Modular multilevel converter verification system

Abstract

The present invention relates to a modular multilevel converter (MMC) verification system and, more specifically, to a verification system for verifying a sub-module (SM) and a SM control algorithm of a MMC. Disclosed is the MMC verification system (10) comprising: a simulation unit (100), which includes an MMC simulation unit (110) for simulating a multi-phase MMC, a load simulation unit (120) for simulating a multi-phase load connected to an output terminal of the MMC, and a controller simulation unit (130) for simulating a controller that generates multi-phase voltage commands (Va*, Vb*, Vc*) for controlling an operation of the MMC; and an SM unit (200) which includes at least one SM connected to each arm of a full-bridge topology, and of which an operation is controlled on the basis of two-phase voltage commands (Va*, Vb*) from among multi-phase voltage commands (Va*, Vb*, Vc*) of the controller.

Description

Modular multilevel converter verification system

[0001] The present invention relates to a modular multilevel converter verification system, and more particularly, to a verification system for verifying submodules and submodule control algorithms of a modular multilevel converter.

[0002] Modular multilevel converters (MMCs) are attracting attention and active research in the high-voltage, high-capacity converter field. MMCs facilitate voltage level expansion through the serial connection of numerous submodules. Their high voltage levels, even at low switching frequencies, enable superior output. These advantages have led to their widespread use in high-voltage direct current (HVDC) transmission, reactive power compensators (STATCOMs), and high-voltage motor drives.

[0003] Figure 1 illustrates a circuit diagram of a half-bridge converter for explaining a submodule (SM) of a modular multilevel converter (MMC). As illustrated in Figure 1, the half-bridge converter comprises two complementary-operating IGBT switches (S1, S2) and a capacitor (C) for storing energy.

[0004] When the dark current (Iarm) is positive, when switch S1 is turned on, the dark current (Iarm) flows through the freewheeling diode (D1) to the capacitor (C), so that the capacitor (C) can be charged. When switch S2 is turned on, the capacitor (C) is bypassed, so the capacitor (C) voltage does not fluctuate.

[0005] Conversely, when the direction of the dark current (Iarm) is negative, when switch S1 is turned on, the dark current flows to the capacitor (C), so the capacitor (C) is discharged. When switch S2 is turned on, the dark current flows to the freewheeling diode (D2), bypassing the capacitor (C), so there is no change in the voltage of the capacitor (C). Therefore, when switch S1 is turned on, the charging and discharging of the capacitor (C) is determined according to the direction of the dark current (Iarm).

[0006] In a modular multilevel converter, N series-connected submodules (SM) and an arm inductor (Larm) form one arm, and two arms are connected based on the AC output terminal to form one leg. The arm inductor (Larm) can prevent a sudden increase in short-circuit current in the event of a short-circuit fault.

[0007] The capacitor (C) voltage of each sub-module (SM) has a size equal to N times the DC link voltage (Vdc) of the DC input terminal, and the voltage output from one arm is equal to the sum of the output voltages of each sub-module (SM) constituting the arm.

[0008] It is very important to maintain the reliability of modular multilevel converters used in high voltage environments, and for this purpose, testing and verification of various characteristics such as sub-module (SM) characteristics and rated capacity are required.

[0009] However, the conventional modular multilevel converter submodule (SM) test device uses a method of verifying whether the submodule (SM) normally reaches the rated voltage and rated current by adjusting the phase of the submodule (SM) switch operation command. Since this is a method of verifying whether the switching control operates properly by the submodule controller until the submodule (SM) reaches the rated capacity, it only allows for the performance verification of the submodule (SM), and there is a problem in that it is difficult to view it as completely verified from the perspective of the entire system of the modular multilevel converter that requires actual layer-by-layer network-based control.

[0010] The purpose of the present invention is to recognize the above problems and provide a modular multi-level converter verification system capable of verifying not only the performance of sub-modules but also the control algorithm.

[0011] In addition, the purpose of the present invention is to provide a modular multi-level converter verification system that enables low-cost system design and hardware manufacturing by building expensive systems with mathematically modeled simulation layers and building sub-modules corresponding to core components with actual hardware layers.

[0012] The present invention comprises an MMC simulation unit (110) that simulates a multi-phase modular multi-level converter, a load simulation unit (120) that simulates a multi-phase load connected to an output terminal of the modular multi-level converter, and a multi-phase voltage command (Va) for controlling the operation of the modular multi-level converter. * , Vb * , Vc * ) including a simulation unit (130) that simulates a controller that generates the multi-phase voltage command (Va) of the controller, and at least one sub-module (SM) connected to each arm of the full bridge topology; * , Vb * , Vc * ) among the two phase voltage command (Va * , Vb * ) is disclosed as a modular multi-level converter verification system including a sub-module section (200) whose operation is controlled based on the sub-module section.

[0013] One of the multi-phase input terminals of the above multi-phase load is connected to the single-phase current (I) of the sub-module (200). sm ) is calculated based on the induced phase current (I sm ') can be entered.

[0014] The above multi-phase load may be a three-phase synchronous motor.

[0015] The number of sub-modules (SM) connected to the female of the above sub-module section (200) is N sm , and the number of sub-modules (SM) connected to the arm of the modular multi-level converter is N. mmc It could be.

[0016] DC link voltage (V) of the above sub-module (200) dc_sm ) is the DC link voltage (V) of the above modular multilevel converter. dc_mmc ) It could be.

[0017] The above induced phase current (I sm ') is the single-phase current (I sm ) It could be.

[0018] The above sub-module (200) is the two-phase voltage command (Va * , Vb * ) may include a sub-module control unit that controls the operation of the sub-module (SM) based on the control variables (Vaa, Vbb) calculated based on each.

[0019] The above control variables (Vaa, Vbb) are the voltage command (Va * , Vb * ) It could be.

[0020] The above sub-module control unit may include an upper control unit that generates a control signal for switching control of each sub-module (SM) based on the control variables (Vaa, Vbb), and a lower control unit of each sub-module (SM) that performs PWM control according to the control signal transmitted from the upper control unit.

[0021] The above multi-phase voltage reference (Va * , Vb * , Vc * ) the operation of the modular multi-level converter can be controlled so that multi-phase currents (Ia, Ib, Ic) can be output.

[0022] The above multi-phase load can be operated by inputting the induced phase current (Ism') and the phase currents (Ib, Ic) of a different phase from the induced phase current (Ism') to the corresponding multi-phase input terminals, respectively.

[0023] The modular multi-level converter verification system according to the present invention has the advantage of being able to verify not only the performance of sub-modules but also the control algorithm.

[0024] Specifically, the modular multi-level converter verification system according to the present invention has the advantage of being able to evaluate the performance of individual sub-modules, and furthermore, verify the controller function of each sub-module and verify the performance of a single-phase modular multi-level converter at the valve unit and phase unit levels.

[0025] That is, the modular multi-level converter verification system according to the present invention not only verifies the performance of sub-modules, but also can prove the validity of the overall system design and the suitability of the control algorithm through the sub-module linkage of the real-time simulation layer and the actual hardware layer.

[0026] In addition, the modular multi-level converter verification system according to the present invention has the advantage of enabling low-cost system design and hardware manufacturing by building expensive systems with mathematically modeled simulation layers and building sub-modules corresponding to core components with actual hardware layers.

[0027] Figure 1 is a half-bridge converter circuit diagram showing a sub-module of a modular multilevel converter.

[0028] Figure 2 is a schematic diagram showing a verification system according to one embodiment of the present invention.

[0029] Figure 3 is a block diagram illustrating the controller of Figure 2.

[0030] Hereinafter, a modular multi-level converter verification system according to one embodiment of the present invention will be described with reference to drawings.

[0031] The verification system (10) for the above modular multi-level converter is a HIL (Hardware in Loop) simulation verification system that includes a simulation unit (100) as a real-time simulation layer and a sub-module unit (200) as a hardware layer including actual sub-modules (SM), as shown in FIG. 2, and a closed loop control method can be applied between the simulation unit (100) and the sub-module unit (200).

[0032] The above simulation unit (100) includes an MMC simulation unit (110) that simulates a multi-phase modular multi-level converter, a load simulation unit (120) that simulates a multi-phase load connected to the output terminal of the modular multi-level converter, and a multi-phase voltage command (Va) for controlling the operation of the modular multi-level converter. * , Vb * , Vc * ) may include a controller simulation unit (130) that simulates a controller that generates the controllers.

[0033] The above MMC simulation unit (110) may be a simulation functional unit that simulates a multi-phase modular multi-level converter.

[0034] The above modular multi-level converter (MMC) includes multiple arms, each arm is configured with multiple sub-modules (SM) connected in series, and may be equipped with a direct current input terminal and a multi-phase alternating current output terminal.

[0035] The power applied to the DC input terminal of the above modular multilevel converter is the DC link voltage (V dc_mmc ), which can be the voltage applied between nodes A and C.

[0036] The above modular multi-level converter includes multiple arms (node ​​A-node B, node B-node C), and the number of sub-modules (SM) connected to each arm (node ​​A-node B, node B-node C) is N. mmc , and at this time, N mmccan be a natural number greater than or equal to 3.

[0037] The upper arm (node ​​A-node B) and the lower arm (node ​​B-node C) of the above modular multi-level converter constitute one leg (node ​​A-node C), and the above modular multi-level converter may include multiple legs.

[0038] The above modular multilevel converter may be provided with multiphase AC output stages at the B nodes between the upper and lower arms. As an example, FIG. 2 illustrates a case where the above modular multilevel converter has three legs and three phase AC output stages, but examples of having four, five, or more multiphase AC output stages are also possible.

[0039] The above load simulation unit (120) may be a simulation function unit that simulates a multi-phase load connected to the AC output terminal of the modular multi-level converter.

[0040] The above multi-phase load is configured to operate by receiving a multi-phase AC signal, and may be, for example, a three-phase permanent magnet synchronous motor (PMSM), but is not limited thereto. As another example, the above multi-phase load may be a power system.

[0041] Figure 2 illustrates an example in which a multi-phase load receives three-phase AC input, but it is of course possible to configure a multi-phase load to receive more than that.

[0042] When the above multi-phase load is composed of a synchronous motor, a variable speed drive system is required to control the operation of the synchronous motor, and a high-voltage variable speed drive system can be configured for high-output, high-torque propulsion.

[0043] The above multi-phase load can be driven by receiving a multi-phase AC input by being connected to the multi-phase output terminal (B node) of the above modular multi-level converter.

[0044] The above control simulation unit (130) controls the operation of the modular multi-level converter by providing a multi-phase voltage command (Va * , Vb * , Vc * ) may be a simulation functional unit that simulates a controller that generates them.

[0045] Multi-phase voltage command (Va) output from the above controller * , Vb * , Vc * ) the switching operation of the modular multilevel converter can be controlled so that the output of the multi-phase output terminal (B node) can be controlled. In other words, the multi-phase voltage command (Va * , Vb * , Vc * ) so that the operation of the modular multi-level converter can be controlled so that multi-phase currents (Ia, Ib, Ic) can be output from the output terminal (node ​​B), and at least one of the multi-phase currents (Ia, Ib, Ic) can be transmitted to the input of a multi-phase load.

[0046] The above controller can be configured in various ways to control multi-phase control variables, and as an example, it can be a variable speed drive that controls the angular speed of a synchronous motor as a multi-phase load.

[0047] At this time, the controller may be applied with a dq transformation algorithm for multi-phase control.

[0048] As an example, the controller, as shown in Fig. 3, controls the DC link voltage (V) of the modular multilevel converter. dc_mmc ), the multi-phase currents (Ia, Ib, Ic) of the multi-phase output terminal (B node) are fed back, and after dq conversion for the multi-phase currents (Ia, Ib, Ic), the multi-phase voltage reference (Va) is generated through PI control. * , Vb * , Vc * ) can be printed.

[0049] Specifically, the controller performs dq conversion on the multi-phase currents (Ia, Ib, Ic) of the multi-phase output terminal (B node) to output the d-axis current (Id) and the q-axis current (Iq), and the DC link voltage (V) of the modular multi-level converter dc_mmc ) and DC link voltage command (V dc_mmc * ) error (V dc_err ) is calculated and the d-axis current command (Id) is set through PI control. * ) d-axis current command output unit (132) that outputs d-axis current (Id) and d-axis current command (Id * ) performs PI control by calculating the error (Id_err) of the d-axis voltage command (Vd) and compensates for the counter electromotive force based on the q-axis current (Iq), the angular velocity (w) of the multi-phase load, and the inductance (L). * ) outputting the d-axis voltage command output unit (133), the q-axis current (Iq) and the q-axis current command (Iq * ) performs PI control by calculating the error (Iq_err) of the d-axis current (Id), the angular velocity of the multi-phase load (w), and the inductance (L) to compensate for the counter electromotive force and obtain the q-axis voltage command (Vq). * ) and the q-axis voltage command output unit (134) that outputs the d-axis voltage command (Vd * ) and q-axis voltage command (Vq * ) is a multi-phase voltage reference (Va * , Vb * , Vc * ) may include a second conversion unit (135) that outputs the signals.

[0050] The controller illustrated in Fig. 3 is only one example of a three-phase control algorithm, and various modifications are of course possible.

[0051] The above sub-module unit (200) is a hardware layer configured to include an actual sub-module (SM), and may include at least one sub-module (SM) connected to each arm of a full bridge topology.

[0052] The above sub-module section (200) can have one or more sub-modules (SM) connected to each arm, and FIG. 2 illustrates an example in which one sub-module (SM) is connected to one arm, but the number of sub-modules (SM) connected to an arm can increase to two, three, etc.

[0053] The number of sub-modules (SM) connected to the female of the above sub-module section (200) is N sm In this case, the Nsm may be a natural number greater than or equal to 1. In addition, the N sm The number N of submodules (SM) connected to the arm of the modular multilevel converter mmc It can be smaller.

[0054] DC link voltage (V) of the above sub-module (200) dc_sm ) is the DC link voltage (V) of the above modular multilevel converter. dc_mmc ), the number N of submodules (SM) connected to the female of the submodule (200) sm , the number N of submodules (SM) connected to the arm of the modular multilevel converter mmc can be determined by

[0055] Specifically, the DC link voltage (V) of the sub-module (200) dc_sm ) can be calculated as in the following equation (1).

[0056] V dc_sm = V dc_mmc (Formula 1)

[0057] For example, the number N of submodules (SM) connected to the arm of the modular multilevel converter mmc is 10, and the number N of sub-modules (SM) connected to the female of the sub-module section (200) sm In this case, the DC link voltage (V) of the sub-module (200) dc_sm ) is the DC link voltage (V) of the above modular multilevel converter. dc_mmc ) may correspond to one-tenth of the total.

[0058] As the above sub-module part (200) is configured with a full-bridge topology circuit structure having two B nodes as shown in FIG. 2, the multi-phase voltage command (Va) of the controller * , Vb * , Vc * ) among the two phase voltage command (Va * , Vb * ) can be used to control the movement.

[0059] For example, in the above controller, the three-phase voltage command (Va * , Vb * , Vc * ) is output, the switching operation of the sub-module (SM) of the sub-module unit (200) can be controlled based on the voltage commands (Va*, Vb*) of phases a and b.

[0060] Specifically, the sub-module (200) is the two-phase voltage command (Va * , Vb * ) may include a sub-module control unit that controls the operation of the sub-module (SM) based on the control variables (Vaa, Vbb) calculated based on each.

[0061] The above sub-module control unit is configured for switching control of each sub-module (SM) of the above sub-module section (200), and can be configured in various ways.

[0062] Here, the control variables (Vaa, Vbb) are the voltage command of the two phases (Va * , Vb * ) can be calculated based on each, and can be derived by the following equations 2 and 3.

[0063] Vaa= Va * (Formula 2)

[0064] Vbb= Vb * (Formula 3)

[0065] That is, the sub-module control unit can receive control variables (Vaa, Vbb) calculated based on voltage commands (Va*, Vb*) of two phases, i.e., phase a and phase b, among multi-phase voltage commands (Va*, Vb*, Vc*), and can perform switching control for each sub-module (SM) using the same.

[0066] According to the above control variables (Vaa, Vbb), the output voltage between the two B nodes of the sub-module (200) is formed, and the single-phase current (I) flowing between the two B nodes sm ) can be printed.

[0067] The above sub-module control unit can be configured as a network-based multi-layer structure.

[0068] For example, the sub-module control unit may include an upper control unit that generates a control signal for switching control of each sub-module (SM) based on the control variables (Vaa, Vbb), and a lower control unit of each sub-module (SM) that performs PWM control according to the control signal transmitted from the upper control unit.

[0069] The control signal output from the upper control unit can be transmitted to the lower control unit of each sub-module (SM) via high-speed serial communication, and each lower control unit can perform PWM synchronous control to minimize circulating current.

[0070] Again, referring to FIG. 2, one of the multi-phase input terminals of the multi-phase load described above is not connected to the B node of the modular multi-level converter, and the single-phase current (I) of the sub-module (200) is applied to the input terminal. sm ) is the induced phase current (I sm ') can be entered.

[0071] That is, the induced phase current (I) is applied to the phase A input terminal, which is one of the multi-phase input terminals of the multi-phase load. sm') is input, and the remaining input terminals (phase b, phase c) are each connected to the B node output terminal of the modular multi-level converter, so that the phase currents (Ib, Ic) of phase a and other phases (phase b and phase c) can be input.

[0072] The above induced phase current (I sm ') is the single-phase current (I) of the above sub-module (200). sm ), the number N of submodules (SM) connected to the female of the submodule (200) sm , the number N of submodules (SM) connected to the arm of the modular multilevel converter mmc can be determined by

[0073] Specifically, the induced phase current (I sm ') can be calculated as in the following formula (4).

[0074] I sm '= I sm (Formula 4)

[0075] For example, the number N of submodules (SM) connected to the arm of the modular multilevel converter mmc is 10, and the number N of sub-modules (SM) connected to the female of the sub-module section (200) sm In this case, the induced phase current (I sm ') is the single-phase current (I) of the above sub-module (200). sm ) can be a single-phase current equivalent to 10 times the current.

[0076] At this time, the multi-phase load can be operated by inputting the induced phase current (Ism') and the phase currents (Ib, Ic) of a different phase from the induced phase current (Ism') to the corresponding multi-phase input terminals, respectively.

[0077] For example, the multi-phase load can be driven by receiving an induced phase current (Ism') derived from the single-phase current (Ism) of the sub-module unit (200) as one phase current (e.g., phase a), and receiving phase currents (Ib, Ic) of a modular multi-level converter for phases b and c, which are phase currents of other phases.

[0078] That is, the present invention performs multi-phase control in the simulation unit (100), and among them, the two-phase voltage command (Va * , Vb*) can be transmitted to the upper control unit of the sub-module unit (200), which is an actual hardware layer. The upper control unit transmits a control signal to the lower control unit of each sub-module (SM) through high-speed serial communication, and each lower control unit controls the sub-module (SM) through PWM synchronous control, and accordingly, the single-phase current (I) flowing in the sub-module unit (200) of the full-bridge topology sm ) can be used again as an input for one phase of the multi-phase load of the real-time simulation unit (100) (for example, input of phase a) to control the multi-phase load together with the phase currents (Ib, Ic) for the remaining phases (phase b and phase c). As a result, a closed-loop HIL (Hardware in Loop) system between the simulation unit (100) and the sub-module unit (200) can be implemented.

[0079]

[0080] The above is only a description of some of the preferred embodiments that can be implemented by the present invention, and as is well known, the scope of the present invention should not be construed as being limited to the above embodiments, and the technical ideas of the present invention described above and the technical ideas underlying them are all included in the scope of the present invention.

Claims

1. An MMC simulation unit (110) that simulates a multi-phase modular multi-level converter, a load simulation unit (120) that simulates a multi-phase load connected to the output terminal of the modular multi-level converter, and a multi-phase voltage command (Va) for controlling the operation of the modular multi-level converter. * , Vb * , Vc * ) and a simulation unit (100) including a controller simulation unit (130) that simulates a controller that generates; At least one sub-module (SM) connected to each arm of the full-bridge topology and configured to provide a multi-phase voltage reference (Va) of the controller * , Vb * , Vc * ) among the two phase voltage command (Va * , Vb * ) includes a sub-module section (200) whose operation is controlled based on the One of the multi-phase input terminals of the above multi-phase load is connected to the single-phase current (I) of the sub-module (200). sm ) is calculated based on the induced phase current (I sm A modular multi-level converter verification system (10) characterized in that a ') is input.

2. In claim 1, A modular multi-level converter verification system (10) characterized in that the above multi-phase load is a three-phase synchronous motor.

3. In claim 1, The number of sub-modules (SM) connected to the female of the above sub-module section (200) is N sm The number of sub-modules (SM) connected to the arm of the modular multi-level converter is N. mmc A modular multi-level converter verification system (10) characterized by:

4. In claim 3, DC link voltage (V) of the above sub-module (200) dc_sm ) is the DC link voltage (V) of the above modular multilevel converter. dc_mmc ) A modular multi-level converter verification system (10) characterized by:

5. In claim 3, The above induced phase current (I sm ') is the single-phase current (I sm ) A modular multi-level converter verification system (10) characterized by:

6. In claim 3, The above sub-module part (200) is the two-phase voltage command (Va * , Vb * ) A modular multi-level converter verification system (10) characterized by including a sub-module control unit that controls the operation of a sub-module (SM) based on control variables (Vaa, Vbb) calculated based on each of the sub-modules.

7. In claim 6, The above control variables (Vaa, Vbb) are the voltage command (Va * , Vb * ) A modular multi-level converter verification system (10) characterized by:

8. In claim 7, The above sub-module control unit, A modular multi-level converter verification system (10) characterized by including an upper control unit that generates a control signal for switching control of each sub-module (SM) based on the above control variables (Vaa, Vbb), and a lower control unit of each sub-module (SM) that performs PWM control according to the control signal transmitted from the upper control unit.

9. In claim 1, The above multi-phase voltage reference (Va * , Vb * , Vc * ) is characterized in that the operation of the modular multi-level converter is controlled according to the multi-phase currents (Ia, Ib, Ic) and the multi-phase currents are output (10).

10. In claim 9, The above multi-load, A modular multi-level converter verification system (10) characterized in that the above-mentioned induced phase current (Ism') and the phase currents (Ib, Ic) of a different phase from the above-mentioned induced phase current (Ism') are input to corresponding multi-phase input terminals and operated.

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