Current transformer bridge arm capacitor voltage ripple equalization control method

Abstract

The invention provides a converter bridge arm capacitor voltage ripple equalization control method, which is applied to a modular multi-level matrix converter, establishes a system state space equation of the modular multi-level matrix converter based on the Kirchhoff's law, decouples the system state space equation through coordinate transformation to obtain a state decoupling equation, and carries out voltage ripple equalization control on the modular multi-level matrix converter. Drawing an equivalent decoupling circuit model by using a system state decoupling equation; establishing a bridge arm capacitor voltage average value-power mathematical model according to the bridge arm power equation; injecting the symmetric circulating current and the common-mode voltage into the modular multi-level matrix converter, and controlling the modular multi-level matrix converter by using the equivalent decoupling circuit model and the bridge arm capacitor voltage average value-power mathematical model to obtain a ripple balance control result of the modular multi-level matrix converter; the power balance control of each phase of bridge arm can be realized, and the voltage ripple of the balance capacitor is effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of converter control, and particularly relates to a method for controlling the balance of the capacitor voltage ripple of a converter arm. Background Art

[0002] In recent years, with the increasingly severe problems such as energy crisis and environmental pollution, countries have paid more attention to the development and utilization of renewable energy. The Modular Multilevel Matrix Converter (M3C) has the advantages of complete modularity, simple expansion to high voltage levels, flexible control, good harmonic quality, good redundancy, etc., and is widely used in high-power high-voltage systems. However, the voltage and current of the 9 arms in the M3C have strongly coupled characteristic points, and it is difficult to directly control. The problem of balancing the capacitor voltage between the arms also needs to be solved by the M3C. The voltage and current frequency coupling relationships on the input side and the output side are more complex compared with the Modular Multilevel Converter (M2C). At present, domestic and foreign literatures have studied the mathematical model and control method of the M3C. For example, some research has proposed the idea of double αβ transformation to achieve the decoupling control of the input and output currents and the arm circulating current. However, the controlled quantities on the input side and the output side of this decoupling model are all alternating quantities, and it is difficult to ensure its dynamic performance under PID control. Some research has proposed to offset the severe oscillation of the capacitor voltage under the condition of low input-side frequency of the M3C through the "instantaneous energy control" of the arm circulating current. However, this method will generate an AC component of the capacitor voltage, resulting in the abnormal operation of the M3C due to the oscillation of the capacitor voltage. Some research has used space vector pulse width modulation to control the input and output side currents. However, due to the lack of real-time monitoring and feedback control of the DC capacitor voltage of the sub-modules on each arm, the voltage sharing effect among the sub-modules in each arm is poor. Some research has achieved the balance control of the capacitor voltage ripple of the converter by adding a DC component to the circulating current and the common-mode voltage. However, this method has the problem of a relatively high amplitude of the capacitor voltage ripple of the sub-module. Some research has effectively solved the problem of capacitor voltage ripple balance control by introducing intermediate adjustment quantities, the circulating current and the common-mode voltage, and setting the combination of fundamental frequency and multiple frequency components in the circulating current and the common-mode voltage. However, the asymmetric circulating current injection method will generate sinusoidal component circulating currents with unequal amplitudes on the three-phase arms, thereby making it difficult to achieve consistent balance of the arm capacitor voltage ripple, seriously affecting the life of some capacitors. Summary of the Invention

[0003] The present invention provides a method for controlling the balance of the capacitor voltage ripple of a converter arm, and its purpose is to reduce the capacitor voltage ripple of the arm and achieve the balanced control of the power of each phase arm.

[0004] To achieve the above object, the present invention provides a control method for balancing the capacitor voltage ripple of the converter arm, which is applied to a modular multilevel matrix converter. The control method includes:

[0005] Step 1, establish the system state space equation of the modular multilevel matrix converter based on Kirchhoff's law, and decouple the system state space equation through coordinate transformation to obtain the state decoupling equation. Use the system state decoupling equation to draw the equivalent decoupled circuit model;

[0006] Step 2, establish the arm capacitor voltage average value - power mathematical model according to the arm power equation;

[0007] Step 3, inject the symmetric circulating current and the common - mode voltage into the modular multilevel matrix converter, and use the equivalent decoupled circuit model and the arm capacitor voltage average value - power mathematical model to control the modular multilevel matrix converter to obtain the ripple balance control result of the modular multilevel matrix converter.

[0008] Furthermore, the expression of the system state space equation is:

[0009]

[0010] Among them, u pa 、u pb 、u pc 、u na 、u nb 、u nc respectively represent the voltages between the arm of each phase, u sa 、u sb 、u sc respectively represent the bus voltages of each phase, u o represents the output voltage, L q represents the arm inductor, i pa 、i pb 、i pc 、i na 、i nb 、i nc respectively represent the arm currents of each phase, u GO represents the common - mode voltage.

[0011] Furthermore, the expression of the system state decoupling equation is:

[0012]

[0013] Among them, represents the component of the arm voltage in the abc - αβ0∑Δ coordinate system, both represent the components of the circulating current in the αβ0 coordinate system, u sα 、u sβ 、isα , i sβ respectively represent the symmetric AC grid voltages and currents obtained through Clarke transformation, and u n represents the common-mode voltage in the αβ0 coordinate system.

[0014] Furthermore, the equivalent decoupling circuit model includes:

[0015] A circulating current system model, including a first circulating current system model composed of the arm inductance L q and the components of the arm voltage in the abc-αβ0∑Δ coordinate system and a second circulating current system model composed of the arm inductance L q and the components of the arm voltage in the abc-αβ0∑Δ coordinate system ;

[0016] A common-mode voltage model, including the common-mode voltage u n in the αβ0 coordinate system and the components of the arm voltage in the abc-αβ0∑Δ coordinate system

[0017] An input system model, including a first input system model composed of the symmetric AC grid voltages u sα obtained through Clarke transformation, the components of the arm voltage in the abc-αβ0∑Δ coordinate system the arm inductance L q and a second input system model composed of the symmetric AC grid voltages u sβ obtained through Clarke transformation, the components of the arm voltage in the abc-αβ0∑Δ coordinate system the arm inductance L q ;

[0018] An output system model, including the output voltage u o , the components of the arm voltage in the abc-αβ0∑Δ coordinate system and the arm inductance L q .

[0019] Furthermore, the arm power equation is:

[0020]

[0021] Among them, represents the rated value of the sub-module capacitor voltage, C represents the sub-module capacitor value, and U Cap , U Cbp , U Ccp respectively represent the sum of the sub-module capacitor voltages of the upper arms of each phase, and U Can , U Cbn , U Ccnrespectively represent the sum of the capacitor voltages of the sub-modules in the lower arm of each phase, p ap 、p bp 、p cp respectively represent the power of the upper arm of each phase, p an 、p bn 、p cn respectively represent the power of the lower arm of each phase.

[0022] Furthermore, the expression of the average bridge-arm capacitor voltage-power mathematical model is:

[0023]

[0024] Among them, respectively represent the inter-phase capacitor voltage differences in the abc-αβ0ΣΔ coordinate system, respectively represent the capacitor voltage differences between the upper and lower arms of each phase in the abs-αβ0ΣΔ coordinate system, represents the sum of the capacitor voltages of the modular multilevel matrix converter, respectively represent the average values of the bridge-arm voltages of each phase in the abc-αβ0∑Δ coordinate system.

[0025] Furthermore, using the equivalent decoupling circuit model and the average bridge-arm capacitor voltage-power mathematical model to control the modular multilevel matrix converter includes:

[0026] Using the equivalent decoupling circuit model and the average bridge-arm capacitor voltage-power mathematical model to control the input current of the modular multilevel matrix converter;

[0027] Using the equivalent decoupling circuit model to control the output voltage of the modular multilevel matrix converter;

[0028] Using the equivalent decoupling circuit model and the average bridge-arm capacitor voltage-power mathematical model to balance the control of the bridge-arm energy of the modular multilevel matrix converter.

[0029] Furthermore, using the equivalent decoupling circuit model and the average bridge-arm capacitor voltage-power mathematical model to control the input current of the modular multilevel matrix converter includes:

[0030] Using the average bridge-arm capacitor voltage-power mathematical model and the PI controller to control the outer loop of the input current to obtain the control result of the outer loop of the input current;

[0031] Using the control result of the outer loop of the input current, the input system model in the equivalent decoupling circuit model and the PR controller to control the input current.

[0032] Furthermore, controlling the output voltage of the modular multilevel matrix converter using the equivalent decoupling circuit model includes:

[0033] Controlling the output voltage of the modular multilevel matrix converter using the output system model and the PR controller in the equivalent decoupling circuit model.

[0034] Furthermore, balancing the arm energy of the modular multilevel matrix converter using the equivalent decoupling circuit model and the average arm capacitor voltage - power mathematical model includes:

[0035] Controlling the average capacitor voltage of the modular multilevel matrix converter using the average arm capacitor voltage - power mathematical model and PI control to obtain the control result of the average capacitor voltage;

[0036] Controlling the circulating current of the modular multilevel matrix converter using the control result of the average capacitor voltage, the circulating current system model in the equivalent decoupling circuit model, and the PR controller to obtain the control result of the circulating current;

[0037] Controlling the common - mode voltage of the modular multilevel matrix converter using the common - mode voltage model and the P controller in the equivalent decoupling circuit model to obtain the control result of the common - mode voltage;

[0038] Balancing the arm energy of the modular multilevel matrix converter using the control result of the circulating current and the control result of the common - mode voltage.

[0039] The above - mentioned solution of the present invention has the following beneficial effects:

[0040] The present invention is applied to the modular multilevel matrix converter. Based on Kirchhoff's law, the system state - space equation of the modular multilevel matrix converter is established, and the system state - space equation is decoupled through coordinate transformation to obtain the state decoupling equation. The equivalent decoupling circuit model is drawn using the system state decoupling equation; the average arm capacitor voltage - power mathematical model is established according to the arm power equation; the symmetric circulating current and the common - mode voltage are injected into the modular multilevel matrix converter, and the modular multilevel matrix converter is controlled using the equivalent decoupling circuit model and the average arm capacitor voltage - power mathematical model to obtain the ripple equilibrium control result of the modular multilevel matrix converter. Compared with the prior art, by injecting the symmetric circulating current and the common - mode voltage into the modular multilevel matrix converter and controlling the modular multilevel matrix converter using the equivalent decoupling circuit model and the average arm capacitor voltage - power mathematical model, the balanced control of the power of each phase arm can be realized, and the ripple of the arm capacitor voltage can be effectively reduced.

[0041] Other beneficial effects of the present invention will be described in detail in the subsequent detailed implementation section. Description of the Drawings

[0042] Figure 1 It is a schematic flow chart of an embodiment of the present invention;

[0043] Figure 2 It is a topological structure diagram of a modular multilevel matrix converter in an embodiment of the present invention;

[0044] Figure 3 It is a schematic diagram of an equivalent decoupling circuit model in an embodiment of the present invention;

[0045] Figure 4 It is a control block diagram of the input current in an embodiment of the present invention;

[0046] Figure 5 It is a control block diagram of the output voltage in an embodiment of the present invention;

[0047] Figure 6 It is a balance control block diagram of the arm energy in an embodiment of the present invention;

[0048] Figure 7 It is a schematic diagram of the steady-state waveforms of the input and output voltages and currents in an embodiment of the present invention;

[0049] Figure 8 It is a steady-state waveform diagram of the upper-bridge-arm capacitor voltage controlled by Method 1 in an embodiment of the present invention;

[0050] Figure 9 It is a steady-state waveform diagram of the upper-bridge-arm capacitor voltage controlled by Method 2 in an embodiment of the present invention. Detailed implementation manners

[0051] To make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following will be described in detail with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0052] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0053] In the description of the present invention, it should be noted that unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a locking connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0054] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0055] The present invention provides a method for controlling the ripple balance of the capacitor voltage of the converter bridge arm in view of the existing problems.

[0056] As Figure 1 shown, an embodiment of the present invention provides a method for controlling the ripple balance of the capacitor voltage of the converter bridge arm, which is applied to a modular multilevel matrix converter. The control method includes:

[0057] Step 1: Establish a system state space equation of the modular multilevel matrix converter based on Kirchhoff's law, decouple the system state space equation through coordinate transformation to obtain a state decoupling equation, and draw an equivalent decoupling circuit model by using the system state decoupling equation;

[0058] Step 2: Establish a mathematical model of the average value of the capacitor voltage - power of the bridge arm according to the bridge arm power equation;

[0059] Step 3: Inject the symmetric circulating current and the common - mode voltage into the modular multilevel matrix converter, and control the modular multilevel matrix converter by using the equivalent decoupling circuit model and the mathematical model of the average value of the capacitor voltage - power of the bridge arm to obtain the ripple balance control result of the modular multilevel matrix converter.

[0060] As Figure 2 shown, the modular multilevel matrix converter mentioned in the embodiment of the present invention includes a three - phase AC power grid, three - phase bridge arms, and each phase bridge arm includes upper and lower two groups of bridge arms, and each group of upper bridge arms includes N sub - modules SM.

[0061] Specifically, Step 1 includes:

[0062] Define the calculation expressions of the input voltage, input current, output voltage, and output current of the modular multilevel matrix converter as:

[0063] u sa =U s cosω m t

[0064] Among them, u sa represents the input voltage, and i sa represents the input current, u o represents the output voltage, and i o represents the output current, U s represents the amplitude of the input voltage, ω m represents the angular frequency on the input side, I s represents the amplitude of the input current, represents the power factor angle on the input side, U o represents the amplitude of the output voltage, ω o represents the angular frequency on the output side, represents the phase difference between the input and output, I o represents the amplitude of the output current, represents the power factor angle on the output side;

[0065] Based on Kirchhoff's law, the system state space equation of the modular multilevel matrix converter in the three-phase stationary coordinate system is as follows:

[0066]

[0067] Among them, u pa , u pb , u pc , u na , u nb , u nc respectively represent the voltages between the bridge arms of each phase, u sa , u sb , u sc respectively represent the bus voltages of each phase, u o represents the output voltage, L q represents the bridge arm inductor, i pa , i pb , i pc , i na , i nb , i nc respectively represent the bridge arm currents of each phase, u GO represents the common-mode voltage;

[0068] The system state space equation in the three-phase stationary coordinate system is decoupled by the abc-αβ0∑Δ coordinate transformation method, including:

[0069] The abc-αβ0∑Δ coordinate transformation is divided into two steps for coordinate transformation. The state matrix H of the converter abc first multiplies the right matrix and then multiplies the left matrix C ∑Δ , and the expression is:

[0070]

[0071] In the formula:

[0072]

[0073] Then, after performing the abc-αβ0ΕΔ transformation on the system state space equation based on the above formula, the state decoupling equation is obtained, and the expression is:

[0074]

[0075] Wherein, represents the component of the arm voltage in the abc-αβ0ΣΔ coordinate system, both represent the components of the circulating current in the αβ0 coordinate system, is proportional to the output current i sa , u sa , u sβ , i sα , i sβ respectively represent the symmetrical AC grid voltages and currents of each phase obtained through the Clarke transformation, and u n represents the common-mode voltage in the αβ0 coordinate system;

[0076] Using the system state decoupling equation to draw the equivalent decoupling circuit model, as shown in Figure 3 shown, the equivalent decoupling circuit model includes:

[0077] Circulating current system model, as shown in Figure 3 (a), including the first circulating current system model composed of the arm inductor L q and the component of the arm voltage in the abc-αβ0∑Δ coordinate system , and the second circulating current system model composed of the arm inductor L q and the component of the arm voltage in the abc-αβ0∑Δ coordinate system ;

[0078] Common-mode voltage model, as shown in Figure 3 (b), including the common-mode voltage u n in the αβ0 coordinate system and the component of the arm voltage in the abc-αβ0∑Δ coordinate system

[0079] Input system model, as shown in Figure 3 (c), including the first input system model composed of the symmetrical AC grid voltages u sα of each phase obtained through the Clarke transformation, the component of the arm voltage in the abc-αβ0∑Δ coordinate system the arm inductor L q And the symmetrical AC grid voltages u of each phase obtained through the Clarke transformation sβ, Components of the arm voltage in the abc-αβ0∑Δ coordinate system Arm inductance L q The second input system model composed of;

[0080] The output system model, as Figure 3 (d) shows, including the output voltage u o , Components of the arm voltage in the abc-αβ0ΕΔ coordinate system And the arm inductance L q .

[0081] Specifically, step 2 includes:

[0082] Perform coordinate transformation on the arm power in the three-phase coordinate system, and transform the arm power to the Δαβ0 coordinate system. The transformation expression is:

[0083]

[0084] The arm power equation obtained through the above transformation expression is:

[0085]

[0086] Among them, Represents the rated value of the sub-module capacitor voltage, C represents the sub-module capacitor value, U Cap , U Cbp , U Ccp Respectively represent the sum of the sub-module capacitor voltages of the upper arm of each phase, U Can , U Cbn , U Ccn Respectively represent the sum of the sub-module capacitor voltages of the lower arm of each phase, p ap , p bp , p cp Respectively represent the power of the upper arm of each phase, p an , p bn , p cn Respectively represent the power of the lower arm of each phase;

[0087] By ignoring the arm inductance voltage and switching losses in the arm power equation and assuming that the capacitor voltages in all sub-modules are adjusted to the reference value, the expression of the mathematical model of the arm capacitor voltage and power is obtained as:

[0088]

[0089] Among them,

[0090]

[0091]

[0092] Taking the average value of the arm capacitance voltage and power mathematical model, the expression of the arm capacitance voltage average - power mathematical model is established as follows:

[0093]

[0094] Wherein, respectively represent the phase - to - phase capacitance voltage difference in the abc - αβ0∑Δ coordinate system, respectively represent the capacitance voltage difference between the upper and lower arms of each phase in the abc - αβ0∑Δ coordinate system. In order to achieve the arm energy balance, it is necessary to adjust the average value of the capacitance voltage imbalance to zero. represents the sum of the capacitance voltages of the modular multilevel matrix converter, which is used to control the average value of the total voltage of the arm. respectively represent the average values of the arm voltages of each phase in the abc - αβ0∑Δ coordinate system.

[0095] Specifically, step 3 includes:

[0096] Injecting the symmetric circulating current and the common - mode voltage into the modular multilevel matrix converter. The symmetric circulating current and the common - mode voltage u n have the following expressions respectively:

[0097]

[0098] u n = U n1 cos(ω m t + α3)+U n2 cos(ω n t + α3)

[0099] In the formula, I z1 、I z5 respectively represent the amplitudes of the positive - sequence and negative - sequence components of the three - phase symmetric circulating current with the injection frequency of ω m , I z2 、I z6 respectively represent the amplitudes of the positive - sequence and negative - sequence components of the three - phase symmetric circulating current with the injection frequency of ω n , U n1 、U n2 respectively represent the amplitudes of the common - mode voltages with the frequencies of ω m 、ω n , and U n2 is a non - zero constant;

[0100] Substituting the expressions of the symmetric circulating current and the common - mode voltage u n into the arm capacitance voltage average - power mathematical model, the following expression is obtained:

[0101]

[0102]

[0103] The modular multilevel matrix converter is controlled by using an equivalent decoupling circuit model and a mathematical model of the average value of the arm capacitor voltage - power to obtain the ripple equalization control result of the modular multilevel matrix converter.

[0104] Since the control of the modular multilevel matrix converter is divided into three parts, namely input current control, output voltage control, and arm energy balance control, the modular multilevel matrix converter is converted from under - actuated to fully actuated by injecting circulating current and common - mode voltage; although the asymmetric circulating current injection method can ensure that the average power is 0 by adjusting the circulating current amplitude, enabling the modular multilevel matrix converter to achieve the balance of the average capacitor voltage, it generates sinusoidal components with unequal amplitudes in the three - phase circulating current, resulting in unbalanced power of each arm, inability to balance the ripple voltage, causing the rated voltage of some capacitors to be too high, and increasing the overall cost of the device; therefore, the embodiments of the present invention control the modular multilevel matrix converter by using an equivalent decoupling circuit model and a mathematical model of the average value of the arm capacitor voltage - power, including:

[0105] Controlling the input current of the modular multilevel matrix converter by using an equivalent decoupling circuit model and a mathematical model of the average value of the arm capacitor voltage - power;

[0106] Controlling the output voltage of the modular multilevel matrix converter by using an equivalent decoupling circuit model;

[0107] Balancing the arm energy of the modular multilevel matrix converter by using an equivalent decoupling circuit model and a mathematical model of the average value of the arm capacitor voltage - power.

[0108] Specifically, controlling the input current of the modular multilevel matrix converter by using an equivalent decoupling circuit model and a mathematical model of the average value of the arm capacitor voltage - power includes:

[0109] Controlling the outer loop of the input current by using a mathematical model of the average value of the arm capacitor voltage - power and a PI controller to obtain the control result of the outer loop of the input current;

[0110] Controlling the input current by using the control result of the outer loop of the input current, the input system model in the equivalent decoupling circuit model, and a PR controller.

[0111] In the embodiments of the present invention, the control block diagram of the input current control is as Figure 4 shown, adding the sum of the given capacitor voltages and the sum of the capacitor voltages The combined input is controlled by a PI controller to obtain the given value of the input active current Set the given value of the input reactive current And Are input into the dp / αβ converter for transformation together, and then output And the AC grid current i output by the first input system model sα Are combined and input into the first PR controller for control to obtain the control signal And the AC grid current i output by the second input system model sβ Are combined and input into the second PR controller for control to obtain the control signal The control signal Is used to control the input current of the modular multilevel matrix converter

[0112] Specifically, the output voltage of the modular multilevel matrix converter is controlled by using an equivalent decoupling circuit model, including:

[0113] The output voltage of the modular multilevel matrix converter is controlled by using the output system model and the PR controller in the equivalent decoupling circuit model

[0114] In the embodiment of the present invention, the control block diagram of the output voltage control is as shown in Figure 5 Shown, the arc suppression voltage command value -e a And u output by the common mode voltage model o Are combined and input into the first PR controller for control, and the output result is combined with the i output by the output system model o And then controlled by the second PR controller to output the control signal The control signal Is used to control the output voltage of the modular multilevel matrix converter, where the arc suppression voltage command value -e a Is the opposite of the fault phase voltage of the distribution network

[0115] Specifically, the arm energy of the modular multilevel matrix converter is balanced by using an equivalent decoupling circuit model and a bridge arm capacitor voltage average - power mathematical model, including:

[0116] The average value of the capacitor voltage of the modular multilevel matrix converter is controlled by using the bridge arm capacitor voltage average - power mathematical model and PI control to obtain the control result of the average value of the capacitor voltage;

[0117] The circulating current of the modular multilevel matrix converter is controlled by using the control result of the average value of the capacitor voltage, the circulating current system model in the equivalent decoupling circuit model and the PR controller to obtain the control result of the circulating current;

[0118] The common-mode voltage of the modular multilevel matrix converter is controlled by using the common-mode voltage model and the P controller in the equivalent decoupling circuit model to obtain the common-mode voltage control result;

[0119] The arm energy of the modular multilevel matrix converter is balanced by using the circulating current control result and the common-mode voltage control result.

[0120] In the embodiment of the present invention, the control block diagram of the arm energy balance control is as Figure 6 shown. The phase-to-phase capacitor voltage difference in the αβ0 coordinate system and the capacitor voltage difference between the upper and lower arms of each phase in the αβ0 coordinate system are both filtered by a low-pass filter to eliminate the ripple components of the capacitor voltage imbalance degree and then input into a PI controller for control, obtaining the positive and negative sequence component amplitudes I m of the three-phase symmetrical circulating current with an injection frequency of ω z1 , I z5 , the positive and negative sequence component amplitudes I n of the three-phase symmetrical circulating current with an injection frequency of ω z2 , I z6 and the common-mode voltage amplitude U m with a frequency of ω n1 . Among them, the positive and negative sequence component amplitudes I m of the three-phase symmetrical circulating current with an injection frequency of ω z1 , I z5 , the positive and negative sequence component amplitudes I n of the three-phase symmetrical circulating current with an injection frequency of ω z2 , I z6 are calculated through the first time-varying function, and the calculation results are all substituted into the symmetrical circulating current and common-mode voltage expressions for calculation, obtaining the calculated value of the symmetrical circulating current The calculated value of the symmetrical circulating current and the symmetrical AC grid currents I zα , i zβ are combined and then input into a PR controller for control, obtaining the circulating current control signal The common-mode voltage amplitude U m with a frequency of ω n1 is calculated through the second time-varying function and then combined with the common-mode voltage amplitude U n with a frequency of ω n2 , and then calculated through the third time-varying function and input into a P controller for control, obtaining the common-mode voltage control signal Based on the circulating current control signal and the common-mode voltage control signal the arm energy of the modular multilevel matrix converter is balanced.

[0121] In the embodiment of the present invention, the first time-varying function includes:

[0122]

[0123] The second time-varying function is as follows:

[0124] f 31 (t) = cos(ω m t + α3)

[0125] The third time-varying function is as follows:

[0126] f 41 (t) = cos(ω n t + α4)

[0127] In the embodiment of the present invention, as shown in the control block diagram of the arm energy balance control Figure 6 there are 5 PI controllers, each capacitor voltage difference corresponds to a PI controller, and there are 2 PR controllers. The control signals output by each PR controller are used to control a set of circulating currents.

[0128] In order to verify the control method proposed in the embodiment of the present invention, a simulation model of the modular multilevel matrix converter is built in MATLAB / Simulink, and the experimental parameters are shown in Table 1:

[0129] Table 1 Experimental parameters

[0130]

[0131]

[0132] The steady-state waveforms of the three-phase input voltage, current and single-phase output voltage and current when the fault resistance is 100Ω are as Figure 7 shown, where Figure 7 (a) shows that the input-side voltage and current are in phase, meeting the requirements of unity power factor control, and (b) shows that the output-side waveform has good sinusoidality and can accurately track the reference value.

[0133] Let the control method provided in the embodiment of the present invention be Method 1, and the capacitor voltage stabilization control method using the combination of asymmetric circulating current and common-mode voltage multi-frequency be Method 2. The steady-state waveform diagrams of the upper-bridge-arm capacitor voltage as shown in Figure 8 and Figure 9 are obtained; it can be seen from Figure 8 and Figure 9 that the maximum value of the fluctuation amplitude of the upper-bridge-arm capacitor voltage in Method 1 differs from the minimum by 10V, while in Method 2 it differs by 43V. The ripple equalization performance of Method 1 is significantly better than that of Method 2, verifying the effectiveness of the method provided in the embodiment of the present invention.

[0134] The embodiments of the present invention are applied to a modular multilevel matrix converter. The system state space equation of the modular multilevel matrix converter is established based on Kirchhoff's law, and the system state space equation is decoupled through coordinate transformation to obtain a state decoupling equation. An equivalent decoupled circuit model is drawn using the system state decoupling equation; a mathematical model of the average value of the arm capacitor voltage - power is established according to the arm power equation; symmetric circulating current and common - mode voltage are injected into the modular multilevel matrix converter, and the modular multilevel matrix converter is controlled using the equivalent decoupled circuit model and the mathematical model of the average value of the arm capacitor voltage - power to obtain the ripple equalization control result of the modular multilevel matrix converter; compared with the prior art, in the embodiments of the present invention, symmetric circulating current and common - mode voltage are injected into the modular multilevel matrix converter, and the modular multilevel matrix converter is controlled using the equivalent decoupled circuit model and the mathematical model of the average value of the arm capacitor voltage - power, which can achieve the balanced control of the power of each phase arm and effectively reduce the ripple of the arm capacitor voltage.

[0135] The above - mentioned is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the principle described in the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for balancing the capacitor voltage ripple of a converter bridge arm, characterized in that Applied to a modular multilevel matrix converter, the control method includes: Step 1: Establish the system state space equation of the modular multilevel matrix converter based on Kirchhoff's law, and decouple the system state space equation through coordinate transformation to obtain the state decoupling equation. Use the system state decoupling equation to draw an equivalent decoupled circuit model; Step 2: Establish the mathematical model of the average bridge arm capacitor voltage - power according to the bridge arm power equation; Step 3: Inject the symmetric circulating current and common - mode voltage into the modular multilevel matrix converter, and use the equivalent decoupled circuit model and the mathematical model of the average bridge arm capacitor voltage - power to control the modular multilevel matrix converter to obtain the ripple equalization control result of the modular multilevel matrix converter.

2. The converter leg capacitor voltage ripple equalization control method according to claim 1, characterized in that, The expression of the system state space equation is: Among them, u pa , u pb , u pc , u na , u nb , u nc respectively represent the voltages between the phase bridge arms, u sa , u sb , u sc respectively represent the phase bus voltages, u o represents the output voltage, L q represents the bridge arm inductor, i pa , i pb , i pc , i na , i nb , i nc respectively represent the phase bridge arm currents, u GO represents the common-mode voltage.

3. The converter leg capacitor voltage ripple equalization control method according to claim 2, wherein The expression of the system state decoupling equation is: Among them, represents the components of the bridge arm voltage in the abc-αβ0ΣΔ coordinate system, both represent the components of the circulating current in the αβ0 coordinate system, u sα and u sβ and i sα and i sβ respectively represent the symmetrical AC grid voltages and currents of each phase obtained by the Clarke transformation, u n represents the common-mode voltage in the αβ0 coordinate system.

4. The converter leg capacitor voltage ripple equalization control method according to claim 2, wherein The equivalent decoupled circuit model includes: Circulation system model, including a first circulation system model composed of arm inductance L q and the components of the arm voltage in the abc-αβ0ΣΔ coordinate system and a second circulation system model composed of arm inductance L q and the components of the arm voltage in the abc-αβ0∑Δ coordinate system ; Common-mode voltage model, including the common-mode voltage u in the αβ0 coordinate system n and the components of the leg voltage in the abc-αβ0∑Δ coordinate system The input system model includes the symmetrical AC grid voltages u of each phase obtained by Clarke transformation sα , the components of the arm voltage in the abc-αβ0∑Δ coordinate system The arm inductor L q to form the first input system model and the symmetrical AC grid voltages u of each phase obtained by Clarke transformation sβ , the components of the arm voltage in the abc-αβ0∑Δ coordinate system The arm inductor L q to form the second input system model; Output system model, including output voltage u o , components of the leg voltage in the abc-αβ0∑Δ coordinate system and leg inductance L q .

5. The converter leg capacitor voltage ripple equalization control method according to claim 4, wherein The bridge arm power equation is: Among them, represents the rated value of the sub-module capacitor voltage, C represents the sub-module capacitance value, U Cap , U Cbp , U Cap respectively represent the sum of the sub-module capacitor voltages of the upper bridge arms of each phase, U Can , U Cbn , U Ccn respectively represent the sum of the sub-module capacitor voltages of the lower bridge arms of each phase, p ap , p bp , p cp respectively represent the power of the upper bridge arms of each phase, p an , p bn , p cn respectively represent the power of the lower bridge arms of each phase.

6. The converter leg capacitor voltage ripple equalization control method according to claim 5, wherein The expression of the mathematical model of the average bridge arm capacitor voltage - power is: Among them, respectively represent the inter-phase capacitor voltage difference in the abc-αβ0ΣΔ coordinate system, respectively represent the capacitor voltage differences between the upper and lower arms of each phase in the abs-αβ0ΣΔ coordinate system, represents the sum of the capacitor voltages of the modular multilevel matrix converter, respectively represent the average values of the arm voltages of each phase in the abc-αβ0∑Δ coordinate system.

7. The converter leg capacitor voltage ripple equalization control method according to claim 6, wherein Using the equivalent decoupled circuit model and the mathematical model of the average bridge arm capacitor voltage - power to control the modular multilevel matrix converter includes: Using the equivalent decoupled circuit model and the mathematical model of the average bridge arm capacitor voltage - power to control the input current of the modular multilevel matrix converter; Using the equivalent decoupled circuit model to control the output voltage of the modular multilevel matrix converter; Using the equivalent decoupled circuit model and the mathematical model of the average bridge arm capacitor voltage - power to balance the bridge arm energy of the modular multilevel matrix converter.

8. The converter leg capacitor voltage ripple equalization control method according to claim 7, characterized in that, Using the equivalent decoupled circuit model and the mathematical model of the average bridge arm capacitor voltage - power to control the input current of the modular multilevel matrix converter includes: Using the mathematical model of the average bridge arm capacitor voltage - power and a PI controller to control the input current outer loop to obtain the input current outer loop control result; Using the input current outer loop control result, the input system model in the equivalent decoupled circuit model and a PR controller to control the input current.

9. The converter leg capacitor voltage ripple equalization control method according to claim 7, characterized in that Using the equivalent decoupled circuit model to control the output voltage of the modular multilevel matrix converter includes: Using the output system model in the equivalent decoupled circuit model and a PR controller to control the output voltage of the modular multilevel matrix converter.

10. The converter leg capacitor voltage ripple equalization control method according to claim 7, characterized in that Using the equivalent decoupled circuit model and the mathematical model of the average bridge arm capacitor voltage - power to balance the bridge arm energy of the modular multilevel matrix converter includes: Using the mathematical model of the average bridge arm capacitor voltage - power and PI control to control the average capacitor voltage of the modular multilevel matrix converter to obtain the average capacitor voltage control result; Using the average capacitor voltage control result, the circulating current system model in the equivalent decoupled circuit model and a PR controller to control the circulating current of the modular multilevel matrix converter to obtain the circulating current control result; The common-mode voltage of the modular multilevel matrix converter is controlled by using the common-mode voltage model and the P controller in the equivalent decoupling circuit model to obtain the common-mode voltage control result; The arm energy of the modular multilevel matrix converter is balanced by using the circulating current control result and the common-mode voltage control result.

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