Method for controlling bus ripple current in inverter system, inverter system and air conditioning system

Abstract

The invention provides a method for controlling bus ripple current in an inverter system. The method comprises the following steps: acquiring a plurality of preset output frequencies corresponding to a plurality of common-bus inverter units; when the frequency difference between the first preset output frequency corresponding to the first inversion unit and the second preset output frequency corresponding to the second inversion unit is smaller than the preset frequency difference, adjusting the first and / or second preset output frequency to limit the frequency difference to be not smaller than the preset frequency difference; acquiring a corresponding optimized frequency range based on the adjusted first and / or second preset output frequency; and performing optimization in the corresponding optimization frequency range to obtain the corresponding optimization frequency of the first and / or second inversion unit when the bus ripple current is minimum. According to the invention, the ripple current of the bus capacitor can be reduced, the usage amount of the bus capacitor is reduced, the cost of the air conditioning system is reduced, the service life of equipment is prolonged, the ripple current of the bus is not obviously increased, and the target of the optimal frequency required by system operation can be met.

Description

Technical Field

[0001] The present application relates to a method for controlling bus ripple current in an inverter system, and in particular to a method for controlling bus ripple current in an inverter system including a plurality of inverter units sharing a common bus. Background Art

[0002] In many applications, multiple inverters with the same or different power are required. Typically, these inverters are completely independent, for example, each containing an independent rectifier circuit, bus capacitor, inverter unit, control unit, etc. In one application, multiple inverter units are connected to a common bus to enable multiple inverter units to drive multiple motors. For this application, in theory, the total ripple current of the bus capacitor is roughly equal to the total current of the superposition of the ripple currents of the individual bus capacitors generated by the multiple inverter units being individually connected to the bus. It is expected that the total ripple current of the bus capacitor in this application can be reduced through appropriate control methods. Summary of the Invention

[0003] The inventors have discovered that an existing control method involves selecting bus capacitors during the design and selection process of an inverter with multiple inverter units having a common bus. However, this control method is applicable to systems with dual inverter units and is not necessarily applicable to systems with three or more inverter units. Moreover, a large amount of simulation and emulation is required during the selection stage of the bus capacitor. In addition, the values ​​(configurations) obtained by selection are fixed, and in actual applications, the combined operating conditions of multiple inverter units may exceed the data range of the simulation, resulting in inappropriate selection data and the inability to obtain a smaller bus capacitor ripple current.

[0004] To address the above-mentioned problems, the present application provides a method for controlling bus ripple current. When the output frequencies of two inverter units are relatively close, the bus ripple current generated by the two inverter units is substantially equal to the total current of the superposition of the bus capacitor ripple currents generated by the inverter units when they are individually connected to the bus. To this end, the present application reduces the bus ripple current by adjusting the output frequencies of the inverter units to limit the frequency difference to no less than the predetermined frequency difference when the frequency difference between the preset output frequencies of the two inverter units (for example, the frequency required to be output according to the unit control requirements) is less than the predetermined frequency difference. Furthermore, the present application optimizes the adjusted output frequency to obtain the optimized output frequency of the inverter unit when the bus ripple current is minimized. The present application dynamically optimizes the minimum frequency difference between the preset output frequencies of multiple inverter units sharing a common bus to reduce the bus ripple current, so that the output frequencies of the inverter units are not completely synchronized, thereby causing a dynamic partial cancellation effect of the bus ripple current, thereby achieving the purpose of reducing the bus ripple current. In addition, by setting the minimum frequency difference and monitoring the peak-to-peak value of the bus ripple voltage, the output frequency of each inverter unit is gradually and dynamically optimized, thereby achieving the goal of the optimal frequency that meets the system operation requirements without significantly increasing the bus ripple current.

[0005] Specifically, according to the first aspect of the present application, the present application provides a method for controlling bus ripple current in an inverter system. The inverter system includes multiple inverter units connected to the same bus. The method includes S1: obtaining multiple corresponding preset output frequencies of the multiple inverter units; S2: when the frequency difference between the corresponding first preset output frequency of the first inverter unit among the multiple inverter units and the corresponding second preset output frequency of the second inverter unit among the multiple inverter units is less than the predetermined frequency difference, adjusting the first preset output frequency and / or the second preset output frequency to limit the frequency difference to not less than the predetermined frequency difference; S3: obtaining the corresponding optimized frequency range based on the adjusted first preset output frequency and / or the second preset output frequency; and S4: performing optimization within the corresponding optimized frequency range to obtain the corresponding optimized frequency of the first inverter unit and / or the second inverter unit when the bus ripple current is minimized.

[0006] According to the first aspect of the present application, the optimized frequency range is within an acceptable offset frequency range so as to meet the operating requirements of the loads controlled by the first inverter unit and the second inverter unit.

[0007] According to the first aspect of the present application, in step S4, the method includes: controlling the first inverter unit and / or the second inverter unit to operate at several frequencies within the corresponding optimized frequency range, obtaining bus ripple parameters associated with the bus ripple current under various operating conditions, and obtaining the corresponding optimized frequency of the first inverter unit and / or the second inverter unit when the bus ripple current corresponding to the bus ripple parameters is minimum.

[0008] According to a first aspect of the present application, the first inverter unit is a main inverter unit, configured to control the operation of a main load. The second inverter unit is an auxiliary inverter unit, configured to control the operation of an auxiliary load. The power required for the operation of the main load is greater than the power required for the operation of the auxiliary load.

[0009] According to the first aspect of the present application, when the corresponding frequency difference between the corresponding second preset output frequency of at least one auxiliary inverter unit among the multiple inverter units and the first preset output frequency of the main inverter unit is less than the predetermined frequency difference, the method includes: S2.1: adjusting each second preset output frequency to limit the corresponding frequency difference to the predetermined frequency difference; S3.1: obtaining the corresponding optimized frequency range based on each adjusted second preset output frequency; and S4.1: optimizing by controlling the main inverter unit to operate at the first preset output frequency and each auxiliary inverter unit to operate at several frequencies within the corresponding optimized frequency range to obtain the corresponding optimized frequency of each auxiliary inverter unit when the bus ripple current is minimized.

[0010] According to the first aspect of the present application, the optimized frequency range is within a frequency range having a predetermined optimized frequency difference from the adjusted second preset output frequency, wherein the predetermined optimized frequency difference is less than or equal to the predetermined frequency difference.

[0011] According to the first aspect of the present application, when the corresponding second preset output frequencies of at least two auxiliary inverter units among the multiple inverter units are the same, the method includes: S2.2: when the frequency difference between the first preset output frequency of the main inverter unit and the same second preset output frequency of the at least two auxiliary inverter units is less than the predetermined frequency difference, adjusting the same second preset output frequency to limit the frequency difference to the predetermined frequency difference; S3.2: obtaining an optimized frequency range based on the adjusted same second preset output frequency; and S4.2: optimizing by controlling the main inverter unit to operate at the first preset output frequency and each auxiliary inverter unit to operate at several frequencies within the obtained optimized frequency range to obtain the optimized frequency of each auxiliary inverter unit when the bus ripple current is minimized, wherein each auxiliary inverter unit operates at the same frequency.

[0012] According to the first aspect of the present application, the bus ripple parameter is the peak-to-peak value of the bus ripple voltage, which is obtained by: sampling the voltage across the bus capacitor to obtain the peak-to-peak value of the bus ripple voltage; and low-pass filtering the obtained peak-to-peak value of the bus ripple voltage to obtain the filtered peak-to-peak value of the bus ripple voltage, and using the filtered peak-to-peak value of the bus ripple voltage as the bus ripple parameter.

[0013] According to the first aspect of the present application, adjusting the second preset output frequency includes: when the second preset output frequency is less than the first preset output frequency, reducing the second preset output frequency; and when the second preset output frequency is greater than the first preset output frequency, increasing the second preset output frequency.

[0014] According to the first aspect of the present application, the multiple frequencies within the optimized frequency range are increased one by one with the same frequency difference.

[0015] According to the first aspect of the present application, after step S4, the method further includes: controlling the first inverter unit and / or the second inverter unit to operate at a corresponding optimized frequency.

[0016] According to the first aspect of the present application, after step S1, the method further includes: when the frequency difference between the corresponding first preset output frequency of the first inverter unit among the multiple inverter units and the corresponding second preset output frequency of the second inverter unit among the multiple inverter units is greater than or equal to the predetermined frequency difference, controlling the first inverter unit and the second inverter unit to operate at the first preset output frequency and the second preset output frequency respectively.

[0017] According to a second aspect of the present application, an inverter system is provided, comprising a plurality of inverter units, a parameter acquisition unit, and a controller. The plurality of inverter units are connected to the same bus. The parameter acquisition unit is configured to acquire a bus ripple parameter associated with the bus ripple current. The controller is configured to receive the bus ripple parameter from the parameter acquisition unit and execute the aforementioned method to control the plurality of inverter units to operate at corresponding frequencies.

[0018] According to a second aspect of the present application, the parameter acquisition unit includes a sampling unit and a filtering unit. The sampling unit is configured to sample the voltage across the bus capacitor C to obtain a peak-to-peak value of the bus ripple voltage. The filtering unit is configured to perform a low-pass filter on the peak-to-peak value of the bus ripple voltage to obtain a filtered peak-to-peak value of the bus ripple voltage, and the filtered peak-to-peak value of the bus ripple voltage is used as the bus ripple parameter.

[0019] According to a third aspect of the present application, the present application provides an air-conditioning system, which includes the aforementioned inverter system. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The drawings are not drawn to scale. In the drawings, each identical or nearly identical component that is represented in different figures is represented by a like reference numeral. For clarity, not every component may be labeled in every figure. In the drawings:

[0021] Figure 1 A schematic structural diagram of an inverter system according to an embodiment of the present application is shown;

[0022] Figure 2A Shown Figure 1 A structural block diagram of a parameter acquisition unit and a controller according to an embodiment of the present invention is shown;

[0023] Figure 2B Shown Figure 1 A structural block diagram of a parameter acquisition unit and a controller according to another embodiment is shown;

[0024] Figure 3 A flow chart of a method for controlling bus ripple current in an inverter system according to an embodiment of the present application is shown;

[0025] Figure 4A Shown according to Figure 3 A detailed flowchart of steps 310-314 of one embodiment is shown;

[0026] Figure 4B Shown according to Figure 3 A detailed flowchart of steps 310-314 of another embodiment is shown; and

[0027] Figure 5 Shown according to Figure 1 The structural block diagram of the controller is shown in Figure 2. DETAILED DESCRIPTION

[0028] Various embodiments of the present application will be described below with reference to the accompanying drawings which constitute a part of this specification. It should be understood that, where possible, the same or similar reference numerals used in this application refer to the same components.

[0029] Figure 1 The block diagram of the inverter system 100 according to one embodiment of the present application is shown below. Figure 1 The functions of the various components of the filter system 100 and the connection and coordination relationships between the various components are introduced.

[0030] like Figure 1As shown, the inverter system 100 includes a power supply 101, a rectifier circuit 102, a bus inductor L, a bus capacitor C, a sensor 103, a plurality of inverter units 104.1, 104.2...104.N, a plurality of loads 105.1, 105.2...105.N, a parameter acquisition unit 111 and a controller 112. The present application includes at least two inverter units and at least two loads corresponding thereto. For example, the load is a motor. In one embodiment, the air-conditioning system includes the inverter system 100, a compressor, a fan, a water pump (not shown), etc. The above-mentioned loads include a motor for the compressor, a motor for the fan, a motor for the water pump, etc.

[0031] like Figure 1 As shown, the power supply 101 is an AC power supply, such as a three-phase AC power supply, and is configured to output AC power. The rectifier circuit 102 is connected to the power supply 101 and is configured to convert the AC power from the power supply 101 into DC power. For example, the rectifier circuit 102 is a three-phase rectifier bridge. The bus inductor L is connected between the rectifier circuit 102 and the bus capacitor C, and the bus capacitor C is connected between the positive pole P and the negative pole N of the bus. The bus inductor L is used to suppress inrush current, reduce harmonic interference, smooth current, protect bus capacitors, improve system stability, etc. The bus capacitor C is used to smooth DC voltage, store energy for buffering, reduce ripple, improve power factor, and suppress electromagnetic interference.

[0032] Multiple inverter units 104.1, 104.2...104.N are connected to the same bus, for example, in parallel between the positive pole P and the negative pole N of the bus. Multiple inverter units 104.1, 104.2...104.N are respectively connected to corresponding multiple loads 105.1, 105.2...105.N, and control the operation of the corresponding loads. In one embodiment, the inverter unit includes three parallel three-phase inverter bridges. The controller 112 is connected to the multiple inverter units 104.1, 104.2...104.N and is configured to control the operation of each inverter unit, thereby controlling the operation of the load. In other embodiments, the present application includes other suitable inverter systems having multiple inverter units with a common bus.

[0033] The controller 112 is configured to process the preset output frequencies of the plurality of inverter units to obtain a corresponding optimized frequency for each inverter unit when the bus ripple current flowing through the bus capacitor C is minimized, and control each inverter unit to operate at the corresponding optimized frequency. In one embodiment, the preset output frequency is the frequency required to be output by each inverter unit according to the unit control requirements. In one embodiment, the controller 112 is configured to, when the frequency difference between a first preset output frequency corresponding to a first inverter unit among the plurality of inverter units and a second preset output frequency corresponding to a second inverter unit among the plurality of inverter units is less than a predetermined frequency difference C, adjust the first preset output frequency and / or the second preset output frequency to limit the frequency difference between the first preset output frequency and the second preset output frequency to no less than the predetermined frequency difference C, obtain a corresponding optimized frequency range based on the adjusted first preset output frequency and / or second preset output frequency, and perform optimization within the corresponding optimized frequency range to obtain the corresponding optimized frequency for the first inverter unit and / or the second inverter unit when the bus ripple current is minimized. When seeking optimization, the controller 112 controls the first inverter unit and / or the second inverter unit to operate at several frequencies within the corresponding optimized frequency range, obtains bus ripple parameters associated with the bus ripple current under various operating conditions, and obtains the corresponding optimized frequency of the first inverter unit and / or the second inverter unit when the bus ripple current corresponding to the bus ripple parameters is minimum.

[0034] The parameter acquisition unit 111 is configured to acquire bus ripple parameters associated with the bus ripple current when the inverter system operates under various operating conditions. The magnitude of the corresponding bus ripple current can be determined based on the bus ripple parameters. In one embodiment, the bus ripple parameter is a stable peak-to-peak value of the bus ripple voltage. The sensor 103 is a voltage sensor connected in parallel with the bus capacitor C and configured to detect the voltage Vdc across the bus capacitor C. For example, the sensor 103 converts the high-voltage DC signal across the bus capacitor C into a low-voltage signal Vdc detectable by a controller (e.g., an MCU). The parameter acquisition unit 111 is connected to the voltage sensor 103 and configured to acquire a stable peak-to-peak value of the bus ripple voltage based on the voltage Vdc across the bus capacitor C received from the sensor 103. When the peak-to-peak value of the bus ripple voltage is small, the bus ripple current is also small. When the peak-to-peak value of the bus ripple voltage is determined to be minimum when the inverter system operates under various operating conditions, the bus ripple current is determined to be minimum. In other embodiments, the present application includes other suitable sensors and parameter acquisition units to implement the above functions.

[0035] Figure 2A Shown Figure 1 The structural block diagram of the parameter acquisition unit 111 and the controller 112 of an embodiment shown in FIG. Figure 2B Shown Figure 1FIG. 1 is a structural block diagram of a parameter acquisition unit 111 and a controller 112 according to another embodiment.

[0036] like Figures 2A-2B As shown, the parameter acquisition unit 111 includes a sampling unit 201 and a filtering unit 202. The sampling unit 201 is connected to the sensor 103 (see Figure 1 ) and is configured to sample the voltage Vdc across the bus capacitor received from sensor 103 to obtain the bus ripple voltage peak-to-peak value Vdcp-p. The bus ripple voltage peak-to-peak value Vdcp-p is the difference between the maximum and minimum values ​​of the sampled bus ripple voltage. Filtering unit 202 is connected to sampling unit 201 via connecting line 207 and is configured to perform low-pass filtering on the bus ripple voltage peak-to-peak value Vdcp-p received from sampling unit 201 to obtain a filtered bus ripple voltage peak-to-peak value LVdcp-p. The ripple voltage is smoothed using a low-pass filtering method to obtain a stable bus ripple voltage peak-to-peak value as a bus ripple parameter related to the bus ripple current. The bus ripple current increases with the increase of the bus ripple voltage peak-to-peak value LVdcp-p and decreases with the decrease of the bus ripple voltage peak-to-peak value LVdcp-p. In one embodiment, the transfer function H(s) of filtering unit 202 is as follows: H(s) = 1 / (Ts+1), where s is a Laplace variable and T is a time constant.

[0037] Controller 112 includes a frequency acquisition module 203, a frequency limiting module 204, and a frequency optimization module 205. Frequency acquisition module 203 receives control input via connection line 209 to acquire a plurality of preset output frequencies corresponding to the plurality of inverter units. For example, frequency acquisition module 203 acquires the corresponding frequencies required to be output by the plurality of inverter units, i.e., the corresponding plurality of preset output frequencies, based on the unit control requirements.

[0038] Figure 2A The figure shows a frequency limiting module 204 and a frequency optimization module 205 according to an embodiment. The frequency limiting module 204 is connected to the frequency acquisition module 203 and is configured to, upon determining that the frequency difference between the first preset output frequency f1 and the second preset output frequency f2 corresponding to two inverter units, e.g., the first and second inverter units, among the plurality of inverter units is less than a predetermined frequency difference C, adjust the second preset output frequency to limit the frequency difference to no less than the predetermined frequency difference C. The frequency optimization module 205 is connected to the frequency limiting module 204 and is configured to obtain a corresponding optimized frequency range based on the adjusted second preset output frequency and perform optimization within the corresponding optimized frequency range to obtain the corresponding optimized frequency of the second inverter unit when the bus ripple current is minimized.

[0039] In one embodiment, when the frequency limiting module 204 determines that the first preset output frequency f1 is greater than the second preset output frequency f2 and the frequency difference therebetween is less than a predetermined frequency difference C, the frequency limiting module 204 adjusts the second preset output frequency f2 to lf2, where lf2 = f1 - C. In another embodiment, when the frequency limiting module 204 determines that the first preset output frequency f1 is less than the second preset output frequency f2 and the frequency difference therebetween is less than a predetermined frequency difference C, the frequency limiting module 204 adjusts the second preset output frequency f2 to lf2, where lf2 = f1 + C. The frequency optimization module 205 obtains an optimized frequency range near the adjusted second preset output frequency lf2, for example, setting the optimized frequency range to the frequency interval [lf2 - C1, lf2 + C1], where the predetermined optimized frequency difference C1 is less than or equal to the predetermined frequency difference C. The frequency optimization module 205 further optimizes within the obtained optimized frequency range [lf2 - C1, lf2 + C1] to obtain the corresponding optimized frequency Slf2 of the second inverter unit when the bus ripple current is minimized. For example, the frequency optimization module 205 controls the first inverter unit to operate at a first preset output frequency f1 and the second inverter unit to operate at several frequencies within the optimized frequency range [lf2-C1, lf2+C1] (for example, several frequencies starting from frequency lf2-C1 and stepping toward frequency lf2+C1 with the same frequency difference), and the parameter acquisition unit 111 obtains the stable bus ripple voltage peak-to-peak value LVdcp-p under various operating conditions. The frequency optimization module 205 obtains the corresponding optimized frequency Slf2 of the second inverter unit when each bus ripple voltage peak-to-peak value LVdcp-p is minimum (that is, the bus ripple current is minimum) based on the peak-to-peak value LVdcp-p of each bus ripple voltage. In other embodiments, the corresponding optimized frequency of the first inverter unit can be obtained in a similar manner to the above while maintaining the second preset output frequency of the second inverter unit. The present application can also implement the above functions in other suitable ways.

[0040] Controller 112 outputs a frequency control signal to the first inverter unit via connection line 210 to control the first inverter unit to operate at a first preset output frequency, and outputs a frequency control signal to the second inverter unit via connection line 211 to control the second inverter unit to operate at an optimized frequency Slf2. In one embodiment, the first inverter unit is a main inverter unit, such as a motor for a compressor in an air conditioning system, and the second inverter unit is an auxiliary inverter unit, such as a motor for a fan or a water pump in the air conditioning system.

[0041] Figure 2BFIG2 shows a frequency limiting module 204 and a frequency optimization module 205 of another embodiment. The frequency limiting module 204 is configured to adjust the preset output frequencies fi, fj to limit the above frequency differences to no less than the predetermined frequency difference C when it is determined that the frequency difference between the corresponding preset output frequencies fi, fj of two inverter units, such as the i-th inverter unit and the j-th inverter unit (such as the auxiliary inverter unit) among the plurality of inverter units and the first preset output frequency f1 of the first inverter unit (such as the main inverter unit) is less than the predetermined frequency difference C. In one embodiment, for adjusting the preset output frequencies fi, fj and obtaining the corresponding optimized frequency range, the frequency limiting module 204 implements the same Figure 2A The same operation as that performed on the second preset output frequency f2 in is performed. For example, the preset output frequency fi is adjusted to lfi and its optimized frequency range is set to the frequency interval [lfi-C1, lfi+C1], and the preset output frequency fj is adjusted to lfj and its optimized frequency range is set to the frequency interval [lfj-C1, lfj+C1]. The frequency optimization module 205 controls the first inverter unit to operate at the first preset output frequency f1, the i-th inverter unit to operate at several frequencies within the optimized frequency range [lfi-C1, lfi+C1], and the j-th inverter unit to operate at several frequencies within the optimized frequency range [lfj-C1, lfj+C1]. The parameter acquisition unit 111 obtains the stable peak-to-peak value of the bus ripple voltage LVdcp-p under various operating conditions. The frequency optimization module 205 obtains the corresponding optimized frequency Slfi of the i-th inverter unit and the corresponding optimized frequency Slfj of the j-th inverter unit when the peak-to-peak value of each bus ripple voltage LVdcp-p is minimum (i.e., the bus ripple current is minimum) based on the peak-to-peak value of each bus ripple voltage LVdcp-p. In other embodiments, the preset output frequency of one of the inverter units can be maintained in a similar manner to obtain the corresponding optimized frequencies of the other two inverter units. The present application can also implement the above functions in other appropriate ways.

[0042] The controller 112 outputs a frequency control signal to the first inverter unit through the connection line 210 to control the first inverter unit to operate at a first preset output frequency, outputs a frequency control signal to the i-th inverter unit through the connection line 212 to control the i-th inverter unit to operate at the optimized frequency Slfi, and outputs a frequency control signal to the j-th inverter unit through the connection line 213 to control the j-th inverter unit to operate at the optimized frequency Slfj.

[0043] When the frequency differences between the preset output frequencies of the three inverter units are all less than the predetermined frequency difference, the inverter is switched on for any two of them. Figure 2A The operation of the three inverter units can be extended to more than three inverter units.

[0044] Figure 3 A flow chart of a method 300 for controlling bus ripple current in an inverter system according to an embodiment of the present application is shown.

[0045] like Figure 3 As shown, at step 302, the method 300 for controlling bus ripple current in an inverter system begins, and then proceeds from step 302 to step 304. At step 304, a plurality of preset output frequencies corresponding to the plurality of inverter units are obtained, and then proceeds from step 304 to step 306. For example, the required output frequencies of the plurality of inverter units are obtained based on the unit control requirements of the air conditioning system. At step 306, a determination is made as to whether the frequency difference between the first preset output frequency corresponding to a first inverter unit among the plurality of inverter units and the second preset output frequency corresponding to a second inverter unit among the plurality of inverter units is less than a predetermined frequency difference C. If the frequency difference is not less than the predetermined frequency difference C, the process proceeds from step 306 to step 308. At step 308, the controller controls the first inverter unit and the second inverter unit to operate at the first preset output frequency and the second preset output frequency, respectively. If the frequency difference is less than the predetermined frequency difference C, the process proceeds from step 306 to step 310.

[0046] At step 310, the first preset output frequency and / or the second preset output frequency are adjusted to limit the frequency difference between the first preset output frequency and the second preset output frequency to no less than a predetermined frequency difference C, and then the process proceeds from step 310 to step 312. At step 312, a corresponding optimized frequency range is obtained based on the adjusted first preset output frequency and / or the second preset output frequency, and then the process proceeds from step 312 to step 314. In one embodiment, the obtained optimized frequency range is within an acceptable offset frequency range so as to meet the operating requirements of the loads controlled by the first inverter unit and the second inverter unit. The corresponding optimized frequency of each inverter unit is within the corresponding acceptable offset frequency range, so that the operation of each inverter unit can meet the operating requirements of the load while ensuring the minimum bus ripple current. For the preset output frequency of each inverter unit, it has a corresponding acceptable offset frequency range, so that each inverter unit can meet the operating requirements of the controlled load when operating at a frequency within the corresponding acceptable offset frequency range.

[0047] At step 314, an optimization is performed within the corresponding optimized frequency range to obtain the corresponding optimized frequency of the first inverter unit and / or the second inverter unit when the bus ripple current is minimized, and then the process proceeds from step 314 to step 316. In one embodiment, the first inverter unit and / or the second inverter unit are controlled to operate at several frequencies within the corresponding optimized frequency range (i.e., to form various operating conditions), and bus ripple parameters associated with the bus ripple current are obtained under each operating condition. The corresponding optimized frequency of the first inverter unit and / or the second inverter unit when the bus ripple current is minimized corresponding to the bus ripple parameters is obtained. In one embodiment, the several frequencies within the optimized frequency range are increased one by one with the same frequency difference. In one embodiment, the bus ripple parameter is the peak-to-peak value of the bus ripple voltage. For example, the bus ripple voltage peak-to-peak value Vdcp-p is obtained by sampling the voltage Vdc across the bus capacitor, and the bus ripple voltage peak-to-peak value Vdcp-p is low-pass filtered to obtain the filtered bus ripple voltage peak-to-peak value LVdcp-p, and the filtered bus ripple voltage peak-to-peak value is used as the bus ripple parameter.

[0048] At step 316, the first inverter unit and / or the second inverter unit are controlled to operate at the corresponding optimized frequency, and then the process proceeds from step 316 to step 318. At step 318, it is determined whether the inverter system needs to be shut down. If the inverter system does not need to be shut down, the process proceeds from step 318 to step 304, repeating the above process to dynamically control the operation of multiple inverter units. If the inverter system needs to be shut down, the process proceeds from step 318 to step 320. At step 320, the method 300 for controlling bus ripple current in the inverter system ends.

[0049] In one embodiment, the first inverter unit is a main inverter unit, which is used to control the operation of the main load. The second inverter unit is an auxiliary inverter unit, which is used to control the operation of the auxiliary load. The power required for the operation of the main load is greater than the power required for the operation of the auxiliary load. For example, the power required for the operation of the main load is several times the power required for the operation of the auxiliary load. The power required for the operation of the main load is greater than the total power required for the operation of each auxiliary load. For example, the main inverter unit controls the operation of the motor of the compressor in the air-conditioning system, and multiple auxiliary inverter units respectively control the operation of the motor of the fan, the motor of the water pump, etc. in the air-conditioning system. In one embodiment, when the frequency difference between the preset output frequencies of the two inverter units is less than the predetermined frequency difference C, the preset output frequency of the main inverter unit is maintained and the preset output frequency of the auxiliary inverter unit is optimized to obtain the optimized frequency.

[0050] For any two inverter units among the multiple inverter units, when the frequency difference between their corresponding preset output frequencies is less than the predetermined frequency difference C, the above steps 310-316 are performed. Two inverter units among the multiple inverter units are referred to as a group of inverter units. When the frequency difference of at least two groups of inverter units is less than the predetermined frequency difference C, the above steps 310-316 are performed for each group of inverter units. In particular, at step 314, a combined optimization is performed within each optimized frequency range of the at least two groups of inverter units to obtain the corresponding optimized frequencies of the at least two groups of inverter units when the bus ripple current is minimized. For example, for each of the at least two groups of inverter units, each inverter unit is controlled to operate at several frequencies within the corresponding optimized frequency range to form various operating conditions of the combination, and the corresponding optimized frequencies of each inverter unit when the bus ripple current is minimized are obtained under each operating condition of these combinations.

[0051] Figure 4A Shown according to Figure 3 A detailed flow chart of steps 310-314 of one embodiment is shown.

[0052] like Figure 4A As shown, in the case where the frequency difference between the corresponding second preset output frequency of at least one auxiliary inverter unit and the first preset output frequency of the main inverter unit among the multiple inverter units is less than the predetermined frequency difference C, Figure 3 Step 306 proceeds to step 402. At step 402, each second preset output frequency is adjusted to limit the corresponding frequency difference to a predetermined frequency difference C, and then the process proceeds to step 404. In one embodiment, when the second preset output frequency f2 is less than the first preset output frequency f1, the second preset output frequency is reduced, for example, to an adjusted second preset output frequency lf2, where lf2 = f1 - C; when the second preset output frequency is greater than the first preset output frequency, the second preset output frequency is increased, for example, to an adjusted second preset output frequency lf2, where lf2 = f1 + C, thereby limiting the frequency difference between the two to the predetermined frequency difference C.

[0053] At step 404, a corresponding optimized frequency range is obtained based on each adjusted second preset output frequency, and then the process proceeds from step 404 to step 406. In one embodiment, the optimized frequency range is within a frequency range having a predetermined optimized frequency difference C1 from the adjusted second preset output frequency, where the predetermined optimized frequency difference C1 is less than or equal to the predetermined frequency difference C. For example, the optimized frequency range for the second preset output frequency is [lf2-C1, lf2+C1]. In other embodiments, other suitable optimized frequency ranges are used.

[0054] At step 406, the optimization is performed by controlling the main inverter unit to operate at the first preset output frequency and each auxiliary inverter unit to operate at several frequencies within the corresponding optimized frequency range (i.e., operating under various combined operating conditions) to obtain the corresponding optimized frequency of each auxiliary inverter unit when the bus ripple current is minimized, and then the process goes to step 406. Figure 3 In step 316 of the optimization frequency range [lf2-C1, lf2+C1], the plurality of frequencies are frequencies that increase with the same frequency difference starting from the minimum frequency lf2-C1, or frequencies that decrease with the same frequency difference starting from the maximum frequency lf2+C1. In other embodiments, the plurality of frequencies within the optimization frequency range are obtained by other suitable means.

[0055] Figure 4B Shown according to Figure 3 FIG. 1 is a detailed flowchart of steps 310 - 314 of another embodiment shown.

[0056] like Figure 4B As shown, in the case where the corresponding second preset output frequencies of at least two auxiliary inverter units in the plurality of inverter units are the same, Figure 3 Step 306 proceeds to step 412. At step 412, when the frequency difference between the first preset output frequency of the main inverter unit and the same second preset output frequency of the at least two auxiliary inverter units is less than a predetermined frequency difference C, the same second preset output frequency is adjusted to limit the frequency difference to the predetermined frequency difference C, and then the process proceeds to step 414. At step 414, an optimized frequency range is obtained based on the adjusted same second preset output frequency, and then the process proceeds to step 416.

[0057] At step 416, the optimization is performed by controlling the main inverter unit to operate at the first preset output frequency and each auxiliary inverter unit to operate at several frequencies within the obtained optimal frequency range (i.e., operating under various combined operating conditions) to obtain the optimal frequency of each auxiliary inverter unit when the bus ripple current is minimized, wherein each auxiliary inverter unit operates at the same frequency, and then the process goes to step 416. Figure 3 Step 316 in . Figure 4B Can be seen as Figure 4A A specific implementation manner in which the corresponding second preset output frequency of the auxiliary inverter unit is the same.

[0058] exist Figures 4A-4B In the embodiment, the preset output frequency of the main inverter unit is referred to as the first preset output frequency, and the preset output frequency of the auxiliary inverter unit is referred to as the second preset output frequency. In other embodiments, other suitable definitions of the preset output frequency may be used.

[0059] Figure 5 Shown according to Figure 1 The structural block diagram of the controller 112 is shown in FIG. Figure 5 As shown, the controller 112 includes a processor 502, a memory 503, an input interface 504, an output interface 505 and a bus 501. The processor 502, the memory 503, the input interface 504 and the output interface 505 are connected to the bus 501. The processor 502 can read a program (or instruction) from the memory 503 and execute the program (or instruction) to perform the processing of data. The processor 502 can also write data or a program (or instruction) into the memory 503. The memory 503 can store programs (instructions) or data. By executing the instructions in the memory 503, the processor 502 can control the memory 503, the input interface 504 and the output interface 505.

[0060] The input interface 504 is configured to receive the stable bus ripple voltage peak-to-peak value LVdcp-p from the parameter acquisition unit 111 through the connection line 208 and receive control input through the connection line 209, such as the frequency control input of each inverter unit according to the unit control requirement.

[0061] The input interface 504 is further configured to convert the received data into data recognizable by the processor 502 and output the data to the processor 502. The processor 502 is configured to process (e.g., calculate) the received data to generate frequency control signals for each inverter unit. In one embodiment, the processor 502 is configured to control and process based on the received frequency control inputs of each inverter unit (e.g., each preset output frequency) and the stable bus ripple voltage peak-to-peak value LVdcp-p, for example, to perform Figure 3 Steps 306-316 and Figures 4A-4B The steps in are used to generate frequency control signals for each inverter unit.

[0062] The output interface 505 is configured to receive a frequency control signal from the processor 502, convert the signal into a signal suitable for each inverter unit, and output the signal to each inverter unit, thereby controlling the operation of each inverter unit. For example, the first frequency control signal is sent to the first inverter circuit via the connection line 210, the i-th frequency control signal is sent to the i-th inverter circuit via the connection line 212, and the j-th frequency control signal is sent to the j-th inverter circuit via the connection line 213.

[0063] The method for controlling bus ripple current in an inverter system having multiple inverter units with a common bus, the inverter system, and the air-conditioning system of the present application have the following advantages:

[0064] First, by dynamically optimizing the minimum frequency difference of multiple inverter units, the output frequencies of each inverter unit are not completely synchronized, so that the bus ripple current has a dynamic partial offset effect, thereby achieving the purpose of reducing the bus ripple current;

[0065] Second, by optimizing the control algorithm, the bus capacitor ripple current is effectively reduced compared to non-common bus solutions, reducing reliance on large-capacity capacitors at the source. This ultimately reduces the amount of bus capacitors used, increases their lifespan, reduces the cost of the entire air conditioning system, and increases equipment lifespan.

[0066] Third, by setting a minimum frequency difference and monitoring the peak-to-peak bus ripple voltage, the output frequency of each inverter unit is dynamically optimized. This minimizes the increase in bus ripple current while maintaining the optimal frequency required for system operation. This adaptive frequency adjustment strategy intelligently implements the frequency regulation process, ensuring the same air conditioning system control requirements and reliability as traditional solutions at a lower system cost.

[0067] Although the present application has been described in conjunction with the examples of the embodiments outlined above, it is likely that various alternatives, modifications, variations, improvements and / or substantial equivalents, whether known or currently or soon foreseeable, will be apparent to those skilled in the art. In addition, the technical effects and / or technical problems described in this specification are exemplary and not restrictive; so the disclosures in this specification may be used to solve other technical problems and have other technical effects and / or may solve other technical problems. Therefore, the examples of the embodiments of the present application as stated above are intended to be illustrative and not restrictive. Various changes may be made without departing from the spirit or scope of the present application. Therefore, the present application is intended to include all known or earlier developed alternatives, modifications, variations, improvements and / or substantial equivalents.

Claims

1. A method for controlling bus ripple current in an inverter system, wherein the inverter system includes a plurality of inverter units connected to the same bus, characterized in that: The method comprises: S1: Obtaining multiple preset output frequencies corresponding to multiple inverter units; S2: when a frequency difference between a first preset output frequency corresponding to a first inverter unit among the plurality of inverter units and a second preset output frequency corresponding to a second inverter unit among the plurality of inverter units is less than a predetermined frequency difference C, adjusting the first preset output frequency and / or the second preset output frequency to limit the frequency difference to be no less than the predetermined frequency difference C; S3: acquiring a corresponding optimized frequency range based on the adjusted first preset output frequency and / or the second preset output frequency; and S4: Optimizing within the corresponding optimized frequency range to obtain the corresponding optimized frequency of the first inverter unit and / or the second inverter unit when the bus ripple current is minimized.

2. The method for controlling bus ripple current in an inverter system according to claim 1, characterized in that: The optimized frequency range is within an acceptable offset frequency range so as to meet the operating requirements of the loads controlled by the first inverter unit and the second inverter unit.

3. The method for controlling bus ripple current in an inverter system according to claim 1, characterized in that: In step S4, the method includes: The first inverter unit and / or the second inverter unit are controlled to operate at several frequencies within a corresponding optimized frequency range, bus ripple parameters associated with the bus ripple current are obtained under various operating conditions, and corresponding optimized frequencies of the first inverter unit and / or the second inverter unit are obtained when the bus ripple current corresponding to the bus ripple parameters is minimum.

4. The method for controlling bus ripple current in an inverter system according to claim 3, wherein: The first inverter unit is a main inverter unit, configured to control the operation of a main load; and The second inverter unit is an auxiliary inverter unit, which is used to control the operation of the auxiliary load. The power required for the main load to operate is greater than the power required for the auxiliary load to operate.

5. The method for controlling bus ripple current in an inverter system according to claim 4, characterized in that: When a corresponding frequency difference between a second preset output frequency of at least one auxiliary inverter unit among the plurality of inverter units and the first preset output frequency of the main inverter unit is less than a predetermined frequency difference C, the method includes: S2.1: Adjust each second preset output frequency to limit the corresponding frequency difference to a predetermined frequency difference C; S3.1: Obtaining a corresponding optimized frequency range based on each adjusted second preset output frequency; and S4.1: Optimizing is performed by controlling the main inverter unit to operate at the first preset output frequency and each auxiliary inverter unit to operate at several frequencies within the corresponding optimized frequency range to obtain the corresponding optimized frequency of each auxiliary inverter unit when the bus ripple current is minimized.

6. The method for controlling bus ripple current in an inverter system according to claim 5, characterized in that: The optimized frequency range is within a frequency range having a predetermined optimized frequency difference C1 from the adjusted second preset output frequency, wherein the predetermined optimized frequency difference C1 is less than or equal to the predetermined frequency difference C.

7. The method for controlling bus ripple current in an inverter system according to claim 4, characterized in that: When the corresponding second preset output frequencies of at least two auxiliary inverter units among the plurality of inverter units are the same, the method includes: S2.2: When a frequency difference between a first preset output frequency of the main inverter unit and the same second preset output frequency of the at least two auxiliary inverter units is less than a predetermined frequency difference C, adjusting the same second preset output frequency to limit the frequency difference to the predetermined frequency difference C; S3.2: Obtaining an optimized frequency range based on the adjusted same second preset output frequency; and S4.2: Optimization is performed by controlling the main inverter unit to operate at the first preset output frequency and each auxiliary inverter unit to operate at several frequencies within the obtained optimized frequency range to obtain the optimized frequency of each auxiliary inverter unit when the bus ripple current is minimized, wherein each auxiliary inverter unit operates at the same frequency.

8. The method for controlling bus ripple current in an inverter system according to claim 3, characterized in that: The bus ripple parameter is the peak-to-peak value of the bus ripple voltage, which is obtained by: Sampling the voltage Vdc across the bus capacitor to obtain a peak-to-peak value of the bus ripple voltage Vdcp-p; and The obtained bus ripple voltage peak-to-peak value Vdcp-p is low-pass filtered to obtain a filtered bus ripple voltage peak-to-peak value LVdcp-p, and the filtered bus ripple voltage peak-to-peak value is used as the bus ripple parameter.

9. The method for controlling bus ripple current in an inverter system according to claim 5, characterized in that: Adjusting the second preset output frequency includes: When the second preset output frequency is lower than the first preset output frequency, reducing the second preset output frequency; and When the second preset output frequency is greater than the first preset output frequency, the second preset output frequency is increased.

10. The method for controlling bus ripple current in an inverter system according to claim 3, characterized in that: The multiple frequencies within the optimized frequency range are increased one by one with the same frequency difference.

11. The method for controlling bus ripple current in an inverter system according to claim 1, characterized in that: After step S4, the method further includes: The first inverter unit and / or the second inverter unit are controlled to operate at a corresponding optimized frequency.

12. The method for controlling bus ripple current in an inverter system according to claim 11, characterized in that: After step S1, the method further includes: When the frequency difference between the corresponding first preset output frequency of the first inverter unit among the multiple inverter units and the corresponding second preset output frequency of the second inverter unit among the multiple inverter units is greater than or equal to the predetermined frequency difference C, the first inverter unit and the second inverter unit are controlled to operate at the first preset output frequency and the second preset output frequency, respectively.

13. An inverter system (100), characterized in that: include: A plurality of inverter units (104.1, 104.2 ... 104.N), wherein the plurality of inverter units are connected to the same bus; a parameter acquisition unit (111), the parameter acquisition unit (111) being configured to acquire a bus ripple parameter associated with the bus ripple current; and A controller (112) is configured to receive the bus ripple parameter from the parameter acquisition unit and execute the method according to any one of claims 1 to 12 to control the plurality of inverter units (104.1, 104.2 ... 104.N) to operate at corresponding frequencies.

14. The inverter system according to claim 13, characterized in that: The parameter acquisition unit (111) comprises: A sampling unit (201), the sampling unit (201) is configured to sample the voltage across the bus capacitor C to obtain a peak-to-peak value of the bus ripple voltage; A filtering unit (202) is configured to perform low-pass filtering on the peak-to-peak value of the bus ripple voltage to obtain a filtered peak-to-peak value of the bus ripple voltage, and the filtered peak-to-peak value of the bus ripple voltage is used as the bus ripple parameter.

15. An air conditioning system, characterized in that: The invention comprises the inverter system (100) according to any one of claims 13 to 14.

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