Motor driving circuit and frequency converter

Abstract

The utility model is applicable to the technical field of electronic circuits, and provides a motor driving circuit and a frequency converter, a filter is coupled to a direct current bus through a reactor at a neutral point of a filter capacitor, common-mode current is introduced to the direct current bus, bus voltage is integrally improved, voltage drop caused by the filter and a long cable between an inverter and a motor is offset, and the frequency converter is enabled to be more stable. Therefore, the voltage output from the inverter to the motor is improved, and the loading capacity of the motor is improved. In addition, according to the scheme, the common-mode current generated by the filter is transmitted to the direct-current bus through the electric reactor, so that the electromagnetic interference of the frequency converter is reduced by reasonably utilizing the common-mode current.

Description

Technical Field

[0001] The present application belongs to the field of electronic circuit technology, and in particular relates to a motor drive circuit and a frequency converter. Background Art

[0002] Frequency converters (VFDs) are a crucial component of AC variable-frequency speed control systems and a key piece of equipment for automating production processes. They offer significant energy savings and bring significant benefits to the national economy. In many industrial applications, such as oilfield drilling, marine surveying, papermaking, and mining, the VFD and motor are not installed in the same location, requiring long cables to transmit the VFD's pulse signals to the motor. Currently, sinusoidal filters are often used to offset the negative effects of these long cables. However, the large filter inductance used in sinusoidal filters, combined with the cable impedance, creates a significant voltage drop in the pulse signal. This results in insufficient line voltage at the motor, forcing the motor to maintain low torque and significantly reducing the VFD's load capacity. Utility Model Content

[0003] The embodiments of the present application provide a motor drive circuit and a frequency converter, which can solve the problem in the prior art that the sinusoidal filter causes a large voltage drop on the pulse signal of the driving motor, resulting in insufficient line voltage obtained at the motor end.

[0004] In a first aspect, an embodiment of the present application provides a filter connected to an inverter and a motor, respectively, including:

[0005] a plurality of filter inductors, wherein a first end of each filter inductor is connected to each output end of the inverter in a one-to-one correspondence, and a second end of each filter inductor is connected to each input end of the motor in a one-to-one correspondence;

[0006] a plurality of filter capacitors, wherein the first end of each filter capacitor is connected to the second end of each filter inductor in a one-to-one correspondence, and the second ends of each filter capacitor are connected in common;

[0007] A reactor, wherein a first end of the reactor is connected to the second end of each of the filter capacitors, and a second end of the reactor is coupled to the DC bus of the inverter, for generating a common-mode current and outputting it to the DC bus to increase the voltage of the DC bus.

[0008] In one embodiment, there are two filter inductors and two filter capacitors.

[0009] In one embodiment, the number of the filter inductors is three and the number of the filter capacitors is three.

[0010] In a second aspect, an embodiment of the present application provides a motor drive circuit, comprising:

[0011] an inverter, connected to direct current via a direct current bus, and configured to output a drive signal based on the direct current;

[0012] a bus capacitor connected between the positive and negative poles of the DC bus; and

[0013] The filter as described above is connected to each output terminal of the inverter and each input terminal of the motor, and is coupled to the DC bus. The filter is used to filter the drive signal and output it to the motor, and generate the common-mode current to increase the voltage of the DC bus.

[0014] In one embodiment, the rectifier is further included, and the inverter is connected to the rectifier via the DC bus.

[0015] In one embodiment, the rectifier includes a three-phase rectifier bridge, the filter is connected to the neutral point of the three-phase power supply, and the rectifier is used to access the alternating current provided by the three-phase power supply and rectify the alternating current to output the direct current.

[0016] In one embodiment, the rectifier includes a first rectifier diode and a second rectifier diode, the first rectifier diode and the second rectifier diode are connected in forward series between the positive pole and the negative pole of the DC bus, and the filter is connected to the series node of the first rectifier diode and the second rectifier diode.

[0017] In one embodiment, the inverter includes a single-phase inverter, and the filter includes a first filter inductor, a second filter inductor, a first filter capacitor, a second filter capacitor, and a reactor;

[0018] The first end of the first filter inductor and the first end of the second filter inductor are connected to the two output ends of the inverter, and the second end of the first filter inductor and the second end of the second filter inductor are connected to the two input ends of the motor through cables respectively;

[0019] The first end of the first filter capacitor is connected to the second end of the first filter inductor, the first end of the second filter capacitor is connected to the second end of the second filter inductor, the second end of the first filter capacitor and the second end of the second filter capacitor are commonly connected to the first end of the inductor, and the second end of the inductor is coupled to the DC bus.

[0020] In one embodiment, the inverter includes a three-phase inverter, and the filter includes a first filter inductor, a second filter inductor, a third filter inductor, a first filter capacitor, a second filter capacitor, a third filter capacitor, and a reactor;

[0021] The first end of the first filter inductor, the first end of the second filter inductor, and the first end of the third filter inductor are connected to three output ends of the three-phase inverter, and the second end of the first filter inductor, the second end of the second filter inductor, and the second end of the third filter inductor are respectively connected to three input ends of the motor through cables;

[0022] The first end of the first filter capacitor is connected to the second end of the first filter inductor, the first end of the second filter capacitor is connected to the second end of the second filter inductor, and the first end of the third filter capacitor is connected to the second end of the third filter inductor, and the second end of the first filter capacitor, the second end of the second filter capacitor, and the second end of the third filter capacitor are connected to the first end of the reactor, and the second end of the reactor is coupled to the DC bus.

[0023] In a third aspect, an embodiment of the present application provides a frequency converter, which further comprises the motor driving circuit as described above.

[0024] Compared with the prior art, the embodiment of the present application has the following beneficial effects:

[0025] In the above scheme, the filter is coupled to the DC bus through the reactor at the neutral point of the filter capacitor, common-mode current is introduced into the DC bus, the bus voltage is overall improved, the voltage drop caused by the filter itself and the long cable between the inverter and the motor is offset, thereby improving the voltage output from the inverter to the motor and improving the load carrying capacity of the motor; in addition, the common-mode current generated by the filter is transmitted to the DC bus through the reactor, so that the common-mode current is reasonably utilized, and the electromagnetic interference (EMI) of the frequency converter is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0027] Figure 1 is a module schematic diagram of the motor driving circuit provided by an embodiment of the present application;

[0028] Figure 2 is a module schematic diagram of the motor driving circuit provided by an embodiment of the present application;

[0029] Figure 3 is a module schematic diagram of the motor driving circuit provided by an embodiment of the present application;

[0030] Figure 4 1 is a circuit diagram of a motor drive circuit provided in one embodiment of the present application;

[0031] Figure 5 1 is a circuit diagram of a motor drive circuit provided in one embodiment of the present application;

[0032] Figure 6 1 is a circuit diagram of a motor drive circuit provided in one embodiment of the present application;

[0033] Figure 7 This is a driving signal simulation diagram of a motor driving circuit provided in one embodiment of the present application;

[0034] Figure 8 This is a driving signal simulation diagram of a motor driving circuit provided in one embodiment of the present application;

[0035] Figure 9 This is a driving signal simulation diagram of a motor driving circuit provided in one embodiment of the present application;

[0036] Figure 10 This is a driving signal simulation diagram of a motor driving circuit provided in one embodiment of the present application. DETAILED DESCRIPTION

[0037] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0038] It should be understood that when used in the present specification and the appended claims, the term "comprising" indicates the presence of described features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or collections thereof.

[0039] It will also be understood that the term "and / or" used in this specification and the appended claims refers to and includes any and all possible combinations of one or more of the associated listed items.

[0040] As used in this specification and the appended claims, the term “if” can be interpreted as “when” or “upon” or “in response to determining” or “in response to detecting” or “under the circumstances of”, depending on the context. Similarly, the phrase “if it is determined” or “if [described condition or event] is detected” can be interpreted as meaning “upon determination” or “in response to determining” or “upon detection of [described condition or event]” or “in response to detecting [described condition or event]”, depending on the context.

[0041] In addition, in the description of this application and the appended claims, the terms "first," "second," "third," etc. are used only to distinguish descriptions and are not to be understood as indicating or implying relative importance. In the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0042] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of the present application include a particular feature, structure, or characteristic described in conjunction with that embodiment. Thus, phrases such as "in one embodiment," "in some embodiments," "in other embodiments," and "in other embodiments" appearing in various places in this specification do not necessarily refer to the same embodiment, but rather mean "one or more but not all embodiments," unless otherwise specifically emphasized. The terms "including," "comprising," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0043] See also Figure 1 and Figure 2 An embodiment of the present application provides a filter 100, which is connected to the inverter 200 and the motor 300 respectively. The filter 100 includes a plurality of filter inductors L f , multiple filter capacitors C f and reactor L n .

[0044] Each filter inductor L f The first ends of the filter inductors L are connected to the output terminals of the inverter 200 in a one-to-one correspondence. f The second ends of the filter capacitors C are connected to the input terminals of the motor 300 in a one-to-one correspondence; f The first end of each filter inductor L f The second ends of the filter capacitors C f The second end of the reactor L is connected in common; n The first end of each filter capacitor C f The second end of the reactor L nThe second end of the filter 100 is coupled to the DC bus of the inverter 200 for transmitting the common-mode current generated by the filter 100 to the DC bus to increase the voltage of the DC bus.

[0045] The filter 100 is a sinusoidal filter, and a plurality of filter capacitors C f It is a star connection, through the filter capacitor C f The neutral point of the reactor draws out the common mode current. n The main function is to adjust the common-mode current loop impedance and the size of the common-mode current to achieve the effect of adjusting the bus voltage.

[0046] See also Figure 1 In one embodiment, the filter inductor L f There are three filter capacitors C f There are three of them, suitable for three-phase three-wire output, used to connect to three-phase AC motor.

[0047] See also Figure 2 In one embodiment, the filter inductor L f There are two filter capacitors C f There are two of them, suitable for single-phase two-wire output, used to connect to single-phase AC motor.

[0048] See also Figure 1 and Figure 2 In a second aspect, an embodiment of the present application provides a motor drive circuit, comprising:

[0049] Inverter 200 is connected to DC power V through DC bus dc , the inverter 200 is used for DC power V dc Output drive signal;

[0050] A bus capacitor C connected between the positive and negative poles of the DC bus; and

[0051] The filter 100 in any of the above embodiments is connected to each output terminal of the inverter 200 and each input terminal of the motor 300, and is coupled to the DC bus. The filter 100 is used to filter the drive signal and output it to the motor 300, and generate a common-mode current to increase the voltage of the DC bus.

[0052] The inverter 200 may be a single-phase full-bridge inverter, see Figure 2 ; It can also be a three-phase full-bridge inverter, see Figure 1 See also Figure 2 In one embodiment, the DC voltage V dc It can be supplied directly by DC power supply. Figures 3 to 6In one of the embodiments, the motor 300 driving circuit further comprises a rectifier 400, and the inverter 200 is connected to the rectifier 400 through a DC bus, so that the DC voltage V dc The AC power output by the rectifier 400 can be rectified.

[0053] The filter 100 is coupled to the DC bus, and can be coupled to the DC bus through the neutral point connected to the AC power supply, as shown in Figure 3 、 4 The filter 100 can also be coupled to the DC bus through the connector rectifier, as shown in Figure 5 、 6 .

[0054] Please refer to Figure 3 and Figure 4 In one of the embodiments, the rectifier 400 comprises a three-phase rectifier bridge, and the filter 100 is connected to the neutral point of the three-phase power supply. The rectifier 400 is used to rectify the AC power provided by the three-phase power supply (i.e. U / V / W) to output the DC voltage V dc In this embodiment, the filter 100 is coupled to the DC bus by connecting the neutral point of the three-phase power supply.

[0055] Please refer to Figure 5 and Figure 6 In one of the embodiments, the rectifier 400 comprises a first rectifier diode D1 and a second rectifier diode D2, and the first rectifier diode D1 and the second rectifier diode D2 are connected in series between the positive and negative poles of the DC bus. The filter 100 is connected to the series node of the first rectifier diode D1 and the second rectifier diode D2 to be coupled to the DC bus.

[0056] Please refer to Figure 4 and Figure 5 In one of the embodiments, the inverter 200 comprises a three-phase inverter 200, and the filter 100 comprises a first filter inductor L1, a second filter inductor L2, a third filter inductor L3, a first filter capacitor C1, a second filter capacitor C2, a third filter capacitor C3, and a reactor L n .

[0057] The first end of the first filter inductor L1, the first end of the second filter inductor L2, and the first end of the third filter inductor L3 are connected to the three output ends of the three-phase inverter, and the second end of the first filter inductor L1, the second end of the second filter inductor L2, and the second end of the third filter inductor L3 are respectively connected to the three input ends of the motor 300 through cables; the first end of the first filter capacitor C1 is connected to the second end of the first filter inductor L1, the first end of the second filter capacitor C2 is connected to the second end of the second filter inductor L2, and the first end of the third filter capacitor C3 is connected to the second end of the third filter inductor L3, and the second end of the first filter capacitor C1, the second end of the second filter capacitor C2, and the second end of the third filter capacitor C3 are commonly connected to the reactor L n The first end of the reactor L n The second end is coupled to the DC bus.

[0058] For example, the reactor L n The second end of the three-phase power supply is connected to the neutral point of the DC bus. Figure 4 As shown; or, reactor L n The second end of the diode is connected to the series connection node of the first rectifier diode D1 and the second rectifier diode D2 to be coupled to the DC bus. Figure 5 shown.

[0059] When common mode current flows in, the rectifier bridge has two working states: dual diode power supply and single diode power supply, such as Figure 4 and Figure 5 In the switch states of 100, 010, and 001, "1" represents that the upper bridge arm of the three-phase inverter 200 is on and the lower bridge arm is off; "0" represents that the upper bridge arm of the three-phase inverter 200 is off and the lower bridge arm is on. Both power supply modes achieve the effect of raising the bus voltage due to the common-mode current flowing into the bus capacitor C. However, during the entire common-mode current cycle, the capacitor charging power of the dual-diode power supply is 0, and the charging power of the single-diode power supply is 4*i cm *V dc , as shown in Table 1 and Table 2, the positive cycle of the common-mode current is analyzed.

[0060]

[0061]

[0062] Table 1: Dual diode power supply - positive cycle common mode current charging power

[0063]

[0064] Table 2: Single diode power supply - positive cycle common mode current charging power

[0065] Based on the above analysis of the mechanism of common-mode current injection to increase bus voltage, it is necessary to ensure that the rectifier diodes of the three-phase rectifier bridge operate in single-diode power supply mode. This can be achieved through full-controlled rectification, but considering the cost and control difficulty, full-controlled rectification is not recommended. Without changing the topology, if the three-phase rectifier bridge is operated in single-diode power supply mode, it is necessary to ensure that the common-mode current is greater than or equal to the load current. The size of the common-mode current needs to be adjusted by properly setting the L in the filter 100. f 、C f and L n Parameters.

[0066] First, L f The pressure drop determines its parameters, usually

[0067]

[0068] According to L f and C f The resonant frequency is determined by C f , since the common mode current needs to be greater than the load current I load , f f The selection should be close to f sw ;

[0069]

[0070] Since the inverter 200 switches one at a time, such as 010 to 011, that is, the W-phase output potential jumps from the negative bus potential to the positive bus potential, the voltage difference of the output potential at each switching action is ±V dc At the same time, since the three-phase filter capacitors of the filter 100 have equal capacitance and are connected in a star configuration, the potential change of the neutral point is as follows:

[0071]

[0072] Finally, due to L n The voltage drop is equal to ΔV n , calculate L using the amplitude and frequency of the common mode current n ;

[0073] |ΔV n |=2πf sw L n i cm

[0074] The above mechanism cannot be used for a two-phase grid without a neutral point, but a set of full-wave rectifier circuits can be added before the bus capacitor C to introduce common-mode current, such as Figure 5The topology utilizes a full-wave rectifier circuit to define the common-mode current direction, keeps the capacitor current positive in different switching modes, and can utilize the common-mode current to increase the bus voltage under any form of power grid. n 、L f and C f The role is to change the power charged to the capacitor by adjusting the common-mode current size.

[0075] In one embodiment, in addition, the filter 100 can not only be applied to three-phase output, but also can be applied to two-phase output, as Figure 6 shown. Compared with the common boost circuit, the high-frequency switch and its control program are reduced, and the EMI current leakage and the total harmonic distortion (THD) of the output current are reduced.

[0076] The inverter 200 includes a single-phase inverter 200, and the filter 100 includes a first filter inductor L1, a second filter inductor L2, a first filter capacitor C1, a second filter capacitor C2, and a reactor L n ;

[0077] The first end of the first filter inductor L1 and the first end of the second filter inductor L2 are connected to two output ends of the inverter 200, and the second end of the first filter inductor L1 and the second end of the second filter inductor L2 are respectively connected to two input ends of the motor 300 through cables; the first end of the first filter capacitor C1 is connected to the second end of the first filter inductor L1, and the first end of the second filter capacitor C2 is connected to the second end of the second filter inductor L2, and the second end of the first filter capacitor C1 and the second end of the second filter capacitor C2 are connected to the first end of the reactor L n , and the second end of the reactor L n is coupled to the DC bus. The second end of the reactor L n is connected to the node of the series connection of the first rectifier diode D1 and the second rectifier diode D2 to be coupled to the DC bus.

[0078] According to the above filter 100 design scheme, the simulation results are as Figure 7-10 shown. In the figure, V(N029, N031) represents the motor 300 terminal voltage, V(N001, N017) represents the bus voltage, Figure 7-10 the reactor L n is respectively: 0.1mH, 0.3mH, 0.5mH, 0.7mH. The results show that reasonable selection of L n parameters can make the bus voltage rise to the target value, and the motor 300 terminal voltage rises with the bus voltage, improving the load carrying capacity of the frequency converter.

[0079] In a third aspect, an embodiment of the present application provides a frequency converter, which also includes the motor drive circuit as described above.

[0080] The filter 100, the motor drive circuit and the inverter provided in the embodiment of the present application are configured to couple the reactor L to the DC bus through the filter. n , introduces common mode current to the DC bus to increase the bus voltage, offsets the voltage drop of the filter 100 and the long cable, and improves the load capacity of the motor 300. The common mode current generated by the filter 100 is used to n The power is transmitted to the DC bus, thereby rationally utilizing the common-mode current, reducing the EMI of the inverter, reducing the output current harmonics and voltage change rate when long cables are used, and reducing the overvoltage and insulation risks of the motor 300.

[0081] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A motor drive circuit, characterized in that: include: an inverter, connected to direct current via a direct current bus, and configured to output a drive signal based on the direct current; a bus capacitor connected between the positive and negative poles of the DC bus; and a filter connected to each output terminal of the inverter and each input terminal of the motor, and coupled to the DC bus, the filter being configured to filter the drive signal and output it to the motor, and generate a common-mode current to increase the voltage of the DC bus; a rectifier, the inverter being connected to the rectifier via the DC bus, the rectifier charging the bus capacitor with power supplied by a single diode when a common-mode current flows therein; The filter comprises: a plurality of filter inductors, wherein a first end of each filter inductor is connected to each output end of the inverter in a one-to-one correspondence, and a second end of each filter inductor is connected to each input end of the motor in a one-to-one correspondence; a plurality of filter capacitors, wherein the first end of each filter capacitor is connected to the second end of each filter inductor in a one-to-one correspondence, and the second ends of each filter capacitor are connected in common; A reactor, wherein a first end of the reactor is connected to the second end of each of the filter capacitors, and a second end of the reactor is coupled to the DC bus of the inverter, and is used to transmit common-mode current to the DC bus to increase the voltage of the DC bus.

2. The motor drive circuit according to claim 1, wherein: The rectifier includes a three-phase rectifier bridge, the filter is connected to the neutral point of the three-phase power supply, and the rectifier is used to access the alternating current provided by the three-phase power supply and rectify the alternating current to output the direct current.

3. The motor drive circuit according to claim 1, wherein: The rectifier includes a first rectifier diode and a second rectifier diode, the first rectifier diode and the second rectifier diode are connected in forward series between the positive pole and the negative pole of the DC bus, and the filter is connected to the series node of the first rectifier diode and the second rectifier diode.

4. The motor drive circuit according to claim 3, wherein: The inverter includes a single-phase inverter, and the filter includes a first filter inductor, a second filter inductor, a first filter capacitor, a second filter capacitor, and a reactor; The first end of the first filter inductor and the first end of the second filter inductor are connected to the two output ends of the inverter, and the second end of the first filter inductor and the second end of the second filter inductor are connected to the two input ends of the motor through cables respectively; The first end of the first filter capacitor is connected to the second end of the first filter inductor, the first end of the second filter capacitor is connected to the second end of the second filter inductor, the second end of the first filter capacitor and the second end of the second filter capacitor are commonly connected to the first end of the inductor, and the second end of the inductor is coupled to the DC bus.

5. The motor drive circuit according to claim 2 or 3, wherein: The inverter includes a three-phase inverter, and the filter includes a first filter inductor, a second filter inductor, a third filter inductor, a first filter capacitor, a second filter capacitor, a third filter capacitor, and a reactor; The first end of the first filter inductor, the first end of the second filter inductor, and the first end of the third filter inductor are connected to the three output ends of the three-phase inverter, and the second end of the first filter inductor, the second end of the second filter inductor, and the second end of the third filter inductor are respectively connected to the three input ends of the motor through cables; The first end of the first filter capacitor is connected to the second end of the first filter inductor, the first end of the second filter capacitor is connected to the second end of the second filter inductor, the first end of the third filter capacitor is connected to the second end of the third filter inductor, the second end of the first filter capacitor, the second end of the second filter capacitor, and the second end of the third filter capacitor are commonly connected to the first end of the inductor, and the second end of the inductor is coupled to the DC bus.

6. The motor drive circuit according to claim 1, wherein: There are two filter inductors and two filter capacitors.

7. The motor drive circuit according to claim 1, wherein: There are three filter inductors and three filter capacitors.

8. A frequency converter, characterized in that: The motor drive circuit comprises the motor drive circuit according to any one of claims 1 to 7.

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