A modulation method and device for midpoint potential self-balancing, equipment and storage medium

Abstract

The application discloses a midpoint potential self-balancing modulation method and device, electronic equipment and a computer readable storage medium. The method comprises the following steps: determining a d-axis input voltage target value and a q-axis input voltage target value; performing two-phase rotation to three-phase rotation coordinate system conversion on the d-axis input voltage target value and the q-axis input voltage target value to obtain corresponding three-phase voltage target values; constructing a power switch modulation matrix for self-balancing of the midpoint potential of a three-level converter and a target equation satisfied by the three-phase voltage target values and a direct-current side capacitor voltage; determining the value of the power switch modulation matrix by solving the target equation; and generating a driving pulse signal of each power switch based on the power switch modulation matrix. The application determines the modulation matrix in the form of algebraic equation solving, can ensure the self-balancing of the midpoint potential without additional control, is simple and easy to implement, has strong stability, and effectively improves the modulation efficiency and quality of the neutral point clamped three-level converter.

Description

Technical Field

[0001] This application relates to the field of power conversion technology, and in particular to a modulation method, apparatus, electronic device and computer-readable storage medium for midpoint potential self-balancing. Background Technology

[0002] Neutral point clamped (NPC) three-level converters are now widely used in fields such as photovoltaic power generation grid connection and flexible power transmission and distribution.

[0003] In NPC converter applications, the most dynamic research topic is balancing the neutral point voltage and suppressing neutral point potential ripple. Conventional solutions include increasing the DC-side capacitor or using two isolated DC power supplies, but these increase system hardware cost and complexity. Currently, the most commonly used solutions that do not require additional hardware include Space Vector Pulse Width Modulation (SVPWM), Carrier-Based Pulse Width Modulation (CBPWM), and Finite Set Predictive Control (FPC). These methods essentially select appropriate vector or switching state combinations to achieve neutral point potential balance; however, they all have certain drawbacks. SVPWM based on virtual vectors may be ineffective at high modulation indices or low power factors and cannot completely eliminate low-frequency NPV oscillations. While CBPWM is more popular in industrial applications due to its simplicity, parameter mismatches and disturbances can lead to potential imbalances, thus requiring additional control. FPC, on the other hand, has long computation times and places high demands on the controller.

[0004] Therefore, providing a solution to the above-mentioned technical problems is something that those skilled in the art urgently need to focus on. Summary of the Invention

[0005] The purpose of this application is to provide a simple, easy-to-implement, stable and effective modulation method, device, electronic device and computer-readable storage medium for neutral point potential self-balancing, thereby improving the modulation efficiency of neutral point clamping three-level converters.

[0006] To address the aforementioned technical problems, this application discloses a modulation method for midpoint potential self-balancing, applied to a neutral-point clamped three-level converter, comprising:

[0007] Determine the target values ​​for the d-axis input voltage and the q-axis input voltage;

[0008] The target values ​​of the d-axis input voltage and the target values ​​of the q-axis input voltage are transformed from a two-phase rotation to a three-phase rotating coordinate system to obtain the corresponding three-phase voltage target values.

[0009] Construct a target equation that satisfies the power switch modulation matrix that enables the midpoint potential of the three-level converter to self-balance, and the target values ​​of the three-phase voltage and the DC-side capacitor voltage.

[0010] The value of the power switch modulation matrix is ​​determined by solving the objective equation;

[0011] The driving pulse signal for each power switch is generated based on the power switch modulation matrix.

[0012] Optionally, the objective equation is specifically:

[0013]

[0014] Among them, u an u bn u cn The three-phase voltage target value; u1 and u2 are the two DC-side capacitor voltages of the three-level converter; M is the power switch modulation matrix; M' is the power switch transition modulation matrix; M0 is the bias matrix; d ij (i = a, b, c; j = P, N) represents the duty cycle of the power switches in the upper and lower bridge arms of the three-level converter, where j = P corresponds to the upper bridge arm and j = N corresponds to the lower bridge arm; d ij ′(i=a,b,c;j=P,N) are the initial duty cycles of the power switches in the upper and lower arms of the three-level converter; X is the bias applied to the power switch in the upper arm, and Y is the bias applied to the power switch in the lower arm.

[0015] Optionally, determining the value of the power switching modulation matrix by solving the objective equation includes:

[0016] The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation; the general solution includes free variable parameters.

[0017] Substitute the general solution into the dynamic equation of midpoint voltage balance to determine the range of values ​​for the free variable parameters;

[0018] The value of the bias matrix is ​​determined based on the initial duty cycle in the power switch transition modulation matrix;

[0019] The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

[0020] Optionally, the non-homogeneous linear equation system is:

[0021]

[0022] The general solution is:

[0023] x=λ1h′1+λ2h′2+λ3h′3+p′;

[0024] Where λ1, λ2, and λ3 are free variable parameters.

[0025]

[0026] Optionally, determining the value of the bias matrix based on the initial duty cycle in the power switch transition modulation matrix includes:

[0027] The values ​​of the bias matrix are determined as follows:

[0028]

[0029] Determining the value of the power switch modulation matrix based on the power switch transition modulation matrix and the bias matrix includes:

[0030] The values ​​of the power switch modulation matrix are determined as follows:

[0031]

[0032] Optionally, determining the target values ​​of the d-axis input voltage and the q-axis input voltage includes:

[0033] Measure the three-phase input voltage and three-phase input current on the AC side;

[0034] Determine the desired values ​​of the d-axis input current and the q-axis input current;

[0035] Based on the AC three-phase input voltage, the AC three-phase input current, the expected value of the d-axis input current, and the expected value of the q-axis input current, determine the target value of the d-axis input voltage and the target value of the q-axis input voltage.

[0036] Optionally, when the DC side of the three-level converter is connected to a DC source, determining the desired value of the d-axis input current includes:

[0037] The magnitude of the DC source current is determined as the desired value of the d-axis input current.

[0038] Optionally, when the DC side of the three-level converter is connected to a load, determining the desired value of the d-axis input current includes:

[0039] The DC-side voltage value is calculated based on the measured DC-side capacitor voltage;

[0040] PI control is performed based on the difference between the expected DC-side voltage value and the DC-side voltage value to calculate the expected d-axis input current value.

[0041] Optionally, the step of performing PI control based on the difference between the desired DC-side voltage value and the DC-side voltage value to calculate the desired d-axis input current value includes:

[0042] The expected value of the d-axis input current is calculated using a PI controller based on the following formula:

[0043]

[0044] Among them, i * d The desired value of the d-axis input current; u dc U1 is the DC-side voltage value; u2 is the first DC-side capacitor voltage; u2 is the second DC-side capacitor voltage; K Pu K is the voltage loop proportional coefficient; Iu This represents the voltage loop integral coefficient.

[0045] Optionally, determining the target values ​​of the d-axis input voltage and the q-axis input voltage based on the three-phase input voltage on the AC side, the three-phase input current on the AC side, the expected value of the d-axis input current, and the expected value of the q-axis input current includes:

[0046] Three-phase phase-locking is performed on the three-phase input voltage on the AC side to extract the voltage phase angle;

[0047] Based on the voltage phase angle, the three-phase input voltage and the three-phase input current on the AC side are transformed into a three-phase rotating coordinate system and a two-phase rotating coordinate system to obtain the AC side d-axis input voltage, AC side q-axis input voltage, AC side d-axis input current and AC side q-axis input current.

[0048] The target values ​​of the d-axis input voltage and the q-axis input voltage are calculated using a PI controller based on the following formulas:

[0049]

[0050] Among them, u d The target value of the d-axis input voltage; u q The target value of the q-axis input voltage; u sd The AC side d-axis input voltage; u sq The AC-side q-axis input voltage; L is the inductance value of the filter inductor in the three-level converter; i d Input current to the d-axis of the AC side; i q Input current to the q-axis of the AC side; i * d The desired value of the d-axis input current; i * q K represents the desired value of the q-axis input current. PiK is the proportionality coefficient of the current loop; Ii is the integral coefficient of the current loop.

[0051] Furthermore, this application also provides a modulation device for midpoint potential self-balancing, applied to a three-level converter with neutral point clamping, comprising:

[0052] A determination unit is used to determine the target values ​​of the d-axis input voltage and the q-axis input voltage.

[0053] The transformation unit is used to perform a two-phase rotation to a three-phase rotating coordinate system transformation on the target value of the d-axis input voltage and the target value of the q-axis input voltage to obtain the corresponding three-phase voltage target value.

[0054] The modulation unit is used to construct a target equation that satisfies the power switch modulation matrix that makes the midpoint potential of the three-level converter self-balanced, and the target values ​​of the three-phase voltage and the DC-side capacitor voltage; by solving the target equation, the value of the power switch modulation matrix is ​​determined.

[0055] The generation unit is used to generate drive pulse signals for each power switch based on the power switch modulation matrix.

[0056] Optionally, the modulation unit is specifically used for:

[0057] The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation; the general solution includes free variable parameters.

[0058] Substitute the general solution into the dynamic equation of midpoint voltage balance to determine the range of values ​​for the free variable parameters;

[0059] The value of the bias matrix is ​​determined based on the initial duty cycle in the power switch transition modulation matrix;

[0060] The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

[0061] In another aspect, this application also discloses an electronic device, comprising:

[0062] Memory, used to store computer programs;

[0063] A processor for executing the computer program to implement the steps of any of the midpoint potential self-balancing modulation methods described above.

[0064] In another aspect, this application also discloses a computer-readable storage medium storing a computer program, which, when executed by a processor, is used to implement the steps of any of the midpoint potential self-balancing modulation methods described above.

[0065] The beneficial effects of the modulation method, apparatus, electronic device and computer-readable storage medium for midpoint potential self-balancing provided in this application are as follows: This application determines the modulation matrix by solving algebraic equations, which can ensure midpoint potential self-balancing without additional control. Therefore, it is simple and easy to implement, and is not affected by capacitor parameters. It has strong stability and effectively improves the modulation efficiency and quality of the neutral point clamping three-level converter. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the prior art and the embodiments of this application, the accompanying drawings used in the description of the prior art and the embodiments of this application will be briefly introduced below. Of course, the accompanying drawings described below with respect to the embodiments of this application are only a part of the embodiments in this application. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort, and such other drawings also fall within the protection scope of this application.

[0067] Figure 1 This is a circuit diagram of a neutral-point clamped three-level converter disclosed in an embodiment of this application;

[0068] Figure 2 This is a schematic diagram of the output state of a conversion circuit disclosed in an embodiment of this application;

[0069] Figure 3 This is a schematic diagram of the output state of another conversion circuit disclosed in an embodiment of this application;

[0070] Figure 4 This is a schematic diagram of the output state of another conversion circuit disclosed in an embodiment of this application;

[0071] Figure 5 This is a flowchart of a modulation method for midpoint potential self-balancing disclosed in an embodiment of this application;

[0072] Figure 6 This is a control principle diagram of a modulation method for midpoint potential self-balancing disclosed in an embodiment of this application;

[0073] Figure 7 This is a flowchart of another modulation method for midpoint potential self-balancing disclosed in an embodiment of this application;

[0074] Figure 8 This is a schematic diagram of carrier modulation of a driving pulse signal disclosed in an embodiment of this application;

[0075] Figure 9 This is a simulation waveform diagram of circuit parameters when a DC source is connected to the DC side, as disclosed in an embodiment of this application.

[0076] Figure 10 This is a simulation waveform diagram of the circuit parameters when a resistive-inductive load is connected to the DC side, as disclosed in an embodiment of this application.

[0077] Figure 11 This is a structural block diagram of a modulation device for midpoint potential self-balancing disclosed in an embodiment of this application;

[0078] Figure 12 This is a structural block diagram of an electronic device disclosed in an embodiment of this application. Detailed Implementation

[0079] The core of this application is to provide a simple, easy-to-implement, stable and effective modulation method, device, electronic device and computer-readable storage medium for neutral point potential self-balancing, thereby improving the modulation efficiency of neutral point clamping three-level converters.

[0080] To provide a clearer and more complete description of the technical solutions in the embodiments of this application, the technical solutions in the embodiments of this application will be described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0081] With the rapid development of society and the economy, the proportion of renewable energy used, such as wind power, photovoltaic, and tidal energy, is increasing. As a key link in renewable energy development, power conversion is particularly important for its research and technological innovation. In the development and utilization of new energy, traditional power converters and switching devices in transmission and distribution systems are gradually being replaced by high-power devices at medium and high voltage levels. However, the development of power converters based on two-level topologies is severely limited by the stress on switching devices under high voltage conditions. Therefore, a multilevel converter, which can significantly reduce the switching stress of devices, has been proposed and is rapidly developing. Furthermore, multilevel converters can achieve multilevel AC side voltage, making it closer to a sine wave, greatly reducing the harmonic content of the AC side waveform and simplifying filter design. Among them, the neutral point clamped (NPC) three-level converter is widely used in photovoltaic power grid connection and flexible transmission and distribution fields.

[0082] Neutral-point clamped three-level converters include T-type converters and diode-clamped converters. Taking the T-type converter as an example, this application discloses a circuit structure for a neutral-point clamped three-level converter, specifically as follows: Figure 1 As shown, it mainly includes AC grid side 1, H-bridge circuit 2, neutral point three-way bidirectional switch 3, DC side capacitor 4, and control circuit 7; the control circuit includes controller 7, drive circuit 8, and corresponding sampling and conditioning circuit 6.

[0083] In this circuit, H-bridge circuit 2 and three-way bidirectional switch 3 are connected to AC power grid 1 via filter inductor L. The three-way bidirectional switch 3 is specifically constructed as two IGBTs (Insulated Gate Bipolar Transistors) with their emitters connected in series. The output terminal of DC-side capacitor 4 is connected in parallel with DC-side load 5. The input terminals of each of the three-phase arm units of H-bridge circuit 2 are connected to 220V AC power grid 1 via grid-side filter inductor L. Part of the sampling and conditioning circuit 6 is used to sample and condition the voltage and current of AC power grid 1, and another part of the sampling and conditioning circuit 6 is used to sample and condition the voltage of DC-side capacitors C1 and C2. Controller 7 is responsible for important tasks such as calculation and modulation, generating PWM waves as drive pulse signals for each power switch and transmitting them to drive circuit 8, thereby achieving the purpose of regulating each power switch and thus adjusting the conversion power of the converter.

[0084] Specifically, the power switches include the upper and lower bridge arm switches of each phase of the H-bridge circuit 2, as well as the three-way bidirectional switch 3. By combining and controlling the on / off states of each power switch, different output states of the T-type converter circuit can be obtained. Specifically, taking the A-phase operation as an example, each phase of the three-level T-type converter circuit has three operating states.

[0085] like Figure 2 The first operating mode shown is the upper bridge arm switch S. ap Open, bidirectional switch S ao and lower bridge arm switch S an When the circuit is off, the output voltage is u1, corresponding to state P.

[0086] like Figure 3 The second operating mode shown is the bidirectional switch S. ao Open, upper bridge arm switch S ap and lower bridge arm switch S an When turned off, the output voltage is 0, corresponding to the O state;

[0087] like Figure 4 The third operating mode shown is the lower bridge arm switch S. an Open, bidirectional switch S ao and upper bridge arm switch S ap When turned off, the output voltage is -u2, corresponding to the N state.

[0088] The key modulation problem addressed in this application is how to generate the drive pulse signals corresponding to each power switch to meet the converter's power requirements and ensure midpoint potential balance. However, existing modulation schemes inevitably have limitations, such as implementation difficulties, high costs, instability, and failure issues. Therefore, this application provides a self-balancing midpoint potential modulation scheme that effectively solves the aforementioned problems.

[0089] See Figure 5 As shown in the figure, this application discloses a modulation method for midpoint potential self-balancing, applied to a neutral-point clamped three-level converter, mainly including:

[0090] S101: Determine the target values ​​for the d-axis input voltage and the q-axis input voltage.

[0091] S102: Perform a two-phase rotation to three-phase rotating coordinate system transformation on the target values ​​of the d-axis input voltage and the q-axis input voltage to obtain the corresponding three-phase voltage target values.

[0092] S103: Construct the target equation that satisfies the power switch modulation matrix that enables the midpoint potential of the three-level converter to be self-balanced with the target values ​​of the three-phase voltage and the DC-side capacitor voltage.

[0093] S104: Determine the value of the power switch modulation matrix by solving the objective equation.

[0094] S105: Generates the drive pulse signal for each power switch based on the power switch modulation matrix.

[0095] Specifically, the target values ​​for both the d-axis and q-axis input voltages are the required dq-axis voltage input values ​​to meet the current power conversion demands. These values ​​can be determined through calculation based on the three-phase AC input voltage. Correspondingly, by performing a coordinate system transformation from two-phase rotation to two-phase stationary to three-phase rotation, the actual three-phase voltages that need to be input to the converter to meet the current power conversion requirements—the target three-phase voltage values—can be obtained. This also serves as the basis for pulse modulation of the power switches.

[0096] When the midpoint potential is balanced, the target values ​​of the three-phase voltages, the modulation matrix of the power switch, and the DC-side capacitor voltage must satisfy a certain voltage balance relationship. Therefore, this application can derive an objective equation regarding the balance relationship among these three components, and then use the equation to solve for the value of the modulation matrix. Specifically, M is the power switch modulation matrix, u... an u bn u cn Let u1 and u2 be the target values ​​for the three-phase voltages; u1 and u2 are the voltages of the two DC-side capacitors of the three-level converter; then the target equation is:

[0097]

[0098] Where, d ij (i = a, b, c; j = P, N) represents the duty cycle of the power switches in the upper and lower arms of the three-level converter. When j = P, it corresponds to the upper arm, and when j = N, it corresponds to the lower arm.

[0099] In other words, the modulation method for midpoint clamped three-level converters provided in this application is specifically an algebraic modulation method. The core of this method's modulation strategy lies in using algebraic methods to convert the modulation matrix between the DC and AC sides into a solution of a non-homogeneous linear equation. This transforms the complex modulation problem into a mathematical problem, and by solving the matrix, the value of the modulation matrix that satisfies the conditions is determined, thereby achieving the goal of balancing the midpoint potential based on this modulation matrix.

[0100] As can be seen, the modulation method for midpoint potential self-balancing provided in this application determines the modulation matrix by solving algebraic equations. It can ensure midpoint potential self-balancing without additional control, so it is simple and easy to implement, and is not affected by capacitor parameters. It has strong stability and effectively improves the modulation efficiency and quality of the neutral point clamping three-level converter.

[0101] As a specific embodiment, the midpoint potential self-balancing modulation method provided in this application, based on the above content, may have the objective equation specifically defined as follows in a particular embodiment:

[0102]

[0103] Among them, u an u bn u cn The three-phase voltage target value; u1 and u2 are the two DC-side capacitor voltages of the three-level converter; M is the power switch modulation matrix; M' is the power switch transition modulation matrix; M0 is the bias matrix; d ij (i = a, b, c; j = P, N) represents the duty cycle of the power switches in the upper and lower arms of the three-level converter. When j = P, it corresponds to the upper arm; when j = N, it corresponds to the lower arm. ij ′(i=a,b,c;j=P,N) are the initial duty cycles of the power switches in the upper and lower arms of the three-level converter; X is the bias applied to the power switch in the upper arm, and Y is the bias applied to the power switch in the lower arm.

[0104] Specifically, in this embodiment, when solving the target equation, M is split into M' and M0. Each element in M' is the initial duty cycle of the drive pulse signal used to change the output target voltage of each power switch. Since the actual equation has more solutions than the actual physical problem, the split M0 is used to implement physical constraints. Each element in M0 is a bias amount used to limit each element to satisfy the physical constraints.

[0105] As a specific embodiment, the modulation method for midpoint potential self-balancing provided in this application, based on the above content, determines the value of the power switch modulation matrix by solving the objective equation, including:

[0106] The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation; the general solution includes free variable parameters.

[0107] Substitute the general solution into the dynamic equation of midpoint voltage balance to determine the range of values ​​for the free variable parameters;

[0108] The value of the bias matrix is ​​determined based on the initial duty cycle in the power switch transition modulation matrix;

[0109] The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

[0110] Specifically, when solving M', the non-homogeneous linear equation system can be transformed into:

[0111]

[0112] Therefore, M' is a partial solution to this non-homogeneous linear system of equations. Algebraically, the coefficient matrix A in this system has a rank of 3, indicating the existence of 3 free variables. Thus, the general solution can be constructed as follows:

[0113] x=d′ aN h1+d′ bN h2+d′ cN h3+p;

[0114] in,

[0115]

[0116] Furthermore, let The general solution of the non-homogeneous linear system of equations can then be transformed into:

[0117] x=λ1h′1+λ2h′2+λ3h′3+p′;

[0118] Where λ1, λ2, and λ3 are free variable parameters.

[0119]

[0120] Then, M' is transformed into an expression with respect to the three free variable parameters λ1, λ2, and λ3:

[0121]

[0122] The range of values ​​for the three free variable parameters λ1, λ2, and λ3 can be determined based on the midpoint voltage balance dynamic equation. Specifically, first, substitute each duty cycle, input voltage, and current into the midpoint voltage balance dynamic equation:

[0123]

[0124] in, u dc =u1-u2;i i (i = a, b, c) represents the three-phase currents;

[0125] make:

[0126]

[0127] Substituting the three free variable parameters, we can obtain:

[0128]

[0129] Analysis of the expression shows that, to ensure the neutral point voltage difference eventually converges to zero, that is, to ensure the midpoint potential voltage eventually reaches equilibrium, therefore... It must be a negative value, therefore we get:

[0130]

[0131] Thus, even if the capacitance values ​​of the DC-side capacitors are unequal, i.e., C1 is not equal to C2, this algebraic modulation method can eliminate the influence of the capacitor mismatch, thereby achieving midpoint potential voltage balance.

[0132] As a specific embodiment, the midpoint potential self-balancing modulation method provided in this application, based on the above content, stipulates that the effect of the bias matrix cannot cancel the effect of the power switch transition modulation matrix; therefore, its value range should be:

[0133]

[0134] Choosing different values ​​for X and Y can produce different modulation effects. To reduce power loss, when determining the value of the bias matrix based on the initial duty cycle in the power switch transition modulation matrix, the specific value of the bias matrix can be determined as follows:

[0135]

[0136] The values ​​of the power switching modulation matrix are determined based on the power switching transition modulation matrix and the bias matrix, including:

[0137] The values ​​of the power switch modulation matrix are determined as follows:

[0138]

[0139] See Figure 6 , Figure 6 This is a schematic diagram of a modulation method for midpoint potential self-balancing disclosed in an embodiment of this application.

[0140] like Figure 6 As shown in the illustration, as a specific embodiment, the modulation method for midpoint potential self-balancing provided in this application, based on the above content, determines the target values ​​of the d-axis input voltage and the q-axis input voltage, including:

[0141] Measure the three-phase input voltage u on the AC side sabc and the three-phase input current IABC on the AC side;

[0142] Determine the desired value of the d-axis input current i * d and the expected value of the q-axis input current i * q ;

[0143] Based on the three-phase AC input voltage, three-phase AC input current, expected d-axis input current, and expected q-axis input current, determine the target value u of the d-axis input voltage. d and the target value of the q-axis input voltage u q .

[0144] As one specific embodiment, such as Figure 6 As shown, when the DC side of the three-level converter is connected to a DC source, determining the desired value of the d-axis input current includes:

[0145] The magnitude of the DC source current is determined as the desired value of the d-axis input current.

[0146] As another specific embodiment, such as Figure 6 As shown, when a load is connected to the DC side of the three-level converter, determining the desired value of the d-axis input current includes:

[0147] The DC-side voltage value u is calculated based on the measured DC-side capacitor voltage. dc ;

[0148] Based on the expected value of DC side voltage u * dc With DC side voltage value u dcThe difference is used for PI control to calculate the expected value of the d-axis input current.

[0149] As a specific embodiment, the midpoint potential self-balancing modulation method provided in this application, based on the above content, performs PI control based on the difference between the desired DC-side voltage value and the DC-side voltage value to calculate the desired d-axis input current value, including:

[0150] The desired value of the d-axis input current is calculated using a PI controller based on the following formula:

[0151]

[0152] Among them, i * d The desired value of the d-axis input current; u dc This is the DC side voltage value; u * dc U is the expected value of the DC-side voltage; u1 is the voltage of the first DC-side capacitor; u2 is the voltage of the second DC-side capacitor; K Pu K is the voltage loop proportionality coefficient; Iu This represents the voltage loop integral coefficient.

[0153] As a specific embodiment, the modulation method for midpoint potential self-balancing provided in this application, based on the above content, determines the target values ​​of the d-axis input voltage and the q-axis input voltage according to the AC three-phase input voltage, AC three-phase input current, expected value of d-axis input current, and expected value of q-axis input current, including:

[0154] A three-phase phase-locked loop (PLL) is performed on the three-phase input voltage on the AC side to extract the voltage phase angle θ;

[0155] Based on the voltage phase angle θ, the three-phase input voltage u on the AC side sabc AC side three-phase input current i abc Perform a three-phase rotating to two-phase rotating coordinate system transformation to obtain the AC side d-axis input voltage u. sd AC side q-axis input voltage u sq AC side d-axis input current i d AC side q-axis input current i q ;

[0156] The target values ​​of the d-axis input voltage and the q-axis input voltage are calculated using the PI controller based on the following formulas:

[0157]

[0158] Among them, u d The target value for the d-axis input voltage; u qThe target value for the q-axis input voltage; u sd The AC side d-axis input voltage; u sq The AC-side q-axis input voltage; L is the inductance value of the filter inductor in the three-level converter; i d For AC side d-axis input current; i q For AC side q-axis input current; i * d i represents the desired value of the d-axis input current. * q K represents the desired value of the q-axis input current. Pi K is the proportionality coefficient of the current loop; Ii is the integral coefficient of the current loop.

[0159] For details, please refer to the above information. Figure 7 , Figure 7 Another modulation method for midpoint potential self-balancing disclosed in this application mainly includes:

[0160] S201: Measure the three-phase input voltage u on the AC side sabc and AC side three-phase input current i abc .

[0161] S202: Determine the desired value of the d-axis input current i * d and the expected value of the q-axis input current i * q .

[0162] S203: For u sabc Three-phase phase-locked loop is performed to extract the voltage phase angle θ.

[0163] S204: Based on θ, for u sabc i abc Perform a three-phase rotating to two-phase rotating coordinate system transformation to obtain the AC side d-axis input voltage u. sd AC side q-axis input voltage u sq AC side d-axis input current i d AC side q-axis input current i q .

[0164] S205: Using a PI controller based on u sd u sq i d i q i * d i * q Determine the target value u of the d-axis input voltage. d and the target value of the q-axis input voltage u q .

[0165] S206: For u d and u q A two-phase rotation to three-phase rotation coordinate system transformation is performed to obtain the corresponding three-phase voltage target value.

[0166] S207: Construct the target equation that satisfies the power switch modulation matrix that enables the midpoint potential of the three-level converter to be self-balanced with the target values ​​of the three-phase voltage and the DC-side capacitor voltage.

[0167] S208: Determine the value of the power switch modulation matrix by solving the objective equation.

[0168] S209: Generate drive pulse signals for each power switch based on the power switch modulation matrix.

[0169] In S209, when the driving pulse signal is generated by modulating the power switch modulation matrix M, a specific carrier modulation diagram can be found in [reference needed]. Figure 8 .

[0170] To improve waveform quality, a bilateral symmetrical switching mode can be used. Taking the operation of phase A for one cycle as an example, in d... ap When S is greater than carrier 1, ap The switching pulse changes from 0 to 1, and the upper bridge arm is clamped by the DC-side capacitor voltage u1; in d ap Less than carrier 1, d an When S is less than carrier 2, ap The switching pulse changes from 1 to 0, and the bidirectional switch S... ao The switching pulse changes from 0 to 1, and the potential at point a is the same as the potential at the neutral point o; at point d... ap Less than carrier 1, d an When the carrier wave is greater than 2, the bidirectional switch S ao The switching pulse changes from 1 to 0, S an The switching pulse changes from 0 to 1, and the lower bridge arm is clamped by the DC-side capacitor voltage -u2; symmetrically, at d ap Less than carrier 1, d an S an The switching pulse changes from 1 to 0, and the bidirectional switch S... ao The switching pulse changes from 0 to 1, and the potential at point a is the same as the potential at the neutral point o; at point d... ap When the carrier wave is greater than 1, the bidirectional switch S ao The switching pulse changes from 1 to 0, S ap The switching pulse changes from 0 to 1, and the upper bridge arm is clamped by the DC side capacitor voltage u1.

[0171] Power flow is defined as flowing out of the power grid as positive power flow and flowing into the power grid as negative power flow. Figure 9Three-phase currents and u under three power flow conditions when the DC side is connected to a DC source. sa and i a And simulation waveforms of the DC-side capacitor voltages u1 and u2. From Figure 9 It can be seen that this modulation strategy can effectively control NPV balance in positive power flow, negative power flow, and pure reactive power conditions.

[0172] Figure 10 The three-phase current u when the DC side is connected to an inductive load. sa and i a And simulation waveforms of DC-side capacitor voltages u1 and u2, from Figure 10 It can be seen that this modulation strategy can also effectively control the balance of the midpoint potential voltage when the DC side is connected to a resistive and inductive load.

[0173] See Figure 11 As shown in the figure, this application discloses a modulation device for midpoint potential self-balancing, applied to a three-level converter with neutral point clamping, mainly comprising:

[0174] Determining unit 301 is used to determine the target values ​​of the d-axis input voltage and the q-axis input voltage;

[0175] The transformation unit 302 is used to perform a two-phase rotation to a three-phase rotating coordinate system transformation on the d-axis input voltage target value and the q-axis input voltage target value to obtain the corresponding three-phase voltage target value.

[0176] The modulation unit 303 is used to construct a target equation that satisfies the power switch modulation matrix that enables the midpoint potential of the three-level converter to self-balance, the target value of the three-phase voltage, and the DC-side capacitor voltage; and to determine the value of the power switch modulation matrix by solving the target equation.

[0177] The generation unit 304 is used to generate drive pulse signals for each power switch based on the power switch modulation matrix.

[0178] As can be seen, the modulation device for midpoint potential self-balancing disclosed in this application determines the modulation matrix by solving algebraic equations. It can ensure midpoint potential self-balancing without additional control, so it is simple and easy to implement. It is not affected by capacitor parameters, has strong stability, and effectively improves the modulation efficiency and quality of the neutral point clamping three-level converter.

[0179] For details regarding the modulation device for midpoint potential self-balancing, please refer to the aforementioned detailed introduction to the modulation method for midpoint potential self-balancing; it will not be repeated here.

[0180] As a specific embodiment, the modulation device for midpoint potential self-balancing disclosed in this application, based on the above content, has the modulation unit 303 specifically used for:

[0181] The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation; the general solution includes free variable parameters.

[0182] Substitute the general solution into the dynamic equation of midpoint voltage balance to determine the range of values ​​for the free variable parameters;

[0183] The value of the bias matrix is ​​determined based on the initial duty cycle in the power switch transition modulation matrix;

[0184] The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

[0185] As a specific embodiment, the target equation of the midpoint potential self-balancing modulation device disclosed in this application is specifically as follows, based on the above content:

[0186]

[0187] Among them, u an u bn u cn The three-phase voltage target value; u1 and u2 are the two DC-side capacitor voltages of the three-level converter; M is the power switch modulation matrix; M' is the power switch transition modulation matrix; M0 is the bias matrix; d ij (i = a, b, c; j = P, N) represents the duty cycle of the power switches in the upper and lower arms of the three-level converter. When j = P, it corresponds to the upper arm; when j = N, it corresponds to the lower arm. ij ′(i=a,b,c;j=P,N) are the initial duty cycles of the power switches in the upper and lower arms of the three-level converter; X is the bias applied to the power switch in the upper arm, and Y is the bias applied to the power switch in the lower arm.

[0188] As a specific embodiment, the modulation device for midpoint potential self-balancing disclosed in this application, based on the above content, wherein the modulation unit 303, when determining the value of the power switch modulation matrix by solving the objective equation, is specifically used for:

[0189] The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation. The general solution includes free variable parameters. The general solution is substituted into the midpoint voltage balance dynamic equation to determine the range of values ​​for the free variable parameters. The value of the bias matrix is ​​determined according to the initial duty cycle in the power switch transition modulation matrix. The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

[0190] As a specific embodiment, the midpoint potential self-balancing modulation device disclosed in this application, based on the above content, has the following non-homogeneous linear equation system:

[0191]

[0192] The general solution is:

[0193] x=λ1h′1+λ2h′2+λ3h′3+p′;

[0194] Where λ1, λ2, and λ3 are free variable parameters.

[0195]

[0196] As a specific embodiment, the modulation device for midpoint potential self-balancing disclosed in this application, based on the above content, wherein when the modulation unit 303 determines the value of the bias matrix according to the initial duty cycle in the power switch transition modulation matrix, it is specifically used for:

[0197] The values ​​of the bias matrix are determined as follows:

[0198]

[0199] The values ​​of the power switching modulation matrix are determined based on the power switching transition modulation matrix and the bias matrix, including:

[0200] The values ​​of the power switch modulation matrix are determined as follows:

[0201]

[0202] As a specific embodiment, the midpoint potential self-balancing modulation device disclosed in this application, based on the above content, specifically uses the determining unit 301 to determine the target values ​​of the d-axis input voltage and the q-axis input voltage when determining the target values:

[0203] Measure the three-phase input voltage and three-phase input current on the AC side;

[0204] Determine the expected values ​​of the d-axis input current and the q-axis input current;

[0205] Based on the three-phase input voltage on the AC side, the three-phase input current on the AC side, the expected value of the d-axis input current, and the expected value of the q-axis input current, determine the target values ​​of the d-axis input voltage and the q-axis input voltage.

[0206] As a specific embodiment, the midpoint potential self-balancing modulation device disclosed in this application, based on the above content, when the DC side of the three-level converter is connected to a DC source, the determining unit 301 is specifically used to determine the desired value of the d-axis input current when determining the desired value of the d-axis input current:

[0207] The magnitude of the DC source current is determined as the desired value of the d-axis input current.

[0208] As a specific embodiment, the midpoint potential self-balancing modulation device disclosed in this application, based on the above content, when the DC side of the three-level converter is connected to a load, the determining unit 301 is specifically used to determine the desired value of the d-axis input current when determining the desired value of the d-axis input current:

[0209] The DC-side voltage value is calculated based on the measured DC-side capacitor voltage;

[0210] PI control is used to calculate the expected value of the d-axis input current based on the difference between the expected value of the DC-side voltage and the DC-side voltage value.

[0211] As a specific embodiment, the midpoint potential self-balancing modulation device disclosed in this application, based on the above content, determines that when the unit 301 performs PI control based on the difference between the desired DC-side voltage value and the DC-side voltage value to calculate the desired d-axis input current value, it is specifically used for:

[0212] The desired value of the d-axis input current is calculated using a PI controller based on the following formula:

[0213]

[0214] Among them, i * d The desired value of the d-axis input current; u dc U1 is the DC-side voltage value; u2 is the voltage of the first DC-side capacitor; u2 is the voltage of the second DC-side capacitor; K Pu K is the voltage loop proportionality coefficient; Iu This represents the voltage loop integral coefficient.

[0215] See Figure 12 As shown in the figure, an embodiment of this application discloses an electronic device, including:

[0216] Memory 401 is used to store computer programs;

[0217] Processor 402 is configured to execute the computer program to implement the steps of any of the midpoint potential self-balancing modulation methods described above.

[0218] Furthermore, embodiments of this application also disclose a computer-readable storage medium storing a computer program, which, when executed by a processor, is used to implement the steps of any of the midpoint potential self-balancing modulation methods described above.

[0219] For details regarding the aforementioned electronic devices and computer-readable storage media, please refer to the aforementioned detailed introduction to the modulation method for midpoint potential self-balancing, which will not be repeated here.

[0220] The various embodiments in this application are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the devices disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0221] It should also be noted that in this application, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0222] The technical solutions provided in this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application. It should be noted that those skilled in the art can make several improvements and modifications to this application without departing from the principles of this application, and these improvements and modifications also fall within the protection scope of this application.

Claims

1. A modulation method for midpoint potential self-balancing, characterized in that, Three-level converters used for neutral point clamping include: Determine the target values ​​for the d-axis input voltage and the q-axis input voltage; The target values ​​of the d-axis input voltage and the target values ​​of the q-axis input voltage are transformed from a two-phase rotation to a three-phase rotating coordinate system to obtain the corresponding three-phase voltage target values. Construct a target equation that satisfies the power switch modulation matrix that enables the midpoint potential of the three-level converter to self-balance, and the target values ​​of the three-phase voltage and the DC-side capacitor voltage. The value of the power switch modulation matrix is ​​determined by solving the objective equation; The driving pulse signal for each power switch is generated based on the power switch modulation matrix. The objective equation is specifically as follows: ； in, u an , u bn , u cn The target value of the three-phase voltage; u 1. u 2 represents the voltages of the two DC-side capacitors of the three-level converter; M represents the power switch modulation matrix; M' represents the power switch transition modulation matrix; M0 represents the bias matrix; The duty cycle of the power switch in the upper and lower bridge arms of the three-level converter is given by j=P, which corresponds to the upper bridge arm and j=N, which corresponds to the lower bridge arm. The initial duty cycle of the power switches in the upper and lower bridge arms of the three-level converter; This is the bias applied to the power switch of the upper bridge arm. This is the bias applied to the power switch of the lower bridge arm; The step of determining the value of the power switch modulation matrix by solving the objective equation includes: The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation; the general solution includes free variable parameters. Substitute the general solution into the dynamic equation of midpoint voltage balance to determine the range of values ​​for the free variable parameters; The value of the bias matrix is ​​determined based on the initial duty cycle in the power switch transition modulation matrix; The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

2. The method according to claim 1, characterized in that, The nonhomogeneous linear equation is: ； The general solution is: ； in, , and For free variable parameters, 。 3. The method according to claim 2, characterized in that, Determining the value of the bias matrix based on the initial duty cycle in the power switch transition modulation matrix includes: The values ​​of the bias matrix are determined as follows: ； Determining the value of the power switch modulation matrix based on the power switch transition modulation matrix and the bias matrix includes: The values ​​of the power switch modulation matrix are determined as follows: 。 4. The method according to any one of claims 1 to 3, characterized in that, Determining the target values ​​of the d-axis input voltage and the q-axis input voltage includes: Measure the three-phase input voltage and three-phase input current on the AC side; Determine the expected values ​​of the d-axis input current and the q-axis input current; Based on the AC three-phase input voltage, the AC three-phase input current, the expected value of the d-axis input current, and the expected value of the q-axis input current, determine the target value of the d-axis input voltage and the target value of the q-axis input voltage.

5. The method according to claim 4, characterized in that, When the DC side of the three-level converter is connected to a DC source, determining the expected value of the d-axis input current includes: The magnitude of the DC source current is determined as the desired value of the d-axis input current.

6. The method according to claim 5, characterized in that, When the DC side of the three-level converter is connected to a load, determining the expected value of the d-axis input current includes: The DC-side voltage value is calculated based on the measured DC-side capacitor voltage; PI control is performed based on the difference between the expected DC-side voltage value and the DC-side voltage value to calculate the expected d-axis input current value.

7. The method according to claim 6, characterized in that, The step of calculating the expected value of the d-axis input current by performing PI control based on the difference between the expected value of the DC-side voltage and the DC-side voltage value includes: The expected value of the d-axis input current is calculated using a PI controller based on the following formula: ； in, The desired value of the d-axis input current; The DC-side voltage value; This is the voltage of the first DC-side capacitor; This is the voltage of the second DC-side capacitor; This is the voltage loop proportionality coefficient; This represents the voltage loop integral coefficient.

8. The method according to claim 7, characterized in that, The step of determining the target values ​​of the d-axis input voltage and the q-axis input voltage based on the AC three-phase input voltage, the AC three-phase input current, the expected value of the d-axis input current, and the expected value of the q-axis input current includes: Three-phase phase-locking is performed on the three-phase input voltage on the AC side to extract the voltage phase angle; Based on the voltage phase angle, the three-phase input voltage and the three-phase input current on the AC side are transformed into a three-phase rotating coordinate system and a two-phase rotating coordinate system to obtain the AC side d-axis input voltage, AC side q-axis input voltage, AC side d-axis input current and AC side q-axis input current. The target values ​​of the d-axis input voltage and the q-axis input voltage are calculated using a PI controller based on the following formulas: ； in, The target value of the d-axis input voltage; The target value for the q-axis input voltage; The AC side d-axis input voltage; The AC side q-axis input voltage; L The inductance value of the filter inductor in the three-level converter; Input current to the d-axis of the AC side; Input current to the q-axis of the AC side; The desired value of the d-axis input current; The desired value of the q-axis input current; This is the proportionality coefficient of the current loop; is the integral coefficient of the current loop.

9. A modulation device for midpoint potential self-balancing, characterized in that, Three-level converters used for neutral point clamping include: A determination unit is used to determine the target values ​​of the d-axis input voltage and the q-axis input voltage. The transformation unit is used to perform a two-phase rotation to a three-phase rotating coordinate system transformation on the d-axis input voltage target value and the q-axis input voltage target value to obtain the corresponding three-phase voltage target value; The modulation unit is used to construct a target equation that satisfies the power switch modulation matrix that makes the midpoint potential of the three-level converter self-balanced, and the target values ​​of the three-phase voltage and the DC-side capacitor voltage; by solving the target equation, the value of the power switch modulation matrix is ​​determined. The generation unit is used to generate drive pulse signals for each power switch based on the power switch modulation matrix. The objective equation is specifically as follows: ； in, u an , u bn , u cn The target value of the three-phase voltage; u 1. u 2 represents the voltages of the two DC-side capacitors of the three-level converter; M represents the power switch modulation matrix; M' represents the power switch transition modulation matrix; M0 represents the bias matrix; The duty cycle of the power switch in the upper and lower bridge arms of the three-level converter is given by j=P, which corresponds to the upper bridge arm and j=N, which corresponds to the lower bridge arm. The initial duty cycle of the power switches in the upper and lower bridge arms of the three-level converter; This is the bias applied to the power switch of the upper bridge arm. This is the bias applied to the power switch of the lower bridge arm; The modulation unit is specifically used for: The general solution of the power switch transition modulation matrix is ​​obtained by solving the corresponding non-homogeneous linear equation; the general solution includes free variable parameters. Substitute the general solution into the dynamic equation of midpoint voltage balance to determine the range of values ​​for the free variable parameters; The value of the bias matrix is ​​determined based on the initial duty cycle in the power switch transition modulation matrix; The sum of the power switch transition modulation matrix and the bias matrix is ​​used to determine the value of the power switch modulation matrix.

10. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the steps of the method as claimed in any one of claims 1 to 8.

11. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the method as described in any one of claims 1 to 8.

Images