A single-phase soft-switching inverter based on auxiliary inductance and a modulation method thereof

Abstract

The application discloses a single-phase soft-switching inverter based on auxiliary inductance and a modulation method thereof V DC , a capacitor C DC , an inverter bridge and a main filter inductance L The soft-switching auxiliary circuit mainly comprises an auxiliary inductance and an auxiliary switch branch; the auxiliary switch branch is a bidirectional switch which is composed of two unidirectional switches in reverse series connection. The bidirectional switch is connected in parallel across the main filter inductance of the inverter. The auxiliary inductance is connected in series with the parallel network composed of the main filter inductance of the inverter and the bidirectional switch. The application combines the grid-connected inverter topology with the soft-switching technology, on the one hand, improves the inverter efficiency through the soft-switching technology, and on the other hand, realizes further improvement of the inverter working frequency and power density.

Description

Technical Field

[0001] This invention relates to the field of soft-switching technology for inverters, and in particular to a single-phase soft-switching inverter based on an auxiliary inductor and its modulation method. Background Technology

[0002] Soft switching can be divided into zero-voltage switching (ZVS) and zero-current switching (ZCS). It effectively reduces the switching losses of the converter, greatly increases the switching frequency, and enables the converter to have higher power density. In traditional single-phase inverters using unipolar commissioning, only one switch can achieve zero-voltage conduction in each half-cycle of the high-frequency switching arm, so half of the high-frequency switches operate in hard switching mode.

[0003] To achieve zero-voltage commutation (ZVS) of power devices in a traditional single-phase inverter, a reverse current needs to be provided during commutation to discharge parasitic capacitances before the switch turns on. One method to provide this reverse current is to reduce the AC-side filter inductance, making the inductor current either positive or negative within a single switching cycle. By appropriately controlling the duty cycle and switching frequency, bidirectional energy flow can be achieved, thus enabling ZVS switching of all power switches. The advantage of this method is that it requires no additional equipment. Its disadvantages include large inductor current ripple and increased current during switch turn-off, making turn-off losses and core losses difficult to ignore. Since the soft-switching characteristics of the converter are entirely achieved by controlling the main filter inductor current, this method significantly alters the original characteristics of the converter. The large ripple current and variable switching frequency control degrade the electromagnetic environment of the converter, placing higher demands on the design of EMI filters, DC-side filter capacitors, and converter control.

[0004] To address these issues, this invention proposes a novel soft-switching topology for single-phase inverters. The proposed topology adds a soft-switching auxiliary circuit to the traditional inverter, primarily comprising an auxiliary inductor and an auxiliary bidirectional switching branch. Based on this topology and through corresponding adjustment methods, all high-frequency switching transistors in the converter achieve zero-voltage turn-on. Furthermore, the added auxiliary switches all achieve zero-current turn-on and turn-off. Summary of the Invention

[0005] The purpose of this invention is to achieve zero-voltage turn-on of all high-frequency switches in a single-phase inverter, and to propose a single-phase soft-switching inverter based on an auxiliary inductor and its modulation method. This invention achieves zero-voltage turn-on of all switches in the high-frequency switching arm of a single-phase inverter, reduces inverter switching losses, and provides a foundation for high-frequency, high-power-density operation of the inverter.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A single-phase soft-switching inverter based on an auxiliary inductor includes an inverter, characterized in that it further includes a bidirectional switch and an auxiliary inductor L connected to the inverter. a The inverter comprises a soft-switching auxiliary circuit and a power supply V. DC Capacitor C DC The inverter bridge and the main filter inductor L, and the capacitor C DC Parallel connection to power supply V DC Above, the inverter bridge is connected in parallel with capacitor C. DC The main filter inductor L is connected in series with the inverter bridge, which includes switches S1, S2, S3, and S4. Switches S1 and S2 are connected in series, and switches S3 and S4 are connected in series. One end of the main filter inductor L is connected between switches S1 and S2, and the other end is connected between switches S3 and S4. A bidirectional switch is connected in parallel across the main filter inductor L of the inverter. The bidirectional switch consists of two switching transistors S5 and S6 connected in reverse series. The auxiliary inductor L... a The auxiliary inductor L is connected in series with the parallel network consisting of the main filter inductor L and the bidirectional switch of the inverter. a The position of the parallel network in series in the AC circuit is not fixed.

[0008] As a preferred technical solution of the present invention: the auxiliary inductor L a It is smaller than the main filter inductance L of the inverter.

[0009] In the above structure: This application adds a soft-switching auxiliary circuit to the traditional inverter. The auxiliary circuit includes a bidirectional switch composed of switches S5 and S6 and an auxiliary inductor L. aThe inverter's main filter inductor is L, and the inverter bridge consists of switches S1-S4. In traditional single-phase inverters using unipolar modulation, only one switch in the high-frequency switching arm has zero-voltage turn-on characteristics within each half-cycle of the power frequency, while the other switch remains in a hard-on state. The core of this invention is to achieve zero-voltage turn-on for the other switch in the hard-switching state by adding a soft-switching auxiliary circuit. The core idea is to turn on the bidirectional switch connected in parallel with the main filter inductor before the commutation dead zone when the high-frequency switch in the hard-switching state turns on, at which point the auxiliary inductor turns on with zero current. This bypasses the main filter inductor, and because the auxiliary inductor is much smaller than the main filter inductor, the grid voltage forces the auxiliary inductor current to reverse rapidly. This reverse current provides the condition for the high-frequency switch in the hard-switching state of a traditional inverter to achieve zero-voltage turn-on. After the high-frequency switch, originally in a hard-switching state, achieves zero-voltage turn-on using a soft-switching auxiliary circuit, the difference between the DC-side voltage and the grid voltage rapidly forces the auxiliary inductor current to increase until it equals the main filter inductor current. At this point, the anti-parallel diode of the added auxiliary switch is reverse-biased and cut off. The main filter inductor and the auxiliary inductor then operate in series in the AC circuit, forming the inverter's total filter inductance. Once the auxiliary inductor current equals the main filter inductor current, the auxiliary switch can be turned off, satisfying the zero-current turn-off condition.

[0010] A modulation method for a single-phase soft-switching inverter based on an auxiliary inductor, characterized in that the inverter employs unipolar modulation, achieving power frequency switching through one bridge arm and high-frequency switching through the other bridge arm. The modulation method includes the following steps:

[0011] During the positive half-cycle of the power frequency, when the bridge arm consisting of switches S1 and S2 switches at power frequency, or when the bridge arm consisting of switches S3 and S4 switches at high frequency, or when the bridge arm consisting of switches S3 and S4 switches at power frequency, or when the bridge arm consisting of switches S1 and S2 switches at high frequency, the inverter contains a total of 6 operating states within one switching cycle, as follows:

[0012] During the time period [0, t1], switches S1 and S3 are turned on, the inverter's main filter inductor and auxiliary inductor are connected in series, and the energy stored in the two inductors is transferred to the AC grid side. At this time, the current equation is as follows:

[0013]

[0014] During the time period [t1, t3], this is an extremely short period before the dead zone commutation of the high-frequency switching bridge arm. During this period, switches S1 and S3 are turned on, and auxiliary switch S5 is turned on at time t2. Since the inductor current cannot change abruptly, S5 achieves zero-current turn-on at this moment. The main filter inductor L is short-circuited by bidirectional switches S5 and S6, and the current flowing through the main filter inductor remains constant. The grid voltage V gForced to flow through auxiliary inductor L a current i La The value decreases rapidly at time t2. La The current drops to zero, and then continues to decrease at the same slope until the switch S3 is turned off at time t3, at which point this stage ends. The current equations at this point are as follows:

[0015]

[0016] The time period [t3, t4] is the commutation dead zone between the turn-off of high-frequency switch S3 and the turn-on of S4, and the auxiliary inductor L... a current i La The voltage is less than zero. Before S4 turns on, its anti-parallel diode is turned on. Switch S4 turns on with zero voltage at time t4. At this time, the circuit equation is as follows:

[0017]

[0018] During the time period [t4, t6], switches S1 and S4 are turned on, and auxiliary switch S5 remains on. During this period, the DC side voltage V... DC With grid voltage V g The pressure difference between them forces the flow through the auxiliary inductor L a current i La The auxiliary inductance L increases rapidly until time t6. a current i La The current i of the main filter inductor L L Similarly, this stage ends, and at this point, the current equations are as follows:

[0019]

[0020] During the time period [t6, t7], switches S1 and S4 are turned on. At time t6, the auxiliary inductor current is the same as the main filter inductor current. The anti-parallel diode D of switch S6... S6 Reverse cutoff, auxiliary inductor L a When connected in series with the main filter inductor L in the AC circuit, during this stage, the auxiliary switch S5 can achieve zero-current turn-off at any time. At this time, the current equation is as follows:

[0021]

[0022] During the time period [t7, t8], this stage is the commutation dead zone between the turn-off of high-frequency switch S4 and the turn-on of S3. Since the inductor current is greater than zero, switch S3 meets the zero-voltage turn-on condition and achieves ZVS turn-on at time t8. At this time, the circuit equation is as follows:

[0023]

[0024] When the power grid is operating in the negative half-cycle of the power frequency, the analysis is similar based on the symmetry of the inverter's operating modes; since the inverter energy can be bidirectionally controlled through a bidirectional switch, the analysis is similar when the inverter is operating in rectification mode, based on the symmetry of the inverter's operating modes.

[0025] In the above structure, the single-phase soft-switching inverter based on auxiliary inductors mainly includes a sinusoidal carrier wave, a modulation wave, and switching timing, reflecting the converter's modulation method. Taking the positive half-cycle of the power grid as an example, the analysis for the negative half-cycle is similar. A total of 6 operating states are included within one switching cycle, and the analysis of each operating state is as follows:

[0026] Mode 1: Time period [0, t1]. During this stage, switches S1 and S3 are turned on, the inverter's main filter inductor and auxiliary inductor are connected in series, and the energy stored in the two inductors is transferred to the AC grid side. The current equation is as follows:

[0027]

[0028] Mode 2: Time period [t1, t3]. This stage is an extremely short time period before the dead zone commutation of the high-frequency switching bridge arm. During this stage, switches S1 and S3 are turned on, and auxiliary switch S5 is turned on at time t2. Since the inductor current cannot change abruptly, S5 achieves zero-current turn-on at this moment. The main filter inductor L is short-circuited by bidirectional switches S5 and S6, and the current flowing through the main filter inductor remains constant. Grid voltage V g Forced to flow through auxiliary inductor L a current i La The value decreases rapidly at time t2. La The current drops to zero, then continues to decrease at the same slope until switch S3 is turned off at time t3, at which point this phase ends. The current equations are as follows:

[0029]

[0030] Mode 3: Time period [t3, t4]. This stage is the commutation dead zone between the high-frequency switch S3 turning off and S4 turning on. Auxiliary inductor L a current i La The voltage is less than zero, ensuring the energy transfer of the high-frequency switch output capacitor. This allows the anti-parallel diode to conduct before S4 turns on, and switch S4 turns on with zero voltage at time t4. The circuit equations are as follows:

[0031]

[0032] Mode 4: Time period [t4, t6]. During this stage, switches S1 and S4 are turned on, and auxiliary switch S5 remains on. The DC side voltage V during this stage... DC With grid voltage V g The pressure difference between them forces the flow through the auxiliary inductor L a current iLa It increases rapidly. Until time t6, the auxiliary inductance L... a current i La The current i of the main filter inductor L L Similarly, this stage ends. The current equations are as follows:

[0033]

[0034] Mode 5: Time period [t6, t7]. During this phase, switches S1 and S4 are turned on. At time t6, the auxiliary inductor current is the same as the main filter inductor current, and the anti-parallel diode D of switch S6... S6 Reverse cutoff. Auxiliary inductor L a It operates in series with the main filter inductor L in the AC circuit. During this stage, the auxiliary switch S5 can achieve zero-current turn-off at any time. The current equation is as follows:

[0035]

[0036] Mode 6: Time period [t7, t8]. This stage is the commutation dead zone between the turn-off of high-frequency switch S4 and the turn-on of S3. Since the inductor current is greater than zero, switch S3 satisfies the zero-voltage turn-on condition and achieves ZVS turn-on at time t8. The circuit equations are as follows:

[0037]

[0038] To further analyze the characteristics of this topology, its steady-state operating point was modeled. To simplify the analysis, the influence of the resonant commutation stage was ignored, and the duty cycle for each stage was defined as follows:

[0039]

[0040] Based on the duty cycle defined above, the voltage transformation ratio of this topology can be derived through inductor volt-second balance as follows. It can be seen that the voltage transformation ratio is no different from that of a conventional topology, namely:

[0041]

[0042] Since the auxiliary inductor is much smaller than the main filter inductor, its influence on the main filter inductor can be ignored, and the topology's operating characteristics will not change significantly. Based on this simplification, the size of the main filter inductor is approximated based on current ripple requirements. Furthermore, according to the modal analysis above, to achieve zero-current switching of the auxiliary switch, time t6 must be less than t7; this constraint can be directly used for the design calculations of the auxiliary inductor.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] 1. The soft-switching auxiliary circuit added in this invention contains only one bidirectional switch and one auxiliary inductor, which is simple in structure and easy to implement. Furthermore, the inductance value of the auxiliary inductor is much smaller than that of the main filter inductor, resulting in low cost.

[0045] 2. This invention achieves zero-voltage turn-on of all high-frequency switches in a traditional inverter by adding a soft-switching auxiliary circuit, thereby reducing switching losses and facilitating high-frequency, high-power-density operation of the inverter.

[0046] 3. The auxiliary bidirectional switch added in this invention has good zero-current characteristics during both the turn-on and turn-off processes, effectively reducing additional switching losses.

[0047] 4. The auxiliary inductor added in this invention is only used for constructing the reverse current during high-frequency switching commutation. In other modes, it is connected in series with the main filter inductor to form the total filter inductor of the inverter. This improves the utilization rate of inductor devices and is beneficial to improving the output performance of the inverter. Attached Figure Description

[0048] Figure 1 This is a topology diagram of the single-phase soft-switching inverter in this invention;

[0049] Figure 2 This is a schematic diagram of the inverter's power frequency cycle soft-switching modulation process in this invention;

[0050] Figure 3 This is a schematic diagram of the steady-state high-frequency periodic switching timing and current waveform in this invention;

[0051] Figure 4 This is a schematic diagram of mode 1 in the present invention;

[0052] Figure 5 This is a schematic diagram of mode 2 in the present invention;

[0053] Figure 6 This is a schematic diagram of mode 3 in this invention;

[0054] Figure 7 This is a schematic diagram of mode 4 in this invention;

[0055] Figure 8 This is a schematic diagram of mode 5 in this invention;

[0056] Figure 9 This is a schematic diagram of mode 6 in this invention. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0058] This invention proposes a single-phase soft-switching inverter based on an auxiliary inductor, comprising an inverter and an auxiliary inductor L connected to the inverter, consisting of a bidirectional switch and an auxiliary inductor L. a The inverter comprises a soft-switching auxiliary circuit and a power supply V. DC Capacitor C DC The inverter bridge and the main filter inductor L, and the capacitor C DC Parallel connection to power supply V DC Above, the inverter bridge is connected in parallel with capacitor C. DC The main filter inductor L is connected in series with the inverter bridge, which includes switches S1, S2, S3, and S4. Switches S1 and S2 are connected in series, and switches S3 and S4 are connected in series. One end of the main filter inductor L is connected between switches S1 and S2, and the other end is connected between switches S3 and S4. A bidirectional switch is connected in parallel across the main filter inductor L of the inverter. The bidirectional switch consists of two switching transistors S5 and S6 connected in reverse series. The auxiliary inductor L... a The auxiliary inductor L is connected in series with the parallel network consisting of the main filter inductor L and the bidirectional switch of the inverter. a The position of the auxiliary inductor L in the AC circuit is not fixed and is connected in series with the parallel network. a It is smaller than the main filter inductance L of the inverter.

[0059] like Figure 1 The diagram shown is a topology of a single-phase soft-switching inverter. This application adds a soft-switching auxiliary circuit to the traditional inverter. The auxiliary circuit includes a bidirectional switch composed of switches S5 and S6 and an auxiliary inductor L. aThe inverter's main filter inductor is L, and the inverter bridge consists of switches S1-S4. In traditional single-phase inverters using unipolar modulation, only one switch in the high-frequency switching arm has zero-voltage turn-on characteristics within each half-cycle of the power frequency, while the other switch remains in a hard-on state. The core of this invention is to achieve zero-voltage turn-on for the other switch in the hard-switching state by adding a soft-switching auxiliary circuit. The core idea is to turn on the bidirectional switch connected in parallel with the main filter inductor before the commutation dead zone when the high-frequency switch in the hard-switching state turns on, at which point the auxiliary inductor turns on with zero current. This bypasses the main filter inductor, and because the auxiliary inductor is much smaller than the main filter inductor, the grid voltage forces the auxiliary inductor current to reverse rapidly. This reverse current provides the condition for the high-frequency switch in the hard-switching state of a traditional inverter to achieve zero-voltage turn-on. After the high-frequency switch, originally in a hard-switching state, achieves zero-voltage turn-on using a soft-switching auxiliary circuit, the difference between the DC-side voltage and the grid voltage rapidly forces the auxiliary inductor current to increase until it equals the main filter inductor current. At this point, the anti-parallel diode of the added auxiliary switch is reverse-biased and cut off. The main filter inductor and the auxiliary inductor then operate in series in the AC circuit, forming the inverter's total filter inductance. Once the auxiliary inductor current equals the main filter inductor current, the auxiliary switch can be turned off, satisfying the zero-current turn-off condition.

[0060] A modulation method for a single-phase soft-switching inverter based on an auxiliary inductor, wherein the inverter employs unipolar modulation, achieving power frequency switching through one bridge arm and high-frequency switching through the other bridge arm, the modulation method comprising the following steps:

[0061] During the positive half-cycle of the power frequency, when the bridge arm consisting of switches S1 and S2 switches at power frequency, or when the bridge arm consisting of switches S3 and S4 switches at high frequency, or when the bridge arm consisting of switches S3 and S4 switches at power frequency, or when the bridge arm consisting of switches S1 and S2 switches at high frequency, the inverter contains a total of 6 operating states within one switching cycle, as follows:

[0062] During the time period [0, t1], switches S1 and S3 are turned on, the inverter's main filter inductor and auxiliary inductor are connected in series, and the energy stored in the two inductors is transferred to the AC grid side. At this time, the current equation is as follows:

[0063]

[0064] During the time period [t1, t3], this is an extremely short period before the dead zone commutation of the high-frequency switching bridge arm. During this period, switches S1 and S3 are turned on, and auxiliary switch S5 is turned on at time t2. Since the inductor current cannot change abruptly, S5 achieves zero-current turn-on at this moment. The main filter inductor L is short-circuited by bidirectional switches S5 and S6, and the current flowing through the main filter inductor remains constant. The grid voltage V g Forced to flow through auxiliary inductor La current i La The value decreases rapidly at time t2. La The current drops to zero, and then continues to decrease at the same slope until the switch S3 is turned off at time t3, at which point this stage ends. The current equations at this point are as follows:

[0065]

[0066] The time period [t3, t4] is the commutation dead zone between the turn-off of high-frequency switch S3 and the turn-on of S4, and the auxiliary inductor L... a current i La The voltage is less than zero. Before S4 turns on, its anti-parallel diode is turned on. Switch S4 turns on with zero voltage at time t4. At this time, the circuit equation is as follows:

[0067]

[0068] During the time period [t4, t6], switches S1 and S4 are turned on, and auxiliary switch S5 remains on. During this period, the DC side voltage V... DC With grid voltage V g The pressure difference between them forces the flow through the auxiliary inductor L a current i La The auxiliary inductance L increases rapidly until time t6. a current i La The current i of the main filter inductor L L Similarly, this stage ends, and at this point, the current equations are as follows:

[0069]

[0070] During the time period [t6, t7], switches S1 and S4 are turned on. At time t6, the auxiliary inductor current is the same as the main filter inductor current. The anti-parallel diode D of switch S6... S6 Reverse cutoff, auxiliary inductor L a When connected in series with the main filter inductor L in the AC circuit, during this stage, the auxiliary switch S5 can achieve zero-current turn-off at any time. At this time, the current equation is as follows:

[0071]

[0072] During the time period [t7, t8], this stage is the commutation dead zone between the turn-off of high-frequency switch S4 and the turn-on of S3. Since the inductor current is greater than zero, switch S3 meets the zero-voltage turn-on condition and achieves ZVS turn-on at time t8. At this time, the circuit equation is as follows:

[0073]

[0074] When the power grid is operating in the negative half-cycle of the power frequency, the analysis is similar based on the symmetry of the inverter's operating modes; since the inverter energy can be bidirectionally controlled through a bidirectional switch, the analysis is similar when the inverter is operating in rectification mode, based on the symmetry of the inverter's operating modes.

[0075] Single-phase soft-switching inverters based on auxiliary inductors, such as Figure 2 The diagram shown illustrates the inverter switching timing over one power frequency cycle, primarily including a sinusoidal carrier wave, a modulation wave, and the switching sequence, reflecting the converter's modulation method. Taking the positive half-cycle of the power grid as an example, the switching sequence and main operating waveforms of the converter within one switching cycle are as follows. Figure 3 As shown, the analysis for the negative half-cycle is similar. A single switching cycle contains six operating states, analyzed as follows:

[0076] like Figure 4 As shown, Mode 1: Time period [0, t1]. During this stage, switches S1 and S3 are turned on, the inverter's main filter inductor and auxiliary inductor are connected in series, and the energy stored in the two inductors is transferred to the AC grid side. The current equation is as follows:

[0077]

[0078] like Figure 5 As shown, Mode 2: Time period [t1, t3]. This stage is an extremely short time period before the dead zone commutation of the high-frequency switching bridge arm. During this stage, switches S1 and S3 are turned on, and auxiliary switch S5 is turned on at time t2. Since the inductor current cannot change abruptly, S5 achieves zero-current turn-on at this moment. The main filter inductor L is short-circuited by bidirectional switches S5 and S6, and the current flowing through the main filter inductor remains constant. Grid voltage V g Forced to flow through auxiliary inductor L a current i La The value decreases rapidly at time t2. La The current drops to zero, then continues to decrease at the same slope until switch S3 is turned off at time t3, at which point this phase ends. The current equations are as follows:

[0079]

[0080] like Figure 6 As shown, Mode 3: Time period [t3, t4]. This stage is the commutation dead zone between the high-frequency switch S3 turning off and S4 turning on. Auxiliary inductor L a current i La The voltage is less than zero, ensuring the energy transfer of the high-frequency switch output capacitor. This allows the anti-parallel diode to conduct before S4 turns on, and switch S4 turns on with zero voltage at time t4. The circuit equations are as follows:

[0081]

[0082] like Figure 7 As shown, Mode 4: Time period [t4, t6]. During this stage, switches S1 and S4 are turned on, and auxiliary switch S5 remains on. The DC side voltage V during this stage... DC With grid voltage V g The pressure difference between them forces the flow through the auxiliary inductor L a current i La It increases rapidly. Until time t6, the auxiliary inductance L... a current i La The current i of the main filter inductor L L Similarly, this stage ends. The current equations are as follows:

[0083]

[0084] like Figure 8 As shown, Mode 5: Time period [t6, t7]. During this stage, switches S1 and S4 are turned on. At time t6, the auxiliary inductor current is the same as the main filter inductor current, and the anti-parallel diode D of switch S6... S6 Reverse cutoff. Auxiliary inductor L a It operates in series with the main filter inductor L in the AC circuit. During this stage, the auxiliary switch S5 can achieve zero-current turn-off at any time. The current equation is as follows:

[0085]

[0086] like Figure 9 As shown, Mode 6: Time period [t7, t8]. This stage is the commutation dead zone between the turn-off of high-frequency switch S4 and the turn-on of S3. Since the inductor current is greater than zero, switch S3 satisfies the zero-voltage turn-on condition and achieves ZVS turn-on at time t8. The circuit equations are as follows:

[0087]

[0088] To further analyze the characteristics of this topology, its steady-state operating point was modeled. To simplify the analysis, the influence of the resonant commutation stage was ignored, and the duty cycle for each stage was defined as follows:

[0089]

[0090] Based on the duty cycle defined above, the voltage transformation ratio of this topology can be derived through inductor volt-second balance as follows. It can be seen that the voltage transformation ratio is no different from that of a conventional topology, namely:

[0091]

[0092] Since the auxiliary inductor is much smaller than the main filter inductor, its influence on the main filter inductor can be ignored, and the topology's operating characteristics will not change significantly. Based on this simplification, the size of the main filter inductor is approximated based on current ripple requirements. Furthermore, according to the modal analysis above, to achieve zero-current switching of the auxiliary switch, time t6 must be less than t7; this constraint can be directly used for the design calculations of the auxiliary inductor.

[0093] The technical approach of the present invention has been described in detail above with reference to examples and accompanying drawings. However, those skilled in the art will readily understand that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions resulting from these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A single-phase soft-switching inverter based on an auxiliary inductor, comprising an inverter, characterized in that, It also includes a bidirectional switch and an auxiliary inductor L connected to the inverter. a The inverter comprises a soft-switching auxiliary circuit and a power supply V. DC Capacitor C DC The inverter bridge and the main filter inductor L, and the capacitor C DC Parallel connection to power supply V DC Above, the inverter bridge is connected in parallel with capacitor C. DC The main filter inductor L is connected in series with the inverter bridge, which includes switches S1, S2, S3, and S4. Switches S1 and S2 are connected in series, and switches S3 and S4 are connected in series. One end of the main filter inductor L is connected between switches S1 and S2, and the other end is connected between switches S3 and S4. A bidirectional switch is connected in parallel across the main filter inductor L of the inverter. The bidirectional switch consists of two switching transistors S5 and S6 connected in reverse series. The auxiliary inductor L... a The auxiliary inductor L is connected in series with the main filter inductor L and the bidirectional switch of the inverter in a parallel network. a The position of the parallel network in series in the AC circuit is not fixed; The inverter employs unipolar modulation, achieving power frequency switching through one bridge arm and high-frequency switching through the other bridge arm. The modulation method includes the following steps: During the positive half-cycle of the power frequency, when the bridge arm consisting of switches S1 and S2 switches at power frequency, or when the bridge arm consisting of switches S3 and S4 switches at high frequency, or when the bridge arm consisting of switches S3 and S4 switches at power frequency, or when the bridge arm consisting of switches S1 and S2 switches at high frequency, the inverter contains a total of 6 operating states within one switching cycle, as follows: During the time period [0, t1], switches S1 and S3 are turned on, the inverter's main filter inductor and auxiliary inductor are connected in series, and the energy stored in the two inductors is transferred to the AC grid side. At this time, the current equation is as follows: ； During the time period [t1, t3], this is an extremely short period before the dead zone commutation of the high-frequency switching bridge arm. During this period, switches S1 and S3 are turned on, and auxiliary switch S5 is turned on at time t2. Since the inductor current cannot change abruptly, S5 achieves zero-current turn-on at this moment. The main filter inductor L is short-circuited by bidirectional switches S5 and S6, and the current flowing through the main filter inductor remains constant. The grid voltage V g Forced to flow through auxiliary inductor L a current i La The value decreases rapidly at time t2. La The current drops to zero, and then continues to decrease at the same slope until the switch S3 is turned off at time t3, at which point this stage ends. The current equations at this point are as follows: ； The time period [t3, t4] is the commutation dead zone between the high-frequency switch S3 turning off and S4 turning on, and the auxiliary inductor L... a current i La The voltage is less than zero. Before S4 turns on, its anti-parallel diode is turned on. Switch S4 turns on with zero voltage at time t4. At this time, the circuit equation is as follows: ； During the time period [t4, t6], switches S1 and S4 are turned on, and auxiliary switch S5 remains on. During this period, the DC side voltage V... DC With grid voltage V g The pressure difference between them forces the flow through the auxiliary inductor L a current i La The auxiliary inductance L increases rapidly until time t6. a current i La The current i of the main filter inductor L L Similarly, this stage ends, and at this point, the current equations are as follows: ； During the time period [t6, t7], switches S1 and S4 are turned on. At time t6, the auxiliary inductor current is the same as the main filter inductor current. The anti-parallel diode D of switch S6... S6 Reverse cutoff, auxiliary inductor L a When connected in series with the main filter inductor L in the AC circuit, during this stage, the auxiliary switch S5 can achieve zero-current turn-off at any time. At this time, the current equation is as follows: ； During the time period [t7, t8], this stage is the commutation dead zone between the turn-off of high-frequency switch S4 and the turn-on of S3. Since the inductor current is greater than zero, switch S3 meets the zero-voltage turn-on condition and achieves ZVS turn-on at time t8. At this time, the circuit equation is as follows: ； When the power grid is operating in the negative half-cycle of the power frequency, the analysis is similar based on the symmetry of the inverter's operating modes; since the inverter energy can be bidirectionally controlled through a bidirectional switch, the analysis is similar when the inverter is operating in rectification mode, based on the symmetry of the inverter's operating modes.

2. A single-phase soft-switching inverter based on an auxiliary inductor according to claim 1, characterized in that, The auxiliary inductor L a It is smaller than the main filter inductance L of the inverter.

3. A modulation method for a single-phase soft-switching inverter based on an auxiliary inductor according to any one of claims 1-2, characterized in that, The inverter employs unipolar modulation, achieving power frequency switching through one bridge arm and high-frequency switching through the other bridge arm. The modulation method includes the following steps: During the positive half-cycle of the power frequency, when the bridge arm consisting of switches S1 and S2 switches at power frequency, or when the bridge arm consisting of switches S3 and S4 switches at high frequency, or when the bridge arm consisting of switches S3 and S4 switches at power frequency, or when the bridge arm consisting of switches S1 and S2 switches at high frequency, the inverter contains a total of 6 operating states within one switching cycle, as follows: During the time period [0, t1], switches S1 and S3 are turned on, the inverter's main filter inductor and auxiliary inductor are connected in series, and the energy stored in the two inductors is transferred to the AC grid side. At this time, the current equation is as follows: ； During the time period [t1, t3], this is an extremely short period before the dead zone commutation of the high-frequency switching bridge arm. During this period, switches S1 and S3 are turned on, and auxiliary switch S5 is turned on at time t2. Since the inductor current cannot change abruptly, S5 achieves zero-current turn-on at this moment. The main filter inductor L is short-circuited by bidirectional switches S5 and S6, and the current flowing through the main filter inductor remains constant. The grid voltage V g Forced to flow through auxiliary inductor L a current i La The value decreases rapidly at time t2. La The current drops to zero, and then continues to decrease at the same slope until the switch S3 is turned off at time t3, at which point this stage ends. The current equations at this point are as follows: ； The time period [t3, t4] is the commutation dead zone between the high-frequency switch S3 turning off and S4 turning on, and the auxiliary inductor L... a current i La The voltage is less than zero. Before S4 turns on, its anti-parallel diode is turned on. Switch S4 turns on with zero voltage at time t4. At this time, the circuit equation is as follows: ； During the time period [t4, t6], switches S1 and S4 are turned on, and auxiliary switch S5 remains on. During this period, the DC side voltage V... DC With grid voltage V g The pressure difference between them forces the flow through the auxiliary inductor L a current i La The auxiliary inductance L increases rapidly until time t6. a current i La The current i of the main filter inductor L L Similarly, this stage ends, and at this point, the current equations are as follows: ； During the time period [t6, t7], switches S1 and S4 are turned on. At time t6, the auxiliary inductor current is the same as the main filter inductor current. The anti-parallel diode D of switch S6... S6 Reverse cutoff, auxiliary inductor L a When connected in series with the main filter inductor L in the AC circuit, during this stage, the auxiliary switch S5 can achieve zero-current turn-off at any time. At this time, the current equation is as follows: ； During the time period [t7, t8], this stage is the commutation dead zone between the turn-off of high-frequency switch S4 and the turn-on of S3. Since the inductor current is greater than zero, switch S3 meets the zero-voltage turn-on condition and achieves ZVS turn-on at time t8. At this time, the circuit equation is as follows: ； When the power grid is operating in the negative half-cycle of the power frequency, the analysis is similar based on the symmetry of the inverter's operating modes; since the inverter energy can be bidirectionally controlled through a bidirectional switch, the analysis is similar when the inverter is operating in rectification mode, based on the symmetry of the inverter's operating modes.

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