Converter control method, control processing unit and network construction type converter

Abstract

The invention discloses a converter control method, a control processing unit and a network construction type converter. The converter control method is applied to the network construction type converter. The converter control method comprises the following steps: acquiring a first internal potential and a transient current amplitude when the grid-forming converter is in a ride-through mode, acquiring a static virtual impedance and a voltage of a filter capacitor, enabling the grid-forming converter to be in the ride-through mode when the voltage of a power grid is disturbed, enabling the grid-forming converter to be in a normal mode when the power grid operates normally, and enabling the grid-forming converter to be in a non-normal mode when the power grid operates normally; the transient current amplitude is the amplitude of the output current of the grid-forming converter when the grid-forming converter is in the ride-through mode, and determining the transient virtual impedance when the grid-forming converter is in the ride-through mode based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor and the static virtual impedance; and based on the transient virtual impedance, carrying out current limiting on the output current of the grid-forming converter. In this way, the risk of overcurrent of the converter can be reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of converter control, and in particular to a converter control method, a control processing unit and a grid-type converter. Background Art

[0002] As the penetration rate of new energy sources such as photovoltaics and wind power gradually increases, traditional grid-following converters do not have virtual rotational inertia, and the inertia of the power system gradually decreases. Therefore, the power system requires the converter to provide a certain inertia, so it has voltage source characteristics, and grid-forming converters that can be applied to a variety of working conditions and provide voltage and frequency support for the power system have become the focus of research. Grid-forming converters adopt power synchronization or DC voltage synchronization control strategies, which can operate stably in extremely weak power grids and isolated grid scenarios, and help improve the stability of systems with a high proportion of new energy. However, in actual applications, since the grid-forming control exhibits voltage source characteristics, when the voltage of the power grid is disturbed, it may cause overcurrent abnormalities in the converter. Summary of the invention

[0003] The embodiments of the present application provide a converter control method, a control processing unit and a grid-type converter, which can reduce the risk of overcurrent in the converter.

[0004] In a first aspect, an embodiment of the present application provides a converter control method, which is applied to a grid-type converter, wherein the grid-type converter includes a bus capacitor, an inverter bridge, a first inductor, a filter capacitor, and a second inductor, wherein the bus capacitor is connected to a DC voltage and the inverter bridge, respectively, the first inductor and the second inductor are connected in series between the inverter bridge and the grid, and the filter capacitor is connected between a connection point between the first inductor and the second inductor and ground, and the method includes:

[0005] Acquire a first internal potential and a transient current amplitude when the grid-type converter is in a ride-through mode, and acquire a static virtual impedance and a voltage of the filter capacitor, wherein the grid-type converter is in a ride-through mode when a disturbance occurs in the voltage of the power grid, and the grid-type converter is in a normal mode when the power grid operates normally, the transient current amplitude is the amplitude of the output current of the grid-type converter when the grid-type converter is in the ride-through mode, and the static virtual impedance is a virtual impedance that simulates the reactance characteristics of a synchronous generator;

[0006] Determining a transient virtual impedance when the grid-connected converter is in a ride-through mode based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor, and the static virtual impedance;

[0007] Based on the transient virtual impedance, the output current of the grid-connected converter is limited.

[0008] In one or more embodiments, determining the transient virtual impedance when the grid-type converter is in the ride-through mode based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor, and the static virtual impedance includes:

[0009] The transient virtual impedance is determined by the following formula:

[0010] X d =K1(U vrt -U c -(X s +X d )*I max );

[0011] Among them, X d is the transient virtual impedance, K1 is a proportional controller, an integral controller or a proportional integral controller, U vrt is the first internal potential, U C is the voltage of the filter capacitor, X S is the static virtual impedance, I max is the transient current amplitude.

[0012] In one or more embodiments, the method further comprises:

[0013] When the grid-connected converter is in the ride-through mode, the following steps are performed:

[0014] If the voltage of the filter capacitor decreases and the decrease value is greater than or equal to a first preset threshold, the reactive current in the output current of the grid-type converter is controlled to be a negative value of the transient current amplitude;

[0015] If the voltage of the filter capacitor decreases and the decrease value is less than the first preset threshold, or the voltage of the filter capacitor increases, the reactive current is controlled to be a negative value of the ratio of a first difference value to a first sum value, wherein the first difference value is a difference between the first internal potential and the voltage of the power grid, and the first sum value is the sum of the static virtual impedance and the impedance of the power grid.

[0016] In one or more embodiments, the method further comprises:

[0017] When the grid-connected converter is in the ride-through mode, the following steps are performed:

[0018] Determine the maximum active power output by the grid-type converter based on the reactive current in the output current of the grid-type converter, the transient current amplitude, the rated current flowing through the grid-type converter output, and the first active power output by the grid-type converter when the grid-type converter is in normal mode;

[0019] When the first active power is less than or equal to the maximum active power, controlling the active power output by the grid-connected converter to be the first active power;

[0020] When the first active power is greater than the maximum active power, the active power output by the grid-connected converter is controlled to be the maximum active power.

[0021] In one or more embodiments, determining the maximum active power output by the grid-type converter based on the reactive current in the output current of the grid-type converter, the transient current amplitude, the rated current flowing through the grid-type converter output, and the first active power output by the grid-type converter when the grid-type converter is in normal mode includes:

[0022] The maximum active power is determined by the following formula:

[0023] P max =((1-(I vrtq ) 2 / (I max ) 2 ) 1 / 2 *(I max ) / (I rate ))*P ref0 ;

[0024] Among them, P max is the maximum active power, I vrtq is the reactive current, I max is the transient current amplitude, I rate is the rated current, P ref0 is the first active power.

[0025] In one or more embodiments, the method further comprises:

[0026] Determining an error angular frequency based on a target active power output by the grid-type converter, an actual active power output by the grid-type converter, a virtual moment of inertia, an active power damping coefficient, and a system angular frequency of the grid-type converter;

[0027] Determining a compensation angular frequency based on a product of a preset compensation function and a q-axis voltage of the filter capacitor;

[0028] Based on the integration result of the sum of the system angular frequency, the error angular frequency and the compensation angular frequency, the angle of the internal potential of the grid-connected converter is determined.

[0029] In one or more embodiments, determining the error angular frequency based on the target active power output by the grid-type converter, the actual active power output by the grid-type converter, the virtual moment of inertia, the active power damping coefficient, and the system angular frequency of the grid-type converter includes:

[0030] The error angular frequency is determined by the following formula:

[0031] Δω=(P ref -P act ) / (ω0*(sJ+D p ));

[0032] Among them, P ref is the target active power, P act is the actual active power, ω0 is the system angular frequency, J is the virtual moment of inertia, D p is the active power damping coefficient.

[0033] In one or more embodiments, the method further comprises:

[0034] The second internal potential when the grid-connected converter is in the normal mode is determined by the following formula:

[0035] E=U n +G QPi (Q ref -Q act +D q *(U n -U c ));

[0036] Where, E is the second internal potential, U n is the rated voltage of the filter capacitor, G QPi is the reactive power controller, Q ref is the target reactive power output by the grid-connected converter, Q act is the actual reactive power output by the grid-connected converter, D q is the reactive power droop coefficient.

[0037] In one or more embodiments, the obtaining of a first internal potential when the grid-connected converter is in a ride-through mode comprises:

[0038] When the grid-connected converter is in the ride-through mode, the input of the reactive power controller is configured to be 0 to obtain the first internal potential.

[0039] In a second aspect, an embodiment of the present application provides a control processing unit, including:

[0040] at least one processor and memory;

[0041] The memory is coupled to the processor, and is used to store instructions or programs. When the instructions or programs are executed by the at least one processor, the at least one processor executes the converter control method as described above.

[0042] In a third aspect, an embodiment of the present application provides a grid-type converter, comprising the control processing unit as described above, wherein the grid-type converter is connected between a DC voltage and a power grid.

[0043] In one or more embodiments, the grid-type converter further includes a bus capacitor, an inverter bridge, a first inductor, a filter capacitor and a second inductor;

[0044] The bus capacitor is connected to the DC voltage and the inverter bridge respectively, the first inductor and the second inductor are connected in series between the inverter bridge and the power grid, and the filter capacitor is connected between the connection point between the first inductor and the second inductor and the ground.

[0045] The beneficial effects of the present application are as follows: the converter control method of the embodiment of the present application constructs a transient virtual impedance based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor and the static virtual impedance when the grid-type converter is in the crossing mode. On the one hand, it can limit the output current of the grid-type converter when the voltage of the power grid is disturbed, so as to reduce the risk of overcurrent in the grid-type converter; on the other hand, the impedance value of the transient virtual impedance can be automatically adjusted based on the actual operating conditions of the grid-type converter. Compared with the use of a virtual resistor with a fixed impedance value, it can more effectively reduce the risk of overcurrent in the grid-type converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] One or more embodiments are exemplarily described by the figures in the corresponding drawings, and these exemplary descriptions are not intended to limit the embodiments. Elements with the same reference numerals in the drawings represent similar elements.

[0047] Figure 1 The process of the converter control method provided in the embodiment of the present application is Figure 1 ;

[0048] Figure 2 is a schematic diagram of the circuit structure of a grid-connected converter provided in an embodiment of the present application;

[0049] Figure 3 This is the implementation process of limiting the output current of the grid-type converter based on transient virtual impedance provided by the embodiment of the present application;

[0050] Figure 4 The process of the converter control method provided in the embodiment of the present application is Figure 2 ;

[0051] Figure 5 yes Figure 2 Schematic diagram of various signals in the grid-type converter shown Figure 1 ;

[0052] Figure 6 yes Figure 2 Schematic diagram of various signals in the grid-type converter shown Figure 2 ;

[0053] Figure 7 The process of the converter control method provided in the embodiment of the present application is Figure 3 ;

[0054] Figure 8 The process of the converter control method provided in the embodiment of the present application is Figure 4 ;

[0055] Fig. 9 This is the first implementation process of determining the angle of the internal potential of the grid-type converter provided in the embodiment of the present application;

[0056] Fig.10 This is the second implementation process of determining the angle of the internal potential of the grid-type converter provided in the embodiment of the present application;

[0057] Fig.11 is the relationship between the voltage and the current before and after the compensation angular frequency is increased provided in the embodiment of the present application;

[0058] Fig.12 is a curve diagram of the angle of the internal potential before and after the compensation angular frequency is increased provided by an embodiment of the present application;

[0059] Fig.13 This is the first implementation process of obtaining the first internal potential and the second internal potential provided in the embodiment of the present application;

[0060] Fig.14 This is the second implementation process of obtaining the first internal potential and the second internal potential provided in the embodiment of the present application;

[0061] Fig.15 It is a structural diagram of the control processing unit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and in detail in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, rather than all the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0063] It should be noted that, when an element is described as being “connected to” another element, it may be directly connected to the other element, or one or more intervening elements may exist therebetween.

[0064] In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as there is no structural conflict between them.

[0065] Please refer to Figure 1 , Figure 1 The flowchart of the converter control method provided in the embodiment of the present application is shown in FIG. Figure 2 An example circuit structure of a grid-type converter is shown. Figure 2 As shown, the grid-type converter 100 includes a bus capacitor C dc , inverter bridge 10, first inductor L1, filter capacitor C f With the second inductor L2, bus capacitor C dc Respectively with DC voltage U dc The first inductor L1 and the second inductor L2 are connected in series between the inverter bridge 10 and the power grid 200, and the filter capacitor C f Connect between the connection point between the first inductor L1 and the second inductor L2 and the ground. Please return to reference Figure 1 ,like Figure 1 As shown, the converter control method includes the following method steps:

[0066] Step 101: Obtain a first internal potential and a transient current amplitude when the grid-type converter is in a ride-through mode, and obtain a static virtual impedance and a voltage of a filter capacitor, wherein the grid-type converter is in a ride-through mode when a voltage disturbance occurs in the grid, and the grid-type converter is in a normal mode when the grid operates normally, the transient current amplitude is the amplitude of the output current of the grid-type converter when the grid-type converter is in the ride-through mode, and the static virtual impedance is a virtual impedance that simulates the reactance characteristics of a synchronous generator.

[0067] Among them, the first internal potential is the internal potential of the grid-type converter when it is in the crossing mode. In the grid-type converter, the internal potential (Internal Electromotive Force, EMF) is a virtual voltage source generated inside the grid-type converter, which imitates the electromotive force characteristics of a traditional synchronous generator. By adjusting the first internal potential, the grid-type converter can effectively control the active power and reactive power it outputs, thereby maintaining the voltage and frequency stability of the power grid. It can be understood that in the embodiments of the present application, the grid-type converter is implemented as a virtual synchronous machine to simulate the dynamic characteristics of the synchronous generator, so that the grid-type converter can autonomously establish and maintain the voltage and frequency of the power grid.

[0068] When the grid-type converter is in the ride-through mode, the grid-type converter can continue to operate without immediate shutdown when a voltage disturbance occurs in the grid 200 (which can also be regarded as a fault or abnormality in the grid 200 ).

[0069] Static Virtual Impedance refers to the control strategy of the grid-connected converter, which simulates the reactance characteristics of the traditional synchronous generator by introducing a virtual impedance in the control loop. This virtual impedance can be used to adjust the distribution of active power and reactive power, and improve the stability and power quality of the system.

[0070] The voltage of the filter capacitor is Figure 2 The filter capacitor C f voltage.

[0071] Step 102: Determine the transient virtual impedance when the grid-connected converter is in the ride-through mode based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor and the static virtual impedance.

[0072] Step 103: Based on the transient virtual impedance, the output current of the grid-connected converter is limited.

[0073] Specifically, the transient virtual impedance is based on the first internal potential, the transient current amplitude, the filter capacitor C when the grid-type converter is in the ride-through mode. f The virtual impedance constructed by the voltage of the grid 200 and the static virtual impedance, on the one hand, through the transient virtual impedance, when the voltage of the grid 200 is disturbed, the output current of the grid-type converter (i.e., the current i flowing through the second inductor L2) is g ) is used to limit the current, which can reduce the risk of overcurrent in the grid-type converter; on the other hand, it can be seen from step 102 that the impedance value of the transient virtual impedance can be automatically adjusted based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor and the static virtual impedance (that is, based on the actual operation of the grid-type converter). Compared with using a virtual resistor with a fixed impedance value, it can more effectively reduce the risk of overcurrent in the grid-type converter 100.

[0074] In some embodiments, the transient virtual impedance includes at least one of a virtual inductor and a virtual resistor. In the subsequent embodiments of the present application, the transient virtual impedance includes a virtual inductor as an example for description.

[0075] In some embodiments, the specific implementation process of determining the transient virtual impedance when the grid-connected converter is in the ride-through mode based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor and the static virtual impedance in step 102 includes: the transient virtual impedance is determined by the following formula (1):

[0076] X d =K1(U vrt -U c -(X s +X d )*I max ) (1).

[0077] Among them, X d is the transient virtual impedance, K1 is a proportional controller, an integral controller or a proportional integral controller, U vrt is the first internal potential, U C is the voltage of the filter capacitor, X S is the static virtual impedance, I max is the transient current amplitude.

[0078] Specifically, when the voltage of the power grid 200 is disturbed and causes the filter capacitor C f When the voltage decreases, the transient virtual impedance X d The impedance value begins to increase; at the same time, the capacitive reactive current rises, so that the filter capacitor C f The voltage of the filter capacitor C f The voltage of the filter capacitor C f The voltage reduction value) is less than the first preset threshold value (i.e., the corresponding filter capacitor C f When the voltage drop is small, under the automatic adjustment of the grid-type converter 100, the filter capacitor C f The voltage U c can gradually return to the first internal potential U vrt The voltage of the transient virtual impedance X d The impedance value gradually decreases to 0; when the filter capacitor C f The voltage of the filter capacitor C f When the voltage drop is large, under the automatic adjustment of the grid-type converter 100, the transient virtual impedance X d The impedance value and filter capacitor C f The voltage U c Finally, they are kept at a stable value, and the transient virtual impedance X d The impedance value of the filter capacitor C f When the voltage increases, in practical applications, due to the filter capacitor C f The voltage U cThe increase in value is usually small, so under the automatic adjustment of the grid-type converter 100, the filter capacitor C f The voltage U c can gradually return to the first internal potential U vrt The voltage of the transient virtual impedance X d The impedance value of the transient virtual impedance X gradually decreases to 0. It can be seen that in this embodiment, the automatic adjustment of the transient virtual impedance X based on the actual operation of the grid-type converter 100 is achieved. d The process of impedance value.

[0079] Please refer to Figure 3 , Figure 3 The example shows the transient virtual impedance X d The specific implementation process of limiting the output current of the grid-type converter 100. Figure 3 As shown, the current i flowing through the second inductor L2 g Converted to the dq coordinate system, the current i g The component on the d-axis (current i gd ) and the component on the q axis (current i gq ). Among them, the dq coordinate system (also called the dq0 coordinate system or Park coordinate system) is a commonly used coordinate transformation method, which converts the variables in the three-phase AC system into a rotating two-phase rectangular coordinate system. gd With current i gq Through the transient virtual impedance X d After the voltage loop and the current loop are controlled, a PWM modulation signal can be output to control the switch tube in the inverter bridge 10, wherein the voltage loop includes the second internal potential E, the filter capacitor C f The voltage U C The component on the d-axis (voltage U cd ) and the component on the q axis (voltage U cq ), voltage controller G u , current controller G i , capacitive reactanceωC f , inductive reactance ωL1, the component of the current flowing through the first inductor L1 on the d-axis (current i Ld ) and the component on the q axis (current i Lq ), the settings of the voltage loop and the current loop are common knowledge to those skilled in the art and will not be elaborated here.

[0080] In some embodiments, Figure 4 As shown, the converter control method also includes the following method steps:

[0081] Step 401: When the grid-type converter is in the ride-through mode, if the voltage of the filter capacitor decreases and the decrease value is greater than or equal to a first preset threshold, the reactive current in the output current of the grid-type converter is controlled to be a negative value of the transient current amplitude.

[0082] Specifically, the first preset threshold value can be set according to the actual application scenario, and the embodiment of the present application does not impose any specific limitation on this. f The voltage of the filter capacitor C is reduced and the reduction value is greater than or equal to the first preset threshold value. f At this time, according to the above description, under the automatic adjustment of the grid-type converter 100, the transient virtual impedance X d The impedance value and filter capacitor C f The voltage U c Finally, they are kept at a stable value, and the transient virtual impedance X d The impedance value remains greater than zero. In this case, the reactive current in the output current of the grid-connected converter 100 is configured to be the negative value of the transient current amplitude (i.e., I vrtq =-I max , where I vrt is the reactive current in the output current of the grid-type converter 100), so that the voltage output by the entire grid-type converter 100 provides voltage support for the power grid 200. Thus, it is possible to maximize the support capacity of the grid-type converter 100 without overcurrent.

[0083] Step 402: When the grid-type converter is in the crossing mode, if the voltage of the filter capacitor decreases and the decrease value is less than the first preset threshold, or the voltage of the filter capacitor increases, the reactive current is controlled to be a negative value of the ratio of the first difference value to the first sum value, wherein the first difference value is the difference between the first internal potential and the voltage of the grid, and the first sum value is the sum of the static virtual impedance and the impedance of the grid.

[0084] Specifically, the filter capacitor C f The voltage U c The corresponding filter capacitor C f The voltage drop is small. At this time, it can be seen from the above description that under the automatic adjustment of the grid-type converter 100, the filter capacitor C f The voltage U c can gradually return to the first internal potential U vrt The voltage of the transient virtual impedance X d The impedance value gradually decreases to 0. In addition, the filter capacitor C f The voltage U c Increase, filter capacitor C f The voltage U cThe increase in value is usually small, so under the automatic adjustment of the grid-type converter 100, the filter capacitor C f The voltage U c can gradually return to the first internal potential U vrt The voltage of the transient virtual impedance X d The impedance value gradually decreases to 0. It can be seen that in the above two cases, the transient virtual impedance X d The impedance value is 0. At this time, the reactive current is configured to be the negative value of the ratio of the first difference value to the first sum value, that is, I vrtq =-(U vrt -U g ) / (X s +Z g ), where U g is the voltage of the power grid 200, Z g is the impedance of the power grid 200.

[0085] In a specific embodiment, Figure 2 The schematic diagram of each signal in the grid-type converter is shown in FIG. Figure 5 As shown. Figure 5 In the figure, the horizontal axis is time, in seconds (s); the vertical axis is per unit value; each signal is the active current I in the output current of the grid-type converter 100. vrt 、Filter capacitor C f The voltage U C , the voltage U of the power grid 200 g and the reactive current I in the output current of the grid-connected converter 100 vrtq .

[0086] Specifically, in this embodiment, the system short circuit ratio is 6, and the transient current amplitude I max The ratio of the rated current output by the grid-type converter 100 is 2, the voltage of the grid 200 decreases and the filter capacitor C f The voltage U C Rated voltage U n 0.8 times (i.e. 0.8U n , corresponding to the filter capacitor C f The voltage drop is small), and the drop time is 1s (between the 3rd and 4th seconds, the grid-connected converter 100 is in the ride-through mode). Figure 5 As shown, from the 3rd second on, the filter capacitor C f The voltage U C Drop to 0.8U n , then, the filter capacitor C f The voltage U C Can maintain the same as before the 3rd second, the active current I vrtCan maintain the same as before the 3rd second, reactive current I vrtq For: I vrtq =-(U vrt -U g ) / (X s +Z g ), the grid-type converter 100 can provide voltage support and frequency support for the power grid 200.

[0087] In another specific embodiment, Figure 2 The schematic diagram of each signal in the grid-type converter is shown in FIG. Figure 6 As shown. Figure 6 In the figure, the horizontal axis is time, in seconds (s); the vertical axis is per unit value; each signal is the active current I in the output current of the grid-type converter 100. vrt 、Filter capacitor C f The voltage U C , the voltage U of the power grid 200 g and the reactive current I in the output current of the grid-connected converter 100 vrtq .

[0088] Specifically, in this embodiment, the system short circuit ratio is 6, and the transient current amplitude I max The ratio of the rated current output by the grid-type converter 100 is 2, the voltage of the grid 200 decreases and the filter capacitor C f The voltage U C Rated voltage U n 0.2 times (i.e. 0.2U n , corresponding to the filter capacitor C f The voltage U C The drop degree is large), and the drop time is 1s (between the 3rd second and the 4th second, the grid-type converter 100 is in the ride-through mode). Figure 5 As shown, from the 3rd second on, the filter capacitor C f The voltage U C Drop to 0.2U n , due to the filter capacitor C f The voltage U C The drop is large, the active current I vrt is 0, the reactive current I vrtq =-I max , the grid-type converter 100 outputs reactive current in full to provide voltage support for the power grid 200.

[0089] In some embodiments, Figure 7 As shown, the converter control method also includes the following method steps:

[0090] Step 701: When the grid-type converter is in the crossing mode, the maximum active power output by the grid-type converter is determined based on the reactive current, transient current amplitude, the rated current output by the grid-type converter and the first active power output by the grid-type converter when the grid-type converter is in the normal mode.

[0091] Step 702: When the grid-type converter is in the ride-through mode and the first active power is less than or equal to the maximum active power, control the active power output by the grid-type converter to be the first active power.

[0092] Step 703: When the grid-type converter is in the ride-through mode and the first active power is greater than the maximum active power, control the active power output by the grid-type converter to be the maximum active power.

[0093] The first active power is the active power output by the grid-type converter 100 when the grid-type converter 100 is in the normal mode. The maximum active power is the maximum value of the active power that the grid-type converter 100 can output.

[0094] In some embodiments, the specific implementation process of determining the maximum active power output by the grid-type converter based on the reactive current, transient current amplitude, rated current flowing through the second inductor, and the first active power output by the grid-type converter when the grid-type converter is in the normal mode in step 701 includes the following steps: The maximum active power is determined by the following formula (2):

[0095] P max =((1-(I vrtq ) 2 / (I max ) 2 ) 1 / 2 *(I max ) / (I rate ))*P ref0 (2).

[0096] Among them, P max is the maximum active power, I vrtq is the reactive current, I max is the transient current amplitude, I rate is the rated current, P ref0 is the first active power.

[0097] Specifically, through formula (2), it is possible to determine the active power (i.e., the maximum active power) that the grid-type converter 100 can still generate after the reactive power is generated. If the first active power is less than or equal to the maximum active power, it means that the grid-type converter 100 can still generate a large amount of active power, so it is only necessary to control the active power output by the grid-type converter 100 to be the first active power; if the first active power is greater than the maximum active power, it means that the grid-type converter 100 can still generate a small amount of active power, and even if all of it is generated, it will not cause abnormalities such as overcurrent, so it is possible to control the active power output by the grid-type converter 100 to be the maximum active power. At this time, the grid-type converter 100 can provide both voltage support and frequency support for the power grid 200.

[0098] Through the above process, not only can the transient virtual impedance X of the impedance value be automatically adjusted when a disturbance occurs in the power grid 200, but also the transient virtual impedance X of the impedance value can be automatically adjusted when a disturbance occurs in the power grid 200. d Current limiting is performed to reduce the risk of overcurrent in the converter. The grid-type converter 100 can also provide voltage support and frequency support for the power grid 200 and maximize the support capacity of the grid-type converter 100.

[0099] In some embodiments, Figure 8 As shown, the converter control method also includes the following method steps:

[0100] Step 801: Determine the error angular frequency based on the target active power output by the grid-type converter, the actual active power output by the grid-type converter, the virtual moment of inertia, the active power damping coefficient and the system angular frequency of the grid-type converter.

[0101] Step 802: Determine a compensation angular frequency based on a product of a preset compensation function and a q-axis voltage of a filter capacitor.

[0102] Step 803: Determine the angle of the internal potential of the grid-connected converter based on the integral result of the sum of the system angular frequency, the error angular frequency and the compensation angular frequency.

[0103] Among them, the target active power is the preset active power required to be output by the grid-type converter 100. The actual active power is the active power actually output by the grid-type converter. In the grid-type converter 100, the virtual moment of inertia is a virtual parameter, which simulates the mechanical inertia of the synchronous generator through the control algorithm. Specifically, the grid-type converter 100 adjusts its output voltage and frequency to make its behavior similar to that of a synchronous generator with a certain moment of inertia. The active power damping coefficient of the grid-type converter 100 refers to a control parameter used to adjust the flow of active power to increase the stability of the system. Specifically, the active power damping coefficient reflects how the grid-type converter 100 responds to frequency changes in the system, thereby providing the necessary damping effect to suppress low-frequency oscillations in the system. The system angular frequency of the grid-type converter is a key parameter that describes the operating state of the system. The system angular frequency reflects the instantaneous phase change rate of the voltage and current in the system. It is a dynamic variable. The system angular frequency can be adjusted in real time according to the operating state and control strategy of the system.

[0104] In some embodiments, the specific implementation process of determining the error angular frequency in step 801 based on the target active power output by the grid-type converter, the actual active power output by the grid-type converter, the virtual moment of inertia, the active power damping coefficient and the system angular frequency of the grid-type converter includes the following steps: The error angular frequency is determined by the following formula (3):

[0105] Δω=(P ref -P act ) / (ω0*(sJ+D p )) (3).

[0106] Among them, P ref is the target active power, P act is the actual active power, ω0 is the system angular frequency, J is the virtual moment of inertia, D p is the active power damping coefficient.

[0107] In some embodiments, the preset compensation function is a proportional function or a high-pass filter function. Of course, in other embodiments, the preset compensation function may also be other functions, which is not specifically limited in the present embodiment. Compensation angular frequency Δω q =Δω q =G uq *U cq , where G uq is the preset compensation function.

[0108] Then, the angle θ of the internal potential of the grid-type converter 100 is: θ=(Δω+Δω q+ω0) / s, that is, the sum of the system angular frequency, the error angular frequency and the compensation angular frequency is integrated to obtain the angle θ.

[0109] The specific process of determining the angle θ can be Fig. 9 and Fig.10 The control strategy shown in FIG. 1 is used for control. When the grid-connected converter is in normal mode, Fig. 9 As shown, the first switch K1 is controlled to be in the first switch state, so that the target active power P ref The first active power P ref0 ; When the grid-connected converter is in ride-through mode, Fig.10 As shown, the first switch K1 is controlled to be in the second switch state, and the target active power P ref is the active power P that the grid-type converter 100 can output vrt .

[0110] In some embodiments, when a part of the power grid 200 fails, in addition to the disturbance of the voltage amplitude, there is also a phase jump. cq To set the compensation angular frequency Δω q The problem of phase jump can be solved.

[0111] Fig.11 The relationship between the voltage and the current before and after the compensation angular frequency is increased is shown by way of example, wherein: Fig.11 Part (a1) in shows the relationship between voltage and current before increasing the compensation angular frequency, Fig.11 Part (a2) in the figure shows the relationship between voltage and current after increasing the compensation angular frequency. Fig.11 As shown in part (a1) of FIG. 1 , the voltage phase jump of the power grid 200 may correspond to the second internal potential jumping from E to E1 and the voltage of the power grid 200 jumping from U g1 Jump to U g2 , without increasing the compensation angular frequency, since the second internal potential phase changes slightly, the transient current amplitude changes from I1 to I2, the transient current amplitude is large, and the adjustment time to reach the new steady state is longer. Fig.11 As shown in part (a2) of FIG. 1 , similarly, the voltage phase jump of the power grid 200 may correspond to the second internal potential jumping from E to E1 and the voltage of the power grid 200 jumping from U g1 Jump to U g2 , but by increasing the compensation angular frequency, U cq becomes smaller, compensating the angular frequency Δω qWhen it is negative, the internal potential angle can be accelerated to change to a new steady state, that is, the transient current amplitude changes from I1 to I2. The transient current amplitude is small, and the adjustment time to reach the new steady state is short, which can reduce the risk of overcurrent in the grid-type converter 100.

[0112] Fig.12 The schematic diagram of the angle of the internal potential before and after the compensation angular frequency is increased is shown as an example, wherein the horizontal axis is time, in seconds (s); the vertical axis is the angle θ of the internal potential, in radians (rad); θ1 is the angle of the internal potential before the compensation angular frequency is increased, and the angle θ2 is the angle of the internal potential before the compensation angular frequency is increased. Fig.12 As shown, at the 3rd or 5th second, the voltage of the power grid 200 undergoes a phase jump. By comparing the angle θ1 and the angle θ2, it can be obtained that when the compensation angular frequency is increased, the change process of the internal potential angle is significantly accelerated, which helps to improve the stability of the grid-type converter 100.

[0113] In some embodiments, the converter control method further includes the following step: determining the second internal potential when the grid-connected converter is in the normal mode by the following formula (4):

[0114] E=U n +G QPi (Q ref -Q act +D q *(U n -U c )) (4).

[0115] Where E is the second internal potential, U n is the rated voltage of the filter capacitor, G QPi is the reactive power controller, Q ref is the target reactive power output by the grid-connected converter, Q act is the actual reactive power output by the grid-connected converter, D q is the reactive power droop coefficient.

[0116] Then, in some embodiments, the specific implementation process of obtaining the first internal potential when the grid-type converter is in the ride-through mode in step 101 includes the following steps: when the grid-type converter is in the ride-through mode, configuring the input of the reactive power controller to 0 to obtain the first internal potential.

[0117] Please refer to Fig.13 and Fig.14 , Fig.13 and Fig.14 , and the like, show the implementation process of obtaining the first internal potential and the second internal potential. When the grid-type converter is in normal mode, as shown in FIG. Fig.13As shown, the second switch K2 is controlled to be in the third switch state to realize the above formula (4) and obtain the second internal potential; when the grid-type converter is in the ride-through mode, as shown Fig.14 As shown, the second switch K2 is controlled to be in the fourth switch state so that the reactive power controller G QPi The input is 0 to obtain the first internal potential.

[0118] Please refer to Fig.15 , Fig.15 This is a schematic diagram of the structure of the control processing unit provided in the embodiment of the present application. Fig.15 As shown, the control processing unit 1500 includes one or more processors 1501 and a memory 1502. Fig.15 A processor 1501 is taken as an example.

[0119] The processor 1501 and the memory 1502 may be connected via a bus or other means. Fig.15 The example of connecting through bus is taken in the following.

[0120] The memory 1502 is a non-volatile computer-readable storage medium that can be used to store non-volatile software programs, non-volatile computer executable programs and modules. The processor 1501 executes various functional applications and data processing of the terminal interaction device by running the non-volatile software programs, instructions and modules stored in the memory 1502, that is, the converter control method in the above method embodiment is implemented.

[0121] The memory 1502 may include a high-speed random access memory, and may also include a non-volatile memory, such as at least one disk storage device, a flash memory device, or other non-volatile solid-state storage devices. In some embodiments, the memory 1502 may optionally include a memory remotely arranged relative to the processor 1501, and these remote memories may be connected to the processor 1501 via a network. Examples of the above-mentioned network include, but are not limited to, the Internet, an intranet, a local area network, a mobile communication network, and combinations thereof.

[0122] The program instructions / modules are stored in the memory 1502, and when executed by the one or more processors 1501, execute the converter control method in any of the above method embodiments, for example, execute the above described Figure 1 , Figure 4 , Figure 7 and Figure 8 The steps shown.

[0123] An embodiment of the present application also provides a non-volatile computer-readable storage medium, which stores computer-executable instructions. When the computer-executable instructions are executed, the converter control method in any embodiment of the present application is implemented.

[0124] An embodiment of the present application also provides a computer program product, which includes a computer program stored on a computer-readable storage medium, and the computer program includes program instructions. When the program instructions are executed by a computer, the computer executes the converter control method in any embodiment of the present application.

[0125] An embodiment of the present application further provides a grid-type converter, which includes the control processing unit 1500 in any embodiment of the present application, wherein the grid-type converter is connected between a DC voltage and a power grid.

[0126] In some embodiments, the grid-type converter further includes a bus capacitor, an inverter bridge, a first inductor, a filter capacitor and a second inductor, wherein the bus capacitor is connected to the DC voltage and the inverter bridge respectively, the first inductor and the second inductor are connected in series between the converter and the grid, and the filter capacitor is connected between the connection point between the first inductor and the second inductor and the ground. Figure 2 The description is not repeated here.

[0127] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

[0128] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit them. Under the idea of ​​the present application, the technical features in the above embodiments or different embodiments can also be combined, and the steps can be implemented in any order. It should be understood by ordinary technicians in this field that they can still modify the technical solutions recorded in the above embodiments, or replace some of the technical features by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A converter control method, characterized in that: Applied to a grid-type converter, the grid-type converter includes a bus capacitor, an inverter bridge, a first inductor, a filter capacitor and a second inductor, the bus capacitor is connected to a DC voltage and the inverter bridge respectively, the first inductor and the second inductor are connected in series between the inverter bridge and the grid, the filter capacitor is connected between a connection point between the first inductor and the second inductor and ground, the method includes: Acquire a first internal potential and a transient current amplitude when the grid-type converter is in a ride-through mode, and acquire a static virtual impedance and a voltage of the filter capacitor, wherein the grid-type converter is in a ride-through mode when a disturbance occurs in the voltage of the power grid, and the grid-type converter is in a normal mode when the power grid operates normally, the transient current amplitude is the amplitude of the output current of the grid-type converter when the grid-type converter is in the ride-through mode, and the static virtual impedance is a virtual impedance that simulates the reactance characteristics of a synchronous generator; Determining a transient virtual impedance when the grid-connected converter is in a ride-through mode based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor, and the static virtual impedance; Based on the transient virtual impedance, the output current of the grid-connected converter is limited.

2. The method according to claim 1, characterized in that The determining, based on the first internal potential, the transient current amplitude, the voltage of the filter capacitor and the static virtual impedance, of the transient virtual impedance when the grid-type converter is in the ride-through mode comprises: The transient virtual impedance is determined by the following formula: X d =K1(U vrt -U c -(X s +X d )*I max ); Among them, X d is the transient virtual impedance, K1 is a proportional controller, an integral controller or a proportional integral controller, U vrt is the first internal potential, U C is the voltage of the filter capacitor, X S is the static virtual impedance, I max is the transient current amplitude.

3. The method according to claim 1 or 2, characterized in that: The method further comprises: When the grid-connected converter is in the ride-through mode, the following steps are performed: If the voltage of the filter capacitor decreases and the decrease value is greater than or equal to a first preset threshold, the reactive current in the output current of the grid-type converter is controlled to be a negative value of the transient current amplitude; If the voltage of the filter capacitor decreases and the decrease value is less than the first preset threshold, or the voltage of the filter capacitor increases, the reactive current is controlled to be a negative value of the ratio of a first difference value to a first sum value, wherein the first difference value is a difference between the first internal potential and the voltage of the power grid, and the first sum value is the sum of the static virtual impedance and the impedance of the power grid.

4. The method according to claim 1 or 2, characterized in that: The method further comprises: When the grid-connected converter is in the ride-through mode, the following steps are performed: Determine the maximum active power output by the grid-type converter based on the reactive current in the output current of the grid-type converter, the transient current amplitude, the rated current flowing through the grid-type converter output, and the first active power output by the grid-type converter when the grid-type converter is in normal mode; When the first active power is less than or equal to the maximum active power, controlling the active power output by the grid-connected converter to be the first active power; When the first active power is greater than the maximum active power, the active power output by the grid-connected converter is controlled to be the maximum active power.

5. The method according to claim 4, characterized in that The determining of the maximum active power output by the grid-type converter based on the reactive current in the output current of the grid-type converter, the transient current amplitude, the rated current flowing through the grid-type converter output, and the first active power output by the grid-type converter when the grid-type converter is in a normal mode comprises: The maximum active power is determined by the following formula: P max =((1-(I vrtq ) 2 / (I max ) 2 ) 1 / 2 *(I max ) / (I rate ))*P ref0 ; Among them, P max is the maximum active power, I vrtq is the reactive current, I max is the transient current amplitude, I rate is the rated current, P ref0 is the first active power.

6. The method according to claim 1, characterized in that The method further comprises: Determining an error angular frequency based on a target active power output by the grid-type converter, an actual active power output by the grid-type converter, a virtual moment of inertia, an active power damping coefficient, and a system angular frequency of the grid-type converter; Determining a compensation angular frequency based on a product of a preset compensation function and a q-axis voltage of the filter capacitor; Based on the integration result of the sum of the system angular frequency, the error angular frequency and the compensation angular frequency, the angle of the internal potential of the grid-connected converter is determined.

7. The method according to claim 6, characterized in that The step of determining the error angular frequency based on the target active power output by the grid-type converter, the actual active power output by the grid-type converter, the virtual moment of inertia, the active power damping coefficient and the system angular frequency of the grid-type converter comprises: The error angular frequency is determined by the following formula: Give=(P ref -P act ) / (ω0*(sJ+D p )); Among them, P ref is the target active power, P act is the actual active power, ω0 is the system angular frequency, J is the virtual moment of inertia, D p is the active power damping coefficient.

8. The method according to claim 1, characterized in that The method further comprises: The second internal potential when the grid-connected converter is in the normal mode is determined by the following formula: E=U n +G QPi (Q ref -Q act +D q *(U n -U c )); Where, E is the second internal potential, U n is the rated voltage of the filter capacitor, G QPi is the reactive power controller, Q ref is the target reactive power output by the grid-connected converter, Q act is the actual reactive power output by the grid-connected converter, D q is the reactive power droop coefficient.

9. The method according to claim 8, characterized in that The obtaining of a first internal potential when the grid-connected converter is in a ride-through mode comprises: When the grid-connected converter is in the ride-through mode, the input of the reactive power controller is configured to be 0 to obtain the first internal potential.

10. A control processing unit, characterized in that: include: at least one processor and memory; The memory is coupled to the processor, and is used to store instructions or programs. When the instructions or programs are executed by the at least one processor, the at least one processor executes the converter control method according to any one of claims 1 to 9.

11. A grid-type converter, characterized in that: It comprises the control processing unit as claimed in claim 10, wherein the grid-type converter is connected between a DC voltage and a power grid.

12. The grid-type converter according to claim 11, characterized in that: The grid-type converter further includes a bus capacitor, an inverter bridge, a first inductor, a filter capacitor and a second inductor; The bus capacitor is connected to the DC voltage and the inverter bridge respectively, the first inductor and the second inductor are connected in series between the inverter bridge and the power grid, and the filter capacitor is connected between the connection point between the first inductor and the second inductor and the ground.

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