Module capacitor voltage balance control method for modular multi-level matrix converter

Abstract

The present invention discloses a module capacitor voltage balance control method for a modular multi-level matrix converter. The additional balancing current is respectively added to the d-axis current on the power frequency side and the frequency division side, and then a modulation wave of input-output control is obtained through a current inner loop; the additional modulation wave of the bridge arm is added to the modulation wave of the input-output control to obtain a final modulation wave signal of the modular multi-level matrix converter; the module capacitor voltage balance control of the modular multi-level matrix converter is performed according to the final modulation wave signal of the modular multi-level matrix converter. The method can realize voltage-capacitance balance of the modular multi-level matrix converter.

Description

Technical Field

[0001] The invention belongs to the field of control strategies for high-voltage and high-power electric power conversion devices, and relates to a module capacitor voltage balance control method for a modular multi-level matrix converter. Background Art

[0002] Modular multilevel matrix converter (M3C) is a new type of AC / AC converter that can realize bidirectional energy flow. It has a series of technical advantages such as high power quality, high reliability, high controllability and easy scalability. It has broad application prospects in high-power and medium- and high-voltage systems.

[0003] M3C relies on the submodule capacitor to achieve the transfer of AC energy, and capacitor voltage balance is the prerequisite for the normal and reliable operation of the entire system. Therefore, the M3C capacitor voltage must be controlled to ensure the reliable operation of the converter. However, the power transfer between the input side and the output side will cause the capacitor voltage on the M3C submodule to fluctuate, which brings difficulties to the voltage balancing link. Chinese patent CN107240922A proposes a circulating current balancing method for M3C, which compares the DC voltage set value of the 9 bridge arms of M3C with the mean value, and obtains 9 active currents, but after proportional integral control, it may have an adverse effect on the input and output sides, and the voltage and capacitance balance of M3C cannot be achieved. Summary of the invention

[0004] The purpose of the present invention is to overcome the disadvantages of the prior art and provide a module capacitor voltage balance control method for a modular multi-level matrix converter, which can achieve capacitor voltage balance of the modular multi-level matrix converter.

[0005] To achieve the above object, the module capacitor voltage balance control method of the modular multi-level matrix converter of the present invention comprises the following steps:

[0006] 1) Subtract the average capacitor voltage of the nine bridge arms from the capacitor voltage of a single bridge arm, and the resulting difference is subjected to proportional integral control and quasi-proportional resonance control to obtain the equivalent DC circulating current of the bridge arm;

[0007] 2) According to the current direction in the bridge arm, the equivalent DC circulating current is multiplied by 1 or -1 to obtain an additional balancing voltage, and the additional balancing voltage is normalized and limited to obtain an additional modulation wave of each bridge arm;

[0008] 3) In the voltage balancing control of the additional balancing voltage of the modular multi-level matrix converter, steps 1) and 2) are performed on four bridge arms, and the modulation waves of the remaining four bridge arms are obtained by the first constraint condition;

[0009] 4) In the voltage balancing control of the additional balancing current of the modular multilevel matrix converter, step 1) is performed on four bridge arms in the modular multilevel matrix converter, and then the equivalent DC circulating current of the four bridge arms is divided by the modulation wave thereof to obtain the circulating current of the four bridge arms, and the circulating current of the other four bridge arms is obtained by the second constraint condition, and the circulating current of all bridge arms in the modular multilevel matrix converter is subjected to Clark transformation and Park transformation to obtain the additional balancing current;

[0010] 5) Adding the additional balancing current to the d-axis current on the power frequency side and the frequency division side respectively, and then passing through the current inner loop to obtain a modulation wave for input and output control; adding the additional modulation wave of the bridge arm to the modulation wave for input and output control to obtain the final modulation wave signal of the modular multi-level matrix converter;

[0011] 6) Performing module capacitor voltage balance control of the modular multi-level matrix converter according to the final modulation wave signal of the modular multi-level matrix converter.

[0012] The specific operation of step 6) is: obtaining a triangular carrier signal of the modular multi-level matrix converter, subtracting the final modulation wave signal from the triangular carrier signal, and obtaining a PWM signal of the actual switch in each full-bridge module in the bridge arm according to the subtraction result, and the PWM signal controls the state of the actual switch of each full-bridge module in each bridge arm to realize the module capacitor voltage balance control of the modular multi-level matrix converter.

[0013] The specific operation process of step 1) is:

[0014] 11) Let the capacitor voltage of the bridge arm be V xy_dc (x∈{u,v,w},y∈{a,b,c}), the average capacitor voltage of the nine bridge arms is in,

[0015]

[0016] The bridge arm current is i xy (x∈{u,v,w},y∈{a,b,c});

[0017] 12) The average capacitor voltage of the nine bridge arms The capacitor voltage V xy_dc Subtract the difference, and after passing the proportional integral controller, the first part of the equivalent DC circulating current i is obtained. xy_dc_cir1 (x∈{u,v,w},y∈{a,b,c}), the difference is passed through the quasi-proportional resonant controller to obtain the second equivalent DC circulating current i xy_dc_cir2 (x∈{u,v,w},y∈{a,b,c}), the first part of the equivalent DC circulating current i xy_dc_cir1(x∈{u,v,w},y∈{a,b,c}) and the equivalent DC circulating current i in the second part xy_dc_cir2 (x∈{u,v,w},y∈{a,b,c}) are added to obtain the final equivalent DC circulating current i of each bridge arm xy_dc_cir (x∈{u,v,w},y∈{a,b,c}).

[0018] The specific process of step 2) is:

[0019] 21) Assume the additional balancing voltage is:

[0020]

[0021] 22) Normalize the additional balance voltage and limit the amplitude to [-0.1, 0.1] to obtain the additional modulation wave m xy_cir for:

[0022]

[0023] The specific process of step 3) is:

[0024] 31) In each voltage balancing control of the additional balancing voltage, 4 signals are selected from the 9 additional modulation waves obtained in step 22), and the remaining 4 signals are obtained by the first constraint condition. A total of two voltage balancing controls are performed, and modulation waves of different bridge arms are selected. The two modulation waves are added to obtain the final additional modulation wave;

[0025] The first constraint condition is:

[0026]

[0027]

[0028] The specific process of step 4) is:

[0029] 41) Assume that the arm circulation i xy-cir for:

[0030]

[0031] Among them, 1 / m xy Clipped to [-1,1];

[0032] 42) In each voltage-balanced control of the additional balancing current, four signals are selected from the nine circulating currents obtained in step 41), and the remaining four signals are obtained by the second constraint condition. The circulating currents of different bridge arms are selected, and the two circulating currents are added to obtain the final circulating current;

[0033] The second constraint is:

[0034]

[0035]

[0036] 43) According to the coordinate transformation matrix C from the three-phase stationary coordinate system to the two-phase stationary coordinate system abc / αβ0 The coordinate transformation matrix C of the two-phase stationary coordinate system to the three-phase stationary coordinate system and its inverse transformation αβ0 / abc , the circulating current i obtained in step 42) xy_cir (x∈{u,v,w},y∈{a,b,c}) performs αβ0 transformation;

[0037] 44) According to the transformation matrix C from the two-phase stationary coordinate system to the dq0 coordinate system αβ0 / dq0_s and C αβ0 / dq0_l , perform Park transformation on the result obtained in step 43);

[0038] 45) The q-axis current and the 0-sequence current of the matrix in the result obtained in step 44) are set to zero, and the additional balancing current is obtained as:

[0039]

[0040] The specific process of step 43) is:

[0041] According to the coordinate transformation matrix C from the three-phase stationary coordinate system to the two-phase stationary coordinate system abc / αβ0 The coordinate transformation matrix C of the two-phase stationary coordinate system to the three-phase stationary coordinate system and its inverse transformation αβ0 / abc , the circulating current i obtained in step 42) xy_cir (x∈{u,v,w},y∈{a,b,c}) is transformed by αβ0, where

[0042]

[0043]

[0044]

[0045]

[0046] The specific process of step 44) is:

[0047] According to the transformation matrix C from the two-phase stationary coordinate system to the dq0 coordinate system αβ0 / dq0_s and C αβ0 / dq0_l , perform Park transformation on the result obtained in step 43), where:

[0048]

[0049]

[0050]

[0051]

[0052] The present invention has the following beneficial effects:

[0053] The module capacitor voltage balance control method of the modular multi-level matrix converter described in the present invention adjusts the voltage sign of the additional balanced voltage strategy according to the direction of the bridge arm current during specific operation to facilitate the adjustment of the energy injected into the bridge arm capacitor. The additional balanced current strategy only changes the d-axis current and only controls the circulating active power. In addition, in order to prevent the circulating power caused by the pressure difference from affecting the power supply on both sides, the two voltage balancing strategies are used to control the voltage balancing of the 8 bridge arms to ensure that the circulating power does not flow out of any star node, so as to achieve the voltage and capacitance balance of the modular multi-level matrix converter. In addition, it should be noted that the voltage balancing method of changing the modulation wave and the bridge arm current used in the present invention not only has a fast adjustment speed, but is also suitable for various operating conditions such as stable operation and faults. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 It is a topological structure diagram of a modular multi-level matrix converter;

[0055] Figure 2 A control block diagram of a module capacitor voltage balance control method for a modular multi-level matrix converter;

[0056] Figure 3 Block diagram of voltage equalization strategy for M3C with additional balanced voltage;

[0057] Figure 4 Block diagram of voltage balancing strategy for M3C with additional balancing current;

[0058] Figure 5 The schematic diagram of the M3C module capacitor voltage balance control method using two voltage equalization cycles;

[0059] Figure 6 The simulation results are as follows: (a) voltage and current waveforms on the frequency division side, (b) input active power and reactive power waveforms on the frequency division side, (c) voltage and current waveforms on the power frequency side, (d) output active power and reactive power on the power frequency side, (e) bridge arm voltage waveform, and (f) sub-converter c waveform. DETAILED DESCRIPTION

[0060] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only an embodiment of a part of the present invention, not all embodiments, and is not intended to limit the scope of the present invention. In addition, in the following description, the description of well-known structures and technologies is omitted to avoid unnecessary confusion of the concepts disclosed in the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work should fall within the scope of protection of the present invention.

[0061] The accompanying drawings show schematic diagrams of structures according to embodiments disclosed in the present invention. These figures are not drawn to scale, and some details are magnified and some details may be omitted for the purpose of clear expression. The shapes of various regions and layers shown in the figures and the relative sizes and positional relationships therebetween are only exemplary, and may deviate in practice due to manufacturing tolerances or technical limitations, and those skilled in the art may additionally design regions / layers with different shapes, sizes, and relative positions according to actual needs.

[0062] The present invention is mainly used for module capacitor voltage balance control of M3C and is widely used in the field of offshore frequency division power transmission. Figure 1 The topology diagram of M3C is shown in Figure 1, where the output side of M3C is the frequency division side, connected to the offshore low-frequency wind farm; the input side of M3C is the power frequency side, connected to the onshore power frequency grid, represented by a, b, c and u, v, w respectively. The three-phase input of the power frequency side of M3C and the three-phase output of the frequency division side are connected in pairs through nine bridge arms, each of which consists of a bridge arm reactance and n series full-bridge modules. Table 1 shows the main parameters of the M3C simulation system.

[0063] Table 1

[0064]

[0065] refer to Figure 2 and Figure 3 The module capacitor voltage balance control method of the modular multi-level matrix converter of the present invention comprises the following steps:

[0066] 1) Subtract the average capacitor voltage of the nine bridge arms from the capacitor voltage of a single bridge arm, and the resulting difference is subjected to proportional integral control and quasi-proportional resonance control to obtain the equivalent DC circulating current of the bridge arm;

[0067] 2) According to the current direction in the bridge arm, the equivalent DC circulating current is multiplied by 1 or -1 to obtain an additional balancing voltage, and the additional balancing voltage is normalized and limited to obtain an additional modulation wave of each bridge arm;

[0068] 3) In the voltage balancing control of the additional balancing voltage of the modular multi-level matrix converter, steps 1) and 2) are performed on four bridge arms, and the modulation waves of the remaining four bridge arms are obtained by the first constraint condition;

[0069] 4) In the voltage balancing control of the additional balancing current of the modular multilevel matrix converter, step 1) is performed on four bridge arms in the modular multilevel matrix converter, and then the equivalent DC circulating current of the four bridge arms is divided by the modulation wave thereof to obtain the circulating current of the four bridge arms, and the circulating current of the other four bridge arms is obtained by the second constraint condition, and the circulating current of all bridge arms in the modular multilevel matrix converter is subjected to Clark transformation and Park transformation to obtain the additional balancing current;

[0070] 5) Adding the additional balancing current to the d-axis current on the power frequency side and the frequency division side respectively, and then passing through the current inner loop to obtain a modulation wave for input and output control; adding the additional modulation wave of the bridge arm to the modulation wave for input and output control to obtain the final modulation wave signal of the modular multi-level matrix converter;

[0071] 6) Obtaining a triangular carrier signal of the modular multi-level matrix converter, subtracting the final modulation wave signal from the triangular carrier signal, and obtaining a PWM signal of an actual switch in each full-bridge module in the bridge arm according to the subtraction result, wherein the PWM signal controls the state of the actual switch of each full-bridge module in each bridge arm, thereby realizing module capacitor voltage balance control of the modular multi-level matrix converter.

[0072] The specific operation process of step 1) is:

[0073] 11) Let the capacitor voltage of the bridge arm be V xy_dc (x∈{u,v,w},y∈{a,b,c}), the average capacitor voltage of the nine bridge arms is in,

[0074]

[0075] The bridge arm current is i xy (x∈{u,v,w},y∈{a,b,c});

[0076] 12) The average capacitor voltage of the nine bridge arms The capacitor voltage V xy_dc Subtract the difference, and after passing the proportional integral controller, the first part of the equivalent DC circulating current i is obtained. xy_dc_cir1 (x∈{u,v,w},y∈{a,b,c}), the difference is passed through the quasi-proportional resonant controller to obtain the second equivalent DC circulating current i xy_dc_cir2 (x∈{u,v,w},y∈{a,b,c}), the first part of the equivalent DC circulating current i xy_dc_cir1(x∈{u,v,w},y∈{a,b,c}) and the equivalent DC circulating current i in the second part xy_dc_cir2 (x∈{u,v,w},y∈{a,b,c}) are added to obtain the final equivalent DC circulating current i of each bridge arm xy_dc_cir (x∈{u,v,w},y∈{a,b,c}).

[0077] The specific process of step 2) is:

[0078] 21) Assume the additional balancing voltage is:

[0079]

[0080] 22) Normalize the additional balance voltage and limit the amplitude to [-0.1, 0.1] to obtain the additional modulation wave m xy_cir for:

[0081]

[0082] The specific process of step 3) is:

[0083] 31) In each voltage balancing control of the additional balancing voltage, 4 signals are selected from the 9 additional modulation waves obtained in step 22), and the remaining 4 signals are obtained by the first constraint condition. A total of two voltage balancing controls are performed, and modulation waves of different bridge arms are selected. The two modulation waves are added to obtain the final additional modulation wave;

[0084] The first constraint condition is:

[0085]

[0086]

[0087] join Figure 4 , the specific process of step 4) is:

[0088] 41) Assume that the arm circulation i xy-cir for:

[0089]

[0090] Among them, 1 / m xy Clipped to [-1,1];

[0091] 42) In each voltage-balanced control of the additional balancing current, four signals are selected from the nine circulating currents obtained in step 41), and the remaining four signals are obtained by the second constraint condition. The circulating currents of different bridge arms are selected, and the two circulating currents are added to obtain the final circulating current;

[0092] The second constraint is:

[0093]

[0094]

[0095] 43) According to the coordinate transformation matrix C from the three-phase stationary coordinate system to the two-phase stationary coordinate system abc / αβ0 The coordinate transformation matrix C of the two-phase stationary coordinate system to the three-phase stationary coordinate system and its inverse transformation αβ0 / abc , the circulating current i obtained in step 42) xy_cir (x∈{u,v,w},y∈{a,b,c}) is transformed by αβ0, where

[0096]

[0097]

[0098]

[0099]

[0100] 44) According to the transformation matrix C from the two-phase stationary coordinate system to the dq0 coordinate system αβ0 / dq0_s and C αβ0 / dq0_l , perform Park transformation on the result obtained in step 43), where:

[0101]

[0102]

[0103]

[0104]

[0105] Figure 5 The principle of using two voltage balancing cycles in the present invention is given. Among them, the white circle indicates that the circulating current or additional modulation wave of the bridge arm is calculated by the voltage control loop, and the black triangle indicates that the circulating current or additional modulation wave of the bridge arm is obtained by the constraint condition. After two voltage balancing cycles, the difference between the capacitor voltage of the 8 bridge arms and the average capacitor voltage is adjusted to 0, so that the voltage balancing between the 9 bridge arms can be completed, and the additional modulation wave and additional bridge arm current of the two cycles are added respectively to obtain the additional modulation wave and additional bridge arm current that finally participate in M3C control.

[0106] 45) The q-axis current and the 0-sequence current of the matrix in the result obtained in step 44) are set to zero, and the additional balancing current is obtained as:

[0107]

[0108] Figure 6It is the simulation result diagram of the present invention, such as Figure 6 As shown, the present invention can realize capacitor voltage balance control of the M3C module.

Claims

1. A module capacitor voltage balance control method for a modular multi-level matrix converter, wherein the modular multi-level matrix converter comprises 9 bridge arms, characterized in that: The following steps are involved: 1) Subtract the average capacitor voltage of the nine bridge arms from the capacitor voltage of a single bridge arm, and the resulting difference is subjected to proportional integral control and quasi-proportional resonance control to obtain the equivalent DC circulating current of the bridge arm; 2) According to the current direction in the bridge arm, the equivalent DC circulating current is multiplied by 1 or -1 to obtain an additional balancing voltage, and the additional balancing voltage is normalized and limited to obtain an additional modulation wave of each bridge arm; 3) In the voltage balancing control of the additional balancing voltage of the modular multi-level matrix converter, steps 1) and 2) are performed on four bridge arms, and the modulation waves of the remaining four bridge arms are obtained by the first constraint condition; 4) In the voltage balancing control of the additional balancing current of the modular multilevel matrix converter, step 1) is performed on four bridge arms in the modular multilevel matrix converter, and then the equivalent DC circulating current of the four bridge arms is divided by the modulation wave thereof to obtain the circulating current of the four bridge arms, and the circulating current of the other four bridge arms is obtained by the second constraint condition, and the circulating current of all bridge arms in the modular multilevel matrix converter is subjected to Clark transformation and Park transformation to obtain the additional balancing current; 5) Adding the additional balancing current to the d-axis current on the power frequency side and the frequency division side respectively, and then passing through the current inner loop to obtain a modulation wave for input and output control; adding the additional modulation wave of the bridge arm to the modulation wave for input and output control to obtain the final modulation wave signal of the modular multi-level matrix converter; 6) performing module capacitor voltage balance control of the modular multi-level matrix converter according to the final modulation wave signal of the modular multi-level matrix converter; The specific operation process of step 1) is: 11) Let the capacitor voltage of the bridge arm be V xy_dc (x∈{u,v,w},y∈{a,b,c}), the average capacitor voltage of the nine bridge arms is V dc ,in, The bridge arm current is i xy (x∈{u,v,w},y∈{a,b,c}); 12) The average capacitor voltage of the nine bridge arms The capacitor voltage V xy_dc Subtract the difference, and after passing the proportional integral controller, the first part of the equivalent DC circulating current i is obtained. xy_dc_cir1 (x∈{u,v,w},y∈{a,b,c}), the difference is passed through the quasi-proportional resonant controller to obtain the second equivalent DC circulating current i xy_dc_cir2 (x∈{u,v,w},y∈{a,b,c}), the first part of the equivalent DC circulating current i xy_dc_cir1 (x∈{u,v,w},y∈{a,b,c}) and the equivalent DC circulating current i in the second part xy_dc_cir2 (x∈{u,v,w},y∈{a,b,c}) are added to obtain the final equivalent DC circulating current i of each bridge arm xy_dc_cir (x∈{u,v,w},y∈{a,b,c}); The specific process of step 2) is: 21) Assume the additional balancing voltage is: 22) Normalize the additional balance voltage and limit the amplitude to [-0.1, 0.1] to obtain the additional modulation wave m xy_cir for: The specific process of step 3) is: 31) In each voltage balancing control of the additional balancing voltage, 4 signals are selected from the 9 additional modulation waves obtained in step 22), and the remaining 4 signals are obtained by the first constraint condition. A total of two voltage balancing controls are performed, and modulation waves of different bridge arms are selected. The two modulation waves are added to obtain the final additional modulation wave; The first constraint condition is: The specific process of step 4) is: 41) Assume that the arm circulation i xy_cir for: Among them, 1 / m xy Clipped to [-1,1]; 42) In each voltage-balanced control of the additional balancing current, four signals are selected from the nine circulating currents obtained in step 41), and the remaining four signals are obtained by the second constraint condition. The circulating currents of different bridge arms are selected, and the two circulating currents are added to obtain the final circulating current; The second constraint is: 43) According to the coordinate transformation matrix C from the three-phase stationary coordinate system to the two-phase stationary coordinate system abc / αβ0 The coordinate transformation matrix C of the two-phase stationary coordinate system to the three-phase stationary coordinate system and its inverse transformation αβ0 / abc , the circulating current i obtained in step 42) xy_cir (x∈{u,v,w},y∈{a,b,c}) performs αβ0 transformation; 44) According to the transformation matrix C from the two-phase stationary coordinate system to the dq0 coordinate system αβ0 / dq0_s and C αβ0 / dq0_l , perform Park transformation on the result obtained in step 43); 45) The q-axis current and the 0-sequence current of the matrix in the result obtained in step 44) are set to zero, and the additional balancing current is obtained as:

2. The module capacitor voltage balance control method of the modular multi-level matrix converter according to claim 1, characterized in that: The specific operation of step 6) is: obtaining a triangular carrier signal of the modular multi-level matrix converter, subtracting the final modulation wave signal from the triangular carrier signal, and obtaining a PWM signal of the actual switch in each full-bridge module in the bridge arm according to the subtraction result, and the PWM signal controls the state of the actual switch of each full-bridge module in each bridge arm to realize the module capacitor voltage balance control of the modular multi-level matrix converter.

3. The module capacitor voltage balance control method of the modular multi-level matrix converter according to claim 1, characterized in that: The specific process of step 43) is: According to the coordinate transformation matrix C from the three-phase stationary coordinate system to the two-phase stationary coordinate system abc / αβ0 The coordinate transformation matrix C of the two-phase stationary coordinate system to the three-phase stationary coordinate system and its inverse transformation αβ0 / abc , the circulating current i obtained in step 42) xy_cir (x∈{u,v,w},y∈{a,b,c}) is transformed by αβ0, where 4. The module capacitor voltage balance control method of the modular multi-level matrix converter according to claim 3, characterized in that: The specific process of step 44) is: According to the transformation matrix C from the two-phase stationary coordinate system to the dq0 coordinate system αβ0 / dq0_s and C αβ0 / dq0_l , perform Park transformation on the result obtained in step 43), where:

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