Multiphase-multiphase direct alternating current-alternating current converter and control method therefor
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-20
- Publication Date
- 2026-08-13
Smart Images
Figure CN2026073588_13082026_PF_FP_ABST
Abstract
Description
Multiphase-to-multiphase direct AC-AC converter and its control method
[0001] This application claims priority to Chinese Patent Application No. 202510141762.1, filed with the Chinese Patent Office on February 8, 2025, the entire contents of which are incorporated herein by reference. Technical Field
[0002] This application belongs to the field of power electronic AC-AC converter technology, and for example relates to a multiphase-to-multiphase direct AC-AC converter and its control method. Background Technology
[0003] With the development of power electronic converter technology, high-voltage, high-capacity AC-AC converters are increasingly widely used in fields such as grid-connected power generation of new energy sources and long-distance power transmission. Especially in scenarios such as asynchronous grid interconnection, offshore wind power transmission, railway traction power supply, and high-power variable frequency speed regulation, in order to improve economic efficiency and technical performance, the power conversion process has new requirements for voltage amplitude, frequency, phase, and number of phases. There is an urgent need to study new AC-AC converter topologies that are flexible, scalable, and have excellent performance.
[0004] Currently, high-voltage, high-capacity AC-AC converters are mainly divided into two topologies: indirect and direct. Indirect AC-AC converters consist of two back-to-back Modular Multilevel Converters (MMCs), with a central DC link allowing complete decoupling of the AC systems on both sides. However, this topology requires a large number of submodules and is costly. Direct AC-AC converters primarily use Modular Multilevel Matrix Converters (M3Cs), with each arm directly connected to the AC systems on both sides. In three-phase to three-phase conversion, the number of submodules is reduced by 25% compared to back-to-back MMCs. However, as voltage levels and conversion capacities increase, the cost of submodules remains high. Some research has proposed hexagonal Modular Multilevel Converters (Hexverters) and Y-type topologies. In three-phase to three-phase conversion, the number of submodules is reduced by 50% compared to back-to-back MMCs. However, these topologies suffer from strong coupling between multiple arms, complex control, and poor scalability, making them difficult to adapt to the diverse power conversion needs of practical applications.
[0005] Therefore, it is of great significance to study novel cross-converter topologies with low submodule usage, good scalability, and flexible transformation. Summary of the Invention
[0006] This application proposes a multiphase-to-multiphase direct AC-AC converter. This AC-AC converter is based on the synthesis logic of differential and common-mode voltage components of the MMC bridge arm. Combined with a three-winding transformer with reverse connection of the same terminal, it can reduce the number of sub-modules in the M3C topology and has good scalability to adapt to various special application scenarios.
[0007] This application provides a multiphase-to-multiphase direct AC-AC converter, which includes a modular multilevel converter and N single-phase three-winding transformers;
[0008] The modular multilevel converter includes X phase units, each phase unit consisting of an upper bridge arm and a lower bridge arm; the input side of the AC-AC converter has m ports, which are connected to the first AC system, and each input port is connected to the midpoint of at least one phase unit; the output side of the AC-AC converter has 2N ports, the upper bridge arms of the X phase units are connected in parallel to form N output ports, the lower bridge arms of the X phase units are connected in parallel to form N output ports, and each pair of output ports is connected to both ends of at least one phase unit;
[0009] The single-phase three-winding transformer includes a first winding, a second winding, and a third winding, with a turns ratio of [value missing]. The first windings of the N single-phase three-winding transformers are respectively connected to the N phases of the second AC system, the second windings are connected to the N output side ports of the upper bridge arm of the modular multilevel converter, and the third windings are connected to the N output side ports of the lower bridge arm of the modular multilevel converter.
[0010] The first AC system is an m-phase system, consisting of phases a, b, c, ..., m; the second AC system is an N-phase system, consisting of phases A, B, C, ..., N; m ≥ 2, N ≥ 1.
[0011] In some embodiments, the i-th input port of the modular multilevel converter is connected to Each phase unit is connected, among which , i = a, b, c, ..., m; the j-th pair of output ports of the modular multilevel converter and Each phase unit is connected, among which j = A, B, C, ..., N; the total number of phase units X ≥ m, X ≥ N, and satisfies:
[0012] .
[0013] In some embodiments, the modular multilevel converter has the same upper and lower bridge arm structure for each phase unit, each including multiple full-bridge sub-modules connected in series and a bridge arm inductor.
[0014] In some embodiments, the single-phase three-winding transformer has the same-name terminal of the first winding connected to the j-th phase of the second AC system, and the other end grounded, j=A, B, C, ..., N; the same-name terminal of the second winding is connected to the i-th output port of the upper arm of the modular multilevel converter, and the other end grounded, i=a, b, c, ..., m; the same-name terminal of the third winding is grounded, and the other end is connected to the i-th output port of the lower arm of the modular multilevel converter.
[0015] In some embodiments of the modular multilevel converter, the upper arm reference voltage of the k-th phase unit... and lower bridge arm reference voltage The expression is:
[0016]
[0017] in, It is the differential-mode component of the bridge arm reference voltage. It is the common-mode component of the bridge arm reference voltage.
[0018] In some embodiments, when the voltage drop across the bridge arm inductance is ignored, the differential-mode component of the reference voltage of the k-th phase unit bridge arm is... and common mode components The expression is:
[0019]
[0020] Where U1 corresponds to the phase voltage amplitude of the first AC system, U2 corresponds to the phase voltage amplitude of the second AC system, ω1 is the angular frequency of the first AC system, ω2 is the angular frequency of the second AC system, and θ i It is the phase shift angle of the first AC system, θ j It is the phase shift angle of the second AC system.
[0021] In some embodiments, the phase of each phase voltage of the first AC system needs to satisfy the condition that the sum of all voltage phasors is equal to 0, while the phase of each phase voltage of the second AC system is not subject to this restriction.
[0022] In some embodiments, the AC-AC converter allows power to flow from the first AC system side to the second AC system side, or from the second AC system side to the first AC system side.
[0023] This application also provides a control method for a multiphase-to-multiphase direct AC-AC converter, applicable to any embodiment of the multiphase-to-multiphase direct AC-AC converter. The method includes: selecting the input-side component, output-side component, and circulating current component of the arm current as state variables to design a control strategy; dividing the control strategy based on the arm current component into an outer loop control and an inner loop control; the inner loop control utilizes arm voltage decoupling transformation to control the input-side component, output-side component, and circulating current component of the arm current respectively; the input-side component and output-side component each have two modes: voltage control and current control, with the appropriate control mode selected according to the setting requirements; the circulating current component only has one mode: current control; when the inner loop control uses AC voltage control, the outer loop control is not required; when the inner loop control uses AC current control, the outer loop control uses active power control or reactive power control.
[0024] In some embodiments, for the outer loop control of the input-side component or the output-side component, the active control adopts capacitor voltage averaging control or active power control, and the reactive control adopts reactive power control; for the outer loop control of the circulating current component, the active control adopts bridge arm balancing control, and the reactive control makes the q-axis reactive component reference value of the circulating current 0. Attached Figure Description
[0025] Figure 1 is a topology diagram of the multiphase-to-multiphase direct cross-converter based on MMC in this application;
[0026] Figure 2 is a block diagram of the control method for the multiphase-to-multiphase direct AC-AC converter based on MMC in this application;
[0027] Figure 3 is a topology diagram of a three-phase to three-phase direct AC-AC converter based on MMC in this application (m=3, N=3, X=3, Y=3). a =Y b =Y c =1, Z A =Z B =Z C =1);
[0028] Figure 4 shows the voltage simulation waveforms on the input and output sides of the three-phase to three-phase direct AC-AC converter shown in Figure 3.
[0029] Figure 5 is another topology diagram of the three-phase to single-phase direct AC-AC converter based on MMC in this application (m=3, N=1, X=3, Y=3). a =Y b =Y c =1, Z A =3);
[0030] Figure 6 shows the voltage simulation waveforms on the input and output sides of the three-phase to single-phase direct AC-AC converter shown in Figure 5.
[0031] Figure 7 is another topology diagram of the three-phase to two-phase direct AC-AC converter based on MMC in this application (m=3, N=2, X=4, Y=4). a =2, Y b =Y c =1, Z A =Z B =2);
[0032] Figure 8 shows the voltage simulation waveforms on the input and output sides of the three-phase to two-phase direct AC-AC converter shown in Figure 7. Detailed Implementation
[0033] The present application will now be described in conjunction with the accompanying drawings and embodiments.
[0034] As shown in Figure 1, this application provides a multiphase-to-multiphase direct AC-AC converter, such as an MMC-based multiphase-to-multiphase direct AC-AC converter. This AC-AC converter consists of a modular multilevel converter and N single-phase three-winding transformers. The input side of the AC-AC converter is connected to an m-phase first AC system, which includes phases a, b, c, ..., m; the output side of the AC-AC converter is connected to an N-phase second AC system, which includes phases A, B, C, ..., N. The number of phases in the first and second AC systems satisfies m ≥ 2 and N ≥ 1.
[0035] The modular multilevel converter includes X phase units. The upper and lower bridge arms of each phase unit have the same structure, each including multiple full-bridge submodules connected in series and a bridge arm inductor. The input side of the AC-AC converter has m ports, which are connected to the first AC system. Each input port is connected to the midpoint of at least one phase unit. The output side of the AC-AC converter has 2N ports. The upper bridge arms of the X phase units are connected in parallel to form N output ports, and the lower bridge arms of the X phase units are connected in parallel to form N output ports. Each pair of output ports is connected to both ends of at least one phase unit.
[0036] The i-th input port of the modular multilevel converter and Each phase unit is connected, among which , i = a, b, c, ..., m; the j-th pair of output ports of the modular multilevel converter and Each phase unit is connected, among which Let j = A, B, C, ..., N. The total number of phase elements X ≥ m, X ≥ N, and satisfy:
[0037] .
[0038] A single-phase three-winding transformer consists of a first winding, a second winding, and a third winding, with a turns ratio of... The first windings of N single-phase three-winding transformers are connected to the N phases of the second AC system, respectively. The second windings are connected to the N output ports of the upper arm of the modular multilevel converter, and the third windings are connected to the N output ports of the lower arm of the modular multilevel converter. The same-name terminal of the first winding is connected to the j-th phase of the second AC system, and the other end (non-same-name terminal) of the first winding is grounded, j=A, B, C, ..., N; the same-name terminal of the second winding is connected to the i-th output port of the upper arm of the modular multilevel converter, and the other end (non-same-name terminal) of the second winding is grounded, i=a, b, c, ..., m; the same-name terminal of the third winding is grounded, and the other end (non-same-name terminal) of the third winding is connected to the i-th output port of the lower arm of the modular multilevel converter.
[0039] Modular multilevel converter, upper arm reference voltage of the k-th phase unit and lower bridge arm reference voltage The expression is:
[0040] ;
[0041] in, These are the differential-mode components of the bridge arm reference voltage, i = a, b, c, ..., m. This is the common-mode component of the bridge arm reference voltage, j = A, B, C, ..., N. The range of k can be written as k = (1, 2, ..., Y). a ), (Y a +1, Y a +2, ..., Y a +Y b ), ..., (XY) m +1, XY m +2, ..., X), the range of k can also be written as k = (1, 2, ..., Z). A ), (Z A +1, Z A +2, ..., Z A +Z B ), ..., (XZ N +1, XZ N +2, ..., X).
[0042] Neglecting the voltage drop across the bridge arm inductance, the differential-mode component of the reference voltage of the k-th phase unit bridge arm. and common mode components The expression is:
[0043] ;
[0044] Where U1 corresponds to the phase voltage amplitude of the first AC system, U2 corresponds to the phase voltage amplitude of the second AC system, ω1 is the angular frequency of the first AC system, ω2 is the angular frequency of the second AC system, and θ i The phase shift angle of the first AC system is i = a, b, c, ..., m, θ. j The phase shift angle of the second AC system, j = A, B, C, ..., N. The phase θ of each phase voltage of the first AC system. i The sum of all voltage phasors must be equal to 0, but there is no such restriction on the phase of each phase voltage in the second AC system.
[0045] ;
[0046] The bridge arm current components of a modular multilevel converter can be divided into three parts: the input side component i i Output component i j Circulation component i cirk Referring to the positive current direction in Figure 1, taking the k-th phase unit as an example, the k-th phase unit is connected to the input phase a and the output phase A. The relationship between the three current components and the upper and lower bridge arm currents is as follows:
[0047] ;
[0048] Among them, i a This represents the current at the input phase a port; i A This represents the current at the A-phase port of the output side; i topk i represents the upper arm current of the k-th phase unit; btmk This represents the lower arm current of the k-th phase unit; the a-phase port on the input side is connected to the Y-phase. a Each phase unit is connected, and the A-phase port on the output side is connected to the Z-phase unit. A Each phase unit is connected.
[0049] Input side component i i The differential-mode component belonging to the bridge arm current, the output-side component i j Circulation component i cirk These all belong to the common-mode component of the bridge arm current. Circulating current component i cirk The calculation method is to subtract the output side component i from the common-mode component of the bridge arm current. j The remaining part.
[0050] The dynamic equations for each component of the bridge arm current are then:
[0051] ;
[0052] Where L is the bridge arm inductance, u a U represents the voltage at the input phase a port. A This indicates the voltage at the A-phase port on the output side.
[0053] The control strategy for the AC-AC converter is designed by selecting the input, output, and circulating current components of the bridge arm current as state variables. Note that not all current components are selected, as some current components satisfy Kirchhoff's current law and are not independent of each other. The bridge arm voltage is selected as the control variable. Therefore, the voltage of the first AC system on the input side and the voltage of the second AC system on the output side can both be considered as disturbances. Decoupling control of the various components of the bridge arm current is achieved by controlling the bridge arm voltage.
[0054] The bridge arms of a modular multilevel converter are composed of full-bridge modules connected in series. The voltage balance of the capacitors in the sub-modules within a single bridge arm is resolved through a modulation stage. At the converter control level, it is also necessary to ensure the stability of the sum of the capacitor voltages in each bridge arm. Depending on the range of the dynamic processes involved, this can be divided into two types of control: one is the control of the average capacitor voltage of the converter, which involves the power balance between the input and output ports of the converter; the other is the control to ensure that the average capacitor voltage of each bridge arm is consistent, which involves the exchange of energy between the bridge arms within the converter.
[0055] In some embodiments, this application also provides a control method for a multiphase-to-multiphase direct AC-AC converter, used in any of the foregoing embodiments of the multiphase-to-multiphase direct AC-AC converter. For example, the control method can be a control method for an MMC-based multiphase-to-multiphase direct AC-AC converter.
[0056] As shown in Figure 2, each bridge arm is connected to the first AC system on the input side and the second AC system on the output side. Therefore, the bridge arm current includes both input and output components. When different bridge arms are connected, the bridge arm current also includes a circulating current component. The input, output, and circulating current components of the bridge arm current are selected as state variables to design a control strategy. The control strategy based on the bridge arm current components is divided into two parts: outer loop control and inner loop control. The inner loop control uses bridge arm voltage decoupling transformation to control the input, output, and circulating current components of the bridge arm current respectively. The input and output components each have two modes: voltage control and current control. The appropriate control mode is selected according to the setting requirements. The circulating current component only has one mode: current control. When the inner loop control uses AC voltage control, the outer loop control is not needed. When the inner loop control uses AC current control, the outer loop control uses either active or reactive power control.
[0057] In some embodiments, the set requirements can be control objectives when the first AC system and the second AC system perform power conversion. These objectives may include technical requirements such as voltage amplitude matching, frequency conversion, phase adjustment, precise power control, and power supply stability assurance. For example, when it is necessary to stabilize the output voltage of the second AC system (e.g., in an independent power supply scenario), a voltage control mode can be selected; when it is necessary to precisely regulate the active / reactive power transmission between the first and second AC systems (e.g., in a grid-connected scenario), a current control mode can be selected. Those skilled in the art can flexibly select the control modes corresponding to the input and output components based on the functional objectives and performance indicators of the actual power conversion scenario, ensuring that the AC-AC converter adapts to the power conversion needs of different application scenarios.
[0058] For the outer loop control of the input or output components, active control uses capacitor voltage averaging control or active power control, while reactive control uses reactive power control. For the outer loop control of the circulating current component, active control uses bridge arm balancing control, while reactive control makes the q-axis reactive component reference value of the circulating current 0.
[0059] This application has at least the following characteristics:
[0060] 1. The multiphase-to-multiphase direct AC-AC converter of this application constructs the differential-mode component of the input voltage of each phase and the common-mode component of the output voltage of each phase in the upper and lower bridge arms. Then, the differential-mode component is canceled and the common-mode component is synthesized through a single-phase three-winding transformer connected in reverse to the same terminal, so as to realize the AC-AC conversion requirements of arbitrary voltage amplitude, frequency, phase and number of phases. This topology has good scalability and can adapt to diverse power conversion requirements.
[0061] 2. The multiphase-to-multiphase direct AC-AC converter of this application can effectively reduce the number of bridge arm submodules. Although a three-winding transformer is required to realize the voltage transformation function, it also plays an isolation role, reducing the overall construction cost of the converter station and the design difficulty of the control algorithm. In three-phase-to-three-phase conversion, the converter topology of this application reduces the number of submodules by 50% compared with the back-to-back MMC topology and by 33% compared with the M3C topology; in three-phase-to-single-phase conversion, the converter topology of this application reduces the number of submodules by 40% compared with the back-to-back MMC topology.
[0062] 3. The multiphase-to-multiphase direct AC-AC converter of this application has the advantages of modular MMC topology design, low harmonic content, bidirectional energy flow, high output level, controllable power factor, fast dynamic response, and high reliability. It can be used in AC-AC conversion fields such as offshore wind power low-frequency transmission, island power supply, urban power grid asynchronous interconnection, and high-power variable frequency speed regulation, and has broad application prospects.
[0063] Application examples
[0064] As shown in Figure 3, m=3, N=3, both the first and second AC systems are three-phase systems with three single-phase three-winding transformers. X=3, the modular multilevel converter has three phase units. , The connection method of each phase unit is shown in Figure 3. Figure 4 is a voltage simulation waveform diagram of the input and output sides of the MMC-based three-phase direct AC-AC converter in this application example. The voltage frequency of the first AC system is f1=50Hz, the voltage amplitude is U1=1kV, and the initial phase is θ. a =0°, the voltage frequency of the second AC system is f2=20Hz, the voltage amplitude is U2=0.7kV, and the initial phase is θ. A =10°, both the first and second AC systems are three-phase symmetrical, with each phase differing from the others by 120°. At this point, the voltages of the six bridge arms can be approximated as:
[0065] .
[0066] As shown in Figure 5, m=3, N=1, the first AC system is a three-phase system, and the second AC system is a single-phase system with one single-phase three-winding transformer. X=3, the modular multilevel converter has three phase units. , The connection method of each phase unit is shown in Figure 5. Figure 6 is the voltage simulation waveform diagram of the input and output sides of the three-phase to single-phase direct AC-AC converter based on MMC in this application example. The voltage frequency of the first AC system is f1=50Hz, the voltage amplitude is U1=1kV, and the initial phase is θ. a =0°, the voltage frequency of the second AC system is f2=20Hz, the voltage amplitude is U2=1.2kV, and the initial phase is θ. A =-30°, the first AC system is three-phase symmetrical, each phase differing from the other by 120°, the initial phase θ of the second AC system A This can be set arbitrarily. At this point, the voltages of the six bridge arms can be approximated as:
[0067] .
[0068] As shown in Figure 7, m=3, N=2, the first AC system is a three-phase system, the second AC system is a two-phase system with two single-phase three-winding transformers, X=4, the modular multilevel converter has four phase units, Y... a =2, , The connection method of each phase unit is shown in Figure 7. Figure 8 is the voltage simulation waveform diagram of the input and output sides of the three-phase to two-phase direct AC-AC converter based on MMC in this application example. The voltage frequency of the first AC system is f1=50Hz, the voltage amplitude is U1=1kV, and the initial phase is θ. a =0°, the voltage frequency of the second AC system is f2=20Hz, the voltage amplitude is U2=1kV, and the initial phase is θ. A =0°, the first AC system is three-phase symmetrical, with each phase differing from the others by 120°, and the second AC system has two-phase orthogonal phases, with each phase differing from the others by 90°. At this point, the voltages of the six bridge arms can be approximated as:
[0069] .
Claims
1. A multi-phase-multi-phase direct AC / AC converter, comprising a modular multilevel converter and N single-phase three-winding transformers; the modular multilevel converter comprises X phase units, each phase unit is composed of an upper bridge arm and a lower bridge arm; the input side of the AC / AC converter has m ports connected to a first AC system, each input side port is connected to the midpoint of at least one phase unit; the output side of the AC / AC converter has 2N ports, the upper bridge arms of the X phase units are connected in parallel to form N output side ports, and the lower bridge arms of the X phase units are connected in parallel to form N output side ports, each pair of output side ports is connected to both ends of at least one phase unit; The single-phase three-winding transformer includes a first winding, a second winding, and a third winding, and a transformation ratio is the first windings of the N single-phase three-winding transformers are connected to N phases of a second AC system respectively, the second windings are connected to the N output side ports of the upper bridge arms of the modular multilevel converter, and the third windings are connected to the N output side ports of the lower bridge arms of the modular multilevel converter; the first AC system is an m-phase system composed of a, b, c, …, m phases; the second AC system is an N-phase system composed of A, B, C, …, N phases; m≥2, N≥1.
2. The multiphase-multiphase direct AC-AC converter of claim 1, wherein, The i-th input-side port of the modular multilevel converter is connected with m phase units, wherein i = a, b, c,..., m; the j-th output-side port of the modular multilevel converter is connected with N phase units, wherein j = A, B, C,..., N; the total number of phase units X ≥ m, X ≥ N, and satisfy: 。 3. The multiphase-multiphase direct AC-AC converter of claim 2, wherein, the upper bridge arm and the lower bridge arm of each phase unit of the modular multilevel converter have the same structure and each comprises a plurality of full-bridge sub-modules and a bridge arm inductor connected in series.
4. The multiphase-multiphase direct AC-AC converter of claim 1, wherein, the single-phase three-winding transformer, the same-named end of the first winding is connected to the jth phase of the second AC system, and the other end is grounded, j=A, B, C, …, N; the same-named end of the second winding is connected to the ith output side port of the upper bridge arm of the modular multilevel converter, and the other end is grounded, i=a, b, c, …, m; the same-named end of the third winding is grounded, and the other end is connected to the ith output side port of the lower bridge arm of the modular multilevel converter.
5. The multiphase-multiphase direct AC-AC converter of claim 2, wherein, The modular multilevel converter, the expression of the reference voltage of the upper bridge arm of the kth phase unit and the reference voltage of the lower bridge arm is: ； wherein is a differential-mode component of the bridge-arm reference voltage, is the common-mode component of the bridge arm reference voltage.
6. The multiphase-multiphase direct AC-AC converter of claim 5, wherein, Neglecting the voltage drop on the bridge arm inductance, the differential mode component of the reference voltage of the kth phase unit bridge arm and the common mode component is given by: ； wherein U1 corresponds to the first AC system phase voltage amplitude, U2 corresponds to the second AC system phase voltage amplitude, ω1 is the first AC system angular frequency, ω2 is the second AC system angular frequency, θ i is the first AC system phase shift angle, and θ j is the second AC system phase shift angle.
7. The multiphase-multiphase direct AC-AC converter of claim 6, wherein, The phases of the voltages of each phase of the first AC system need to satisfy that the sum of all voltage phasors is equal to 0, and the phases of the voltages of each phase of the second AC system are not subject to such a limitation.
8. The multiphase-multiphase direct AC-AC converter of any of claims 1-7, wherein, Power flows from the first AC system side to the second AC system side, or from the second AC system side to the first AC system side.
9. A control method of a multi-phase-multi-phase direct AC / AC converter, for the multi-phase-multi-phase direct AC / AC converter of any one of claims 1-8, comprising: selecting the input side component, the output side component and the circulating current component in the bridge arm current as state variables to design the control strategy, dividing the control strategy based on the bridge arm current component into two parts of outer loop control and inner loop control, the inner loop control uses bridge arm voltage decoupling transformation to control the input side component, the output side component and the circulating current component of the bridge arm current respectively, wherein the input side component and the output side component each have voltage control and current control two modes, and the corresponding control mode is selected according to the setting requirement; the circulating current component only has current control one mode; when the inner loop control adopts AC voltage control, the outer loop control is not needed; when the inner loop control adopts AC current control, the outer loop control adopts active type control or reactive type control.
10. The control method according to claim 9, wherein For outer loop control of input side component or output side component, active type control adopts capacitor voltage average control or active power control, and reactive type control adopts reactive power control; for outer loop control of circulating current component, active type control adopts inter-bridge arm balance control, and reactive type control makes q-axis reactive component reference value of circulating current to be 0.