Two-stage inverter and method of reducing ripple current in two-stage inverter

Abstract

The application discloses a two-stage inverter and a method for reducing the ripple current of the two-stage inverter. The method comprises the following steps: separating the input current of a switching conversion circuit to obtain a direct current component and a ripple component; performing a first operation on the direct current component to obtain a gain base for controlling the output of the switching conversion circuit; performing a second operation on the ripple component to obtain a disturbance coefficient for representing the disturbance characteristics of the ripple component; superimposing the gain base and the disturbance coefficient, and generating a pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal. The application can effectively reduce the ripple current, improve the stability of the two-stage inverter, reduce the volume of the two-stage inverter and reduce the hardware cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inverters, in particular to a two-stage inverter and a method for reducing the current ripple of the two-stage inverter. BACKGROUND

[0002] In a two-stage inverter containing a DCDC conversion circuit (switching conversion circuit), there is a relatively large disturbance ripple in the DC bus voltage of the inverter circuit, which is transmitted to the input side of the DCDC conversion circuit, resulting in a large input current ripple of the DCDC conversion circuit, and further affecting the working state of the control system of the two-stage inverter and the efficiency of the entire control system.

[0003] The traditional method for suppressing the current ripple by hardware is to reduce the ripple of the DC bus voltage by increasing the capacitance of the input bus, which often requires the use of a large-capacity electrolytic capacitor. However, the electrolytic capacitor has a large volume, a short service life, and is prone to failure. Alternatively, a bidirectional converter can be connected in parallel to the input bus to provide the required ripple power for the inverter, thereby reducing the current ripple on the DC side. However, this not only increases the size of the machine, increases the system cost and control complexity, and reduces the reliability, but also significantly increases the hardware cost. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a two-stage inverter and a method for reducing the current ripple of the two-stage inverter.

[0005] The technical solution adopted by the present application to solve the technical problem is to construct a method for reducing the current ripple of a two-stage inverter, wherein the two-stage inverter comprises an inverter circuit and a switching conversion circuit connected to the inverter circuit, and the method comprises the following steps:

[0006] S1, separating and processing the input current of the switching conversion circuit to obtain a DC component and a ripple component;

[0007] S2, performing first operation processing on the DC component to obtain a gain base for controlling the output of the switching conversion circuit;

[0008] S3, performing second operation processing on the ripple component to obtain a disturbance coefficient for representing the disturbance characteristics of the ripple component;

[0009] S4, superimposing the gain base and the disturbance coefficient, and generating a pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal.

[0010] Preferably, in the S1, the separation processing comprises:

[0011] The ripple signal in the input current is filtered according to the filtering frequency range to obtain the DC component; the input current minus the DC component is obtained as the ripple component.

[0012] Preferably, in the S1, the separation processing further comprises: setting the filtering frequency range based on the output signal frequency of the inverter circuit.

[0013] Preferably, in the S2, the first operation processing comprises: proportionally integrating the DC component to obtain the gain base.

[0014] Preferably, in the S3, the second operation processing comprises: proportionally resonating the ripple component to obtain the disturbance coefficient.

[0015] Preferably, in the S4, the generating the pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal comprises:

[0016] Dividing the superimposed signal by the DC bus voltage to obtain a modulation signal; comparing the modulation signal with a set triangular wave to generate the pulse signal.

[0017] The application also constructs a two-stage inverter, comprising an inverter circuit, a switching conversion circuit connected with the inverter circuit, and a control circuit for generating a control signal for controlling the operation of the switching conversion circuit, the control circuit comprising:

[0018] A separation processing unit for separating the input current of the switching conversion circuit to output a DC component and a ripple component;

[0019] A first operation unit connected with the separation processing unit for performing first operation processing on the DC component to output a gain base for controlling the output of the switching conversion circuit;

[0020] A second operation unit connected with the separation processing unit for performing second operation processing on the ripple component to output a disturbance coefficient for representing the disturbance characteristics of the ripple component;

[0021] A signal generating unit connected with the first operation unit and the second operation unit for superimposing the gain base and the disturbance coefficient to obtain a superimposed signal, and generating a pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal.

[0022] Preferably, the separation processing unit comprises:

[0023] A frequency setting unit for setting a filtering frequency range based on the output signal frequency of the inverter circuit;

[0024] The separating unit is connected with the frequency setting unit, and is used for filtering out ripple signals in the input current according to the filtering frequency range to obtain the direct current component; the input current is subtracted by the direct current component, and the ripple component is output.

[0025] Preferably, the first operation unit comprises a proportional integral regulator connected with the separating processing unit, and is used for proportional integral regulating the direct current component to output the gain base.

[0026] The second operation unit comprises a proportional resonance regulator connected with the separating processing unit, and is used for proportional resonance regulating the ripple component to output the disturbance coefficient.

[0027] Preferably, the signal generating unit comprises:

[0028] The superimposing unit is connected with the first operation unit and the second operation unit, and is used for superimposing the gain base and the disturbance coefficient to output a superimposed signal.

[0029] The divider is connected with the superimposing unit, and is used for dividing the superimposed signal by the direct current bus voltage to output a modulation signal.

[0030] The comparing unit is connected with the divider, and is used for comparing the modulation signal with a set triangular wave to generate the pulse signal.

[0031] The present application has at least the following beneficial effects: providing a method for reducing ripple current of two-stage inverter; separating the input current of the switching conversion circuit to obtain a direct current component and a ripple component; then performing targeted operation processing on the direct current component and the ripple component to obtain a gain base for controlling the output of the switching conversion circuit and a disturbance coefficient for representing the disturbance characteristics of the ripple component; finally generating a pulse signal for controlling the operation of the switching conversion circuit according to a superimposed signal obtained by superimposing the gain base and the disturbance coefficient; implementing the present application can not only effectively reduce the ripple current and improve the stability of the two-stage inverter, but also is conducive to realizing zero static error control on the direct current component and the ripple component respectively, enabling the corresponding regulator to be independently set, simplifying the control system, making the corresponding parameter design simpler, and playing a positive role in reducing the size and cost of the two-stage inverter. BRIEF DESCRIPTION OF DRAWINGS

[0032] The present application will be further described below in combination with the drawings and embodiments, and the drawings are as follows:

[0033] Figure 1 is a flowchart of the method for reducing ripple current of two-stage inverter provided by the present application;

[0034] Figure 2 Figure 1 is a structural schematic diagram of a two-stage inverter provided by the present application. DETAILED DESCRIPTION

[0035] In order to have a clearer understanding of the technical features, objectives and effects of the present application, the specific embodiments of the present application will be described in detail with reference to the accompanying drawings.

[0036] It should be noted that the flowchart shown in the accompanying drawings is only illustrative, and does not necessarily include all the contents and operations / steps, nor does it necessarily execute in the order described. For example, some operations / steps can be further decomposed, and some operations / steps can be combined or partially combined, so the actual execution order can be changed according to the actual situation.

[0037] The block diagram shown in the accompanying drawings is only a functional entity, which does not necessarily correspond to a physically independent entity. That is, these functional entities can be implemented in the form of software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0038] Reference Figure 1 The present application provides a method for reducing the ripple current of a two-stage inverter, the two-stage inverter comprising an inverter circuit and a switching conversion circuit connected to the inverter circuit, the method comprising steps S1, S2, S3 and S4:

[0039] Step S1 comprises separating the input current of the switching conversion circuit to obtain a direct current component and a ripple component.

[0040] Specifically, in the two-stage inverter, the output alternating voltage of the inverter circuit after voltage conversion is expressed as: U o = U m sinωt(1), where U o is the output voltage, U m is the peak value of the output voltage, ω is the angular frequency of the output voltage, and t is the time; Since, in general, there is a certain phase angle difference (i.e. phase angle difference) between the alternating current output by the inverter circuit and the alternating voltage, the output current expression is: where I o is the output current, I m is the peak value of the output current, is the phase angle difference. According to the power formula, formula (1) and formula (2), we have: Po This represents the output power of the inverter circuit.

[0041] According to the law of conservation of energy, assuming that the input power of a two-stage inverter equals its output power, i.e., P in =P o P in Let be the input power of the switching circuit; combining with formula (3), we can further obtain:

[0042] Among them, I in U is the input current of the switching circuit (corresponding to the output current of the DC source). in This is the input voltage of the switching circuit (corresponding to the output voltage of the DC source).

[0043] Due to phase angle difference It is basically a constant value, and U is ignored. in In the case of ripple voltage, Generally, this is a constant value, which is understandable; it's the DC component. And 2ωt is a value that changes with time, i.e. It changes over time; that is, the ripple component. Furthermore, in practical applications, the relationship between the input power and output power, i.e., P, can be determined based on the conversion efficiency of the two-stage inverter. o =nP in , where n is the conversion efficiency.

[0044] It should be noted that the working principle of the two-stage inverter in this embodiment is as follows: First, the switching circuit converts the DC signal output from the DC source (energy storage device such as a battery) (including voltage conversion and constant current conversion), and supplies the converted DC signal (including DC current and DC voltage) to the input side of the inverter circuit; then, the inverter circuit inverts the DC signal on the input side. The control principle of the switching circuit is: by collecting the converted DC signal and the reference data of the feedback loop, the converted DC signal is stabilized. However, as can be seen from formula (4), the input current of the switching circuit (corresponding to the current output by the DC source) will change with the ripple component. This fluctuation will affect the output signal of the switching circuit, and the equivalent resistance of the input side of the inverter circuit will also change with the input frequency (the presence of the ripple component will affect the input frequency). Ultimately, the voltage and current of the input side of the inverter circuit will also fluctuate. This will not only increase the loss on the input side of the inverter circuit, but also increase the stress of the switching transistor in the inverter circuit, affect the inductor flux swing in the inverter circuit, and increase the core loss, but also reduce the stability of the two-stage inverter.

[0045] In some embodiments, the separating processing in step S1 comprises: filtering out the ripple signal in the input current according to a filtering frequency range to obtain a direct current component; and subtracting the direct current component from the input current to obtain the ripple component.

[0046] Specifically, as can be seen from equation (4), the input current is equal to the sum of the direct current component and the ripple component, and thus in a preferred embodiment, a notch filter can be used to filter out the ripple component according to a filtering frequency range to obtain the direct current component, and then the ripple component can be obtained by subtracting the direct current component from the input current. It should be noted that the input current refers to the current input from the direct current source to the switching conversion circuit, and the sampling can be achieved by means of shunt or voltage division, but when the separating processing is performed, the sampling signal needs to be amplified to restore the original input current. In addition, the advantage of separating the direct current component and the ripple component is that the subsequent steps can be performed on the direct current component and the ripple component for targeted processing to improve the effect of the corresponding processing, thereby reducing the adverse effects of the ripple component on the two-stage inverter.

[0047] As can be seen from equation (6), the angular frequency of the ripple component is a function of time, and the angular frequency of the ripple component is 2ω. wherein "2ω" corresponds to the angular frequency of the ripple component, and according to the relationship between the frequency and the angular frequency: f = ω / 2π, it can be known that the angular frequency is proportional to the frequency, and thus in some embodiments, the separating processing in step S1 further comprises: setting the filtering frequency range based on the output signal frequency of the inverter circuit. Further, the center point of the filtering frequency range is set to be twice the output signal frequency of the inverter circuit, for example, the filtering frequency range is set to 1.5ω to 2.5ω.

[0048] Step S2 comprises: performing first operation processing on the direct current component to obtain a gain base for controlling the output of the switching conversion circuit.

[0049] Specifically, since the switching conversion circuit outputs a direct current signal, and the direct current component therein can reflect the real-time voltage or current size of the switching conversion circuit output to a large extent, the gain base can be calculated through the direct current component, thereby providing basic reference data for calculating the pulse signal in the subsequent steps.

[0050] In some embodiments, the first operation processing in step S2 comprises: performing proportional integral adjustment on the direct current component to obtain the gain base. Specifically, first, the difference between the output given value of the switching conversion circuit (which is generally determined when the switching conversion circuit is designed) and the direct current component is calculated, and then the proportional integral adjustment is performed on the difference to achieve the non-static difference of the direct current component close to the output given value.

[0051] Step S3 comprises: performing second operation processing on the ripple component to obtain a disturbance coefficient for representing the disturbance characteristics of the ripple component.

[0052] Specifically, since the phase angle difference between the AC voltage and the AC current at the output side of the inverter is difficult to eliminate, that is, the ripple component is basically present, in order to make the output voltage of the switching conversion circuit more stable, the ripple component should also participate in the operation process of the feedback loop (generally belongs to negative feedback regulation) of the switching conversion circuit to make a corresponding response to the ripple component, so as to reduce the influence of the ripple component on the output voltage of the switching conversion circuit; if the amplitude of the ripple component is large, it may cause the output signal of the switching conversion circuit to oscillate seriously, reducing the stability of the inverter, so it is necessary to suppress the ripple component, and the second operation processing of the ripple component is to suppress the ripple component.

[0053] In some embodiments, the second operation processing in step S3 includes: proportionally resonant regulating the ripple component to obtain the disturbance coefficient.

[0054] In a preferred embodiment, the proportionally resonant regulating of the ripple component can be performed by a proportional resonant regulator to obtain the disturbance coefficient.

[0055] Step S4 includes: superimposing the gain base and the disturbance coefficient, and generating a pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal. Specifically, since the superimposed signal obtained by superimposing the gain base and the disturbance coefficient can reflect the size of the real-time DC signal output by the switching conversion circuit and has the ripple component disturbance characteristic, the pulse signal for controlling the operation of the switching conversion circuit calculated by using the superimposed signal is a signal that changes with the ripple component disturbance.

[0056] In some embodiments, the generation of the pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal in step S4 includes: dividing the superimposed signal by the DC bus voltage to obtain a modulation signal; comparing the modulation signal with a set triangular wave to generate a pulse signal. Wherein, the DC bus voltage corresponds to the input voltage of the inverter circuit.

[0057] Specifically, since the ripple in the input current of the switching conversion circuit is still transmitted to the DC bus during conversion, the DC bus voltage has secondary pulsation, and the DC bus voltage will affect the reference value input to the feedback loop to fluctuate with the change of the DC bus voltage, increasing the difficulty of the feedback loop parameter design. Taking the switching conversion circuit with constant current conversion as an example, the mathematical model of the transfer function of the current feedback loop can be simplified as G(s) = Vbus / sL; wherein Vbus is the DC bus voltage, s is the Laplace transform operator, and L is the inductance value; therefore, dividing the superimposed signal by the DC bus voltage simplifies the mathematical model to 1 / sL, that is, the influence of the secondary pulsation of the DC bus voltage can be effectively eliminated, the ripple current is further reduced, and the parameter design of the feedback loop of the switching conversion circuit does not need to consider the influence of the DC bus voltage, thereby simplifying the model design of the feedback loop. It should be noted that the DC bus voltage refers to the voltage input from the switching conversion circuit to the inverter circuit, and sampling can be achieved by shunt or voltage division. However, when performing algorithm operation, the sampling signal needs to be amplified to restore the original DC bus voltage.

[0058] In addition, the process of comparing the modulation signal with the set triangular wave includes: outputting a high level when the modulation signal is greater than the triangular wave, and outputting a low level when the modulation signal is less than the triangular wave, so as to control the duty cycle of the pulse signal. Moreover, the frequency of the pulse signal can be set by setting the frequency of the triangular wave.

[0059] In some embodiments, the method for reducing the ripple current of the two-stage inverter further comprises: step S5: repeatedly performing steps S1 to S4 to enable the switching conversion circuit to continuously and stably provide the input signal for the inverter circuit.

[0060] Reference Figure 2 The application also provides a two-stage inverter, comprising an inverter circuit 1, a switching conversion circuit 2 connected to the inverter circuit 1, and a control circuit 3 for generating a control signal to control the operation of the switching conversion circuit 2, wherein the control circuit 3 comprises a separation processing unit 31, a first operation unit 32, a second operation unit 33, and a signal generation unit 34.

[0061] The separation processing unit 31 is configured to separate the input current of the switching conversion circuit to output a DC component and a ripple component.

[0062] In some embodiments, the separation processing unit 31 comprises a frequency setting unit and a separation unit. The frequency setting unit is configured to set a filtering frequency range based on the output signal frequency of the inverter circuit 1; the separation unit is connected to the frequency setting unit and is configured to filter out the ripple signal in the input current according to the filtering frequency range to obtain the DC component; and the input current is subtracted by the DC component to output the ripple component.

[0063] In some embodiments, the separation unit comprises a notch filter.

[0064] The first operation unit 32 is connected with the separation processing unit 31, and is configured to perform a first operation on the DC component to output a gain base for controlling the gain of the switching conversion circuit 2.

[0065] In some embodiments, the first operation unit 32 comprises a proportional-integral regulator. The proportional-integral regulator is connected with the separation processing unit 31, and is configured to perform proportional-integral regulation on the DC component to output the gain base.

[0066] The second operation unit 33 is connected with the separation processing unit 31, and is configured to perform a second operation on the ripple component to output a disturbance coefficient representing the disturbance characteristics of the ripple component.

[0067] In some embodiments, the second operation unit 33 comprises a proportional-resonant regulator. The proportional-resonant regulator is connected with the separation processing unit 31, and is configured to perform proportional-resonant regulation on the ripple component to output the disturbance coefficient.

[0068] The signal generation unit 34 is connected with the first operation unit 32 and the second operation unit 33, and is configured to perform superposition processing on the gain base and the disturbance coefficient to obtain a superposition signal, and generate a pulse signal for controlling the operation of the switching conversion circuit 2 according to the superposition signal.

[0069] In some embodiments, the signal generation unit 34 comprises a superposition unit, a divider, and a comparison unit.

[0070] The superposition unit is connected with the first operation unit 32 and the second operation unit 33, and is configured to perform superposition processing on the gain base and the disturbance coefficient to output a de-superposition signal.

[0071] The divider is connected with the superposition unit, and is configured to divide the superposition signal by the DC bus voltage to output a modulation signal.

[0072] The comparison unit is connected with the divider, and is configured to perform comparison processing on the modulation signal and a set triangular wave to generate the pulse signal.

[0073] It can be understood that the present application not only effectively reduces the ripple current and improves the stability of the two-stage inverter, but also facilitates the realization of zero-static-error control on the DC component and the ripple component respectively, enables the corresponding regulators to be independently set, simplifies the control system, makes the corresponding parameter design simpler, and plays a positive role in reducing the size and cost of the two-stage inverter.

[0074] The various embodiments are described in the specification in a progressive manner, each embodiment focusing on the differences from other embodiments, and the same or similar parts between embodiments can be mutually referred to. For the device disclosed by the embodiments, since it corresponds to the method disclosed by the embodiments, the description is relatively simple, and the relevant parts can be referred to the method part.

[0075] It can be understood that the above embodiments only express the preferred implementation of the present application, which is described in a more specific and detailed manner, but it cannot be understood as a limitation on the patent scope of the present application; it should be pointed out that for ordinary skilled in the art, the above technical features can be freely combined without departing from the concept of the present application, and some modifications and improvements can be made, which are within the protection scope of the present application; therefore, any equivalent transformation and modification within the scope of the claims of the present application shall be within the scope of the claims of the present application.

Claims

1. A method of reducing a ripple current of a two-stage inverter, the two-stage inverter including an inverter circuit and a switching conversion circuit connected to the inverter circuit, characterized by, The method comprises the following steps: S1, separating the input current of the switching conversion circuit to obtain a DC component and a ripple component; S2, performing first operation processing on the DC component to obtain a gain base for controlling the output of the switching conversion circuit; S3, performing second operation processing on the ripple component to obtain a disturbance coefficient for representing the disturbance characteristics of the ripple component; S4, superimposing the gain base and the disturbance coefficient, and generating a pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal; In the S2, the first operation processing comprises: proportional integral adjustment on the DC component to obtain the gain base; In the S3, the second operation processing comprises: proportional resonant adjustment on the ripple component to obtain the disturbance coefficient; In the S4, the generation of the pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal comprises: dividing the superimposed signal by the DC bus voltage to obtain a modulation signal; comparing the modulation signal with a set triangular wave to generate the pulse signal; wherein the comparison process of the modulation signal and the set triangular wave comprises: setting the pulse signal to high level when the modulation signal is greater than the set triangular wave, and setting the pulse signal to low level when the modulation signal is less than the set triangular wave.

2. The method of claim 1, wherein the two-stage inverter ripple current reduction method is characterized by, In the S1, the separation processing comprises: filtering out the ripple signal in the input current according to a filtering frequency range to obtain the DC component; and subtracting the DC component from the input current to obtain the ripple component.

3. The method of claim 2, wherein, In the S1, the separation processing further comprises: setting the filtering frequency range based on the output signal frequency of the inverter circuit.

4. A two-stage inverter comprising an inverter circuit (1), a switching conversion circuit connected to the inverter circuit (1), and a control circuit (3) for generating a control signal for operating the switching conversion circuit, characterized in that The control circuit (3) comprises: a separation processing unit (31) for separating the input current of the switching conversion circuit to output a DC component and a ripple component; a first operation unit (32) connected with the separation processing unit (31) and configured to perform first operation processing on the DC component to output a gain base for controlling the output of the switching conversion circuit; a second operation unit (33) connected with the separation processing unit (31) and configured to perform second operation processing on the ripple component to output a disturbance coefficient for representing the disturbance characteristics of the ripple component; a signal generation unit (34) connected with the first operation unit (32) and the second operation unit (33) and configured to superimpose the gain base and the disturbance coefficient to obtain a superimposed signal, and generate a pulse signal for controlling the operation of the switching conversion circuit according to the superimposed signal; the first operation unit (32) comprises a proportional integral regulator connected with the separation processing unit (31) and configured to perform proportional integral adjustment on the DC component to output the gain base; the second operation unit (33) comprises a proportional resonant regulator connected with the separation processing unit (31) and configured to perform proportional resonant adjustment on the ripple component to output the disturbance coefficient; The signal generating unit (34) comprises: a superposition unit connected with the first operation unit (32) and the second operation unit (33), configured to perform superposition processing on the gain base and the disturbance coefficient, and output a de-superposition signal; a divider connected with the superposition unit, configured to divide the de-superposition signal by a direct current bus voltage, and output a modulation signal; a comparison unit connected with the divider, configured to perform comparison processing on the modulation signal and a set triangular wave, and generate the pulse signal; wherein the comparison processing of the modulation signal and the set triangular wave comprises: when the modulation signal is greater than the set triangular wave, setting the pulse signal to a high level; and when the modulation signal is less than the set triangular wave, setting the pulse signal to a low level.

5. The two-stage inverter of claim 4, characterized in that The separation processing unit (31) comprises: a frequency setting unit configured to set a filtering frequency range based on an output signal frequency of the inverter circuit (1); a separation unit connected with the frequency setting unit, configured to filter out a ripple signal in the input current according to the filtering frequency range, to obtain the direct current component; and subtract the direct current component from the input current, and output the ripple component.

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