Control method and circuit for suppressing starting overcurrent of Vienna rectifier

Abstract

The invention discloses a control method and circuit for suppressing starting overcurrent of a Vienna rectifier. The method comprises the following steps: S1, pre-charging a direct current bus capacitor through a negative temperature coefficient thermistor; s2, when the voltage change rate of the direct-current bus capacitor meets the voltage change rate threshold value requirement, a current limiting switch connected with one negative temperature coefficient thermistor in parallel is closed, and the corresponding negative temperature coefficient thermistor is cut off from the circuit; s3, when the voltage of the direct-current bus capacitor reaches a set value, an electricity load is connected, the set value of the voltage of the direct-current bus capacitor is increased to an expected value according to a preset slope, a current limiting switch connected with the other negative temperature coefficient thermistor in parallel is closed, and the corresponding negative temperature coefficient thermistor is cut off from the circuit; the problem that the starting current of the Vienna rectifier is too large can be solved, and the starting stability and reliability of the Vienna rectifier are improved.

Description

Technical Field

[0001] The invention relates to the field of electrical technology, and in particular to a control method and a circuit for suppressing overcurrent at the start-up of a Vienna rectifier. Background Art

[0002] Vienna rectifier can actively control the "harmonic" pollution of the power grid, improve the power quality of the power grid and realize power factor correction. It has the advantages of high power factor, low input current harmonic content, low switch stress, no dead zone setting and few switching devices, and is suitable for high-power applications. Therefore, Vienna rectifier has been used in aviation power supply, electric vehicle charger, wind power generation, uninterruptible power supply and other fields.

[0003] When the Vienna rectifier is working normally, it usually adopts a dual closed-loop control method of DC voltage outer loop and inductor current inner loop. However, at startup, due to the low DC side voltage and weak AC side output capacity of the rectifier, a large inrush current will be generated on the inductor at the moment of startup until the DC side voltage rises to the set value. The large inrush current increases the selection margin of power electronic devices and the capacity of the filter inductor, thereby increasing the cost of the equipment. Excessive inrush current may even cause the overcurrent protection of the equipment to operate, causing the equipment to malfunction.

[0004] At present, in order to solve the problem of excessive starting impact current of three-phase active rectifier circuits, a common method is to add a pre-charging process during the startup process, that is, to increase the DC voltage of the system to a value close to the given DC voltage, and then switch to the PWM rectification state; however, during the rectifier starting process, due to the conversion from uncontrolled rectification to Vienna rectification, the DC bus voltage given value is a step signal, which causes the bus voltage to increase rapidly, generates impact current, and causes the switching devices to bear a large current stress, affecting the safety and reliability of the system.

[0005] In order to avoid the impact of excessive starting surge current on electronic devices, technical personnel in this field have been seeking a control method for suppressing the starting overcurrent of the Vienna rectifier, which can smoothly adjust the DC bus voltage and reduce the instantaneous current surge at startup, so as to effectively suppress the surge current during the startup phase of the Vienna rectifier and improve the startup stability and reliability of the Vienna rectifier. Summary of the invention

[0006] The purpose of the present invention is to provide a control method and circuit for solving the problem of excessive starting current of a Vienna rectifier, improving the starting stability and reliability of the Vienna rectifier, and suppressing the starting overcurrent of the Vienna rectifier.

[0007] In a first aspect, an embodiment of the present invention provides a control method for suppressing overcurrent at startup of a Vienna rectifier, which is special in that it includes the following steps:

[0008] S1, connecting negative temperature coefficient thermistors in series in at least two phases between the AC source and the rectifier circuit, each negative temperature coefficient thermistor is connected in parallel with a current limiting switch, disconnecting the current limiting switch, turning on the AC source, and precharging the DC bus capacitor through the negative temperature coefficient thermistor;

[0009] S2, detecting the voltage change rate of the DC bus capacitor, and when the voltage change rate of the DC bus capacitor meets the voltage change rate threshold requirement, closing a current limiting switch connected in parallel with one of the negative temperature coefficient thermistors, and removing the corresponding negative temperature coefficient thermistor from the circuit;

[0010] S3. When the voltage of the DC bus capacitor reaches the set value, the power load is connected, the set value of the voltage of the DC bus capacitor increases to the expected value according to the preset slope, and the current limiting switch connected in parallel with another negative temperature coefficient thermistor is closed to cut off the corresponding negative temperature coefficient thermistor from the circuit.

[0011] As a preferred solution, in step S1, the DC bus capacitor is precharged, and the current limiting resistor used to reduce the starting current is a negative temperature coefficient thermistor, and the expression of the initial resistance value of the negative temperature coefficient thermistor is:

[0012]

[0013] Among them, R start Indicates the resistance of the negative temperature coefficient thermistor in its initial state. Indicates the maximum voltage in the rectifier circuit, I limit Indicates the maximum current in the rectifier circuit.

[0014] Furthermore, the initial resistance values ​​of the negative temperature coefficient thermistors connected in series at least two phases are the same.

[0015] As a preferred solution, the expression for the law of the change of the resistance of the negative temperature coefficient thermistor with temperature is:

[0016]

[0017] Where R(T) represents the resistance of the negative temperature coefficient thermistor at temperature T, R 25 It indicates the reference resistance of the negative temperature coefficient thermistor at a reference temperature of 25°C, B indicates the material constant of the negative temperature coefficient thermistor, T indicates the absolute temperature corresponding to the current temperature, T 25 Indicates the absolute temperature corresponding to the reference temperature.

[0018] As a preferred solution, in step S2, the expression of the voltage change rate threshold is:

[0019]

[0020] Among them, dU dc represents the voltage change of the DC bus capacitor, dt represents the time change, and m represents the voltage change rate threshold of the DC bus capacitor.

[0021] Furthermore, the voltage change rate threshold m of the DC bus capacitor is set to 0.

[0022] As a preferred solution, in step S3, the set value of the voltage of the DC bus capacitor is increased to a desired value according to a preset slope, and the expression of the slope is:

[0023] U dc (t) = U dc, Steady state*(1-e -γt )

[0024] Among them, U dc (t) represents the voltage of the DC bus capacitor, U dc,稳态 It represents the expected value of the voltage of the DC bus capacitor, and γ represents the rise rate coefficient.

[0025] In a second aspect, an embodiment of the present invention provides a control circuit for suppressing overcurrent at startup of a Vienna rectifier, the control circuit comprising: a three-phase AC power supply, a first three-phase inductor, a first current limiting resistor Rg1, a first current limiting switch Sg1, a second current limiting resistor Rg2, a second current limiting switch Sg2, a second three-phase inductor, first to sixth power diodes, first to sixth power switch tubes, a first DC bus capacitor C1 and a second DC bus capacitor C2, the six power diodes are connected in pairs to form a three-phase bridge arm, the six power switch tubes are connected in pairs to form a three-phase bridge arm, the first DC The DC bus capacitor C1 and the second DC bus capacitor C2 are respectively connected to the two ends of the midpoint of the DC side; the special feature is that: the power output end of the three-phase AC power supply is connected to the power input end of the first three-phase inductor, the two phases of the power output end of the first three-phase inductor are connected to one end of the first current limiting resistor Rg1 and the second current limiting resistor Rg2, the other end of the first current limiting resistor Rg1 and the second current limiting resistor Rg2 is connected to the power input end of the second three-phase inductor, and the power output end of the second three-phase inductor is connected to the input end of the three-phase bridge arm.

[0026] As a preferred solution, the first current limiting switch Sg1 is connected in parallel with the first current limiting resistor Rg1; the second current limiting switch Sg2 is connected in parallel with the second current limiting resistor Rg2.

[0027] As a preferred solution, the three-phase output terminals of the power supply of the first three-phase inductor are correspondingly connected to the three-phase input terminals of the AC side filter circuit.

[0028] The present invention has the following beneficial effects:

[0029] (1) The present invention connects negative temperature coefficient thermistors in series for pre-charging at least two phases between the AC source and the rectifier circuit, and adopts a control strategy of cutting off the negative temperature coefficient thermistors in stages, which effectively suppresses the huge surge current generated by the charging of the DC bus capacitor at the moment of Vienna rectifier startup. In the first stage, a negative temperature coefficient thermistor is cut off when the bus voltage change rate tends to be stable, ensuring that the switching is performed when the charging current has been significantly reduced, avoiding switching shock; in the second stage, after the bus voltage reaches the set value and starts to soft-start and boost according to the preset slope, another negative temperature coefficient thermistor is cut off, achieving a smooth transition from pre-charging to normal operation. Compared with traditional one-time switching or switching based only on voltage thresholds, this staged, state-judgment-based control method can manage the current during the startup process more accurately and gently, significantly reducing the impact on the power grid, reducing the electrical stress on the power devices inside the rectifier and the DC bus capacitor, and improving the startup reliability and device life of the system.

[0030] (2) The present invention optimizes the integration of the pre-charging circuit and the Vienna rectifier by arranging the negative temperature coefficient thermistor and its parallel current limiting switch between the first three-phase inductor and the second three-phase inductor. This layout allows the first-stage inductor to perform preliminary filtering and smoothing on the input current in the pre-charging stage, reducing the current impact on the negative temperature coefficient thermistor; at the same time, the negative temperature coefficient thermistor is located before the main boost inductor, which can effectively limit the charging current flowing into the rectifier bridge arm and the DC bus capacitor. When the negative temperature coefficient thermistor is cut off, the two-stage inductor can jointly or according to design requirements assume its filtering and boosting functions when the Vienna rectifier is working normally, without the need for additional switching or complex circuit reconstruction. This structure not only achieves effective startup current suppression, but also simplifies the transition between the main circuit and the pre-charging circuit, improves the overall integration and operating efficiency of the circuit, and may help improve the electromagnetic compatibility of the system in different working stages. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The present invention is a flow chart of a specific embodiment of a control method for suppressing overcurrent during startup of a Vienna rectifier.

[0032] Figure 2 The present invention is a schematic structural diagram of a specific embodiment of a control circuit for suppressing overcurrent at startup of a Vienna rectifier.

[0033] Figure 3 The present invention is a schematic structural diagram of a specific embodiment of a control circuit for suppressing overcurrent at startup of a Vienna rectifier, in which a current-limiting resistor is removed.

[0034] Figure 4 The present invention is a schematic structural diagram of a specific embodiment of a control circuit for suppressing overcurrent at startup of a Vienna rectifier in which a current-limiting resistor is completely removed.

[0035] Explanation of the accompanying drawings: 1. three-phase AC power supply; 2. first three-phase inductor; 3. second three-phase inductor; 4. first to sixth power diodes; 5. first to sixth power switch tubes. DETAILED DESCRIPTION

[0036] Embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein, which are instead provided for a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are only for exemplary purposes and are not intended to limit the scope of protection of the present invention.

[0037] The technical solution of the present invention is described in detail with specific embodiments below. The following specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments.

[0038] like Figure 1 and Figure 4 As shown, an embodiment of the present invention discloses a control method and circuit for suppressing overcurrent at startup of a Vienna rectifier.

[0039] Example 1

[0040] This embodiment discloses a control method for suppressing overcurrent at the start-up of a Vienna rectifier, the method comprising the following steps:

[0041] Step S1, connecting negative temperature coefficient thermistors in series at least two phases between the AC source and the rectifier circuit, each negative temperature coefficient thermistor is respectively connected in parallel with a current limiting switch, disconnecting the current limiting switch, turning on the AC source, and precharging the DC bus capacitor through the negative temperature coefficient thermistor;

[0042] Step S2, detecting the voltage change rate of the DC bus capacitor, and when the voltage change rate of the DC bus capacitor meets the voltage change rate threshold requirement, closing a current limiting switch connected in parallel with one of the negative temperature coefficient thermistors, and removing the corresponding negative temperature coefficient thermistor from the circuit;

[0043] It should be noted that the DC bus capacitor is charged by full-bridge uncontrolled rectification. The circuit at this stage is equivalent to the equivalent circuit of uncontrolled rectification, and the equivalent circuits of other current limiting switch states can also be understood in this way. In the case of uncontrolled rectification, the maximum output voltage can reach 2.45 times the effective value of the phase voltage. Calculated based on the effective value of the input voltage of 220V, the maximum output voltage at this time is 539V. However, this voltage value is still far from the target value (640V DC output voltage). Therefore, in order to achieve the required DC output voltage, it is necessary to continue charging the capacitor.

[0044] Step S3, when the voltage of the DC bus capacitor reaches the set value, the power load is connected, the set value of the voltage of the DC bus capacitor increases to the expected value according to the preset slope, and the current limiting switch connected in parallel with another negative temperature coefficient thermistor is closed to cut off the corresponding negative temperature coefficient thermistor from the circuit.

[0045] In this embodiment, in step S1, the DC bus capacitor is precharged, and the current limiting resistor used to reduce the starting current is a negative temperature coefficient thermistor, and the expression of the initial resistance value of the negative temperature coefficient thermistor is:

[0046]

[0047] Among them, R start Indicates the resistance of the negative temperature coefficient thermistor in its initial state. Indicates the maximum voltage in the rectifier circuit, I limit Indicates the maximum current in the rectifier circuit.

[0048] In this embodiment, the initial resistance values ​​of the negative temperature coefficient thermistors connected in series in at least two phases are the same.

[0049] In this embodiment, the expression for the law of the change of the resistance of the negative temperature coefficient thermistor with temperature is:

[0050]

[0051] Where R(T) represents the resistance of the negative temperature coefficient thermistor at temperature T, R 25 It indicates the reference resistance of the negative temperature coefficient thermistor at a reference temperature of 25°C, B indicates the material constant of the negative temperature coefficient thermistor, T indicates the absolute temperature corresponding to the current temperature, T 25 Indicates the absolute temperature corresponding to the reference temperature. It should be noted that when the Vienna rectifier is started, the initial temperature is low and the resistance is large, which limits the inrush current; as the current flows, the resistor heats up and the resistance automatically decreases, improving the system efficiency. The structure is simple and does not require additional control circuits. Moreover, its adaptive adjustment does not affect the subsequent steady-state operation.

[0052] In this embodiment, in step S2, the voltage change rate threshold is expressed as:

[0053]

[0054] Among them, dU dc represents the voltage change of the DC bus capacitor, dt represents the time change, and m represents the voltage change rate threshold of the DC bus capacitor.

[0055] In this embodiment, the value of the voltage change rate threshold m of the DC bus capacitor is 0.

[0056] In this embodiment, in step S3, the set value of the voltage of the DC bus capacitor is increased to a desired value according to a preset slope, and the expression of the slope is:

[0057] U dc (t) = U dc, Steady state*(1-e -γt )

[0058] Among them, U dc (t) represents the voltage of the DC bus capacitor, U dc,稳态 It represents the expected value of the voltage of the DC bus capacitor, and γ represents the rise rate coefficient.

[0059] In this embodiment, the setting of the slope also takes into account the dynamic characteristics of the circuit, including the charge and discharge rate of the output capacitor, the current limit of the inductor, and the response characteristics of the control loop. These factors will affect the adaptability of the rectifier to current changes during the startup process. This means that the rectifier gradually reaches its operating point voltage in a smooth manner, ensuring the stability and safety of the transition process. In actual use, the determination of the preset slope usually requires adjusting the slope according to the specific parameters and performance requirements of the circuit until the best balance point is found, which can not only ensure the rapid response of the rectifier, but also avoid the generation of excessive impact current. In the end, all current limiting resistors are cut off to ensure its stable operation. Instead of cutting off the current limiting resistors instantly, the resistance value is gradually reduced, and the resistors are cut off step by step from large resistors to small resistors. While ensuring its efficiency, it also tries its best to reduce the size of its impact current.

[0060] Example 2

[0061] The present embodiment discloses a control circuit for suppressing overcurrent at the start-up of a Vienna rectifier, the control circuit comprising: a three-phase AC power supply 1, a first three-phase inductor 2, a first current limiting resistor Rg1, a first current limiting switch Sg1, a second current limiting resistor Rg2, a second current limiting switch Sg2, a second three-phase inductor 3, first to sixth power diodes 4, first to sixth power switch tubes 5, a first DC bus capacitor C1 and a second DC bus capacitor C2, six power diodes connected in pairs to form a three-phase bridge arm, and six power switch tubes connected in pairs to form a The three-phase bridge arm, the first DC bus capacitor C1 and the second DC bus capacitor C2 are respectively connected to the two ends of the midpoint of the DC side; the power output end of the three-phase AC power supply 1 is connected to the power input end of the first three-phase inductor 2, the two phases of the power output end of the first three-phase inductor 2 are connected to one end of the first current limiting resistor Rg1 and the second current limiting resistor Rg2, the other end of the first current limiting resistor Rg1 and the second current limiting resistor Rg2 are connected to the power input end of the second three-phase inductor 3, and the power output end of the second three-phase inductor 3 is connected to the input end of the three-phase bridge arm.

[0062] The first current limiting switch Sg1 is connected in parallel with the first current limiting resistor Rg1; the second current limiting switch Sg2 is connected in parallel with the second current limiting resistor Rg2.

[0063] The three-phase output terminals of the power supply of the first three-phase inductor 2 are correspondingly connected to the three-phase input terminals of the AC side filter circuit.

[0064] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A control method for suppressing overcurrent during startup of a Vienna rectifier, characterized in that: The steps include: S1, connecting negative temperature coefficient thermistors in series in at least two phases between the AC source and the rectifier circuit, each negative temperature coefficient thermistor is connected in parallel with a current limiting switch, disconnecting the current limiting switch, turning on the AC source, and precharging the DC bus capacitor through the negative temperature coefficient thermistor; S2, detecting the voltage change rate of the DC bus capacitor, and when the voltage change rate of the DC bus capacitor meets the voltage change rate threshold requirement, closing a current limiting switch connected in parallel with one of the negative temperature coefficient thermistors, and removing the corresponding negative temperature coefficient thermistor from the circuit; S3. When the voltage of the DC bus capacitor reaches the set value, the power load is connected, the set value of the voltage of the DC bus capacitor increases to the expected value according to the preset slope, and the current limiting switch connected in parallel with another negative temperature coefficient thermistor is closed to cut off the corresponding negative temperature coefficient thermistor from the circuit.

2. The control method for suppressing overcurrent during startup of Vienna rectifier according to claim 1, characterized in that: In step S1, the DC bus capacitor is precharged, and the current limiting resistor used to reduce the starting current is a negative temperature coefficient thermistor. The expression of the initial resistance value of the negative temperature coefficient thermistor is: Among them, R start Indicates the resistance of the negative temperature coefficient thermistor in its initial state. Indicates the maximum voltage in the rectifier circuit, I limit Indicates the maximum current in the rectifier circuit.

3. The control method for suppressing overcurrent during startup of Vienna rectifier according to claim 2, characterized in that: The initial resistance values ​​of the negative temperature coefficient thermistors connected in series in at least two phases are the same.

4. The control method for suppressing overcurrent during startup of Vienna rectifier according to claim 3, characterized in that: The expression of the law of the change of the resistance of the negative temperature coefficient thermistor with temperature is: Where R(T) represents the resistance of the negative temperature coefficient thermistor at temperature T, R 25 It indicates the reference resistance of the negative temperature coefficient thermistor at a reference temperature of 25°C, B indicates the material constant of the negative temperature coefficient thermistor, T indicates the absolute temperature corresponding to the current temperature, T 25 Indicates the absolute temperature corresponding to the reference temperature.

5. The control method for suppressing overcurrent during startup of Vienna rectifier according to claim 1, characterized in that: In step S2, the voltage change rate threshold is expressed as: Among them, dU dc represents the voltage change of the DC bus capacitor, dt represents the time change, and m represents the voltage change rate threshold of the DC bus capacitor.

6. The control method for suppressing overcurrent at start-up of Vienna rectifier according to claim 5, characterized in that: The voltage change rate threshold m of the DC bus capacitor is set to 0.

7. The control method for suppressing overcurrent during startup of a Vienna rectifier according to claim 1, characterized in that: In step S3, the set value of the voltage of the DC bus capacitor is increased to a desired value according to a preset slope, and the expression of the slope is: U dc (t)=U dc , 稳态 *(1-e -γt ) Among them, U dc (t) represents the voltage of the DC bus capacitor, U dc,稳态 It represents the expected value of the voltage of the DC bus capacitor, and γ represents the rise rate coefficient.

8. A control circuit for suppressing overcurrent at start-up of a Vienna rectifier, the control circuit comprising: A three-phase AC power supply (1), a first three-phase inductor (2), a first current limiting resistor Rg1, a first current limiting switch Sg1, a second current limiting resistor Rg2, a second current limiting switch Sg2, a second three-phase inductor (3), first to sixth power diodes (4), first to sixth power switch tubes (5), a first DC bus capacitor C1 and a second DC bus capacitor C2, the six power diodes being connected in pairs to form a three-phase bridge arm, the six power switch tubes being connected in pairs to form a three-phase bridge arm, the first DC bus capacitor C1 and the second DC bus capacitor C2 being connected in pairs to form a three-phase bridge arm, At both ends of the midpoint of the DC side; characterized in that: the power output end of the three-phase AC power supply (1) is connected to the power input end of the first three-phase inductor (2), two phases of the power output end of the first three-phase inductor (2) are connected to one end of the first current limiting resistor Rg1 and the second current limiting resistor Rg2, the other ends of the first current limiting resistor Rg1 and the second current limiting resistor Rg2 are connected to the power input end of the second three-phase inductor (3), and the power output end of the second three-phase inductor (3) is connected to the input end of the three-phase bridge arm.

9. The control circuit for suppressing overcurrent at start-up of a Vienna rectifier according to claim 8, characterized in that: The first current limiting switch Sg1 is connected in parallel with the first current limiting resistor Rg1; the second current limiting switch Sg2 is connected in parallel with the second current limiting resistor Rg2.

10. The control circuit for suppressing overcurrent at start-up of a Vienna rectifier according to claim 8, characterized in that: The three-phase output end of the power supply of the first three-phase inductor (2) is correspondingly connected to the three-phase input end of the AC side filter circuit.

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