阅读说明：本技术 一种ow-pmsm系统的有限开关序列模型预测电流控制方法 (Limited switch sequence model prediction current control method of OW-PMSM system ) 是由 吴迪 朱芮 陈继峰 胡家全 华国武 王影 于 2020-05-19 设计创作，主要内容包括：一种OW-PMSM系统的有限开关序列模型预测电流控制方法,采取每个周期作用三个电压矢量的策略,并且以减少开关次数为目标,对开关状态作用顺序进行分配,使每个周期在实现电流跟踪控制的同时,固定开关频率；矢量组合序列选定后,先确定序列中各个开关状态对应的作用时间,再根据无差拍控制思想,按照每个周期作用三个电压矢量,重新建立电流预测模型,计算每组开关序列中各个矢量的作用时间,得到预测电流值,最后通过价值函数进行遍历,在考虑开关作用顺序的基础上,选出系统最优输出开关组合序列。该方法在抑制零序电流的同时,解决转矩磁链脉动较大及开关频率不固定的问题,提高系统的控制性能。(A limited switching sequence model prediction current control method of an OW-PMSM system adopts a strategy of acting three voltage vectors in each period, and takes reducing the switching times as a target to distribute the acting sequence of the switching states, so that the switching frequency is fixed while the current tracking control is realized in each period; after the vector combination sequence is selected, determining action time corresponding to each switch state in the sequence, then acting three voltage vectors according to each period according to the dead beat control thought, reestablishing a current prediction model, calculating the action time of each vector in each group of switch sequences to obtain a predicted current value, traversing through a value function, and selecting the optimal output switch combination sequence of the system on the basis of considering the switch action sequence. The method solves the problems of large torque flux linkage pulsation and unfixed switching frequency while inhibiting zero sequence current, and improves the control performance of the system.)

1. A finite switch sequence model prediction current control method of an OW-PMSM system is characterized by comprising the following steps: according to the method, on the premise of eliminating a switching state containing zero sequence voltage, a finite set is determined as 6 groups of switching sequences according to the principle of minimum switching frequency, action time corresponding to each group of vectors is sequentially obtained in a dead-beat control mode, and finally, an optimal switching sequence is obtained through online optimization.

2. The finite switching sequence model predictive current control method of an OW-PMSM system according to claim 1, characterized in that: the method comprises the following specific steps:

(1) at kth_sPeriodically, carrying out sampling observation on the OW-PMSM system to obtain a stator three-phase current i_abc ^kAnd motor speed omega_e ^k；

(2) Reference value of torque current i_q ^refFrom speed feedback via PI controller i_d ^ref＝0；

(3) Calculating the corresponding slope of the voltage vector, and calculating the action time of the corresponding voltage vector for the limited vector combination sequence in the control set according to the formula 1;

wherein S is_d1、S_d2、S_d0And S_q1、S_q2、S_q0Respectively, the current change rate, t, corresponding to each vector in the sequence₁，t₂，t₀Respectively corresponding action time of each vector;

(4) carrying out feasibility judgment according to the formula 2, and selecting a switch sequence meeting the requirements; the action time of the vector sequence to be adjusted is redistributed by the formula 3;

in formula 2, t₁，t₂Representing the effective voltage vector acting time; t is t₀Representing the zero vector action time;

in formula 3: t is t_a、t_bActing time for the adjusted effective vector; t is t_zThe zero voltage vector action time after adjustment;

(5) the predicted current values at different slopes are calculated according to equation 4: i.e. i_dq ^k+1；

Wherein S is_d1、S_d2、S_d0And S_q1、S_q2、S_q0Respectively, the current change rate, t, corresponding to each vector in the sequence₁，t₂，t₀Respectively corresponding action time of each vector;

(6) adopting online rolling optimization on the limited switching sequence through formula 5, selecting an optimal switching sequence which enables the value function to take the minimum value, storing the optimal switching sequence, and applying the optimal switching sequence to a double-inverter system in the next period;

wherein

In formula 5: j belongs to {1, 2, 3, 4, 5, 6 }; i belongs to {1, 2, 0 };

(7) at (k +1) T_sAnd repeating the steps periodically.

3. The finite switching sequence model predictive current control method of an OW-PMSM system according to claim 2, characterized in that: in the step (2), for the surface-mounted motor, a control method that id is equal to 0 is adopted, and a flux linkage current reference value i is adopted_d ^ref＝0。

4. The finite switching sequence model predictive current control method of an OW-PMSM system according to claim 2, characterized in that: according to the OW-PMSM voltage equation, the change rate of dq axis current is defined as

In the formula, S_dIs the d-axis current rate of change, S_qIs the rate of change of the q-axis current.

Technical Field

The invention relates to the technical field of motor model prediction current control, in particular to a finite switch sequence model prediction current control method of an OW-PMSM system.

Background

The common direct current bus OW-PMSM system is only powered by a single power supply, has a simple structure and high reliability, can reduce the cost by being powered by the single power supply, and has a very wide application prospect.

However, different from a dual power supply OW-PMSM, the system can generate a zero sequence current path during operation, and the control performance of the system is influenced; therefore, for a single-power-supply double-inverter OW-PMSM system, an applicable algorithm is proposed, and meanwhile, zero-sequence current suppression work needs to be considered, which is very important for improving the performance of the motor and reducing the loss of the motor system.

Particularly, in the OW-PMSM control process, not only the dynamic and static performances of the control system need to be met, but also different limiting conditions need to be considered, and the hardware system cannot simultaneously solve excessive constraints.

Disclosure of Invention

The invention aims to solve the technical problem of the prior art, and provides a finite switch sequence model prediction current control method of an OW-PMSM (open-loop-clamped multi-state machine) system, which can increase the degree of freedom of a system target through a cost function, realize the simultaneous control of a plurality of control target variables, meet system constraint conditions and solve the multi-constraint problem from an algorithm level.

The technical problem to be solved by the present invention is achieved by the following technical means. The invention relates to a finite switching sequence model prediction current control method of an OW-PMSM system, which determines a finite set into 6 groups of switching sequences on the premise of eliminating a switching state containing zero sequence voltage according to the principle of minimum switching frequency, sequentially solves the action time corresponding to each group of vectors by using a dead-beat control mode, and finally obtains an optimal switching sequence through online optimization.

The technical problem to be solved by the invention can be further realized by the following technical scheme, and the method for controlling the current by predicting the limited switching sequence model of the OW-PMSM system comprises the following specific steps:

(1) at kth_sPeriodically, carrying out sampling observation on the OW-PMSM system to obtain a stator three-phase current i_abc ^kAnd motor speed omega_e ^k；

(2) Reference value of torque current i_q ^refFrom speed feedback via PI controller i_d ^ref＝0；

(3) Calculating the corresponding slope of the voltage vector, and calculating the action time of the corresponding voltage vector for the limited vector combination sequence in the control set according to the formula 1;

wherein S is_d1、S_d2、S_d0And S_q1、S_q2、S_q0Respectively, the current change rate, t, corresponding to each vector in the sequence₁，t₂，t₀Respectively corresponding action time of each vector;

(4) carrying out feasibility judgment according to the formula 2, and selecting a switch sequence meeting the requirements; the action time of the vector sequence to be adjusted is redistributed by the formula 3;

in the formula, t₁，t₂Representing the effective voltage vector acting time; t is t₀Representing the zero vector action time;

in the formula: t is t_a、t_bTo adjust forThe effective vector action time later; t is t_zThe zero voltage vector action time after adjustment;

(5) the predicted current values at different slopes are calculated according to equation 4: i.e. i_dq ^k+1；

Wherein S is_d1、S_d2、S_d0And S_q1、S_q2、S_q0Respectively, the current change rate, t, corresponding to each vector in the sequence₁，t₂，t₀Respectively the action time corresponding to each vector.

(6) Adopting online rolling optimization on the limited switching sequence through formula 5, selecting an optimal switching sequence which enables the value function to take the minimum value, storing the optimal switching sequence, and applying the optimal switching sequence to a double-inverter system in the next period;

wherein

In the formula: j belongs to {1, 2, 3, 4, 5, 6 }; i belongs to {1, 2, 0 };

(7) at (k +1) T_sAnd repeating the steps periodically.

The technical problem to be solved by the present invention can be further solved by adopting the following technical scheme that, for the above-mentioned limited switching sequence model prediction current control method of the OW-PMSM system, in the step (2), for the surface-mounted motor, a control method with id ═ 0 is adopted, and a flux linkage current reference value i is adopted_d ^ref＝0。

The technical problem to be solved by the invention can be further realized by the following technical scheme that for the finite switching sequence model prediction current control method of the OW-PMSM system, according to an OW-PMSM voltage equation, the change rates of dq axis current are defined as

In the formula, S_dIs the d-axis current rate of change, S_qIs the rate of change of the q-axis current.

Compared with the prior art, the invention provides a model prediction current control strategy of a limited switching sequence based on zero sequence current suppression for suppressing zero sequence current in a common bus OW-PMSM system and improving the control performance of the system, adopts a strategy of acting three voltage vectors in each period, and distributes the action sequence of the switching state with the aim of reducing the switching times, so that the switching frequency is fixed while the current tracking control is realized in each period; after the vector combination sequence is selected, determining action time corresponding to each switch state in the sequence, then acting three voltage vectors according to each period according to the dead beat control thought, reestablishing a current prediction model, calculating the action time of each vector in each group of switch sequences to obtain a predicted current value, traversing through a value function, and selecting the optimal output switch combination sequence of the system on the basis of considering the switch action sequence.

The invention has the following beneficial effects:

1. the zero-sequence circulating current of the single-power-supply open-winding permanent magnet synchronous motor system is inhibited;

2. the torque pulsation of a motor system is reduced;

4. the problem of unfixed switching frequency is solved.

Drawings

FIG. 1 is a flow chart of an algorithm of the present invention;

FIG. 2 is a voltage vector space distribution diagram without zero sequence voltage according to the present invention;

FIG. 3 is a schematic diagram of the switching vector selection of the present invention;

FIG. 4 is a diagram of the current trend of the system during one cycle of the present invention;

FIG. 5 is a schematic diagram of the sequence of actions of the switching sequence of the present invention;

FIG. 6 is a schematic diagram of the sequence of actions of the improved switching sequence of the present invention;

FIG. 7 is a block diagram of the overall simulation control of the present invention;

FIG. 8 is a simulation block diagram of the OW-PMSM according to the present invention;

FIG. 9 is a graph of simulated action time according to the present invention;

FIG. 10 is a waveform diagram illustrating the simulation of no-load starting of the motor according to the present invention;

FIG. 11 is a waveform diagram of a sudden loading simulation of the present invention;

FIG. 12 is a waveform of the sudden load reduction simulation of the present invention;

FIG. 13 is a graph comparing the response characteristics of the system of the present invention with those of the prior art algorithm.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Referring to fig. 1, a finite switching sequence model prediction current control method of an OW-PMSM system, that is, a model prediction current control method of a finite switching sequence based on zero-sequence current suppression, solves the problems of large torque flux ripple and unfixed switching frequency while suppressing zero-sequence current, and improves the control performance of the system; the OW-PMSM refers to an open-winding permanent magnet synchronous motor.

In order to improve the control performance of the system, a strategy of applying three voltage vectors in each cycle is adopted, and if the switching sequence is selected, namely three switching state combination sequences are applied in each cycle, the switching state combination sequences are not a single switching state combination. And with the aim of reducing the switching times, the switching state action sequence needs to be distributed, so that the switching frequency is fixed while the current tracking control is realized in each period;

referring to fig. 2, the space voltage vector distribution diagram without zero sequence voltages adopted by the dual two-level inverter at this time is still a regular hexagon, and includes six effective voltage vectors with zero. Compared with the two-level inverter voltage space vector distribution diagram, the voltage space vector distribution diagram has a deviation of only 30 degrees, and redundant switch states still exist.

For the convenience of analysis, the 12 switch states corresponding to the six effective vectors are firstly divided into the following two groups: 24 ', 35', 46 ', 51', 62 ', 13' are in one group; 15 ', 26', 31 ', 42', 53 ', 64' is another group. At the moment, the effective voltage vectors of each group have uniquely determined switch states corresponding to the effective voltage vectors one by one, and the selection of the switch sequence can be converted into the selection of the voltage vector sequence.

Conventional FCS-MPCs only act on one voltage vector for one cycle, during which the current either increases or decreases constantly or may not change, resulting in an inaccurate tracking of the reference current. Therefore, if precise control of the current is to be achieved, with as little deviation as possible between the actual current and the reference current, the sequence of voltage vectors in the limited control set will generally contain voltage vectors that enable both an increase and a decrease, respectively, in the dq-axis current component. However, it should be noted that a voltage vector capable of increasing the current and a voltage vector capable of decreasing the current do not need to be provided at the same time, and the final target can be continuously close to the given value.

According to the OW-PMSM voltage equation, the change rate of dq axis current is defined as

In the formula, S_dIs the d-axis current rate of change, S_qAs rate of change of q-axis current, i_d ^k,i_q ^kThe current is a sampling value of the current at the current moment; l is_d，L_qRepresenting an inductance; psi_fRepresents a permanent magnetic flux linkage;

stray resistance R in neglect mode_sThe method comprises the following steps:

to analyze u_d、u_qInfluence on the rate of change of current, let omega_eL_qi_q＝V_d，-ω_eL_di_d-ω_eψ_f＝V_qWhen V is_d，V_qIn the position shown in FIG. 3, taking sector I as an example, the voltage vector that can be taken into account in this case has u₀、u₁And u₂. When V is_d>0, when the voltage vector determined by sector I is at the rate S at which the d-axis current changes_dTo the right of the line of zero, i.e. u₀、u₁And u₂The d-axis current component is increased, and only the speed and the magnitude of the change are different; in the same way, when V_q>0, the q-axis current will also increase. When V is_dWhen < 0, only u is present₁On the right side of the line giving zero rate of change of d-axis current, i.e. u₁The d-axis current component can be increased, and u on the left side₀And u₂Will reduce the d-axis current component; in the same way, when V_qAt < 0, when u₂Above the line that makes the rate of change of the q-axis current zero, u₂The q-axis current component can be increased and u located below₀And u₁The q-axis current component is reduced.

Through analysis, the voltage vector which increases the current and the voltage vector which decreases the current exist in the sector I, which is beneficial to the accurate control of the current. Therefore, by adopting the latest three-vector principle, the effective voltage vector and the zero vector of each sector are combined according to a certain rule to obtain a virtual voltage vector, namely a group of alternative voltage vector sequences.

Thus, according to the above principles, a total of six sets of finite vector sequence combinations can be determined, as shown in table 1;

TABLE 1 finite vector sequence control set

Sector number	Vector sequence combining
		Ⅰ	VOH、VOJ、VOO
Ⅱ	VOJ、VOL、VOO
		Ⅲ	VOL、VON、VOO
Ⅳ	VON、VOQ、VOO
		Ⅴ	VOQ、VOS、VOO
Ⅵ	VOS、VOH、VOO

At this time, in an ideal case, a dq-axis current track in one period is as shown in fig. 3, and in an ideal case, when three voltage vectors act in one period, a dq-axis current changes according to a trend of a polygonal line and finally approaches a reference current value; if only one voltage vector is applied in one period, the current changes according to the trend of a blue dotted line and is easy to deviate from the reference current value finally, so that the control effect of three vectors is better than that of a single vector.

After the vector combination sequence is selected, action time corresponding to each switch state in the sequence needs to be determined, three voltage vectors act in each period according to the dead-beat control idea, a current prediction model is reestablished, and the action time of each vector in each group of switch sequences is calculated.

In combination with the effect of the rate of change of the current on the actual current, the dq-axis current prediction model is:

wherein S is_d1、S_d2、S_d0And S_q1、S_q2、S_q0Respectively, the current change rate, t, corresponding to each vector in the sequence₁，t₂，t₀Respectively the action time corresponding to each vector.

In the formula S_di，S_qiIs kT_sRate of change of current, u, corresponding to the voltage vector at time_di、u_qiRepresents the projection of the converter voltage vector on the dq axis, i ∈ {1, 2, 0 };

in order to make the predicted current follow the given current and realize dead-beat tracking control, the predicted current is equal to the reference value in the current prediction model, and the error between the predicted current and the reference value is zero, namely

According to the formula, the action time of 3 different switch states in each group of switch sequence is obtained by solving:

as with the conventional FCS-MPC strategy, the FSS-MPCC still performs online optimization of vector combination sequences in a limited control set through rolling optimization. The difference is that the FSS-MPCC needs to calculate the action time corresponding to the six groups of voltage vectors respectively, then obtains the predicted current value by formula, finally traverses through the value function, and selects the optimal output switch combination sequence of the system on the basis of considering the switch action sequence.

The FSS-MPCC cost function is shown as:

wherein

Wherein j ∈ {1, 2, 3, 4, 5, 6}, and i ∈ {1, 2, 0 }.

In addition, it should be noted that, in each online optimization, after the action time of each group of vector sequences is calculated by the formula, the feasibility judgment needs to be performed by the substitution formula. t is t₁，t₂Representing the effective voltage vector acting time; t is t₀Representing zero vector action time.

If the vector action time meets the formula, the vector sequence meeting the requirement is provided, otherwise, the vector sequence group is discarded; there is a case where the appropriate reallocation can be made to meet the desired requirements, i.e. from t₁＞0、t₂> 0 and t₀The vector sequence with less than 0 is preferred and adjusted as follows:

in the formula: t is t_a、t_bActing time for the adjusted effective vector; t is t_zThe zero voltage vector action time after adjustment.

After the finite vector combination is subjected to rolling online optimization by using the cost function to determine the optimal vector combination, the problem of unfixed switching frequency still exists because the voltage vector acting in each period has randomness, and the switching stress of each phase of the inverter cannot be evenly distributed. At this time, the vector sequence needs to be sorted according to the switch states, so as to obtain the optimal switch combination sequence of the system desired target.

From the foregoing analysis, if the difference (ten in total) of the zero vector switch states is considered, there will be ten corresponding sets of switch sequences for one set of vector sequence combinations. There are ten corresponding sets of switching sequences in the remaining five sectors. It should be noted that, in order to reduce the switching loss and solve the problem of non-fixed switching frequency, the zero vector needs to be screened.

The selection of the zero vector is the most flexible, and the proper selection of the zero vector can avoid the switching action of the switching device when the load current is large as much as possible, thereby reducing the switching loss to the maximum extent. Therefore, the switching times generated when the switching states of each fixed switching sequence are switched are all fixed values according to the concept of minimum loss vector pulse width modulation. For example, when the selected non-zero voltage vector is u₁And u₂If the corresponding switch sequences are 24 '-35' -77 '-77' -35 '-24' and 35 '-24' -88 '-88' -24 '-35', the switching sequence of the switch states of the switch sequences 24 '-35' -77 '-77' -35 '-24' is shown in fig. 5.

In a group of corresponding switching sequences, only two phases of a single inverter are switched in one period, the switching times are twice, and the switching state of the remaining one phase is always in a low level or high level state. And only the switching state of one phase changes every time the switching state is switched. In addition, the action time of the two half periods is evenly distributed in a symmetrical mode.

At this time, there are a total of 12 possible switch combination sequences as shown in table 2. However, such a combination of switching sequences can only make the switching frequency substantially constant, and does not achieve the purpose of continuous frequency setting. In order to achieve the purpose of continuous frequency setting, a zero vector is reasonably used, so that zero vectors are inserted into each group of switching sequence combination at the beginning and the end of each half period, and the symmetrical distribution is maintained.

TABLE 2 switch combination sequence

	Switching sequence of switches
		1	24′35′77′77′35′24′
2	35′24′88′88′24′35′
		3	46′35′77′77′35′46′
4	35′46′88′88′46′35′
		5	46′51′77′77′51′46′
6	51′46′88′88′46′51′
		7	62′51′77′77′51′62′
8	51′62′88′88′62′51′
		9	62′13′77′77′13′62′
10	13′62′88′88′62′13′
		11	24′13′77′77′13′24′
12	13′24′88′88′24′13′

As shown in fig. 6, in this case, in one control period, there is a switching action in all the three-phase switching tubes of the single inverter, and there is no state where one phase is suppressed to be at a low potential or a high potential, and both half periods still maintain a symmetrical distribution. Furthermore, since the same zero switching state (88') is used at both the beginning and end of each cycle, no jump in switching state occurs when the vector sequence is alternated between adjacent cycles, thereby achieving a fixed switching frequency.

Finally, there are a total of 6 possible switch combination sequences, as shown in table 3. It can be seen that the switching mode adopted finally is very similar to SVPWM, and the switching state combination is performed by using two effective vectors and a zero vector, so as to fix the switching frequency. However, the conventional SVPWM needs to perform sector judgment and generate a switching state through a modulator after a series of complex calculations, and in addition, in an open-winding motor fed by a double inverter, the conventional SVPWM cannot be directly used, and a voltage vector needs to be decoupled; the method avoids the processes of sector judgment and voltage vector decoupling, can select the optimal voltage vector sequence of the system by only utilizing one cost function, and directly acts the switching state on the inverter.

TABLE 3 improved switch combination sequence

	Switching sequence of switches
		1	88′24′35′77′77′35′24′88′
2	88′46′35′77′77′35′46′88′
		3	88′46′51′77′77′51′46′88′
4	88′62′51′77′77′51′62′88′
		5	88′62′13′77′77′13′62′88′
6	88′24′13′77′77′13′24′88′

Simulation analysis:

in order to analyze and research the improved algorithm, a simulation model of the FSS-MPCC strategy of the OW-PMSM system based on zero-sequence current suppression is built by using Simulink, as shown in FIGS. 7-8; the motor parameters are as follows: stator flux linkage amplitude given psi_s0.15Wb, and 0.013kg m²D.c. supply voltage V of inverter_dc300V, stator resistance R of open winding PMSM_s＝0.3Ω，L＝4e-4H，Permanent magnetic linkage psi_f0.15Wb, and the mutual inductance M between the windings is 1 e-5H.

FIG. 9 is a diagram of the variation of the voltage vector with time of action, at steady state, t, calculated using a finite switching sequence model predictive control strategy_a、t_b、t_zThe current deviation of the period is reduced as much as possible under the action of three vectors; and during dynamic, the action time is quickly adjusted, so that the actual current can reach a reference value in the period.

The simulation waveform of the no-load starting of the motor is shown in fig. 10, the system is started stably, and the rotating speed is increased linearly, so that the quick response can be followed with a given value. Due to the amplitude limiting effect of the outer ring PI of the rotating speed, the q-axis current is constant when being started, the three-phase current waveform is stable, and i is adopted in the text_dControlling q-axis current as 0, and limiting the starting current of the three-phase current to be constant; after the current stabilized, the torque output was 0N · m. As the applied voltage vector increases per cycle, both current and torque ripple are reduced.

Fig. 11-12 are graphs of simulated waveforms corresponding to the sudden increase and decrease of the electromagnetic torque at a given rotation speed, respectively. In fig. 11, the load torque is abruptly increased from 0N · m to 10N · m, and in fig. 12, the load torque is abruptly decreased from 10N · m to 5N · m. During the process of sudden load addition and reduction, the rotating speed, the three-phase current, the q-axis torque current and the electromagnetic torque all have the phenomena of overshoot and oscillation; in addition, when the torque is suddenly increased or decreased, the three-phase current, the q-axis current and the torque can quickly follow the given value, and the response is quick; the FSS-MPCC strategy has good dynamic and static performances.

In order to compare the algorithms before and after improvement, the system simulation conditions are set as follows: the initial torque of the motor is as follows: the load torque is loaded to 5 N.m at 0 N.m, 0.1s, and is continuously loaded to 15 N.m at 0.15s, and the given rotating speed of the motor is 1000r/min constantly.

The system response characteristics of the two algorithms are shown in fig. 13, and in the diagram, it can be seen by comparing the response characteristics of the running states of the two different algorithms that one period of the control strategy before the improvement only has one voltage vector function, the three-phase stator current pulsation is large and the torque pulsation of the motor system is also large, and one period of the control strategy after the improvement has three voltage vectors functions, so that the three-phase stator current and the torque pulsation are reduced. Simulation results show that the improved algorithm has an effect of suppressing torque and current ripple.

In conclusion, the single power supply OW-PMSM system adopting the improved strategy can have excellent dynamic and static performances even if only partial voltage vectors are used.