A servo drive soft start system and control method thereof

Abstract

A servo drive soft start system and soft start control method, when the system is initially powered on, by sampling the three-phase AC input voltage and DC bus voltage, driving the thyristor in the three-phase bridge type half-controlled rectifier circuit, taking the voltage value comparison method, charging the filter capacitor of the filter circuit in sections, the charging process is not affected by power grid fluctuations, more stable and reliable. The present invention eliminates the need for a soft start relay and a pre-charging resistor, reduces mechanical contacts, reduces the volume, and enhances reliability.

Description

Technical Field

[0001] The invention belongs to the technical field of variable pitch system control and relates to a soft starting system of a servo drive and a control method thereof. Background Art

[0002] The variable pitch system is one of the three major electrical systems for the safe operation of wind turbines. It changes the pitch angle of the blades according to the wind conditions in the environment where the wind turbine is located to achieve the purpose of adjusting power and protecting the wind turbine. The servo drive is the core component and execution structure of the variable pitch system. The variable pitch controller controls the variable pitch motor through the servo drive to achieve the purpose of adjusting the angle of the wind turbine blades. The main circuit structure of the servo drive generally adopts an uncontrolled rectifier + inverter method. The rectifier circuit of this structure is the simplest and does not require a control circuit. However, since the DC voltage of the uncontrolled rectifier circuit cannot be controlled, a soft start circuit is required at the moment of power-on.

[0003] The common soft start circuits are Figure 1 As shown, the soft start circuit includes a diode rectifier unit 1, a soft start unit 2, a bus voltage detection unit 3, a digital signal processor 4, a soft start relay coil (not shown), a filter capacitor 5, and voltage divider resistors 6 and 7. The diode rectifier unit 1 is a rectifier bridge composed of 6 diodes, and the soft start unit 2 includes a pre-charge resistor 8 and a soft start relay contact 9 connected in parallel. At the moment of power-on, the soft start relay coil is not conducting, and the soft start relay contact 9 is in an open state. The diode rectifier unit 1 charges the filter capacitor 5 through the pre-charge resistor 8. After the bus voltage rises to a preset voltage value and delays for a period of time, the digital signal processor 4 controls the soft start relay coil to conduct, and the soft start relay contact 9 is closed, and the pre-charge resistor 8 is short-circuited. It can be seen that the disadvantage of this soft start circuit is that the soft start relay and the pre-charge resistor are used, and the conductive part of the soft start relay is an active contact, which is not suitable for passing large currents. In addition, the action voltage of the soft start relay will shake and oscillate, causing the entire operation to be unreliable. Summary of the invention

[0004] (I) Purpose of the invention

[0005] The purpose of the present invention is to provide a servo drive soft start system and soft start control method. When the system is initially powered on, the three-phase AC input voltage and the DC bus voltage are sampled to drive the thyristor in the three-phase bridge type half-controlled rectifier circuit, and the filter capacitor of the filter circuit is charged in sections by comparing the voltage values. The charging process is not affected by power grid fluctuations and is more stable and reliable. The present invention eliminates the need for a soft start relay and a pre-charging resistor, reduces mechanical contacts, reduces the volume, and enhances reliability.

[0006] (II) Technical solution

[0007] To solve the above problems, the first aspect of the present invention provides a soft start system for a servo drive, comprising a three-phase bridge half-controlled rectifier circuit, a filter circuit, a bus voltage detection circuit, a three-phase AC voltage detection circuit, a drive circuit and a microprocessor; the three-phase bridge half-controlled rectifier circuit is connected to a three-phase AC input power supply and a filter circuit; the three-phase AC voltage detection circuit detects the three-phase AC voltage at the input end of the three-phase bridge half-controlled rectifier circuit, the bus voltage detection circuit detects the DC bus voltage at the output end of the three-phase bridge half-controlled rectifier circuit, and the bus voltage detection circuit and the three-phase AC voltage detection circuit are both connected to the microprocessor; the microprocessor controls the three-phase bridge half-controlled rectifier circuit through the drive circuit.

[0008] According to another aspect of the present invention, the three-phase bridge half-controlled rectifier circuit includes a three-phase half-wave uncontrolled rectifier circuit and a three-phase half-wave controlled rectifier circuit.

[0009] According to another aspect of the present invention, the above-mentioned three-phase half-wave uncontrolled rectifier circuit is composed of three rectifier diodes with anodes connected together, and the connected anodes serve as the negative electrode of the output end of the three-phase bridge half-controlled rectifier circuit, that is, the negative electrode of the DC bus.

[0010] According to another aspect of the present invention, the above-mentioned three-phase half-wave controlled rectifier circuit is composed of three thyristors with connected cathodes, and the connected cathodes serve as the positive pole of the output end of the three-phase bridge half-controlled rectifier circuit, that is, the positive pole of the DC bus.

[0011] According to another aspect of the present invention, the filter circuit comprises at least one group or multiple groups of filter capacitors connected in series in pairs, and the filter capacitors comprise electrolytic capacitors.

[0012] Another aspect of the present invention provides a control method for the servo drive soft start system as described above, the method comprising:

[0013] Step 1, setting a soft start initial voltage value (VREF1), a first preset voltage value (VREF2), and a second preset voltage value (VREF3);

[0014] Step 2, determining whether each phase voltage is within its corresponding soft start region;

[0015] Step 3, comparing the AC voltage value of each phase with the initial voltage value of the soft start, if the AC voltage value of each phase is less than the initial voltage value of the soft start, driving the thyristor of the three-phase bridge half-controlled rectifier circuit to charge the filter circuit;

[0016] Step 4, compare the actual bus voltage value with the soft start initial voltage value, and reset the soft start initial voltage value;

[0017] Step 5: Compare the actual bus voltage value with the second preset voltage value to determine whether to end the soft start.

[0018] According to another aspect of the present invention, step 1 further includes: setting the soft start initial voltage value (VREF1) and the first preset voltage value (VREF2) according to the charging current, and setting the above-mentioned second preset voltage value to be smaller than the DC bus voltage value of the normal working state of the drive circuit.

[0019] According to another aspect of the present invention, step 2 further includes: comparing the AC voltage value of each phase with 0.9Upeak, where Upeak is the peak voltage value of the three-phase AC input, if the AC voltage value of each phase is greater than 0.9Upeak, then the voltage soft start flag of each phase is set to 1; when the voltage soft start flags of two adjacent phases are set to 1, and the AC voltage value of the phase in the current waveform is less than 0.5Upeak, it means that the voltage waveform of this phase has entered its corresponding soft start area.

[0020] According to another aspect of the present invention, step 4 further includes: comparing the bus voltage value with the soft start initial voltage value, if the bus voltage value is equal to the soft start initial voltage value, setting the soft start initial voltage value to the sum of the current soft start initial voltage value and the first preset voltage value, that is, VREF1=VREF1+VREF2.

[0021] According to yet another aspect of the present invention, step 5 further includes ending the soft start if the actual bus voltage value is greater than or equal to a second preset voltage value.

[0022] (III) Beneficial effects

[0023] The above technical solution of the present invention has the following beneficial technical effects: since the bus voltage rises gently, no excessive current impact will be caused during the soft start of the rectifier system. In addition, the present invention eliminates the need for a soft start relay and a pre-charging resistor, reduces mechanical contacts, reduces volume, and enhances reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a structural schematic diagram of a soft start circuit of an uncontrolled rectifier system in the prior art;

[0025] Figure 2 The overall structural block diagram of a soft start system of a servo drive provided by the present invention;

[0026] Figure 3 A schematic flow chart of a soft start control method provided by the present invention. DETAILED DESCRIPTION

[0027] In order to make those skilled in the art better understand the technical solutions in the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, in the following description, the description of known structures and technologies is omitted to avoid unnecessary confusion of the concept of the present invention.

[0028] Figure 2 An example of an overall structural block diagram of a servo drive soft start system is given, which includes a three-phase bridge half-controlled rectifier circuit 10, a filter circuit 11, a bus voltage detection circuit 12, a three-phase AC voltage detection circuit 13, a thyristor drive circuit 14, and a digital signal processor 15 (i.e., a microprocessor).

[0029] The three-phase bridge type half-controlled rectifier circuit 10 is composed of a three-phase half-wave uncontrolled rectifier circuit and a three-phase half-wave controlled rectifier circuit connected in series, wherein the three-phase half-wave uncontrolled rectifier circuit is composed of three rectifier diodes with anodes connected together, and the connected anodes serve as the negative pole of the output end of the three-phase bridge type half-controlled rectifier circuit, that is, the negative pole of the DC bus; the three-phase half-wave controlled rectifier circuit is composed of three thyristors with cathodes connected together, and the connected cathodes serve as the positive pole of the output end of the three-phase bridge type half-controlled rectifier circuit, that is, the positive pole of the DC bus; the DC bus positive pole and the DC bus negative pole constitute the DC bus voltage. The connection point of the three-phase half-wave uncontrolled rectifier circuit and the three-phase half-wave controlled rectifier circuit is connected to the three-phase AC input power supply as the input end of the three-phase bridge type half-controlled rectifier circuit. This circuit has both controllable and uncontrollable characteristics. For three thyristors with a common cathode, the thyristor with a higher anode potential and applied with a trigger pulse is turned on. For three rectifier diodes with a common anode, the rectifier diode with the lowest cathode potential is turned on. By adjusting the thyristor trigger angle, a DC bus voltage of any value between zero and the three-phase peak voltage can be obtained.

[0030] The filter circuit 11 is composed of one or more groups of electrolytic capacitors connected in series, and the electrolytic capacitors are connected in parallel between the positive pole of the DC bus and the negative pole of the DC bus. The electrolytic capacitors use the charge and discharge of their own energy to achieve a filtering function so as to smooth the voltage across the DC bus.

[0031] The bus voltage detection circuit 12 is connected to the output end of the three-phase bridge half-controlled rectifier circuit 10, and is used to detect the DC bus voltage and send the sampling signal to the digital signal processor 15. The bus voltage sampling circuit includes a voltage divider and a bus voltage detection module. The voltage divider is composed of two or more resistors connected in series, and is used to divide the bus voltage for detection.

[0032] The digital signal processor 15 is used to collect AC and DC voltage signals and control the conduction of the thyristors in a timely manner to realize the soft start function of the half-controlled rectifier system. Specifically, the sampling signal sent by the bus voltage sampling circuit 12 is amplified by a certain multiple to generate the actual DC bus voltage value, and cooperates with the three-phase AC voltage detection circuit 13 to determine whether to start or end the soft start.

[0033] The input end of the three-phase AC voltage detection circuit 13 is connected to the three-phase AC input power supply, and is used to detect the three-phase AC input voltage. The three-phase AC voltage detection circuit includes a sampling unit, a filtering unit and a comparator. The sampling unit adopts a resistor series step-down two-by-two differential amplifier circuit to sample the three-phase AC input voltage. The filtering unit adopts a Butterworth second-order low-pass filter to suppress differential mode interference. The comparator is a voltage comparator, which is used to convert the sinusoidal synchronous voltage signal into a square wave signal with the same frequency as the three-phase AC power supply, and is used to determine the phase sequence of the three-phase power connected during system self-test. After the three-phase AC power is divided by resistors, it is differentiated between the two, and then the op amp chip is used for second-order low-pass filtering to obtain a sampling signal with high-order harmonics filtered out. In order to meet the 0-3V input requirement of the AD sampling port of the DSP, a 1.5V DC bias voltage is superimposed on the signal, and a three-phase voltage sampling signal with a bias of 1.5V is obtained after limiting. This sampling signal is sent to the digital signal processor 15. The digital signal processor 15 amplifies the acquisition signal sent by the three-phase AC voltage detection circuit 13 by a certain multiple to generate an actual three-phase AC voltage value, and determines whether the thyristor of the three-phase bridge half-controlled rectifier circuit 10 is triggered according to the actual three-phase AC voltage value.

[0034] The input end of the thyristor drive circuit 14 is connected to the digital signal processor 15, and the output end is connected to the three-phase bridge half-controlled rectifier circuit 10. The thyristor drive circuit is composed of a buffer, a drive chip and a pulse voltage device. The buffer is a three-state buffer protector, which is used to prevent the thyristor from being triggered by mistake. The drive chip adopts a power amplifier chip, which is used to drive the thyristor to conduct and enhance the circuit driving ability. The power amplifier chip is an insulated gate bipolar transistor (MOSFET). The pulse transformer is a high-frequency pulse transformer to achieve isolation between the main circuit and the control circuit.

[0035] The trigger pulse output by the digital signal processor 15 is sent to the thyristor drive circuit 14 to control the MOSFET tube to turn on and generate a square wave voltage at the primary side of the pulse transformer. This square wave voltage generates a drive pulse at the secondary side of the pulse transformer. The output end of the drive pulse is sent to the control end of the three-phase half-wave controlled rectifier circuit in the three-phase bridge half-controlled rectifier circuit 10 to drive the thyristor to turn on.

[0036] The digital signal processor 15 is respectively connected to the output end of the three-phase AC voltage detection circuit 13 and the sampling signal output end of the bus voltage detection circuit 12, and generates a trigger signal after calculation and processing according to the sampling signal output by the three-phase AC voltage detection circuit 13 and the sampling signal output by the bus voltage detection circuit 12. The trigger signal controls the three-phase half-wave controlled rectifier circuit of the three-phase bridge half-controlled rectifier circuit 10 through the thyristor drive circuit 14, thereby realizing the charging of the filter circuit 11.

[0037] Corresponding to the soft start system embodiment provided by the present invention, the present invention also provides a thyristor soft start control method.

[0038] See also Figure 3 , is a flow chart of a soft start control method provided by an embodiment of the present invention, the control method comprising:

[0039] Step S1: setting a soft start initial voltage value VREF1, a first preset voltage value VREF2, and a second preset voltage value VREF3.

[0040] When setting the soft start initial voltage value VREF1 and the first preset voltage value VREF2, it is necessary to consider keeping the charging current within a safe range. The magnitude of the charging current mainly depends on the degree of subdivision of the charging voltage in the program and the circuit characteristics of the power supply system hardware. During the entire process of charging the energy storage circuit, the maximum value of the charging current is the peak value of the charging current during the first charging process after adjusting the soft start initial voltage. According to the selected parameters, the soft start initial voltage value and the first preset voltage value VREF2 are set. The above second preset voltage value is smaller than the DC bus voltage value of the normal working state of the drive circuit.

[0041] Step S2: Determine whether each phase voltage is within its corresponding soft start region.

[0042] The soft start area of ​​each phase voltage is the falling section of each phase voltage wave peak. When the AC voltage value of each phase exceeds 0.9 times the peak voltage value Upeak, the voltage over-peak flag of each phase is set to 1, and Upeak represents the three-phase AC input peak voltage. Once the voltage over-peak flags of two adjacent phases are both 1 and the AC voltage value of the previous waveform is less than 0.5Upeak, it is considered that the voltage waveform of this phase has entered its corresponding soft start area. When the AC voltage value of each phase is negative, the flag is cleared.

[0043] Step S3: Compare the AC voltage value of each phase with the soft start initial voltage value. If the AC voltage value of each phase is less than the soft start initial voltage value, drive the thyristor of each phase to conduct.

[0044] Three detectable phase voltages Uuv, Uvw and Uwu are extracted from the three-phase AC power grid through resistor voltage division and differential amplification links; the detected voltages Uuv, Uvw and Uwu of each phase are sent to a digital signal processor, and the processor compares the AC voltage value with the initial voltage value of the soft start. If the AC voltage value of each phase is less than the initial voltage value of the soft start, the processor gives a trigger signal to drive the thyristors of each phase of the three-phase bridge half-controlled rectifier circuit to turn on, and the filter capacitor of the filter circuit is charged.

[0045] Step S4: Compare the actual bus voltage value with the soft start initial voltage value, and reset the soft start initial voltage value.

[0046] A detectable bus voltage Udc is extracted from the DC bus through a resistor voltage divider and an isolation amplifier link, and the bus voltage Udc is sent to a digital signal processor. The digital signal processor compares the bus voltage value with the soft start initial voltage value. If the actual bus voltage value Udc is equal to the soft start initial voltage value VREF1, the soft start initial voltage value VREF1 is set to the sum of the current soft start initial voltage value VREF1 and the first preset voltage VREF2, that is, VREF1=VREF1+VREF2.

[0047] Step S5: Compare the actual bus voltage value with the second preset voltage value to determine whether to end the soft start.

[0048] The voltage of each phase when triggered increases continuously according to the soft start initial voltage value VREF1, and the actual bus voltage value Udc continues to increase. When the actual bus voltage value Udc rises to the second preset voltage value VREF3, the soft start ends and switches to the normal working state. At this time, the conduction angle is zero during normal operation and no excessive charging current surge impact is caused.

[0049] The present invention is further described below with reference to a specific embodiment.

[0050] Assume that the actual bus voltage value UDC=0V at the initial stage, set the soft start initial voltage value VREF1 to 10V, the first preset voltage value VREF2 to 10V, and the second preset voltage value VREF3 to 500V. Once the phase voltage in the soft start area is detected to be lower than VREF1, the digital signal processor 15 gives a trigger signal to trigger the corresponding thyristors in the three-phase half-wave controlled rectifier circuit of the three-phase bridge half-controlled rectifier circuit 10 to turn on and charge the filter capacitor. After several such charging processes, the DC bus voltage value UDC rises to 10V. When the bus voltage value UDC rises to 10V, VREF1 is set to the sum of the current soft start initial voltage value VREF1 (set value 10V) and the first preset voltage value VREF2 (set value 10V), that is, VREF1 = 20V, then the voltage value of each phase is judged in the next cycle. Once the voltage value of each phase in the soft start area is lower than VREF1 at this time, the digital signal processor 15 gives a trigger signal again to trigger the thyristor to turn on and charge the filter capacitor, and so on. The voltage of each phase when triggered continues to increase according to the VREF1 value, and the actual bus voltage value UDC continues to rise. When the actual bus voltage value UDC rises to the second preset voltage value VREF3 (set value 500V), the three-phase bridge half-controlled rectifier circuit 10 can be safely switched to the state where the thyristor conduction angle is zero during normal operation, and the soft start process ends. Since the bus voltage rises gently, it will not cause excessive current shock during the soft start process of the rectifier system.

[0051] In summary, the present invention provides a servo drive soft start control system and method thereof, the system includes a three-phase bridge half-controlled rectifier circuit, a filter circuit, a bus voltage detection circuit, a three-phase AC voltage detection circuit, a drive circuit and a microprocessor. The method includes: obtaining the initial value of the soft start voltage, judging whether a phase in the three-phase electricity is in its corresponding soft start area; when the processor detects that a phase in the three-phase electricity is in its corresponding soft start area, comparing the actual phase voltage of the phase with the initial value of the soft start voltage, judging whether the current phase voltage is less than the initial value of the soft start voltage; when the phase voltage value is lower than the initial value of the soft start voltage, the corresponding thyristor is triggered, and the thyristor is turned on to charge the filter capacitor until the voltage across the thyristor is negative and it is automatically cut off. After several cycles of such charging process, the DC bus voltage value can reach the initial value of the soft start voltage. At this time, the initial value of the soft start voltage is increased to the sum of the previous initial value of the soft start voltage and the first preset voltage value, so that the soft start system can start charging the filter capacitor at a higher voltage during the next charging; when it is detected that the bus voltage value is greater than the second preset voltage value, the soft start process ends. The charging process of the present invention is not affected by power grid fluctuations, is more stable and reliable, eliminates the need for a soft start relay and a pre-charging resistor, reduces mechanical contacts, reduces volume, and enhances reliability.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A soft start system for a servo drive, characterized in that: It includes a three-phase bridge type half-controlled rectifier circuit, a filter circuit, a bus voltage detection circuit, a three-phase AC voltage detection circuit, a drive circuit and a microprocessor; The three-phase bridge half-controlled rectifier circuit is connected to a three-phase AC input power supply and a filter circuit; the three-phase AC voltage detection circuit detects the three-phase AC voltage at the input end of the three-phase bridge half-controlled rectifier circuit, and the bus voltage detection circuit detects the DC bus voltage at the output end of the three-phase bridge half-controlled rectifier circuit, and the bus voltage detection circuit and the three-phase AC voltage detection circuit are both connected to a microprocessor; the microprocessor controls the three-phase bridge half-controlled rectifier circuit through a drive circuit; The three-phase bridge half-controlled rectifier circuit includes a three-phase half-wave uncontrolled rectifier circuit and a three-phase half-wave controlled rectifier circuit; the filter circuit includes at least one group or multiple groups of filter capacitors connected in series, and the filter capacitors include electrolytic capacitors.

2. The soft start system according to claim 1, wherein the three-phase half-wave uncontrolled rectifier circuit is composed of three rectifier diodes whose anodes are connected together, and the connected anodes serve as the negative pole of the output end of the three-phase bridge half-controlled rectifier circuit, that is, the negative pole of the DC bus.

3. The soft start system according to claim 1, wherein the three-phase half-wave controlled rectifier circuit is composed of three thyristors with cathodes connected together, and the connected cathodes serve as the positive pole of the output end of the three-phase bridge half-controlled rectifier circuit, that is, the positive pole of the DC bus.

4. A control method for a soft start system of a servo drive according to any one of claims 1 to 3, the method comprising: Step 1, setting a soft start initial voltage value VREF1, a first preset voltage value VREF2, and a second preset voltage value VREF3; Step 2, determining whether each phase voltage is within its corresponding soft start region; Step 3, comparing the AC voltage value of each phase with the initial voltage value of the soft start, if the AC voltage value of each phase is less than the initial voltage value of the soft start, driving the thyristor of the three-phase bridge half-controlled rectifier circuit to charge the filter circuit; Step 4, compare the actual bus voltage value with the soft start initial voltage value, and reset the soft start initial voltage value; Step 5: Compare the actual bus voltage value with the second preset voltage value to determine whether to end the soft start.

5. The control method according to claim 4, wherein step 1 further comprises: The soft start initial voltage value VREF1 and the first preset voltage value VREF2 are set according to the charging current, and the second preset voltage value is set to be smaller than the DC bus voltage value of the driving circuit in normal operation.

6. The control method according to claim 4, wherein step 2 further comprises: Compare the AC voltage value of each phase with 0.9Upeak, where Upeak is the peak voltage value of the three-phase AC input. If the AC voltage value of each phase is greater than 0.9Upeak, the voltage soft-start flag of each phase is set to 1; when the voltage soft-start flags of two adjacent phases are both set to 1, and the AC voltage value of this phase in the previous waveform is less than 0.5Upeak, it means that the voltage waveform of this phase has entered its corresponding soft-start area.

7. The control method according to claim 4, wherein step 4 further comprises: The bus voltage value is compared with the soft start initial voltage value. If the bus voltage value is equal to the soft start initial voltage value, the soft start initial voltage value is reset to the sum of the current soft start initial voltage value and the first preset voltage value, that is, VREF1=VREF1+VREF2.

8. The control method according to claim 4, wherein step 5 further comprises ending the soft start if the actual bus voltage value is greater than or equal to a second preset voltage value.

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