tubes (the first switch tube S1 and the fourth switch tube S4, the second switch tube S2 and the third switch tube S3) in the full-bridge module are controlled, that is, in the positive half-cycle and the negative half-cycle of the grid voltage, only the first switch tube S1 and the fourth switch tube S4, the second switch tube S2 and the third switch tube S3 need to be controlled respectively. This is because the chopper module has only one energy transmission path in the process of transmitting power. At this time, the grid voltage is directly added to the secondary side of the transformer. In order to avoid the voltage of the primary side and the secondary side being connected in series, the output voltage of the full-bridge module must always be consistent with the polarity of the grid voltage.

[0059] Since the full-bridge module only controls a pair of diagonal switch tubes in half of the power frequency cycle, at this time, the excitation inductance of the high-frequency isolation transformer is only magnetized in one direction, so the energy release path of the excitation inductance must be considered. This can be solved by setting the dead zone of the full-bridge module. When all the switch tubes of the full-bridge module are turned off, due to the existence of the transformer equivalent inductance (excitation inductance, leakage inductance), the current will not change suddenly, and will be freewheeling through the parallel diodes of the other pair of diagonal switch devices. At this time, the energy stored in the inductance will also be returned to the DC voltage source through the freewheeling path to demagnetize the excitation inductance. Therefore, in order to ensure that the energy in the excitation inductance is completely released, sufficient dead time should be reserved.

[0060] At the same time, due to the existence of transformer leakage inductance, once the transformer secondary current suddenly changes during the switching process between the energy transfer state and the freewheeling state, this will cause a huge voltage spike. Therefore, the switching process of the two states must be reasonably designed to ensure that when the energy transfer state switches to the freewheeling state, the leakage inductance current has decayed to 0, and when the freewheeling state switches to the energy transfer state, the leakage inductance current has increased to the size of the grid current.

[0061] In one embodiment, as shown in Figure 4, the first modulation strategy of the present application is: in the working cycle of the first quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the first switch tube S1 and the fourth switch tube S4 are controlled to be turned on, and the seventh switch tube S7 is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube S1 and the fourth switch tube S4 are controlled to be turned off, and the seventh switch tube S7 is controlled to be turned on; in the working cycle of the first quadrant of the inverter, the second switch tube S2, the third switch tube S3 and the sixth switch tube S6 are controlled to be turned off, and the fifth switch tube S5 and the eighth switch tube S8 are controlled to be turned on.

[0062] The modulation process of the first modulation strategy in the first quadrant is described in detail below. As shown in FIG5 , it is the modulation process in the switching cycle scale.

[0063] When t∈[t0,t1], the inverter works in the freewheeling state, and its corresponding circuit diagram is shown in Figure 6. At this time, the primary current of the transformer is intermittent, and the inductive current i p The same is 0, the AC current i ac The channel provided by the eighth switch tube S8 and the diode D7 connected in parallel with the seventh switch tube S7 performs freewheeling.

[0064] When t∈[t1,t2], the inverter works in the commutation stage, and its corresponding circuit diagram is shown in Figure 7. At t1, the first switch tube S1 and the fourth switch tube S4 realize ZCS (Zero Current Switch) conduction, u p =Udc At the same time, since the fifth switch tube S5 is continuously turned on during half of the power frequency cycle, at this stage, the right side potential u of the transformer leakage inductance q The freewheeling path formed by the eighth switch tube S8 and the diode D7 connected in parallel with the seventh switch tube S7 is short-circuited. At this time, the voltage drop on the leakage inductance can be calculated by the following formula. Under the action of the positive voltage, the leakage inductance current will increase linearly.

[0065]

[0066] When t∈[t2,t3], the inverter works in the energy transfer state, and its corresponding circuit diagram is shown in Figure 8. In this stage, the AC current is completely controlled by i p The freewheeling branch is intermittent, but the eighth switch tube S8 continues to be turned on to prepare for the next transition of the inverter to the freewheeling state.

[0067] When t∈[t3,t4], the inverter operates in another commutation state, i p Xiangi q The corresponding circuit diagram is shown in FIG9 . At time t3, the first switch tube S1 and the fourth switch tube S4 are turned off. Due to the existence of the parasitic capacitance of the switch tube, the tube voltage drop of the first switch tube S1 and the fourth switch tube S4 will not change suddenly. At this time, the primary side current of the transformer will charge the parasitic capacitance of the first switch tube S1 and the fourth switch tube S4. Therefore, the tube voltage drop of the first switch tube S1 and the fourth switch tube S4 will increase from 0 to U dc , so the first switch tube S1 and the fourth switch tube S4 are turned off as ZVS (Zero Voltage Switch). At the same time, the primary current of the transformer will also extract energy from the parasitic capacitance of the second switch tube S2 and the third switch tube S3. When the energy is released, the diode D2 connected in parallel with the second switch tube S2 and the diode D3 connected in parallel with the third switch tube S3 are turned on, which provides a demagnetization channel for the excitation inductor on the one hand, and promotes i p Xiangi q The current is commutated, which can be explained by the following formula:

[0068]

[0069] At this time, the voltage applied to the leakage inductance is a negative voltage, i p Linearly decreases, according to Kirchhoff's current law, i q will increase, thus promoting i p Xiangi q At time t4, p decays to 0, but since the sixth switch tube S6 is continuously turned off in the positive half cycle, i pIt will not increase in the reverse direction, so the inverter will naturally transition from the energy transfer state to the freewheeling state. At the same time, when the commutation ends, the fifth switch tube S5 does not act, preparing for the next energy transfer state. The following table shows the actions of the switch tubes at each moment in the DC-AC direction, and all the switch tubes are soft switches.

[0070]

[0071] In one embodiment, as shown in FIG10 , the second modulation strategy is: in the working cycle of the second quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the first switch tube S1 and the fourth switch tube S4 are controlled to be turned on after a first preset time delay, and the second switch tube S2 and the third switch tube S3 are controlled to be turned on for the first preset time, and the seventh switch tube S7 is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube S1, the fourth switch, the second switch tube S2 and the third switch tube S3 are controlled to be turned off, and the seventh switch tube S7 is controlled to be turned on; in the working cycle of the second quadrant of the inverter, the fifth switch tube S5 is controlled to be turned off, and the sixth switch tube S6 and the eighth switch tube S8 are controlled to be turned on.

[0072] The modulation process of the second modulation strategy in the second quadrant is described in detail below. As shown in FIG11 , it is the modulation process in the switching cycle scale.

[0073] When t∈[t0,t1], the inverter works in the freewheeling state, and its corresponding circuit diagram is shown in Figure 12. At this time, the AC current i ac The freewheeling channel constructed by the seventh switch tube S7 and the diode D8 connected in parallel with the eighth switch tube S8 performs freewheeling.

[0074] When t∈[t1,t2], the inverter works in the commutation state, and its corresponding circuit diagram is shown in FIG13. At t1, the second switch tube S2, the third switch tube S3 and the sixth switch tube S6 are all ZCS-on. At this time, u p =-U dc ,u q The seventh switch tube S7 and the diode D8 connected in parallel with the eighth switch tube S8 are short-circuited. Therefore, the voltage applied to the leakage inductance of the transformer can be expressed by the following formula:

[0075]

[0076] i p It decreases linearly under the negative voltage shown in the formula and decreases to -i at time t2. ac At the same time, the inverter in this stage is also accompanied by i qand increases to 0 at time t2. Ideally, the second switch tube S2, the third switch tube S3 and the seventh switch tube S7 are turned off at time t2, and the inverter can naturally transition to the energy transmission state. But in fact, the AC current is a sine wave, i ac The amplitude of changes with the phase of the AC voltage, so it is difficult to accurately calculate the conduction time of the second switch and the third switch, and too short a conduction time will cause i p and -i ac There is a certain degree of error between them, and eventually a large voltage spike is induced on the leakage inductance of the transformer. Therefore, the present application appropriately extends the conduction time of the second switch tube S2 and the third switch tube S3, that is, the first preset time, which is the current i flowing through the fifth switch tube S5 or the sixth switch tube S6. p , changes from zero to the maximum AC current i ac-max The maximum AC current i ac-max 1.1 times the rated AC current i ac .

[0077] When t∈[t2,t3], the second switch tube S2, the third switch tube S3 and the eighth switch continue to be turned on, and the corresponding circuit diagram is shown in FIG14. q After decreasing to 0, the freewheeling channel formed by the eighth switch tube S8 and the diode D7 connected in parallel with the seventh switch tube S7 will continue to increase in the reverse direction to i ac-max -i ac .

[0078] When t∈[t3,t4], the inverter enters another commutation stage, and the corresponding circuit diagram is shown in Figure 15. At t3, the second switch tube S2, the third switch tube S3 and the seventh switch tube S7ZVS are turned off, and the first switch tube S1 and the fourth switch tube S4ZVS are turned on, wherein the turn-off process of the second switch tube S2 and the third switch tube S3 is similar to the first switch tube S1 and the fourth switch tube S4 mentioned above, and will not be repeated here. In this stage, no current passes through the first switch tube S1 and the fourth switch tube S4, and the primary side current completes energy transmission only through the diode D1 connected in parallel with the first switch tube S1 and the diode D4 connected in parallel with the fourth switch tube S4. The voltage drop on the leakage inductance in this stage can be expressed by the following formula:

[0079]

[0080] Under the action of this voltage, i p will increase linearly, and i q It decreases linearly and returns to 0 again at time t4. Since the seventh switch tube S7 has been turned off at this time, i p Will not continue to decrease, so the inverter will naturally transition to the energy transfer state.

[0081] When t∈[t4,t5], the inverter works in the energy transfer state, and its corresponding circuit diagram is shown in Figure 16. In this stage, the AC current is completely controlled by i p Take responsibility, the freewheeling branch is intermittent.

[0082] When t∈[t5,t6], the inverter transitions to the freewheeling state, and its corresponding circuit diagram is shown in Figure 17. At this time, only the seventh switch needs to be turned on, u q The seventh switch tube S7 and the diode D8 connected in parallel with the eighth switch tube S8 are automatically short-circuited. The voltage drop on the leakage inductance at this stage can be expressed as follows:

[0083]

[0084] Under the action of this voltage, i p It will increase linearly and return to 0 at time t6. The following table shows the action of the switch tube at each moment in the AC-DC direction. All the switch tubes are soft switches.

[0085]

[0086] In one embodiment, as shown in FIG4 , the third modulation strategy is: in the working cycle of the third quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the second switch tube S2 and the third switch tube S3 are controlled to be turned on, and the eighth switch tube S8 is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the second switch tube S2 and the third switch tube S3 are controlled to be turned off, and the eighth switch tube S8 is controlled to be turned on; in the working cycle of the third quadrant of the inverter, the first switch tube S1, the fourth switch tube S4 and the fifth switch tube S5 are controlled to be turned off, and the sixth switch tube S6 and the seventh switch tube S7 are controlled to be turned on. Specifically, the third modulation strategy in the third quadrant is symmetrical with the first modulation strategy in the first quadrant, and the modulation process is similar, which will not be repeated here.

[0087] In one embodiment, as shown in Figure 10, the fourth modulation strategy is: in the working cycle of the fourth quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the second switch tube S2 and the third switch tube S3 are controlled to be turned on after a first preset time delay, and the first switch tube S1 and the fourth switch tube S4 are controlled to be turned off after the first preset time, and the eighth switch tube S8 is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube S1, the fourth switch S4, the second switch tube S2 and the third switch tube S3 are controlled to be turned off, and the eighth switch tube S8 is controlled to be turned on; in the working cycle of the fourth quadrant of the inverter, the fifth switch tube S5 and the seventh switch tube S7 are controlled to be turned on, and the sixth switch tube S6 is controlled to be turned off.

[0088] Specifically, the fourth modulation strategy in the fourth quadrant is symmetrical to the second modulation strategy in the second quadrant, and the modulation processes are similar, which will not be described in detail here. The first preset time is the current i flowing through the fifth switch tube S5 or the sixth switch tube S6. p From zero to maximum AC current i ac-max The maximum AC current i ac-max 1.1 times the rated AC current i ac .

[0089] The advantages of the control method of the single-stage bidirectional high-frequency isolation inverter of the present application are described in detail below. Fig.18 As shown in Figure 1, it is a simulation waveform of energy transmission from the DC side to the AC side at a unit power factor; as shown in Figure 19, it is a simulation waveform of energy transmission from the AC side to the DC side at a unit power factor; as shown in Figure 20, it is a simulation waveform when the current leads the voltage; as shown in Figure 21, it is a simulation waveform when the current lags the voltage. The harmonic content of the current is detected respectively, and the total harmonic distortion THD (Total Harmonic Distortion) is 0.86%, 2.32%, 2.83%, and 3.34% respectively, which verifies the effectiveness of the control method of the single-stage bidirectional high-frequency isolation inverter of the present application.

[0090] It should be understood that, although the various steps in the flowcharts involved in the above-mentioned embodiments are displayed in sequence according to the indication of the arrows, these steps are not necessarily executed in sequence according to the order indicated by the arrows. Unless there is a clear explanation in this article, the execution of these steps is not strictly limited in order, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-mentioned embodiments can include multiple steps or multiple stages, and these steps or stages are not necessarily executed at the same time, but can be executed at different times, and the execution order of these steps or stages is not necessarily carried out in sequence, but can be executed in turn or alternately with other steps or at least a part of the steps or stages in other steps.

[0091] In one embodiment, an inverter is provided, including a memory and a processor. The memory stores a computer program, and the processor implements the steps in the above method embodiments when executing the computer program.

[0092] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the processor executes the computer program, the steps in the above-mentioned method embodiments are implemented.

[0093] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. As an illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM). The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. Non-relational databases may include distributed databases based on blockchains, etc., but are not limited to this. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but are not limited to this.

[0094] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A control method for a single-stage bidirectional high-frequency isolation inverter, characterized in that: The invention is applied to the control of an inverter, wherein the inverter comprises: a primary side circuit, a high frequency isolation transformer, a secondary side circuit and a filter circuit, wherein the primary side circuit comprises: a full bridge module composed of a first switch tube, a second switch tube, a third switch tube and a fourth switch tube, and the secondary side circuit comprises: a chopper module composed of a fifth switch tube, a sixth switch tube, a seventh switch tube and an eighth switch tube; and the method comprises: Obtaining the voltage polarity of the secondary side circuit and the power transmission direction of the inverter; determining a current operating quadrant of the inverter based on the voltage polarity and the power transmission direction; Determine the modulation strategy corresponding to the current working quadrant based on the sinusoidal modulation signal and the triangular wave signal; The working state of the switch tube in the inverter is controlled based on the modulation strategy.

2. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 1, characterized in that: The current working quadrant is one of the first quadrant, the second quadrant, the third quadrant, and the fourth quadrant, and the modulation strategy is one of the first modulation strategy corresponding to the first quadrant, the second modulation strategy corresponding to the second quadrant, the third modulation strategy corresponding to the third quadrant, and the fourth modulation strategy corresponding to the fourth quadrant.

3. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 2, characterized in that: The determining the modulation strategy corresponding to the current working quadrant based on the sinusoidal modulation signal and the triangular wave signal includes: Taking an absolute value of the sinusoidal modulation signal to obtain a target modulation signal; A modulation strategy corresponding to the current working quadrant is determined based on the target modulation signal and the triangular wave signal.

4. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 3 is characterized in that: The first modulation strategy is: In a working cycle of the first quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the first switch tube and the fourth switch tube are controlled to be turned on, and the seventh switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube and the fourth switch tube are controlled to be turned off, and the seventh switch tube is controlled to be turned on; In a working cycle of the first quadrant of the inverter, the second switch tube, the third switch tube and the sixth switch tube are controlled to be turned off, and the fifth switch tube and the eighth switch tube are controlled to be turned on.

5. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 3, characterized in that: The second modulation strategy is: In the working cycle of the second quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the first switch tube and the fourth switch tube are controlled to be turned on after a first preset time delay, and the second switch tube and the third switch tube are controlled to be turned on for the first preset time, and the seventh switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube, the fourth switch tube, the second switch tube and the third switch tube are controlled to be turned off, and the seventh switch tube is controlled to be turned on; In a working cycle of the second quadrant of the inverter, the fifth switch tube is controlled to be turned off, and the sixth switch tube and the eighth switch tube are controlled to be turned on.

6. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 3, characterized in that: The third modulation strategy is: In a working cycle of the third quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the second switch tube and the third switch tube are controlled to be turned on, and the eighth switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the second switch tube and the third switch tube are controlled to be turned off, and the eighth switch tube is controlled to be turned on; In a working cycle of the third quadrant of the inverter, the first switch tube, the fourth switch tube and the fifth switch tube are controlled to be turned off, and the sixth switch tube and the seventh switch tube are controlled to be turned on.

7. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 3, characterized in that: The fourth modulation strategy is: In a working cycle of the fourth quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, the second switch tube and the third switch tube are controlled to be turned on after a first preset time delay, and the first switch tube and the fourth switch tube are controlled to be turned off after the first preset time, and the eighth switch tube is controlled to be turned off; when the target modulation signal is less than the triangular wave signal, the first switch tube, the fourth switch, the second switch tube and the third switch tube are controlled to be turned off, and the eighth switch tube is controlled to be turned on; In a working cycle of the fourth quadrant of the inverter, the sixth switch tube is controlled to be turned off, and the fifth switch tube and the seventh switch tube are controlled to be turned on.

8. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 5 or 7, characterized in that: The first preset time is the time when the current flowing through the fifth switch tube or the sixth switch tube changes from zero to the maximum AC current.

9. An inverter, comprising a memory and a processor, wherein the memory stores a computer program, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 1 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 8 are implemented.

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