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

Abstract

The invention 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 an inverter comprises a capacitive circuit, S1, acquiring an output voltage corresponding to the inverter in real time and judging whether zero crossing occurs or not; s2, when no zero passage occurs, obtaining a target output current of the inverter according to a voltage difference value between the output voltage and a preset reference voltage and a preset voltage control ring; s3, obtaining a current difference value between the output current of the inverter and the target output current, and obtaining a duty ratio correction value according to the current difference value and a preset current control loop; and S4, obtaining an initial duty ratio of the inverter according to an input voltage of the inverter and a preset reference voltage, taking the sum of the duty ratio correction value and the initial duty ratio as a target duty ratio to control the first power switch tube or the second power switch tube to be switched on, and executing the step S1. According to the invention, the capacity of the inverter for carrying the RLC load and the capacitive load can be greatly improved, and the use experience of a terminal user is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of inverters, and more specifically, to an off-grid inverter control method and device, and an off-grid inverter. Background Art

[0002] Off-grid inverters are widely used in home backup power, emergency power, outdoor power and other fields. During operation, they can convert the electric energy in the battery into the AC power required by the loads in the above application fields. Load capacity is a key indicator for evaluating the performance of an off-grid inverter. The RLC load and capacitor load capacity are key indicators for judging the load capacity of an off-grid inverter.

[0003] When the off-grid load is an RLC or capacitive load, the traditional control method can generally achieve 70% of the rated power output of the inverter. For example, an inverter with a rated output power of 1kVA can only carry 700VA of RLC or capacitive load, which limits the use scenarios of the inverter. Summary of the invention

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

[0005] The technical solution adopted by the present invention to solve the 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 high-frequency tubes connected in series, 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; the method includes:

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

[0007] S1. Obtaining the output voltage corresponding to the inverter in real time, and determining whether the output voltage is zero-crossing;

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

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

[0010] S4. Obtain an initial duty cycle corresponding to the inverter according to an input voltage corresponding to the inverter and the preset reference voltage, take the sum of the duty cycle correction value and the initial duty cycle as a target duty cycle, and control the first power switch tube or the second power switch tube to turn on according to the target duty cycle and execute step S1.

[0011] Preferably, in an embodiment of the off-grid inverter control method of the present invention, the method further includes:

[0012] S21. When the output voltage passes through zero, switch the third power switch tube or the fourth power switch tube to conduct.

[0013] Preferably, in an embodiment of the off-grid inverter control method of the present invention, the method further includes:

[0014] S0. Acquire the output voltage corresponding to the inverter in real time, determine whether the output voltage changes suddenly, and when the output voltage changes suddenly, determine that the load corresponding to the inverter includes a capacitive circuit.

[0015] Preferably, in an embodiment of the off-grid inverter control method of the present invention, the determining whether the output voltage suddenly changes comprises:

[0016] A voltage difference between the output voltage and a preset reference voltage is determined. When the voltage difference is not zero, it is determined that a sudden change occurs in the output voltage.

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

[0018] Preferably, in an embodiment of the off-grid inverter control method described in the present invention, in 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.

[0019] Preferably, in an embodiment of the off-grid inverter control method described in the present invention, 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.

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

[0021] The present invention also constructs an off-grid inverter control device for an inverter, wherein the inverter includes 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 includes: a module for executing the method described above.

[0022] The present invention also constructs 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 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;

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

[0024] An off-grid inverter control method, device and off-grid inverter implementing the present invention have the following beneficial effects: without increasing the hardware cost, the ability of the inverter to carry RLC load and capacitive load can be significantly improved, the load types applicable to the inverter can be increased, the application scope of the off-grid inverter can be expanded, and the user experience of the end user can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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

[0029] Figure 4 It is a program flow chart of an embodiment of an off-grid inverter control method of the present invention;

[0030] Figure 5 is a program flow chart of another embodiment of an off-grid inverter control method of the present invention;

[0031] Figure 6 It is a logic relationship diagram of a control process in an off-grid inverter control method of the present invention. DETAILED DESCRIPTION

[0032] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0033] The current typical full-bridge inverter circuit is as follows Figure 1 As shown, the unipolar modulation process corresponding to the full-bridge inverter circuit is as follows Figure 2 As shown. In the high frequency arm, the power tubes Q1 and Q2 work in the high frequency state, and in the low frequency arm, the power tubes Q3 and Q4 work in the low frequency state. The switching method of the power tubes Q3 and Q4 in the low frequency arm is generally to switch at a fixed frequency and time. Figure 2 As shown, that is, when Uinvref corresponds to the preset reference voltage crossing zero from positive to negative, the power tube Q4 is turned off and the power tube Q3 is turned on; or when Uinvref crosses zero from negative to positive, 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 tubes Q3 and Q4 in the low-frequency arm are switched when Uinvref is zero, and no large peak current will be generated. When the off-grid inverter is put into operation with a large RLC load or capacitive load, assuming that the time of input is t1, at this time, since the voltage of the load capacitor is zero, the output voltage of the inverter will be pulled down (clamped), such as Figure 3 As shown by the solid line, if the power tubes Q3 and Q4 in the low-frequency arm are switched at a fixed frequency and time according to the original strategy, that is, the switching time is t0, at t0, due to the control system, the actual output voltage of the inverter is generally no longer zero, such as Figure 3 As shown by the solid line, the switching of power tubes Q3 and Q4 in the low-frequency arm will generate a large peak current when the output voltage is not zero. This current is uncontrollable and easily triggers overcurrent protection, affecting the user's product experience. Therefore, the inverter using this control algorithm has poor ability to carry RLC loads and capacitive loads, and supports fewer load types.

[0034] Based on the above process, Figure 4 As shown, the present invention provides an embodiment of an off-grid inverter control method. The inverter structure is as follows: Figure 1As shown, a bridge circuit is 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] exist Figure 4 In an embodiment of the off-grid inverter control method of the present invention shown, the specific method includes the following steps: S1, obtaining 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 a preset reference voltage, and a preset voltage control loop, wherein the preset voltage control loop includes 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 a preset current control loop, wherein the preset current control loop includes 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 duty cycle correction value and the initial duty cycle as the target duty cycle, and controlling the first power switch tube or the second power switch tube to turn on according to the target duty cycle and executing the step S1.

[0036] Based on step S1 and step S2, when it is determined that the load corresponding to the inverter includes a capacitive circuit, when there is a 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 determine 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 that the inverter expects to output, and when the actual output voltage of the bridge circuit deviates from the preset reference voltage, it is necessary to perform an output voltage control process. The output voltage control process is specifically to construct a preset voltage control loop including a first PI controller, and obtain the target output current corresponding to the inverter through the voltage difference between the output voltage and the preset reference voltage, so that the output voltage of the inverter is adjusted in a direction close to the preset reference voltage through the target output current.

[0037] Based on step S3, after the target output current of the inverter is obtained based on the voltage deviation, the current deviation of the inverter is confirmed again, that is, the current difference between the output current corresponding to the inverter and the target output current is actually measured, and the control is performed through a preset current control loop according to the current difference. The specific control process in the current control loop is implemented by the second PI controller. That is, the duty cycle correction value is obtained by the second PI controller, so that the output current of the bridge circuit is as close to the target output current as possible by correcting the duty cycle of the high-frequency tube in the bridge circuit.

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

[0039] Through this process, the bridge circuit can gradually approach the preset reference voltage, and finally the output of the inverter can meet the requirement 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, it also includes: S21, when the output voltage passes through zero, switching the third power switch tube or the fourth power switch tube to conduct. That is, when it is determined that the output voltage of the bridge circuit passes through zero, the corresponding switching power tube Q3 or the power tube Q4 is turned on. The signals of the power tube Q3 and the power tube 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 also includes: S0, real-time acquisition of the output voltage corresponding to the inverter, judging whether the output voltage has a sudden change, and when the output voltage has a sudden change, judging that the load corresponding to the inverter includes a capacitive circuit. Specifically, the judgment result of whether the load of the bridge circuit includes a capacitive circuit can be obtained according to the output voltage change of the bridge circuit. That is, the output voltage corresponding to the inverter is obtained, and it is judged whether the output voltage has a sudden change. When the output voltage has a sudden change, it is judged that the load corresponding to the inverter includes a capacitive circuit.

[0042] Further, the determination of whether the output voltage has a sudden change includes: the voltage difference between the output voltage and a preset reference voltage, and when the voltage difference is not zero, determining that the output voltage has a sudden change. Specifically, it includes but is not limited to determining whether the output voltage of the bridge circuit has a sudden change 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 means that the output voltage of the inverter has a sudden change. Wherein, the preset reference voltage can be a standard sine wave.

[0043] Optionally, in one embodiment of the off-grid inverter control method of the present invention, in 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. The first PI controller is an inverter voltage controller, the given value is the inverter voltage given (sine wave), the feedback value is the inverter voltage sampling value, and the correction amount is generated through the PI loop. The correction amount is the current value, and the output of PI1 is used as the given value of PI2.

[0044] Optionally, in one embodiment of the off-grid inverter control method of the present invention, in 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. The second PI controller is an inverter inductor current controller, the given value is the inverter current given value, the feedback value is the inverter current sampling value, and the correction value is generated through the PI loop. The duty cycle is the duty cycle correction value, and the duty cycle is obtained by superimposing the feedforward.

[0045] like Figure 6 As shown, in a specific embodiment, the duty cycle feedforward output D1 is obtained according to UinVef and Ubus, where D1 = Uinvref / Ubus, Uinvref is the inverter reference voltage, that is, the standard sine wave, and Ubus is the voltage provided by Ubus, which can also be understood as the voltage between the DC bus (BUS+, BUS-) of the inverter, that is, the input voltage of the inverter. The target current output of the inverter is obtained by the first PI controller PI1. D2 is the duty cycle control loop output, which can also be understood as the preset voltage control loop, and Uinv is Figure 1 The voltage of the inverter capacitor Cout is the actual output voltage of the inverter. Iinv is the actual inverter output current, that is, Figure 1The current on Linv is obtained by the second PI controller PI2. The high-frequency arm duty cycle D is set so that D=D1+D2. D1 enables Uinv to follow Uinvref, and D2 enables Uinv to quickly recover to the reference voltage Uinvref when subjected to large interference such as capacitive load switching. For example, Figure 3 As shown in the figure, when RLC load or capacitive load is put into operation at time t1, Uinv decreases, D1 decreases, and D2 is increased by controlling D2, so that D increases. After adjustment, Uinv increases and quickly recovers to follow Uinvref. In the duty cycle control process, the output voltage of the inverter is detected in real time, and the power frequency arm is switched according to whether the output voltage passes zero. When the output voltage is zero, the power frequency arm is switched. Figure 3 As shown in the figure, the switching time of the power frequency arm is changed from t0 to t2. In this process, the power switch tube is controlled to switch at the output voltage zero crossing time t2 according to the actual output voltage and loop regulation to reduce the impact current. At the same time, when the RLC or capacitive load is suddenly added, the high-frequency tube drive can be changed in time to reduce the impact of the sudden load.

[0046] Through the process of the present invention, the current distortion of the inverter when carrying RLC load can be effectively reduced, and the ability of the inverter to carry RLC load can be significantly improved. It can carry higher-power electrical appliances: such as computers, televisions and other equipment powered by switching power supplies, and batteries of some battery vehicles.

[0047] Optionally, in an embodiment of the off-grid inverter control method of the present invention, it further includes: when the load corresponding to the inverter is an RLC load or a capacitive load, determining that the load corresponding to the inverter includes a capacitive circuit. That is, it is possible to directly determine whether the load of the inverter is an RLC load or a capacitive load. If so, it is possible to directly count whether the load corresponding to the inverter is a capacitive load.

[0048] In addition, an off-grid inverter control device of the present invention is used for an inverter, wherein 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 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 includes: a module for executing the method described above. The control device has the function of implementing the corresponding steps executed in the above method. Each function can be implemented by hardware, or by hardware executing the corresponding software. The corresponding hardware or software includes one or more modules corresponding to the above functions. That is, the steps in the above method are respectively executed by one or more modules. The specific coordination operation between the modules can refer to the specific process of the above method, which will not be repeated here.

[0049] In addition, the off-grid inverter of the present invention 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 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 to execute the steps of the off-grid inverter control method described above. In the off-grid inverter, the process of the above method is implemented by the controller, and finally the working process of the off-grid inverter is realized. The specific working process of the controller can refer to the specific process of the above method, which will not be repeated here.

[0050] It can be understood that the above embodiments only express the preferred implementation modes of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the patent scope of the present invention. It should be pointed out that, for ordinary technicians in this field, the above technical features can be freely combined without departing from the concept of the present invention, and several deformations and improvements can be made, which all belong to the protection scope of the present invention. Therefore, all equivalent changes and modifications made to the scope of the claims of the present invention should belong to the coverage of the claims of the present invention.

Claims

1. A method for controlling an off-grid inverter, 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 high-frequency tubes connected in series, 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; the method comprises: When the load corresponding to the inverter includes a capacitive circuit, the following steps are performed: S1. Obtaining the output voltage corresponding to the inverter in real time, and determining whether the output voltage is zero-crossing; S2, when the output voltage does not cross zero, obtaining a target output current corresponding to the inverter according to a voltage difference between the output voltage and a preset reference voltage and a preset voltage control loop, wherein the preset voltage control loop includes a first PI controller; S3, obtaining a current difference between an output current corresponding to the inverter and the target output current, and obtaining a corresponding duty cycle correction value according to the current difference and a preset current control loop, wherein the preset current control loop includes a second PI controller; S4. Obtain an initial duty cycle corresponding to the inverter according to an input voltage corresponding to the inverter and the preset reference voltage, take the sum of the duty cycle correction value and the initial duty cycle as a target duty cycle, and control the first power switch tube or the second power switch tube to turn on according to the target duty cycle and execute step S1.

2. The off-grid inverter control method according to claim 1, characterized in that: The method further comprises: S21. When the output voltage passes through zero, switch the third power switch tube or the fourth power switch tube to conduct.

3. The off-grid inverter control method according to claim 1, characterized in that: The method further comprises: S0. Acquire the output voltage corresponding to the inverter in real time, determine whether the output voltage changes suddenly, and when the output voltage changes suddenly, determine that the load corresponding to the inverter includes a capacitive circuit.

4. The off-grid inverter control method according to claim 3, characterized in that: The determining whether the output voltage has a sudden change includes: A voltage difference between the output voltage and a preset reference voltage is determined. When the voltage difference is not zero, it is determined that a sudden change occurs in the output voltage.

5. The off-grid inverter control method according to claim 4, characterized in that: The preset reference voltage is a standard sine wave.

6. The off-grid inverter control method according to claim 1, characterized in that: In 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.

7. The off-grid inverter control method according to claim 1, characterized in that: In 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.

8. The off-grid inverter control method according to claim 1, characterized in that: The method further includes: determining that the load corresponding to the inverter includes a capacitive circuit when the load corresponding to the inverter is an RLC load or a capacitive load.

9. An off-grid inverter control device, characterized in that: Used for an inverter, 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 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 includes: a module for executing the method described in any one of claims 1 to 8.

10. An off-grid inverter, characterized in that: include: 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 to execute the steps of the off-grid inverter control method according to any one of claims 1 to 8.

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