CN210167966U - Soft start circuit of three-phase PWM rectifier - Google Patents
Soft start circuit of three-phase PWM rectifier Download PDFInfo
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- CN210167966U CN210167966U CN201921507498.5U CN201921507498U CN210167966U CN 210167966 U CN210167966 U CN 210167966U CN 201921507498 U CN201921507498 U CN 201921507498U CN 210167966 U CN210167966 U CN 210167966U
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Abstract
The utility model discloses a soft start circuit of a three-phase PWM rectifier, which comprises a first current transformer, a second current transformer, a third current transformer, a resistance bleeder circuit and a voltage comparison circuit; the control circuit is internally provided with a current threshold and a voltage threshold of the three-phase PWM rectifier. Detecting the current in the starting process of the three-phase PWM rectifier in real time through each current transformer, and stopping in time once the current exceeds a current threshold; the resistance voltage division circuit is used for acquiring an actual value of the direct current voltage and transmitting the actual value to the voltage comparison circuit and the control circuit respectively after acquisition; after the control circuit acquires the actual value of the direct-current voltage, a segmented starting boosting value is obtained according to the voltage threshold; and controlling the three-phase PWM rectifier to output direct-current voltage according to the segmented starting boost value. It is visible the utility model discloses a mode that the segmentation was stepped up makes three-phase PWM rectifier start-up in-process, avoids appearing because of the start-up that the voltage sudden change arouses phenomenon of overflowing, simple structure, easy realization.
Description
Technical Field
The utility model relates to a variable frequency power supply technical field especially relates to a soft start circuit of three-phase PWM rectifier.
Background
In the existing non-ferrous metal smelting process, in order to make the molten non-ferrous metal alloy components fully uniform and improve the melting speed, an electromagnetic stirrer is generally required for stirring, and the power supply used by the existing electromagnetic stirrer adopts an AC-DC frequency conversion mode. Because the load carried by the electromagnetic stirrer is a large inductance coil, the power factor is very low, the capacitance capacity required by the direct current filtering link is large, and the capacitor needs to be precharged through the rectifier when the main loop is electrified.
The existing method for rectifying the AC-DC-AC variable frequency power supply mainly comprises diode rectification and silicon controlled rectifier rectification, wherein the silicon controlled rectifier rectification can pre-charge the DC bus capacitor by controlling a phase angle in the process of electrifying a main circuit, and the phase is called as the pre-charging of the uncontrolled rectification.
Typically, three-phase PWM rectifier start-up is divided into two phases: the first stage is an uncontrolled (or semi-controlled) rectification stage and is started according to the uncontrolled rectification working mode; the second stage is to switch from the uncontrolled (or semi-controlled) rectification working mode to the PWM rectification working mode for starting. In the second stage, if the three-phase PWM rectifier is started by directly boosting the voltage to the proper position, the three-phase PWM rectifier is easily damaged due to the over-current during the starting process of the three-phase PWM rectifier.
SUMMERY OF THE UTILITY MODEL
To the above-mentioned not enough, the utility model discloses the technical problem that will solve is: the soft start circuit of the three-phase PWM rectifier is provided, and the circuit avoids the starting overcurrent phenomenon caused by voltage mutation in the starting process of the three-phase PWM rectifier in a sectional boosting mode.
In order to solve the technical problem, the technical scheme of the utility model is that:
a soft start circuit of a three-phase PWM rectifier is based on a variable frequency power supply, wherein the variable frequency power supply comprises a three-phase PWM rectifier, an intermediate energy storage circuit and a control circuit, the control circuit is electrically connected with the three-phase PWM rectifier, the intermediate energy storage circuit comprises a first direct current bus capacitor and a second direct current bus capacitor, one end of the first direct current bus capacitor is connected with one end of the second direct current bus capacitor, the other end of the first direct current bus capacitor is a P end, and the other end of the second direct current bus capacitor is an N end; the soft start circuit comprises a first current transformer, a second current transformer, a third current transformer, a resistance voltage division circuit and a voltage comparison circuit which are respectively electrically connected with the control circuit; the control circuit is internally provided with a voltage threshold value after the three-phase PWM rectifier is started and a current threshold value of the three-phase PWM rectifier; the first current transformer, the second current transformer and the third current transformer are respectively arranged at the three-phase input end of the three-phase PWM rectifier and are used for acquiring a three-phase input current real-time value; the control circuit controls the three-phase PWM rectifier to work and stop by comparing the three-phase input current real-time value with the current threshold value; the input end of the resistance voltage division circuit is respectively and electrically connected with the P end and the N end and is used for collecting the actual value of the direct current voltage, and the output end of the resistance voltage division circuit is respectively and electrically connected with the positive phase input end of the voltage comparison circuit and the control circuit; the inverting input end of the voltage comparison circuit is electrically connected with the control circuit, and the output end of the voltage comparison circuit is electrically connected with the control circuit; the voltage comparison circuit compares the actual value of the direct current voltage with a set value of the direct current voltage transmitted by the control circuit and outputs a corresponding electric signal to the control circuit; the control circuit divides the difference between the voltage threshold value and the actual value of the direct current voltage into N sections, and each section of voltage value is a section starting boosting value; the set value of the direct current voltage is the sum of the actual value of the direct current voltage and the N times of the segmented starting and boosting value; the control circuit controls the three-phase PWM rectifier to output a segmented starting and boosting value by adjusting PI gain values of active components and reactive components of the three-phase PWM rectifier; the control circuit controls the three-phase PWM rectifier to output a sectional starting boost value or stop outputting according to the electric signal transmitted by the voltage comparison circuit; wherein N is a positive integer.
Preferably, the voltage comparison circuit comprises an LM393 voltage comparison chip.
Preferably, the control circuit comprises a DSP 28335.
Preferably, the soft start circuit further comprises a signal conditioning circuit for amplifying the current signal, an input end of the signal conditioning circuit is electrically connected with the first current transformer, the second current transformer and the third current transformer respectively, and an output end of the signal conditioning circuit is electrically connected with the control circuit.
Preferably, the first current transformer, the second current transformer and the third current transformer are hall current sensors.
After the technical scheme is adopted, the beneficial effects of the utility model are that:
the soft start circuit of the three-phase PWM rectifier comprises a first current transformer, a second current transformer, a third current transformer, a resistance bleeder circuit and a voltage comparison circuit which are respectively electrically connected with a control circuit; and a voltage threshold value after the three-phase PWM rectifier is started and a current threshold value of the three-phase PWM rectifier are arranged in the control circuit. The three-phase PWM rectifier circuit comprises a first current transformer, a second current transformer and a third current transformer, wherein the first current transformer, the second current transformer and the third current transformer are used for acquiring an actual value of three-phase input current, the current in the starting process of the three-phase PWM rectifier is detected in real time through each current transformer, and the three-phase PWM rectifier is stopped in time once the current exceeds a current threshold value, so that the three-phase PWM rectifier is effectively protected; the resistance voltage dividing circuit is used for acquiring an actual value of the direct current voltage and transmitting the actual value to the voltage comparison circuit and the control circuit respectively after acquisition; after the control circuit acquires the actual value of the direct-current voltage, a segmented starting boosting value is obtained according to the voltage threshold; and the three-phase PWM rectifier is controlled to output direct current voltage according to the step-up starting value, so that the three-phase PWM rectifier is started in a step-up mode, the overcurrent phenomenon caused by sudden voltage change is avoided, and the direct current power supply is stably and reliably increased. It can be seen that, the utility model discloses make three-phase PWM rectifier start-up in-process, avoid appearing because of the start-up that the sudden change of voltage arouses phenomenon of overflowing, and simple structure, easy realization.
Drawings
FIG. 1 is a circuit diagram of a variable frequency power supply employing a soft start circuit of a three-phase PWM rectifier;
fig. 2 is a schematic block diagram of a soft start circuit of a three-phase PWM rectifier according to the present invention;
in the figure: the system comprises a 1-PWM rectifier, a 2-intermediate energy storage circuit, a 3-PWM inverter, a CT 1-a first current transformer, a CT 2-a second current transformer, a CT 3-a third current transformer, a KM 1-a first alternating current contactor, a KM 2-a second alternating current contactor, a U1-a control circuit and a U2-a voltage comparison circuit.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1 and 2, a soft start circuit of a three-phase PWM rectifier is based on a variable frequency power supply, the variable frequency power supply includes a three-phase PWM rectifier 1, an intermediate energy storage circuit 2 and a control circuit U1, the control circuit U1 is electrically connected to the three-phase PWM rectifier 1, the intermediate energy storage circuit 2 includes a first dc bus capacitor C1 and a second dc bus capacitor C2, one end of the first dc bus capacitor C1 is connected to one end of the second dc bus capacitor C2, the other end of the first dc bus capacitor C1 is a P terminal, and the other end of the second dc bus capacitor C2 is an N terminal.
The soft start circuit of the utility model comprises a first current transformer CT1, a second current transformer CT2, a third current transformer CT3, a resistance bleeder circuit and a voltage comparison circuit U2 which are respectively and electrically connected with a control circuit U1; a voltage threshold (for example, DC700V) for starting the three-phase PWM rectifier 1 and a current threshold of the three-phase PWM rectifier 1 are built in the control circuit U1; preferably, the control circuit U1 includes the DSP 28335.
The first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 are respectively arranged at the three-phase input end of the three-phase PWM rectifier 1 and are used for acquiring a three-phase input current real-time value; the control circuit U1 controls the three-phase PWM rectifier 1 to work and stop by comparing the real-time value of the three-phase input current with the current threshold value; preferably, the first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 are all hall current sensors. In this embodiment: the current amplifier further comprises a signal conditioning circuit for amplifying current signals, the input end of the signal conditioning circuit is electrically connected with the first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 respectively, and the output end of the signal conditioning circuit is electrically connected with the control circuit U1. Since signal conditioning circuits are prior art, they will not be described in detail here.
The input end of the resistance voltage division circuit is respectively and electrically connected with the P end and the N end and is used for collecting the actual value of the direct current voltage, and the output end of the resistance voltage division circuit is respectively and electrically connected with the positive phase input end of the voltage comparison circuit U2 and the control circuit U1.
The inverting input end of the voltage comparison circuit U2 is electrically connected with the control circuit U1, and the output end OUT of the voltage comparison circuit U2 is electrically connected with the control circuit; the voltage comparison circuit U2 compares the actual value of the direct current voltage with the set value of the direct current voltage transmitted by the control circuit U1 and outputs a corresponding electric signal to the control circuit U1; preferably, the voltage comparison circuit U2 includes a voltage comparator LM 393.
The control circuit U1 divides the difference between the actual value of the direct current voltage and the voltage threshold into N sections, and each section of voltage value is a section starting boosting value; the set value of the direct current voltage is the sum of the actual value of the direct current voltage and the N times of the segmented starting and boosting value; the control circuit U1 controls the three-phase PWM rectifier 1 to output a step-up starting value by adjusting the PI gain values of the active component and the reactive component of the three-phase PWM rectifier 1; meanwhile, the control circuit U1 controls the three-phase PWM rectifier 1 to output a sectional start boost value or stop outputting according to the electric signal transmitted by the voltage comparison circuit U2; where N is a positive integer, in this embodiment N is 6. When the actual value of the direct-current voltage collected by the resistance voltage-dividing circuit is DC541V and the voltage threshold value after the three-phase PWM rectifier 1 is started is DC700V, the step-up voltage value is 31V at the moment. Of course, the step-up voltage value is not limited to 31V according to the actual value of the collected dc voltage.
The utility model discloses a soft start circuit of three-phase PWM rectifier, the theory of operation as follows:
as shown in fig. 1 and fig. 2, when a power grid is connected, since the three-phase PWM rectifier 1 is not operated, the dc voltages applied to the P terminal and the N terminal at this time are obtained by rectifying the three-phase voltages through the parallel diodes (VD1, VD2, VD3, VD4, VD5, VD6) of the six IGBT tubes (T1, T2, T3, T4, T5, T6) in the three-phase PWM rectifier 1, and at this time, the first dc bus capacitor C1 and the second dc bus capacitor C2 can be precharged through an ac side or a dc side.
When the three-phase PWM rectifier 1 is in operation, the actual dc voltage value (voltage value between the P terminal and the N terminal) is first collected by the resistance voltage divider circuit, and the actual dc voltage value is transmitted to the control circuit U1 and the voltage comparator circuit U2, respectively. In this embodiment, the actual value of the DC voltage is DC541V, and at this time, the control circuit U1 makes a difference between the built-in voltage threshold DC700V and the actual value of the DC voltage, which is DC514V, where the difference is 186V; the difference 186V is divided into six sections (not limited to six sections), and each section is 31V, that is, the section start boost value is 31V.
After the step-up starting value is obtained, the control circuit U1 controls the three-phase PWM rectifier 1 to output the step-up starting value by adjusting the PI gain values of the active component and the reactive component of the three-phase PWM rectifier 1, so that the two ends of the first dc bus capacitor C1 and the second dc bus capacitor C2 are boosted. Meanwhile, the actual value of the direct-current voltage at two ends of the first direct-current bus capacitor C1 and the second direct-current bus capacitor C2 is transmitted to the positive phase input end of the voltage comparison circuit U2, the control circuit U1 transmits the set value of the direct-current voltage in the section to the voltage comparison circuit U2, the set value of the direct-current voltage is the sum of the actual value of the direct-current voltage and the N-time segmented starting and boosting value, and the set value of the direct-current voltage in the first section is DC 545V; when the actual value of the direct current voltage is larger than the set value of the direct current voltage at the section, the voltage comparison circuit U2 outputs a high level to the control circuit U1, the control circuit U1 performs second-stage boosting, after the second-stage boosting is completed, third-stage boosting, fourth-stage boosting, fifth-end boosting and sixth-stage boosting are performed, and the three-phase PWM rectifier 1 is started. It can be seen that, the utility model discloses make three-phase PWM rectifier start-up in-process, avoid appearing because of the start-up that the sudden change of voltage arouses phenomenon of overflowing, and simple structure, easy realization.
In this example, the set value of the DC voltage boosted in the second stage is DC545 plus 31V and is DC576V, the set value of the DC voltage boosted in the third stage is DC607V, the set value of the DC voltage boosted in the fourth stage is DC638V, the set value of the DC voltage boosted in the fifth stage is DC669, and the set value of the DC voltage boosted in the sixth stage is DC 700V.
In the whole process, the first current transformer CT1, the second current transformer CT2 and the third current transformer CT3 collect three-phase input current actual values in real time, the three-phase input current actual values are amplified by the signal conditioning circuit and then transmitted to the control circuit U1, the control circuit U1 compares the three-phase input current actual values with a built-in current threshold, once the three-phase input current actual values are larger than the current threshold, the control circuit U1 stops the three-phase PWM rectifier 1, damage to the three-phase PWM rectifier 1 is prevented, and current monitoring is achieved.
The following are specifically mentioned: the variable frequency power supply in the embodiment is an alternating current-direct current double-PWM variable frequency power supply for the electromagnetic stirrer.
As shown in FIG. 1, the voltage type AC-DC-AC double PWM variable frequency power supply for the electromagnetic stirrer comprises a PWM rectifier 1, a first DC bus capacitor C1, a first DC bus capacitor C2, voltage-sharing resistors R1 and R2, a PWM inverter 3 and the like, wherein the PWM rectifier 1 comprises six IGBT (T1, T2, T3, T4, T5 and T6) of anti-parallel diodes, the T1, T2 and T3 are connected in a common cathode mode, and the T4, T5 and T6 are connected in a common anode mode. The common anode connection ends of the T4, the T5 and the T6 are connected with the negative end of a second direct current bus capacitor C2, voltage equalizing resistors R1 and R2 are respectively connected with the first direct current bus capacitor C1 and the second direct current bus capacitor C2 in parallel, the direct current bus capacitors are connected with the PWM inverter 3, the PWM inverter 3 is composed of six anti-parallel diode IGBTs (T11, T12, T13, T14, T15 and T16), the T11, T12 and T13 are connected with a common cathode, the T14, T15 and T16 are connected with a common anode, the positive end of the first direct current bus capacitor C1 is connected with the common cathode end of the T11, the T12 and the T13, the negative end of the second direct current bus capacitor C2 is connected with the common anode of the T14, the T15 and the T16, and the PWM inverter 3 is connected with a load-side three-phase electromagnetic coil (electromagnetic coil). In this embodiment: the power grid is accessed through three incoming line reactor groups L1, a first alternating current contactor KM1 and a second alternating current contactor KM2 are arranged on a three-phase line, resistors R11, R12 and R13 are respectively connected on the second alternating current contactor KM2 in series, filter circuits are further respectively arranged on the three-phase line, and the three-phase line is respectively provided with a capacitor C1, a resistor R4, a capacitor C2, a resistor R5, a capacitor C3, a resistor R6 and a filter inductor group L2 which are connected in series.
As shown in fig. 1 and fig. 2, the working process of this embodiment is as follows:
and when the PWM rectification is not in operation: after the power grid is connected, at the moment, the second alternating current contactor KM2 is attracted, three-phase power firstly passes through line-incoming impedance L1, resistor R11, resistor R12, resistor R13, capacitor C1, capacitor C2, capacitor C3, resistor R4, resistor R5, resistor R6 and filter inductor L2 for filtering and voltage reduction, alternating current is rectified into direct current through VD1, VD2, VD3, VD4, VD5 and VD6 in the IGBT, the first direct current bus capacitor C1 and the second direct current bus capacitor C2 are precharged, when the voltage between the P end and the N end reaches a certain value, such as DC480V, the first alternating current contactor KM1 is attracted, and the precharging of uncontrolled rectification is completed.
When the three-phase PWM rectifier 1 starts to operate: the voltage threshold value (for example, DC700V) of the three-phase PWM rectifier is subtracted from the initial value of the direct current voltage actual value (for example, DC514V), the voltage difference is segmented (for example, six segments), the voltage increment of each segment is 31V, and the voltage increment is respectively and sequentially added to the two sides of the P end and the N end. In the process of step-up in sections, the actual value of the three-phase input current is detected by a first current transformer CT1, a second current transformer CT2 and a third current transformer CT3 which are arranged at the input end, and is transmitted to an internal AD circuit of the DSP28335 after passing through a signal conditioning circuit, and current detection is carried out after processing. After the DSP28335 converts the set value of the DC voltage (DC545V) at the first stage by D/a, the set value is output from the port IO5 to the inverting input terminal of the voltage comparing circuit U2, and the non-inverting input terminal of the voltage comparing circuit U2 is used to access the actual value of the DC voltage collected by the resistor voltage dividing circuit. When the actual value of the direct current voltage is larger than the set value of the direct current voltage, the output end OUT outputs high level to be fed back to the port IO6 of the DSP28335, meanwhile, the DSP28335 collects the actual value of the direct current voltage through the port IO4, and when the actual value of the direct current voltage is the same as the set value of the direct current voltage at the first section, the second stage of boosting is carried OUT. The port IO1, the port IO2 and the port IO3 of the DSP28335 are respectively connected with a three-phase input current actual value, the three-phase input current actual value is compared with a built-in current threshold value, when the three-phase input current actual value is larger than the current threshold value, the three-phase PWM rectifier 1 is stopped, and it is ensured that the three-phase input current is within an allowable range of the IGBT when the control circuit U1 performs PI gain adjustment on an active component and a reactive component of the three-phase PWM rectifier 1 in the boosting process.
The above-mentioned preferred embodiments of the present invention are not intended to limit the present invention, and any modifications made within the spirit and principles of the present invention, such as the improvement of the soft start circuit of the three-phase PWM rectifier, should be included within the scope of the present invention.
Claims (5)
1. The soft start circuit of the three-phase PWM rectifier is based on a variable frequency power supply, the variable frequency power supply comprises a three-phase PWM rectifier, an intermediate energy storage circuit and a control circuit, the control circuit is electrically connected with the three-phase PWM rectifier, the intermediate energy storage circuit comprises a first direct current bus capacitor and a second direct current bus capacitor, one end of the first direct current bus capacitor is connected with one end of the second direct current bus capacitor, the other end of the first direct current bus capacitor is a P end, and the other end of the second direct current bus capacitor is an N end;
it is characterized in that the preparation method is characterized in that,
the soft start circuit comprises a first current transformer, a second current transformer, a third current transformer, a resistance voltage division circuit and a voltage comparison circuit which are respectively electrically connected with the control circuit; the control circuit is internally provided with a voltage threshold value after the three-phase PWM rectifier is started and a current threshold value of the three-phase PWM rectifier;
the first current transformer, the second current transformer and the third current transformer are respectively arranged at the three-phase input end of the three-phase PWM rectifier and are used for acquiring a three-phase input current real-time value; the control circuit controls the three-phase PWM rectifier to work and stop by comparing the three-phase input current real-time value with the current threshold value;
the input end of the resistance voltage division circuit is respectively and electrically connected with the P end and the N end and is used for collecting the actual value of the direct current voltage, and the output end of the resistance voltage division circuit is respectively and electrically connected with the positive phase input end of the voltage comparison circuit and the control circuit;
the inverting input end of the voltage comparison circuit is electrically connected with the control circuit, and the output end of the voltage comparison circuit is electrically connected with the control circuit; the voltage comparison circuit compares the actual value of the direct current voltage with a set value of the direct current voltage transmitted by the control circuit and outputs a corresponding electric signal to the control circuit;
the control circuit divides the difference between the voltage threshold value and the actual value of the direct current voltage into N sections, and each section of voltage value is a section starting boosting value; the set value of the direct current voltage is the sum of the actual value of the direct current voltage and the N times of the segmented starting and boosting value;
the control circuit controls the three-phase PWM rectifier to output a segmented starting and boosting value by adjusting PI gain values of active components and reactive components of the three-phase PWM rectifier; the control circuit controls the three-phase PWM rectifier to output a sectional starting boost value or stop outputting according to the electric signal transmitted by the voltage comparison circuit; wherein N is a positive integer.
2. The soft-start circuit of a three-phase PWM rectifier of claim 1, wherein said voltage comparison circuit comprises a LM393 voltage comparison chip.
3. The soft-start circuit of a three-phase PWM rectifier according to claim 1, wherein said control circuit comprises DSP 28335.
4. The soft-start circuit of the three-phase PWM rectifier according to any one of claims 1 to 3, further comprising a signal conditioning circuit for amplifying the current signal, wherein the input terminal of the signal conditioning circuit is electrically connected to the first current transformer, the second current transformer and the third current transformer, respectively, and the output terminal of the signal conditioning circuit is electrically connected to the control circuit.
5. The soft-start circuit of a three-phase PWM rectifier of claim 4, wherein said first current transformer, said second current transformer and said third current transformer are Hall current sensors.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4016824A1 (en) * | 2020-12-17 | 2022-06-22 | Gefran Drives and Motion Srl | Method for controlling a frequency converter configured to drive an inductive load |
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2019
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP4016824A1 (en) * | 2020-12-17 | 2022-06-22 | Gefran Drives and Motion Srl | Method for controlling a frequency converter configured to drive an inductive load |
| WO2022130314A1 (en) * | 2020-12-17 | 2022-06-23 | Gefran Drives And Motion S.R.L. | Method for controlling a frequency converter configured to drive an inductive load |
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