Power Converters and Variable Frequency Drives

Abstract

To provide a power converter and a variable frequency drive that achieve more excellent stabilization effect and filtering effect.SOLUTION: A power converter 100 for receiving an AC input voltage VAC and converting AC to DC, comprises: a power storage unit; a plurality of silicon controlled rectifiers 1; and a first control unit 3. The silicon-controlled rectifier 1 becomes a full-bridge rectifier, being electrically connected to the power storage unit, being switched between a conductive state and a non-conductive state based on a received control signal S, and being capable of converting the AC input voltage VAC into a DC output voltage VO1 to output a DC voltage VO1 to the power storage unit. The first control unit 3 detects a zero-crossing point of the AC input voltage VAC and the DC output voltage VO1, and generates a control signal S based on the zero-crossing point and the DC output voltage VO1, so that the DC output voltage VO1 can be set to a predetermined voltage.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to power converters and variable frequency drives, and in particular to power converters and variable frequency drives having supercapacitors or lithium ion capacitors. [Background technology]

[0002] A variable-frequency drive (VFD) is a device that can smoothly control the speed and torque of an AC motor by changing the frequency or amplitude of the operating voltage of the AC motor.

[0003] The configuration of the conventional variable frequency drive described in Patent Document 1 will be described with reference to Fig. 1. Here, Fig. 1 is a block diagram showing the conventional variable frequency drive described in Patent Document 1.

[0004] As shown in FIG. 1, a conventional variable frequency drive is electrically connected to an AC power source 18 and an inductive load 19, and includes a rectifier unit 11, an inverter unit 12, a control unit 13, a filter capacitor 14, and a braking unit 15.

[0005] The rectifier unit 11 receives an AC voltage V1 from an AC power supply 18 and converts the AC voltage V1 into a DC input voltage V2.

[0006] As shown in FIG. 1, the inverter unit 12 is electrically connected to the rectifier unit 11 and the inductive load 19 .

[0007] 1, the control unit 13 is electrically connected to the inverter unit 12 and controls the inverter unit 12 to convert the DC input voltage V2 received from the rectifier unit 11 into an AC output voltage V3, and outputs the AC output voltage V3 to the inductive load 19. The control unit 13 can also control the frequency or amplitude of the AC output voltage V3.

[0008] The filter capacitor 14 is an electrolytic capacitor, and as shown in FIG. 1, is located between the rectifier unit 11 and the inverter unit 12 and is electrically connected to the rectifier unit 11 and the inverter unit 12, and can filter and stabilize the DC input voltage V2.

[0009] 1, the braking unit 15 includes a switch 152 and a bleeder resistor 151. The switch 152 and the bleeder resistor 151 are located between one end of the filter capacitor 14 and the ground point and are connected in series with the one end of the filter capacitor 14 and the ground point, respectively.

[0010] The bleeder resistor 151 is a power resistor. The switch 152 can be controlled by other detection circuits or components. When the inductive load 19 does not generate a back electromotive force, the switch 152 is controlled to be in a non-conducting state, whereas when the inductive load 19 generates a back electromotive force, the switch 152 is controlled to be in a conducting state.

[0011] Therefore, the energy of the back electromotive force generated by the inductive load 19 can be released through the switch 152 and the bleeder resistor 151. This prevents the rectifier unit 11, the inverter unit 12, and the filter capacitor 14 from being damaged by the back electromotive force.

[0012] Here, if the filter capacitor 14 is an electrolytic capacitor, the conventional variable frequency drive needs to include a braking unit 15 to prevent the back electromotive force generated by the inductive load 19 from damaging the components in the conventional variable frequency drive. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] Taiwan Patent No. I787845 Specification Summary of the Invention [Problem to be solved by the invention]

[0014] However, when a supercapacitor is installed in the conventional variable frequency drive described in Patent Document 1, the configuration may become complicated. Therefore, there is room for improvement in this conventional technology.

[0015] Therefore, in view of the above problems, an object of the present invention is to provide a power converter and a variable frequency drive that can solve the above drawbacks. [Means for solving the problem]

[0016] As a means for achieving the above object, the present invention provides a power converter for receiving an AC input voltage and converting AC into DC, the power converter comprising: The power supply includes a power storage unit, a plurality of silicon-controlled rectifiers, and a first control unit, The power storage unit is one of a supercapacitor and a lithium ion capacitor, the plurality of silicon-controlled rectifiers are electrically connected to each other, and form a full-bridge rectifier arranged to receive the AC input voltage; the silicon-controlled rectifiers are electrically connected to the power storage unit, and are configured to receive a control signal and be controlled to be switched between a conductive state and a non-conductive state based on the control signal, thereby converting the AC input voltage into a DC output voltage and outputting the DC output voltage to the power storage unit; The first control unit is configured to detect zero crossing points of the AC input voltage and the DC output voltage, generate the control signal based on the zero crossing points and the DC output voltage, and make the DC output voltage a predetermined voltage.

[0017] Also, a variable frequency drive applied to an AC power source and an inductive load, comprising: The power converter includes the power converter, an inverter unit, and a second control unit, the power converter is configured to receive the AC input voltage from the AC power supply and convert the AC input voltage into the DC output voltage; the inverter unit is electrically connected to the power converter, so that it can be controlled to receive the DC output voltage from the power converter and convert the DC output voltage into an AC output voltage, and is electrically connected to the inductive load, so that it can output the AC output voltage to the inductive load; The second control unit is electrically connected to the inverter unit and configured to control the inverter unit to generate the AC output voltage and to control either the frequency or the amplitude of the AC output voltage.

[0018] Further, there is provided a variable frequency drive for application to an AC power source and an inductive load, comprising: The power supply includes a power storage unit, a plurality of silicon-controlled rectifiers, a first control unit, an inverter unit, and a second control unit, The power storage unit is one of a supercapacitor and a lithium ion capacitor, the plurality of silicon-controlled rectifiers are electrically connected to each other, and form a full-bridge rectifier arranged to receive the AC input voltage; the silicon-controlled rectifiers are electrically connected to the power storage unit, and are configured to receive a control signal and be controlled to be switched between a conductive state and a non-conductive state based on the control signal, thereby converting the AC input voltage into a DC output voltage and outputting the DC output voltage to the power storage unit; the first control unit is configured to detect a zero cross point of the AC input voltage and the DC output voltage, generate the control signal based on the zero cross point and the DC output voltage, make the DC output voltage a predetermined voltage, and adjust the predetermined voltage based on a power level of the power storage unit, the inverter unit is electrically connected to the power converter, so that it can be controlled to receive the DC output voltage from the power converter and convert the DC output voltage into an AC output voltage, and is electrically connected to the inductive load, so that it can output the AC output voltage to the inductive load; The second control unit is electrically connected to the inverter unit and configured to control the inverter unit to generate the AC output voltage and to control either the frequency or the amplitude of the AC output voltage. [Effects of the Invention]

[0019] In the power converter and variable frequency drive according to the present invention, the storage unit is a supercapacitor or lithium ion capacitor with a high capacitance, which has an excellent stabilizing effect and filtering effect on the DC output voltage generated by the full-bridge rectifier consisting of multiple silicon-controlled rectifiers. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a block diagram showing a conventional variable frequency drive described in Patent Document 1. [Figure 2] 1 is a block diagram showing a power converter according to an embodiment of the present invention; [Figure 3] FIG. 4 is a timing diagram illustrating control signals of a first control unit according to an embodiment of the present invention. [Figure 4] FIG. 10 is a timing diagram illustrating control signals of a first control unit according to another embodiment of the present invention. [Figure 5] 1 is a block diagram illustrating a variable frequency drive according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, a power converter and a variable frequency drive according to the present invention will be described with reference to the drawings.

[0022] The configuration of a power converter according to the present invention will be described with reference to Figures 2 to 4. Here, Figure 2 is a block diagram showing a power converter 100 according to one embodiment of the present invention, Figure 3 is a timing diagram showing a control signal S of a first control unit 3 according to one embodiment of the present invention, and Figure 4 is a timing diagram showing a control signal S of a first control unit 3 according to another embodiment of the present invention.

[0023] As shown in FIG. 2, a power converter 100 according to an embodiment of the present invention receives an AC input voltage V ACThe power converter receives power from a power source and converts AC to DC, and includes a plurality of silicon controlled rectifiers (abbreviated as SCRs) 1, a power storage unit, and a first control unit 3.

[0024] In this embodiment, the power storage unit is a supercapacitor 2.

[0025] In this embodiment, the AC power supply 88 receives an AC input voltage V having a voltage of 220 V (effective value) and a frequency of 60 Hz, for example. AC However, the present invention is not limited to this.

[0026] As shown in FIG. 2, the plurality of silicon-controlled rectifiers 1 are electrically connected to each other and are connected to an AC input voltage V AC In this embodiment, the full-bridge rectifier is configured from four silicon-controlled rectifiers 1, but is not limited to this.

[0027] In addition, the plurality of silicon-controlled rectifiers 1 are electrically connected to the supercapacitors 2, as shown in FIG. 2, and are configured to receive a control signal S from the first control unit 3, and can be controlled to switch between a conductive state and a non-conductive state based on the control signal S.

[0028] When the logic value of the control signal S is equal to a first logic value, the plurality of silicon-controlled rectifiers 1 are switched to a non-conductive state, whereas when the logic value of the control signal S is equal to a second logic value, the plurality of silicon-controlled rectifiers 1 are switched to a conductive state, where the first logic value is, for example, 0 corresponding to 0 volts, while the second logic value is, for example, 1 corresponding to a voltage based on the specifications of the silicon-controlled rectifiers 1.

[0029] When multiple silicon-controlled rectifiers 1 are in a conducting state, the full-bridge rectifier consisting of multiple silicon-controlled rectifiers 1 operates in a manner similar to that of the AC input voltage V AC DC output voltage V O1 and convert it into DC output voltage V O1 can be output to supercapacitor 2.

[0030] The supercapacitor 2 receives the DC output voltage V from the silicon controlled rectifier 1. O1 In this embodiment, the supercapacitor 2 is an electric double layer capacitor (abbreviated as EDLC), which is an electrochemical capacitor with high energy density. The capacitance of the supercapacitor 2 is generally several hundred to several thousand times larger than that of a conventional electrolytic capacitor.

[0031] For example, the capacitance of the filter capacitor 14 (see FIG. 1) used in a conventional variable frequency driver is about several hundred μF, whereas the capacitance of the supercapacitor 2 of this embodiment is, for example, 2.65 F, but is not limited thereto.

[0032] In this embodiment, the power converter 100 uses a supercapacitor 2, but this is not limited thereto. In other embodiments, a lithium-ion capacitor may be used as the power storage unit instead of the supercapacitor 2.

[0033] Since the supercapacitor 2 has a high capacitance, the full-wave rectified signal passing through the full-bridge rectifier, i.e., the DC output voltage V O1 can be stabilized to be a stable DC signal.

[0034] The first control unit 3 is, for example, a microcontroller unit (abbreviated as MCU) or a combination of a microcontroller unit and a peripheral circuit, and is configured to receive an AC input voltage V AC and is electrically connected to an AC power supply 88 so as to be able to detect the zero crossing point of the DC output voltage V O1 The power supply 1 is electrically connected to a plurality of silicon controlled rectifiers 1 so as to be able to detect the power supply voltage Vcc.

[0035] The first control unit 3 also controls the AC input voltage V AC The zero crossing point and DC output voltage V O1 A control signal S is generated based on the DC output voltage V O1 is configured to be able to set the voltage to a predetermined value.

[0036] As an example, a half-bridge rectifier converts the AC input voltage V AC The positive half-period signal V is acquired, and the high peak value (e.g., 311 V) of the positive half-period signal is converted by an optical coupler into an AC voltage signal (e.g., amplitude 3.3 V) that has the same phase as the positive half-period signal and a relatively small amplitude. Then, a comparator (e.g., operational amplifier) ​​compares the AC voltage signal with a reference voltage (e.g., 0.2 V) to obtain the AC input voltage V AC The zero crossing point can be obtained.

[0037] Here, many techniques and circuits are AC , but for the sake of brevity, a detailed description thereof will be omitted.

[0038] The first control unit 3 determines whether a change in logic value of the generated control signal S is a function of the AC input voltage V AC The logic value of the control signal S is controlled so that it occurs at one zero crossing point in the AC input voltage V AC can be made to be equal to either the first logic value or the second logic value throughout any period in the

[0039] The first control unit 3 controls the DC output voltage V O1 is determined to be greater than the specified voltage, the AC input voltage V AC Here, the voltage rise period is the number of periods during which the logic value of the control signal S remains equal to the second logic value within a predetermined period of time. AC That is, the first control unit 3 controls the AC input voltage V AC This can reduce the frequency of occurrence of voltage rise periods in the

[0040] On the other hand, the first control unit 3 controls the DC output voltage V O1 is determined to be smaller than the specified voltage, the AC input voltage V AC That is, the first control unit 3 can increase the number of periods of the voltage rise in the AC input voltage V AC This can increase the frequency of occurrence of voltage rise periods in the

[0041] The above-mentioned predetermined period is AC That is, the first control unit 3 controls the total length of the period in which the silicon-controlled rectifier 1 is in a conducting state within a predetermined period, thereby controlling the corresponding DC output voltage V O1 can be adjusted.

[0042] As shown in FIG. 3, for example, the predetermined voltage is 310 V, and the predetermined period P1 is 1 second. AC contains a sine wave signal with 60 periods in a predetermined period P1. Here, the logic value of the control signal S is AC and a second logic value corresponding to one period of the AC input voltage V AC is equal to the first logic value corresponding to 59 periods in

[0043] Here, Figure 3 shows the AC input voltage V ACand the logic value of the control signal S, and the DC output voltage V O1 This does not mean that the control signal S will be stable when it reaches a predetermined voltage.

[0044] In some embodiments, the first control unit 3 may be configured to detect any change in logic value from a first logic value to a second logic value in the control signal S as a function of the AC input voltage V AC The control signal S can be controlled to occur at one zero crossing point in the AC input voltage V AC 4 shows that the period of the control signal S is equal to the period of the AC input voltage V. AC This shows that the period is equal to

[0045] The first control unit 3 controls the DC output voltage V O1 is determined to be greater than a predetermined voltage, the duty cycle D of the control signal S may be reduced while the DC output voltage V O1 is determined to be less than the predetermined voltage, the duty cycle D of the control signal S can be increased, where the duty cycle D of the control signal S is the ratio of the period during which the logic value of the control signal S is equal to the second logic value to the period of the control signal S.

[0046] That is, the first control unit 3 controls the length of time that each silicon-controlled rectifier 1 is in a conducting state in each cycle (for example, 1 / 60 seconds) of the control signal S, and accordingly controls the DC output voltage V O1 Adjust.

[0047] The configuration of a variable frequency drive according to the present invention will be described with reference to Fig. 5. Here, Fig. 5 is a block diagram showing a variable frequency drive according to an embodiment of the present invention.

[0048] A variable frequency drive according to one embodiment of the present invention is applied to an AC power source 88 and an inductive load 89, as shown in Figure 5. In this embodiment, the inductive load 89 is a motor.

[0049] As shown in FIG. 5, the variable frequency drive of this embodiment includes the above-mentioned power converter 100, an inverter unit 4, and a second control unit 5, and receives an AC input voltage V from an AC power source 88. AC DC output voltage V O1 and converts it into a DC output voltage V O1 AC output voltage V O2 By further converting this into the above, the speed and torque of the motor can be smoothly controlled.

[0050] In this embodiment, the inverter unit 4 is a power converter that converts DC to AC, and as shown in FIG. 5, is electrically connected to the power converter 100 for converting AC to DC, and outputs a DC output voltage V O1 You can receive the following.

[0051] The inverter unit 4 is controlled by the second control unit 5 to generate a DC output voltage V O1 AC output voltage V O2 and converts it into AC output voltage V O2 5, the inverter unit 4 is electrically connected to an inductive load 89, and thereby the AC output voltage V O2 can be output to the inductive load 89.

[0052] Therefore, the inductive load 89 outputs an AC output voltage V O2 and a back EMF is generated when the motor is slowing down or braking.

[0053] As shown in FIG. 5, the second control unit 5 is electrically connected to the inverter unit 4 and controls the inverter unit 4 to generate an AC output voltage V O2 and generates an AC output voltage V O2This allows the phase (or frequency) and amplitude of the AC output voltage V to be controlled. O2 (different amplitudes of the signal) can be used to control the torque of a motor, for example.

[0054] Here, the second control unit 5 is for example a microcontroller unit or any known control circuit that can be used to control the inverter unit 4 .

[0055] As an example, the variable frequency drive of this embodiment is applied to an elevator. In this case, the motor has an AC output voltage V O2 It is operated based on the above and is used to allow the elevator to go up and down.

[0056] When the elevator is ascending, the second control unit 5 controls the AC output voltage V O2 By controlling the frequency and amplitude of the signal, the rotational speed and torque of the motor can be smoothly controlled. Meanwhile, when the elevator is descending, the motor (i.e., the inductive load 89) slows down or brakes, generating a counter electromotive force (EMF).

[0057] The supercapacitor 2 can absorb and store the energy of the back electromotive force, so even when the motor is decelerating or braking, the DC output voltage V O1 This makes it possible to prevent the full-bridge rectifier (silicon-controlled rectifier 1) and the inverter unit 4 from being damaged by the back electromotive force.

[0058] Furthermore, after the back electromotive force is generated in the motor, the second control unit 5 controls the inverter unit 4 to generate the AC output voltage V O2When the elevator is to be regenerated (for example, when the elevator is about to change from descending to ascending), the energy due to the back electromotive force stored in the supercapacitor 2 is transferred to the inductive load 89 via the inverter unit 4, thereby reducing the amount of power required by the inductive load 89 and supplied by the AC power supply 88.

[0059] For example, when the variable frequency drive of this embodiment is applied to an elevator, i.e., when the inductive load 89 is an elevator motor, the variable frequency drive of the present invention can reduce the power consumption by at least 60% compared with the conventional one using an electrolytic capacitor. That is, when the motor is decelerating or braking, the energy generated by the back electromotive force can be stored in the supercapacitor 2 and can be used by the motor in the future.

[0060] Compared with the conventional example in which the back electromotive force energy is released through the bleeder resistor 151 of the braking unit 15 as shown in FIG. 1 to prevent damage to the variable frequency drive, the supercapacitor 2 of the variable frequency drive of this embodiment not only protects other components in the variable frequency drive to prevent their damage, but also stores the back electromotive force energy for reuse.

[0061] Furthermore, since the supercapacitor 2 of this embodiment is smaller in size than an electrolytic capacitor, the configuration of the variable frequency drive of this embodiment can be made smaller and simpler than conventional ones.

[0062] Note that for simplicity, Figures 1, 2 and 5 only show a single circuit. In practice, the AC input voltage V AC and AC output voltage V O2 are both three-phase power supplies, and the power converter 100 and the variable frequency drive are connected to an AC input voltage V AC and AC output voltage V O2 It has a three-phase circuit corresponding to

[0063] If the motor does not need to be running all the time (for example, if the motor is used to drive an elevator), the power output (kW) required for the motor may be supplied by AC power supply 88 alone, or may be supplied by supercapacitor 2 and AC power supply 88 together.

[0064] Here, the output required of the motor is, for example, 6 kW, of which 3 kW is immediately supplied by the AC power supply 88, and the other 3 kW is taken from the energy stored in the supercapacitor 2. Of course, the present invention is not limited to this.

[0065] In this embodiment, when the first control unit 3 of the variable frequency drive receives the activation signal, the variable frequency drive activates the AC input voltage V AC At this time, the first control unit 3 performs a slow start procedure based on the start signal.

[0066] In this slow start procedure, the first control unit 3 controls the DC output voltage V O1 By gradually increasing the DC output voltage V from 0 volts, it is possible to prevent a short circuit of the supercapacitor 2. After the slow start procedure is performed, the first control unit 3 O1 is controlled to a predetermined voltage.

[0067] Specifically, the start signal is a signal generated by, for example, a user pressing a start button (not shown). The first control unit 3 controls the AC input voltage V AC or gradually increasing the duty cycle D of the control signal S until the voltage across the supercapacitor 2 reaches a predetermined value, thereby O1 This prevents the formation of a short circuit in the supercapacitor 2.

[0068] The voltage across supercapacitor 2 is the DC output voltage V measured near supercapacitor 2.O1 and reflects the actual stored voltage of the supercapacitor 2 when taking into account the line impedance, where the predetermined value is, for example, 90% of the predetermined voltage.

[0069] In some embodiments, in the slow start procedure, the first control unit 3 determines whether the AC input voltage V AC Alternatively, the duty cycle D of the control signal S can be controlled to increase until the voltage across the supercapacitor 2 reaches a predetermined value.

[0070] In addition, in this embodiment, instead of using an open-loop control method to adjust the control signal S according to a predetermined mode, the first control unit 3 uses a closed-loop control method to adjust the control signal S based on the voltage across the supercapacitor 2, thereby ensuring that the slow start procedure is completed only when the voltage across the supercapacitor 2 reaches a predetermined value.

[0071] In this way, by using the closed-loop control method, in the slow-start procedure, the first control unit 3 can control the increase in the duty cycle of the control signal until the voltage across the supercapacitor 2 reaches a predetermined value, thereby avoiding the slow-start procedure from terminating when there is a difference between the voltage across the supercapacitor 2 and the predetermined value, as occurs when the first control unit 3 uses the open-loop control method.

[0072] 5, the variable frequency drive of this embodiment further includes a switch 6. The switch 6 is, for example, a relay, and has a first end electrically connected to the supercapacitor 2, a second end grounded, and a control end receiving a turn-off signal.

[0073] When the control end of the switch 6 receives a turn-off signal, the switch 6 electrically connects the first end and the second end to discharge the supercapacitor 2 so that the voltage across the supercapacitor 2 becomes 0 volts. On the other hand, when the control end of the switch 6 does not receive a turn-off signal, the switch 6 cuts off the electrical connection between the first end and the second end.

[0074] More specifically, the turn-off signal may be generated, for example, by a user releasing the start button, and sent to the first control unit 3 and the switch 6. The first control unit 3 controls the silicon-controlled rectifier 1 based on the turn-off signal to turn on the DC output voltage V O1 The output of the switch 6 is stopped, and the energy stored in the supercapacitor 2 is released, and the supercapacitor 2 is discharged to 0 volts via the second terminal of the switch 6 which is grounded.

[0075] Therefore, according to the above-described configuration, the variable frequency drive of the embodiment can comply with safety regulations and prevent a user from getting an electric shock when touching the variable frequency drive.

[0076] It should be noted that due to the large capacitance of the supercapacitor 2, the switch 6 can slowly discharge the supercapacitor 2 without damaging other components in the variable frequency drive of this embodiment, whereas the switch 152 of the braking unit 15 in a conventional variable frequency drive (see FIG. 1 ) needs to be quickly switched to a conducting state to release the back electromotive force before it can damage other components.

[0077] That is, the switch 6 of the variable frequency drive of this embodiment does not need to quickly discharge the supercapacitor 2, while in the case of a conventional variable frequency drive, the switch 152 needs to quickly discharge the back electromotive force. Therefore, the variable frequency drive of the present invention and the conventional variable frequency drive are different in terms of the operating principle, the problem to be solved, and the specifications of the components.

[0078] In some embodiments, the first control unit 3 controls the DC output voltage V based on the power level of the supercapacitor 2. O1 Specifically, the predetermined voltage pre-set and stored in the first control unit 3 is equal to a first set value (e.g., 310V), and the first control unit 3 determines the power level of the supercapacitor 2 based on the voltage across the supercapacitor 2, or can use a coulomb meter to determine the power level of the supercapacitor 2.

[0079] When the first control unit 3 determines that the power level of the supercapacitor 2 is less than the threshold value, it adjusts the predetermined voltage from the first set value to a second set value (e.g., 312V) greater than the first set value, thereby increasing the charging speed of the supercapacitor 2 and increasing the DC output voltage V O1 The time required for the temperature to reach the first set value can be shortened.

[0080] When the first control unit 3 attempts to determine the power level of the supercapacitor 2 based on the voltage across the supercapacitor 2, when the first control unit 3 determines that the voltage across the supercapacitor 2 is, for example, less than 50% of a first set value (i.e., the threshold value corresponds to 50% of the first set value), the first control unit 3 determines that the power level of the supercapacitor 2 is less than the threshold value.

[0081] In some embodiments, the variable frequency drive includes the above-described power converter 100, a plurality of inverter units 4, and a plurality of second control units 5.

[0082] The inverter units 4 are electrically connected to the power converter 100, and thereby generate a DC output voltage V O1 It can receive a DC output voltage V O1 multiple AC output voltages V O2 and are electrically connected to a plurality of inductive loads 89, thereby generating a plurality of AC output voltages V O2 can be output to a plurality of inductive loads 89, respectively.

[0083] That is, the power converter 100 of the variable frequency drive has not only one inverter unit 4 but also multiple DC output voltages V O1 can be output to a plurality of inverter units 4, respectively.

[0084] In this case, the plurality of second control units 5 are electrically connected to the plurality of inverter units 4, respectively, and each second control unit 5 controls the corresponding inverter unit 4 to generate the corresponding AC output voltage V O2 and generates a corresponding AC output voltage V O2 The frequency and amplitude of the signal can be controlled.

[0085] In summary, in the power converter 100 and variable frequency drive according to the present invention, the power storage unit is a supercapacitor 2 or a lithium ion capacitor with a high capacitance, so that the DC output voltage V generated by the full-bridge rectifier consisting of multiple silicon-controlled rectifiers 1 can be O1 It has excellent stabilizing and filtering effects.

[0086] In addition, the variable frequency drive according to the present invention is configured such that the first control unit 3 controls the silicon controlled rectifier 1 to control the AC input voltage V AC DC output voltage V O1and the switch 6 can prevent short circuit and electric shock hazards when starting or stopping the variable frequency drive of the present invention.

[0087] Furthermore, the variable frequency drive of the present invention does not require the braking unit 15 required in the conventional one to discharge the back electromotive force generated by the inductive load 89, and can effectively absorb and store the energy of the back electromotive force generated by the inductive load 89 in the power storage unit.

[0088] Although numerous specific details are set forth above to provide a thorough understanding of the present invention, it will be apparent to one skilled in the art that one or more other embodiments may be practiced without these specific details.

[0089] While the preferred embodiments and variations of the present invention have been described above, the present invention is not limited to these and encompasses all modifications and equivalents as various configurations falling within the spirit and scope of the broadest interpretation. [Industrial Applicability]

[0090] The power converter and variable frequency drive according to the present invention have excellent stabilizing and filtering effects on the DC output voltage generated by a silicon-controlled rectifier that converts an AC input voltage into a DC output voltage, and are therefore industrially applicable. [Explanation of symbols]

[0091] 11 Rectification unit 12 Inverter unit 13 Control Unit 14 Filter capacitor 15 Braking unit 151 Bleeder resistor 152 Switch 18 AC power supply 19 Inductive load V1 AC voltage V2 DC input voltage V3 AC output voltage 100 Power Converter 1 Silicon Controlled Rectifier 2 Supercapacitors 3. First control unit 4 Inverter Unit 5. Second control unit 6 Switch 88 AC power supply 89 Inductive load S control signal D Duty Cycle P1 Predetermined period V AC AC input voltage V O1 DC Output Voltage V O2 AC Output Voltage

Claims

1. A variable frequency drive applied to an AC power source and an inductive load, comprising: a power converter having a power storage unit, a plurality of silicon-controlled rectifiers, and a first control unit; an inverter unit; and a second control unit; The power storage unit is one of a supercapacitor and a lithium ion capacitor, the plurality of silicon-controlled rectifiers are electrically connected to each other and form a full-bridge rectifier arranged to receive an AC input voltage from the AC power supply, and are electrically connected to the power storage unit and configured to receive a control signal and be controlled to switch between a conductive state and a non-conductive state based on the control signal, thereby converting the AC input voltage into a DC output voltage and outputting the DC output voltage to the power storage unit; the first control unit is configured to detect a zero cross point of the AC input voltage and the DC output voltage, generate the control signal based on the zero cross point and the DC output voltage, make the DC output voltage a predetermined voltage, and adjust the predetermined voltage based on a power level of the power storage unit, the inverter unit is electrically connected to the power converter, so that it can be controlled to receive the DC output voltage from the power converter and convert the DC output voltage into an AC output voltage, and is electrically connected to the inductive load, so that it can output the AC output voltage to the inductive load; the second control unit is electrically connected to the inverter unit and configured to control the inverter unit to generate the AC output voltage and to control either a frequency or an amplitude of the AC output voltage. A variable frequency drive characterized by:

2. When the power level of the power storage unit is lower than a threshold value, the first control unit adjusts the predetermined voltage from a first set value to a second set value that is higher than the first set value, thereby increasing the charging speed of the power storage unit and shortening the time required for the DC output voltage to reach the first set value.

2. The variable frequency drive of claim 1.

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