A zero sequence injection modulation method for modular multilevel matrix converter

Abstract

This invention discloses a zero-sequence injection modulation method for a modular multilevel matrix converter, relating to the field of power electronics control technology. The modular multilevel matrix converter connects two AC systems of different frequencies. The method includes: obtaining modulation wave components for the input and output three-phase systems respectively through capacitor voltage outer loop control, input current inner loop control, and overall output current control via a sub-converter; calculating the corresponding modulation wave for each bridge arm based on the two modulation wave components; calculating the zero-sequence modulation voltage based on the modulation wave components of the input three-phase system; injecting the zero-sequence modulation voltage into each modulation wave to obtain the zero-sequence modulation wave; and using carrier modulation on all zero-sequence modulation waves to generate trigger pulses that are distributed to the switching devices of the corresponding bridge arm. This method, by injecting zero-sequence components into the modulation waves, can expand the linear modulation range and operating range of the modular multilevel matrix converter and improve the utilization rate of the sub-module capacitor voltage.

Description

Technical Field

[0001] This invention relates to the field of power electronic control technology, and in particular to a zero-sequence injection modulation method for a modular multilevel matrix converter. Background Technology

[0002] Modular multilevel technology has been rapidly applied to various fields of power electronics in recent years. Unlike back-to-back technology for AC-AC conversion, the Modular Multilevel Matrix Converter (M3C) can complete AC-AC conversion without an intermediate DC link. This makes the converter more efficient and eliminates the need for DC devices such as smoothing reactors and DC circuit breakers.

[0003] The topology of the converter is as follows: Figure 1 As shown, there are 9 bridge arms, each consisting of several sub-modules and a bridge arm inductor. Each sub-module consists of an H-bridge circuit and a capacitor. Each H-bridge circuit consists of 4 fully controlled power electronic switching devices. The input side x, y, z phases and the output side u, v, w phases are connected to 3 bridge arms respectively.

[0004] The M3C can decouple the input and output sides, enabling frequency and voltage conversion between them. It operates over a wide frequency range, including zero-frequency on one side, low-frequency on the other, input and output at the same frequency, and with a high conversion ratio. Therefore, the M3C can be applied in low-frequency power transmission, motor drives, and train traction.

[0005] The operating range of M3C is constrained by many factors, such as grid strength, device voltage and current withstand capabilities, and system control strategies. These constraints have a significant impact on the modulation range of M3C. Under existing modulation methods, the linear modulation range and operating range are relatively narrow, and the utilization rate of submodules is low. Summary of the Invention

[0006] To address the aforementioned technical problems in the prior art, this invention provides a zero-sequence injection modulation method for a modular multilevel matrix converter.

[0007] Specifically, the modular multilevel matrix converter connects two AC systems of different frequencies, and the technical solution includes the following steps:

[0008] Step S1: Perform capacitor voltage outer loop and input current inner loop control on the sub-converter in M3C to obtain the first modulation wave component of the input three-phase system;

[0009] By performing overall output current control on M3C, the second modulation wave component of the three-phase system on the output side is obtained;

[0010] For each arm of the M3C, calculate the difference between the first modulation wave component and the second modulation wave component, and normalize it to obtain the corresponding modulation wave.

[0011] Step S2: Take the average of the maximum and minimum values ​​in the first modulated wave component to calculate the zero-sequence modulation voltage;

[0012] Step S3: Inject the zero-sequence modulation voltage into each modulation wave to obtain the corresponding zero-sequence modulation wave;

[0013] Step S4: Use carrier modulation to modulate all zero-sequence modulation waves, generate trigger pulses and distribute them to the switching devices of the corresponding bridge arms to achieve modulation of the modular multilevel matrix converter.

[0014] Compared to existing technologies, the technical solution provided by this invention can expand the linear modulation range and operating range of the M3C and improve the utilization rate of the submodule capacitor voltage by injecting zero-sequence modulation voltage into the modulation wave. Furthermore, the use of a sub-converter to control the capacitor voltage outer loop and input current inner loop, as well as the overall output current, during the generation of the modulation wave, zero-sequence modulation voltage, and zero-sequence modulation wave helps to improve the modulation accuracy. Attached Figure Description

[0015] Figure 1 This is a topology diagram of M3C in one embodiment of the present invention.

[0016] Figure 2 This is a schematic diagram of a zero-sequence component calculation method in one embodiment of the present invention.

[0017] Figure 3 This is a schematic diagram of a zero-sequence component injection method in one embodiment of the present invention.

[0018] Figure 4 This is a schematic diagram of a method for generating a zero-sequence modulated wave in one embodiment of the present invention.

[0019] Figure 5 In one embodiment of the present invention, the input-side three-phase system Mutually, Mutually, Three-phase system with phase and output side Waveform diagram of the original ideal modulation wave of the phase-to-phase bridge arm.

[0020] Figure 6 In one embodiment of the present invention, the input-side three-phase system Mutually, Mutually, Three-phase system with phase and output side Waveform diagram of the original ideal modulation wave of the phase-to-phase bridge arm.

[0021] Figure 7In one embodiment of the present invention, the input-side three-phase system Mutually, Mutually, Three-phase system with phase and output side Waveform diagram of the original ideal modulation wave of the phase-to-phase bridge arm.

[0022] Figure 8 This is a waveform diagram of the injected zero-sequence component in one embodiment of the present invention.

[0023] Figure 9 In one embodiment of the present invention, the input-side three-phase system Mutually, Mutually, Three-phase system with phase and output side Waveform of the modulated wave after zero-sequence component is injected into the phase-to-phase bridge arm.

[0024] Figure 10 In one embodiment of the present invention, the input-side three-phase system Mutually, Mutually, Three-phase system with phase and output side Waveform of the modulated wave after zero-sequence component is injected into the phase-to-phase bridge arm.

[0025] Figure 11 In one embodiment of the present invention, the input-side three-phase system Mutually, Mutually, Three-phase system with phase and output side Waveform of the modulated wave after zero-sequence component is injected into the phase-to-phase bridge arm.

[0026] Figure 12 This is a diagram of the input current of the M3C after injecting a zero-sequence component in one embodiment of the present invention.

[0027] Figure 13 This is a diagram of the output current of M3C after injecting a zero-sequence component in one embodiment of the present invention. Detailed Implementation

[0028] The technical solutions provided by the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0029] Example 1:

[0030] like Figure 1 As shown, the M3C has a total of 9 bridge arms. to Each bridge arm is connected sequentially to the input and output sides according to phase. Each bridge arm consists of N full-bridge submodules and their associated DC capacitors and bridge arm inductors. Each full-bridge submodule consists of 4 switching transistors and 1 capacitor. For example... Figure 1The M3C shown in this embodiment provides a modulation method based on zero-sequence injection to extend its power operating range, including the following steps:

[0031] Step 1: Define the M3C modulation scheme and write the M3C bridge arm voltage expression based on the M3C operating principle.

[0032] The operating range of the M3C is limited by its own modulation range, which is affected by three parts: the input AC voltage, the output AC voltage, and the bridge arm capacitor voltage, as shown in the following formula:

[0033] ;

[0034] ;

[0035] ;

[0036] In the formula, The modulation index for M3C is typically greater than 0 and less than 1. This refers to the voltage amplitude on the input side of the M3C. This refers to the voltage amplitude on the output side of the M3C. This refers to the number of sub-modules in the bridge arm of a modular multilevel matrix converter. This refers to the capacitor voltage of a single submodule. Indicates the phase of the input-side three-phase system. Indicates the phase of the three-phase system on the output side. , and This indicates the three phases of the input-side three-phase system. , and The three phases of the output-side three-phase system.

[0037] Define the M3C input side Phase voltage and input side Phase current (include , and The formula is as follows:

[0038] ;

[0039] ;

[0040] In the formula, For the input side three-phase system Phase frequency; For time; For the input side three-phase system Phase, the corresponding value represents a different phase of the input three-phase system; This refers to the current amplitude on the input side. This refers to the power factor of the three-phase system on the input side. Specifically, the input side... Phase voltage include , and Input side Phase current include , and ; Input side three-phase system Three-phase system with phase and output side The phase-to-phase bridge arm current is ,include , , , , , , , and . For input side Phase to output side The voltage between the bridge arms of the phases.

[0041] Define the output side of M3C Phase voltage and input side Phase current The formula is as follows:

[0042] ;

[0043] ;

[0044] In the formula, For the output side three-phase system Phase frequency; For the output side three-phase system Phase, the corresponding value represents a different phase of the three-phase system on the output side; This refers to the current amplitude on the output side. The initial phase difference between the input-side three-phase system and the output-side three-phase system under initial conditions; This refers to the power factor of the three-phase system on the output side. Specifically, the power factor on the output side... Phase voltage include , and Output side Phase current include , and .

[0045] The formula for calculating the bridge arm voltage is as follows:

[0046] ;

[0047] In the formula, For bridge arm inductance, The differential symbol, For time, This represents the voltage difference between the grounding points of the input-side three-phase system and the output-side three-phase system.

[0048] Step 2: During normal operation, the input three-phase system is completely symmetrical, and the output three-phase system is also completely symmetrical. Therefore, the ideal expression for the bridge arm voltage can be obtained as follows:

[0049] ;

[0050] ;

[0051] ;

[0052] Specifically, the input-side voltage, output-side voltage, and voltage of each bridge arm capacitor of the M3C are collected and input into the controller. Using the controller's input-side control output and output-side output as references, the difference between the two voltages is calculated to obtain the ideal bridge arm voltage. Since each of the three sub-converters has one arm connected to the output phase, the corresponding ideal modulated waves differ only in phase. In the M3C, this includes arm-based... It consists of 9 sub-converters.

[0053] In the control system, the bridge arm voltage in the above formula is... Per-unit modulation, as the modulated wave of the M3C bridge arm It should be noted that in actual control systems, the output of the input-side control system is usually subtracted from the output-side control system, and then normalized to obtain the modulated wave of the bridge arm.

[0054] Step 3: Collect the three-phase AC voltage and calculate the zero-sequence modulation wave.

[0055] The modulation method described above requires the calculation of the zero-sequence modulation wave. In practical applications, the three-phase voltage on the input side is first collected by a voltage sensor, then input into the control system through a filter, and finally the zero-sequence modulation wave is calculated from the collected three-phase voltage.

[0056] like Figure 2As shown, the generation rule is to collect the maximum and minimum values ​​of the input-side voltages of all bridge arms, and then multiply them by a scaling factor of -0.5 to calculate the zero-sequence component (zero-sequence modulation voltage) injected into the M3C. The formula is as follows:

[0057] ;

[0058] ;

[0059] ;

[0060] In the formula, , and For the input side three-phase system Mutually, Harmony Corresponding to the input side voltage. In the diagram, PCC1 and PCC2 are two grid connection points. Indicates M3C, The input grid voltage amplitude, For line impedance, For the input grid-connected inductance, This indicates the input port voltage of the converter. This indicates the voltage at the converter output port. To output the grid-connected inductor on the grid side, For line impedance, This is the output grid voltage amplitude.

[0061] The zero-sequence modulation voltage injected into each bridge arm is exactly the same. Therefore, whether it is the zero-sequence modulation voltage injected into the input sub-converter or the zero-sequence modulation voltage injected into the output sub-converter, it is exactly the same. Thus, injecting the zero-sequence modulation voltage wave of this invention will not affect the power quality of the input and output sides of the M3C system.

[0062] Step 4: Inject the zero-sequence modulation voltage calculated in Step 3 into the modulation wave output by the control system of the M3C bridge arm, as shown in the following formula:

[0063] ;

[0064] In the formula, For input side Phase to output side Zero-sequence modulation wave between phase arms, For bridge arm voltage The modulated wave obtained after standardization.

[0065] Specifically, such as Figure 3As shown, injecting the zero-sequence modulation voltage into the corresponding modulation wave yields the zero-sequence modulation wave for each bridge arm, as shown in the following formula:

[0066] ;

[0067] ;

[0068] ;

[0069] ;

[0070] ;

[0071] ;

[0072] ;

[0073] ;

[0074] ;

[0075] After injection, due to the special nature of the M3C topology, the injected components of the modulation wave in all bridge arms are exactly the same. Thus, for the entire converter system, whether from the input side or the output side, it does not affect the overall input and output. The injected zero-sequence voltage only improves the utilization rate of the capacitor voltage of each submodule in the bridge arm within the system.

[0076] Example 2:

[0077] like Figure 4 As shown, in this embodiment, in order to improve the accuracy of the modulation method, the generation methods of the modulation wave, zero-sequence modulation voltage and zero-sequence modulation wave in Embodiment 1 were adjusted. Then, the carrier modulates all the zero-sequence modulation waves, generates trigger pulses and distributes them to the switching devices of the corresponding bridge arms, thereby realizing the modulation of the modular multilevel matrix converter.

[0078] Specifically, the method for generating the zero-sequence modulated wave in this embodiment includes steps S1 to S4.

[0079] Obtain the voltage phase at the input-side grid connection point Voltage phase with the output side grid connection point The three-phase voltage input PLL (Phase-Locked Loop) at the input side grid connection point of the M3C is acquired to obtain the voltage phase at the input side grid connection point. The three-phase voltage input PLL at the output-side grid connection point of the M3C is acquired to obtain the voltage phase at the output-side grid connection point. .

[0080] Step S1 includes steps S11 to S13:

[0081] Step S11: Based on voltage phase By performing capacitor voltage outer loop and input current inner loop control on the sub-converter in M3C, the first modulation wave component of the input three-phase system is obtained.

[0082] For the input-side three-phase system: the d-axis current reference value Add 1 / 3 and then subtract the d-axis current. The difference is used for PI control to obtain the d-axis voltage. ; set the q-axis current reference value Subtract q-axis current The difference is used for PI control to obtain the q-axis voltage. Based on voltage phase d-axis voltage reference value Subtract d-axis voltage The difference between the q-axis voltage reference value and the q-axis voltage reference value Subtract q-axis voltage The difference is used to perform an inverse Clarke transform to obtain the first modulation wave component of each phase of the input three-phase system. , and .

[0083] Step S12: Based on voltage phase By controlling the overall output current of M3C, the second modulation wave component of the three-phase system on the output side is obtained.

[0084] For the output-side three-phase system: the d-axis current reference value Subtract d-axis current The difference is used for PI control to obtain the d-axis voltage. ; set the q-axis current reference value Subtract q-axis current The difference is used for PI control to obtain the q-axis voltage. Based on voltage phase d-axis voltage reference value Add d-axis voltage The sum of the q-axis voltage reference values Add q-axis voltage The sum is subjected to an inverse Clarke transform to obtain the second modulation wave component of each phase of the output three-phase system. , and .

[0085] Step S13: For each arm of the M3C, calculate the difference between the first modulation wave component and the second modulation wave component and normalize it to obtain the corresponding modulation wave.

[0086] For each bridge arm Calculate the corresponding first modulation wave component. Subtract the modulated wave component The difference is obtained and normalized to obtain the modulated wave. ;in, ; .

[0087] Specifically, for each phase of the three-phase output system, the capacitor voltages in the corresponding three sub-converters are collected and summed to obtain the actual value. Then filtering is performed; the reference value of the sum of capacitor voltages is then used. Subtract the filtered actual value After obtaining the difference, PI control is then performed to obtain the d-axis current reference value for the inner loop control of the three-phase system input current on the input side. .

[0088] Step S2: Take the average of the maximum and minimum values ​​in the first modulated wave component, and calculate the zero-sequence modulation voltage using the following formula:

[0089] ;

[0090] ;

[0091] ;

[0092] In the formula, The maximum value of the first modulated wave component. This is the minimum value of the first modulated wave component. It is a zero-sequence modulation voltage.

[0093] Step S3: Inject the zero-sequence modulation voltage into each modulation wave to obtain the corresponding zero-sequence modulation wave, as shown in the following formula:

[0094] ;

[0095] In the formula, For bridge arm The corresponding zero-sequence modulation wave.

[0096] Step S4: Use carrier modulation to modulate all zero-sequence modulation waves, generate trigger pulses and distribute them to the switching devices of the corresponding bridge arms to achieve modulation of the modular multilevel matrix converter.

[0097] Before zero-sequence modulation voltage injection, the input side three-phase system Three-phase system with phase and output side Alternating bridge arms The original ideal modulated wave, such as Figures 5 to 7 As shown, the bridge arm Specifically including , , , , , , , and The waveform shape of the injected zero-sequence component is as follows: Figure 8 As shown. The bridge arm obtained after zero-sequence modulation voltage injection. The waveform of the zero-sequence modulated wave is as follows Figures 9 to 11 As shown. The M3C input-side current after injecting the zero-sequence component is as follows: Figure 12 As shown, the output current of the M3C after injecting the zero-sequence component is as follows: Figure 13 As shown.

[0098] As can be seen, before the injection, the amplitude of the modulated wave is infinitely close to 1, i.e., at full modulation. However, after the zero-sequence component is injected into the modulated wave, the peak value of the modulated wave in the corresponding bridge arm decreases. According to the operating principle of the M3C itself, and since there is no connection between the neutral point of the M3C's input and output terminals, the injected zero-sequence component will not affect either the input current or the output current.

[0099] Finally, the nine zero-sequence modulation waves are injected into the switching devices of their respective bridge arms to achieve modulation of the modular multilevel matrix converter.

[0100] As can be seen from the above embodiments and accompanying drawings, compared with the prior art, the technical solution provided by the present invention can expand the linear modulation range and operating range of the M3C and improve the utilization rate of the submodule capacitor voltage by injecting zero-sequence modulation voltage into the modulation wave. Furthermore, the use of a sub-converter to control the capacitor voltage outer loop and the input current inner loop, as well as the overall output current, in the process of generating the modulation wave, zero-sequence modulation voltage, and zero-sequence modulation wave helps to improve the modulation accuracy.

Claims

1. A zero-sequence injection modulation method for a modular multilevel matrix converter, wherein the modular multilevel matrix converter is connected to two AC systems of different frequencies, characterized in that, Includes the following steps: Step S1: Perform capacitor voltage outer loop and input current inner loop control on the sub-converter in M3C to obtain the first modulation wave component of the input three-phase system; By performing overall output current control on M3C, the second modulation wave component of the three-phase system on the output side is obtained; For each arm of the M3C, calculate the difference between the first modulation wave component and the second modulation wave component, and normalize it to obtain the corresponding modulation wave. Step S2: Take the average of the maximum and minimum values ​​in the first modulated wave component to calculate the zero-sequence modulation voltage; Step S3: Inject the zero-sequence modulation voltage into each modulation wave to obtain the corresponding zero-sequence modulation wave; Step S4: Use carrier modulation to modulate all zero-sequence modulation waves, generate trigger pulses and distribute them to the switching devices of the corresponding bridge arms to achieve modulation of the modular multilevel matrix converter.

2. The zero-sequence injection modulation method for a modular multilevel matrix converter as described in claim 1, characterized in that, Step S1 includes: For the input-side three-phase system: the d-axis current reference value Add 1 / 3 and then subtract the d-axis current. The difference is used for PI control to obtain the d-axis voltage. ; set the q-axis current reference value Subtract q-axis current The difference is used for PI control to obtain the q-axis voltage. Based on voltage phase d-axis voltage reference value Subtract d-axis voltage The difference between the q-axis voltage reference value and the q-axis voltage reference value Subtract q-axis voltage The difference is used to perform an inverse Clarke transform to obtain the first modulation wave component of each phase of the input three-phase system. , and ; For the output-side three-phase system: the d-axis current reference value Subtract d-axis current The difference is used for PI control to obtain the d-axis voltage. ; set the q-axis current reference value Subtract q-axis current The difference is used for PI control to obtain the q-axis voltage. Based on voltage phase d-axis voltage reference value Add d-axis voltage The sum of the q-axis voltage reference values Add q-axis voltage The sum is subjected to an inverse Clarke transform to obtain the second modulation wave component of each phase of the output three-phase system. , and ; For each bridge arm Calculate the corresponding first modulation wave component. Subtract the second modulated wave component The difference is obtained and normalized to obtain the modulated wave. ;in, ; .

3. The zero-sequence injection modulation method for a modular multilevel matrix converter as described in claim 2, characterized in that, Also includes: The three-phase voltage input PLL at the input side grid connection point of the M3C is acquired to obtain the voltage phase at the input side grid connection point. ; The three-phase voltage input PLL at the output-side grid connection point of the M3C is acquired to obtain the voltage phase at the output-side grid connection point. .

4. The zero-sequence injection modulation method for a modular multilevel matrix converter as described in claim 2, characterized in that, Also includes: For each phase of the three-phase output system, the capacitor voltages in the corresponding three sub-converters are collected and summed to obtain the actual value. Then filter is performed; Reference value of the sum of capacitor voltages Subtract the filtered actual value After obtaining the difference, PI control is then performed to obtain the d-axis current reference value for the inner loop control of the three-phase system input current on the input side. .

5. The zero-sequence injection modulation method for a modular multilevel matrix converter as described in claim 2, characterized in that, The formula for step S2 is as follows: ； ； ； In the formula, The maximum value of the first modulated wave component. This is the minimum value of the first modulated wave component. It is a zero-sequence modulation voltage.

6. The zero-sequence injection modulation method for a modular multilevel matrix converter as described in claim 5, characterized in that, The formula for step S3 is as follows: ； In the formula, For bridge arm The corresponding zero-sequence modulated wave.

7. The zero-sequence injection modulation method for a modular multilevel matrix converter as described in claim 1, characterized in that, This also includes adjusting the system by calculation. The modulation range of the modular multilevel matrix converter is determined by the following formula: ； ； ； In the formula, The voltage amplitude at the input side of the modular multilevel matrix converter. The voltage amplitude at the output side of the modular multilevel matrix converter. This refers to the number of sub-modules in the bridge arm of a modular multilevel matrix converter. This refers to the capacitor voltage of a single submodule. Indicates the phase of the input-side three-phase system. Indicates the phase of the three-phase system on the output side. , and This indicates the three phases of the input-side three-phase system. , and The three phases of the output-side three-phase system.

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