A bus voltage control method of a grid-connected inverter

Abstract

The application discloses a BUS voltage control method of a grid-connected inverter, and the method comprises the following steps: if the difference between the input voltages of two boost circuits is less than a fifth threshold value, and if it is determined that the difference between the input voltages of the two boost circuits is less than a sixth threshold value and the reference voltages of the two boost circuits are both greater than the standard BUS voltage, then BoostOffEnable_Cnt is incremented by one; when BoostOffEnable_Cnt is greater than a seventh threshold value, the driving of the two boost circuits is set to 0, uwDualBoostOffEnable is equal to 1, BoostOffEnable_Cnt is equal to 0, and the average value of the input voltages of the two boost circuits is taken as a variable; the counting is performed again, BoostOffEnable_Cnt is incremented by one, and when BoostOffEnable_Cnt is greater than or equal to an eighth threshold value and the difference between the reference voltages of the two boost circuits and the variable is greater than a ninth threshold value, the driving of the two boost circuits is set to 1, uwDualBoostOffEnable is equal to 1, and BoostOffEnable_Cnt is equal to 0. When the input condition is high voltage, the driving of the boost circuit can be changed, so that the MPPT efficiency and the anti-interference capability in the high-voltage state are improved.

Description

Technical Field

[0001] This invention belongs to the field of grid-connected inverter control, and relates to a BUS voltage control method for grid-connected inverters, especially a BUS voltage control method under high voltage input conditions. Background Technology

[0002] In the photovoltaic system field, the BUS voltage mainly operates under three conditions: low voltage, medium voltage, and high voltage. Under normal circumstances, the BUS voltage stabilizes near the standard BUS voltage, exhibiting a certain steady-state characteristic. However, in some remote areas where the mains voltage is relatively high or the input-side panel is over-matched, the BUS voltage can significantly exceed the standard BUS voltage, especially during periods of relatively strong afternoon sunlight. Operating under these conditions increases the ripple current on the inductor, potentially leading to high-voltage overcurrent or BUS overvoltage risks. It also reduces the dynamic efficiency of the MPPT and lowers interference immunity. Therefore, logic processing under high-voltage BUS conditions is essential. Summary of the Invention

[0003] To address the aforementioned technical problems, the present invention aims to provide a BUS voltage control method for grid-connected inverters, which allows the boost circuit drive to be variable when the input condition is high voltage, thereby improving MPPT efficiency and anti-interference capability under high voltage conditions.

[0004] A method for controlling the BUS voltage of a grid-connected inverter includes the following steps:

[0005] Obtain the average BUS voltage, standard BUS voltage, input voltage of the two boost circuits, and reference voltage of the two boost circuits;

[0006] Determine whether the average value of the BUS voltage is greater than the first threshold. If the result is yes, then the drive of both boost circuits is 0; if the result is no, then execute the following steps.

[0007] A0. Determine whether the difference between the input voltages of the two boost circuits is less than the second threshold. If the result is yes, set the drive of the first boost circuit to 1 and execute the following step A1; if the result is no, execute the following step B0.

[0008] A1. Determine whether the reference voltage of the second boost circuit is less than the third threshold. If the result is yes, then set the drive of the second boost circuit to 1. Determine whether the reference voltage of the second boost circuit is greater than the fourth threshold. If the result is yes, then set the drive of the second boost circuit to 0. The third threshold and the fourth threshold are set according to the standard BUS voltage.

[0009] B0. Determine whether the difference between the input voltages of the two boost circuits is less than the fifth threshold. If the result is yes, then proceed to step B1 below; if the result is no, then proceed to step C0 below.

[0010] B1. Determine whether the difference between the input voltages of the two boost circuits is less than the sixth threshold and whether the reference voltages of the two boost circuits are both greater than the standard BUS voltage. If the result is yes, then BoostOffEnable_Cnt++, where BoostOffEnable represents the time period for switching the boost circuit on and off; when BoostOffEnable_Cnt is greater than the seventh threshold, set the drive of the two boost circuits to 0, uwDualBoostOffEnable=1, BoostOffEnable_Cnt=0, and use the average value of the input voltages of the two boost circuits as a variable, where uwDualBoostOffEnable represents the enable flag bit for the two boost circuits to not operate; count again, BoostOffEnable_Cnt++; when BoostOffEnable_Cnt is greater than or equal to the eighth threshold and the difference between the reference voltages of the two boost circuits and the variable is greater than the ninth threshold, set the drive of the two boost circuits to 1, uwDualBoostOffEnable=1, BoostOffEnable_Cnt=0;

[0011] C0. Determine whether the difference between the input voltages of the two boost circuits is greater than the tenth threshold. If the result is yes, set the drive of the second boost circuit to 1 and execute the following step C1.

[0012] C1. Determine whether the reference voltage of the first boost circuit is less than the eleventh threshold. If the result is yes, then set the drive of the first boost circuit to 1. Determine whether the reference voltage of the first boost circuit is greater than the twelfth threshold. If the result is yes, then set the drive of the first boost circuit to 0. The eleventh threshold and the twelfth threshold are set according to the standard BUS voltage.

[0013] According to a preferred aspect of the present invention, the BUS voltage control method further includes the following steps prior to step A0: determining whether the average value of the BUS voltage is less than a thirteenth threshold; if the result is yes, then step A0 is executed.

[0014] More preferably, the thirteenth threshold is less than the first threshold.

[0015] Furthermore, the first threshold is 495V, and the thirteenth threshold is 480V.

[0016] According to a preferred aspect of the invention, the second threshold is -20V, and the fifth threshold and the tenth threshold are both 20V; and / or, the fifth threshold and the tenth threshold are equal.

[0017] According to a preferred aspect of the invention, the third threshold is less than the fourth threshold, the third threshold is less than the BUS voltage standard value, and the fourth threshold is greater than the BUS voltage standard value; and / or, the third threshold = the BUS voltage standard value - 2V, and the fourth threshold = the BUS voltage standard value + 5V.

[0018] According to a preferred aspect of the invention, the sixth threshold is 10V and the ninth threshold is 10V.

[0019] According to a preferred aspect of the invention, the seventh threshold is 300 and the eighth threshold is 3000.

[0020] According to a preferred aspect of the invention, the eleventh threshold is equal to the third threshold, and the twelfth threshold is equal to the fourth threshold; and / or, the eleventh threshold is less than the twelfth threshold, the eleventh threshold is less than the BUS voltage standard value, and the twelfth threshold is greater than the BUS voltage standard value; and / or, the eleventh threshold = the BUS voltage standard value - 2V, and the twelfth threshold = the BUS voltage standard value + 5V.

[0021] According to a preferred aspect of the invention, the average BUS voltage is calculated from the BUS voltage over a set time period; and / or, the standard BUS voltage is obtained based on the mains voltage; and / or, the reference voltage of the boost circuit is determined by tracking changes through MPPT.

[0022] The present invention adopts the above solution, which has the following advantages compared with the prior art:

[0023] The BUS voltage control method of the grid-connected inverter of the present invention determines the on or off of the two boost drives by the magnitude of the BUS voltage under high voltage conditions. Especially in the case of high and low voltage matching, it can ensure that the low voltage path is forced to start boost under high BUS voltage by the voltage difference between the two input voltages, so that the low voltage path works near the maximum power of the MPPT point, thereby improving MPPT efficiency and increasing anti-interference capability. Attached Figure Description

[0024] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a flowchart of a BUS voltage control method according to an embodiment of the present invention.

[0026] Figure 2 The waveform diagrams are shown when both boost circuits have high voltage inputs.

[0027] Figure 3 The waveform is the overall waveform when both boost circuits have low-voltage inputs.

[0028] Figure 4 for Figure 3 A partial unfolded diagram.

[0029] Figure 5 The waveform is the overall waveform when one boost circuit has a high voltage input and the other has a low voltage input.

[0030] Figure 6 for Figure 5 A partial unfolded diagram. Detailed Implementation

[0031] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art. It should be noted that the description of these embodiments is for the purpose of aiding understanding the present invention, but does not constitute a limitation thereof. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0032] Typically, under high-voltage conditions, grid-connected inverters determine the on / off state of the two boost drives based on the magnitude of the BUS voltage. Especially in high-low configurations, the low-voltage boost drive may not operate, leading to decreased MPPT efficiency. In this embodiment, the method compares the two input voltages and determines the on / off state of the two boost drives based on the magnitude of the BUS voltage. Particularly in high-low configurations, by using the voltage difference between the two input voltages, it ensures that under high BUS voltage, the low-voltage boost drive is forced to operate, keeping it near the maximum power of the MPPT point, thereby improving MPPT efficiency and increasing interference immunity.

[0033] Reference Figure 1As shown, the BUS voltage control method of this grid-connected inverter mainly uses: the average BUS voltage, which is calculated from the BUS voltage over 20ms using uwBus_Volt_Ave; and the difference between the input voltages of the two boost circuits, which is obtained by subtracting the average input voltages of the two boost circuits over 20ms, i.e., wDelataPvVoltAver = uwPv1_Volt_Ave – uwPv2_Volt_Ave, uwPv1 _Volt_Ave and uwPv2_Volt_Ave are the average 20ms input voltages of the first and second boost circuits, respectively; the BUS standard voltage uwBus_Volt_Std is obtained from the mains voltage, i.e., uwBus_Volt_Std = 1.414 * mains voltage + 30V; the reference voltages fCtrl_Pv1_VoltRef and fCtrl_Pv2_VoltRef of the two boost circuits are given by tracking changes through MPPT. The driving mode of the two boost circuits is mainly determined by the difference wDelataPvVoltAve between their input voltages. fMppInfo_Vmpp is also introduced, which is equal to the average of the two input voltages, i.e., fMppInfo_Vmpp = (uwPv1_Volt_Ave + uwPv2_Volt_Ave) * 0.5.

[0034] The specific detection logic is as follows:

[0035] 1. If the voltage uwBus_Volt_Ave is greater than 495V, the boost driver for Pv1 and Pv2 is 0, that is, no driver is enabled. Then strPv1_BoostCtrl.uwBoostCtrlEnable (this enable flag represents the first boost driver flag, 0 means the first channel is not boosted, 1 means the first channel is boosted) = 0, and strPv2_BoostCtrl.uwBoostCtrlEnable (this enable flag represents the second boost driver flag, 0 means the second channel is not boosted, 1 means the second channel is boosted) = 0;

[0036] 2. If the voltage uwBus_Volt_Ave is less than 485V, the drive of the two boost circuits is determined by wDelataPvVoltAver. 485V is taken into account the existence of BUS voltage ripple of about 10 volts, to ensure that the low-voltage circuit can quickly start boost drive when high and low voltage are matched.

[0037] Specifically as follows:

[0038] 1) If wDelataPvVoltAver is less than -20V, strPv1_BoostCtrl.uwBoostCtrlEnable = 1, that is, enable the first boost driver.

[0039] 2) If fCtrl_Pv2_VoltRef is less than uwBus_Volt_Std-2V, strPv2_BoostCtrl.uwBoostCtrlEnable = 1, i.e., enable the second boost driver. This ensures the boost on / off logic for the low-voltage path. The voltage reference for the low-voltage path depends on the standard bus voltage, and no additional judgment conditions are needed.

[0040] 3) If fCtrl_Pv2_VoltRef is greater than uwBus_Volt_Std+5V, strPv2_BoostCtrl.uwBoostCtrlEnable = 0.

[0041] 3. If wDelataPvVoltAver is less than 20V, the two input voltages are relatively close. If wDelataPvVoltAver is less than 10V and both fCtrl_Pv1_VoltRef and fCtrl_Pv2_VoltRef are greater than uwBus_Volt_Std, BoostOffEnable_Cnt++.

[0042] When BoostOffEnable_Cnt>300, strPv1_BoostCtrl.uwBoostCtrlEnable=0, strPv2_BoostCtrl.uwBoostCtrlEnable =0; uwDualBoostOffEnable=1; BoostOffEnable_Cnt=0; fMppInfo_Vmpp=(uwPv1_Volt_Ave+uwPv2_Volt_Ave)*0.5.

[0043] The BoostOffEnable_Cnt++ counter is used again. When BoostOffEnable_Cnt>=3000 and uwPv1_Volt_Ave-fMppInfo_Vmpp>10V and uwPv2_Volt_Ave-fMppInfo_Vmpp>10V, strPv1_BoostCtrl.uwBoostCtrlEnable=1, strPv2_BoostCtrl.uwBoostCtrlEnable=1; uwDualBoostOffEnable=0; BoostOffEnable_Cnt=0; thus realizing the switching logic of the two input boosts under the high voltage of the BUS.

[0044] 4. If wDelataPvVoltAver is greater than or equal to 20V, strPv2_BoostCtrl.uwBoostCtrlEnable = 1, meaning the second boost driver is enabled. If fCtrl_Pv1_VoltRef is less than (uwBus_Volt_Std - 2V), strPv1_BoostCtrl.uwBoostCtrlEnable = 1. If fCtrl_Pv1_VoltRef is greater than (uwBus_Volt_Std + 5V), strPv1_BoostCtrl.uwBoostCtrlEnable = 0.

[0045] The test results of the grid-connected inverter using the present invention are as follows:

[0046] 1. Both boost circuits have high voltage inputs, so neither boost circuit operates, and the drive is 0. The waveform is shown below. Figure 2 As shown, waveform 1 on the lower side is the output current waveform, and lines 2 and 3 on the upper side represent the two drive signals.

[0047] 2. Both boost circuits have low-voltage inputs, both boost circuits are active, and the drive is 1. The overall waveform is shown in Figure 3, and the partial expansion is shown below. Figure 4 The waveform 1 on the lower side is the output current waveform, and the lines 2 and 3 on the upper side represent the two drive signals.

[0048] 3. The input consists of both high and low voltage. The low voltage boost is activated, while the high voltage boost is not activated. The overall waveform is shown in Figure 5, and the partial waveform is shown in Figure 6. Figure 6 The waveform on the bottom is 1, which is the output current waveform; 2 represents the low-voltage input waveform; and 3 represents the high-voltage input waveform.

[0049] The above embodiments are merely illustrative of the technical concept and features of the present invention, and are preferred embodiments. Their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and they should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made according to the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A BUS voltage control method for a grid-connected inverter, characterized in that, Includes the following steps: The average BUS voltage, standard BUS voltage, input voltages of two boost circuits, and reference voltages of two boost circuits are obtained, wherein the reference voltages of the boost circuits are determined by MPPT tracking changes. Determine whether the average value of the BUS voltage is greater than a first threshold, which is 495V. If the result is yes, then the drive of both boost circuits is 0. If the result is negative, proceed with the following steps; A0. Determine whether the difference between the input voltages of the two boost circuits is less than the second threshold, which is -20V. If the result is yes, set the drive of the first boost circuit to 1 and execute the following step A1; if the result is no, execute the following step B0. A1. Determine whether the reference voltage of the second boost circuit is less than the third threshold. If the result is yes, then set the drive of the second boost circuit to 1. Determine whether the reference voltage of the second boost circuit is greater than the fourth threshold. If the result is yes, then set the drive of the second boost circuit to 0. The third threshold is less than the fourth threshold, and the third threshold and the fourth threshold are set according to the standard BUS voltage. The third threshold is less than the standard BUS voltage, and the fourth threshold is greater than the standard BUS voltage. B0. Determine whether the difference between the input voltages of the two boost circuits is less than the fifth threshold, which is 20V. If the result is yes, then proceed to step B1 below; if the result is no, then proceed to step C0 below. B1. Determine whether the difference between the input voltages of the two boost circuits is less than the sixth threshold and whether the reference voltages of the two boost circuits are both greater than the standard BUS voltage. The sixth threshold is 10V. If the result is yes, then BoostOffEnable_Cnt++, where BoostOffEnable represents the time period for switching the boost circuit on and off. When BoostOffEnable_Cnt is greater than the seventh threshold, set the drive of the two boost circuits to 0, uwDualBoostOffEnable=1, BoostOffEnable_Cnt=0, and set the drive of the two boost circuits to 0. The average value of the input voltage is used as a variable, where uwDualBoostOffEnable represents the enable flag for the two boost circuits to not operate; counting again, BoostOffEnable_Cnt++, when BoostOffEnable_Cnt is greater than or equal to the eighth threshold and the difference between the reference voltage of the two boost circuits and the variable is greater than the ninth threshold, the drive of the two boost circuits is set to 1, uwDualBoostOffEnable=0, BoostOffEnable_Cnt=0; the seventh threshold is 300, the eighth threshold is 3000, and the ninth threshold is 10V; C0. Determine whether the difference between the input voltages of the two boost circuits is greater than the tenth threshold, which is 20V. If the result is yes, then set the drive of the second boost circuit to 1 and execute the following step C1. C1. Determine whether the reference voltage of the first boost circuit is less than the eleventh threshold. If the result is yes, then set the drive of the first boost circuit to 1. Determine whether the reference voltage of the first boost circuit is greater than the twelfth threshold. If the result is yes, then set the drive of the first boost circuit to 0. The eleventh threshold and the twelfth threshold are set according to the standard BUS voltage. The eleventh threshold is less than the standard BUS voltage value, the twelfth threshold is greater than the standard BUS voltage value, the eleventh threshold is equal to the third threshold, and the twelfth threshold is equal to the fourth threshold.

2. The BUS voltage control method according to claim 1, characterized in that, The BUS voltage control method further includes the following steps before step A0: determining whether the average value of the BUS voltage is less than the thirteenth threshold; if the result is yes, then step A0 is executed.

3. The BUS voltage control method according to claim 2, characterized in that, The thirteenth threshold is less than the first threshold.

4. The BUS voltage control method according to claim 3, characterized in that, The thirteenth threshold is 480V.

5. The BUS voltage control method according to claim 1 or 2, characterized in that, The third threshold is equal to the standard value of the BUS voltage - 2V, and the fourth threshold is equal to the standard value of the BUS voltage + 5V.

6. The BUS voltage control method according to claim 1 or 2, characterized in that, The eleventh threshold is equal to the standard BUS voltage value minus 2V, and the twelfth threshold is equal to the standard BUS voltage value plus 5V.

7. The BUS voltage control method according to claim 1, characterized in that, The average BUS voltage is calculated from the BUS voltage within a set time period; and / or, the standard BUS voltage is obtained based on the mains voltage.

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