Control method and system of rectification circuit in light load state

Abstract

The invention relates to a control method and system for a rectification circuit in a light load state, and the method comprises the steps: additionally adding a preset negative bias to a three-phase current sampling value when the rectification circuit is in a light load operation mode, enabling the sum of the sampling value and the bias value of each phase to be smaller than a given value, and enabling the three-phase waves to be symmetrical. According to the invention, the negative bias is increased by sampling the input current during light load, so that the three-phase wave sending duty ratio difference caused by the hardware difference of the three-phase current sampling circuit is reduced. The finally presented effects are that the three-phase wave sending duty ratio is more average, the error of input voltage sampling is eliminated, false triggering of system input undervoltage or overvoltage alarm is avoided, and the stability of the system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rectifier circuit control, and in particular to a control method and system for a rectifier circuit under a light load state. Background Art

[0002] The three-phase three-level Vienna rectifier circuit is a commonly used rectifier circuit topology with the advantages of high power factor and low harmonic content. When the rectifier circuit is closed-loop controlled, the duty cycle of each phase is determined by the current error of each phase input. The given value of the input current is determined by the output voltage error, and the sampled value of the input current is composed of the real current and the sampling error. The sampling error includes factors such as the operational amplifier bias, shunt and sampling resistor temperature drift of the sampling circuit.

[0003] Under light load conditions, the sampling errors of the input currents of each phase are different, which will cause the actual duty cycles of each phase to vary greatly. If one phase continues to output a large duty cycle while the duty cycles of other phases are close to zero, the sampling of the input grid voltage will be abnormal. When the sampling error of the input grid voltage is large, it will mistakenly trigger the system's input undervoltage or overvoltage alarm, causing the rectifier circuit to shut down abnormally.

[0004] Therefore, it is necessary to provide an effective control method to avoid false alarms in this light load situation. Summary of the invention

[0005] In view of this, it is necessary to provide a control method for a rectifier circuit under a light load state, so as to solve the problem in the prior art that the rectifier circuit under a light load condition may cause abnormal sampling of the input grid voltage due to different sampling errors of the input currents of each phase, thereby falsely triggering the input undervoltage or overvoltage alarm of the system, causing the rectifier circuit to shut down abnormally.

[0006] In order to solve the above problems, the present invention provides a control method for a rectifier circuit under a light load state, including: when the rectifier circuit is in a light load operation mode, a preset negative bias is additionally added to the three-phase current sampling value so that the sum of the sampling value and the bias value of each phase is less than a given value, so as to make the three-phase wave symmetrical.

[0007] In some possible implementations, the method further includes: Initialize the configuration, set the light load mode current Is and the preset negative bias Ib; When the system is powered on, the input current is detected.

[0008] In some possible implementations, the method further includes: Check whether the three-phase input currents are all less than Is; If yes, enter the light load mode, subtract Ib from the three-phase current sampling value, and then calculate the duty cycle of each phase; If not, exit the light load mode and calculate the duty cycle of each phase according to the actual sampling value of the three-phase current.

[0009] In some possible implementations, the method further includes: After calculating the duty cycle of each phase, the system enters a stable operating state and detects the input current in real time.

[0010] In order to solve the above problem, the present invention further provides a control system for a rectifier circuit in a light load state, comprising: The preset module is used to add a preset negative bias to the three-phase current sampling value when the rectifier circuit is in light load operation mode, so that the sum of the sampling value and the bias value of each phase is less than a given value, so that the three-phase wave is symmetrical.

[0011] In some possible implementations, the control system further includes: The initialization module is used to initialize the configuration, set the light load mode current Is and the preset negative bias Ib; when the system is turned on, the input current is detected.

[0012] In some possible implementations, the control system further includes: A detection module is used to detect whether the three-phase input currents are all less than Is; If yes, enter the light load mode, subtract Ib from the three-phase current sampling value, and then calculate the duty cycle of each phase; If not, exit the light load mode and calculate the duty cycle of each phase according to the actual sampling value of the three-phase current.

[0013] In some possible implementations, the control system further includes: The stable control module is used to control the system to a stable operating state after calculating the duty cycle of each phase, and to detect the input current in real time.

[0014] The beneficial effect of the present invention is that the present invention reduces the difference in the three-phase wave duty cycle caused by the hardware difference of the three-phase current sampling circuit by adding a negative bias to the input current sampling when the load is light. The final effect presented is that the three-phase wave duty cycle is more even, the error of input voltage sampling is eliminated, the false triggering of the system input undervoltage or overvoltage alarm is avoided, and the stability of the system is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0016] Figure 1 It is a circuit schematic diagram of a three-phase three-level Vienna rectifier circuit in the prior art; Figure 2 It is a flow chart of a closed-loop control method of a rectifier circuit in the prior art; Figure 3 It is a sampling schematic diagram of the duty cycle of each phase input current and the driving voltage changing with time in the prior art; Figure 4 It is a circuit schematic diagram of an input voltage sampling circuit of a rectifier circuit in the prior art; Figure 5 A flow chart of a control method of a rectifier circuit under light load state provided by the present invention; Figure 6 A schematic diagram of sampling of the duty cycle of each phase input current and the driving voltage varying with time provided by the present invention. DETAILED DESCRIPTION

[0017] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0018] The descriptions of "first", "second", etc. involved in the embodiments of the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the technical features defined as "first" or "second" may explicitly or implicitly include at least one of the features.

[0019] Reference to an "embodiment" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present invention. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0020] Before describing the specific embodiments of the present invention, the technical problems existing in the rectifier circuit in the prior art are described in detail. Figure 1-Figure 4 .

[0021] The three-phase three-level Vienna rectifier circuit is a commonly used rectifier circuit topology with the advantages of high power factor and low harmonic content. Figure 1 shown.

[0022] Furthermore, the closed-loop control method of the rectifier circuit is as follows: Figure 2 As shown, are the output voltage and input current sampling signals, They are all functions of the circuit controlled object. is the negative feedback control function, For output voltage setting, feedback, error signal, are input current given, feedback, error signal, and D is the control duty cycle.

[0023] Depend on Figure 2 From the control block diagram, we can see that the duty cycle D of each phase is determined by the current error of each phase input. Determine the given value of input current Output voltage error The sampling value of the input current is determined It is composed of real current and sampling error. The sampling error includes factors such as operational amplifier bias, shunt and sampling resistor temperature drift of the sampling circuit.

[0024] Under light load conditions, the output voltage error Very small, the given value of input current is also very small; and the actual input current tends to 0, making the sampling value of the input current With feedback value Determined by the sampling error, the error signal of the input current The duty cycle value D is also determined by the sampling error. Therefore, under light load conditions, the sampling errors of the input currents of each phase are different, which will lead to large differences in the actual duty cycles of each phase, such as Figure 3 shown.

[0025] If one phase continues to send a large duty cycle, while the duty cycle of other phases is close to zero, it will cause abnormal sampling of the input grid voltage. Figure 4 As shown, the sampling signal is obtained by dividing the sampling resistors R1~R6. Assuming that phase B continues to send a large duty cycle, while phases A and C have almost no duty cycle, then the input of phase B is approximately connected to the bus midpoint O, and a loop is formed through the primary and secondary coupling capacitors C1 of the auxiliary power transformer. Under this condition, the sampling resistors R3, R4 are connected in parallel with the equivalent impedance Xc of C1; Set the midpoint instantaneous voltage of the sampling resistor to , the instantaneous phase voltage of the three phases is Then we have: ; From R1=R3=R5, R2=R4=R6, and We can get: ; The calculated value according to this method is That is the transient error of phase voltage sampling.

[0026] When the sampling error of the input voltage is large, it will falsely trigger the input undervoltage or overvoltage alarm of the system, causing the rectifier circuit to shut down abnormally. Therefore, it is necessary to provide an effective control method to avoid false alarms for this light load situation.

[0027] Based on the above-mentioned technical problems, the present invention provides a control method for a rectifier circuit under a light load state. Under light load conditions, by setting a negative bias for the input current sampling of the rectifier circuit, the three-phase control wave duty cycle is made more balanced, thereby avoiding the input voltage sampling abnormality caused by the parasitic capacitance of the auxiliary power transformer and preventing the input undervoltage or overvoltage alarm of the system from being falsely triggered.

[0028] In order to solve the above technical problems, the present invention provides a control method for a rectifier circuit under a light load state, including: when the rectifier circuit is in a light load operation mode, a preset negative bias is additionally added to the three-phase current sampling value so that the sum of the sampling value and the bias value of each phase is less than a given value, so as to make the three-phase wave symmetrical.

[0029] In some possible implementations, the method further includes: Initialize the configuration, set the light load mode current Is and the preset negative bias Ib; When the system is powered on, the input current is detected.

[0030] In some possible implementations, the method further includes: Check whether the three-phase input currents are all less than Is; If yes, enter the light load mode, subtract Ib from the three-phase current sampling value, and then calculate the duty cycle of each phase; If not, exit the light load mode and calculate the duty cycle of each phase according to the actual sampling value of the three-phase current.

[0031] In some possible implementations, the method further includes: After calculating the duty cycle of each phase, the system enters a stable operating state and detects the input current in real time.

[0032] A specific embodiment of the present invention, as Figure 5 As shown, the present invention provides a flow chart of a control method of a rectifier circuit under a light load state, including: (0), (1), (2) The system is initialized and started, and the light load mode judgment current Is and the current sampling negative bias Ib are set; (3), (4), (5), (6), (7) The system performs input current detection. When it is detected that the three-phase input current is less than Is, it enters the light load mode, subtracts Ib from the three-phase current sampling value, and then calculates the duty cycle of each phase; (8) and (9) the system performs input current detection. When it detects that the input current of a phase is greater than Is, it exits the light load mode and calculates the duty cycle of each phase according to the actual sampling values ​​of the three-phase current.

[0033] Combined with the above analysis, the present invention provides a control method: when lightly loaded, the input current sampling is negatively biased, thereby reducing the difference in the three-phase wave duty cycle caused by the hardware difference of the three-phase current sampling circuit. The final effect presented is: the three-phase wave duty cycle is more even, the error of input voltage sampling is eliminated, the false triggering of the system input undervoltage or overvoltage alarm is avoided, and the stability of the system is improved.

[0034] Furthermore, in order to solve the above problem, the present invention also provides a control system for a rectifier circuit in a light load state, comprising: The preset module is used to add a preset negative bias to the three-phase current sampling value when the rectifier circuit is in light load operation mode, so that the sum of the sampling value and the bias value of each phase is less than a given value, so that the three-phase wave is symmetrical.

[0035] In some possible implementations, the control system further includes: The initialization module is used to initialize the configuration, set the light load mode current Is and the preset negative bias Ib; when the system is turned on, the input current is detected.

[0036] In some possible implementations, the control system further includes: A detection module is used to detect whether the three-phase input currents are all less than Is; If yes, enter the light load mode, subtract Ib from the three-phase current sampling value, and then calculate the duty cycle of each phase; If not, exit the light load mode and calculate the duty cycle of each phase according to the actual sampling value of the three-phase current.

[0037] In some possible implementations, the control system further includes: The stable control module is used to control the system to a stable operating state after calculating the duty cycle of each phase, and to detect the input current in real time.

[0038] In summary, the beneficial effect of the present invention is that the present invention reduces the difference in the three-phase wave duty cycle caused by the hardware difference of the three-phase current sampling circuit by adding a negative bias to the input current sampling when the load is light. The final effect presented is that the three-phase wave duty cycle is more even, the error of input voltage sampling is eliminated, the false triggering of the system input undervoltage or overvoltage alarm is avoided, and the stability of the system is improved.

[0039] The above are only preferred specific implementations of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A control method for a rectifier circuit under light load condition, characterized in that: include: When the rectifier circuit is in light load operation mode, a preset negative bias is added to the three-phase current sampling value so that the sum of the sampling value and the bias value of each phase is less than a given value, so that the three-phase wave is symmetrical.

2. The control method of the rectifier circuit under light load state according to claim 1, characterized in that: Also includes: Initialize the configuration, set the light load mode current Is and the preset negative bias Ib; When the system is powered on, the input current is detected.

3. The control method of the rectifier circuit under light load state according to claim 2, characterized in that: Also includes: Check whether the three-phase input currents are all less than Is; If yes, enter the light load mode, subtract Ib from the three-phase current sampling value, and then calculate the duty cycle of each phase; If not, exit the light load mode and calculate the duty cycle of each phase according to the actual sampling value of the three-phase current.

4. The control method of the rectifier circuit under light load state according to claim 3, characterized in that: Also includes: After calculating the duty cycle of each phase, the system enters a stable operating state and detects the input current in real time.

5. A control system for a rectifier circuit under light load condition, characterized in that: The control system comprises: The preset module is used to add a preset negative bias to the three-phase current sampling value when the rectifier circuit is in light load operation mode, so that the sum of the sampling value and the bias value of each phase is less than a given value, so that the three-phase wave is symmetrical.

6. The control system of the rectifier circuit under light load state according to claim 5, characterized in that: The control system further comprises: The initialization module is used to initialize the configuration, set the light load mode current Is and the preset negative bias Ib; when the system is turned on, the input current is detected.

7. The control system of the rectifier circuit under light load state according to claim 6, characterized in that: The control system further comprises: A detection module is used to detect whether the three-phase input currents are all less than Is; If yes, enter the light load mode, subtract Ib from the three-phase current sampling value, and then calculate the duty cycle of each phase; If not, exit the light load mode and calculate the duty cycle of each phase according to the actual sampling value of the three-phase current.

8. The control system of the rectifier circuit under light load state according to claim 7, characterized in that: The control system further comprises: The stable control module is used to control the system to a stable operating state after calculating the duty cycle of each phase, and to detect the input current in real time.

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