Improved active neutral point clamped topology high reactive power overload control method and device

Abstract

The application discloses an improved high reactive power overload control method and device of an active neutral point clamped topology, and the method comprises the following steps: obtaining an output voltage and a phase angle according to three-phase voltage and three-phase current of a grid-connected point of the topology; obtaining a delay angle according to total loss of an auxiliary diode in the topology; obtaining a zero sequence component according to the delay angle and the phase angle; obtaining d-axis and q-axis target current components according to the output voltage and the phase angle; comparing the q-axis target current component with a preset threshold to obtain an overload flag bit; respectively limiting the amplitude of the d-axis and q-axis target current components according to the overload flag bit to obtain a first current instruction and a second current instruction; obtaining three-phase modulation signals according to the first current instruction and the second current instruction; when the overload flag bit shows that the topology is in a normal state, modulating switching signals of IGBT tubes according to the three-phase modulation signals, otherwise, injecting the zero sequence component into the three-phase modulation signals and then modulating.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power electronics, and in particular to a high reactive power overload control method and device for an improved active neutral point clamped topology. BACKGROUND

[0002] With the continuous increase of new energy penetration, the short-circuit ratio and voltage support capability of the power grid decrease year by year, and the grid-connected converter is required to provide network support. GFMCs (Grid-Forming Converters) can provide virtual inertia and damping for the grid by simulating the physical characteristics of synchronous generators, so they are widely used.

[0003] An important feature of GFMCs is to maintain voltage source characteristics in operation. In the event of a power grid fault, the voltage difference generated by the grid connection point is responded to the reactive power to achieve voltage support and enhance the transient stability of the system. However, the traditional GFMCs are limited by the junction temperature of power devices during the fault process, and must be current-limited, which seriously affects the voltage support capability of the grid. In order to improve the voltage support effect of GFMCs, it is necessary to improve the short-time overload capacity, and the core is to suppress the rapid rise of device junction temperature and avoid thermal protection action under overload conditions. The research on the reactive power overload capacity of active neutral point clamped topology GFMCs usually starts from three aspects of control optimization, heat dissipation improvement and hardware redundancy. In the aspect of control optimization, the device junction temperature is reduced by adjusting the loss-related parameters such as switching frequency and duty cycle, and the control optimization method has low implementation cost, but the change of modulation parameters may cause fluctuations in system control performance, and the cooling effect is limited; in the aspect of heat dissipation improvement, the instantaneous heat of power devices is absorbed by using phase change heat conduction materials to enhance the short-time overload capacity, but this scheme does not consider the problem of heat accumulation under long-time reactive output; in the aspect of hardware redundancy, the capacity expansion is realized by selecting larger capacity devices and device parallel connection, and the hardware redundancy method has significant effect, but greatly increases the volume and cost of the system. That is, the existing technology usually faces the problems of insufficient dynamic adaptability, cost increase or structural complexity, and it is difficult to controllably improve the reactive power overload capacity of the active neutral point clamped topology.

[0004] Therefore, there is an urgent need for a new technical solution to solve the technical problem of how to improve the reactive power overload capacity of the active neutral point clamped topology. SUMMARY

[0005] The present application provides an improved active neutral point clamped topology high reactive power overload control method and device to solve the technical problem of how to improve the reactive power overload capacity of the active neutral point clamped topology.

[0006] To achieve the above purpose, the present application provides an improved active neutral point clamped topology high reactive power overload control method, comprising:

[0007] obtaining output voltage and phase angle according to grid-connected point three-phase voltage and three-phase current of the topology; obtaining delay angle according to total loss of auxiliary diode in the topology; the total loss includes conduction loss and reverse recovery loss under modulation signal considering the delay angle; obtaining zero sequence component according to the delay angle and the phase angle;

[0008] obtaining d-axis and q-axis target current components according to the output voltage and the phase angle; comparing the q-axis target current component with a preset threshold to obtain an overload flag bit;

[0009] amplifying the d-axis and q-axis target current components respectively according to the overload flag bit to obtain first and second current instructions; obtaining three-phase modulation signal according to the first and second current instructions;

[0010] when the overload flag bit shows that the topology is in a normal state, modulating switching signal of IGBT according to the three-phase modulation signal, otherwise injecting zero sequence component to the three-phase modulation signal and then modulating.

[0011] Preferably, obtaining output voltage and phase angle according to grid-connected point three-phase voltage and three-phase current of the topology comprises:

[0012] obtaining grid-connected point three-phase voltage and three-phase current of the topology; performing Park transformation on the grid-connected point three-phase voltage and three-phase current respectively to obtain dq voltage component and dq current component;

[0013] performing instantaneous power calculation according to the dq voltage component and the dq current component to obtain instantaneous active and reactive power;

[0014] performing amplitude calculation according to the dq voltage component to obtain system voltage amplitude;

[0015] obtaining output voltage and phase angle according to the instantaneous active and reactive power and the system voltage amplitude.

[0016] Preferably, obtaining delay angle according to total loss of auxiliary diode in the topology comprises:

[0017] modeling conduction loss and reverse recovery loss of the auxiliary diode in the topology to obtain a first expression;

[0018] modeling modulation signal considering the delay angle to obtain a second expression;

[0019] solving the first expression and the second expression to obtain total loss expression of the auxiliary diode;

[0020] solving the total loss expression to obtain the delay angle.

[0021] Preferably, solving the total loss expression to obtain the delay angle comprises:

[0022] Deriving the total loss expression, the interval where the total loss maximum value is located is obtained, denoted as a first interval;

[0023] If the total loss expression is continuous and piecewise derivable in the first interval, the solution at the derivative of 0 is the delay angle; if there is no solution at the derivative of 0, the delay angle appears at the piecewise point, and the delay angle is obtained by comparing the values of the piecewise points.

[0024] Preferably, the zero sequence component is obtained according to the delay angle and the phase angle, and includes:

[0025] The selection coefficient is obtained according to the delay angle and the phase angle k , the selection coefficient k includes a square wave signal three times the fundamental frequency, including:

[0026] ;

[0027] wherein, that is, the selection coefficient k ; represents the delay angle; represents the phase angle; n and d has no actual meaning, and is used to represent n is an odd number or an even number;

[0028] The zero sequence component is obtained according to the selection coefficient and the maximum value and the minimum value of the three-phase voltage, and includes:

[0029] ;

[0030] ;

[0031] wherein, and represent the three-phase voltage.

[0032] Preferably, the d-axis and q-axis target current components are obtained according to the output voltage and the phase angle, and include:

[0033] The d-axis and q-axis target current components are obtained according to the output voltage and the phase angle in combination with an impedance equation between the virtual internal potential and the point of interconnection, and include:

[0034] ;

[0035] ;

[0036] wherein, and are the three-phase virtual internal potentials, which are obtained according to the output voltage and the phase angle. and respectively represent q-axis output voltage component and d-axis output voltage component; and respectively represent d-axis and q-axis target current component; represents virtual resistance; represents virtual reactance; represents angular frequency; represents grid point d-axis voltage component; represents grid point q-axis voltage component.

[0037] Preferably, the q-axis target current component is compared with a preset threshold to obtain an overload flag, including:

[0038] When the q-axis target current component is less than or equal to the preset threshold, it indicates that the converter is in a normal state, and the overload flag is equal to 0; when the q-axis target current component is greater than the preset threshold, it indicates that the converter is in an overload state, and the overload flag is equal to 1.

[0039] Preferably, the d-axis and q-axis target current components are respectively limited according to the overload flag to obtain the first current instruction and the second current instruction, including:

[0040] When the overload flag is equal to 0, the current limiting value of the d-axis and the q-axis is set to the maximum value of the rated current, and the phase angle remains unchanged, to obtain the first current instruction and the second current instruction respectively;

[0041] When the overload flag is equal to 1, the d-axis current limiting value is set to 0 to obtain the first current instruction; the q-axis current limiting value is increased to a preset overload threshold to obtain the second current instruction.

[0042] Preferably, the three-phase modulation signal is obtained according to the first current instruction and the second current instruction, including:

[0043] The uncompensated voltage reference signal is obtained according to the first current instruction, the second current instruction and the dq current component; the three-phase modulation signal is obtained by performing inverse Park transformation on the uncompensated voltage reference signal after compensating the dq voltage component.

[0044] The application also provides an improved active neutral point clamped topology high reactive power overload control device, which is used in the method of the application, and the device includes a first module, a second module, a third module and a fourth module;

[0045] The first module is used to obtain the output voltage and the phase angle according to the grid point three-phase voltage and three-phase current of the topology; the delay angle is obtained according to the total loss of the auxiliary diode in the topology; the total loss includes the conduction loss and the reverse recovery loss under the modulation signal considering the delay angle; the zero sequence component is obtained according to the delay angle and the phase angle;

[0046] The second module is used to obtain the target current components of the d-axis and q-axis based on the output voltage and phase angle; the target current component of the q-axis is compared with a preset threshold to obtain the overload flag bit;

[0047] The third module is used to limit the target current components of the d-axis and q-axis according to the overload flag, and obtain the first current command and the second current command; and to obtain the three-phase modulation signal according to the first current command and the second current command.

[0048] The fourth module is used to modulate the switching signal of the IGBT tube according to the three-phase modulation signal when the overload flag indicates that the topology is in a normal state; otherwise, it injects a zero-sequence component into the three-phase modulation signal before modulation.

[0049] The present invention has the following beneficial effects:

[0050] The improved reactive power overload control method for active neutral point clamping topology of this invention preferentially guides reactive current to the auxiliary diode circuit, thereby reducing the junction temperature of the ANPC bridge arm and effectively improving the reactive power overload capacity of the three-level topology converter without significantly increasing costs, thus enhancing the grid voltage support effect of the grid-connected converter. This invention also clamps the modulation wave to ±1 by injecting a zero-sequence component into the three-phase sinusoidal reference modulation signal, thereby keeping the auxiliary diode in a continuously conducting or continuously off state for one-third of the power frequency cycle, improving the loss sharing effect of the auxiliary diode.

[0051] The high reactive power overload control device of the improved active midpoint clamping topology of the present invention, when used in the method of the present invention, has the same beneficial effects as the method of the present invention.

[0052] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0053] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0054] Figure 1 This is a schematic diagram of an improved active midpoint clamping topology according to a preferred embodiment of the present invention.

[0055] Figure 2 This is a schematic diagram of the auxiliary diode providing a new freewheeling path for the ANPC bridge arm in a preferred embodiment of the present invention.

[0056] Figure 3 This is a schematic diagram of the method flow of a preferred embodiment of the present invention.

[0057] Figure 4 is a method control block diagram of a preferred embodiment of the present application.

[0058] Figure 5 is a schematic diagram of a prior art auxiliary diode shunt of a preferred embodiment of the present application.

[0059] Figure 6 is a schematic diagram of a calculated delay angle at different switching frequencies of a preferred embodiment of the present application.

[0060] Figure 7 is a thermal simulation result diagram of a conventional ANPC converter under maximum overload condition of a preferred embodiment of the present application.

[0061] Figure 8 is a thermal simulation result diagram of the topology of the present application under maximum overload condition of a preferred embodiment of the present application. DETAILED DESCRIPTION

[0062] Embodiments of the present application are described in detail below with reference to the accompanying drawings, but the present application can be implemented in various different ways as defined and covered by the claims.

[0063] Referring to Figure 1 , the improved active neutral point clamped topology of a preferred embodiment of the present application comprises an ANPC (Active Neutral Point Clamped) bridge arm and an auxiliary diode bridge arm; the ANPC bridge arm and the auxiliary diode bridge arm each comprise a structure same as and three phases, and the and three phases of the ANPC bridge arm and the auxiliary diode bridge arm are connected correspondingly.

[0064] In each phase of the ANPC bridge arm, IGBT tubes T 1 , T 2 , T 3 , T 4 , T 5 and T 6 as well as anti-parallel diodes D 2 、 D 3 、D 5 and D 6 ; and T 1the collector electrode of the diode is electrically connected to the positive pole of the DC bus V P the emitter electrode of the diode is electrically connected to the positive pole of the DC bus T 2 the collector electrode of the diode is electrically connected to the positive pole of the DC bus T 5 the collector electrode of the diode is electrically connected to the positive pole of the DC bus T 2 the emitter electrode of the diode is electrically connected to the positive pole of the DC bus T 3 the collector electrode of the diode is electrically connected to the positive pole of the DC bus T 5 the emitter electrode of the diode is electrically connected to the positive pole of the DC bus T 6 the collector electrode of the diode is electrically connected to the positive pole of the DC bus O ; T 3 the emitter electrode of the diode is electrically connected to the positive pole of the DC bus T 6 the emitter electrode of the diode is electrically connected to the positive pole of the DC bus T 4 the collector electrode of the diode is electrically connected to the positive pole of the DC bus T 4 the emitter electrode of the diode is electrically connected to the positive pole of the DC bus V N the positive pole of the upper capacitor is electrically connected to the positive pole of the DC bus C dc1 the positive pole of the upper capacitor is electrically connected to the positive pole of the DC bus V P the negative pole of the lower capacitor is electrically connected to the negative pole of the DC bus C dc2 the negative pole of the lower capacitor is electrically connected to the negative pole of the DC bus V N ，C dc1 the negative pole of the lower capacitor is electrically connected to the negative pole of the DC bus C dc2 the positive pole of the upper capacitor is electrically connected to the positive pole of the DC bus to form a neutral point O. In the above device, T 2 , T 3 , T 5 and T 6 a power module with an anti-parallel diode is used, T 1 and T 4 a single tube module is used.

[0065] In each phase of the auxiliary diode bridge arm, an auxiliary diode and is included; and the auxiliary diodes are connected in series in the same direction, the cathode is electrically connected to the positive pole of the DC bus , the anode is electrically connected to the negative pole of the DC bus , Anode and Cathode is electrically connected to the converter output. When selecting the auxiliary diode of the improved active neutral point clamped topology of the application, the maximum reverse breakdown voltage value should be set according to the sum of the maximum voltage of T 1 and T 2 .

[0066] The auxiliary diode in the improved active neutral point clamped topology can provide a freewheeling path for current in a specific working state, realize shunt of ANPC bridge arm devices, reduce device junction temperature, and thus improve the reactive overload capacity of the system. The specific principle includes:

[0067] The traditional ANPC bridge arm can output three different levels, which are positive level (P), negative level (N) and zero level (O). When the traditional ANPC converter outputs reactive power, the voltage phase leads the current by 90°, at this time, if the converter outputs P or N state, and the current is negative, the current will flow through the antiparallel diode, resulting in significant conduction loss and reverse recovery loss of the antiparallel diode. These losses not only cause serious self-heating of the diode, but also cause significant thermal coupling to the power devices in the same package, thereby limiting the reactive overload capacity of the converter. However, in the improved active neutral point clamped topology of the application, referring to Figure 2 , the auxiliary diode provides a new freewheeling path for the ANPC bridge arm. In the ANPC bridge arm D 2 and D 3 The device loss is reduced, and considering the thermal coupling effect, the corresponding IGBT device T 2 and T 3 The thermal stress is reduced; and because the original ANPC bridge arm device D 1 and D 4 is moved out to become and , T 1 and T 4 No longer affected by the thermal coupling of the original diode D 1 and D 4 . In summary, compared with the traditional ANPC topology, the addition of the auxiliary diode in the improved active neutral point clamped topology can directly alleviate the thermal stress of the external device T 1 , T 2 ,D 2 、 T 3 、 T 4 and D 3 thermal stress.

[0068] In the improved active neutral point clamped topology of the present application, the ANPC bridge arm can achieve the redistribution of power device loss distribution by selecting the switching combination of different O levels, thereby effectively balancing the thermal stress of each device. Considering that the auxiliary diode in the improved active neutral point clamped topology can only alleviate the thermal stress of external devices T 1 、 T 2 、 D 2 、 T 3 、 T 4 and D 3 thermal stress, in order to reduce the junction temperature of all devices during overload and improve the overall reactive overload capability, it is necessary to optimize the commutation loop and modulation strategy to simultaneously reduce the thermal stress of internal devices T 5 、 D 5 、 T 6 and D 6 thermal stress. To this end, the ANPC bridge arm in the improved active neutral point clamped topology of the present application adopts the switching state shown in Table 1.

[0069] Table 1 ANPC switching state table

[0070]

[0071] wherein, x represents and three-phase; represents the DC voltage of the converter. The switching signals in Table 1 are generated using the double carrier PWM modulation method. state is only used in the positive half cycle of the current, state is only used in the negative half cycle of the current. By selecting the switching state in Table 1, the switching times of internal devices T 5 、 D 5 、 T 6 and D 6 can be reduced, thereby reducing their thermal stress.

[0072] Considering the cost and performance benefits of the device, the selected topology in the application can significantly enhance the system voltage support capability, has higher economy, and has the potential for large-scale industrial application in network type converter scenarios. In addition, in various multi-level topologies, auxiliary diodes can be used to share reactive loss, which can improve the overload capacity of the converter without increasing the cost too much. The application scheme can derive more topologies and modulation strategies, and broaden the application range of network type energy storage.

[0073] In order to make the auxiliary diode share the loss as much as possible, and further reduce the power loss of the internal device T 5 、 D 5 、 T 6 and D 6 , see Figures 3-4 , the preferred embodiment of the application provides a high reactive overload control method of an improved active neutral point clamping topology, comprising:

[0074] F1, obtain the output voltage and phase angle according to the grid-connected point three-phase voltage and three-phase current of the topology; obtain the delay angle according to the total loss of the auxiliary diode in the topology; the total loss includes the conduction loss and reverse recovery loss under the modulation signal considering the delay angle; obtain the zero sequence component according to the delay angle and the phase angle.

[0075] In the preferred embodiment of the application, obtaining the output voltage and phase angle according to the grid-connected point three-phase voltage and three-phase current of the topology comprises:

[0076] Referring to Figure 4 , the grid-connected point three-phase voltage and three-phase current of the topology are obtained by sampling the control unit; the grid-connected point three-phase voltage and three-phase current are respectively Park transformed to obtain the dq voltage component and the dq current component . In Figure 4 , the line impedance is , and the grid voltage is .

[0077] According to the dq voltage component and the dq current component, the instantaneous power is calculated to obtain the instantaneous active power and the reactive power , comprising:

[0078] ;

[0079] Among them, is the grid-connected point voltage; is the filter reactance; is the system power angle.

[0080] According to the amplitude calculation of the dq voltage component, the system voltage amplitude , comprising:

[0081] ;

[0082] wherein, represents the d-axis voltage component of the grid-connected point; represents the q-axis voltage component of the grid-connected point.

[0083] Referring to Figure 4 , the output voltage and the phase angle are obtained by the grid construction control unit according to the instantaneous active power and the reactive power E and the system voltage amplitude , comprising:

[0084] ;

[0085] ;

[0086] wherein, is the inertia constant; and respectively represent the voltage amplitude and the angular frequency of the grid-connected point; represents the angular frequency; t represents time; and respectively represent the reference values of the active power, the reactive power and the rated voltage; D p and D q respectively deploy the droop coefficients of the active-frequency and the reactive-voltage; represents the reactive integral coefficient.

[0087] In the preferred embodiment of the application, the delay angle is obtained according to the total loss of the auxiliary diode in the topology, comprising:

[0088] According to the modeling of the conduction loss and the reverse recovery loss of the auxiliary diode in the topology, the first expression is obtained, comprising:

[0089] The conduction loss and reverse recovery loss of the auxiliary diode can be expressed as:

[0090]

[0091]

[0092] The following parameters can be obtained by interpolation according to the typical values in the device data manual: where, and are the conduction and turn-off time of the device in one fundamental period; is the current flowing through the diode; is the modulation signal considering the delay angle; is the frequency of the inverter switch; and the conduction voltage drop of the diode change approximately linearly with temperature; is the energy consumed in the primary turn-off process of the diode, and its expression includes:

[0093]

[0094] where, A , B and C are the quadratic function fitting coefficients; and are the typical voltages and temperatures in the data manual; and are the reverse recovery loss correction coefficients; is the DC voltage of the inverter, is the working junction temperature of the device.

[0095] The modulation signal considering the delay angle is modeled to obtain the second expression, including:

[0096]

[0097]

[0098]

[0099] where, m is the modulation degree.

[0100] ​​​​​​According to the first expression and the second expression, a total loss expression of the auxiliary diode is obtained, including:

[0101] ;

[0102] ;

[0103] wherein, represents the total loss of the auxiliary diode; represents an instantaneous conduction loss, wherein and respectively represent a forward voltage drop and a conduction resistance of the anti-parallel diode; the above parameters can be extracted from a device data manual. and represents a modulation waveform of the modulation signal in different intervals considering a delay angle; represents a zero-crossing point of the modulation wave after injecting a zero sequence component. is a current flowing through the diode; is a switching frequency of the converter, and the above parameters are determined by the design of the converter.

[0104] According to the total loss expression, the delay angle is obtained.

[0105] In the preferred embodiment of the present application, according to the total loss expression, the delay angle is obtained, including:

[0106] It can be approximately considered that when the auxiliary diode shares the maximum power loss, the device junction temperature of the ANPC bridge arm is the lowest, and the converter obtains the maximum overload capacity. The total loss expression is derived to obtain an interval where the maximum value of the total loss is located, which is recorded as a first interval;

[0107] If the total loss expression is continuous and piecewise derivable in the first interval, the solution at the point where the derivative is 0 is the delay angle; if there is no solution at the point where the derivative is 0, the delay angle appears at the piecewise point, and the delay angle is obtained by comparing the values of the piecewise points.

[0108] In the preferred embodiment of the present application, when the auxiliary diode shares the maximum loss; by derivation of , the interval where the maximum value is located can be determined; in the interval , the maximum value is obtained in the interval . In the interval, the function is continuous and piecewise derivable, so the internal point where the derivative is 0 corresponds to the optimal delay angle, that is, the solution of the first calculation formula in the interval ; if there is no solution of the first calculation formula in the interval, the optimal delay angle appears at the piecewise point, and the optimal delay angle is obtained by comparing the values of the piecewise points. The first calculation formula includes:

[0109] ;

[0110] wherein, is the current amplitude, determined by the converter design.

[0111] In the preferred embodiment of the present application, referring to Figure 4 , the zero sequence component is obtained by the GDPWM modulation unit according to the delay angle and the phase angle, comprising:

[0112] The selection coefficient is obtained according to the delay angle and the phase angle k , the selection coefficient k comprises a square wave signal three times the fundamental frequency, comprising:

[0113] ;

[0114] wherein, that is, the selection coefficient k ; represents the delay angle, used to control the angle between the square wave signal k and the sine target signal, thereby affecting the position of the "continuous conduction" region of the auxiliary diode and adjusting the loss sharing effect. represents the phase angle generated by the grid forming control unit; n and d have no actual meaning, and are used to represent n is an odd number or an even number.

[0115] The zero sequence component is obtained according to the selection coefficient and the maximum value and the minimum value of the three-phase voltage, comprising:

[0116] ;

[0117] ;

[0118] wherein, and represent the three-phase voltage.

[0119] F2, obtaining the d-axis and q-axis target current components according to the output voltage and the phase angle; comparing the q-axis target current component with a preset threshold to obtain an overload flag bit.

[0120] In the preferred embodiment of the present application, obtaining the d-axis and q-axis target current components according to the output voltage and the phase angle comprises:

[0121] Obtaining the d-axis and q-axis target current components according to the output voltage and the phase angle in combination with an impedance equation between the virtual internal potential and the grid connection point, comprising:

[0122] ;

[0123] ;

[0124] wherein, and are the virtual internal potentials of the three phases, which are derived from the output voltage and the phase angle; and represent the q-axis output voltage component and the d-axis output voltage component, respectively; and represent the d-axis and q-axis target current components, respectively; represents the virtual resistance; represents the virtual reactance; represents the angular frequency; represents the grid point d-axis voltage component; represents the grid point q-axis voltage component.

[0125] In the preferred embodiment of the present application, referring to Figure 4 , the q-axis target current component is compared with a preset threshold value by the overload control unit to obtain an overload flag, including:

[0126] When the q-axis target current component is less than or equal to the preset threshold value, it indicates that the converter is in a normal state, and the overload flag is equal to 0; when the q-axis target current component is greater than the preset threshold value, it indicates that the converter is in an overload state, and the overload flag is equal to 1. The preset threshold value is a preset maximum value, i.e. Figure 4 . .

[0127] F3, according to the overload flag, the d-axis and q-axis target current components are respectively limited in amplitude to obtain the first current instruction and the second current instruction; and according to the first current instruction and the second current instruction, a three-phase modulation signal is obtained.

[0128] In the preferred embodiment of the present application, according to the overload flag, the d-axis and q-axis target current components are respectively limited in amplitude to obtain the first current instruction and the second current instruction, including:

[0129] Referring to Table 2, when the overload flag is equal to 0, the current limiting values of the d-axis and q-axis are both set to the maximum value of the rated current, and the phase angle remains unchanged, to obtain the first current instruction and the second current instruction . When the overload flag is equal to 1, the d-axis current limiting value is set to 0 to obtain the first current instruction ; the q-axis current limiting value is increased to a preset overload threshold value to obtain the second current instruction to achieve the maximum reactive output capability without triggering the thermal protection.

[0130] Table 2 current limiting value setting table

[0131]

[0132] In the preferred embodiment of the present application, obtaining the three-phase modulation signal according to the first current instruction and the second current instruction comprises:

[0133] Referring to Figure 4 , obtaining the uncompensated voltage reference signal through the current inner loop according to the first current instruction, the second current instruction and the dq current component; performing Park inverse transformation on the uncompensated voltage reference signal after compensation through the dq voltage component to obtain the three-phase modulation signal and comprise:

[0134] ;

[0135] wherein, is a Park inverse transformation matrix; and are proportional and integral coefficients of the current inner loop; s is a Laplace operator; and are the d-axis current component and the q-axis current component of the grid-connected point respectively.

[0136] F4, when the overload flag bit shows that the topology is in a normal state, modulating the switching signal of the IGBT tube according to the three-phase modulation signal, otherwise injecting a zero sequence component into the three-phase modulation signal and then modulating. Comparing the final modulation signal with the carrier to generate the corresponding switching signal, and driving the IGBT to turn on and off.

[0137] Figure 5 The waveforms of the final modulation signal , phase current and auxiliary diode current before and after injecting the zero sequence component are shown. It can be seen from the comparison that after the zero sequence component is injected, the auxiliary diode appears in the "continuous conduction" region, which can share more ANPC bridge arm power loss. In the continuous conduction region, the converter maintains the output P or N state, prolongs the conduction time of the auxiliary diode, thereby enhancing its loss sharing capability; in addition, due to the reduction of the O output state, the conduction loss of the internal device is further reduced.

[0138] The high reactive power overload control method of the improved active neutral point clamped topology of the application preferentially guides the reactive current to the auxiliary diode loop, thereby reducing the ANPC bridge arm junction temperature, effectively improving the reactive power overload capacity of the three-level topology converter, and improving the grid voltage support effect of the grid-connected converter.

[0139] In the preferred embodiment of the application, an improved high reactive power overload control device for the active neutral point clamped topology is also provided, which is used in the method of the application, and the device comprises a first module, a second module, a third module and a fourth module.

[0140] The first module is used to obtain an output voltage and a phase angle according to three-phase voltages and three-phase currents at a grid-connected point of the topology, to obtain a delay angle according to total losses of auxiliary diodes in the topology, and to obtain a zero sequence component according to the delay angle and the phase angle, wherein the total losses include conduction losses and reverse recovery losses under a modulation signal considering the delay angle.

[0141] The second module is used to obtain d-axis and q-axis target current components according to the output voltage and the phase angle, and to obtain an overload flag by comparing the q-axis target current component with a preset threshold.

[0142] The third module is used to limit the d-axis and q-axis target current components according to the overload flag to obtain a first current instruction and a second current instruction, and to obtain a three-phase modulation signal according to the first current instruction and the second current instruction.

[0143] The fourth module is used to modulate switching signals of IGBTs according to the three-phase modulation signal when the overload flag indicates that the topology is in a normal state, or to modulate the switching signals after injecting a zero sequence component into the three-phase modulation signal.

[0144] The improved high reactive power overload control device for the active neutral point clamped topology of the application is used in the method of the application, and has the same beneficial effects as the method of the application.

[0145] Verification part:

[0146] The method of the application is verified by Simulink / Plecs software.

[0147] Referring to Figure 1 the circuit structure and Figure 4 the control block diagram, a circuit model is built in simulation software, and device selection and parameters are shown in Table 3, and device thermal simulation parameters are provided by Infineon data manual and official simulation model.

[0148] Table 3. Simulation Parameters of Low-Cost High Reactive Power Overload Energy Storage Converter Topology

[0149]

[0150] The auxiliary diode module is a passive device, requiring no gate drive, and is less expensive than the IGBT module. Therefore, adding an auxiliary diode branch does not significantly increase device cost. In a traditional ANPC converter, the total cost of the power module (FF300R12ME4) and drive circuit (2SP0115T) is 9585 yuan (LCSC Mall). Introducing three auxiliary diodes (DD220N22S) increases the device cost by an additional 1014 yuan, accounting for only 9.6% of the total device cost. The improved active midpoint clamping topology of the preferred embodiment of this invention achieves a significant performance improvement with only a slight increase in cost.

[0151] To verify the effectiveness of the optimal delay angle calculation method of the present invention. Figure 6 The optimal delay angle values ​​obtained through calculation and simulation methods at different switching frequencies are presented. The dashed line represents the delay angle values ​​obtained through simulation at different switching frequencies. The solid line is The auxiliary diode loss sharing curve obtained through modeling has its extreme points corresponding to those calculated by the first formula. The value is represented by a circular ring. At the switching frequency... The results were obtained through calculations at 3k, 5k, 7.5k, and 10k. The values ​​are 1.951, 1.953, 1.997, and 2.015, respectively, which agree well with the simulation results. This method can effectively calculate the optimal delay angle that enables the improved active midpoint clamping topology of the preferred embodiment of the present invention to achieve the maximum overload capacity. .

[0152] Figure 7 The inherent transient overload capability of a conventional ANPC topology converter at a rated switching frequency of 5kHz was tested. To simulate daily operating conditions, the converter stably outputs 0.9 pu of active power before overload. To ensure safe operation, the junction temperature limit was set to 125℃. A symmetrical fault occurred after 3 seconds, and the grid voltage... U g The voltage dropped to 0.6 pu, and the grid voltage returned to normal after 0.2 seconds. (PCC point (grid connection point) voltage) Current The highest junction temperature of the device in the ANPC bridge arm is as follows: Figure 7 As shown.

[0153] The traditional ANPC topology converter without any overload capacity enhancement control strategy can output 1.337 p.u. maximum reactive current after grid voltage drop fault, and can support the PCC point voltage to 0.775 p.u. under the working condition of the embodiment. T 1 The switching frequency is high, the current flowing through is large, and the junction temperature is the highest among all switching devices, and first reaches 125 DEG C.

[0154] The simulation conditions are kept unchanged, Figure 8 The PCC point voltage, current, the highest device junction temperature in the ANPC bridge arm and the auxiliary diode junction temperature of the improved active neutral point clamped topology of the preferred embodiment of the present application are given after the method of the present application is added.

[0155] As analyzed in the foregoing, when the converter is normally working, the current only flows through the ANPC bridge arm, and the auxiliary diode is in a hot standby state; when the grid voltage drops, the converter adopting the grid-forming control method outputs a large amount of reactive power to support the grid voltage, at this time, the auxiliary diode shares the ANPC bridge arm current, effectively reduces the ANPC bridge arm junction temperature, and improves the overload capacity of the converter.

[0156] By adopting the method of the present application, 1.835 p.u. maximum reactive current can be output after grid voltage drop fault, and the PCC point voltage can be supported to 0.842 p.u. under the working condition. Similarly, since the switching devices T 1 The switching frequency is high, the current flowing through is large, and the junction temperature is the highest among all switching devices, and first reaches 125 DEG C. Through simulation verification, the topology and modulation strategy of the preferred embodiment of the present application can enhance the reactive overload capacity of the converter, and can effectively improve the grid voltage support effect of the grid-forming converter.

[0157] The above only describes the preferred embodiments of the present application and is not used to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for high reactive power overload control of an improved active neutral point clamped topology, characterized in that, The method comprises the following steps: obtaining output voltage and phase angle according to grid-connected point three-phase voltage and three-phase current of the topology; obtaining delay angle according to total loss of auxiliary diode in the topology; the total loss comprises conduction loss and reverse recovery loss under modulation signal considering the delay angle; obtaining zero sequence component according to the delay angle and the phase angle; obtaining d-axis and q-axis target current components according to the output voltage and phase angle; comparing the q-axis target current component with a preset threshold to obtain an overload flag bit; amplifying the d-axis and q-axis target current components respectively according to the overload flag bit to obtain first and second current instructions; obtaining three-phase modulation signal according to the first and second current instructions; when the overload flag bit shows that the topology is in a normal state, modulating switching signal of IGBT according to the three-phase modulation signal, otherwise, injecting the zero sequence component into the three-phase modulation signal before modulation.

2. The improved high reactive load overload control method of active neutral point clamped topology according to claim 1, characterized in that, The step of obtaining output voltage and phase angle according to grid-connected point three-phase voltage and three-phase current of the topology comprises the following steps: obtaining grid-connected point three-phase voltage and three-phase current of the topology; performing Park transformation on the grid-connected point three-phase voltage and three-phase current respectively to obtain dq voltage component and dq current component; performing instantaneous power calculation according to the dq voltage component and the dq current component to obtain instantaneous active and reactive power; performing amplitude calculation according to the dq voltage component to obtain system voltage amplitude; obtaining the output voltage and phase angle according to the instantaneous active and reactive power and the system voltage amplitude.

3. The improved high reactive load overload control method of active neutral point clamped topology according to claim 2, characterized in that, The step of obtaining delay angle according to total loss of auxiliary diode in the topology comprises the following steps: modeling conduction loss and reverse recovery loss of auxiliary diode in the topology according to the first expression; modeling modulation signal considering the delay angle according to the second expression; solving the first expression and the second expression to obtain total loss expression of the auxiliary diode; solving the total loss expression to obtain the delay angle.

4. The improved high reactive load overload control method of active neutral point clamped topology according to claim 3, characterized in that, The step of solving the total loss expression to obtain the delay angle comprises the following steps: deriving the total loss expression to obtain a total loss maximum value interval, denoted as a first interval; if the total loss expression is continuous and piecewise derivable in the first interval, the solution at the point where the derivative is 0 is the delay angle; if there is no solution at the point where the derivative is 0, the delay angle appears at the piecewise point, and the delay angle is obtained by comparing the values of the piecewise points.

5. The improved high reactive load overload control method of active neutral point clamped topology according to claim 3, characterized in that, The step of obtaining zero sequence component according to the delay angle and the phase angle comprises the following steps: a selection coefficient is obtained from the delay angle and the phase angle k , the selection coefficient k comprising a square wave signal three times the fundamental frequency, comprising: ； wherein i.e. selection coefficient k ; denotes the delay angle; denotes the phase angle; n and d has no actual meaning and is used to denote n is odd or even; According to the selection coefficient and the maximum value of the three-phase voltage and the minimum value to obtain the zero sequence component comprising: ； ； wherein u a , u b and u c denotes a three-phase voltage.

6. The improved high reactive load overload control method of active neutral point clamped topology according to claim 5, characterized in that, The step of obtaining d-axis and q-axis target current components according to the output voltage and phase angle comprises the following steps: obtaining the d-axis and q-axis target current components according to the output voltage and phase angle and impedance equation between virtual internal potential and grid-connected point, comprising: ； ； wherein and is a virtual internal potential of the three phases, derived from the output voltage and the phase angle; E d and E q denote the q-axis and d-axis output voltage components, respectively; and denote the d-axis and q-axis target current components, respectively; denotes a virtual resistance; denotes a virtual reactance; denotes an angular frequency; denotes the d-axis voltage component at the point of common coupling; denotes the q-axis voltage component at the point of common coupling.

7. The improved high reactive load overload control method of active neutral point clamped topology according to claim 6, characterized in that, The step of comparing the q-axis target current component with a preset threshold to obtain an overload flag bit comprises the following steps: when the q-axis target current component is less than or equal to the preset threshold, it indicates that the converter is in a normal state, and the overload flag bit is equal to 0; when the q-axis target current component is greater than the preset threshold, it indicates that the converter is in an overload state, and the overload flag bit is equal to 1.

8. The improved high reactive load overload control method of active neutral point clamped topology according to claim 7, characterized in that, The d-axis and q-axis target current components are respectively limited according to the overload flag, to obtain a first current instruction and a second current instruction, which comprises: When the overload flag is equal to 0, the current limiting values of the d-axis and q-axis are both set as the maximum value of the rated current, and the phase angle is kept unchanged, to obtain the first current instruction and the second current instruction respectively; When the overload flag is equal to 1, the d-axis current limiting value is set as 0 to obtain the first current instruction, and the q-axis current limiting value is increased to a preset overload threshold to obtain the second current instruction.

9. The improved active neutral point clamped topology high reactive load control method according to claim 8, characterized in that, The three-phase modulation signal is obtained according to the first current instruction and the second current instruction, which comprises: The uncompensated voltage reference signal is obtained according to the first current instruction, the second current instruction and the dq current components; and the three-phase modulation signal is obtained by performing inverse Park transformation on the uncompensated voltage reference signal after compensation of the dq voltage components.

10. A high reactive power overload control device for an improved active neutral point clamped topology for use in the method of any one of claims 1 to 9, characterized in that, The device comprises a first module, a second module, a third module and a fourth module; The first module is used for obtaining an output voltage and a phase angle according to a grid-connected point three-phase voltage and three-phase current of a topology, obtaining a delay angle according to a total loss of an auxiliary diode in the topology, and obtaining a zero sequence component according to the delay angle and the phase angle, wherein the total loss comprises a conduction loss and a reverse recovery loss under a modulation signal considering the delay angle; The second module is used for obtaining d-axis and q-axis target current components according to the output voltage and the phase angle; The overload flag is obtained by comparing the q-axis target current component with a preset threshold; The third module is used for limiting the d-axis and q-axis target current components according to the overload flag, to obtain a first current instruction and a second current instruction; and obtaining a three-phase modulation signal according to the first current instruction and the second current instruction; The fourth module is used for modulating a switching signal of an IGBT tube according to the three-phase modulation signal when the overload flag indicates that the topology is in a normal state, or modulating the three-phase modulation signal after injecting the zero sequence component.

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