A three-phase soft-switching inverter and its operation control strategy

Abstract

The present invention discloses a three-phase soft-switching inverter and its operation control strategy. The inverter is used to drive a three-phase AC load and includes a DC power supply connected in parallel in sequence, a DC side filter capacitor, a three-phase auxiliary inverter switch tube circuit composed of auxiliary switch tubes, and a three-phase main inverter switch tube circuit composed of main switch tubes, and a first-phase commutation inductor, a second-phase commutation inductor, and a third-phase commutation inductor respectively connected between the corresponding bridge arms of the three-phase auxiliary inverter switch tube circuit and the three-phase main inverter switch tube circuit. The present invention utilizes the commutation inductor to buffer the current rise rate on the corresponding phase so that the corresponding auxiliary switch tube can achieve zero current switching, and can also be used as an energy storage element to create conditions for the corresponding main switch tube in the three-phase main inverter switch tube circuit to achieve soft switching action; at the same time, based on the twelve-sector space vector pulse width modulation method and load adaptive control, the switching loss of the inverter can be effectively reduced and the system efficiency can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of power electronic conversion, in particular to a three-phase soft-switch inverter and an operation control strategy thereof. Background Art

[0002] As we all know, three-phase non-isolated inverters have been widely used in many occasions such as uninterruptible power supply, communication power supply, motor drive, grid-connected power generation, etc. Traditional three-phase non-isolated inverters are generally based on hard switching. Due to low power density and large switching loss, they often need to work at a lower switching frequency, resulting in a larger size and weight of the inverter; at the same time, in applications with high requirements for inverter output performance, most of them need to increase the switching frequency of the inverter, but the further increase in switching frequency will further increase the switching loss. In addition, the spike voltage generated by hard switching is not only easy to cause secondary breakdown of the device, which will have an adverse effect on the safe operation of the system, but also will produce serious electromagnetic interference, affecting the insulation life and reliability of the system.

[0003] In view of this, in order to improve the efficiency, power density and system reliability of the inverter, the industry has proposed a variety of different types of three-phase non-isolated soft-switching inverter topology solutions, which are mainly divided into two categories: DC side auxiliary resonant circuit and AC side auxiliary resonant circuit; among them, the DC side auxiliary resonant circuit solution, when used in high-power occasions, needs to bear large conduction losses on the auxiliary components, so the efficiency improvement ability of the inverter is limited; and the AC side auxiliary resonant circuit solution usually has the problem of using more switching devices or other passive components, and cannot take into account the performance requirements of high efficiency and high power density.

[0004] Therefore, it is necessary to propose a more optimized solution to the problems existing in the existing three-phase non-isolated soft-switching inverter. Summary of the invention

[0005] In view of the deficiencies in the above-mentioned prior art, the first object of the present invention is to provide a three-phase soft-switching inverter; the second object of the present invention is to provide an operation control strategy based on the above-mentioned three-phase soft-switching inverter.

[0006] In order to achieve the above object, the first technical solution adopted by the present invention is:

[0007] A three-phase soft-switching inverter is used to drive a three-phase AC load, which includes a first-phase commutation inductor, a second-phase commutation inductor and a third-phase commutation inductor, a DC power supply connected in parallel step by step, a DC side filter capacitor, a three-phase auxiliary inverter switch tube circuit and a three-phase main inverter switch tube circuit;

[0008] One end of the first-phase commutation inductor is connected to the midpoint of the first bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the first bridge arm of the three-phase main inverter switch tube circuit, and the first phase of the three-phase AC load is connected to the midpoint of the first bridge arm of the three-phase main inverter switch tube circuit;

[0009] One end of the second-phase commutation inductor is connected to the midpoint of the second bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the second bridge arm of the three-phase main inverter switch tube circuit, and the second phase of the three-phase AC load is connected to the midpoint of the second bridge arm of the three-phase main inverter switch tube circuit;

[0010] One end of the third-phase commutation inductor is connected to the midpoint of the third bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the third bridge arm of the three-phase main inverter switch tube circuit. The third phase of the three-phase AC load is connected to the midpoint of the third bridge arm of the three-phase main inverter switch tube circuit.

[0011] Preferably, the three-phase auxiliary inverter switch tube circuit comprises a first auxiliary bridge arm, a second auxiliary bridge arm and a third auxiliary bridge arm each consisting of two auxiliary switch tubes, the two auxiliary switch tubes constituting the first auxiliary bridge arm are respectively a first-phase upper auxiliary switch tube and a first-phase lower auxiliary switch tube, the two auxiliary switch tubes constituting the second auxiliary bridge arm are respectively a second-phase upper auxiliary switch tube and a second-phase lower auxiliary switch tube, and the two auxiliary switch tubes constituting the third auxiliary bridge arm are respectively a third-phase upper auxiliary switch tube and a third-phase lower auxiliary switch tube;

[0012] The drain of the auxiliary switch tube on the first phase is simultaneously connected to the drain of the auxiliary switch tube on the second phase, the drain of the auxiliary switch tube on the third phase, the positive electrode of the DC power supply and the positive electrode of the DC side filter capacitor, the source of the auxiliary switch tube on the first phase is simultaneously connected to the source of the auxiliary switch tube on the second phase, the source of the auxiliary switch tube on the third phase, the negative electrode of the DC power supply and the negative electrode of the DC side filter capacitor, the source of the auxiliary switch tube on the first phase is simultaneously connected to the drain of the auxiliary switch tube on the first phase and one end of the first phase commutation inductor, the source of the auxiliary switch tube on the second phase is simultaneously connected to the drain of the auxiliary switch tube on the second phase and one end of the second phase commutation inductor, and the source of the auxiliary switch tube on the third phase is simultaneously connected to the drain of the auxiliary switch tube on the third phase and one end of the third phase commutation inductor;

[0013] The three-phase main inverter switch tube circuit comprises a first main bridge arm, a second main bridge arm and a third main bridge arm each consisting of two main switch tubes, wherein the two main switch tubes constituting the first main bridge arm are respectively a first-phase upper main switch tube and a first-phase lower main switch tube, the two main switch tubes constituting the second main bridge arm are respectively a second-phase upper main switch tube and a second-phase lower main switch tube, and the two main switch tubes constituting the third main bridge arm are respectively a third-phase upper main switch tube and a third-phase lower main switch tube;

[0014] The drain of the main switch tube on the first phase is simultaneously connected to the drain of the main switch tube on the second phase, the drain of the main switch tube on the third phase, the positive electrode of the DC power supply and the positive electrode of the DC side filter capacitor; the source of the main switch tube on the first phase is simultaneously connected to the source of the main switch tube on the second phase, the source of the main switch tube on the third phase, the negative electrode of the DC power supply and the negative electrode of the DC side filter capacitor; the source of the main switch tube on the first phase is simultaneously connected to the drain of the main switch tube on the first phase, the other end of the first phase commutation inductor and the first phase of the three-phase AC load; the source of the main switch tube on the second phase is simultaneously connected to the drain of the main switch tube on the second phase, the other end of the second phase commutation inductor and the second phase of the three-phase AC load; the source of the main switch tube on the third phase is simultaneously connected to the drain of the main switch tube on the third phase, the other end of the third phase commutation inductor and the third phase of the three-phase AC load.

[0015] Preferably, the auxiliary switch tube is a wide bandgap semiconductor device, and the main switch tube is a Si semiconductor device.

[0016] Preferably, the DC side filter capacitor includes at least one first capacitor group, and each of the first capacitor groups is formed by two first high-voltage ceramic capacitors connected in series.

[0017] Preferably, the DC side filter capacitor includes at least two first capacitor groups connected in parallel with each other; the midpoints of two adjacent first capacitor groups are connected to each other, or all the first capacitor groups are divided into two groups and the midpoints of two adjacent first capacitor groups in the same group are connected to each other.

[0018] Preferably, the DC side filter capacitor further includes at least one second high-voltage ceramic capacitor connected in parallel with the first capacitor group, and the capacity of the second high-voltage ceramic capacitor is smaller than the capacity of the first high-voltage ceramic capacitor.

[0019] The second technical solution adopted by the present invention is:

[0020] An operation control strategy of the aforementioned three-phase soft-switching inverter comprises:

[0021] S1. Based on the space vector pulse width modulation method and the space vector synthesized according to the inverter requirements, calculate the action time of each main switch tube corresponding to each phase of the three-phase AC load;

[0022] S2. Determine the auxiliary switch tube that needs to be activated in the corresponding phase according to the load current of the corresponding phase of the three-phase AC load and calculate the time for the auxiliary switch tube to activate according to Formula 1; Formula 1 is:

[0023]

[0024] Where Δt is the time difference between the main switch action time corresponding to a phase of the three-phase AC load and the auxiliary switch conduction time of the corresponding phase; L rx is the inductance value of the commutation inductor corresponding to a phase of the three-phase AC load, and x corresponds to the commutation inductor of the first phase, the second phase or the third phase; i y is the load current value of a phase of the three-phase AC load, y corresponds to the first phase, the second phase or the third phase of the three-phase AC load; V dc is the output voltage value of the DC power supply;

[0025] S3, turning on the auxiliary switch tube of the corresponding phase at a time Δt before the main switch tube corresponding to a phase of the three-phase AC load is actuated;

[0026] S4. Detect the load current of each phase of the three-phase AC load in real time.

[0027] Preferably, when it is detected that the current on the commutation inductor corresponding to a phase of the three-phase AC load is greater than the load current of the corresponding phase and the main switch tube of the phase is clamped to zero voltage, the main switch tube is turned on; when the main switch tube is turned on at zero voltage, the auxiliary switch tube of the corresponding phase is turned off simultaneously or with a delay of one to two control cycles.

[0028] Preferably, the space vector of the inverter is synthesized based on a twelve-sector space vector pulse width modulation method.

[0029] Due to the adoption of the above scheme, the present invention has the following advantages:

[0030] 1. The commutation inductor can be used to buffer the current rise rate on the corresponding phase so that the corresponding auxiliary switch tube can achieve zero current opening, and can also be used as an energy storage element to create conditions for the corresponding main switch tube in the three-phase main inverter switch tube circuit to achieve soft switching action.

[0031] 2. The twelve-sector space vector pulse width modulation method and load adaptive control method can realize dynamic adjustment of the peak current of the commutation inductor, effectively reduce the switching loss of the inverter and improve the working efficiency of the inverter system.

[0032] 3. Compared with the existing DC side auxiliary resonance scheme, since a large current does not flow through the commutation inductor for a long time, it can not only effectively reduce the loss on the inductor, but also reduce the size of the inverter and increase the power density of the inverter by selecting a smaller specification inductor. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a schematic diagram of a system application circuit according to an embodiment of the present invention;

[0034] Figure 2 It is a schematic diagram of twelve sectors when the embodiment of the present invention is applied in the system;

[0035] Figure 3 is a modulation rule chart corresponding to the twelve-sector partitions of an embodiment of the present invention;

[0036] Figure 4 is a schematic diagram of a first phase equivalent circuit of an embodiment of the present invention;

[0037] Figure 5 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 1;

[0038] Figure 6 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 2;

[0039] Figure 7 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 3;

[0040] Figure 8 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 4;

[0041] Fig. 9 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 5;

[0042] Fig.10 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 6;

[0043] Fig.11 is a schematic diagram of a single-phase equivalent circuit of an embodiment of the present invention during working mode 7;

[0044] Fig.12 It is a simulation waveform diagram of the time Δt and the peak current of the commutation inductor changing with the load current according to the embodiment of the present invention. DETAILED DESCRIPTION

[0045] The embodiments of the present invention are described in detail below with reference to the accompanying drawings, but the present invention can be implemented in many different ways as defined and covered by the claims.

[0046] like Figures 1 to 12 As shown, this embodiment provides a three-phase soft-switching inverter, which is used to drive a three-phase AC load Load, and mainly includes:

[0047] A three-phase auxiliary inverter switch tube circuit, comprising a first bridge arm, a second bridge arm and a third bridge arm;

[0048] A three-phase main inverter switch circuit, comprising a first bridge arm, a second bridge arm and a third bridge arm;

[0049] DC power supply V dc And the DC side filter capacitor C dc , DC power supply V dc , DC side filter capacitor C dc , the three-phase auxiliary inverter switch tube circuit and the three-phase main inverter switch tube circuit are connected in parallel in a step-by-step sequence; wherein the DC power supply V dc Mainly used to provide driving power for three-phase AC load Load, DC side filter capacitor C dc It is mainly used to buffer the instantaneous power difference between the AC and DC sides and filter out high-frequency ripples. The three-phase auxiliary inverter switch tube circuit is mainly used to control and transfer the current on the three-phase main inverter switch tube circuit to assist in realizing the soft switching action of the three-phase main inverter switch tube circuit, while the three-phase main inverter switch tube circuit mainly realizes the output control of the three-phase AC load Load through its switch on and off action;

[0050] The first phase commutation inductor L r1 , one end of which is connected to the midpoint of the first bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the first bridge arm of the three-phase main inverter switch tube circuit, and the first phase of the three-phase AC load Load is connected to the midpoint of the first bridge arm of the three-phase main inverter switch tube circuit; the first phase commutation inductor L r1 Under the control of the switch tube in the first bridge arm of the three-phase auxiliary inverter switch tube circuit, the charge-discharge conversion action is performed, so as to provide a condition for the zero current conduction of the switch tube in the first bridge arm of the three-phase auxiliary inverter switch tube circuit by buffering the current rise rate, and at the same time, it acts as an energy storage element to provide a condition for the zero voltage conduction of the switch tube in the first bridge arm of the three-phase main inverter switch tube circuit;

[0051] The second phase commutation inductor L r2 , one end of which is connected to the midpoint of the second bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the second bridge arm of the three-phase main inverter switch tube circuit, and the second phase of the three-phase AC load Load is connected to the midpoint of the second bridge arm of the three-phase main inverter switch tube circuit; the second phase commutation inductor L r2Under the control of the switch tube in the second bridge arm of the three-phase auxiliary inverter switch tube circuit, the charge-discharge conversion action is performed, so as to provide a condition for the zero current conduction of the switch tube in the second bridge arm of the three-phase auxiliary inverter switch tube circuit by buffering the current rise rate, and at the same time, it serves as an energy storage element to provide a condition for the zero voltage conduction of the switch tube in the second bridge arm of the three-phase main inverter switch tube circuit;

[0052] as well as

[0053] A third phase commutation inductor L r3 , one end of which is connected to the midpoint of the third bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the third bridge arm of the three-phase main inverter switch tube circuit, and the third phase of the three-phase AC load Load is connected to the midpoint of the third bridge arm of the three-phase main inverter switch tube circuit; the third phase commutation inductor L r3 The charge-discharge conversion action is performed under the control of the switch tube in the third bridge arm of the three-phase auxiliary inverter switch tube circuit, thereby providing conditions for zero current conduction of the switch tube in the third bridge arm of the three-phase auxiliary inverter switch tube circuit by buffering the current rise rate, and at the same time, serving as an energy storage element to provide conditions for zero voltage conduction of the switch tube in the third bridge arm of the three-phase main inverter switch tube circuit.

[0054] Thus, when the inverter of this embodiment is used to drive and control the three-phase AC load Load, by adding a commutation inductor between the corresponding bridge arm (or corresponding phase) of the three-phase auxiliary inverter switch tube circuit and the three-phase main inverter switch tube circuit, not only can the commutation inductor be used to buffer the current rise rate on the corresponding phase so that the corresponding auxiliary switch tube in the three-phase auxiliary inverter switch tube circuit can achieve zero current switching, but also the commutation inductor is used as an energy storage element to create conditions for the corresponding main switch tube in the three-phase main inverter switch tube circuit to achieve soft switching action; in actual application, using the system architecture of the inverter of this embodiment, a load adaptive control method can be used to achieve dynamic adjustment of the peak current on the commutation inductor, which not only creates conditions for selecting a commutation inductor with a smaller volume and inductance, but also can avoid the phenomenon of a large current flowing through the commutation inductor for a long time as much as possible, thereby, compared with the existing DC side auxiliary resonance scheme, it can not only effectively improve the efficiency of the inverter application system by reducing the loss of the commutation inductor, but also reduce the volume of the inverter and improve the power density of the inverter.

[0055] In order to optimize the system circuit structure of the entire inverter to the maximum extent, the three-phase auxiliary inverter switch tube circuit and the three-phase main inverter switch tube circuit of this embodiment may preferably have the following specific structure, namely:

[0056] The three-phase auxiliary inverter switch tube circuit includes a first auxiliary bridge arm, a second auxiliary bridge arm and a third auxiliary bridge arm, each of which is composed of two auxiliary switch tubes. The two auxiliary switch tubes constituting the first auxiliary bridge arm are respectively the auxiliary switch tube S on the first phase X1 and the first phase lower auxiliary switch tube S X2 The two auxiliary switch tubes constituting the second auxiliary bridge arm are the second phase upper auxiliary switch tube S X3 and the second phase auxiliary switch tube S X4 The two auxiliary switch tubes constituting the third auxiliary bridge arm are the third phase upper auxiliary switch tube S X5 And the third phase auxiliary switch tube S X6 ; Among them, the auxiliary switch tube S on the first phase X1 The drain of the second phase is connected to the auxiliary switch S X3 The drain of the third phase auxiliary switch tube S X5 Drain, DC power supply V dc The positive pole and DC side filter capacitor C dc The positive electrode of the first phase is connected to the auxiliary switch tube S X2 The source of the second phase auxiliary switch S X4 The source of the third phase auxiliary switch tube S X6 The source, DC power supply V dc The negative pole and DC side filter capacitor C dc The negative pole of the first phase is connected to the auxiliary switch tube S X1 The source of the first phase auxiliary switch S X2 The drain and the first phase commutation inductor L r1 The auxiliary switch tube S on the second phase X3 The source of the second phase auxiliary switch S X4 The drain and the second phase commutation inductor L r2 The auxiliary switch tube S on the third phase X5 The source of the third phase auxiliary switch S X6 The drain and the third phase commutation inductor L r3 One end is connected;

[0057] The three-phase main inverter switch tube circuit includes a first main bridge arm, a second main bridge arm and a third main bridge arm respectively composed of two main switch tubes, wherein the two main switch tubes constituting the first main bridge arm are respectively the first phase upper main switch tube S1 and the first phase lower main switch tube S2, the two main switch tubes constituting the second main bridge arm are respectively the second phase upper main switch tube S3 and the second phase lower main switch tube S4, and the two main switch tubes constituting the third main bridge arm are respectively the third phase upper main switch tube S5 and the third phase lower main switch tube S6; wherein the drain of the first phase upper main switch tube S1 is simultaneously connected to the drain of the second phase upper main switch tube S3, the drain of the third phase upper main switch tube S5, and the DC power supply V dc The positive pole and DC side filter capacitor C dc The source of the main switch tube S2 under the first phase is connected to the source of the main switch tube S4 under the second phase, the source of the main switch tube S6 under the third phase, and the DC power supply V dc The negative pole and DC side filter capacitor C dc The source of the first phase upper main switch tube S1 is connected to the drain of the first phase lower main switch tube S2 and the first phase commutation inductor L r1 The other end of the three-phase AC load Load is connected to the first phase, and the source of the second phase main switch tube S3 is connected to the drain of the second phase main switch tube S4 and the second phase commutation inductor L r2 The other end of the three-phase AC load Load is connected to the second phase, and the source of the third-phase upper main switch tube S5 is connected to the drain of the third-phase lower main switch tube S6 and the third-phase commutation inductor L r3 The other end of the three-phase AC load is connected to the third phase of the three-phase AC load Load. It should be noted that all auxiliary switch tubes and main switch tubes are anti-parallel connected with diodes.

[0058] In this way, during the operation of the inverter, the auxiliary switch tube S on the first phase can be used to X1 To control the first phase commutation inductor L r1 The charging and discharging process is used to transfer the current in the main switch tube S2 of the first phase, thereby providing conditions for the zero voltage conduction of the main switch tube S1 of the first phase; the auxiliary switch tube S X2 To control the first phase commutation inductor L r1 The charging and discharging process is to transfer the current in the main switch tube S1 of the first phase, thereby providing conditions for the zero voltage conduction of the main switch tube S2 of the first phase; and the first phase commutation inductor L r1 The buffer current rise rate is used to provide the auxiliary switch S on the first phase. X1 and the first phase lower auxiliary switch tube S X2The conditions for zero current switching are provided, and the conditions for zero voltage switching of the main switch tube S1 on the first phase and the main switch tube S2 on the first phase are provided by serving as an energy storage element; the switch tubes and commutation inductors associated with the second and third phases of the three-phase AC load Load play the same role as the first phase in the corresponding phase, and the principle is not repeated here.

[0059] In order to improve the power density of the inverter, a commutation inductor with a smaller inductance is usually selected, which results in a higher current di / dt passing through the coil in the commutation inductor. In view of the fact that conventional switching tubes made of Si semiconductor materials are difficult to withstand higher di / dt; therefore, in order to maximize the performance of the entire inverter and comprehensively consider the inverter cost factors, as a preferred solution, the auxiliary switching tube of this embodiment is preferably a wide bandgap semiconductor device with higher saturated electron drift velocity, higher critical breakdown field strength, better high temperature tolerance and other properties, while the main switching tube is preferably a Si semiconductor device with a smaller on-resistance, thereby forming a hybrid device structure of the inverter circuit.

[0060] In order to effectively buffer the instantaneous power difference between the AC and DC sides, the DC side filter capacitor C dc It includes at least one first capacitor group, each of which is composed of two first high-voltage ceramic capacitors connected in series (as a preferred solution, the DC side filter capacitor C dc It includes at least two first capacitor groups connected in parallel; the midpoints of two adjacent first capacitor groups are connected to each other, or all the first capacitor groups are divided into two groups and the midpoints of two adjacent first capacitor groups in the same group are connected to each other, which is beneficial to improve the reliability of the capacitor group and take into account the layout design of the circuit board. In order to effectively filter out the high-frequency ripple in the inverter, the DC side filter capacitor C dc At least one second high-voltage ceramic capacitor can be arranged in parallel with the first capacitor group, and it is best to ensure that the capacity of the second high-voltage ceramic capacitor is smaller than that of the first high-voltage ceramic capacitor. In addition, since all capacitors are ceramic capacitors, it is also beneficial to improve the power density of the inverter.

[0061] In addition, in order to maximize the working efficiency of the inverter system, the following selection ideas can be referred to when selecting the key components that constitute the inverter. Specifically: Since the conduction time of the auxiliary switch tube is relatively short, it is best to focus on selecting devices with better switching parameters when selecting the auxiliary switch tube to reduce the switching loss of the auxiliary switch tube, while the parameters of the conduction loss can be considered second; since the conduction time of the main switch tube is relatively long, and in view of the zero voltage conduction requirement of the main switch tube, when selecting the main switch tube, the device parameters in terms of conduction loss are given priority, and the parameters in terms of switching loss are considered second.

[0062] Based on the system structure of the aforementioned three-phase soft-switching inverter and the roles that its components can play, an embodiment of the present invention further provides an operation control strategy for the aforementioned three-phase soft-switching inverter, which includes:

[0063] S1. Based on the space vector pulse width modulation method and the space vector synthesized according to the inverter needs, calculate the action time of each main switch tube corresponding to each phase of the three-phase AC load Load;

[0064] S2. Determine the auxiliary switch tube that needs to be activated in the corresponding phase according to the load current of the corresponding phase of the three-phase AC load Load and calculate the time for the auxiliary switch tube to activate according to Formula 1; Formula 1 is:

[0065]

[0066] Where Δt is the time difference between the main switch action time corresponding to a phase of the three-phase AC load Load and the conduction time of the auxiliary switch tube of the corresponding phase; L rx is the inductance value of the commutation inductance corresponding to a phase of the three-phase AC load Load, and x corresponds to the commutation inductance of the first phase, the second phase or the third phase; i y is the load current value of a phase of the three-phase AC load Load, and y corresponds to the first phase, the second phase or the third phase of the three-phase AC load Load; V dc is the output voltage value of the DC power supply;

[0067] S3, turning on the auxiliary switch tube of the corresponding phase at the time Δt before the main switch tube corresponding to a phase of the three-phase AC load Load is actuated;

[0068] S4, real-time detection of the load current on each phase of the three-phase AC load Load.

[0069] Therefore, by utilizing the principle of space vector pulse width modulation, the auxiliary switch tube of the corresponding phase is turned on at time Δt before the main switch tube that needs to assist in realizing soft switching is actuated. The time Δt will change with the change of load current. At this time, the charging time of the commutation inductor can be dynamically adjusted by detecting the load current, thereby realizing dynamic adjustment of the peak current of the commutation inductor and realizing load adaptive control, which can effectively reduce the loss of the commutation inductor and further improve the system efficiency of the inverter.

[0070] In order to further optimize the control strategy of the inverter, when it is detected that the current on the commutation inductor corresponding to a phase of the three-phase AC load Load is greater than the load current of the corresponding phase, the anti-parallel diode on the main switch tube of the corresponding phase that needs to assist in realizing soft switching will be turned on, so that the main switch tube is clamped to zero voltage. At this time, the main switch tube (it should be noted that: the switch tube should be turned on as soon as possible, otherwise, when the current on the commutation inductor of the corresponding phase drops below the load current of the corresponding phase, the parasitic capacitance on the switch tube will be reversely charged, and the zero voltage turn-on of the switch tube cannot be achieved) ; When the main switch is turned on at zero voltage, the auxiliary switch of the corresponding phase is turned off at the same time or with a delay of one to two control cycles (mainly because after the main switch is turned on, the potential difference across the commutation inductor will drop to and approach zero, so it is best to turn off the auxiliary switch as soon as possible). In this way, a large current will not flow through the commutation inductor of the corresponding phase for a long time, and the current will be commutated to the anti-parallel diode of another auxiliary switch in the same bridge arm (i.e., the same phase). As the current flowing through the commutation inductor gradually decreases, the anti-parallel diode of the aforementioned auxiliary switch can achieve a natural zero current shutdown. It should be noted that when designing the control strategy, the auxiliary switch cannot be turned off too early before the corresponding main switch is turned on. Otherwise, if the current on the corresponding commutation inductor drops below the load current when the main switch is turned on, the parasitic capacitance of the main switch will be fully charged again, causing the main switch to lose the condition for zero voltage conduction.

[0071] In order to reduce the number of auxiliary switch tube actions, reduce losses and improve efficiency, the control strategy of this embodiment is preferably based on the twelve-sector space vector pulse width modulation method to synthesize the space vector of the inverter. As a result, in each switching cycle, the auxiliary switch tube only needs to act once, effectively reducing the corresponding losses, and there is no need to use traditional seven-segment space vector pulse width modulation methods, because in each switching cycle, the auxiliary switch tube needs to act three times, which leads to the problem of too many auxiliary switch tube actions.

[0072] In summary, since space vector pulse width modulation is used to control the inverter, the action time of each main switch tube can be calculated according to the space vector that the inverter needs to synthesize, and then the auxiliary switch tube that needs to be activated and the action time of the auxiliary switch tube can be determined according to the size and direction of the corresponding phase load current; the auxiliary switch tube should be turned on at the time Δt before the action of the main switch tube that needs to assist in realizing soft switching, and the auxiliary commutation inductor should be charged in advance, so as to transfer the current of the main switch tube that needs to assist in realizing soft switching to another main switch tube on the same bridge arm, and ensure the zero voltage conduction of the main switch tube; at the same time, based on the formed load adaptive control method, the efficiency of the system can be effectively improved.

[0073] In order to more clearly explain the principle of the entire control strategy and the technical effects that can be obtained, the control strategy of this embodiment is further explained by explaining the rules of twelve-sector space vector pulse width modulation and analyzing the working conditions of each mode of the inverter (it should be pointed out that only the following is given as follows Figure 4 The equivalent schematic diagram of the single-phase (a phase, i.e., the first phase) circuit shown and the current is referenced to the positive direction and Figures 5 to 11 Shown Figure 4 The equivalent schematic diagram in the working mode equivalent circuit diagram when the load current is positive in one switching cycle; the current is negative and the three-phase circuit can be deduced based on this, and no further details are given below; and if there are processes or parameters that are not particularly described in detail below, they can be understood or implemented by those skilled in the art with reference to the prior art), specifically:

[0074] like Figure 2 The control strategy shown in the diagram is divided into sectors and Figure 3 The corresponding switch sequence modulation rules shown in the figure show that in the modulation rules, "1" represents that the upper tube of the bridge arm is turned on and the lower tube is turned off, "0" represents that the upper tube of the bridge arm is turned off and the lower tube is turned on; "100" represents that the upper tube of the first bridge arm is turned on, and the lower tubes of the second and third bridge arms are turned on, and so on. In this twelve-sector modulation strategy, in each switching cycle, the auxiliary switch tube only needs to act once, and at other times, the main switch tubes of the three bridge arms can achieve natural soft switching, unlike the traditional seven-segment space vector modulation strategy, because in one switching cycle, the auxiliary switch tube needs to act three times and multiple auxiliary main switches are needed to achieve soft switching.

[0075] Working mode 1 (such as Figure 5 Schematic diagram of a single-phase equivalent circuit during the conduction period of the main switch tube S2 in the first phase shown in FIG.

[0076] The main switch tube S2 under the first phase is turned on. Because the conduction time is short, the first phase current of the three-phase AC load Load is equivalent to a constant current source. The current flows out in the forward direction, passes through the source of the main switch tube S2 under the first phase, flows to the drain of the main switch tube S2 under the first phase, and then flows back.

[0077] Working mode 2 (such as Figure 6 The auxiliary switch tube S on the first phase shown X1 Single-phase equivalent circuit diagram when the main switch tube S2 of the first phase is turned on and not turned off):

[0078] The auxiliary switch S on the first phase is turned on at a time Δt before the main switch S1 on the first phase is turned on. X1 , due to the first phase commutation inductance L r1 The inductor current cannot change suddenly due to the existence of , so the auxiliary switch tube S on the first phase X1Zero current conduction. The first phase commutation inductor L r1 The current on V dc / L rx The slope of the current gradually increases. According to the KCL law, the current flowing through the first phase main switch tube S2 gradually decreases and gradually transfers to the first phase commutation inductor L r1 superior.

[0079] Working mode 3 (such as Figure 7 The auxiliary switch tube S in the first phase is shown X1 Schematic diagram of a single-phase equivalent circuit during the period when the first phase main switch tube S1 is turned on, the anti-parallel diode of the first phase main switch tube S1 is not turned on, and the first phase main switch tube S2 is turned off):

[0080] Before the current of the first phase main switch tube S2 drops to zero, the first phase main switch tube S2 is turned off, and the current of the first phase main switch tube S2 is transferred to its anti-parallel diode; when the first phase commutation inductor L r1 When the current on the first phase rises to be equal to the current of the first phase of the three-phase AC load Load, the main switch tube S2 under the first phase is naturally turned off at zero current; then, the parasitic capacitance of the main switch tube S2 under the first phase is charged, and its drain and source voltages gradually increase; and at the same time, the parasitic capacitance of the main switch tube S1 on the first phase is discharged, so that its drain and source voltages gradually decrease.

[0081] Working mode 4 (such as Figure 8 The auxiliary switch tube S in the first phase is shown X1 Single-phase equivalent circuit diagram during the period when the main switch tube S2 is turned on and the first phase is turned off):

[0082] When the drain and source voltage of the main switch tube S1 on the first phase drops to zero, its anti-parallel diode is turned on. After the anti-parallel diode of the main switch tube S1 on the first phase is turned on, the main switch tube S1 on the first phase can be turned on with zero voltage, and the auxiliary switch tube S1 on the first phase can be turned off with zero voltage. X1 The auxiliary switch tube S on the first phase X1 It cannot be turned off too early before the main switch S1 on the first phase is turned on, otherwise, the first phase commutation inductor L r1 The current on the first phase will drop rapidly and may drop to a level lower than the current of the first phase of the three-phase AC load Load, resulting in a problem in which the current reversely charges the parasitic capacitance of the main switch tube S1 on the first phase, causing the main switch tube S1 on the first phase to be unable to achieve soft switching; in addition, the auxiliary switch tube S1 on the first phase X1 It is also not advisable to shut down the main switch S1 on the first phase for too long after it is turned on, otherwise the first phase commutation inductor L r1 When a large current flows through the capacitor for a long time, the loss will increase.

[0083] Working mode 5 (such as Fig. 9The auxiliary switch tube S in the first phase is shown X1 Turn off the auxiliary switch tube S of the first phase X2 Schematic diagram of the single-phase equivalent circuit when the anti-parallel diode is not conducting and the main switch tube S1 of the first phase is conducting):

[0084] The main switch tube S1 on the first phase is turned on, and the current is transferred from its anti-parallel diode to the main switch tube S1 on the first phase itself; at the same time, the auxiliary switch tube S1 on the first phase X1 The capacitor starts to charge and the auxiliary switch S on the first phase X1 The voltage across the drain and source of the first phase begins to rise; and the auxiliary switch tube S X2 The parasitic capacitance begins to discharge, and the voltage across the drain and source begins to drop.

[0085] Working mode 6 (such as Fig.10 The auxiliary switch tube S in the first phase is shown X1 Turn off the auxiliary switch tube S of the first phase X2 Schematic diagram of the single-phase equivalent circuit when the anti-parallel diode is turned on and the main switch S1 on the first phase is turned on):

[0086] When the auxiliary switch tube S of the first phase X2 When the drain and source voltages of the first phase are zero, the auxiliary switch S X2 The anti-parallel diode is turned on, then the DC power supply V dc Reversely add the first phase commutation inductor L r1 On the first phase, the commutation inductor L r1 The current on the first phase decreases rapidly until it reaches zero, and the auxiliary switch tube S X2 The anti-parallel diode realizes natural soft turn-off.

[0087] Working mode 7 (such as Fig.11 The auxiliary switch tube S in the first phase is shown X2 Schematic diagram of the single-phase equivalent circuit when the anti-parallel diode is turned off and the main switch S1 on the first phase is turned on):

[0088] The first phase lower auxiliary switch tube S X2 After shutdown, the current no longer flows from the first phase commutation inductor L r1 Feedback to the DC power supply V through the main switch tube S1 on the first phase dc , but from the DC power supply V dc Starting from the positive electrode, it flows forward through the main switch tube S1 on the first phase, then flows through the first phase of the three-phase AC load Load, and finally flows back to the DC power supply V dc of the negative electrode.

[0089] In addition, through Fig.12The simulated waveforms of the time Δt and the peak current of the commutation inductor in the inverter system shown in the figure change with the load current (in the figure, the first two lines are the control signals of the main switch tube and the auxiliary switch tube of the a phase, the load current of the a phase and the commutation inductor L of the first phase r1 The last two lines are the control signals of the c-phase main switch and auxiliary switch, as well as the c-phase load current and the third-phase commutation inductor L r3 From the analysis of the current), we can see that the load current of phase a is about 70A, the load current of phase c is about 50A, and the time Δt required for the zero voltage turn-on of the main switch tube increases with the increase of load current. At the same time, the peak current of the auxiliary commutation inductor also changes accordingly, thereby realizing the current adaptive control of the commutation inductor in the inverter.

[0090] The above embodiments are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for controlling the operation of a three-phase soft-switching inverter, wherein the three-phase soft-switching inverter comprises a first-phase commutation inductor (Lr1), a second-phase commutation inductor (Lr2), and a third-phase commutation inductor (Lr3), and a DC power supply (Vdc) connected in parallel in sequence, a DC side filter capacitor (Cdc), a three-phase auxiliary inverter switch tube circuit, and a three-phase main inverter switch tube circuit; One end of the first-phase commutation inductor (Lr1) is connected to the midpoint of the first bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the first bridge arm of the three-phase main inverter switch tube circuit, and the first phase of the three-phase AC load (Load) is connected to the midpoint of the first bridge arm of the three-phase main inverter switch tube circuit; One end of the second-phase commutation inductor (Lr2) is connected to the midpoint of the second bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the second bridge arm of the three-phase main inverter switch tube circuit, and the second phase of the three-phase AC load (Load) is connected to the midpoint of the second bridge arm of the three-phase main inverter switch tube circuit; One end of the third-phase commutation inductor (Lr3) is connected to the midpoint of the third bridge arm of the three-phase auxiliary inverter switch tube circuit, and the other end is connected to the midpoint of the third bridge arm of the three-phase main inverter switch tube circuit, and the third phase of the three-phase AC load (Load) is connected to the midpoint of the third bridge arm of the three-phase main inverter switch tube circuit; Features: The operation control method comprises: S1. Based on the space vector pulse width modulation method and the space vector synthesized according to the inverter needs, calculate the action time of each main switch tube corresponding to each phase of the three-phase AC load (Load); S2. According to the load current of the corresponding phase of the three-phase AC load (Load), the auxiliary switch tube that needs to be activated in the corresponding phase is determined, and the time for the auxiliary switch tube to be activated is calculated according to Formula 1; Formula 1 is: In the formula, The time difference between the action time of the upper switch tube of a phase of the three-phase AC load and the upper auxiliary switch tube of the corresponding phase, or the action time of the lower switch tube of a phase and the conduction time of the lower auxiliary switch tube of the corresponding phase is the inductance value of the commutation inductor corresponding to a phase of the three-phase AC load (Load), Corresponding to the first phase, second phase or third phase commutation inductor; is the load current value of one phase of the three-phase AC load (Load), Corresponding to the first phase, second phase or third phase of the three-phase AC load (Load); is the output voltage value of the DC power supply; S3, before the switch tube on a phase of the three-phase AC load (Load) acts The upper auxiliary switch tube of the corresponding phase is turned on at any time, or the lower switch tube of a phase is turned on before the action Turn on the lower auxiliary switch tube of the corresponding phase at all times; S4. Detect the load current of each phase of the three-phase AC load (Load) in real time.

2. The operation control method of a three-phase soft-switching inverter according to claim 1, characterized in that: The three-phase auxiliary inverter switch tube circuit comprises a first auxiliary bridge arm, a second auxiliary bridge arm and a third auxiliary bridge arm, each of which is composed of two auxiliary switch tubes. The two auxiliary switch tubes constituting the first auxiliary bridge arm are respectively a first-phase upper auxiliary switch tube (SX1) and a first-phase lower auxiliary switch tube (SX2). The two auxiliary switch tubes constituting the second auxiliary bridge arm are respectively a second-phase upper auxiliary switch tube (SX3) and a second-phase lower auxiliary switch tube (SX4). The two auxiliary switch tubes constituting the third auxiliary bridge arm are respectively a third-phase upper auxiliary switch tube (SX5) and a third-phase lower auxiliary switch tube (SX6). The drain of the auxiliary switch tube (SX1) on the first phase is simultaneously connected to the drain of the auxiliary switch tube (SX3) on the second phase, the drain of the auxiliary switch tube (SX5) on the third phase, the positive electrode of the DC power supply (Vdc) and the positive electrode of the DC side filter capacitor (Cdc); the source of the auxiliary switch tube (SX2) on the first phase is simultaneously connected to the source of the auxiliary switch tube (SX4) on the second phase, the source of the auxiliary switch tube (SX6) on the third phase, the negative electrode of the DC power supply (Vdc) and the negative electrode of the DC side filter capacitor (Cdc); the source of the auxiliary switch tube (SX1) on the first phase is simultaneously connected to the drain of the auxiliary switch tube (SX2) on the first phase and one end of the first phase commutation inductor (Lr1); the source of the auxiliary switch tube (SX3) on the second phase is simultaneously connected to the drain of the auxiliary switch tube (SX4) on the second phase and one end of the second phase commutation inductor (Lr2); the source of the auxiliary switch tube (SX5) on the third phase is simultaneously connected to the drain of the auxiliary switch tube (SX4) on the second phase and one end of the second phase commutation inductor (Lr2); ) is connected to the drain of the auxiliary switch tube (SX6) of the third phase and one end of the third phase commutation inductor (Lr3); The three-phase main inverter switch tube circuit comprises a first main bridge arm, a second main bridge arm and a third main bridge arm, each of which is composed of two main switch tubes. The two main switch tubes constituting the first main bridge arm are respectively a first-phase upper main switch tube (S1) and a first-phase lower main switch tube (S2). The two main switch tubes constituting the second main bridge arm are respectively a second-phase upper main switch tube (S3) and a second-phase lower main switch tube (S4). The two main switch tubes constituting the third main bridge arm are respectively a third-phase upper main switch tube (S5) and a third-phase lower main switch tube (S6). The drain of the first-phase main switch tube (S1) is simultaneously connected to the drain of the second-phase main switch tube (S3), the drain of the third-phase main switch tube (S5), the positive electrode of the DC power supply (Vdc) and the positive electrode of the DC side filter capacitor (Cdc); the source of the first-phase main switch tube (S2) is simultaneously connected to the source of the second-phase main switch tube (S4), the source of the third-phase main switch tube (S6), the negative electrode of the DC power supply (Vdc) and the negative electrode of the DC side filter capacitor (Cdc); the source of the first-phase main switch tube (S1) is simultaneously connected to the source of the first-phase main switch tube (S4), the source of the third-phase main switch tube (S6), the negative electrode of the DC power supply (Vdc) and the negative electrode of the DC side filter capacitor (Cdc). The drain of the main switch tube (S2), the other end of the first phase commutation inductor (Lr1) and the first phase of the three-phase AC load (Load) are connected, the source of the main switch tube (S3) on the second phase is simultaneously connected to the drain of the main switch tube (S4) under the second phase, the other end of the second phase commutation inductor (Lr2) and the second phase of the three-phase AC load (Load), and the source of the main switch tube (S5) on the third phase is simultaneously connected to the drain of the main switch tube (S6) under the third phase, the other end of the third phase commutation inductor (Lr3) and the third phase of the three-phase AC load (Load).

3. The operation control method of a three-phase soft-switching inverter according to claim 2, characterized in that: The auxiliary switch tube is a wide bandgap semiconductor device, and the main switch tube is a Si semiconductor device.

4. The operation control method of a three-phase soft-switching inverter according to claim 2, characterized in that: The DC side filter capacitor (Cdc) includes at least one first capacitor group, and each of the first capacitor groups is formed by two first high-voltage ceramic capacitors connected in series.

5. The operation control method of a three-phase soft-switching inverter according to claim 4, characterized in that: The DC side filter capacitor (Cdc) includes at least two first capacitor groups connected in parallel with each other; the midpoints of two adjacent first capacitor groups are connected with each other, or all the first capacitor groups are divided into two groups and the midpoints of two adjacent first capacitor groups in the same group are connected with each other.

6. The operation control method of a three-phase soft-switching inverter according to claim 4, characterized in that: The DC side filter capacitor (Cdc) also includes at least one second high-voltage ceramic capacitor connected in parallel with the first capacitor group, and the capacity of the second high-voltage ceramic capacitor is smaller than the capacity of the first high-voltage ceramic capacitor.

7. The operation control method of a three-phase soft-switching inverter according to claim 1, characterized in that: When it is detected that the current on the commutation inductor corresponding to a phase of the three-phase AC load (Load) is greater than the load current of the corresponding phase and the main switch tube of the phase is clamped to zero voltage, the main switch tube is turned on; after the main switch tube is turned on at zero voltage, the auxiliary switch tube of the corresponding phase is turned off simultaneously or with a delay of one to two control cycles.

8. The operation control method of a three-phase soft-switching inverter according to claim 1, characterized in that: The space vector of the inverter is synthesized based on the twelve-sector space vector pulse width modulation method.

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