A bus voltage sampling method

Abstract

The present application discloses a bus voltage sampling method for realizing the control of an inverter; the method comprises the following steps: setting an indirect fast calculation module at the input end of a bus voltage loop, converting the collected grid voltage v g , grid side current i AC , DC bus voltage v DC And the duty cycle d a The instantaneous DC component of the DC bus voltage is calculated by the indirect fast calculation module, and the calculation result of the indirect fast calculation module is used as the feedback value of the bus voltage loop to participate in the control. The beneficial effects of the present application are as follows: an indirect fast calculation module is set up to calculate the instantaneous DC component or the sliding window average value, and the calculated result is used to replace the traditional bus voltage value or the average value of half the power frequency cycle as the feedback value of the bus voltage loop, thereby eliminating the influence of the bus voltage double frequency ripple on the control algorithm, and at the same time, the response speed can be effectively improved.

Description

Technical Field

[0001] The present application relates to the field of renewable energy power generation technology, and in particular to a bus voltage sampling method. Background Art

[0002] like Figure 1 The schematic diagram of an existing single-phase grid-connected inverter topology and control method is shown. The specific control method for the inverter topology is as follows: sampling bus voltage v DC and bus voltage setting value V DC * By comparison, the reference value I of the d-axis current is obtained through the PI controller. d * , and compare it with the d-axis current i d By comparison, the d-axis duty cycle d is obtained through the PI controller. d At the same time, the q-axis current reference value I q * =0 and q-axis current i q By comparison, the q-axis duty cycle d is obtained through the PI controller. q . d With d q After the dq / abc inverse transformation, the duty cycle information d of the corresponding switch tube of the DC / AC circuit can be obtained. a , sent to the PWM generation module to obtain the switch tube PWM signal of the DC / AC circuit, realizing the control of the grid side current i AC The control of d 、i q for i AC Transform to the dq coordinate system to obtain.

[0003] In practical applications, bus capacitors are often used to achieve power decoupling between the PV side and the grid side. The actual bus voltage is the superposition of the DC component and the double frequency ripple of the power frequency, while the d-axis current reference on the grid side is obtained by comparing the bus voltage set value with the bus voltage sampling value through the PI regulator. Therefore, if there is a double frequency ripple on the bus voltage sampling value, it will inevitably cause a double frequency ripple in the d-axis current reference value, thereby affecting the implementation of the grid side control algorithm. In practice, the common practice is to calculate the average value of the bus voltage within half a power frequency cycle as the bus voltage sampling value to eliminate the double frequency ripple, but this will bring about the problem of slow response speed. In view of this, there is an urgent need for a new bus voltage sampling method to eliminate the impact of the double frequency ripple. Summary of the invention

[0004] One of the objectives of the present application is to provide a bus voltage sampling method that can solve at least one of the defects in the above-mentioned background technology.

[0005] In order to achieve at least one of the above purposes, the technical solution adopted by the present application is: a bus voltage sampling method for realizing the control of the inverter; comprising the following steps: setting an indirect fast calculation module at the input end of the bus voltage loop, converting the collected grid voltage v g , grid side current i AC , DC bus voltage v DC And the duty cycle d a Sent to the indirect fast calculation module; the instantaneous DC component V of the DC bus voltage is calculated by the indirect fast calculation module DC The calculation result of the indirect fast calculation module is used as the feedback value of the bus voltage loop to participate in the control.

[0006] Preferably, the instantaneous DC component V DC The calculation process is as follows: The double frequency ripple power p on the grid side rip The grid side power p AC and the average power on the grid side P avg Calculated; According to the instantaneous power balance, there is a ripple power p on the DC side that is twice the frequency of the grid side rip The double frequency ripple power is equal to the value; when the bus capacitor realizes the power decoupling between the DC side and the grid side, the double frequency ripple power will be completely provided by the instantaneous power of the capacitor; then according to the instantaneous power of the capacitor and the double frequency ripple power p on the grid side rip The calculation formula for the instantaneous DC component V is derived from DC The calculation formula is: V DC =-p rip / i C ; where i C Indicates the bus capacitance current.

[0007] Preferably, the grid-side double frequency ripple power p rip And the instantaneous power p emitted by the bus capacitor C The calculation formula is as follows:

[0008] p C =-v DC ×i C =-V DC ×C DC ×[2ω×V rip cos(2ωt+θ)]-C DC ×V 2 rip ×ωsin(4ωt+2θ);

[0009] p rip =p AC -P avg =v g ×i AC -v gd ×id ;

[0010] Among them, v gd represents the d-axis component of the grid voltage, i d Represents the d-axis component of the grid-side current, V rip Indicates the bus voltage double frequency ripple amplitude, C DC represents the bus capacitance value, θ represents the phase difference between the bus capacitance voltage and the grid voltage, and ω represents the grid angular frequency.

[0011] Preferably, the busbar capacitance current i C Suitable for duty cycle d a and the grid-side current i AC Calculate and get; bus capacitance current i C The specific calculation formula is as follows:

[0012] i C =i DC_in -i DC_out ;i DC_in =P avg / v DC ;i DC_out =d a ×i AC ;

[0013] Among them, i DC_in Indicates the DC input current, i DC_out Indicates the DC side output current, P avg Indicates the average power on the grid side.

[0014] Preferably, the indirect fast calculation module includes calculation modules 1 to 3 and 5 to 8; the calculation module 1 calculates the voltage v of the power grid according to the voltage v g and the grid-side current i AC Grid side power p AC Calculation module 2 calculates the grid voltage v g and the grid-side current i AC The d-axis component v gd and i d The average power P on the grid side avg Calculation module 3 calculates the power of the grid side according to the calculated power p AC and the average power on the grid side P avg The grid side double frequency ripple power p rip Calculation module 6 according to the duty cycle d a and the grid-side current i AC The DC side output current i DC_out Calculation module 7 calculates the average power P on the grid side avg and DC bus voltage v DCThe DC input current i DC_in Calculation module 8 according to the calculated DC side input current i DC_in and the output current i DC_out Bus capacitance current i C Calculation module 5 is calculated based on the grid side double frequency ripple power p rip and busbar capacitance current i C Carry out instantaneous DC component V DC Calculation.

[0015] Compared with the prior art, the beneficial effects of this application are:

[0016] This method calculates the instantaneous DC component V of the DC bus voltage by setting an indirect fast calculation module. DC Or the sliding window average win_avg is calculated, and the calculated result is used to replace the traditional bus voltage value or the average value of half the power frequency cycle as the bus voltage loop feedback value, thereby eliminating the influence of the bus voltage double frequency ripple on the control algorithm, and at the same time can effectively improve the response speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The schematic diagram is a conventional single-phase grid-connected inverter topology and control method.

[0018] Figure 2 Schematic diagram of the waveforms of grid-side voltage, current and power of the existing inverter topology.

[0019] Figure 3 A schematic diagram of a waveform of a double frequency ripple voltage generated by an existing inverter topology.

[0020] Figure 4 A topological diagram of the indirect fast computing module in the present invention.

[0021] Figure 5 It is a structural diagram of one embodiment of the indirect fast calculation module in the present invention.

[0022] Figure 6 Schematic diagram of the topological structure of the inverter using H4 bridge in the present invention.

[0023] Figure 7 It is a structural diagram of another embodiment of the indirect fast calculation module in the present invention.

[0024] Figure 8 It is a structural schematic diagram of another embodiment of the indirect fast calculation module in the present invention connected to the bus voltage loop.

[0025] Fig. 9 It is a schematic diagram of the sliding window calculation window in the present invention. DETAILED DESCRIPTION

[0026] Below, the present application is further described in conjunction with specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0027] In the description of the present application, it should be noted that directional words, such as the terms "center", "lateral", "longitudinal", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", etc., indicating directions and positional relationships are based on the directions or positional relationships shown in the accompanying drawings, which are only for the convenience of narrating the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and cannot be understood as limiting the specific scope of protection of the present application.

[0028] It should be noted that the terms "first", "second", etc. in the description and claims of the present application are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence.

[0029] The terms "including" and "having" and any variations thereof in the specification and claims of this application are intended to cover non-exclusive inclusions. For example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0030] To facilitate the understanding of the solution, the double frequency voltage pulsation generated by the traditional single-phase grid-connected inverter topology during operation can be analyzed below.

[0031] The specific control method of the inverter has been introduced in the background technology, so it will not be repeated here. Those skilled in the art should know that since the voltage and current on the grid side are both sinusoidal waves, and the power is the product of the voltage and the current; therefore, the power frequency doubled power will be generated, which will also bring double frequency power on the DC side.

[0032] The calculation formulas for the grid side voltage and current are as follows:

[0033] v g =V g sin(ωt) (1).

[0034]

[0035] in, Indicates the phase difference between the inverter grid-connected current and the grid voltage, which represents different power factors; V g and I AC They represent the amplitude of grid voltage and output current respectively, and ω represents the grid angular frequency.

[0036] Grid side power, that is, output instantaneous power p AC The calculation formula is as follows:

[0037]

[0038] Among them, p rip Indicates the double frequency ripple power on the grid side, P avg Indicates the average power on the grid side.

[0039] It can be seen from the above formula (3) that the grid side power p AC With a constant average power P avg and a ripple power p at twice the power frequency rip Superposition. Figure 2 As shown in Figure 2, according to the instantaneous power balance, the corresponding double frequency ripple power will appear on the DC side. This will produce the following on the bus voltage: Figure 3 The ripple voltage shown is twice the industrial frequency.

[0040] Depend on Figure 1 It can be seen that the d-axis current reference on the grid side is obtained by comparing the bus voltage set value with the bus voltage sampling value through the PI regulator. Therefore, if there is a double frequency ripple on the bus voltage sampling value, it will inevitably cause a double frequency ripple on the d-axis current reference value, thereby affecting the control of the grid-side current loop. Of course, in the actual grid-side loop control, the method of finding the average bus voltage within a power frequency cycle as the bus voltage sampling value is usually used to eliminate the double frequency ripple, but this will bring about the problem of slow response speed.

[0041] In summary, the existing technology cannot achieve both elimination of the double frequency ripple and improvement of the response speed. Based on this, the purpose of this solution is to eliminate the impact of the double frequency ripple and improve the response speed as much as possible.

[0042] One of the preferred embodiments of the present application is as follows: Figure 4 As shown in FIG. 1 , a bus voltage sampling method is used to control the inverter. The method includes the following specific steps: setting an indirect fast calculation module at the input end of the bus voltage loop to collect the grid voltage v g , grid side current i AC , DC bus voltage v DC And the duty cycle d aThe instantaneous DC component V of the DC bus voltage is calculated by the indirect fast calculation module. DC Or the sliding window average win_avg, the calculation result of the indirect fast calculation module is used as the feedback value of the bus voltage loop to participate in the control.

[0043] It can be understood that the instantaneous DC component V of the DC bus voltage DC Or the sliding window average win_avg replaces the traditional bus voltage value or the average value of half a power frequency cycle as the bus voltage loop feedback value. DC is the DC amplitude, the sliding window average win_avg is a constant value, so the instantaneous DC component V DC The sliding window average win_avg does not contain double frequency ripple, and thus in the process of participating in the control, the influence of double frequency ripple on the loop control can be effectively avoided.

[0044] At the same time, an indirect fast calculation module is set at the input end of the bus voltage loop to calculate the instantaneous DC component V of the DC bus voltage. DC Or the sliding window average win_avg can effectively improve the response speed. Specifically, the traditional method uses the average value of half a power frequency cycle as the feedback value of the bus voltage loop, that is, the feedback of the average value needs to go through half a power frequency cycle to complete the calculation, which will lead to a slow control response of the bus voltage loop. In this embodiment, the instantaneous DC component V DC Feedback does not need to go through half of the power frequency cycle, which can improve the response speed of the bus voltage loop. The sliding window adopts the "one in, one out" algorithm, which can change the response data to improve the response speed of the bus voltage loop.

[0045] When performing loop control, the sampled data can be directly sent to the indirect calculation module for instantaneous DC component V DC Or the calculation of the sliding window average win_avg, while the control loop itself is also performing the corresponding voltage loop and current loop action process, the two are moving in parallel. The control loop only needs to receive the feedback value of the bus voltage loop output by the indirect fast calculation module. Compared with the traditional method, it avoids the control loop from calculating the feedback value of the bus voltage loop, thereby effectively improving the response speed of the control loop.

[0046] It should be known that for the grid voltage v g , grid side current i AC And the DC bus voltage v DC The collection can be detected by setting corresponding sensors in the topological circuit. The specific structure, working method and setting position of the sensor are well-known technologies to those skilled in the art, so they will not be elaborated here in detail.

[0047] It should also be known that the calculation methods of the feedback values ​​of different bus voltage loops are different; the corresponding structures of the indirect fast calculation modules are also different; for the convenience of understanding, the following will be explained through specific embodiments. Among them, for the instantaneous DC component V of the DC bus voltage DC The calculation method includes the following embodiment 1 and embodiment 2, and the calculation method of the sliding window average win_avg includes the following embodiment 3.

[0048] Embodiment 1:

[0049] In this embodiment, Figure 4 and Figure 5 As shown, the collected grid voltage v g and the grid-side current i AC By transforming, we can get the component v on the dq axis gd and i d ; That is v gd represents the d-axis component of the grid voltage, i d represents the d-axis component of the grid-side current. Then, by substituting the grid voltage v g , grid side current i AC , DC bus voltage v DC , the d-axis component v of the grid voltage gd and the d-axis component i of the grid-side current d Sent to the indirect fast calculation module, the required instantaneous DC component V of the DC bus voltage can be calculated DC .

[0050] It should be known that based on the grid-side current i AC and grid voltage v g Perform dq transformation to obtain the corresponding d-axis component i d and v gd The specific methods and processes are well known to those skilled in the art and will not be described in detail here.

[0051] For ease of understanding, the instantaneous DC component V DC The specific calculation process is analyzed in detail.

[0052] From the above formula (3), we can know that the grid side power p AC The average power P on the grid side avg and the grid side double frequency ripple power p rip The average power on the grid side P avg The grid voltage v g and the grid-side current i AC The product of the components on the d-axis is obtained. The specific calculation formula is as follows:

[0053] P avg = v gd ×i d (4).

[0054] Combining the above formulas (3) and (4), we can get the grid-side double frequency ripple power p rip The calculation formula is as follows:

[0055] p rip =p AC -P avg =v g ×i AC -v gd ×i d (5).

[0056] From the instantaneous power balance, we know that there will be a ripple power p on the DC side that is twice the frequency of the grid side. rip The double frequency ripple power is equal to the value of the bus capacitor. When the bus capacitor realizes the power decoupling between the DC side and the grid side, the double frequency ripple power will be completely provided by the instantaneous power of the capacitor. The bus capacitor voltage, that is, the DC side bus voltage, will be as shown in the following formula (6). Then the bus capacitor current i C It can be expressed by the following formula (7): the instantaneous power p emitted by the bus capacitor is C It can be expressed by the following formula (8).

[0057] v DC =V DC +V rip sin(2ωt+θ) (6).

[0058] i C =C DC ×dv DC / dt (7).

[0059] p C =-v DC ×i C =-v DC ×C DC ×dv DC / dt=-V DC ×C DC ×[2ω×V rip cos(2ωt+θ)]-C DC ×V 2 rip ×ωsin(4ωt+2θ)(8).

[0060] Since the double frequency ripple power in the above formula (5) and formula (8) is equal, the following formula (9) can be obtained by calculation and simplification.

[0061] V DC =-p rip / i C (9).

[0062] Among them, V rip Indicates the bus voltage double frequency ripple amplitude, dv DC / dt represents the DC bus voltage v DC The rate of change over time t, C DC represents the bus capacitance value, and θ represents the phase difference between the bus capacitance voltage and the grid voltage.

[0063] In this embodiment, Figure 5 As shown, based on the above calculation process, it can be digitized by an indirect fast calculation module. The indirect fast calculation module includes calculation modules 1 to 5, and the specific formation process of calculation modules 1 to 5 is as follows: the above formula (3) is digitized to obtain the corresponding calculation module 1; the above formula (4) is digitized to obtain the corresponding calculation module 2; the above formula (5) is digitized to obtain the corresponding calculation module 3; the above formula (7) is digitized to obtain the corresponding calculation module 4; the above formula (9) is digitized to obtain the corresponding calculation module 5.

[0064] For ease of understanding, Figure 5 As shown, the specific working process of the indirect fast calculation module at time k will be described in detail below.

[0065] The sampling signal of the grid voltage v g (k) and the grid-side current sampling signal i AC (k) is sent to the calculation module 1, and the calculation module 1 calculates the grid side power p according to the corresponding formula AC Calculation of (k).

[0066] Convert the grid voltage sampling signal to the signal v on the d-axis gd (k) and the grid-side current is converted to the signal i on the d-axis d (k) is sent to the calculation module 2, and the calculation module 2 calculates the average power P of the grid side according to the corresponding formula avg Calculation of (k).

[0067] The grid-side power p calculated by calculation module 1 and calculation module 2 are AC (k) and the average power on the grid side P avg (k) is sent to the calculation module 3, and the calculation module 3 calculates the grid side double frequency ripple power p according to the corresponding formula rip Calculation of (k).

[0068] The DC bus voltage v corresponding to the current k moment DC (k) and the DC bus voltage v corresponding to the previous moment DC (k-1) is sent to the calculation module 4; then the calculation module 4 calculates according to the formula i C (k) = C DC ×[v DC (k)-v DC (k-1)] / T s Bus capacitance current i C (k) calculation; where T s It represents the interval sampling time between adjacent moments, that is, the sampling period.

[0069] The grid-side double frequency ripple power p calculated by calculation modules 3 and 4 is rip (k) and busbar capacitance current i C (k) is sent to the calculation module 5, and the calculation module 5 calculates the instantaneous DC component V according to the corresponding formula DC Calculation of (k).

[0070] It is understandable that the value of k is any integer. For the formula corresponding to the calculation module 4, in the actual calculation process, dv DC / dt is a differential component that cannot be directly used in the calculation, so it is represented by the voltage change corresponding to one sampling period, that is, [v DC (k)-v DC (k-1)] / T s .

[0071] Embodiment 2:

[0072] In this embodiment, for the instantaneous DC component V DC The calculation formula of V is the same as that listed in Example 1 DC =-p rip / i C Same; at the same time, for the double frequency ripple power p on the grid side rip The calculation formula is the same, which is p rip =p AC -P avg =v g ×i AC -v gd ×i d The difference between this embodiment and the first embodiment is that the busbar capacitance current i C The specific calculation method is different. Specifically, Figure 6 and Figure 7 As shown, for a specific inverter topology, the bus capacitor current i C The duty cycle d a and the grid-side current i ACTo calculate it.

[0073] For ease of understanding, the busbar capacitance current i C The specific calculation process is analyzed in detail; for the convenience of analysis, this embodiment can adopt the following inverter topology: Figure 6 The H4 bridge inverter topology structure shown in the figure is used as an example for explanation; of course, in this embodiment, the bus capacitor current i C The calculation method is also applicable to other topology circuits.

[0074] From the mechanism of H4 bridge topology, we know that the DC side output current i DC_out The grid-side current i AC and duty cycle d a The specific calculation formula is as follows:

[0075] i DC_out =d a ×i AC (10).

[0076] The DC input current i DC_in It can be obtained from the average power on the AC side, that is, the average power on the grid side P avg and DC bus voltage v DC The specific calculation formula is as follows:

[0077] i DC_in =P avg / v DC (11).

[0078] According to KCL law (Kirchhoff's current law), the bus capacitance current i can be obtained C The calculation formula is as follows:

[0079] i C =i DC_in -i DC_out (12).

[0080] In order to obtain the bus capacitance current i C After that, the result of formula (12) can be substituted into formula (9) to calculate the DC component of bus voltage V DC That's it.

[0081] In this embodiment, Figure 7As shown, based on the above calculation process, it can be digitized by an indirect fast calculation module. The indirect fast calculation module includes calculation modules 1 to 3 and 5 to 8. The specific formation process of calculation modules 1 to 3 and 5 to 8 is as follows: the above formula (3) is digitized to obtain the corresponding calculation module 1; the above formula (4) is digitized to obtain the corresponding calculation module 2; the above formula (5) is digitized to obtain the corresponding calculation module 3; the above formula (9) is digitized to obtain the corresponding calculation module 5; the above formula (10) is digitized to obtain the corresponding calculation module 6; the above formula (11) is digitized to obtain the corresponding calculation formula 7; the above formula (12) is digitized to obtain the corresponding calculation module 8.

[0082] For ease of understanding, Figure 7 As shown, the specific working process of the indirect fast calculation module at time k will be described in detail below.

[0083] The sampling signal of the grid voltage v g (k) and the grid-side current sampling signal i AC (k) is sent to the calculation module 1, and the calculation module 1 calculates the grid side power p according to the corresponding formula AC Calculation of (k).

[0084] Convert the grid voltage sampling signal to the signal v on the d-axis gd (k) and the grid-side current is converted to the signal i on the d-axis d (k) is sent to the calculation module 2, and the calculation module 2 calculates the average power P of the grid side according to the corresponding formula avg Calculation of (k).

[0085] The grid-side power p calculated by calculation module 1 and calculation module 2 are AC (k) and the average power on the grid side P avg (k) is sent to the calculation module 3, and the calculation module 3 calculates the grid side double frequency ripple power p according to the corresponding formula rip Calculation of (k).

[0086] The duty cycle d of the inverter topology a (k) and the grid-side current sampling signal i AC (k) is sent to the calculation module 6, and the calculation module 6 calculates the DC side output current i according to the corresponding formula DC_out Calculation of (k).

[0087] The DC bus voltage sampling signal v DC (k) and the average power P of the grid side calculated by calculation module 2 avg(k) is sent to the calculation module 7, and the calculation module 7 calculates the DC side input current i according to the corresponding formula DC_in Calculation of (k).

[0088] The DC side output current i calculated by calculation module 6 and calculation module 7 is DC_out (k) and DC side input current i DC_in (k) is sent to the calculation module 8, and the calculation module 8 calculates the bus capacitance current i according to the corresponding formula C Calculation of (k).

[0089] The grid-side double frequency ripple power p calculated by calculation modules 3 and 8 respectively rip (k) and busbar capacitance current i C (k) is sent to the calculation module 5, and the calculation module 5 calculates the instantaneous DC component V according to the corresponding formula DC Calculation of (k).

[0090] Embodiment three:

[0091] Compared with the indirect fast calculation module in the first embodiment and the second embodiment, the instantaneous DC component V is calculated by the formula DC In this embodiment, the indirect fast calculation module calculates the sliding window average win_avg as the feedback value of the bus voltage loop through the sliding window algorithm. Specifically, take the sliding window average win_avg(k) corresponding to time k as an example; Figure 8 and Fig. 9 As shown, the DC bus voltage v corresponding to the current k moment DC (k) and the sliding window and win_sum(k-1) recorded at the previous moment and the DC bus voltage v before a window time T DC [kT] is calculated to obtain the sliding window sum win_sum(k) at time k. The sliding window sum win_sum(k) at time k is divided by the number of sampling points win_s to obtain the sliding window average win_avg(k) at time k.

[0092] For ease of understanding, the above calculation process can be expressed by the following calculation formulas (13) and (14).

[0093] win_sum(k)= win_sum(k-1)+ v DC (k)- v DC [kT] (13).

[0094] win_avg(k)= win_sum(k) / win_s (14).

[0095] It should be known that the so-called sliding window is a sliding window algorithm, which is widely used in harmonic detection of power systems; the specific working principle of the sliding window algorithm is well known to those skilled in the art, so it will not be elaborated in detail here. The number of sampling points in a sliding window is win_s, and the sliding window sum win_sum is the sum of the bus voltage sampling values ​​corresponding to the win_s sampling points in the window.

[0096] It is important to know that in the sliding window algorithm, the sampling frequency is an integer multiple of the double power frequency. The window time of the sliding window is generally smaller than the power frequency period. Specifically, the power frequency period can be taken as N times the window width, and the value of N can be any positive integer. For example, the window time of the sliding window can be taken as half of the power frequency period π / ω, that is, the value of N is 0.5. Then v DC [kT] can be obtained by v DC [k-π / (ωT s )], T s is the sampling period; then the above formula (13) can be re-expressed as:

[0097] win_sum(k)= win_sum(k-1)+ v DC (k)- v DC [k-π / (ωT s )] (15).

[0098] For ease of understanding, the following Fig. 9 The sliding window calculation window corresponding to the k moment and the k-1 moment explains the above formula (15) in detail.

[0099] At time k-1, the corresponding sliding window sum can be calculated as win_sum(k-1). To calculate the sliding window sum win_sum(k) at time k, it is necessary to add the bus voltage sampling value v at time k to the sliding window sum win_sum(k-1). DC (k), and minus the bus voltage sampling value v corresponding to time k before π / ω DC [k-π / (ωT s )], and then the above expression of formula (15) can be obtained.

[0100] In this embodiment, Figure 8As shown, based on the above calculation process, it can be digitized through an indirect fast calculation module. The indirect fast calculation module includes a storage unit 1, a storage unit 2, a calculation unit 1 and a calculation unit 2. The specific formation process of the calculation units 1 and 2 is as follows: the above formula (15) is digitized to obtain the corresponding calculation unit 1; the above formula (14) is digitized to obtain the corresponding calculation unit 2. The result of the calculation unit 1 is stored as a reference for the next calculation, and the corresponding storage unit 1 can be obtained; the bus voltage sampling value v DC [k-π / (ωT s )] for storage, the corresponding storage unit 2 can be obtained.

[0101] For ease of understanding, Figure 8 As shown, the specific working process of the indirect fast calculation module at time k will be described in detail below.

[0102] According to the DC bus voltage sampling signal v at time k DC (k), retrieve the sliding window sum win_sum(k-1) and bus voltage sampling value v recorded in storage unit 1 and storage unit 2 DC [k-π / (ωT s )].

[0103] The data retrieved from storage unit 1 and storage unit 2 and the DC bus voltage sampling signal v DC (k) is sent to calculation unit 1 together, then calculation unit 1 can calculate the sliding window and win_sum(k) according to the corresponding formula, and the calculation result can be sent to calculation unit 2 for subsequent calculation, and can also be sent to storage unit 1 for recording as a historical data reference at the next moment. After receiving the result of calculation unit 1 and the value of the sampling point number win_s, calculation unit 2 can calculate the sliding window average win_avg(k) according to the corresponding formula. Then the calculated sliding window average win_avg(k) can be input as the feedback value of the bus voltage loop to participate in the control process.

[0104] The above describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and the specification only describe the principles of the present application. The present application may have various changes and improvements without departing from the spirit and scope of the present application, and these changes and improvements fall within the scope of the present application for which protection is sought. The scope of protection claimed by the present application is defined by the attached claims and their equivalents.

Claims

1. A bus voltage sampling method for realizing control of an inverter; characterized in that: The steps include: An indirect fast calculation module is set at the input end of the bus voltage loop to collect the grid voltage v g , grid side current i AC , DC bus voltage v DC And the duty cycle d a Sent to the indirect fast calculation module; The instantaneous DC component V of the DC bus voltage is calculated by the indirect fast calculation module DC , the calculation result of the indirect fast calculation module is used as the feedback value of the bus voltage loop to participate in the control; Instantaneous DC component V DC The calculation process is as follows: Grid side double frequency ripple power p rip The grid side power p AC and the average power on the grid side P avg Calculated; According to the instantaneous power balance, there is a double frequency ripple power p on the DC side. rip The double frequency ripple power is equal in value; When the bus capacitor realizes the power decoupling between the DC side and the grid side, the double frequency ripple power will be completely provided by the instantaneous power of the capacitor; Then, according to the instantaneous power of the capacitor and the double frequency ripple power p on the grid side, rip The calculation formula for the instantaneous DC component V is derived from DC The calculation formula is: V DC =-p rip / i C ; where i C Indicates bus capacitance current; Grid side double frequency ripple power p rip And the instantaneous power p emitted by the bus capacitor C The calculation formula is as follows: p C =-v DC ×i C =-V DC ×C DC ×[2ω×V rip cos(2ωt+θ)]-C DC ×V 2 rip ×ωsin(4ωt+2θ); p rip =p AC -P avg =v g ×i AC -v gd ×i d ; Among them, v gd represents the d-axis component of the grid voltage, i d Represents the d-axis component of the grid-side current, V rip Indicates the bus voltage double frequency ripple amplitude, C DC represents the bus capacitance value, θ represents the phase difference between the bus capacitance voltage and the grid voltage, and ω represents the grid angular frequency; Bus capacitance current i C Suitable for duty cycle d a and the grid-side current i AC Calculate and get; bus capacitance current i C The specific calculation formula is as follows: i C =i DC_in -i DC_out ; i DC_in =P avg / v DC ; i DC_out =d a ×i AC ; Among them, i DC_in Indicates the DC input current, i DC_out Indicates the DC side output current, P avg Indicates the average power on the grid side.

2. The bus voltage sampling method according to claim 1, characterized in that: The indirect fast calculation module includes calculation modules 1 to 3 and 5 to 8; Calculation module 1 calculates the grid voltage v g and the grid-side current i AC Grid side power p AC Calculation of Calculation module 2 calculates the grid voltage v g and the grid-side current i AC The d-axis component v gd and i d The average power P on the grid side avg Calculation of The calculation module 3 calculates the grid side power p AC and the average power on the grid side P avg The grid side double frequency ripple power p rip Calculation of The calculation module 6 calculates the duty cycle d a and the grid-side current i AC The DC side output current i DC_out Calculation of The calculation module 7 calculates the average power P of the grid side avg and DC bus voltage v DC The DC input current i DC_in Calculation of The calculation module 8 calculates the DC side input current i DC_in and the output current i DC_out Bus capacitance current i C Calculation of The calculation module 5 calculates the grid-side double frequency ripple power p rip and busbar capacitance current i C Carry out instantaneous DC component V DC Calculation.

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