CN107846164B - Motor driving system based on MMC and discrete control method thereof - Google Patents

Abstract

The invention discloses a motor drive system based on a modularized multilevel converter and a discrete control method thereof. The system comprises a modularized multilevel converter and a motor, and an output end of the modularized multilevel converter is connected to the motor; It includes three phases, each phase includes upper and lower bridge arms, both upper and lower bridge arms include N identical submodules and bridge arm inductances connected in series, the input end of the first submodule of the upper bridge arm and the lower bridge The output end of the last sub-module of the arm is connected to the DC bus respectively, the output end of the previous sub-module is connected to the input end of the next sub-module, and the output end of the last sub-module of the upper bridge arm is connected to the lower arm through the upper and lower arm inductances. The input end of the first sub-module of the bridge arm is connected; the connection point of the upper and lower bridge arm inductances of each phase is its output end, and the three output ends are connected with the three phases of the motor. The invention discretizes the motor drive system based on the modularized multi-level converter, and realizes the stable operation of the motor under the multi-level drive.

Description

Motor drive system based on MMC and its discrete control method

technical field

The invention relates to a motor drive control technology, in particular to a discrete control method of a motor drive system based on a Modular Multilevel Converter (MMC).

Background technique

Modular Multilevel Converter (MMC) is a new type of multilevel converter with a highly modular structure, high efficiency, easy to expand the system voltage and capacity, and realize industrialized production. The modular multi-level converter drives the high-speed permanent magnet motor, which can realize high-voltage multi-level output through low-voltage switching without a large-capacity transformer. The equivalent switching frequency is high, and the waveform is closer to a sine wave, which can reduce system losses.

For digital control technology, the traditional motor drive controller design often adopts the method of zero-order keeper, assuming that in a cycle, the system voltage, current and other parameters remain unchanged, and then design the controller in the frequency domain. However, for the motor drive system based on modular multilevel converters, the amount of data is large, especially in the high frequency stage, the assumption that the parameters remain unchanged within a sampling period is no longer established. It is necessary to establish a more accurate mathematical model, and design the corresponding controller according to the state equation of the model.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide a motor drive system based on a modular multilevel converter (MMC) and a discrete control method thereof, so as to solve the deficiencies of the prior art.

Technical solution: the motor drive system based on the modular multi-level converter of the present invention includes a modular multi-level converter and a motor, and the output end of the modular multi-level converter is connected to the motor;

The modular multilevel converter includes three phases, each phase includes an upper bridge arm and a lower bridge arm, and both the upper bridge arm and the lower bridge arm include N identical sub-modules SMi connected in series, i=1,2 ,...,N and a bridge arm inductance L, the input end of the first submodule of the upper bridge arm and the output end of the last submodule of the lower bridge arm are respectively connected to the DC bus, and the output of the upper submodule The terminal is connected to the input terminal of the next sub-module, and the output terminal of the last sub-module of the upper bridge arm is connected to the input terminal of the first sub-module of the lower bridge arm through the inductance of the upper bridge arm and the inductance of the lower bridge arm; The connection point of the upper bridge arm and the lower bridge arm inductance is the output end of the modular multi-level converter, and the three output ends are connected with the three-phase motor.

Further, the sub-module is a half-bridge module, including high-power controllable power electronic switches T1 and T2, two diodes and a capacitor C, wherein T1 and T2 are respectively connected in anti-parallel with a diode, then connected in series, and finally connected in parallel with the capacitor C. connect.

Further, the high-power controllable power electronic switches T1 and T2 are insulated gate bipolar transistors.

Further, the numbers of the sub-modules of the upper bridge arm and the lower bridge arm are respectively even numbers.

Another embodiment, a discrete control method for a motor drive system based on a modular multilevel converter, includes the following steps:

(1) Establish MMC output mathematical model equation

According to Kirchhoff's law, the bridge arm voltage can be expressed as:

Among them, E is the DC bus voltage, v _pj , v _nj are the upper and lower arm voltages of the j-phase, respectively, _ipj , _inj are the j-phase upper and lower arm currents, respectively, i _j is the AC side j-phase current, L is the bridge arm inductance, L _s is the motor winding inductance, R _s is the motor winding resistance, e _j is the opposite potential of the motor, j=a, b, c;

Therefore, the mathematical model equation of the MMC output can be obtained from the mathematical model equation of the bridge arm voltage:

则MMC输出数学模型方程为：definition

Then the MMC output mathematical model equation is:

(2) Perform Clarke and Park transformations on the MMC output mathematical model equation (2) to obtain the MMC output mathematical model in the dq coordinate system:

Among them, v _d , v _q are the d-axis and q-axis components transformed from v _j to the dq coordinate system, respectively, ed , e _q are the _d -axis and q-axis components transformed from e _j to the dq coordinate system, respectively, i _d , i _q are the d-axis and q-axis components transformed from i _j to the dq coordinate system, respectively;

According to the MMC output mathematical model equation (4), we can get:

Among them, ω _e is the angular velocity of the motor;

Discretize (5) to establish a discrete domain model:

in,

Among them, i _d (t _n ) and i _q (t _n ) are the d-axis and q-axis currents obtained by sampling and calculation at time t _n , respectively, and v _d (t _n ) and v _q (t _n ) are respectively calculated at time t _n The obtained d-axis and q-axis voltages, ed (t _n ), _{e q} (t _n ) are the back EMF of the motor d-axis and q-axis at the time of t _n respectively, T _s is the sampling period of the current loop, and ω _e is the motor angular velocity;

(3) MMC current loop design

The discrete controller is designed as follows:

分别为d轴和q轴电流指令值，K为控制系数，进一步可得到z域下传递函数：in,

are the current command values of the d-axis and q-axis respectively, K is the control coefficient, and the transfer function in the z domain can be further obtained:

为

在Z域下的表达形式，为了保证系统稳定性，且所有极点都在单位圆内，所以K的范围为0<K<1；Among them, I _d is the expression form of _id (t _n +T _s ) in the Z domain,

for

In the expression form in the Z domain, in order to ensure the stability of the system, and all poles are in the unit circle, the range of K is 0<K<1;

By formulas (6) and (10), we can get:

so,

Therefore, the d-axis and q-axis currents i _d (t _n ) and i _q (t _n ) obtained by the MMC sampling and calculation at time t _n in the dq coordinate system and the d-axis and q-axis output voltages at the next moment v _d (t _n + The relationship between T _s ) and v _q (t _n +T _s ) is:

in,

Φ _PM is the permanent magnet flux linkage of the motor;

(4) Transform v _d (t _n +T _s ) and v _q (t _n +T _s ) through dq/abc to obtain three-phase output voltages v _a (t _n +T _s ), v _b (t _n + T _s ) and _vc (t _n +T _s ), as three-phase modulation signals of the MMC, perform carrier phase-shift modulation on the MMC.

Beneficial effects: compared with the prior art, the present invention discretizes the motor drive system based on the modular multi-level converter, establishes a discrete mathematical model, and designs the drive system according to the delay-one-beat characteristic of the digital signal processor. The system discrete controller realizes stable operation under the multi-level drive of the motor. Its discrete control method has the following advantages:

(1) Modular multi-level Each bridge arm consists of N sub-modules, and each sub-module withstands a voltage of Vdc/N (Vdc is the DC bus voltage). Specification requirements, easy to achieve system expansion;

(2) The equivalent switching frequency of the modular multi-level converter is high, which reduces the requirement of the motor for the high switching frequency of the switching device and the system loss, and saves hardware resources;

(3) The designed discrete controller has strong dynamic characteristics and is suitable for the actual operation of the digital signal processor;

(4) The stable operation of the motor drive system based on MMC is realized, and the reliability is high.

Description of drawings

Figure 1 is a topology diagram of a motor drive system based on a modular multilevel converter;

Figure 2 is a circuit diagram of a motor drive system based on a modular multilevel converter;

FIG. 3 is a schematic diagram of discrete sampling and duty cycle update of a digital signal processor.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

Figure 1 is a topology diagram of a motor drive system based on a modular multi-level converter, which is composed of a modular multi-level converter and a motor, and the output end of the modular multi-level converter is connected to the motor. Among them, the modular multi-level converter includes three phases A, B and C, each phase is composed of an upper bridge arm, a lower bridge arm and a bridge arm inductance L in series, and the upper and lower bridge arms each include N sub-modules SM1-SMn, In order to enable the modular multilevel converter to output zero level, the number of bridge arm sub-modules is an even number; the connection point of the upper and lower bridge arm inductors L is the AC side electrical interface of the modular multilevel converter, three AC The node is connected to the external motor, and the circuit topology of all sub-modules SM1-SMn is the same, and they are all half-bridge modules.

Wherein, each sub-module includes high-power controllable power electronic switches T1 and T2, and T1 and T2 can be insulated gate bipolar transistors (IGBT for short); anti-parallel diodes of T1 and T2; sub-module DC capacitor C; each sub-module The module is a half-bridge structure; the switching devices T1 and T2 are respectively connected in anti-parallel with a diode, then connected in series, and then connected in parallel with the capacitor C. Both the upper bridge arm and the lower bridge arm are composed of N sub-modules in series. The input end of the first sub-module of the upper bridge arm and the output end of the last sub-module of the lower bridge arm are respectively connected to the DC bus, and the output end of the upper sub-module is connected to the DC bus respectively. Connect to the input of the next submodule.

A method for discrete control of a motor drive system based on a modular multi-level converter, including establishing an MMC output mathematical model equation, discretely establishing a discrete domain model, designing a discrete controller, and calculating the following according to the current sampled at the current moment. The modulation voltage signal of the MMC required at a moment, the carrier phase-shift modulation is performed on the MMC. Specifically include the following steps:

(1) Establish MMC output mathematical model equation

Figure 2 is a circuit diagram of a motor drive system based on a modular multilevel converter. According to Kirchhoff's law, the bridge arm voltage can be expressed as:

Among them, E is the DC bus voltage, v _pj , v _nj are the upper and lower arm voltages of the j-phase, respectively, _ipj , _inj are the j-phase upper and lower arm currents, respectively, i _j is the AC side j-phase current, L is the bridge arm inductance, L _s is the motor winding inductance, R _s is the motor winding resistance, e _j is the opposite potential of the motor, j=a, b, c.

Therefore, the mathematical model equation of the MMC output can be obtained from the mathematical model equation of the bridge arm voltage:

则MMC输出数学模型方程为：definition

Then the MMC output mathematical model equation is:

(2) Perform Clarke and Park transformations on the MMC output mathematical model equation (2) to obtain the MMC output mathematical model in the dq coordinate system:

Among them, v _d , v _q are the d-axis and q-axis components transformed from v _j to the dq coordinate system, respectively, ed , e _q are the _d -axis and q-axis components transformed from e _j to the dq coordinate system, respectively, i _d , i _q are the d-axis and q-axis components transformed from i _j to the dq coordinate system, respectively.

Figure 3 is a schematic diagram of discrete sampling and duty cycle update of the digital signal processor. The current sampling is performed at the starting point of the carrier cycle at time t _n , and the duty cycle obtained by the operation of the sampled current value will be updated at the next sampling point t _n +T _s time , that is, there is a delay of one carrier cycle (current loop sampling cycle).

According to the state space equation in the continuous time domain:

Among them, X(t) is an n-dimensional state vector, U(t) is an r×1 input column vector, A is an n×n square matrix, and B is an n×r control matrix.

and discretizing it, we get:

X(t _n +T _s )=F(T _s )X(t _n )+G(T _s )V (6);

Among them, F(T _s ) is an m×n output matrix, and G(T _s ) is an m×r direct transfer matrix.

Rewrite formula (4) as:

Among them, ω _e is the angular velocity of the motor.

Discretize equation (7) to establish a discrete domain model:

in,

Among them, i _d (t _n ) and i _q (t _n ) are the d-axis and q-axis currents obtained by sampling and calculation at time t _n , respectively, and v _d (t _n ) and v _q (t _n ) are respectively calculated at time t _n The obtained d-axis and q-axis voltages, ed (t _n ) and _{e q} (t _n ) are the back-EMF of the motor d-axis and q-axis at time t _n , respectively, T _s is the current loop sampling period, and ω _e is the motor angular velocity.

(3) MMC current loop design

The discrete controller is designed as follows:

分别为d轴和q轴电流指令值，K为控制系数，进一步可得到z域下传递函数：in,

are the current command values of the d-axis and q-axis respectively, K is the control coefficient, and the transfer function in the z domain can be further obtained:

为

在Z域下的表达形式，为了保证系统稳定性，且所有极点都应在单位圆内，所以K的范围为0<K<1。Among them, I _d is the expression form of _id (t _n +T _s ) in the Z domain,

for

In the expression form in the Z domain, in order to ensure the stability of the system, and all poles should be within the unit circle, the range of K is 0<K<1.

By formulas (8) and (12), we can get:

so,

Therefore, the d-axis and q-axis currents i _d (t _n ) and i _q (t _n ) obtained by the MMC sampling and calculation at time t _n in the dq coordinate system and the d-axis and q-axis output voltages at the next moment v _d (t _n + The relationship between T _s ) and v _q (t _n +T _s ) is:

in,

Φ _PM is the permanent magnet flux linkage of the motor.

(4) Transform v _d (t _n +T _s ) and v _q (t _n +T _s ) through dq/abc to obtain three-phase output voltages v _a (t _n +T _s ), v _b (t _n + T _s ) and _vc (t _n +T _s ) are the three-phase modulation signals of the MMC.

Taking the obtained v _a (t _n +T _s ), v _b (t _n +T _s ) and v _c (t _n +T _s ) required for the next moment as the modulation signal of the MMC, the carrier phase shift is performed on the MMC Modulation, so as to realize the stable operation of the modular multilevel converter for the motor drive system in the practical engineering application using the digital signal processor.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the principles of the present invention, several improvements and modifications can be made. It should be regarded as the protection scope of the present invention.

Claims (1)

1. a discrete control method for a motor drive system based on a modularized multilevel converter, is characterized in that, comprises the following steps: (1) Establish MMC output mathematical model equation According to Kirchhoff's law, the bridge arm voltage can be expressed as:

Among them, E is the DC bus voltage, v _pj , v _nj are the upper and lower arm voltages of the j-phase, respectively, _ipj , _inj are the j-phase upper and lower arm currents, respectively, i _j is the AC side j-phase current, L is the bridge arm inductance, L _s is the motor winding inductance, R _s is the motor winding resistance, e _j is the opposite potential of the motor, j=a, b, c; Therefore, the mathematical model equation of the MMC output can be obtained from the mathematical model equation of the bridge arm voltage:

definition

Then the MMC output mathematical model equation is:

(2) Perform Clarke and Park transformations on the MMC output mathematical model equation (2) to obtain the MMC output mathematical model in the dq coordinate system:

Among them, v _d , v _q are the d-axis and q-axis components transformed from v _j to the dq coordinate system, respectively, ed , e _q are the _d -axis and q-axis components transformed from e _j to the dq coordinate system, respectively, i _d , i _q are the d-axis and q-axis components transformed from i _j to the dq coordinate system, respectively; According to the MMC output mathematical model equation (4), we can get:

Among them, ω _e is the angular velocity of the motor; Discretize (5) to establish a discrete domain model:

in,

Among them, i _d (t _n ) and i _q (t _n ) are the d-axis and q-axis currents obtained by sampling and calculation at time t _n , respectively, and v _d (t _n ) and v _q (t _n ) are respectively calculated at time t _n The obtained d-axis and q-axis voltages, ed (t _n ), _{e q} (t _n ) are the back EMF of the motor d-axis and q-axis at the time of t _n respectively, T _s is the sampling period of the current loop, and ω _e is the motor angular velocity; (3) MMC current loop design The discrete controller is designed as follows:

in,

are the current command values of the d-axis and q-axis respectively, K is the control coefficient, and the transfer function in the z domain can be further obtained:

Among them, I _d is the expression form of _id (t _n +T _s ) in the Z domain,

for

In the expression form in the Z domain, in order to ensure the stability of the system and all poles are within the unit circle, the range of K is 0<K<1; By formulas (6) and (10), we can get:

so,

Therefore, the d-axis and q-axis currents i _d (t _n ) and i _q (t _n ) obtained by the MMC sampling and calculation at time t _n in the dq coordinate system and the d-axis and q-axis output voltages at the next moment v _d (t _n + The relationship between T _s ) and v _q (t _n +T _s ) is:

in,

Φ _PM is the permanent magnet flux linkage of the motor; (4) Transform v _d (t _n +T _s ) and v _q (t _n +T _s ) through dq/abc to obtain three-phase output voltages v _a (t _n +T _s ), v _b (t _n + T _s ) and _vc (t _n +T _s ), as three-phase modulation signals of the MMC, perform carrier phase-shift modulation on the MMC.

Images