Common-mode voltage adjustment method, device and control system

Abstract

The application discloses a common-mode voltage adjusting method, device and control system, and relates to the technical field of electronics. A controller can generate an injection instruction of a first common-mode voltage according to a first modulation mode; generate an injection instruction of a second common-mode voltage according to a second modulation mode; and during a time period for switching the modulation mode, the controller can generate an injection instruction of a third common-mode voltage according to the injection instruction of the first common-mode voltage and the injection instruction of the second common-mode voltage; the injection instruction of the third common-mode voltage can be used to control a voltage inverter circuit to output the third common-mode voltage; at any time during the time period for switching the modulation mode, the third common-mode voltage is between the first common-mode voltage and the second common-mode voltage; the third common-mode voltage is switched from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage is switched from the second common-mode voltage to the first common-mode voltage. The method can reduce damage to devices of the voltage inverter circuit when the modulation mode is switched, and further prolong the service life of the devices.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a common-mode voltage regulation method, device and control system. Background Technology

[0002] Three-phase three-level inverters have advantages such as multiple output levels, low voltage stress, low ripple current, and good harmonic characteristics, and are therefore widely used in the field of power electronics. Typically, injecting a three-phase common-mode voltage into the pulse-width modulation waveform can improve the DC voltage utilization of the three-phase three-level inverter, reduce switching losses, and optimize harmonic characteristics.

[0003] Common-mode voltage injection control methods for three-phase three-level inverters include continuous pulse width modulation (CPWM) and discontinuous pulse width modulation (DPWM). However, when using CPWM, the ripple current flowing through the bus capacitor of the three-phase three-level inverter is relatively small, which leads to an increase in the power of the switching devices of the three-phase three-level inverter and affects efficiency. When using DPWM, the switching power of the switching devices of the three-phase three-level inverter is smaller, but the ripple current flowing through the bus capacitor is relatively larger.

[0004] Related technologies also propose that when the leakage current and modulation of a three-phase three-level inverter meet preset conditions, CPWM can be converted to DPWM or DPWM can be converted to CPWM. However, although this method can reduce ripple current and losses of switching devices, it does not take into account the current operating conditions of the three-phase three-level inverter when switching modulation modes, and directly switches the lifespan of easily damaged devices. Summary of the Invention

[0005] This application provides a common-mode voltage adjustment method, apparatus, and control system to reduce device losses and extend device lifespan.

[0006] Firstly, embodiments of this application provide a common-mode voltage adjustment method, which can be applied to a controller. The controller generates control commands for a voltage inverter circuit. This voltage inverter circuit converts AC voltage into DC voltage. The voltage inverter circuit can be implemented using an inverter or other circuits, such as switching circuits or filtering circuits. This application does not specifically limit the implementation form of the voltage inverter circuit. When executing the common-mode voltage adjustment method of this application, the controller can perform the following:

[0007] A first common-mode voltage injection command is generated according to a first modulation method; the first common-mode voltage injection command is used to control the voltage inverter circuit to output the first common-mode voltage; the controller generates a second common-mode voltage injection command according to a second modulation method; the second common-mode voltage injection command is used to control the voltage inverter circuit to output the second common-mode voltage; during the modulation method switching time period, the controller generates a third common-mode voltage injection command according to the first and second common-mode voltage injection commands; the third common-mode voltage injection command is used to control the voltage inverter circuit to output the third common-mode voltage; at any time during the modulation method switching time period, the third common-mode voltage is between the first and second common-mode voltages; the third common-mode voltage changes from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage changes from the second common-mode voltage to the first common-mode voltage; wherein, the first modulation method is continuous modulation; the second modulation method is discontinuous modulation.

[0008] In this application, the controller generates different common-mode voltage injection commands based on different modulation methods. When switching modulation methods, the controller references the different common-mode voltage injection commands (first common-mode voltage injection command and second common-mode voltage injection command) to obtain the injection command for the third common-mode voltage within the modulation method switching time period. Under the action of the third common-mode voltage injection command, the third common-mode voltage output by the voltage inverter circuit gradually changes from the first common-mode voltage to the second common-mode voltage, or vice versa. This method can reduce damage to the components of the voltage inverter circuit during modulation method switching and further extend the service life of the components.

[0009] In one possible implementation, the controller may acquire a pre-stored mode factor; the mode factor is used to indicate the weight value of the injection command for the second common-mode voltage; and the injection command for the third common-mode voltage is generated by weighting the injection command for the first common-mode voltage, the injection command for the second common-mode voltage, and the mode factor.

[0010] It should be noted that, in order to reduce device losses when adjusting the pulse width of the common-mode voltage, this application introduces a mode factor. During the modulation mode switching period of the voltage inverter circuit, the mode factor is used as a weighting value to calculate the injection command for the third common-mode voltage. This method comprehensively considers the influence of the injection commands for the common-mode voltage corresponding to each modulation mode on the common-mode voltage during the switching period. The pulse width of the common-mode voltage of the voltage inverter circuit can be adjusted by the slow change of the injection value of the common-mode voltage (the injection command and the injection value of the common-mode voltage correspond one-to-one). This method avoids instantaneous switching between modulation modes and reduces device losses. Furthermore, with reduced device losses, the device lifespan can be further extended.

[0011] In one possible implementation, the pattern factor may increase exponentially over time, or the pattern factor may decrease exponentially over time, or the pattern factor may decrease stepwise over time and the pattern factor may increase stepwise over time.

[0012] It should be noted that by changing the mode factor over time in the manner described above, the common-mode voltage can be guaranteed to change slowly rather than abruptly during the modulation switching period. This method can reduce the degree of damage to the device.

[0013] In one possible implementation, the weight value of the injection command for the first common-mode voltage is summed with the mode factor to equal 1.

[0014] During the modulation mode switching period, when switching between the first and second modulation modes, the weight value of the injection command for the second common-mode voltage is indicated by the mode factor. It is clear that the weight value of the injection command for the first common-mode voltage is 1 minus the value of the mode factor. This method ensures that the third common-mode voltage changes continuously and slowly during the modulation mode switching period.

[0015] In one possible implementation, if the mode factor is 1, the third common-mode voltage is the same as the second common-mode voltage; if the mode factor is 0, the third common-mode voltage is the same as the first common-mode voltage.

[0016] In one possible implementation, the first modulation method is CPWM and the second modulation method is DPWM.

[0017] It should be noted that when CPWM modulation is used, the ripple current flowing through the bus capacitor of the voltage inverter circuit is relatively small, and when DPWM modulation is used, the losses of the switching devices in the voltage inverter circuit are relatively small. This application considers the common-mode voltage injection commands of both modulation methods during the modulation mode switching period, ensuring that the ripple current of the bus capacitor is small while minimizing losses to the switching devices during modulation mode switching. Secondly, embodiments of this application provide a common-mode voltage adjustment device, including: a controller and a voltage inverter circuit;

[0018] The controller can be used to generate an injection command for a first common-mode voltage according to a first modulation scheme; the injection command for the first common-mode voltage is used to control the voltage inverter circuit to output the first common-mode voltage; and to generate an injection command for a second common-mode voltage according to a second modulation scheme; the injection command for the second common-mode voltage is used to control the voltage inverter circuit to output the second common-mode voltage; during the modulation scheme switching time period, the controller generates an injection command for a third common-mode voltage according to the injection commands for the first and second common-mode voltages; the injection command for the third common-mode voltage is used to control the voltage inverter circuit to output the third common-mode voltage; at any time during the modulation scheme switching time period, the third common-mode voltage is between the first and second common-mode voltages; the third common-mode voltage changes from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage changes from the second common-mode voltage to the first common-mode voltage.

[0019] The voltage inverter circuit can be used to receive a third common-mode voltage injection command and output a third common-mode voltage; wherein, the first modulation method is continuous modulation; and the second modulation method is discontinuous modulation.

[0020] In one possible implementation, the controller is specifically configured to: acquire a pre-stored mode factor; the mode factor is used to indicate the weight value of the injection command for the second common-mode voltage; and generate an injection command for the third common-mode voltage by weighting the injection command for the first common-mode voltage, the injection command for the second common-mode voltage, and the mode factor.

[0021] In one possible implementation, the pattern factor increases exponentially over time, or decreases exponentially over time, or decreases stepwise over time, or increases stepwise over time.

[0022] In one possible implementation, the weight value of the injection command for the first common-mode voltage is summed with the mode factor to equal 1.

[0023] In one possible implementation, if the mode factor is 1, the third common-mode voltage is the same as the second common-mode voltage; if the mode factor is 0, the third common-mode voltage is the same as the first common-mode voltage.

[0024] In one possible implementation, the first modulation method is CPWM and the second modulation method is DPWM.

[0025] Thirdly, embodiments of this application provide a control system, including: a power command generation unit, a data acquisition unit, and a common-mode voltage adjustment device as described in the second aspect; the controller of the common-mode voltage adjustment device is connected to the power command generation unit and the data acquisition unit respectively; the data acquisition unit is also connected to the voltage inverter circuit of the common-mode voltage adjustment device; the data acquisition unit is used to acquire the voltage at the output port of the voltage inverter circuit and the bus voltage of the voltage inverter circuit; the power command generation unit is used to generate an output power command and an output current command of the voltage inverter circuit according to the scheduling command issued by the host computer; the controller determines the control command according to the output power command, the output current command, the bus voltage of the voltage inverter circuit, and the voltage at the output port of the voltage inverter circuit.

[0026] The technical effects of the corresponding solutions in the second and third aspects described above can be referred to the technical effects achievable by the corresponding solutions in the first aspect, and the repetitions will not be detailed here. These or other aspects of this application will become more apparent in the following description of the embodiments. Attached Figure Description

[0027] Figure 1 A schematic diagram of a three-phase three-level inverter is shown.

[0028] Figure 2 A schematic diagram of the structure of the control system provided in an embodiment of this application is shown;

[0029] Figure 3 A schematic flowchart of the common-mode voltage adjustment method provided in an embodiment of this application is shown;

[0030] Figure 4 A schematic diagram illustrating the functional relationship of the mode factors provided in an embodiment of this application is shown;

[0031] Figure 5 A schematic diagram illustrating the functional relationship of the mode factors provided in an embodiment of this application is shown;

[0032] Figure 6A A schematic flowchart of the common-mode voltage adjustment method provided in an embodiment of this application is shown;

[0033] Figure 6B A schematic diagram illustrating the common-mode voltage variation trend provided in the embodiments of this application is shown;

[0034] Figure 7 A schematic diagram of the common-mode voltage adjustment device provided in an embodiment of this application is shown. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in detail below with reference to the accompanying drawings.

[0036] It should be noted that the voltage inverter circuit mentioned in this application can convert AC voltage into DC voltage. This voltage inverter circuit can be implemented through an inverter or other circuits, such as switching circuits and filtering circuits. This application does not specifically limit the implementation form of the voltage inverter circuit. Here, only a three-phase three-level inverter is used as an example for illustration. Figure 1 The three-phase three-level inverter shown includes a positive DC bus, a negative DC bus, a neutral line, a positive bus capacitor, a negative bus capacitor, a three-phase DC-AC inverter circuit, a three-phase filter, and three-phase AC output terminals. Wherein, C1 is the positive bus capacitor, and C2 is the negative bus capacitor. Figure 1 Q1-Q18 are switching devices in a three-phase three-level inverter. These switching devices form a three-phase DC-AC inverter circuit. Inductor group L1, capacitor group C0, and inductor group L2 form a three-phase filter. The positive terminal of the three-phase DC-AC inverter circuit is connected to the positive terminal of the positive bus capacitor C1, serving as the positive DC bus. The negative terminal of the three-phase DC-AC inverter circuit is connected to the negative terminal of the negative bus capacitor C2, serving as the negative DC bus. The neutral terminal of the three-phase DC-AC inverter circuit is connected to the negative terminal of the positive bus capacitor C1 and the positive terminal of the negative bus capacitor C2, serving as the neutral line. The three-phase output terminals of the three-phase DC-AC inverter circuit are each connected to one end of the three-phase filter. The other end of the three-phase filter is connected to the three-phase AC output terminal, serving as the output port of the three-phase three-level voltage inverter circuit, which is connected to a three-phase transformer or directly to the three-phase AC power grid via cables.

[0037] It should be noted that the DC voltage flows into the three-phase three-level inverter through the positive terminal of capacitor C1 and the negative terminal of capacitor C2. Vbus is the bus voltage. The DC voltage and common-mode voltage injection commands are processed by the switching devices Q1-Q18, and then filtered by the three-phase filter composed of inductor group L1, capacitor group C0, and inductor group L2 to obtain the inverter voltage (i.e., AC voltage). Specifically, when the three-phase three-level inverter is operating, the average value of the voltages across each capacitor in capacitor group C0 is taken as the common-mode voltage of the three-phase three-level inverter.

[0038] As described in the background section, injecting a three-phase common-mode voltage into a pulse-width modulation (PWM) waveform can improve the DC voltage utilization of a three-phase three-level inverter. However, when using CPWM, the ripple current flowing through the bus capacitor of the three-phase three-level inverter is relatively small, but it leads to an increase in the power of the switching devices, affecting efficiency. When using DPWM, the switching power of the switching devices of the three-phase three-level inverter is smaller, but the ripple current flowing through the bus capacitor is relatively larger. Therefore, it is necessary to switch between the two modulation methods to ensure a smaller current in the bus capacitor ripple current and a smaller power of the switching devices. However, the instantaneous switching between the two modulation methods can easily damage the devices. Therefore, this application provides a new common-mode voltage adjustment method to reduce device losses and extend the device's service life.

[0039] The method of this application can be applied to a variety of application scenarios, such as converting light energy into DC voltage in a photovoltaic voltage inverter circuit and then converting it into AC voltage through the scheme of this application, or converting wind energy into DC voltage in a wind power converter and then converting it into AC voltage through the scheme of this application. This application will not be described in detail here. The scheme of this application can be used in any application scenario that has a voltage inverter circuit.

[0040] It should be noted that voltage inverter circuits are typically composed of electronic components such as capacitors, inductors, transistors, and diodes. This application does not limit the connection relationship of the various electronic components in the voltage inverter circuit. Any connection method of electronic components that can convert DC voltage into AC voltage is applicable to the voltage inverter circuit described in this application. The following description uses a three-phase three-level inverter circuit as an example, but in practical applications, the type of voltage inverter circuit is not limited.

[0041] Figure 2 A schematic diagram of a control system to which this application can be applied is shown. The control system includes a power command generation unit, a data acquisition unit, and a common-mode voltage regulation device. The common-mode voltage regulation device includes a controller and a voltage inverter circuit. The controller is connected to both the power command generation unit and the data acquisition unit; the data acquisition unit is also connected to the voltage inverter circuit. Figure 2 The voltage inverter circuit shown is an inverter constructed from a three-phase three-level inverter circuit, multiple capacitors, and inductors. The voltage between the positive DC bus and the negative DC bus is the bus voltage, i.e. Figure 2The inverter's AC output voltages, Ua, Ub, and Uc, are shown in the diagram. The data acquisition unit can collect the inverter's AC output voltages Ua, Ub, and Uc, as well as the inverter's bus voltage Ubus, in real time. The power command generation unit generates the inverter's output power and output current commands based on scheduling commands issued by the host computer. The controller determines the control commands based on the output power command, output current command, the inverter's bus voltage acquired by the data acquisition unit, and the inverter's output port voltage. Furthermore, in actual execution, some of the controller's functions can be implemented through a common-mode voltage injection calculation unit and a drive unit. For example, the common-mode voltage injection calculation unit calculates and generates the common-mode voltage injection value based on the output current command, bus voltage, and port voltage. The drive unit generates a control command, i.e., a common-mode voltage injection command, that matches the common-mode voltage injection value. Additionally, other units in the control system can be implemented through multiple units; this application does not specifically limit this.

[0042] The following is through Figure 3 This application introduces a common-mode voltage adjustment method, which can be achieved through the above... Figure 2 The controller in the system will execute the command. The specific execution steps are as follows:

[0043] Step 301: Generate a first common-mode voltage injection command according to the first modulation method; the first common-mode voltage injection command is used to control the voltage inverter circuit to output the first common-mode voltage.

[0044] Step 302: Generate a second common-mode voltage injection command according to the second modulation method; the second common-mode voltage injection command is used to control the voltage inverter circuit to output the second common-mode voltage.

[0045] It should be noted that steps 301 and 302 are not in any particular order of execution.

[0046] Step 303: During the modulation mode switching time period, the controller generates a third common-mode voltage injection command based on the first common-mode voltage injection command and the second common-mode voltage injection command; the third common-mode voltage injection command is used to control the voltage inverter circuit to output the third common-mode voltage; at any time during the modulation mode switching time period, the third common-mode voltage is between the first common-mode voltage and the second common-mode voltage; the third common-mode voltage is converted from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage is converted from the second common-mode voltage to the first common-mode voltage.

[0047] The first modulation method is continuous modulation; the second modulation method is discontinuous modulation.

[0048] As described above, to ensure a small current in the bus capacitor ripple current and a small power of the switching devices, it is necessary to switch the modulation mode. The method provided in this application is applicable to the modulation mode switching process. Related technologies directly switch the modulation mode, which may result in a very short switching time, making the switching almost instantaneous. However, this application, after determining that a modulation mode switch is needed, sets a time period for switching the modulation mode. During this time period, the injection value of the common-mode voltage is slowly adjusted to avoid damage to the devices caused by instantaneous modulation mode switching.

[0049] Furthermore, the modulation switching time period can be set according to user needs. If the user is not concerned about device losses and prefers a shorter modulation switching time, the modulation switching time period can be set shorter. If the user is very concerned about device losses, the modulation switching time period can be set longer.

[0050] It should be noted that, in order to achieve a slow change in the third common-mode voltage during the modulation switching period, it can be determined by weighted calculation of the injection commands of the first and second common-mode voltages, or by other methods, as long as the common-mode voltage of the voltage inverter circuit changes slowly.

[0051] In this application, at any point during the modulation mode switching period, the third common-mode voltage is between the first and second common-mode voltages. It is guaranteed that the value of the third common-mode voltage varies between the first and second common-mode voltages during the modulation mode switching period. For example, if the modulation mode switching period is 5 seconds, the starting time is A, the first common-mode voltage is 3V, and the second common-mode voltage is 4V, at the time corresponding to A+3 seconds, the value of the third common-mode voltage is between 3V and 4V, possibly 3.5V, or other values. Furthermore, the conversion of the third common-mode voltage from the first to the second common-mode voltage, or vice versa, ensures that when switching from the first to the second modulation mode, the value of the third common-mode voltage changes slowly from the first to the second common-mode voltage, or vice versa.

[0052] In this application, the controller generates different common-mode voltage injection commands based on different modulation methods. When switching modulation methods, the controller references the different common-mode voltage injection commands (first common-mode voltage injection command and second common-mode voltage injection command) to obtain the injection command for the third common-mode voltage within the modulation method switching time period. Under the action of the third common-mode voltage injection command, the third common-mode voltage output by the voltage inverter circuit gradually changes from the first common-mode voltage to the second common-mode voltage, or vice versa. This method can reduce damage to the components of the voltage inverter circuit during modulation method switching and further extend the service life of the components.

[0053] In one optional implementation, the controller can acquire a pre-stored mode factor and generate a third common-mode voltage injection command by weighting the injection commands for the first and second common-mode voltages and the mode factor. This mode factor can be used to indicate the weight value of the second common-mode voltage injection command or the weight value of the first common-mode voltage injection command. Which common-mode voltage injection command's weight value it indicates can be set according to user needs; this application does not impose specific limitations in practical applications.

[0054] It should also be noted that when determining the injection command for the third common-mode voltage using the mode factor, the time period for switching modulation modes can also be set according to the changes in the mode factor. The mode factor usually follows a fixed functional law, such as having a certain functional relationship with time. The time value corresponding to the critical point of the function or the intersection with the horizontal axis can be used as the time period for switching modulation modes. This application does not specifically limit how to determine the time period for switching modulation modes; any time period required for switching modulation modes is considered the time period for switching modulation modes.

[0055] The aforementioned model factors and time may vary continuously or discontinuously, such as... Figure 4 As shown, assuming the maximum value of the mode factor is 1, the time period of the modulation switching can be normalized. Assuming the time period of the modulation switching is 0-5 seconds, after normalization, the value corresponding to 3 seconds is 0.6 (3 / 5*1=0.6). This is only an example and does not specifically limit the method of mode factor normalization. Figure 4 Figure (a) shows a schematic diagram of the functional relationship of the model factor changing continuously with time. When the time is 0.5, the corresponding model factor is 0.75. Figure 4 Figure (b) shows another schematic diagram illustrating the change of the model factor over time. In (b), the value of the model factor changes stepwise with time, with a value of 0.60 corresponding to a time of 0.8. This application does not specifically limit the trend of the model factor's change over time.

[0056] When determining the injection value of the common-mode voltage in the voltage inverter circuit, the mode factor corresponding to each common-mode voltage injection command can be weighted and summed with the injection value of the common-mode voltage corresponding to each common-mode voltage injection command to determine the injection value of the common-mode voltage input to the voltage inverter circuit at different times during the switching time period. During the time period when the voltage inverter circuit switches modulation modes, the mode factor is multiplied by the common-mode voltage injection command as a weight value to calculate the injection value of the common-mode voltage, and the voltage inverter circuit is controlled based on the common-mode voltage injection command that matches the injection value of the common-mode voltage. This method comprehensively considers the influence of the injection value of the common-mode voltage corresponding to each modulation mode on the common-mode voltage of the voltage inverter circuit during the modulation mode switching time period, and can adjust the common-mode voltage of the voltage inverter circuit through the slow change of the injection value of the common-mode voltage. This method can avoid instantaneous switching between modulation modes and can better reduce the degree of device loss. With the reduction of device loss, the service life of the device is further extended.

[0057] In one alternative implementation, the change of the model factor over time includes one or more of the following: the model factor increases exponentially over time, such as... Figure 5 As shown in (a), the growth rate of the model factor decreases exponentially over time. Figure 5 As shown in (b), the model factor decreases stepwise over time. Figure 5 As shown in (c), the model factor increases stepwise over time. Figure 5 As shown in (d), the mode factor changes with time in a first-order filtering manner. Figure 5 As shown in (e). Figure 5 In the model, the maximum value of the pattern factor is 1. Figure 5 The transition time periods shown in the diagram have been normalized.

[0058] It should be noted that the value of the mode factor changes over time in the manner described above, which ensures that the third common-mode voltage changes slowly during the modulation switching period.

[0059] In one optional implementation, if the mode factor indicates the weight value of the injection command for the second common-mode voltage, then the sum of the weight value of the injection command for the first common-mode voltage and the mode factor is 1. Alternatively, if the mode factor is 1, the third common-mode voltage is the same as the second common-mode voltage. This can be understood as follows: during the modulation mode switching period, the modulation mode switches from the second modulation mode to the first modulation mode. At the moment of the modulation mode switch, the injection command for the third common-mode voltage received by the voltage inverter circuit can be considered as the injection command for the second common-mode voltage; therefore, the third common-mode voltage is the same as the second common-mode voltage. Or, during the modulation mode switching period, the modulation mode switches from the first modulation mode to the second modulation mode. Upon completion of the modulation mode switch, the injection command for the third common-mode voltage received by the voltage inverter circuit can be considered as the injection command for the second common-mode voltage; therefore, the third common-mode voltage is the same as the second common-mode voltage. If the mode factor is 0, the third common-mode voltage is the same as the first common-mode voltage. This can be understood as follows: during the modulation mode switching period, the modulation mode switches from the first modulation mode to the second modulation mode. When the modulation mode just switches, the third common-mode voltage control command received by the voltage inverter circuit can be regarded as the injection command of the first common-mode voltage. Therefore, the third common-mode voltage is the same as the first common-mode voltage. Alternatively, during the modulation mode switching period, the modulation mode switches from the second modulation mode to the first modulation mode. When the modulation mode switching is completed, the third common-mode voltage injection command received by the voltage inverter circuit can be regarded as the injection command of the first common-mode voltage. Therefore, the third common-mode voltage is the same as the first common-mode voltage.

[0060] In another optional implementation, if the mode factor indicates the weight value of the injection command for the first common-mode voltage, then the weight value of the injection command for the second common-mode voltage, when summed with the mode factor, is 1. Alternatively, if the mode factor is 1, the third common-mode voltage is the same as the first common-mode voltage. This can be understood as follows: during the modulation mode switching period, the modulation mode switches from the first modulation mode to the second modulation mode. At the moment of the modulation mode switch, the injection command for the third common-mode voltage received by the voltage inverter circuit can be considered as the injection command for the first common-mode voltage; therefore, the third common-mode voltage is the same as the first common-mode voltage. Or, during the modulation mode switching period, the modulation mode switches from the second modulation mode to the first modulation mode. Upon completion of the modulation mode switch, the injection command for the third common-mode voltage received by the voltage inverter circuit can be considered as the injection command for the first common-mode voltage; therefore, the third common-mode voltage is the same as the first common-mode voltage. If the mode factor is 0, the third common-mode voltage is the same as the second common-mode voltage. This can be understood as follows: during the modulation mode switching period, the modulation mode switches from the second modulation mode to the first modulation mode. When the modulation mode just switches, the injection command of the third common-mode voltage received by the voltage inverter circuit can be regarded as the injection command of the second common-mode voltage. Therefore, the third common-mode voltage is the same as the second common-mode voltage. Alternatively, during the modulation mode switching period, the modulation mode switches from the first modulation mode to the second modulation mode. When the modulation mode switching is completed, the injection command of the third common-mode voltage received by the voltage inverter circuit can be regarded as the injection command of the second common-mode voltage. Therefore, the third common-mode voltage is the same as the second common-mode voltage.

[0061] In one optional implementation, the first modulation method can be CPWM, and the second modulation method can be DPWM. In practical applications, the mode factor can be used to indicate only the weight value corresponding to CPWM, then the weight value corresponding to DPWM is 1 minus the mode factor. In practical applications, this application does not specifically limit whether the mode factor indicates the weight value of CPWM or the weight value of DPWM.

[0062] It should be noted that when using CPWM modulation, the ripple current flowing through the bus capacitor of the voltage inverter circuit is relatively small, while when using DPWM modulation, the losses of the switching devices in the voltage inverter circuit are relatively small. This application, during the modulation mode switching period, through weighted calculations of the mode factor, the injection command of the first common-mode voltage, and the injection command of the second common-mode voltage, ensures that the ripple current of the bus capacitor is small while minimizing losses to the switching devices during modulation mode switching. During the modulation mode switching period, when switching between CPWM and DPWM, the mode factor indicates the weight value of DPWM; it is clear that the weight value of CPWM is 1 minus the value of the mode factor. This method ensures that the common-mode voltage changes slowly during the modulation mode switching period.

[0063] The following is through Figure 6A This schematic diagram illustrates a common-mode voltage adjustment method to demonstrate how to determine the injected common-mode voltage value when the modulation methods include CPWM and DPWM. The following explanation uses the example of the mode factor indicating the weight of DPWM for illustration only.

[0064] The data acquisition unit can first acquire the voltage Ubus between the positive and negative buses of the three-phase three-level voltage inverter circuit, as well as the output voltages Ua, Ub, and Uc of the AC port. The controller can calculate the injection value of the common-mode voltage corresponding to CPWM and the injection value of the common-mode voltage corresponding to DPWM based on the values ​​of Ubus, Ua, Ub, and Uc.

[0065] It should be noted that the common-mode voltage injection value u required for CPWM to generate the common-mode voltage injection command is... cmvCpwm And the common-mode voltage injection value u required for DPWM to generate the common-mode voltage injection command. cmvDpwm When calculating, the following rules can be used as a reference:

[0066] (1) Calculate the maximum value Umax of Ua, Ub and Uc, and the minimum value Umin of Ua, Ub and Uc;

[0067] (2)u cmvCpwm = -0.5(Umax + Umin);

[0068] (3)u cmvDpwmMax = -0.5Ubus-Umax;

[0069] (4)u cmvDpwmMin = -0.5Ubus-Umin;

[0070] (5) Calculate u using the following formula cmvDpwm :

[0071] if |u cmvDpwmMax |<|u cmvDpwmMin |, then u cmvDpwm =u cmvDpwmMax Otherwise, u cmvDpwm =u cmvDpwmMin .

[0072] It should be noted that the common-mode voltage calculation methods provided here for continuous pulse width modulation (PWM) and discontinuous pulse width modulation (PWM) are only one of many feasible methods. For PWM, the common-mode voltage injection value can also be obtained by using the third harmonic injection method, as described in reference 1 ("Research on Multi-Level Voltage Inverter Circuit Based on Carrier Phase Shift THI-PWM Technology", Yang Hang, Yang Jianfeng, Wang Shuai, *Electrical Measurement & Instrumentation*). For PWM, the common-mode voltage injection value can also be obtained by using the DPWM1, DPWMmax, and DPWMmin methods given in reference 2 ("A New Unified Implementation Method for Discontinuous PWM", An Shaoliang, Sun Xiangdong, Chen Yingjuan, Zhong Yanru, Ren Biying, *Proceedings of the CSEE*). Furthermore, other calculation methods for u may exist in existing technologies. cmvCpwm and u cmvDpwm The method used in this application will not be elaborated further here; all existing technologies for calculating u... cmvCpwm and u cmvDpwm All methods are applicable to the scheme of this application.

[0073] Next, the controller needs to determine the switching direction, and based on the switching direction, determine whether to switch the modulation scheme from CPWM to DPWM or from DPWM to CPWM. If the modulation scheme is switching from DPWM to CPWM, a function graph of the mode factor changing from 1 to 0 over time can be selected; if the modulation scheme is switching from CPWM to DPWM, a function graph of the mode factor changing from 0 to 1 over time can be selected. Based on the mode factor r... mode The graph of the model factor as a function of time determines the values ​​of the model factor at different times. If the values ​​of the model factor exhibit a certain relationship with time... Figure 5 The functional relationship of the first-order filter shown in (e) can be referenced at different times within different switching time periods. Figure 5 The injection value of the common-mode voltage is calculated by weighting and summing the values ​​of the mode factors in (e). The injection value u of the common-mode voltage can be determined by referring to Formula 1 below. cmv .

[0074] u cmv =u cmvDpwm *r mode +u cmvCpwm *(1-r mode ), r mode ∈[0,1] Formula 1

[0075] It should be noted that CPWM may include various continuous pulse modulation methods, such as sinusoidal pulse width modulation (SPWM), third-harmonic-injected pulse width modulation (THIPWM), and space vector pulse width modulation (SVPWM). DPWM may include various discontinuous pulse modulation methods, such as DPWMmax and DPWMmin. This application does not specifically limit the types of pulse modulation methods included in CPWM and DPWM.

[0076] When calculating the common-mode voltage injection value using Formula 1, first determine which CPWM switches to which DPWM, or which DPWM switches to which CPWM, during the modulation mode switching period. Then determine the common-mode voltage injection value corresponding to CPWM and DPWM during the modulation mode switching period. Finally, calculate the weighted common-mode voltage injection value according to Formula 1. Taking the modulation modes included in CPWM and DPWM as an example, if switching from SPWM to DPWMmax during the modulation mode switching period, it is necessary to determine the common-mode voltage value 1 corresponding to SPWM and the common-mode voltage value 2 corresponding to DPWMmax. Substitute common-mode voltage value 1 and common-mode voltage value 2 into Formula 1 for calculation: Common-mode voltage injection value = common-mode voltage value 2 * r mode +Common-mode voltage value 1*(1-r) mode ).

[0077] It should be noted that when switching between different modulation methods, when passing through Figure 6A After determining the common-mode voltage injection value using the method described above, a common-mode voltage injection command is generated. Upon receiving the common-mode voltage injection command, the voltage inverter circuit can change the value of its common-mode voltage as follows: Figure 6B As shown, the pulse width of the common-mode voltage in the voltage inverter circuit gradually decreases, slowly switching to the pulse width of the common-mode voltage under another modulation mode. The method provided in this application can avoid the losses to the device caused by instantaneous switching between modulation modes.

[0078] To reduce device losses when adjusting the pulse width of the common-mode voltage, this application introduces a mode factor. During the time period when the voltage inverter circuit switches common-mode voltage modulation modes, the mode factor is multiplied by the common-mode voltage injection command as a weighting value to calculate the injected common-mode voltage value. This method comprehensively considers the impact of various modulation modes on the common-mode voltage of the voltage inverter circuit during the switching time period, and can adjust the pulse width of the common-mode voltage of the voltage inverter circuit through the gradual change of the injected common-mode voltage value. This method avoids instantaneous switching between modulation modes, reducing device losses. With reduced device losses, the device's lifespan is further extended.

[0079] Figure 7 This application provides a common-mode voltage adjustment device according to an embodiment of the present application. It should be noted that the above-mentioned device... Figure 2 The control unit in the middle can be a common-mode voltage adjustment device, which may include: This application provides a common-mode voltage adjustment device, including: a controller 71 and a voltage inverter circuit 72.

[0080] The controller 71 can be used to generate an injection command for a first common-mode voltage according to a first modulation method; the injection command for the first common-mode voltage is used to control the voltage inverter circuit to output the first common-mode voltage; and to generate an injection command for a second common-mode voltage according to a second modulation method; the injection command for the second common-mode voltage is used to control the voltage inverter circuit to output the second common-mode voltage; during the modulation method switching time period, the controller generates an injection command for a third common-mode voltage according to the injection command for the first common-mode voltage and the injection command for the second common-mode voltage; the injection command for the third common-mode voltage is used to control the voltage inverter circuit to output the third common-mode voltage; at any time during the modulation method switching time period, the third common-mode voltage is between the first common-mode voltage and the second common-mode voltage; the third common-mode voltage changes from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage changes from the second common-mode voltage to the first common-mode voltage.

[0081] The voltage inverter circuit 72 can be used to receive the third common-mode voltage injection command and output the third common-mode voltage; wherein, the first modulation method is continuous modulation; and the second modulation method is discontinuous modulation.

[0082] In this application, the controller generates different common-mode voltage injection commands based on different modulation methods. When switching modulation methods, the controller references the different common-mode voltage injection commands (first common-mode voltage injection command and second common-mode voltage injection command) to obtain the injection command for the third common-mode voltage within the modulation method switching time period. Under the action of the third common-mode voltage injection command, the third common-mode voltage output by the voltage inverter circuit gradually changes from the first common-mode voltage to the second common-mode voltage, or vice versa. This method can reduce damage to the components of the voltage inverter circuit during modulation method switching and further extend the service life of the components.

[0083] In one possible implementation, the controller is specifically configured to: acquire a pre-stored mode factor; the mode factor is used to indicate the weight value of the injection command for the second common-mode voltage; and generate an injection command for the third common-mode voltage by weighting the injection command for the first common-mode voltage, the injection command for the second common-mode voltage, and the mode factor.

[0084] It should be noted that, in order to reduce device losses when adjusting the pulse width of the common-mode voltage, this application introduces a mode factor. During the modulation mode switching period of the voltage inverter circuit, the mode factor is used as a weighting value to calculate the injection command for the third common-mode voltage. This method comprehensively considers the influence of the injection commands corresponding to each modulation mode on the common-mode voltage during the switching period, and the pulse width of the common-mode voltage of the voltage inverter circuit can be adjusted by slowly changing the injection value of the common-mode voltage. This method avoids instantaneous switching between modulation modes and reduces device losses. Furthermore, with reduced device losses, the device lifespan can be further extended.

[0085] In one possible implementation, the pattern factor increases exponentially over time, or decreases exponentially over time, or decreases stepwise over time, or increases stepwise over time.

[0086] It should be noted that by changing the mode factor over time in the manner described above, the common-mode voltage can be ensured to change slowly rather than abruptly during the modulation switching period, which can reduce the degree of damage to the device.

[0087] In one possible implementation, the weight value of the injection command for the first common-mode voltage is summed with the mode factor to equal 1.

[0088] In one possible implementation, if the mode factor is 1, the third common-mode voltage is the same as the second common-mode voltage; if the mode factor is 0, the third common-mode voltage is the same as the first common-mode voltage.

[0089] In one possible implementation, the first modulation method is CPWM and the second modulation method is DPWM.

[0090] It should be noted that when using CPWM modulation, the ripple current flowing through the bus capacitor of the voltage inverter circuit is relatively small, while when using DPWM modulation, the losses of the switching devices in the voltage inverter circuit are relatively small. This application considers the common-mode voltage injection commands of both modulation methods during the modulation mode switching time period, ensuring that during modulation, the ripple current of the bus capacitor is small while minimizing losses to the switching devices.

[0091] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0092] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to this application. It should be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0093] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0094] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0095] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the scope of protection of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. A common-mode voltage regulation method, said method being applied to a controller, the controller being used to generate control commands for a control voltage inverter circuit, characterized in that, include: The controller generates an injection command for the first common-mode voltage according to the first modulation method; The injection command for the first common-mode voltage is used to control the voltage inverter circuit to output the first common-mode voltage; The controller generates an injection command for the second common-mode voltage according to the second modulation method; the injection command for the second common-mode voltage is used to control the voltage inverter circuit to output the second common-mode voltage. During the modulation mode switching period, the controller acquires a pre-stored mode factor; the mode factor is used to indicate the weight value of the injection command for the second common-mode voltage; by weighting the injection command for the first common-mode voltage, the injection command for the second common-mode voltage, and the mode factor, an injection command for the third common-mode voltage is generated; the injection command for the third common-mode voltage is used to control the voltage inverter circuit to output a third common-mode voltage; at any time during the modulation mode switching period, the third common-mode voltage is between the first common-mode voltage and the second common-mode voltage; the third common-mode voltage converts from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage converts from the second common-mode voltage to the first common-mode voltage; Wherein, the first modulation method is continuous modulation; the second modulation method is discontinuous modulation; the mode factor increases exponentially with time, or the mode factor decreases exponentially with time, or the mode factor decreases stepwise with time, or the mode factor increases stepwise with time.

2. The method according to claim 1, characterized in that, The weight value of the injection command of the first common-mode voltage, when summed with the mode factor, is 1.

3. The method according to claim 2, characterized in that, If the mode factor is 1, the third common-mode voltage is the same as the second common-mode voltage; if the mode factor is 0, the third common-mode voltage is the same as the first common-mode voltage.

4. The method according to any one of claims 1-3, characterized in that, The first modulation method is continuous pulse width modulation (CPWM), and the second modulation method is discontinuous pulse width modulation (DPWM).

5. A common-mode voltage adjustment device, characterized in that, include: Controller and voltage inverter circuit; The controller is used to generate an injection command for a first common-mode voltage according to a first modulation scheme; The injection command for the first common-mode voltage is used to control the voltage inverter circuit to output the first common-mode voltage; And the injection command to generate the second common-mode voltage according to the second modulation method; The injection command for the second common-mode voltage is used to control the voltage inverter circuit to output the second common-mode voltage; During the modulation mode switching period, the controller acquires a pre-stored mode factor; the mode factor is used to indicate the weight value of the injection command for the second common-mode voltage; by weighting the injection command for the first common-mode voltage, the injection command for the second common-mode voltage, and the mode factor, an injection command for the third common-mode voltage is generated; the injection command for the third common-mode voltage is used to control the voltage inverter circuit to output a third common-mode voltage; at any time during the modulation mode switching period, the third common-mode voltage is between the first common-mode voltage and the second common-mode voltage; the third common-mode voltage converts from the first common-mode voltage to the second common-mode voltage, or the third common-mode voltage converts from the second common-mode voltage to the first common-mode voltage; The voltage inverter circuit is used to receive the third common-mode voltage injection command and output the third common-mode voltage; Wherein, the first modulation method is continuous modulation; the second modulation method is discontinuous modulation; the mode factor increases exponentially with time, or the mode factor decreases exponentially with time, or the mode factor decreases stepwise with time, or the mode factor increases stepwise with time.

6. The apparatus according to claim 5, characterized in that, The weight value of the injection command of the first common-mode voltage, when summed with the mode factor, is 1.

7. The apparatus according to claim 6, characterized in that, If the mode factor is 1, the third common-mode voltage is the same as the second common-mode voltage; if the mode factor is 0, the third common-mode voltage is the same as the first common-mode voltage.

8. The apparatus according to any one of claims 5-7, characterized in that, The first modulation method is continuous pulse width modulation (CPWM), and the second modulation method is discontinuous pulse width modulation (DPWM).

9. A control system, characterized in that, include: The power command generation unit, the data acquisition unit, and the common-mode voltage adjustment device as described in any one of claims 5-8; The controller of the common-mode voltage regulator is connected to the power command generation unit and the data acquisition unit respectively; the data acquisition unit is also connected to the voltage inverter circuit of the common-mode voltage regulator. The data acquisition unit is used to acquire the voltage at the output port of the voltage inverter circuit and the bus voltage of the voltage inverter circuit. The power command generation unit is used to generate the output power command and output current command of the voltage inverter circuit according to the scheduling command issued by the host computer. The controller determines the control command based on the output power command, the output current command, the bus voltage of the voltage inverter circuit, and the voltage of the output port of the voltage inverter circuit.

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