WO2015158134A1 - 一种变频器的控制方法、设备和系统 - Google Patents

一种变频器的控制方法、设备和系统 Download PDF

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Publication number
WO2015158134A1
WO2015158134A1 PCT/CN2014/092009 CN2014092009W WO2015158134A1 WO 2015158134 A1 WO2015158134 A1 WO 2015158134A1 CN 2014092009 W CN2014092009 W CN 2014092009W WO 2015158134 A1 WO2015158134 A1 WO 2015158134A1
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Prior art keywords
current
power factor
bus
control
positive
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PCT/CN2014/092009
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English (en)
French (fr)
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唐杰
裔杰
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华为技术有限公司
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Publication of WO2015158134A1 publication Critical patent/WO2015158134A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/40—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc
    • H02M5/42—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters
    • H02M5/44—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases with intermediate conversion into dc by static converters using discharge tubes or semiconductor devices to convert the intermediate dc into ac

Definitions

  • the present invention relates to the field of power electronics, and in particular, to a control method, device and system for a frequency converter.
  • the frequency converter is widely used in motor speed regulation.
  • the topology of the commonly used inverter can be seen in Figure 1.
  • the frequency converter mainly comprises a rectifier 100, a DC bus capacitor Cdc and an inverter 200;
  • the input voltage Vin is rectified by the rectifier 100 to become a DC voltage Vdc, and one end of the DC bus capacitor Cdc is connected to the positive bus and the other end is connected to the negative bus.
  • the inverter 200 inverts the DC voltage Vdc into an AC voltage Vout and outputs it.
  • the inverter 200 includes six switching devices Q1-Q6;
  • the inverter 200 generally adopts SVPWM wave or SPWM wave to control the switching state of the switching device therein.
  • the DC bus current Idc is positive in some wave states and negative in some wave states, so Cdc is repeated. Discharge. For example, when Idc is positive, energy is output from the DC bus through the inverter 200 to the Vout side; when Idc is negative, Vout is fed back to the bus side through the inverter 200.
  • the bus voltage will be charged higher when the energy is fed back to the bus. If the bus voltage is too high, the Cdc and switching devices will be damaged.
  • Cdc must be installed on the DC bus, and electrolytic capacitors are generally used.
  • Figure 2 provides a way to replace the rectifier side diode with a fully controlled switching device (such as an IGBT).
  • a fully controlled switching device such as an IGBT.
  • Idc When Idc is negative, the energy is fed back to the DC bus and the energy is fed back to the rectifier side (T1-T6). Grid. This energy will not stay on the bus, but can be directly fed back to the grid. Therefore, there is no need to install a DC bus capacitor.
  • Idc is positive, energy is passed from the grid through the rectification side to the DC bus and then to the load via the inverter side.
  • those skilled in the art need to provide a control method for the frequency converter, which can reduce the capacity of the DC bus capacitor without changing the topology of the frequency converter.
  • Embodiments of the present invention provide a control method, device, and system for a frequency converter, which can reduce the capacity of a DC bus capacitor without changing the topology of the frequency converter.
  • a method of controlling a frequency converter including:
  • the selecting according to the positive and negative states of the three-phase currents I a , I b , and I c , selecting a wave state of the PWM wave transmitter, specifically:
  • the wave state of the tube is the following five states: on, off, on, on, off, off, on, on, off, on, on, on, off, off, off, controlling the wave state and control of the tube Complementary to the upper tube;
  • the three upper tubes of the control inverter issued by the PWM wave generator are selected.
  • the state of the wave is the following five states: On, Off, Off, On, On, Off, Off, On, Off, On, On, On, Off, Off, Off, Off, Control the wave state and control of the tube Complementary tube
  • the three upper tubes of the control inverter that are issued by the PWM transmitter are selected.
  • the state of the wave is the following five states: open, open, close, close, open, close, close, open, open, open, open, closed, closed, closed, control the wave state and control of the lower tube Complementary tube
  • the wave state of the tube is the following five states: off, on, on, off, off, on, on, off, on, on, on, on, off, off, off, controlling the wave state and control of the tube Complementary to the upper tube;
  • the wave state of the tube is the following five states: off, off, on, on, off, on, on, off, off, on, on, on, off, off, off; controlling the wave state and control of the lower tube The complement of the upper tube.
  • the current power factor to the target power factor is adjusted according to the DC bus current, specifically:
  • the current power factor is controlled to stop decreasing and begins to increase until the DC bus current is positive.
  • the method further includes: detecting a DC bus voltage and a DC bus current;
  • the PWM transmitter When the DC bus voltage exceeds a preset threshold, and/or when the DC bus current is negative, the PWM transmitter is controlled to stop emitting PWM waves.
  • a control device for a frequency converter comprising: a detecting unit and a power factor control Unit, field current given unit, target voltage determining unit, switch state selecting unit, and switch state determining unit;
  • the detecting unit is configured to detect a three-phase voltage and three-phase currents I a , I b and I c of the inverter side output of the frequency converter;
  • the power factor control unit is configured to obtain a current power factor of the frequency converter from the three-phase voltage and the three-phase current, and adjust the current power factor to a target power factor according to the DC bus current;
  • the excitation current given unit is configured to determine a magnitude of the excitation given current according to the target power factor and the given torque current;
  • the target voltage determining unit is configured to determine a target voltage from the excitation given current and the given torque current, the given torque current is a given known amount; the switch state selecting unit, The method for selecting a wave state of the PWM wave generator according to the positive and negative states of the three-phase currents I a , I b , and I c ;
  • the switch state determining unit is configured to determine, according to the target voltage, at least three wave states from among the selected wave states to control a switching state of the switching device in the inverter, so that the inverter outputs The three-phase voltage synthesizes the target voltage, which causes no energy on the inverter side to be fed back to the DC bus.
  • the power factor control unit includes: a DC bus current judging subunit and a power factor control subunit;
  • the DC bus current judging subunit is configured to determine the positive and negative of the DC bus current, and send the determination result to the power factor control subunit;
  • the power factor control subunit configured to: when the DC bus current judging subunit determines that the DC bus current is positive, control the current power factor to start to decrease to a power factor corresponding to the maximum torque current, when When the DC bus current judging subunit determines that the DC bus current is negative, the current power factor is controlled to stop decreasing and starts to increase until the DC bus current is positive.
  • the method further includes: a DC bus voltage determining unit and a protection unit;
  • the DC bus voltage determining unit is configured to send a voltage protection signal to the protection unit when the DC bus voltage exceeds a preset threshold
  • the DC bus current judging subunit is configured to send a current protection signal to the protection unit when the DC bus current is negative;
  • the protection unit is configured to control the PWM transmitter to stop emitting a PWM wave upon receiving the voltage protection signal and/or the current protection signal.
  • a control system for a frequency converter including: a rectifier, an inverter, a DC bus, a controller, and a PWM wave generator;
  • the rectifier is configured to rectify alternating current into direct current and output the same to the inverter;
  • the inverter is configured to invert the DC power into AC power and supply power to the load;
  • the controller is configured to obtain a current power factor of the frequency converter by the three-phase voltage and the three-phase current, and adjust the current power factor to a target power factor according to the DC bus current; according to the target power factor and Determining the magnitude of the excitation given current for a given torque current, the excitation given current and the given torque current determining a target voltage, selecting according to the positive and negative states of the three-phase currents I a , I b and I c a state of the wave of the PWM wave generator, determining at least three wave states from the selected wave states according to the target voltage to control a switching state of the switching device in the inverter, so that the inverter outputs The three-phase voltage synthesizes the target voltage; the target voltage causes no energy to be fed back to the DC bus on the inverter side.
  • the controller is configured to control a target power factor according to a DC bus current and a three-phase voltage outputted by the inverter side and the three-phase current, specifically: If the DC bus current is positive, then controlling the current power factor starts to decrease to a power factor corresponding to the maximum torque current, and if the DC bus current is negative, controlling the current power factor to stop decreasing, starting Increase until the DC bus current is positive.
  • the controller is further configured to: when the DC bus voltage exceeds a preset threshold, and/or The DC bus current is negative, and the PWM transmitter is controlled to stop emitting PWM waves.
  • the load is a permanent magnet synchronous motor, and the permanent magnet synchronous motor is in an electric state.
  • the above technical solution can make the DC bus current always positive by the control method without changing the topology of the inverter, and the energy is directly supplied from the power grid to the inverter side through the rectification side, and the inverter side has no energy feedback to the DC bus.
  • the energy (current) of the DC bus capacitor can be reduced, so that the capacity of the DC bus capacitor can be reduced, and even the DC bus capacitor can be omitted, thereby reducing the capacitance.
  • the cost of the inverter improves the operational reliability of the inverter.
  • FIG. 1 is a schematic diagram of a topology of a frequency converter with a DC bus capacitor in the prior art
  • FIG. 2 is a schematic diagram of a topology of a frequency converter without a DC bus capacitor in the prior art
  • FIG. 3 is a schematic diagram of a load of a frequency converter provided by the present invention as a permanent magnet synchronous motor;
  • Embodiment 4 is a flow chart of Embodiment 1 of a control method of a frequency converter provided by the present invention
  • Figures 5a-5e are five conductive state diagrams corresponding to five switch states
  • Embodiment 6 is a flow chart of Embodiment 2 of a control method of a frequency converter provided by the present invention.
  • Figure 7 is a control block diagram of a control method provided by the present invention.
  • FIG. 8 is a control block diagram of another control method provided by the present invention.
  • Embodiment 9 is a schematic diagram of Embodiment 1 of a control device for a frequency converter provided by the present invention.
  • Embodiment 10 is a schematic diagram of Embodiment 2 of a control device for a frequency converter provided by the present invention.
  • Embodiment 3 is a schematic diagram of Embodiment 3 of a control device for a frequency converter provided by the present invention.
  • FIG. 12 is a schematic diagram of Embodiment 1 of a control system of a frequency converter provided by the present invention.
  • the excitation given current Determining a magnitude of the excitation given current according to the target power factor and the given torque current according to the DC bus current and the three-phase voltage outputted by the inverter side and the three-phase current control target power factor; the excitation given current Determining the target voltage with the given torque current;
  • the load of the frequency converter may be a permanent magnet synchronous motor, for example, a permanent magnet synchronous motor is embedded inside the direct current variable frequency compressor and the variable frequency fan.
  • FIG. 3 the figure shows a schematic diagram of a load of a frequency converter provided by the present invention as a permanent magnet synchronous motor.
  • the alternating current Vin is rectified to a direct current voltage Vdc by a rectifier, and then Vdc is inverted by the inverter into an alternating current Vout, and then the permanent magnet synchronous motor M is driven.
  • the load of the frequency converter can also be higher (close to 1) for other power factors and Loads that cannot return energy, such as pure resistive load, resistive load, and resistive load.
  • the power factor is uncontrollable, so it is easier to control than the load is a permanent magnet synchronous motor.
  • the load is a permanent magnet synchronous motor as an example.
  • the control method for controlling the permanent magnet synchronous motor is also applicable to other types of loads, and the basic principle is the same, and the difference is described later.
  • FIG. 4 a flow chart of a first embodiment of a method for controlling a frequency converter according to the present invention is shown.
  • S402 Obtain a current power factor of the frequency converter from the three-phase voltage and the three-phase current, and adjust the current power factor to a target power factor according to the DC bus current; determine according to the target power factor and the given torque current. Exciting a magnitude of a given current; determining the target voltage by the excitation given current and the given torque current;
  • the current power factor of the frequency converter can be obtained from the three-phase voltage and the three-phase current output from the inverter side. That is, the starting point for adjusting the power factor is the current power factor. Then according to the DC bus current from the current power factor adjustment, the adjusted power factor is the target power factor.
  • the current power factor is 0.9 based on the three-phase voltage and the three-phase current, and the DC bus current is negative, the adjusted power factor increases from 0.9, but the power factor cannot exceed 1, and the maximum value is 1. If the power factor is adjusted to 1, and the DC bus current is still negative, the power factor will not be increased. If the DC bus current is not positive when the power factor is less than 1, the regulation is stopped.
  • the DC bus current can be estimated based on the three-phase current output from the inverter side and the PWM wave state sent by the PWM transmitter, or can be directly detected.
  • the target power factor can be determined by the DC bus current, the three-phase voltage output from the inverter side, and the three-phase current.
  • the excitation given current can be determined from the target power factor and the given torque current, which is a prior art in motor control.
  • the target voltages Varef, Vbref, Vcref can be determined from the excitation given current and the given torque current.
  • S403 Select a wave state of the PWM wave according to the positive and negative states of the three-phase currents I a , I b , and I c , and determine at least three wave waves from the selected wave state according to the target voltage. a state to control a switching state of the switching device in the inverter, such that a three-phase voltage output by the inverter is combined with the target voltage; the target voltage causes no energy to be fed back to the DC bus on the inverter side.
  • the target voltage is known and the three-phase target voltages are Varef, Vbref, Vcref.
  • each current state combination corresponds to the five switching states, and it is necessary to explain that In order to make the DC bus current positive, each current state needs to be synthesized by selecting at least three switching states from the five switching states.
  • the three upper tubes shown in Table 2 are fully open, or the three upper tubes are completely closed. Only the two switching states cannot synthesize the target voltage, and at least three switching states are required to synthesize the target voltage.
  • the first switch state 101 corresponds to FIG. 5a, and the states of the three upper tubes are: on, off, and on;
  • the second switch state 100 corresponds to FIG. 5b, and the states of the three upper tubes are: turn-on, turn-off, and turn-off;
  • the third switch state 110 corresponds to FIG. 5c, and the states of the three upper tubes are: on, on, and off;
  • the fourth switch state 111 corresponds to FIG. 5d, and the states of the three upper tubes are: conduction, conduction, and conduction, respectively.
  • the fifth switch state 000 corresponds to Figure 5e, and the states of the three upper tubes are: off, off, and off, respectively.
  • Figure 5a-5d is a schematic diagram of the topology of the inverter, the arrows in the figure show the direction of the current,
  • the switching states of the three lower tubes are exactly opposite to the switching states of the three upper tubes, that is, the complementary conduction: when the upper tube is turned on, the lower tube is turned off; when the upper tube is turned off; The lower tube is turned on.
  • the embodiment of the invention provides a control method of the frequency converter, which can make the DC bus current always positive by the control method without changing the topology of the frequency converter, and the energy is directly supplied to the inverter side from the power grid through the rectification side, which can reduce the DC
  • the energy (current) of the bus capacitor is charged and discharged, thereby reducing the capacity of the DC bus capacitor, and even eliminating the DC bus capacitor, reducing the cost of the inverter and improving the operational reliability of the inverter.
  • FIG. 6 a flow chart of a second embodiment of a method for controlling a frequency converter according to the present invention is shown.
  • the control method provided in this embodiment needs to control in addition to the state of controlling the PWM wave.
  • the target power factor controls the frequency converter to control the maximum torque current of the motor by controlling the target power factor, which can improve the working efficiency of the inverter.
  • FIG. 7 there is shown a control block diagram of a control method provided by the present invention.
  • the DC bus current in this embodiment is derived from the bus current estimator 10.
  • Bus current estimator 10 may estimate the DC bus current Idc according to the PWM wave hair hair wave state 70 Pwma, Pwmb, Pwmc and three phase currents I a, I b and I c.
  • DC bus current Idc can also be obtained by direct measurement.
  • the power factor controller 20 determines the target power based on the DC bus current, the three-phase voltages Vout-a, Vout-b, Vout-c of the inverter-side output, and the three-phase currents I a , I b , and I c of the inverter-side output. a factor phi; obtaining, by the three-phase voltage and the three-phase current, a current power factor of the frequency converter, and adjusting the current power factor to a target power factor according to the DC bus current;
  • the torque current setter 30 sends a given torque current Iref2 to the excitation current given generator 40;
  • the excitation current given generator 40 determines the excitation given current Iref1 from the target power factor phi and the given torque current Iref2;
  • the field current controller 50 outputs a given current and a given torque current Iref1 and Iref2 three phase currents I a, I b and I c to determine the target voltage Varef, Vbref, Vcref.
  • the switch state selector 60 determines the switch states Cmpa, Cmpb, Cmpc based on the target voltages Varef, Vbref, Vcref and the three-phase currents I a , I b , I c .
  • the PWM transmitter 70 outputs PWM waves Pwma, Pwmb, and Pwmc in accordance with the switching states Cmpa, Cmpb, and Cmpc.
  • a protection measure is also provided, that is, the protector 80 receives the DC bus voltage Udc and the DC bus current Idc.
  • the PWM transmitter 70 When the DC bus voltage Udc exceeds a predetermined threshold, and/or, when the DC bus current Idc is negative, the PWM transmitter 70 will stop emitting PWM waves. That is, the PWM transmitter 70 blocks the output of the PWM wave, thereby protecting the inverter from damage.
  • the preset threshold is a preset voltage value
  • the voltage value can be based on The specific application scenarios are set, for example, according to some parameters of the inverter and the permanent magnet synchronous motor.
  • the numerical value is not specifically limited herein.
  • the load of the inverter is taken as an example of a permanent magnet synchronous motor, and when the load is other loads, since there is no energy feedback, the power factor is determined by the load, so there is no way. The power factor is adjusted, and therefore, the bus current estimator 10 and the power factor controller 20 in Fig. 7 are omitted.
  • control principle diagram is shown in FIG. 8 , and the working principle diagram is the same in FIG. 7 , and details are not described herein again.
  • the embodiment of the present invention further provides a control device for the frequency converter, which is described in detail below with reference to the accompanying drawings.
  • FIG. 9 is a schematic diagram of a first embodiment of a control device for a frequency converter provided by the present invention.
  • the control device of the frequency converter includes: a detecting unit 901, a power factor control unit 902, an excitation current given unit 903, a target voltage determining unit 904, a switch state selecting unit 905, and a switch state determining unit 906;
  • the detecting unit 901 is configured to detect three-phase currents I a , I b and I c of the inverter side output of the frequency converter;
  • the power factor control unit 902 is configured to control a target power factor according to a DC bus current and a three-phase voltage output by the inverter side and the three-phase current;
  • the excitation current given unit 903 is configured to determine a magnitude of the excitation given current according to the target power factor and the given torque current;
  • the target voltage determining unit 904 is configured to determine a target voltage from the excitation given current and the given torque current;
  • the DC bus current can be estimated based on the three-phase current output from the inverter side and the PWM wave state sent by the PWM transmitter, or can be directly detected.
  • the target power factor can be determined by the DC bus current, the three-phase voltage output from the inverter side, and the three-phase current.
  • the excitation given current can be determined from the target power factor and the given torque current.
  • the target voltages Varef, Vbref, Vcref can be determined from the excitation given current and the given torque current.
  • the switch state selection unit 905 is configured to select a wave state of the PWM wave generator according to the positive and negative states of the three-phase currents I a , I b , and I c ;
  • the switch state determining unit 906 is configured to determine, according to the target voltage, at least three wave states from among the selected wave states to control a switching state of the switching device in the inverter, so that the inverter outputs The three-phase voltage synthesizes the target voltage, and the target voltage causes no energy to be fed back to the DC bus on the inverter side.
  • the target voltage is known and the three-phase target voltages are Varef, Vbref, Vcref.
  • the embodiment of the invention provides a control device for the frequency converter, which can make the DC bus current always positive by the control method without changing the topology of the frequency converter, and the energy is directly supplied from the power grid to the inverter side through the rectification side, which can reduce the DC
  • the energy (current) of the bus capacitor is charged and discharged, thereby reducing the capacity of the DC bus capacitor, and even eliminating the DC bus capacitor, reducing the cost of the inverter and improving the operational reliability of the inverter.
  • FIG. 10 it is a schematic diagram of Embodiment 2 of a control device for a frequency converter provided by the present invention.
  • the power factor control unit 902 includes: a DC bus current judging subunit 902a and a power factor control subunit 902b;
  • the DC bus current judging subunit 902a is configured to determine the positive and negative of the DC bus current, and send the determination result to the power factor control subunit 902b;
  • the power factor control subunit 902b is configured to control the current power factor to decrease from 1 to a power factor corresponding to the maximum torque current when the DC bus current judging subunit 902a determines that the DC bus current is positive When the DC bus current judging subunit 902a determines that the DC bus current is negative, the current power factor is controlled to stop decreasing and begins to increase until the DC bus current is positive. It can be understood that the power factor is increased up to 1 and cannot exceed 1.
  • the control device provided in this embodiment in addition to controlling the state of the PWM wave, also needs to control the target power factor, and controls the target power factor to control the frequency converter to operate at the maximum torque current of the motor, thereby improving the operation of the frequency converter. effectiveness.
  • FIG. 11 is a schematic diagram of Embodiment 3 of a control device for a frequency converter provided by the present invention.
  • the control device of the frequency converter provided by this embodiment further includes: a DC bus voltage determination unit 907 and a protection unit 908;
  • the DC bus voltage determining unit 907 is configured to send a voltage protection signal to the protection unit 908 when the DC bus voltage exceeds a preset threshold;
  • the preset threshold is a preset voltage value, which can be set according to a specific application scenario, for example, according to some parameters of the inverter and the permanent magnet synchronous motor.
  • the numerical value is not specifically limited herein.
  • the DC bus current judging subunit 902a is configured to send a current protection signal to the protection unit 908 when the DC bus current is negative;
  • the protection unit 908 is configured to control the PWM transmitter to stop emitting a PWM wave upon receiving the voltage protection signal and/or the current protection signal.
  • the load of the inverter is taken as an example of a permanent magnet synchronous motor, and when the load is other loads, since there is no energy feedback, the power factor is determined by the load, so there is no way. Adjust the power factor.
  • the embodiment of the present invention further provides a control system for the frequency converter, which is described in detail below with reference to the accompanying drawings.
  • FIG. 12 it is a schematic diagram of a first embodiment of a control system for a frequency converter provided by the present invention.
  • the control system of the frequency converter includes: a rectifier 1200, an inverter 1300, DC bus 1400, controller 1500 and PWM transmitter 1600;
  • the rectifier 1200 is configured to rectify alternating current into direct current and output to the inverter 1300;
  • the inverter 1300 is configured to invert the DC power into an AC power and supply power to the load;
  • the DC bus 1400 is between the rectifier 1200 and the inverter 1300;
  • the controller 1500 is configured to obtain, by the three-phase voltage and a three-phase current, a current power factor of the frequency converter, and adjust the current power factor to a target power factor according to the DC bus current; according to the target power factor and Determining a magnitude of the excitation given current for a given torque current; determining the target voltage by the excitation given current and the given torque current; and positive and negative according to the three-phase currents I a , I b , and I c
  • the state selects a wave state of the PWM wave 1600, and determines at least three wave states from the selected wave states according to the target voltage to control a switching state of the switching device in the inverter, so that the inverter
  • the three-phase voltage output by the device synthesizes the target voltage; the target voltage causes no energy to be fed back to the DC bus 1400 on the inverter side.
  • the DC bus current can be estimated based on the three-phase current output from the inverter side and the PWM wave state sent by the PWM transmitter, or can be directly detected.
  • the target power factor can be determined by the DC bus current, the three-phase voltage output from the inverter side, and the three-phase current.
  • the excitation given current can be determined from the target power factor and the given torque current.
  • the target voltages Varef, Vbref, Vcref can be determined from the excitation given current and the given torque current.
  • the target voltage is known and the three-phase target voltages are Varef, Vbref, Vcref.
  • the PWM transmitter 1600 is used to send PWM waves to each tube in the inverter to control the switching state of each tube. For example, when the PWM wave is at a high level, the corresponding tube is turned on, and when the PWM wave is at a low level, the corresponding tube is turned off.
  • the embodiment of the invention provides a control system of the frequency converter, which can change the topology of the frequency converter Under the control method, the DC bus current is always positive, and the energy is directly supplied to the inverter side from the grid through the rectification side, which can reduce the energy (current) charged and discharged on the DC bus capacitor, thereby reducing the capacity of the DC bus capacitor. It can even save the DC bus capacitor, reduce the cost of the inverter, and improve the working reliability of the inverter.
  • the load of the frequency converter may be a permanent magnet synchronous motor, for example, a DC variable frequency compressor and an inverter fan are embedded with a permanent magnet synchronous motor. Since the DC bus current is always positive, the permanent magnet synchronous motor can always operate in an electric state.
  • the load of the frequency converter can also be other loads with higher power factor (close to 1) and unable to return energy, such as pure resistive load, resistive load, and RC load, for loads that cannot feed back energy,
  • the power factor is uncontrollable, so it is much simpler to control than a permanent magnet synchronous motor load. No further details are provided here.
  • control principle reference may be made to the corresponding embodiment of FIG. 8.
  • the controller is configured to adjust the current power factor to a target power factor according to a DC bus current, specifically: if the DC bus current is positive, control the current power factor to decrease from 1 to a maximum turn The power factor corresponding to the moment current; if the DC bus current is negative, the current power factor is stopped to decrease and begins to increase until the DC bus current is positive. It can be understood that the power factor is increased up to 1 and cannot exceed 1.
  • control method provided by this embodiment in addition to controlling the state of the PWM wave, also needs to control the target power factor, and control the target power factor to control the frequency converter to work at the maximum torque current of the motor, thereby improving the operation of the frequency converter. effectiveness.
  • the controller provided in the embodiment of the system of the invention also has a protection function.
  • the controller is further configured to control the PWM transmitter to stop emitting a PWM wave when the DC bus voltage exceeds a preset threshold, and/or when the DC bus current is negative. Blockade PWM Waves, this protects the inverter from damage.
  • the preset threshold is a preset voltage value, which can be set according to a specific application scenario, for example, according to some parameters of the inverter and the permanent magnet synchronous motor.
  • the numerical value is not specifically limited herein.
  • the method, device and system provided by the above embodiments can control the DC bus current in the frequency converter to be positive, so that no energy is fed back to the DC bus on the inverter side, which can reduce the charge and discharge capacity of the DC bus capacitor, thereby reducing
  • the capacitance of the small DC bus capacitor reduces the size of the entire inverter and reduces the hardware cost.
  • the various embodiments in the present invention are described by taking the load of the frequency converter as a permanent magnet synchronous motor as an example. Since the load is a permanent magnet synchronous motor, the power factor can be controlled. When the load is other types of loads, since there is no energy feedback, the power factor is determined by the load and is uncontrollable. Therefore, the control is simpler than when the load is a permanent magnet synchronous motor, and will not be specifically described here. . For example, when the load is a pure resistive load, there is no need to use this method for control.

Abstract

一种变频器的控制方法、设备和系统，检测变频器的逆变侧输出的三相电压（Vout-abc）和三相电流（I abc）；获得变频器当前的功率因数，根据直流母线电流（Idc）来调节当前的功率因数到目标功率因数（phi）；根据目标功率因数和给定转矩电流（I ref2）确定励磁给定电流（I ref1）的大小，励磁给定电流和给定转矩电流确定目标电压（Varef, Vbref, Vcref），根据三相电流的正负状态选择PWM发波器的发波状态，根据目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使逆变器输出的三相电压合成目标电压，目标电压使逆变侧没有能量回馈到直流母线。使得直流母线电流始终为正，能量从电网经过整流侧提供给逆变侧，减小直流母线电容（Cdc）上充放电的能量，减小直流母线电容的容量。

Description

一种变频器的控制方法、设备和系统
本申请要求于2014年4月17日提交中国专利局、申请号为201410155047.5、发明名称为“一种变频器的控制方法、设备和系统”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及电力电子技术领域，特别涉及一种变频器的控制方法、设备和系统。
背景技术
变频器广泛应用于电机调速，常用的变频器的拓扑结构可以参见图1所示。
变频器主要包括整流器100、直流母线电容Cdc和逆变器200；
其中输入电压Vin经过整流器100整流后变为直流电压Vdc，直流母线电容Cdc的一端连接在正母线上，另一端连接在负母线上。
逆变器200将直流电压Vdc逆变为交流电压Vout进行输出。逆变器200包括六个开关器件Q1-Q6；
逆变器200一般采用SVPWM发波或SPWM发波控制其中的开关器件的开关状态，直流母线电流Idc在某些发波状态时为正，在某些发波状态时为负，这样Cdc被反复充放电。例如，当Idc为正时，能量从直流母线经过逆变器200输出到Vout侧；当Idc为负时，Vout经过逆变器200回馈到母线侧。
如果Cdc的容量太小，当能量回馈到母线后，母线电压会被充得较高，如果母线电压太高将会导致Cdc和开关器件损坏。
为了解决直流母线电容以上存在的问题，现有技术中通常有以下两种方式。
第一种方式是：直流母线上必须安装容量较大的Cdc，一般采用电解电容。
但是，Cdc容量较大时，对应的体积较大，成本高，并且散热处理比较困难。同时，电解电容的寿命较短需要定期更换。
第二种方式是：采用可回馈能量的整流器，参见图2，该图为现有技术中的没有直流母线电容的变频器拓扑图。
图2提供的方式是将整流侧的二极管替换为全控型开关器件(例如IGBT)，当Idc为负时，能量回馈到直流母线后，立刻通过控制整流侧(T1-T6)将能量回馈到电网。这样能量就不会停留在母线上，而能够直接回馈到电网， 因此，不需要安装直流母线电容。同样，当Idc为正时，能量从电网经过整流侧到直流母线，然后经过逆变侧提供给负载。
但是，图2的方式虽然可以省去直流母线电容，但是需要将整流侧的二极管替换为全控型开关器件，同时在输入侧需要增加LC滤波器，整个变频器的成本升高、拓扑结果和控制变得更复杂。
综上，本领域技术人员需要提供一种变频器的控制方法，能够在不改变变频器拓扑的情况下，可以减小直流母线电容的容量。
发明内容
本发明实施例提供一种变频器的控制方法、设备和系统，能够在不改变变频器拓扑的情况下，可以减小直流母线电容的容量。
第一方面，提供一种变频器的控制方法，包括：
检测变频器的逆变侧输出的三相电压和三相电流Ia、Ib和Ic；
由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；
根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小，所述励磁给定电流和所述给定转矩电流确定目标电压，所述给定转矩电流为给定的已知量；
根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压，所述目标电压使逆变侧没有能量回馈到直流母线。
在第一方面的第一种可能的实现方式中，所述根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，具体为：
当所述三相电流Ia、Ib和Ic的正负状态为：Ia为正、Ib为负和Ic为负时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：开、关、开，开、关、关，开、开、关，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
当所述三相电流Ia、Ib和Ic的正负状态为：Ia为正、Ib为正和Ic为负时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态： 开、关、关，开、开、关，关、开、关，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
当所述三相电流Ia、Ib和Ic的正负状态为：Ia为负、Ib为正和Ic为负时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：开、开、关，关、开、关，关、开、开，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
当所述三相电流Ia、Ib和Ic的正负状态为：Ia为负、Ib为正和Ic为正时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：关、开、关，关、开、开，关、关、开，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
当所述三相电流Ia、Ib和Ic的正负状态为：Ia为负、Ib为负和Ic为正时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：关、开、开，关、关、开，开、关、开，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
当所述三相电流Ia、Ib和Ic的正负状态为：Ia为正、Ib为负和Ic为正时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：关、关、开，开、关、开，开、关、关，开、开、开，关、关、关；控制下管的发波状态与控制上管的互补。
结合第一方面及上述任一种可能的实现方式中，在第二种可能的实现方式中，根据直流母线电流来调节所述当前的功率因数到目标功率因数，具体为：
如果所述直流母线电流为正，则控制所述当前的功率因数开始减小到最大转矩电流对应的功率因数；
如果所述直流母线电流为负，则控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
结合第一方面及上述任一种可能的实现方式中，在第三种可能的实现方式中，还包括：检测直流母线电压和直流母线电流；
当所述直流母线电压超过预设阈值，和/或，当所述直流母线电流为负，控制所述PWM发波器停止发出PWM波。
第二方面，提供一种变频器的控制设备，包括：检测单元、功率因数控制 单元、励磁电流给定单元、目标电压确定单元、开关状态选择单元和开关状态确定单元；
所述检测单元，用于检测变频器的逆变侧输出的三相电压和三相电流Ia、Ib和Ic；
所述功率因数控制单元，用于由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；
所述励磁电流给定单元，用于根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小；
所述目标电压确定单元，用于由所述励磁给定电流和所述给定转矩电流确定目标电压，所述给定转矩电流为给定的已知量；所述开关状态选择单元，用于根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态；
所述开关状态确定单元，用于根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压，所述目标电压使逆变侧没有能量回馈到直流母线。
在第二方面的第一种可能的实现方式中，所述功率因数控制单元包括：直流母线电流判断子单元和功率因数控制子单元；
所述直流母线电流判断子单元，用于判断直流母线电流的正负，将判断结果发送给所述功率因数控制子单元；
所述功率因数控制子单元，用于当所述直流母线电流判断子单元判断直流母线电流为正时，控制所述当前的功率因数开始减小到最大转矩电流对应的功率因数，当所述直流母线电流判断子单元判断直流母线电流为负时，控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
结合第二方面及上述任一种可能的实现方式中，在第二种可能的实现方式中，还包括：直流母线电压判断单元和保护单元；
所述直流母线电压判断单元，用于判断所述直流母线电压超过预设阈值时，发送电压保护信号给所述保护单元；
所述直流母线电流判断子单元，用于判断所述直流母线电流为负时，发送电流保护信号给所述保护单元；
所述保护单元，用于在收到所述电压保护信号和/或电流保护信号时，控制所述PWM发波器停止发出PWM波。
第三方面，提供一种变频器的控制系统，包括：整流器、逆变器、直流母线、控制器和PWM发波器；
所述整流器，用于将交流电整流为直流电后输出给所述逆变器；
所述逆变器，用于将所述直流电逆变为交流电后给负载供电；
所述整流器和逆变器之间为直流母线；
所述控制器，用于由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；，根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小，所述励磁给定电流和所述给定转矩电流确定目标电压，根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压；所述目标电压使逆变侧没有能量回馈到直流母线。
在第三方面的第一种可能的实现方式中，所述控制器，用于根据直流母线电流以及逆变侧输出的三相电压和所述三相电流控制目标功率因数，具体为：如果所述直流母线电流为正，则控制所述当前的功率因数开始减小到最大转矩电流对应的功率因数，如果所述直流母线电流为负，则控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
结合第三方面及上述任一种可能的实现方式中，在第二种可能的实现方式中，所述控制器，还用于当所述直流母线电压超过预设阈值，和/或，当所述直流母线电流为负，控制所述PWM发波器停止发出PWM波。
结合第三方面及上述任一种可能的实现方式中，在第三种可能的实现方式中，所述负载为永磁同步电机，所述永磁同步电机处于电动状态。
以上技术方案，可以在不改变变频器拓扑的情况下，通过控制方法使得直流母线电流始终为正，能量从电网经过整流侧直接提供给逆变侧，逆变侧没有能量回馈到直流母线，因此可以减小直流母线电容上充放电的能量(电流)，从而可以减小直流母线电容的容量，甚至可以省掉直流母线电容，进而降低了 变频器的成本，提高了变频器的工作可靠性。
附图说明
图1是现有技术中的一种带有直流母线电容的变频器拓扑示意图；
图2是现有技术中没有直流母线电容的变频器拓扑示意图；
图3是本发明提供的变频器的负载为永磁同步电机的示意图；
图4是本发明提供的变频器的控制方法实施例一流程图；
图5a-5e是五种开关状态对应的五种导通状态图；
图6是本发明提供的变频器的控制方法实施例二流程图；
图7是本发明提供的控制方法的控制框图；
图8是本发明提供的另一种控制方法的控制框图；
图9是本发明提供的变频器的控制设备实施例一示意图；
图10是本发明提供的变频器的控制设备实施例二示意图；
图11是本发明提供的变频器的控制设备实施例三示意图；
图12是本发明提供的变频器的控制系统实施例一示意图。
具体实施方式
首先对本发明实施例实现一种变频器的控制方法进行说明，包括：
检测变频器的逆变侧输出的三相电流Ia、Ib和Ic；
根据直流母线电流以及逆变侧输出的三相电压和所述三相电流控制目标功率因数，根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小；所述励磁给定电流和所述给定转矩电流确定所述目标电压；
根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来合成所述目标电压；所述目标电压使逆变侧没有能量回馈到直流母线。
需要说明的是，变频器的负载可以为永磁同步电机，例如直流变频压缩机和变频风机等内部均嵌有永磁同步电机。参见图3，该图为本发明提供的变频器的负载为永磁同步电机的示意图。
交流电Vin通过整流器整流为直流电压Vdc，然后Vdc经过逆变器逆变为交流电Vout，再驱动永磁同步电机M。
可以理解的是，变频器的负载也可以为其他功率因数较高(接近1)并且 不能回馈能量的负载，例如纯阻性负载、阻感负载、阻容负载，对于不能回馈能量的负载，其功率因数不可控制，因此控制起来比负载为永磁同步电机更简单，下面以变频器的负载为永磁同步电机为例进行介绍。当然，控制永磁同步电机的控制方法同样适用于其他类别的负载，其基本原理相同，区别点后续介绍。
方法实施例一：
参见图4，该图为本发明提供的变频器的控制方法实施例一流程图。
S401：检测变频器的逆变侧输出的三相电压和三相电流Ia、Ib和Ic；
由于逆变侧输出的三相电流的状态不同，对应的PWM发波器的发波状态不同，因此需要检测三相电流的状态。
由于三相电流不可能全为正，也不可能全为负，因此，三相电流Ia、Ib和Ic的组合状态一共有以下六种：
正、负、负；
正、正、负；
负、正、负；
负、正、正；
负、负、正；
正、负、正。
S402：由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小；所述励磁给定电流和所述给定转矩电流确定所述目标电压；
可以理解的是，由逆变侧输出的三相电压和三相电流可以得到变频器当前的功率因数。即调节功率因数的起点是当前的功率因数。再根据直流母线电流从当前的功率因数开始调整，调整后的功率因数便是目标功率因数。
例如，根据三相电压和三相电流得到当前的功率因数是0.9，而直流母线电流为负，则调节功率因数从0.9开始增大，但是功率因数不能超过1，最大值为1。如果功率因数调节到1了，直流母线电流还是为负，则不会再增加功率因数，如果功率因数没有到1时直流母线电流已经为正了，则停止调节。
需要说明的是，直流母线电流可以根据逆变侧输出的三相电流和PWM发波器发出的PWM发波状态来推算，也可以直接检测得到。
目标功率因数可以由直流母线电流，逆变侧输出的三相电压和三相电流来确定。
由目标功率因数和给定转矩电流可以确定励磁给定电流，这个是电机控制中的现有技术。
可以理解的是，给定转矩电流为已知量。
由励磁给定电流和给定转矩电流可以确定目标电压Varef，Vbref，Vcref。
S403：根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压；所述目标电压使逆变侧没有能量回馈到直流母线。
对于PWM发波器来说，目标电压是已知的，三相目标电压分别为Varef，Vbref，Vcref。
由于在逆变器中，同一个桥臂上的上管和下管的开关状态正好相反，例如，对于A相桥臂来说，上管Q1为导通时，对应的下管Q2为关断。因此，为了方便描述，以逆变器中三个上管为例进行描述，三个下管的状态与三个上管的状态相反，在此不再具体介绍。
表1
Figure PCTCN2014092009-appb-000001
Figure PCTCN2014092009-appb-000002
由表1可以看出，为了保证直流母线电流为正，则三相电流的每种组合状态对应的三个上管的开关状态为三种，可以理解的是，开关状态中的“1”代表管子导通，“0”代表管子关断。由于逆变器中的每个管子的开关状态是由PWM波来驱动的，即，管子导通对应的PWM波为高电平，管子关断对应的PWM波为低电平。
另外，除了表1中的每种电流状态组合对应3种开关状态外，还可以添加以下表2中所示的两种开关状态，即每种电流状态组合对应5中开关状态，需要说明的是，为了使直流母线电流为正，每种电流状态需要从5种开关状态中选择至少3种开关状态来合成。
表2
Figure PCTCN2014092009-appb-000003
需要说明的是，单纯由表2所示的三个上管全开，或者三个上管全关，仅由这两种开关状态无法合成目标电压，至少需要三种开关状态才能合成目标电压。
例如，以第一个电流组合状态为例进行说明，A相电流为正，B相和C相电流均为负，则可以选择五种开关状态101，100，110，111，000来合成目标电压Varef，Vbref，Vcref。
第一种开关状态101对应图5a，三个上管的状态分别是：导通、关断和导通；
第二种开关状态100对应图5b，三个上管的状态分别是：导通、关断和关断；
第三种开关状态110对应图5c，三个上管的状态分别是：导通、导通和关断；
第四种开关状态111对应图5d，三个上管的状态分别是：导通、导通和导通。
第五种开关状态000对应图5e，三个上管的状态分别是：关断、关断和关断。
图5a-5d中是逆变器的拓扑示意图，图中的箭头示出了电流的方向，
从图5a-5d中也可以看出，三个下管的开关状态与三个上管的开关状态正好相反，即互补导通：上管导通时，下管关断；上管关断时，下管导通。
本发明实施例提供变频器的控制方法，可以在不改变变频器拓扑的情况下，通过控制方法使得直流母线电流始终为正，能量从电网经过整流侧直接提供给逆变侧，可以减小直流母线电容上充放电的能量(电流)，从而可以减小直流母线电容的容量，甚至可以省掉直流母线电容，降低了变频器的成本，提高了变频器的工作可靠性。
方法实施例二：
参见图6，该图为本发明提供的变频器的控制方法实施例二流程图。
为了提高变频器的工作效率，使永磁同步电机在接近最大转矩电流比时工作，需要控制目标功率因数。本实施例中具体介绍目标功率因数的控制方法。
S601：检测直流母线电流的正负；
S602：如果所述直流母线电流为正，则控制所述当前的功率因数从1开始减小到最大转矩电流对应的功率因数；
S603：如果所述直流母线电流为负，则控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
可以理解的是，功率因数最大增大到1，不可能超过1。
可以理解的是，S602和S603没有先后顺序。
需要说明的是，目标功率因数的调节是由功率因数控制器来完成的。下面结合控制框图来说明本发明提供的控制方法的主要工作原理。
本实施例提供的控制方法，除了控制PWM发波的状态以外，还需要控制 目标功率因数，通过控制目标功率因数来控制变频器工作在电机的最大转矩电流处，这样可以提高变频器的工作效率。
方法实施例三：
参见图7，该图为本发明提供的控制方法的控制框图。
本实施例中的直流母线电流是由母线电流推测器10推算出来的。
母线电流推测器10可以根据PWM发波器70的发波状态Pwma、Pwmb、Pwmc和三相电流Ia、Ib和Ic来推算直流母线电流Idc。
可以理解的是，直流母线电流Idc也可以直接测量获得。
功率因数控制器20根据直流母线电流、逆变侧输出的三相电压Vout-a、Vout-b、Vout-c和逆变侧输出的三相电流Ia、Ib和Ic来确定目标功率因数phi；由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；
转矩电流给定器30将给定转矩电流Iref2发给励磁电流给定生成器40；
可以理解的是，给定转矩电流Iref2是已知的。
励磁电流给定生成器40由目标功率因数phi和给定转矩电流Iref2确定励磁给定电流Iref1；
输出电流控制器50根据励磁给定电流Iref1和给定转矩电流Iref2以及三相电流Ia、Ib和Ic来确定目标电压Varef，Vbref，Vcref。
开关状态选择器60根据目标电压Varef，Vbref，Vcref和三相电流Ia、Ib、Ic来确定开关状态Cmpa、Cmpb、Cmpc。
PWM发波器70根据开关状态Cmpa、Cmpb、Cmpc来输出PWM波Pwma、Pwmb、Pwmc。
需要说明的是，本实施例中还提供了保护措施，即保护器80，接收直流母线电压Udc和直流母线电流Idc。
当所述直流母线电压Udc超过预设阈值，和/或，当所述直流母线电流Idc为负，所述PWM发波器70将停止发出PWM波。即PWM发波器70封锁PWM波的输出，从而保护逆变器不被损坏。
可以理解的是，预设阈值是预先设定的一个电压值，这个电压值可以根据 具体的应用场景来设定，例如根据变频器和永磁同步电机的一些参数来设定。在此不具体限定数值。
需要说明的是，以上实施例中均是以变频器的负载为永磁同步电机为例进行介绍的，而当负载为其他负载时，由于没有能量回馈，其功率因数由负载决定，因此没有办法对功率因数进行调节，因此，省略了图7中的母线电流推测器10、功率因数控制器20。
其控制原理图如图8所示，工作原理图图7中的相同，在此不再赘述。
基于以上实施例提供的一种变频器的控制方法，本发明实施例还提供了一种变频器的控制设备，下面结合附图进行详细介绍。
设备实施例一：
参见图9，该图为本发明提供的变频器的控制设备实施例一示意图。
本实施例提供的变频器的控制设备，包括：检测单元901、功率因数控制单元902、励磁电流给定单元903、目标电压确定单元904、开关状态选择单元905和开关状态确定单元906；
所述检测单元901，用于检测变频器的逆变侧输出的三相电流Ia、Ib和Ic；
由于逆变侧输出的三相电流的状态不同，对应的PWM发波器的发波状态不同，因此需要检测三相电流的状态。
所述功率因数控制单元902，用于根据直流母线电流以及逆变侧输出的三相电压和所述三相电流控制目标功率因数；
所述励磁电流给定单元903，用于根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小；
所述目标电压确定单元904，用于由所述励磁给定电流和所述给定转矩电流确定目标电压；
需要说明的是，直流母线电流可以根据逆变侧输出的三相电流和PWM发波器发出的PWM发波状态来推算，也可以直接检测得到。
目标功率因数可以由直流母线电流，逆变侧输出的三相电压和三相电流来确定。
由目标功率因数和给定转矩电流可以确定励磁给定电流。
由励磁给定电流和给定转矩电流可以确定目标电压Varef，Vbref，Vcref。
所述开关状态选择单元905，用于根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态；
所述开关状态确定单元906，用于根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压，所述目标电压使逆变侧没有能量回馈到直流母线。
对于PWM发波器来说，目标电压是已知的，三相目标电压分别为Varef，Vbref，Vcref。
本发明实施例提供变频器的控制设备，可以在不改变变频器拓扑的情况下，通过控制方法使得直流母线电流始终为正，能量从电网经过整流侧直接提供给逆变侧，可以减小直流母线电容上充放电的能量(电流)，从而可以减小直流母线电容的容量，甚至可以省掉直流母线电容，降低了变频器的成本，提高了变频器的工作可靠性。
设备实施例二：
参见图10，该图为本发明提供的变频器的控制设备实施例二示意图。
为了提高变频器的工作效率，使永磁同步电机在接近最大转矩电流比时工作，需要控制目标功率因数。本实施例中具体介绍目标功率因数的控制设备。
本实施例提供的变频器的控制设备，所述功率因数控制单元902包括：直流母线电流判断子单元902a和功率因数控制子单元902b；
所述直流母线电流判断子单元902a，用于判断直流母线电流的正负，将判断结果发送给所述功率因数控制子单元902b；
所述功率因数控制子单元902b，用于当所述直流母线电流判断子单元902a判断直流母线电流为正时，控制所述当前的功率因数从1开始减小到最大转矩电流对应的功率因数；当所述直流母线电流判断子单元902a判断直流母线电流为负时，控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。可以理解的是，功率因数最大增大到1，不可能超过1。
需要说明的是，目标功率因数的调节是由功率因数控制器来完成的。下面 结合控制框图来说明本发明提供的控制方法的主要工作原理。
本实施例提供的控制设备，除了控制PWM发波的状态以外，还需要控制目标功率因数，通过控制目标功率因数来控制变频器工作在电机的最大转矩电流处，这样可以提高变频器的工作效率。
设备实施例三：
参见图11，该图为本发明提供的变频器的控制设备实施例三示意图。
本实施例提供的变频器的控制设备，还包括：直流母线电压判断单元907和保护单元908；
所述直流母线电压判断单元907，用于判断所述直流母线电压超过预设阈值时，发送电压保护信号给所述保护单元908；
可以理解的是，预设阈值是预先设定的一个电压值，这个电压值可以根据具体的应用场景来设定，例如根据变频器和永磁同步电机的一些参数来设定。在此不具体限定数值。
所述直流母线电流判断子单元902a，用于判断所述直流母线电流为负时，发送电流保护信号给所述保护单元908；
所述保护单元908，用于在收到所述电压保护信号和/或电流保护信号时，控制所述PWM发波器停止发出PWM波。
可以理解的是，当直流母线电压超过阈值时，需要封锁PWM波的输出；当直流母线电流为负时，也需要封锁PWM波的输出。这样可以保护逆变器不被损坏。
需要说明的是，以上实施例中均是以变频器的负载为永磁同步电机为例进行介绍的，而当负载为其他负载时，由于没有能量回馈，其功率因数由负载决定，因此没有办法对功率因数进行调节。
基于以上实施例提供的一种变频器的控制方法和控制设备，本发明实施例还提供了一种变频器的控制系统，下面结合附图进行详细介绍。
参见图12，该图为本发明提供的变频器的控制系统实施例一示意图。
本实施例提供的变频器的控制系统，包括：整流器1200、逆变器1300、 直流母线1400、控制器1500和PWM发波器1600；
所述整流器1200，用于将交流电整流为直流电后输出给所述逆变器1300；
所述逆变器1300，用于将所述直流电逆变为交流电后给负载供电；
所述整流器1200和逆变器1300之间为直流母线1400；
所述控制器1500，用于由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小；所述励磁给定电流和所述给定转矩电流确定所述目标电压；根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器1600的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压；所述目标电压使逆变侧没有能量回馈到直流母线1400。
可以理解的是，所述给定转矩电流为已知量。
由于逆变侧输出的三相电流的状态不同，对应的PWM发波器的发波状态不同，因此需要检测三相电流的状态。
需要说明的是，直流母线电流可以根据逆变侧输出的三相电流和PWM发波器发出的PWM发波状态来推算，也可以直接检测得到。
目标功率因数可以由直流母线电流，逆变侧输出的三相电压和三相电流来确定。
由目标功率因数和给定转矩电流可以确定励磁给定电流。
由励磁给定电流和给定转矩电流可以确定目标电压Varef，Vbref，Vcref。
对于PWM发波器来说，目标电压是已知的，三相目标电压分别为Varef，Vbref，Vcref。
需要说明的是，PWM发波器1600用来发出PWM波给逆变器中的各个管子，控制各个管子的开关状态。例如，PWM波为高电平时，对应的管子导通，PWM波为低电平时，对应的管子关断。
由于在逆变器中，同一个桥臂上的上管和下管的开关状态正好相反，例如，对于A相桥臂来说，上管Q1为导通时，对应的下管Q2为关断。
本发明实施例提供变频器的控制系统，可以在不改变变频器拓扑的情况 下，通过控制方法使得直流母线电流始终为正，能量从电网经过整流侧直接提供给逆变侧，可以减小直流母线电容上充放的能量(电流)，从而可以减小直流母线电容的容量，甚至可以省掉直流母线电容，降低了变频器的成本，提高了变频器的工作可靠性。
需要说明的是，系统实施例一中变频器的负载可以为永磁同步电机，例如直流变频压缩机和变频风机等内部均嵌有永磁同步电机。由于直流母线电流一直为正，因此永磁同步电机可以一直工作在电动状态。
可以理解的是，变频器的负载也可以为其他功率因数较高(接近1)并且不能回馈能量的负载，例如纯阻性负载、阻感负载、阻容负载，对于不能回馈能量的负载，其功率因数不可控制，因此控制起来比永磁同步电机负载更为简单。在此不再赘述，控制原理可以参见图8对应的实施例。
系统实施例二：
为了提高变频器的工作效率，使永磁同步电机在接近最大转矩电流比时工作，需要控制目标功率因数。本实施例中具体介绍目标功率因数的控制。
所述控制器，用于根据直流母线电流来调节所述当前的功率因数到目标功率因数，具体为：如果所述直流母线电流为正，则控制当前的功率因数从1开始减小到最大转矩电流对应的功率因数；如果所述直流母线电流为负，则控制当前的功率因数停止减小，开始增大到直流母线电流为正为止。可以理解的是，功率因数最大增大到1，不可能超过1。
本实施例提供的控制方法，除了控制PWM发波的状态以外，还需要控制目标功率因数，通过控制目标功率因数来控制变频器工作在电机的最大转矩电流处，这样可以提高变频器的工作效率。
系统实施例三：
为了保证整个变频器的安全运行，本发明系统实施例中提供的控制器还具有保护功能。
所述控制器，还用于当所述直流母线电压超过预设阈值，和/或，当所述直流母线电流为负，控制所述PWM发波器停止发出PWM波。即封锁PWM 波，这样可以保护逆变器不被损坏。
可以理解的是，预设阈值是预先设定的一个电压值，这个电压值可以根据具体的应用场景来设定，例如根据变频器和永磁同步电机的一些参数来设定。在此不具体限定数值。
以上各个实施例提供的方法、设备和系统可以控制变频器中的直流母线电流一直为正，从而使逆变侧没有能量回馈到直流母线，这样可以减小直流母线电容的充放电量，从而减小直流母线电容的容值，进而减小整个变频器的体积，降低硬件成本。
本发明中的各个实施例是以变频器的负载为永磁同步电机为例进行介绍的，由于负载为永磁同步电机时，其功率因数是可以控制的。当负载为其他类型的负载时，由于没有能量回馈，所以功率因数是由负载决定的，是不可控的，因此，控制起来比负载为永磁同步电机时更为简单，在此不再具体介绍。例如，当负载为纯阻性负载时，也没有使用该方法进行控制的必要。
以上所述，仅是本申请的较佳实施例而已，并非对本申请作任何形式上的限制。虽然本申请已以较佳实施例揭露如上，然而并非用以限定本申请。任何熟悉本领域的技术人员，在不脱离本申请技术方案范围情况下，都可利用上述揭示的方法和技术内容对本申请技术方案做出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本申请技术方案的内容，依据本申请的技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均仍属于本申请技术方案保护的范围内。

Claims (11)

  1. 一种变频器的控制方法，其特征在于，包括：
    检测变频器的逆变侧输出的三相电压和三相电流Ia、Ib和Ic；
    由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；
    根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小，所述励磁给定电流和所述给定转矩电流确定目标电压，所述给定转矩电流为给定的已知量；
    根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压，所述目标电压使逆变侧没有能量回馈到直流母线。
  2. 根据权利要求1所述的变频器的控制方法，其特征在于，所述根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，具体为：
    当所述三相电流Ia、Ib和Ic的正负状态为：Ia为正、Ib为负和Ic为负时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：开、关、开，开、关、关，开、开、关，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
    当所述三相电流Ia、Ib和Ic的正负状态为：Ia为正、Ib为正和Ic为负时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：开、关、关，开、开、关，关、开、关，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
    当所述三相电流Ia、Ib和Ic的正负状态为：Ia为负、Ib为正和Ic为负时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：开、开、关，关、开、关，关、开、开，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
    当所述三相电流Ia、Ib和Ic的正负状态为：Ia为负、Ib为正和Ic为正时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：关、开、关，关、开、开，关、关、开，开、开、开，关、关、关，控制下管 的发波状态与控制上管的互补；
    当所述三相电流Ia、Ib和Ic的正负状态为：Ia为负、Ib为负和Ic为正时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：关、开、开，关、关、开，开、关、开，开、开、开，关、关、关，控制下管的发波状态与控制上管的互补；
    当所述三相电流Ia、Ib和Ic的正负状态为：Ia为正、Ib为负和Ic为正时，选择PWM发波器发出的控制逆变器三个上管的发波状态为以下五种状态：关、关、开，开、关、开，开、关、关，开、开、开，关、关、关；控制下管的发波状态与控制上管的互补。
  3. 根据权利要求1或2所述的变频器的控制方法，其特征在于，根据直流母线电流来调节所述当前的功率因数到目标功率因数，具体为：
    如果所述直流母线电流为正，则控制所述当前的功率因数开始减小到最大转矩电流对应的功率因数；
    如果所述直流母线电流为负，则控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
  4. 根据权利要求3所述的变频器的控制方法，其特征在于，还包括：检测直流母线电压和直流母线电流；
    当所述直流母线电压超过预设阈值，和/或，当所述直流母线电流为负，控制所述PWM发波器停止发出PWM波。
  5. 一种变频器的控制设备，其特征在于，包括：检测单元、功率因数控制单元、励磁电流给定单元、目标电压确定单元、开关状态选择单元和开关状态确定单元；
    所述检测单元，用于检测变频器的逆变侧输出的三相电压和三相电流Ia、Ib和Ic；
    所述功率因数控制单元，用于由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；
    所述励磁电流给定单元，用于根据所述目标功率因数和给定转矩电流确定励磁给定电流的大小；
    所述目标电压确定单元，用于由所述励磁给定电流和所述给定转矩电流确 定目标电压，所述给定转矩电流为给定的已知量；所述开关状态选择单元，用于根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态；
    所述开关状态确定单元，用于根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压，所述目标电压使逆变侧没有能量回馈到直流母线。
  6. 根据权利要求5所述的变频器的控制设备，其特征在于，所述功率因数控制单元包括：直流母线电流判断子单元和功率因数控制子单元；
    所述直流母线电流判断子单元，用于判断直流母线电流的正负，将判断结果发送给所述功率因数控制子单元；
    所述功率因数控制子单元，用于当所述直流母线电流判断子单元判断直流母线电流为正时，控制所述当前的功率因数开始减小到最大转矩电流对应的功率因数，当所述直流母线电流判断子单元判断直流母线电流为负时，控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
  7. 根据权利要求5或6所述的变频器的控制设备，其特征在于，还包括：直流母线电压判断单元和保护单元；
    所述直流母线电压判断单元，用于判断所述直流母线电压超过预设阈值时，发送电压保护信号给所述保护单元；
    所述直流母线电流判断子单元，用于判断所述直流母线电流为负时，发送电流保护信号给所述保护单元；
    所述保护单元，用于在收到所述电压保护信号和/或电流保护信号时，控制所述PWM发波器停止发出PWM波。
  8. 一种变频器的控制系统，其特征在于，包括：整流器、逆变器、直流母线、控制器和PWM发波器；
    所述整流器，用于将交流电整流为直流电后输出给所述逆变器；
    所述逆变器，用于将所述直流电逆变为交流电后给负载供电；
    所述整流器和逆变器之间为直流母线；
    所述控制器，用于由所述三相电压和三相电流获得变频器当前的功率因数，根据直流母线电流来调节所述当前的功率因数到目标功率因数；，根据所 述目标功率因数和给定转矩电流确定励磁给定电流的大小，所述励磁给定电流和所述给定转矩电流确定目标电压，根据所述三相电流Ia、Ib和Ic的正负状态选择PWM发波器的发波状态，根据所述目标电压从已经选择出的发波状态中确定至少三种发波状态来控制逆变器中开关器件的开关状态，使所述逆变器输出的三相电压合成所述目标电压；所述目标电压使逆变侧没有能量回馈到直流母线。
  9. 根据权利要求8所述的变频器的控制系统，其特征在于，所述控制器，用于根据直流母线电流以及逆变侧输出的三相电压和所述三相电流控制目标功率因数，具体为：如果所述直流母线电流为正，则控制所述当前的功率因数开始减小到最大转矩电流对应的功率因数，如果所述直流母线电流为负，则控制所述当前的功率因数停止减小，开始增大到直流母线电流为正为止。
  10. 根据权利要求8所述的变频器的控制系统，其特征在于，所述控制器，还用于当所述直流母线电压超过预设阈值，和/或，当所述直流母线电流为负，控制所述PWM发波器停止发出PWM波。
  11. 根据权利要求8-10任一项所述的变频器的控制系统，其特征在于，所述负载为永磁同步电机，所述永磁同步电机处于电动状态。
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