An off-grid inverter control method and device and off-grid inverter

Abstract

The application relates to an off-grid inverter control method and device and an off-grid inverter. The method comprises the following steps: when a load corresponding to the inverter contains a capacitive circuit, S1, acquiring an output voltage corresponding to the inverter in real time and judging whether the output voltage is zero; S2, when the output voltage is not zero, obtaining a target output current of the inverter according to a voltage difference between the output voltage and a preset reference voltage and a preset voltage control loop; S3, obtaining a current difference between an output current of the inverter and the target output current, and obtaining a duty cycle correction value according to the current difference and a preset current control loop; S4, obtaining an initial duty cycle of the inverter according to an input voltage of the inverter and the preset reference voltage, taking a sum of the duty cycle correction value and the initial duty cycle as a target duty cycle, and taking the target duty cycle to control the first power switch tube or the second power switch tube to be turned on and execute the step S1. The application can greatly improve the capacity of the inverter to carry RLC loads and capacitive loads, and improve the use experience of terminal users.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inverters, in particular to an off-grid inverter control method, device and off-grid inverter. BACKGROUND

[0002] The off-grid inverter is widely used in fields such as home standby power, emergency power supply and outdoor power supply, and can convert the electric energy in the battery into alternating current energy required by the load in the above application fields during the working process. The load capacity is a key indicator for evaluating the performance of an off-grid inverter, and the RLC load and capacitor load capacity is a key indicator for judging the load capacity of an off-grid inverter.

[0003] When the off-grid load is an RLC or capacitor load, the traditional control method can generally achieve 70% of the rated power output of the inverter, for example, a 1kVA inverter can only carry a 700VA RLC or capacitor load, which limits the use scenario of the inverter. SUMMARY

[0004] The technical problem to be solved by the present application is to provide an off-grid inverter control method, device and off-grid inverter to solve the above technical defects of the prior art.

[0005] The technical solution adopted by the present application to solve its technical problem is: constructing an off-grid inverter control method, the inverter includes a bridge circuit composed of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, wherein the first power switch tube and the second power switch tube are series-connected high-frequency tubes, the third power switch tube and the fourth power switch tube are series-connected low-frequency tubes, the input end of the bridge circuit is connected to the power input of the inverter, and the output end of the bridge circuit is used to connect the load of the inverter; the method comprises:

[0006] When the load corresponding to the inverter contains a capacitive circuit, the following steps are performed:

[0007] S1, the output voltage corresponding to the inverter is obtained in real time, and it is judged whether the output voltage is zero or not;

[0008] S2, when the output voltage is not zero, the target output current corresponding to the inverter is obtained according to the voltage difference between the output voltage and the preset reference voltage, and the preset voltage control loop, wherein the preset voltage control loop contains a first PI controller;

[0009] S3, the current difference between the output current corresponding to the inverter and the target output current is obtained, and the corresponding duty cycle correction value is obtained according to the current difference and the preset current control loop, wherein the preset current control loop contains a second PI controller;

[0010] S4, obtaining an initial duty ratio corresponding to the inverter according to the input voltage corresponding to the inverter and the preset reference voltage, taking a sum of the initial duty ratio and the duty ratio correction value as a target duty ratio, and controlling the first power switch tube or the second power switch tube to be turned on according to the target duty ratio and performing the step S1.

[0011] Preferably, in the embodiment of the off-grid inverter control method, the method further comprises:

[0012] S21, switching the third power switch tube or the fourth power switch tube to be turned on when the output voltage is zero.

[0013] Preferably, in the embodiment of the off-grid inverter control method, the method further comprises:

[0014] S0, obtaining an output voltage corresponding to the inverter in real time, judging whether the output voltage is mutated, and determining that a load corresponding to the inverter contains a capacitive circuit when the output voltage is mutated.

[0015] Preferably, in the embodiment of the off-grid inverter control method, the judging whether the output voltage is mutated comprises:

[0016] a voltage difference between the output voltage and a preset reference voltage, and judging that the output voltage is mutated when the voltage difference is not zero.

[0017] Preferably, in the embodiment of the off-grid inverter control method, the preset reference voltage is a standard sine wave.

[0018] Preferably, in the embodiment of the off-grid inverter control method, in the step S2, an expression of the first PI controller is PI1=Kpv*Err1+(Kiv / Ts)*Err1, PI1 is a target output current corresponding to the preset voltage control loop, Kpv and Kiv are constants, Ts is time, and Err1 is the voltage difference.

[0019] Preferably, in the embodiment of the off-grid inverter control method, in the step S3, an expression of the second PI controller is PI2=Kpi*Err2+(Kii / Ts)*Err2, wherein PI2 is the duty ratio correction value, Kpi and Kii are constants, Ts is time, and Err2 is the output current difference.

[0020] Preferably, in the embodiment of the off-grid inverter control method of the present application, the method further comprises: determining that the load corresponding to the inverter contains a capacitive circuit when the load corresponding to the inverter is an RLC load or a capacitive load.

[0021] The present application also provides an off-grid inverter control device for an inverter, the inverter comprising a bridge circuit composed of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, wherein the first power switch tube and the second power switch tube are series-connected high-frequency tubes, and the third power switch tube and the fourth power switch tube are series-connected low-frequency tubes; the control device comprising a module for executing the method as described above.

[0022] The present application also provides an off-grid inverter, comprising a bridge circuit composed of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, and a controller, wherein the first power switch tube and the second power switch tube are series-connected high-frequency tubes, and the third power switch tube and the fourth power switch tube are series-connected low-frequency tubes.

[0023] The controller is configured to execute the steps of the off-grid inverter control method as described above.

[0024] The off-grid inverter control method, device and inverter of the present application have the following advantages: without increasing the hardware cost, the capacity of the inverter to carry RLC loads and capacitive loads can be greatly improved, the types of loads applicable to the inverter are increased, the application range of the off-grid inverter is expanded, and the user experience is improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] The present application will be further described below with reference to the accompanying drawings and embodiments, in which:

[0026] Figure 1 is a partial circuit schematic diagram of a full-bridge inverter circuit;

[0027] Figure 2 is a signal relationship schematic diagram in a typical unipolar modulation process of a full-bridge inverter circuit;

[0028] Figure 3 is an inverter output voltage change schematic diagram in the off-grid inverter control method of the present application;

[0029] Figure 4 is a program flowchart of an embodiment of the off-grid inverter control method of the present application;

[0030] Figure 5 is a program flowchart of another embodiment of the off-grid inverter control method of the present application;

[0031] Figure 6 is a control process logical relationship diagram in a kind of off-grid inverter control method of the application. DETAILED DESCRIPTION

[0032] In order to have more clear understanding of the technical features, objects and effects of the present application, the specific embodiments of the present application will be described in detail with reference to the drawings.

[0033] The current typical full-bridge inverter circuit is as shown in Figure 1 The corresponding single-polarity modulation process of the full-bridge inverter circuit is as shown in Figure 2 The power tube Q1 and the power tube Q2 in the high-frequency arm work in high-frequency state, and the power tube Q3 and the power tube Q4 in the low-frequency arm work in low-frequency state. The general switching method of the power tube Q3 and the power tube Q4 in the low-frequency arm is to switch according to fixed frequency and time. As shown in Figure 2 That is, when Uinvref corresponds to the preset reference voltage from positive to negative zero-crossing time, the power tube Q4 is turned off, and the power tube Q3 is turned on; or when Uinvref is from negative to positive zero-crossing time, the power tube Q3 is turned off, and the power tube Q4 is turned on. UAB is the voltage on the inductor LInv. In this way, the power tube Q3 and the power tube Q4 in the low-frequency arm are switched when Uinvref is zero, and no large peak current is generated. When the off-grid inverter is put into a large RLC load or a capacitive load, it is assumed that the put-in time is t1, at this time, due to the voltage of the load capacitor being zero, the output voltage of the inverter will be pulled down (clamped), as shown in Figure 3 The solid line, if the power tube Q3 and the power tube Q4 in the low-frequency arm are still switched according to the original strategy of fixed frequency and time, that is, the switching time is t0, and at t0 time, due to the action of the control system, the actual output voltage of the inverter is generally no longer zero, as shown in Figure 3 The solid line, in this way, the switching of the power tube Q3 and the power tube Q4 in the low-frequency arm at the time when the output voltage is not zero will generate a large peak current. This current is uncontrollable, and is easy to trigger overcurrent protection, affecting the product use experience of the user. Therefore, the inverter using this control algorithm has poor ability to carry RLC load and capacitive load, and supports less load types.

[0034] Based on the above process, as shown in Figure 4 The present application provides an embodiment of an off-grid inverter control method. Wherein, the inverter structure is as shown in Figure 1As shown, the inverter comprises a bridge circuit composed of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, wherein the first power switch tube and the second power switch tube are high-frequency tubes connected in series, and the third power switch tube and the fourth power switch tube are low-frequency tubes connected in series. The input end of the bridge circuit is connected to the power input of the inverter, and the output end of the bridge circuit is used to connect the load of the inverter. It can be understood that the first power switch tube corresponds to the power tube Q1, the second power switch tube corresponds to the power tube Q2, the third power switch tube corresponds to the power tube Q3, and the fourth power switch tube corresponds to the power tube Q4.

[0035] In Figure 4 In an embodiment of the off-grid inverter control method of the present application, the specific method comprises the following steps: S1, acquiring the output voltage corresponding to the inverter in real time, and judging whether the output voltage is zero-crossing; S2, when the output voltage is not zero-crossing, obtaining the target output current corresponding to the inverter according to the voltage difference between the output voltage and the preset reference voltage and the preset voltage control loop, wherein the preset voltage control loop comprises a first PI controller; S3, obtaining the current difference between the output current corresponding to the inverter and the target output current, and obtaining the corresponding duty cycle correction value according to the current difference and the preset current control loop, wherein the preset current control loop comprises a second PI controller; S4, obtaining the initial duty cycle corresponding to the inverter according to the input voltage corresponding to the inverter and the preset reference voltage, taking the sum of the initial duty cycle and the duty cycle correction value as the target duty cycle, and controlling the first power switch tube or the second power switch tube to be turned on according to the target duty cycle and performing the step S1.

[0036] Based on the step S1 and the step S2, when it is judged that the load corresponding to the inverter comprises a capacitive circuit, when there is voltage input at the input end of the bridge circuit, the output voltage at the output end of the bridge circuit is monitored in real time to judge whether the output voltage is zero-crossing. When the output voltage is not zero-crossing, it is confirmed whether there is a deviation between the output voltage and the preset reference voltage, wherein the preset reference voltage can be understood as the standard voltage expected to be output by the inverter, and when there is a deviation between the actual output voltage of the bridge circuit and the preset reference voltage, the output voltage control process needs to be performed. The output voltage control process specifically comprises constructing a preset voltage control loop comprising a first PI controller, obtaining the target output current corresponding to the inverter through the voltage difference between the output voltage and the preset reference voltage, and adjusting the output voltage of the inverter to the direction close to the preset reference voltage through the target output current.

[0037] Based on step S3, after obtaining the target output current of the inverter based on the voltage deviation, the current deviation of the inverter is confirmed again. That is, the current difference between the actual measured output current of the inverter and the target output current is determined, and control is performed through a preset current control loop based on this current difference. The specific control process in the current control loop is implemented through a second PI controller. Specifically, the duty cycle correction value is obtained through the second PI controller, so as to correct the duty cycle of the high-frequency transistors in the bridge circuit and make the output current of the bridge circuit as close as possible to the target output current.

[0038] Based on step S4, the initial duty cycle of the control signal for the bridge circuit is calculated according to the input voltage and the preset reference voltage. The target duty cycle is then obtained by comparing the obtained duty cycle with the initial duty cycle. The drive signal for power transistor Q1 or Q2 is then obtained using the target duty cycle to control the conduction process of power transistor Q1 or Q2. The drive signals for power transistors Q1 and Q2 are complementary high-frequency signals.

[0039] This process allows the bridge circuit to gradually approach the preset reference voltage, ultimately enabling the inverter output to meet the requirements of the preset reference voltage.

[0040] like Figure 5 As shown, in one embodiment of the off-grid inverter control method of the present invention, the method further includes: S21, when the output voltage crosses zero, switching the third power switch or the fourth power switch to conduct. That is, when it is determined that the output voltage of the bridge circuit crosses zero, the corresponding switching power switch Q3 or power switch Q4 is turned on. The signals of power switch Q3 and power switch Q4 are complementary low-frequency signals.

[0041] like Figure 5 As shown, in one embodiment of the off-grid inverter control method of the present invention, it further includes: S0, acquiring the output voltage corresponding to the inverter in real time, determining whether the output voltage undergoes a sudden change, and determining that the load corresponding to the inverter contains a capacitive circuit when the output voltage undergoes a sudden change. Specifically, the determination result of whether the load of the bridge circuit contains a capacitive circuit can be obtained based on the output voltage change of the bridge circuit. That is, acquiring the output voltage corresponding to the inverter and determining whether the output voltage undergoes a sudden change; when the output voltage undergoes a sudden change, it is determined that the load corresponding to the inverter contains a capacitive circuit.

[0042] Further, the judging whether the output voltage is mutated includes that a voltage difference between the output voltage and a preset reference voltage is not zero, and the output voltage is judged to be mutated. Specifically, but not limited to, whether the output voltage of the bridge circuit is mutated is judged by the voltage difference between the output voltage and the preset reference voltage. That is, when the voltage difference is not equal to zero, it is indicated that the output voltage of the inverter is mutated. The preset reference voltage can be a standard sine wave.

[0043] Optionally, in an embodiment of the off-grid inverter control method, in the step S2, an expression of the first PI controller is PI1=Kpv*Err1+(Kiv / Ts)*Err1, PI1 is a target output current corresponding to the preset voltage control loop, Kpv and Kiv are constants, Ts is time, and Err1 is the voltage difference. The first PI controller is an inverter voltage controller, a given value is an inverter voltage given (sine wave), a feedback value is an inverter voltage sampling value, and a correction amount is generated through a PI loop. The correction amount is a current value, and an output of PI1 is used as a given value of PI2.

[0044] Optionally, in an embodiment of the off-grid inverter control method, in the step S3, an expression of the second PI controller is PI2=Kpi*Err2+(Kii / Ts)*Err2, wherein PI2 is the duty cycle correction value, Kpi and Kii are constants, Ts is time, and Err2 is the output current difference. The second PI controller is an inverter inductance current controller, a given value is an inverter current given value, a feedback value is an inverter current sampling value, and a correction amount is generated through a PI loop. The duty cycle is a duty cycle correction value, and a duty cycle is obtained after superposition of the feedforward.

[0045] As shown in FIG. 1, Figure 6 In a specific embodiment, a duty cycle feedforward output D1 is obtained according to Uinvref and Ubus, wherein D1=Uinvref / Ubus, Uinvref is an inverter reference voltage, i.e., a standard sine wave, and Ubus is a voltage provided by a graph Ubus, which can also be understood as a voltage between a direct current bus (BUS+, BUS-) of the inverter, i.e., an input voltage of the inverter. A target current output of the inverter is obtained through the first PI controller PI1. D2 is a duty cycle control loop output, which can also be understood as a preset voltage control loop, Uinv is a voltage of an inverter capacitor Cout in FIG. 2, i.e., an actual output voltage of the inverter. Iinv is an actual output current of the inverter. Figure 1 In a specific embodiment, a duty cycle feedforward output D1 is obtained according to Uinvref and Ubus, wherein D1=Uinvref / Ubus, Uinvref is an inverter reference voltage, i.e., a standard sine wave, and Ubus is a voltage provided by a graph Ubus, which can also be understood as a voltage between a direct current bus (BUS+, BUS-) of the inverter, i.e., an input voltage of the inverter. A target current output of the inverter is obtained through the first PI controller PI1. D2 is a duty cycle control loop output, which can also be understood as a preset voltage control loop, Uinv is a voltage of an inverter capacitor Cout in FIG. 2, i.e., an actual output voltage of the inverter. Iinv is an actual output current of the inverter. Figure 1The current on the middle Linv. D2 is obtained through the second PI controller PI2. The duty cycle D of the high-frequency arm is set so that D = D1 + D2. D1 enables Uinv to follow Uinvref, and D2 ensures that when subjected to large disturbances such as capacitive load switching, Uinv quickly recovers to the reference voltage Uinvref. For example... Figure 3 As shown, when an RLC load or capacitive load is applied at time t1, Uinv decreases, D1 decreases, and D2 is increased by controlling it, thus increasing D. After adjustment, Uinv increases and quickly recovers to follow Uinvref. During duty cycle control, the inverter's output voltage is monitored in real time, and the power frequency arm is switched based on whether the output voltage crosses zero. The power frequency arm is switched when the output voltage reaches zero. Figure 3 As shown, the switching time of the power frequency arm is modified from t0 to t2. During this process, the power switching transistor is controlled to switch at the zero-crossing point t2 of the output voltage based on the actual output voltage and loop regulation, in order to reduce inrush current. At the same time, it can also promptly change the high-frequency transistor drive when a sudden RLC or capacitor load is applied, reducing the impact of the sudden load.

[0046] Through the process of this invention, current distortion when the inverter is powered by an RLC load can be effectively reduced, significantly improving the inverter's ability to power RLC loads. This enables it to power higher-power electrical appliances, such as computers, televisions, and other devices powered by switching power supplies, as well as batteries in some electric vehicles.

[0047] Optionally, in one embodiment of the off-grid inverter control method of the present invention, the method further includes: determining that the load corresponding to the inverter contains a capacitive circuit when the load corresponding to the inverter is an RLC load or a capacitive load. That is, the load of the inverter can be directly determined to be either an RLC load or a capacitive load. If so, the load corresponding to the inverter can be directly identified as a capacitive load.

[0048] Furthermore, this invention provides an off-grid inverter control device for an inverter. The inverter includes a bridge circuit composed of a first power switch, a second power switch, a third power switch, and a fourth power switch. The first and second power switches are high-frequency transistors connected in series, and the third and fourth power switches are low-frequency transistors connected in series. The control device includes modules for executing the methods described above. Specifically, the control device has the function of implementing the corresponding steps performed in the above methods. Each function can be implemented by hardware or by hardware executing corresponding software. The corresponding hardware or software includes one or more modules corresponding to the above functions. That is, the steps in the above methods are executed by one or more modules respectively. The specific cooperative operation between the modules can be referred to the specific process of the above methods, and will not be repeated here.

[0049] In addition, the off-grid inverter of the present application comprises a bridge circuit composed of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, and a controller, wherein the first power switch tube and the second power switch tube are series-connected high-frequency tubes, and the third power switch tube and the fourth power switch tube are series-connected low-frequency tubes; the controller is used to execute the steps of the off-grid inverter control method described above. In the off-grid inverter, the controller realizes the process of the above method, and finally realizes the working process of the off-grid inverter. The specific working process of the controller can refer to the specific process of the above method, which will not be described here.

[0050] It can be understood that the above embodiments only express the preferred embodiments of the present application, which are described in detail and specifically, but cannot be understood as the limitation of the patent scope of the present application; it should be pointed out that for those skilled in the art, the above technical features can be freely combined without departing from the concept of the present application, and some modifications and improvements can be made, which all belong to the protection scope of the present application; therefore, any equivalent transformation and modification within the scope of the claims of the present application shall belong to the scope of the claims of the present application.

Claims

1. An off-grid inverter control method, characterized in that, The inverter comprises a bridge circuit composed of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, wherein the first power switch tube and the second power switch tube are series-connected high-frequency tubes, the third power switch tube and the fourth power switch tube are series-connected low-frequency tubes, the input end of the bridge circuit is connected with the power input of the inverter, and the output end of the bridge circuit is used for connecting the load of the inverter; the method comprises: S0, real-time acquisition of the output voltage corresponding to the inverter, judgment of whether the output voltage is mutated, and determination of the load corresponding to the inverter containing a capacitive circuit when the output voltage is mutated, wherein the judgment of whether the output voltage is mutated comprises a voltage difference between the output voltage and a preset reference voltage, and the judgment of the output voltage being mutated is that the voltage difference is not zero; When the load corresponding to the inverter contains a capacitive circuit, the following steps are executed: S1, real-time acquisition of the output voltage corresponding to the inverter, judgment of whether the output voltage is zero-crossed; S2, when the output voltage is not zero-crossed, the target output current corresponding to the inverter is obtained according to the voltage difference between the output voltage and a preset reference voltage and a preset voltage control loop, wherein the preset voltage control loop contains a first PI controller; S3, acquisition of the current difference between the output current corresponding to the inverter and the target output current, and acquisition of the corresponding duty cycle correction value according to the current difference and a preset current control loop, wherein the preset current control loop contains a second PI controller; S4, acquisition of the initial duty cycle corresponding to the inverter according to the input voltage of the inverter and the preset reference voltage, taking the sum of the initial duty cycle and the duty cycle correction value as a target duty cycle, and controlling the first power switch tube or the second power switch tube to be turned on according to the target duty cycle and executing the step S1; The method further comprises: S21, when the output voltage is zero-crossed, the third power switch tube or the fourth power switch tube is turned on.

2. The off-grid inverter control method of claim 1, wherein, The preset reference voltage is a standard sine wave.

3. The off-grid inverter control method of claim 1, wherein, In the step S2, the expression of the first PI controller is PI1=Kpv*Err1+(Kiv / Ts)*Err1, PI1 is the target output current corresponding to the preset voltage control loop, Kpv and Kiv are constants, Ts is time, and Err1 is the voltage difference.

4. The off-grid inverter control method of claim 1, wherein, In the step S3, the expression of the second PI controller is PI2=Kpi*Err2+(Kii / Ts)*Err2, wherein PI2 is the duty cycle correction value, Kpi and Kii are constants, Ts is time, and Err2 is the output current difference.

5. The off-grid inverter control method of claim 1, wherein, The method further comprises: when the load corresponding to the inverter is an RLC load or a capacitive load, determining that the load corresponding to the inverter contains a capacitive circuit.

6. An off-grid inverter control device, characterized in that, The application relates to an inverter comprising a bridge circuit consisting of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, wherein the first power switch tube and the second power switch tube are high-frequency tubes connected in series, and the third power switch tube and the fourth power switch tube are low-frequency tubes connected in series; the control device comprises a module for executing the method as claimed in any one of claims 1 to 5.

7. An off-grid inverter, characterized in that Comprise: a bridge circuit consisting of a first power switch tube, a second power switch tube, a third power switch tube and a fourth power switch tube, and a controller, wherein the first power switch tube and the second power switch tube are high-frequency tubes connected in series, and the third power switch tube and the fourth power switch tube are low-frequency tubes connected in series; the controller is used for executing the steps of the off-grid inverter control method as claimed in any one of claims 1 to 5.

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