Control Method, Inverter and Storage Medium of Single-Stage Bidirectional High-Frequency Isolated Inverter

Abstract

The present application relates to a control method, an inverter and a storage medium for a single-stage bidirectional high-frequency isolation inverter. 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 a modulation strategy corresponding to the current working quadrant based on a sine modulation signal and a triangular wave signal; and controlling the working state of the switching tubes in the inverter based on the modulation strategy. By arranging a full-bridge module in the primary-side circuit and a chopper module in the secondary-side circuit, 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 switching tubes in the inverter, so as to complete the normal operation of the inverter under non-unit power factor conditions.

Description

Technical Field

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

[0002] Due to the relatively high switching frequency of the Power Electronic Transformer (PET), it has the advantages of small volume, light weight, compact structure, flexible power flow control, etc. At the same time, with the rapid development of power electronic technology, PET is widely used in scenarios that require functions such as electrical isolation, voltage transformation, and power flow control. A scenario that has received much attention is the bidirectional AC-DC isolation system. PETs in this field can be further divided into single-stage or multi-stage topologies according to the number of energy transfer stages. Among them, the single-stage topology has a more compact structure, higher energy transfer efficiency, and longer service life, thus receiving extensive attention.

[0003] In traditional technologies, there is a case of applying a dual active bridge to an AC-DC isolation system, which transforms the secondary side into a matrix converter and implements a quasi-single-stage double-frequency phase-shifted 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 a 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 that can operate at a non-unit power factor 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 the inverter. The inverter includes: a primary side circuit, a high-frequency isolation transformer, a secondary side circuit, and a filter circuit. The primary side circuit includes: a full-bridge module composed of a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube. The secondary side circuit includes: 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 sine modulation signal and a triangular wave signal; and controlling the working states of the switch tubes 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 embodiment, determining the modulation strategy corresponding to the current working quadrant based on the sine modulation signal and the triangular wave signal includes: taking the absolute value of the sine 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: within the working cycle of the first quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, controlling the first switch tube and the fourth switch tube to conduct, and controlling the seventh switch tube to turn off; when the target modulation signal is less than the triangular wave signal, controlling the first switch tube and the fourth switch tube to turn off, and controlling the seventh switch tube to conduct; within the working cycle of the first quadrant of the inverter, controlling the second switch tube, the third switch tube, and the sixth switch tube to turn off, and controlling the fifth switch tube and the eighth switch tube to conduct.

[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, controlling the first switch tube and the fourth switch tube to conduct after a first preset time delay, and controlling the second switch tube and the third switch tube to conduct for the first preset time, and controlling the seventh switch tube to turn off; when the target modulation signal is less than the triangular wave signal, controlling the first switch tube, the fourth switch, the second switch tube, and the third switch tube to turn off, and controlling the seventh switch tube to conduct; within the working cycle of the second quadrant of the inverter, controlling the fifth switch tube to turn off, and controlling the sixth switch tube and the eighth switch tube to conduct.

[0011] In one embodiment, the third modulation strategy is as follows: within the working cycle of the third quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, control the second switch tube and the third switch tube to conduct, and control the eighth switch tube to turn off; when the target modulation signal is less than the triangular wave signal, control the second switch tube and the third switch tube to turn off, and control the eighth switch tube to conduct; within the working cycle of the third quadrant of the inverter, control the first switch tube, the fourth switch tube, and the fifth switch tube to turn off, and control the sixth switch tube and the seventh switch tube to conduct.

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

[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 alternating current.

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

[0015] In a third aspect, the present application also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the steps of the above method are implemented.

[0016] For the above control method, inverter, and storage medium of the single-stage bidirectional high-frequency isolation inverter, a full-bridge module is provided in the primary-side circuit, and a chopper module is provided in the secondary-side circuit. Then, according to the voltage polarity of the secondary-side circuit and the power transmission direction of the inverter, the working quadrant of the inverter is determined, and the corresponding modulation strategy is determined according to the working quadrant to control the working state of the switch tubes in the inverter, so as to complete the normal operation of the inverter under non-unit power factor conditions. Description of the Drawings

[0017] Figure 1Circuit diagram of an inverter in an embodiment;

[0018] Figure 2 Schematic flowchart of a control method in an embodiment;

[0019] Figure 3 Schematic flowchart of a control method in another embodiment;

[0020] Figure 4 Waveform schematic diagrams of the first modulation strategy and the third modulation strategy in an embodiment;

[0021] Figure 5 For Figure 4 Waveform schematic diagram of the first modulation strategy on the scale of the switching period in ;

[0022] Figure 6 For Figure 5 Circuit schematic diagram from time t0 to t1 in ;

[0023] Figure 7 For Figure 5 Circuit schematic diagram from time t1 to t2 in ;

[0024] Figure 8 For Figure 5 Circuit schematic diagram from time t2 to t3 in ;

[0025] Figure 9 For Figure 5 Circuit schematic diagram from time t3 to t4 in ;

[0026] Figure 10 Waveform schematic diagrams of the second modulation strategy and the fourth modulation strategy in an embodiment;

[0027] Figure 11 For Figure 10 Waveform schematic diagram of the second modulation strategy on the scale of the switching period in ;

[0028] Figure 12 For Figure 11 Circuit schematic diagram from time t0 to t1 in ;

[0029] Figure 13 For Figure 11 Circuit schematic diagram from time t1 to t2 in ;

[0030] Figure 14 For Figure 11 Circuit schematic diagram from time t2 to t3 in ;

[0031] Figure 15 For Figure 11 Circuit schematic diagram from time t3 to t4 in ;

[0032] Figure 16 ForFigure 11 Schematic diagram of the circuit from time t4 to t5

[0033] Figure 17 is Figure 11 Schematic diagram of the circuit from time t5 to t6

[0034] Figure 18 is the simulation waveform diagram of energy transmission from the DC side to the AC side under unity power factor in one embodiment

[0035] Figure 19 is the simulation waveform diagram of energy transmission from the AC side to the DC side under unity power factor in one embodiment

[0036] Figure 20 is the simulation waveform diagram when the current leads the voltage in one embodiment

[0037] Figure 21 is the simulation waveform diagram when the current lags behind the voltage in one embodiment Detailed implementation manners

[0038] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application will be further described in detail below with reference to 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 by the embodiment of the present application can be applied to an inverter as 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 switch the polarity of the high-frequency pulsating direct current with the polarity of the grid voltage at the power frequency. The high-frequency isolation transformer is used for electrical isolation and voltage conversion, and it is used to step up the high-frequency pulsating direct current to obtain high-voltage 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, and it is used to filter the high-frequency pulsating power-frequency alternating current output by the chopper module to filter out high-order harmonic components, so as to obtain power-frequency alternating current for use by the power grid or AC load

[0040] The primary-side circuit includes: a full-bridge module composed of a first switching tube S1, a second switching tube S2, a third switching tube S3 and a fourth switching tube S4. Each switching tube is correspondingly provided with a diode (denoted as D1 to D4 respectively) and a capacitor connected in anti-parallel. The left side of the full-bridge module is connected to the DC-side power supply U dc and the right side of the full-bridge module is connected to the high-frequency isolation transformer. The leakage inductances of the primary side and the secondary side of the high-frequency isolation transformer are equivalently combined as Lδ and is connected to the secondary circuit. 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. Each switch tube is also correspondingly provided with a diode connected in antiparallel (denoted as D5 to D8 respectively).

[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 (or sources of MOSFETs) of two IGBTs 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 inverted "Γ" structure. According to the different functions of the switch tubes in the energy transfer process, it can be divided into an energy transfer path (the fifth switch tube S5 and the sixth switch tube S6) and a free - wheeling path (the seventh switch tube S7 and the eighth switch tube S8). Among them, different switching states of the fifth switch tube S5 and the sixth switch tube S6 correspond to power conduction paths with different flow directions, and the seventh switch tube S7 and the eighth switch tube S8 are mainly responsible for providing a free - wheeling channel for the filter inductor and isolating the power frequency environment.

[0042] The filter circuit can be an LCL - type filter, and the filter circuit includes a first inductor L1, a second inductor L2, and a filter capacitor C1. The filter circuit is connected to an AC load or the power grid. The inverter of the present application is of a single - stage structure, without the participation of additional energy storage elements in the middle, without the use of electrolytic capacitors, which is beneficial to the high - efficiency and miniaturization of the device and has a longer service life. At the same time, it also has the ability of bidirectional energy flow and operation at non - unity power.

[0043] When energy is transmitted from the DC side to the AC side, according to the different polarities of the voltage U ac and current i ac (taking the direction of the current flowing into the AC power supply as the positive direction of the current and the direction of the current injecting into the AC power supply as the positive direction of the voltage), it can be divided into two cases: U ac is positive and i ac is positive, U ac is negative and i ac is negative. These two cases respectively correspond to the power flowing in the first quadrant and the third quadrant. Correspondingly, when energy is transmitted from the AC side to the DC side, there are U ac is positive and i ac is negative, U ac is negative and i acWhen it is positive, there are two cases, which respectively correspond to the power flowing in the second quadrant and the fourth quadrant. The inverter of the present application can achieve four-quadrant power flow, but limited by the asymmetric structure of this topology, the modulation strategies under different power flow directions are also different.

[0044] In one embodiment, as Figure 2 shown, a control method for a single-stage bidirectional high-frequency isolation inverter is provided. Taking the inverter in Figure 1 as an example for illustration, it includes the following steps:

[0045] Step S110, obtain 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 voltage polarity of the secondary-side circuit and the power transmission direction of the inverter are first obtained. In some embodiments, the direction in which the current in the secondary-side circuit injects into the AC power supply is taken as the positive direction of the voltage. The power transmission direction of the inverter includes: the power is transmitted from the DC side to the AC side, or the power is transmitted from the AC side to the DC side.

[0047] Step S120, determine 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. 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 judged.

[0049] Step S130, determine the modulation strategy corresponding to the current working quadrant based on the sine modulation signal and the triangular 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. Among them, the modulation strategy is determined according to the sine 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, control the working state of the switching tubes in the inverter based on the modulation strategy.

[0052] Specifically, after determining the corresponding modulation strategy, the working states of the switching tubes in the inverter can be controlled according to the modulation strategy, so as to control the switching tubes correspondingly according to different working quadrants of the inverter, so that the inverter can invert direct current into alternating current or rectify alternating current into direct current.

[0053] The control method of the above single-stage bidirectional high-frequency isolation inverter sets a full-bridge module in the primary-side circuit and a chopper module in the secondary-side circuit, then determines 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 determines the corresponding modulation strategy according to the working quadrant to control the working states of the switching tubes in the inverter, so as to complete the normal operation of the inverter under non-unit power factor conditions.

[0054] In one embodiment, as Figure 3 shown, in step S130, determining the 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 the target modulation signal;

[0056] Step S132, determining the 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 switching tubes in the inverter, first obtain the sinusoidal modulation signal that changes in a sine wave and the triangular wave signal that changes in a triangular wave, then take the absolute value of the sinusoidal modulation signal to make the signal amplitude in the negative half cycle of the sinusoidal modulation signal positive, and use it as the target modulation signal. Finally, compare the target modulation signal and the triangular wave signal, and adopt a cross modulation strategy based on the comparison result to determine the corresponding modulation strategy, and control the working states of the switching tubes accordingly, that is, use the intersection point of the target modulation signal and the triangular wave signal to control the on and off of the switching tubes in the inverter. In some other embodiments, the corresponding modulation strategy can also be directly determined based on the intersection point of the sinusoidal modulation signal and the triangular wave signal.

[0058] In the four - quadrant modulation strategy of the embodiment of this application, in the full - bridge module on the DC side, the unipolar SPWM modulation idea is adopted. The sine modulation signal after taking the absolute value is compared with the triangular wave signal, so as to obtain the trigger pulses of the corresponding switching tubes to control the on - off of the switching tubes. However, different from the conventional modulation, within half of the power - frequency cycle, only a pair of diagonal switching tubes in the full - bridge module (the first switching tube S1 and the fourth switching tube S4, the second switching tube S2 and the third switching tube S3) are controlled. That is, in the positive half - cycle and negative half - cycle of the grid voltage, only the first switching tube S1 and the fourth switching tube S4, the second switching tube S2 and the third switching tube S3 need to be controlled respectively. This is because there is only one energy - transmission path when the chopper module transmits power. At this time, the grid voltage is directly applied to the secondary side of the transformer. In order to avoid the series connection of the voltages on the primary side and the secondary side, 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 switching tubes within half of the power - frequency cycle, at this time, the exciting inductance of the high - frequency isolation transformer is magnetized only in one direction. Therefore, the energy - release path of the exciting inductance must be considered. It can be solved by setting the dead - time of the full - bridge module. When all the switching tubes of the full - bridge module are turned off, due to the existence of the equivalent inductance of the transformer (exciting inductance, leakage inductance), the current will not change suddenly and will flow through the parallel diodes of the other pair of diagonal switching devices for free - wheeling. At this time, the energy stored in the inductance will also be sent back to the DC voltage source through this free - wheeling path, so that the exciting inductance is demagnetized. Therefore, in order to ensure the complete release of the energy in the exciting inductance, sufficient dead - time should be reserved.

[0060] At the same time, due to the existence of the leakage inductance of the transformer, once a sudden change in the secondary - side current of the transformer occurs during the switching process between the energy - transmission state and the free - wheeling state of the chopper module, this will cause a huge voltage spike. Therefore, the switching process between the two states must be reasonably designed to ensure that when switching from the energy - transmission state to the free - wheeling state, the magnitude of the leakage - inductance current has decayed to 0, and when switching from the free - wheeling state to the energy - transmission state, the magnitude of the leakage - inductance current has increased to the magnitude of the grid current.

[0061] In one embodiment, as Figure 4 shown, the first modulation strategy of this application is: within the working cycle of the first quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, control the first switching tube S1 and the fourth switching tube S4 to conduct, and control the seventh switching tube S7 to turn off; when the target modulation signal is less than the triangular wave signal, control the first switching tube S1 and the fourth switching tube S4 to turn off, and control the seventh switching tube S7 to conduct; within the working cycle of the first quadrant of the inverter, control the second switching tube S2, the third switching tube S3 and the sixth switching tube S6 to turn off, and control the fifth switching tube S5 and the eighth switching tube S8 to conduct.

[0062] The modulation process of the first modulation strategy in the first quadrant is described in detail below. As Figure 5 shown, it is the modulation process on the scale of the switching period.

[0063] When t ∈ [t0, t1], the inverter operates in the freewheeling state, and the corresponding circuit diagram is as Figure 6 shown. At this time, the primary side current of the transformer is discontinuous, and the induced current i on the secondary side p is also 0, and the AC current i ac flows through the freewheeling path provided by the eighth switch tube S8 and the diode D7 in parallel with the seventh switch tube S7.

[0064] When t ∈ [t1, t2], the inverter operates in the commutation stage, and the corresponding circuit diagram is as Figure 7 shown. At time t1, the first switch tube S1 and the fourth switch tube S4 achieve ZCS (Zero Current Switch) conduction, and u p = U dc . At the same time, since the fifth switch tube S5 conducts continuously within half a power frequency cycle, in this stage, the right potential u of the leakage inductance of the transformer q will be short-circuited by the freewheeling path formed by the eighth switch tube S8 and the diode D7 in parallel with the seventh switch tube S7. At this time, the voltage drop across the leakage inductance can be calculated by the following formula, and under the action of this positive voltage, the leakage inductance current will increase linearly.

[0065]

[0066] When t ∈ [t2, t3], the inverter operates in the energy transfer state, and the corresponding circuit diagram is as Figure 8 shown. In this stage, the AC current is completely borne by i p , and the freewheeling branch is discontinuous, but at this time the eighth switch tube S8 continues to conduct 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, that is, i p commutates to i q , and the corresponding circuit diagram is as Figure 9 shown. 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 tubes, the voltage drops across 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 capacitances of the first switch tube S1 and the fourth switch tube S4. Therefore, the voltage drops across 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 p It 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, Figure 10 As shown, 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, 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. Figure 11 As shown, this is the modulation process on the switching cycle scale.

[0073] When t∈[t0,t1], the inverter works in the freewheeling state, and the corresponding circuit diagram is as follows: Figure 12As shown. At this time, the alternating current i ac is freewheeling through the freewheeling path formed by the seventh switch tube S7 and the diode D8 in parallel with the eighth switch tube S8.

[0074] When t ∈ [t1, t2], the inverter operates in the commutation state, and its corresponding circuit diagram is as shown in Figure 13 At the moment of t1, the second switch tube S2, the third switch tube S3, and the sixth switch tube S6 are all conducting with zero current switching (ZCS). At this time, u p =-U dc and u q is short-circuited by the seventh switch tube S7 and the diode D8 in parallel with the eighth switch tube S8. Therefore, the voltage applied to the leakage inductance of the transformer can be expressed by the following formula:

[0075]

[0076] i p decreases linearly under the action of the negative voltage shown in the formula and decreases to -i ac at the moment of t2. At the same time, the inverter in this stage is also accompanied by the increase of i q and increases to 0 at the moment of t2. Ideally, at the moment of t2, turning off the second switch tube S2, the third switch tube S3, and the seventh switch tube S7, the inverter can naturally transition to the energy transfer state. However, in reality, the alternating current is a sine wave, and the amplitude of i ac changes continuously with the phase of the alternating voltage. Therefore, it is difficult to accurately calculate the conduction time of the second switch and the third switch, and too short conduction time will lead to a certain degree of error between i p and -i ac , and finally a large voltage spike is induced on the leakage inductance of the transformer. Therefore, in this application, the conduction time of the second switch tube S2 and the third switch tube S3 is appropriately extended, that is, the first preset time. The first preset time is the time when the current i p flowing through the fifth switch tube S5 or the sixth switch tube S6 changes from zero to the maximum alternating current i ac-max . The maximum alternating current i ac-max is 1.1 times the rated alternating current i ac .

[0077] When t ∈ [t2, t3], the second switch tube S2, the third switch tube S3, and the eighth switch continue to conduct in this stage, and its corresponding circuit diagram is as shown in Figure 14 When i q decreases to 0, it will continue to increase in the reverse direction to i ac-max -i ac through the freewheeling path formed by the eighth switch tube S8 and the diode D7 in parallel with the seventh switch tube S7.

[0078] When \(t\in[t_3,t_4]\), the inverter enters another commutation stage, and its corresponding circuit diagram is as Figure 15 shown. At time \(t_3\), the second switch tube \(S2\), the third switch tube \(S3\) and the seventh switch tube \(S7\) turn off under zero voltage switching (ZVS), and the first switch tube \(S1\) and the fourth switch tube \(S4\) turn on under ZVS. The turn-off processes of the second switch tube \(S2\) and the third switch tube \(S3\) are similar to those of the first switch tube \(S1\) and the fourth switch tube \(S4\) described above, and will not be elaborated here. In this stage, there is no current passing through the first switch tube \(S1\) and the fourth switch tube \(S4\), and the primary side current only completes energy transfer 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 across 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 at the same time \(i\) q will decrease linearly, and return to 0 again at time \(t_4\). Since the seventh switch tube \(S7\) has been turned off at this time, \(i\) p will not continue to decrease. Therefore, the inverter will naturally transition to the energy transfer state.

[0081] When \(t\in[t_4,t_5]\), the inverter operates in the energy transfer state, and its corresponding circuit diagram is as Figure 16 shown. In this stage, the alternating current is completely borne by \(i\) p , and the freewheeling branch is discontinuous.

[0082] When \(t\in[t_5,t_6]\), the inverter transitions to the freewheeling state, and its corresponding circuit diagram is as Figure 17 shown. At this time, only the seventh switch needs to be turned on, and \(u\) q is automatically short-circuited by the seventh switch tube \(S7\) and the diode \(D8\) connected in parallel with the eighth switch tube \(S8\). The voltage drop across the leakage inductance in this stage can be expressed by the following formula:

[0083]

[0084] Under the action of this voltage, \(i\) p will increase linearly and return to 0 at time \(t_6\). The following table shows the actions of the switch tubes at each moment in the AC-DC direction, and all the switch tubes are soft-switched.

[0085]

[0086] In one embodiment, as Figure 4As shown in the figure, the third modulation strategy is as follows: during the working cycle of the third quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, control the second switch tube S2 and the third switch tube S3 to conduct, and control the eighth switch tube S8 to turn off; when the target modulation signal is less than the triangular wave signal, control the second switch tube S2 and the third switch tube S3 to turn off, and control the eighth switch tube S8 to conduct; during the working cycle of the third quadrant of the inverter, control the first switch tube S1, the fourth switch tube S4, and the fifth switch tube S5 to turn off, and control the sixth switch tube S6 and the seventh switch tube S7 to conduct. Specifically, the third modulation strategy in the third quadrant is symmetric to the first modulation strategy in the first quadrant, and their modulation processes are similar, so they will not be elaborated one by one here.

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

[0088] Specifically, the fourth modulation strategy in the fourth quadrant is symmetric to the second modulation strategy in the second quadrant, and their modulation processes are similar, so they will not be elaborated one by one here. The first preset time is the time when the current i flowing through the fifth switch tube S5 or the sixth switch tube S6 p changes from zero to the maximum alternating current i ac-max . The maximum alternating current i ac-max is 1.1 times the rated alternating current i ac .

[0089] Next, the advantages of the control method of the single-stage bidirectional high-frequency isolation inverter of the present application will be described in detail. As Figure 18 shown, it is the simulation waveform of energy transmission from the DC side to the AC side under unity power factor; as Figure 19 shown, it is the simulation waveform of energy transmission from the AC side to the DC side under unity power factor; as Figure 20 shown, it is the simulation waveform when the current leads the voltage; as Figure 21As shown, it is the simulation waveform when the current lags behind the voltage. The harmonic content of the current is detected respectively, and the total harmonic distortion (THD) is 0.86%, 2.32%, 2.83%, and 3.34% in sequence, verifying the effectiveness of the control method of the single-stage bidirectional high-frequency isolation inverter of this application.

[0090] It should be understood that although the steps in the flowcharts involved in the above-described embodiments are shown sequentially according to the indications of the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless there is a clear indication in this article, there is no strict order restriction for the execution of these steps, and these steps can be executed in other orders. Moreover, at least a part of the steps in the flowcharts involved in the above-described embodiments may include multiple steps or multiple stages. These steps or stages are not necessarily executed at the same moment, but can be executed at different moments. The execution order of these steps or stages is not necessarily sequential, but can be executed alternately or in turn with at least a part of other steps or steps or stages in other steps.

[0091] In one embodiment, an inverter is provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above method embodiments are implemented.

[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 method embodiments are implemented.

[0093] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. 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 methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. 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. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc. The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logic devices, data processing logics based on quantum computing, etc., without limitation.

[0094] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, 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, it should be considered as the scope recorded in this specification.

[0095] The above-described embodiments merely represent several implementation manners of the present application. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the patent scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, 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 appended claims.

Claims

1. A control method for a single-stage bidirectional high-frequency isolation inverter, characterized in that Applied to the control of an inverter, the inverter includes: a primary-side circuit, a high-frequency isolation transformer, a secondary-side circuit, and a filter circuit. The primary-side circuit includes: a full-bridge module composed of a first switch tube, a second switch tube, a third switch tube, and a fourth switch tube. The first switch tube and the third switch tube are connected in series to form a first bridge arm, and the midpoint of the first bridge arm is connected to the opposite-named end of the primary winding of the high-frequency isolation transformer. The second switch tube and the fourth switch tube are connected in series to form a second bridge arm, and the midpoint of the second bridge arm is connected to the opposite-named end of the primary winding of the high-frequency isolation transformer. The first bridge arm and the second bridge arm are connected in parallel with a DC power supply. The secondary-side circuit includes: a chopper module composed of a fifth switch tube, a sixth switch tube, a seventh switch tube, and an eighth switch tube. The fifth switch tube and the sixth switch tube are connected in series to form a first series circuit, and the first end of the first series circuit is connected to the same-named end of the secondary winding of the high-frequency isolation transformer. The seventh switch tube and the eighth switch tube are connected in series to form a second series circuit, and the first end of the second series circuit is connected to the opposite-named end of the secondary winding of the high-frequency isolation transformer. The second end of the first series circuit is connected to the second end of the second series circuit, and the second series circuit is connected in parallel with an AC power supply. The method includes: Obtain the voltage polarity of the secondary-side circuit and the power transmission direction of the inverter; Determine the current working quadrant of the inverter based on the voltage polarity and the power transmission direction; wherein, the current working quadrant is one of the first quadrant, the second quadrant, the third quadrant, and the fourth quadrant; Take the absolute value of the sinusoidal modulation signal to obtain a target modulation signal; Determine the modulation strategy corresponding to the current working quadrant based on the target modulation signal and the triangular wave signal; wherein, the modulation strategy is one of a first modulation strategy corresponding to the first quadrant, a second modulation strategy corresponding to the second quadrant, a third modulation strategy corresponding to the third quadrant, and a fourth modulation strategy corresponding to the fourth quadrant. The first modulation strategy is: within the working cycle of the first quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, control the first switch tube and the fourth switch tube to conduct, and control the seventh switch tube to turn off; when the target modulation signal is less than the triangular wave signal, control the first switch tube and the fourth switch tube to turn off, and control the seventh switch tube to conduct; within the working cycle of the first quadrant of the inverter, control the second switch tube, the third switch tube, and the sixth switch tube to turn off, and control the fifth switch tube and the eighth switch tube to conduct; Control the working states of the switch tubes in the inverter based on the modulation strategy.

2. The control method of the single-stage bidirectional high-frequency isolated inverter according to claim 1, characterized in that The second modulation strategy is: During the working cycle of the second quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, control the first switch tube and the fourth switch tube to conduct after a first preset time delay, and control the second switch tube and the third switch tube to conduct for the first preset time, and control the seventh switch tube to turn off; when the target modulation signal is less than the triangular wave signal, control the first switch tube, the fourth switch, the second switch tube and the third switch tube to turn off, and control the seventh switch tube to conduct; During the working cycle of the second quadrant of the inverter, control the fifth switch tube to turn off, and control the sixth switch tube and the eighth switch tube to conduct.

3. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 1, characterized in that, 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, control the second switch tube and the third switch tube to conduct, and control the eighth switch tube to turn off; when the target modulation signal is less than the triangular wave signal, control the second switch tube and the third switch tube to turn off, and control the eighth switch tube to conduct; During the working cycle of the third quadrant of the inverter, control the first switch tube, the fourth switch tube and the fifth switch tube to turn off, and control the sixth switch tube and the seventh switch tube to conduct.

4. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 1, wherein, The fourth modulation strategy is: During the working cycle of the fourth quadrant of the inverter, when the target modulation signal is greater than the triangular wave signal, control the second switch tube and the third switch tube to conduct after a first preset time delay, and control the first switch tube and the fourth switch tube to turn off after the first preset time, and control the eighth switch tube to turn off; when the target modulation signal is less than the triangular wave signal, control the first switch tube, the fourth switch, the second switch tube and the third switch tube to turn off, and control the eighth switch tube to conduct; During the working cycle of the fourth quadrant of the inverter, control the sixth switch tube to turn off, and control the fifth switch tube and the seventh switch tube to conduct.

5. The control method of the single-stage bidirectional high-frequency isolation inverter according to claim 2 or 4, 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 alternating current.

6. An inverter, comprising a memory and a processor, the memory storing 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 5 are implemented.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, the steps of the method according to any one of claims 1 to 5 are implemented.

Images