Five-leg inverter dual permanent magnet motor phase current reconstruction method

Abstract

The application discloses a five-bridge-arm inverter double-permanent-magnet-motor phase current reconstruction method. The five-bridge-arm inverter double-permanent-magnet motor is set, the corresponding relationship between the direct-current bus current in the five-bridge-arm inverter double-permanent-magnet motor and the phase currents of the two permanent magnet motors under different switching states is adopted to perform phase current reconstruction by using an effective vector sampling method, and under the phase current reconstruction blind area introduced by non-ideal factors, the double-permanent-magnet-motor pulse shift method is adopted to correct the phase current reconstruction. The method realizes the phase current reconstruction of the two permanent magnet motors, and realizes the independent control of the two permanent magnet motors by using the reconstructed phase currents, reduces the number of current sensors for obtaining the phase current information of the two permanent magnet motors, which can reduce the system volume, reduce the system cost and improve the system reliability.

Description

Technical Field

[0001] This invention relates to the field of multi-permanent magnet motor control. In particular, it relates to a phase current reconfiguration method for a dual permanent magnet synchronous permanent magnet motor system in a five-bridge inverter. Background Technology

[0002] In recent years, the collaborative control technology of two permanent magnet motors has become indispensable in many industrial applications such as electric vehicles, wind power generation, and CNC machine tools. Furthermore, some applications require control systems with varying control performance. Therefore, scholars have continuously proposed new control theories and algorithms to improve the control performance of permanent magnet synchronous motors (PMSMs). In these systems, each PMSM is typically driven by a three-phase bridge arm, thus requiring numerous IGBTs for PMSM control, which increases the system's failure rate. When any phase bridge arm of a traditional multi-PMSM system fails, the entire control system may malfunction. Traditional two-PMSM drive systems typically use a six-bridge-arm voltage source inverter to drive both PMSMs. A five-bridge-arm voltage source inverter can serve as a fault-tolerant solution when one phase bridge arm of a six-bridge-arm voltage source inverter fails. This not only improves the reliability of the drive system but also reduces system cost and size, attracting considerable attention from scholars in recent years.

[0003] Meanwhile, the control of permanent magnet motors relies heavily on accurate phase current information, which typically requires installing multiple current sensors on the winding side of the permanent magnet motor to simultaneously sample the three-phase winding current. This not only increases the system's cost and size, but also introduces measurement errors due to parameter differences between the current sensors. Therefore, to reduce the impact of multiple current sensors on system control, utilizing phase current reconstruction technology to obtain the phase current information of permanent magnet motors is of great research significance in modern industry. Summary of the Invention

[0004] To fill the gap in the existing technology, this invention aims to propose a phase current reconstruction algorithm in a five-bridge inverter dual permanent magnet motor system that uses only a single current sensor installed on the DC bus to obtain the phase current information of the two permanent magnet motors. This algorithm can achieve independent control of the two three-phase permanent magnet synchronous motors while reducing the system size and cost, improving the reliability of system operation, and ensuring that the steady-state and dynamic performance of the permanent magnet motors are not affected.

[0005] While traditional half-control cycle modulation strategies can achieve independent control of two permanent magnet motors, each permanent magnet motor will always be controlled by a zero vector for half of a control cycle. In a permanent magnet synchronous motor control system, the operating speed range of the permanent magnet motor is closely related to the operating range of the effective voltage vector. The half-control cycle modulation strategy limits the operating range of the effective voltage vector of the two permanent magnet motors, thus restricting the speed regulation range of the two permanent magnet motors.

[0006] To address the problem that the speed regulation range of permanent magnet motors is limited by the semi-controlled periodic modulation strategy used in five-arm inverters, this invention employs a centralized modulation strategy to extend the speed regulation range of the two permanent magnet motors. Under the condition that the duty cycles on the common arm are equal, the effective vector operating range of the two permanent magnet motors can be effectively extended, thereby expanding the speed regulation range of the two permanent magnet motors.

[0007] The specific technical solution of the present invention is as follows.

[0008] For the dual permanent magnet motors in the five-bridge inverter, the effective vector sampling method is used to reconstruct the phase current based on the correspondence between the DC bus current and the phase current of the two permanent magnet motors in different switching states. Furthermore, under the phase current reconstruction blind zone introduced by non-ideal factors, the dual permanent magnet motor pulse shift method is used to correct the phase current reconstruction.

[0009] Under different switching states of the five-arm inverter, the current flow path is different. The DC bus current contains different phase current information of the two permanent magnet motors. The bridge arm inverter drives the dual permanent magnet motor system using a centralized modulation strategy.

[0010] The effective vector sampling method involves setting a current sensor on the DC bus of each of the five arms in the dual permanent magnet motor of the five-arm inverter. The five PWM signals of the five-arm inverter in each control cycle include four different switching states. The DC bus current is sampled by the current sensor during the action time of each switching state to obtain four DC bus currents. Then, based on the relationship between each DC bus current and the phase currents of the two permanent magnet motors, two phase currents of each permanent magnet motor are obtained. Finally, based on the fact that the sum of the three phase currents of the permanent magnet motor stator windings is zero when they are connected in a star configuration, the remaining third phase current of each permanent magnet motor is obtained, thus realizing the current reconstruction of the two permanent magnet motors.

[0011] The four different switching states specifically refer to the states under four different numbers of bridge arms being controlled for conduction.

[0012] This method samples the DC bus current during the action time of four adjacent switching states within a control cycle, and then reconstructs the phase current based on the different phase current information of the two permanent magnet motors contained in the DC bus current under different switching states.

[0013] When using the effective vector sampling method of the present invention for current reconstruction, under ideal conditions, the DC bus current sampling can be completed instantly and accurately, thereby realizing current reconstruction.

[0014] However, in practical applications, due to the existence of non-ideal factors, DC bus current sampling cannot be completed instantaneously. There are situations where the sampling requirements are not met in the sampling interval time of the DC bus current corresponding to the four switching states in each control cycle. As a result, DC bus current sampling cannot be accurately completed in a single control cycle, which leads to unsuccessful phase current reconstruction and the appearance of a phase current reconstruction blind zone.

[0015] To address the problem of current reconstruction failure in the phase current reconstruction blind zone of the effective vector sampling method, this invention proposes a pulse shifting strategy, which uses a dual permanent magnet motor pulse shifting method to accurately sample the DC bus current and realize the phase current reconstruction of the two permanent magnet motors.

[0016] The aforementioned dual permanent magnet motor pulse shifting method involves shifting the drive signals of each arm of the five-arm inverter left and right within the phase current reconstruction blind zone. This ensures that the sampling interval of the DC bus current corresponding to the four switching states in each control cycle meets the sampling requirements, thereby accurately sampling the DC bus current and realizing the phase current reconstruction of the two permanent magnet motors.

[0017] The method first determines the phase current reconstruction dead zone:

[0018] When a phase current reconfiguration dead zone occurs, the driving signals of each bridge arm are first shifted and corrected using the dual permanent magnet motor pulse shifting method, and then the effective vector sampling method is used for phase current reconfiguration.

[0019] When no phase current reconfiguration dead zone occurs, the effective vector sampling method is directly used for phase current reconfiguration. The method determines whether a phase current reconfiguration dead zone exists according to the following formula:

[0020] T min ≥T set +T on +T AD +T d

[0021] In the formula, T min T represents the minimum time required to complete DC bus current sampling. set T represents the time it takes for the current to reach steady state due to the parasitic parameters of the switching transistor and the inductance of the permanent magnet motor. on T is the turn-on time of the power switch transistor. AD T represents the delay time between the filter circuit and the AD sampling; d Dead time;

[0022] When the above formula is satisfied, the DC bus current sampling interval meets the sampling requirements and no current reconstruction blind zone occurs;

[0023] If the above formula is not met, the DC bus current sampling interval will not meet the sampling requirements, resulting in a current reconstruction blind zone.

[0024] The specific method of pulse shifting using dual permanent magnet motors is as follows:

[0025] First, the sampling interval is obtained by processing the relationship between the sampling interval of the DC bus current and the duty cycle of each phase of the five-arm inverter according to the following formula:

[0026]

[0027] In the formula, ΔT1, ΔT2, ΔT3, and ΔT4 represent the action times of the first, second, third, and fourth switching states within the first half of the control cycle, respectively, which are the sampling interval times of the DC bus current within the first, second, third, and fourth switching states; λ n This is the duty cycle of the nth bridge arm, where n represents the arm's index (n = 1, 2, 3, 4, 5), and λ1 to λ5 are the duty cycles of the five bridge arms arranged from largest to smallest. s Indicates the discrete control period;

[0028] Then, the drive signals for the five bridge arms are pulse-shifted in sequence as follows:

[0029] If ΔT1 <T min The drive signal of the bridge arm corresponding to the maximum duty cycle λ1 is shifted forward by T. min -ΔT1;

[0030] If ΔT2 <T min The drive signals of the bridge arms corresponding to the largest duty cycle λ1 and the second largest duty cycle λ2 are shifted forward by T. min -ΔT2;

[0031] If ΔT1 <T min and ΔT2 <T min The drive signal of the bridge arm corresponding to the maximum duty cycle λ1 is shifted forward by 2T. min -ΔT1-ΔT2 shifts the drive signal of the bridge arm corresponding to the second largest duty cycle λ2 forward by T. min -ΔT2;

[0032] If ΔT3 <T min The drive signals for the bridge arms corresponding to the second smallest duty cycle λ4 and the smallest duty cycle λ5 are shifted backward by T. min -ΔT3;

[0033] If ΔT4 <Tmin The drive signal of the bridge arm corresponding to the minimum duty cycle λ5 is shifted backward by T. min -ΔT4;

[0034] If ΔT3 <T min and ΔT4 <T min The drive signal of the bridge arm corresponding to the second smallest duty cycle λ4 is shifted backward by T. min -ΔT3, and shift the drive signal of the bridge arm corresponding to the minimum duty cycle λ5 backward by 2T. min -ΔT3-ΔT4.

[0035] The intermediate duty cycle λ3 corresponds to the common bridge arm.

[0036] This pulse shifting process ensures that the time interval for each sampling is greater than or equal to T. min It can accurately sample the DC bus current, thereby enabling the phase current reconstruction of two permanent magnet motors.

[0037] The effective vector sampling method is specifically as follows:

[0038] The relationship between the five bridge arm phase currents and the DC bus currents obtained from four samplings under four different switching states is expressed by the following formula. The input DC bus current is then processed to obtain the phase currents of the five bridge arms:

[0039]

[0040] Where, λ n This is the duty cycle of the nth bridge arm, where n represents the arm's index, n = 1, 2, 3, 4, 5, and λ1 to λ5 are the duty cycles of the five bridge arms arranged from largest to smallest; i λn It is a duty cycle of λ n The phase current corresponding to the bridge arm; i sam1 i sam2 i sam3 i sam4 These are the DC bus currents sampled during the operating time of the four switching states.

[0041] The phase currents corresponding to the five bridge arms are reconstructed using the above formulas. Then, the two-phase currents of each permanent magnet motor are reconstructed based on the phase currents corresponding to each bridge arm. Finally, the remaining last phase current is obtained, thereby realizing the phase current reconstruction of the two permanent magnet motors.

[0042] Among them, i sam1 It is the DC bus current sampled during the first switching state's operating time, i sam2 It is the DC bus current sampled during the second switching state's operating time, i sam3 It is the DC bus current sampled during the third switch state's operating time, isam4 It is the DC bus current sampled during the fourth switch state's operating time.

[0043] Let S x As a switching function, the five-phase bridge arms x of the five-bridge-arm inverter are divided into A, B, C, D, and E. A, B, C, D, and E represent the common bridge arm, the bridge arm connected to the b1 phase winding of the first motor, the bridge arm connected to the c1 phase winding of the first motor, the bridge arm connected to the b2 phase winding of the second motor, and the bridge arm connected to the c2 phase winding of the second motor, respectively.

[0044] For each phase arm of a five-arm inverter, when the upper switch is turned on and the lower switch is turned off, let the switching function S... x =1; When the upper switch is off and the lower switch is on, let the switching function S = 1. x =0; The first switching state specifically refers to the state when only one phase bridge arm is switched, function S x The second switching state specifically refers to the switching state when there is a two-phase bridge arm switching function S. x The switching state when it is 1, the third switching state specifically refers to the state when there is a three-phase bridge arm switching function S. x The fourth switching state specifically refers to the state when the four-phase bridge arm switching function S is 1. x The switch state when it is 1.

[0045] The five-arm inverter dual permanent magnet motor includes two permanent magnet motors and an inverter consisting of five arms. The five arms are connected in parallel, with the midpoints of three arms connected to the three-phase lines of one of the permanent magnet motors and the midpoints of the other three arms connected to the three-phase lines of the other permanent magnet motor. There is one and only one shared arm among the three arms connected to the two permanent magnet motors as a common arm.

[0046] Each bridge arm consists of two switching transistors connected in series.

[0047] This invention analyzes the correspondence between the DC bus current and the phase current of the two permanent magnet motors in a five-arm inverter dual permanent magnet motor system under different switching states. Based on the centralized modulation strategy, an effective vector sampling method is proposed for phase current reconstruction. Furthermore, the blind zone of phase current reconstruction introduced by non-ideal factors is analyzed. To address the problem of unsuccessful current reconstruction in the blind zone, a dual permanent magnet motor pulse shifting method is proposed, realizing phase current reconstruction of the five-arm inverter driving the dual permanent magnet motors.

[0048] The features and beneficial effects of this invention are:

[0049] This invention is a phase current reconstruction algorithm applied to a dual permanent magnet motor system in a five-bridge inverter. It realizes the phase current reconstruction of the two permanent magnet motors by using a single current sensor installed on the DC bus, and uses the reconstructed phase current to realize the independent control of the two permanent magnet motors.

[0050] Compared to traditional dual permanent magnet motor drive systems, phase current reconstruction reduces the number of current sensors required to acquire phase current information from the two permanent magnet motors. This can reduce system size, lower system cost, and improve system reliability. Attached Figure Description

[0051] Figure 1 This is a topology diagram of a five-bridge inverter dual permanent magnet motor system.

[0052] Figure 2 This is a switching sequence diagram of a five-bridge inverter based on two modulation strategies.

[0053] Figure 3 This is a switching sequence diagram when the voltage vectors of both permanent magnet motors are located in sector II.

[0054] Figure 4 This is a schematic diagram of the blind zone in sector II of PMSM1.

[0055] Figure 5 This is a schematic diagram of the blind zone within the operating region of the PMSM1 voltage vector.

[0056] Figure 6 It is a switching sequence after pulse shifting.

[0057] Figure 7 This is a control block diagram of a dual permanent magnet motor system based on phase current reconstruction.

[0058] Figure 8 This is the experimental procedure flowchart.

[0059] Figure 9 The figure shows the experimental results of two permanent magnet motors running at a speed of 50 r / min under a load of 2 Nm.

[0060] Figure 10 The figure shows the experimental results of PMSM1 running at 400 r / min under a 5 Nm load and PMSM2 running at 300 r / min under a 6 Nm load.

[0061] Figure 11 The figure shows the experimental results of PMSM1 running at a constant speed of 700 r / min under a load of 5 Nm and PMSM2 running at a speed of 50 r / min under a load of 2 Nm.

[0062] Figure 12The figure shows the experimental results of PMSM1 operating at a triangular wave speed of 100 r / min to 500 r / min under a 5 Nm load, and PMSM2 operating at a speed of 300 r / min under a 6 Nm load.

[0063] Figure 13 The figure shows the experimental results of PMSM1 running at a constant speed of 300 r / min under a step load and PMSM2 running at a constant speed of 300 r / min under a 6 Nm load. Detailed Implementation

[0064] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0065] This invention utilizes a single current sensor mounted on the DC bus to reconstruct the phase currents of two permanent magnet synchronous motors (PMSMs) in a five-arm inverter-driven dual PMSM system, and employs the reconstructed phase currents for closed-loop control of the PMSMs. Since traditional modulation strategies are no longer suitable for five-arm inverters, this invention adopts a centralized modulation strategy to achieve independent control of the two PMSMs. Based on this modulation strategy, the principle of phase current reconstruction based on the DC bus current and the phase current reconstruction blind zone are analyzed in detail. Addressing the problem that the effective vector sampling method cannot accurately complete current reconstruction within the phase current reconstruction blind zone, this invention proposes a pulse shifting method to achieve phase current reconstruction of the two PMSMs within the blind zone.

[0066] The control method of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0067] The topology of a five-bridge voltage source inverter driving a dual permanent magnet synchronous permanent magnet motor system is as follows: Figure 1 As shown. V dc The voltage on the DC side is the capacitor voltage. On the right is a five-arm inverter and two permanent magnet synchronous motors (PMSMs), PMSM1 and PMSM2. Arm A serves as the common arm, forming inverter 1 with arms B and C to drive PMSM1, and with arms D and E to form inverter 2 to drive PMSM2. Compared to a traditional six-arm inverter driving dual permanent magnet motor system, this system reduces two IGBT power switches.

[0068] Step 1: Modulation strategy for the five-arm inverter.

[0069] This invention employs a centralized modulation strategy to maintain equal duty cycles for two permanent magnet motors on the common bridge arm A, thereby achieving independent control of the two permanent magnet motors. In a permanent magnet synchronous motor control system, the operating speed range of the motor is closely related to the operating range of the effective voltage vector. While the traditional half-control cycle modulation strategy can achieve independent control of the two permanent magnet motors, each permanent magnet motor is always controlled by a zero vector for half of a control cycle, which limits the operating range of the effective voltage vector of the two permanent magnet motors, thus restricting their speed range. The centralized modulation strategy, while ensuring equal duty cycles on the common bridge arm, effectively expands the operating range of the effective vector of the two permanent magnet motors, thereby expanding their speed range. The switching sequences of the five-bridge arm inverter under the half-control cycle modulation strategy and the centralized modulation strategy are as follows: Figure 2 (a) and Figure 2 As shown in (b), the centralized modulation strategy is no longer limited to outputting the voltage vectors required to control the two permanent magnet motors in the first and second half-control cycles respectively. Therefore, the centralized modulation strategy can synthesize voltage vectors with larger amplitudes, thereby expanding the speed range of the permanent magnet motors.

[0070] Step 2: Phase current reconstruction of the five-bridge inverter-driven dual permanent magnet motor system

[0071] By analyzing the relationship between the DC bus current and the phase current of the two permanent magnet motors in a five-bridge inverter dual permanent magnet motor system under different switching states, an effective vector sampling method for phase current reconstruction is proposed based on the centralized modulation strategy. The phase current reconstruction blind zone introduced by non-ideal factors is analyzed. Then, to address the problem of unsuccessful current reconstruction in the blind zone, a dual permanent magnet motor pulse shift method is proposed to realize the phase current reconstruction of the two permanent magnet motors.

[0072] 1. Phase current reconfiguration principle of five-bridge inverter

[0073] Under different switching states of the five-bridge inverter, the current flow path is different, and the DC bus current will contain different phase current information of the two permanent magnet motors.

[0074] Let S x Let S be the switching function, where x represents the five phase arms of the five-arm inverter, x = A, B, C, D, E, where A, B, C, D, E represent the common arm, the arm connected to the b1 phase winding of motor 1, the arm connected to the c1 phase winding of motor 1, the arm connected to the b2 phase winding of motor 2, and the arm connected to the c2 phase winding of motor 2, respectively. When the upper switch of each phase arm of the five-arm inverter is turned on and the lower switch is turned off, let S... x =1; When the upper switch is off and the lower switch is on, let S = 1; x =0.

[0075] When the upper switch of each phase arm of the five-arm inverter is turned on and the lower switch is turned off, S is set to... x =1; When the upper switch is off and the lower switch is on, let S = 1; x =0.

[0076] The DC bus current and the switching function have a corresponding relationship as shown in equation (1), where the direction of current flowing into the winding is defined as positive and the direction of current flowing out of the winding is defined as negative.

[0077] i dc =S A i a +S B i b1 +S C i c1 +S D i b2 +S E i c2 (1)

[0078] In the formula, i dc Represents DC bus current; i b1 i c1 These represent the phase currents b1 and c1 of PMSM1, respectively; i b2 i c2 These represent the phase currents b2 and c2 of PMSM2, respectively; i a Represents the common phase current.

[0079] From equation (1), it can be seen that when the switch state is [0 0 0 0 0] and [1 1 1 1 1], i dc The total value is zero, at which point the DC bus does not contain the phase current information of the two permanent magnet motors. [0 0 0 0 0] represents the switching state when all five phase arm switching functions of the five-arm inverter are 0, and [1 1 1 1 1] represents the switching state when all five phase arm switching functions of the five-arm inverter are 1.

[0080] In the remaining 30 switching states, i dc Each control cycle contains different phase current information for the two permanent magnet motors. The five-bridge inverter driving dual permanent magnet motor system adopts a centralized modulation strategy, which includes four different switching states within each control cycle. Then, the DC bus current is sampled during the duration of each switching state, resulting in four independent equations for the DC bus current with respect to the phase currents of the two permanent magnet motors.

[0081] Then, the two-phase current of each permanent magnet motor can be obtained through the system of equations. Then, based on the fact that the sum of the three-phase currents of the permanent magnet motor stator windings is zero when they are connected in a star configuration, the three-phase current of each permanent magnet motor can be obtained, and finally the current reconfiguration is achieved.

[0082] 2. Effective Vector Sampling Method

[0083] Based on the phase current reconstruction principle of a five-bridge inverter dual permanent magnet motor system, this invention proposes an effective vector sampling method for reconstructing the phase current of the two permanent magnet motors. This method samples the DC bus current during the four adjacent switching states within a control cycle, and then reconstructs the phase current based on the different phase current information of the two permanent magnet motors contained in the DC bus current under different switching states.

[0084] The DC bus current flows into the windings from the arms with a switching function of 1 in the five-arm inverter and flows out of the windings from the arms with a switching function of 0. Therefore, the DC bus current under different switching states is the sum of the phase currents corresponding to the arms with a switching function of 1, and also the negative of the sum of the phase currents corresponding to the arms with a switching function of 0.

[0085] The phase currents corresponding to the five-phase bridge arms and the DC bus currents obtained from the four samplings have a corresponding relationship as shown in Equation (2).

[0086]

[0087] Where, λ n (n = 1, 2, 3, 4, 5) represent the duty cycles of the five phases arranged from largest to smallest; i λn (n = 1, 2, 3, 4, 5) represent the duty cycles of λ. n The phase current corresponding to the bridge arm; i sam1 i sam2 i sam3 i sam4 These are the DC bus currents sampled during the four switching states.

[0088] Then, the phase currents i corresponding to the five phase bridge arms can be reconstructed using equation (2). m_re (m = a, b1, c1, a2, b2). When the permanent magnet motor windings are connected in a star configuration, the sum of the three-phase currents is zero. Therefore, as long as the b-phase and c-phase currents of each permanent magnet motor are reconstructed using equation (2), the phase current reconstruction of the two permanent magnet motors can be achieved.

[0089] Taking the example that the voltage vectors of PMSM1 and PMSM2 are both located in sector II, the switching sequence of the five-arm inverter in one control cycle is as follows: Figure 3 As shown in the figure, the duty cycles of the five phases of the five-arm inverter during this control cycle are λ from largest to smallest. B , λ D , λ A , λ E , λ C That is, λ1 = λB λ2=λ D ,λ3=λ A λ4=λ E λ5=λ C Then, through the correspondence shown in equation (2), the reconfiguration currents of phases b and c of the two permanent magnet motors can be obtained as shown in equation (3):

[0090]

[0091] Based on the fact that the sum of the three-phase currents in the star connection of the permanent magnet motor windings is zero, the phase a current of each permanent magnet motor can be obtained, and then the three-phase current of each permanent magnet motor can be reconstructed.

[0092] 3. Analysis of the phase current reconfiguration blind zone of a dual permanent magnet motor system

[0093] When using the effective vector sampling method for current reconstruction, under ideal conditions, current reconstruction can be achieved because DC bus current sampling can be completed instantaneously and accurately. However, in practical applications, due to non-ideal factors, DC bus current sampling cannot be completed instantaneously; the sampling interval must be at least equal to the minimum sampling time T. min Only then can the DC bus current be accurately sampled to achieve current reconstruction. And T min Equation (4) needs to be satisfied.

[0094] T min ≥T set +T on +T AD +T d (4)

[0095] In the formula, T set T represents the time it takes for the current to reach steady state due to the parasitic parameters of the switching transistor and the inductance of the permanent magnet motor. on T is the turn-on time of the power switch transistor. AD T represents the delay time between the filter circuit and the AD sampling; d This refers to the dead zone time.

[0096] If the sampling interval of the DC bus current does not meet the sampling requirements, the DC bus current cannot be accurately sampled, which will lead to unsuccessful current reconstruction and a phase current reconstruction blind zone.

[0097] In a five-bridge inverter driving dual permanent magnet motor system, when the five-bridge inverter adopts a centralized modulation strategy for phase current reconstruction, there is a relationship between the DC bus current sampling interval and the duty cycle of each phase of the five-bridge inverter as shown in equation (5).

[0098]

[0099] In the formula, ΔT1, ΔT2, ΔT3 and ΔT4 are the sampling interval times, that is, the duration of action of four adjacent switch states in the first half of the control cycle.

[0100] Similarly Figure 3 Taking the switching sequence of the five-arm inverter shown as an example, the effective voltage vectors of PMSM1 and PMSM2 have an action time greater than 2T. min However, both the sampling intervals ΔT1 and ΔT4 are less than T. min This can lead to inaccurate sampling of the DC bus current, resulting in current reconstruction failure within the control cycle and creating a new phase current reconstruction dead zone. To analyze the process of new dead zone generation in detail, we take the example where the voltage vector of PMSM2 remains constant in sector II, while the voltage vector of PMSM1 changes arbitrarily within sector II. The correspondence between the four sampling intervals and the action time of the basic voltage vectors of the two permanent magnet motors is shown in Table 1.

[0101] Table 1. Correspondence between sampling interval time and basic voltage vector duration

[0102]

[0103] Since the voltage vectors of the two permanent magnet motors are not located in the sector boundary region or the low modulation region, the duration of the basic voltage vectors used to synthesize the reference voltage vectors of the two permanent magnet motors is greater than 2T. min Therefore, as shown in Table 1, the sampling intervals ΔT2 and ΔT3 are always greater than T. min Therefore, as shown in Table 1, the sampling intervals ΔT2 and ΔT3 are always greater than T. min As long as the time of the two effective voltage vectors of PMSM1 satisfies t 2a -2T min <t 1a <t 2a -2T min or t 2b -2T min <t 1b <t 2b -2T min When the sampling intervals ΔT1 and ΔT4 are less than T, min Therefore, current reconfiguration cannot be achieved. Consequently, in sector II of PMSM1, the following will occur: Figure 4 The new blind spot area is shown.

[0104] Similarly, we can analyze the new dead zone region generated when the voltage vector of PMSM2 remains constant in sector II, while the voltage vector of PMSM1 changes arbitrarily in other sectors. The new dead zone region generated throughout the entire voltage vector operating region of PMSM1 is as follows: Figure 5 As shown.

[0105] 4. Pulse shifting strategy

[0106] To address the issue of current reconstruction failure in the phase current reconstruction blind zone using the effective vector sampling method, this invention proposes a pulse shifting strategy. By shifting the drive signal of the five-arm inverter left and right within the phase current reconstruction blind zone, the sampling intervals of the four DC bus currents in each control cycle meet the sampling requirements, thereby accurately sampling the DC bus current and realizing phase current reconstruction of the two permanent magnet motors.

[0107] Assume the duty cycles of the five-phase drive signals of the five-bridge inverter are arranged in descending order as λ. n (n = 1, 2, 3, 4, 5). The basic principle of the pulse shift method is to keep the drive signal of the bridge arm with a duty cycle of λ3 unchanged in each control cycle within the current dead zone, if the sampling interval ΔT1 <T min or ΔT2 <T min Then the drive signals of the bridge arms with duty cycles of λ1 and λ2 will be shifted forward; if the sampling interval ΔT3 <T min or Δ T4 <T min Then the drive signals for the bridge arms with duty cycles of λ4 and λ5 will be shifted backward.

[0108] The time interval of each sampling after pulse shift is greater than or equal to T. min It can accurately sample the DC bus current, thereby enabling the phase current reconstruction of two permanent magnet motors.

[0109] The specific implementation scheme for pulse shifting is as follows:

[0110] (1) If ΔT1 <T min The drive signal for the bridge arm corresponding to λ1 is shifted forward by T. min -ΔT1;

[0111] (2) If ΔT2 <T min The drive signals for the bridge arms corresponding to λ1 and λ2 are shifted forward by T. min -ΔT2;

[0112] (3) If ΔT1 <T min and ΔT2 <T min The drive signal for the bridge arm corresponding to λ1 is shifted forward by 2T. min -ΔT1- ΔT2, shift the drive signal of the bridge arm corresponding to λ2 forward by T. min -ΔT2;

[0113] (4) If ΔT3 <T min The drive signals for the bridge arms corresponding to λ4 and λ5 are shifted backward by T. min -ΔT3;

[0114] (5) If ΔT4 <T min Shift the drive signal of the bridge arm corresponding to λ5 backward by T. min -ΔT4;

[0115] (6) If ΔT3 <T min and ΔT4 <T min The drive signal for the bridge arm corresponding to λ4 is shifted backward by T. min -ΔT3 shifts the drive signal of the bridge arm corresponding to λ5 backward by 2T. min -ΔT3-ΔT4.

[0116] by Figure 3 Taking the control cycle shown as an example, since ΔT1 and ΔT4 are less than T... min The DC bus current i cannot be accurately sampled within this control cycle. sam1 i sam4 This leads to an inability to accurately reconfigure the current. Then, according to the proposed pulse shift strategy, the drive signal of the B-arm with a duty cycle of λ1 is shifted forward by T. min -ΔT1 shifts the drive signal of the C-bridge arm with a duty cycle of λ5 backward by T. min -ΔT4, the shifted switch sequence is as follows Figure 6 As shown. The sampling interval after pulse shifting is no less than T. min Therefore, it can accurately complete four DC bus current samplings, thereby realizing the phase current reconstruction of the two permanent magnet motors.

[0117] When a pulse shift strategy is used for phase current reconstruction, the drive signals of the five-arm inverter in the current reconstruction dead zone no longer satisfy the symmetry relationship. Therefore, an additional voltage vector is introduced to synthesize the reference voltage vector. Assume that the reference voltage vectors of PMSM1 and PMSM2 are synthesized from eight basic effective vectors, as shown in Equation (6).

[0118]

[0119] In the formula, u iref (i = 1, 2) represents the reference voltage vectors of the two motors, where 1 and 2 represent PMSM1 and PMSM2, respectively; u i0 u i1 u i2 u i3 u i4 u i5 u i6 u i7 These represent the eight basic effective voltage vectors of the two motors; T i(000) T i(100) T i(110) T i(010) Ti(011) T i(001) T i(101) T i(111) The durations of action of the eight basic voltage vectors (000), (100), (110), (010), (011), (001), (101), and (111) are respectively.

[0120] Among them, u i2 =u i1 +u i3 (i = 1, 2), u i4 =u i3 +u i5 (i = 1, 2), u i6 =u i1 +u i5 (i = 1, 2), u i2 =u i1 +u i3 +u i5 (i = 1, 2), then substituting into equation (6) yields:

[0121]

[0122] Let T i(100) +T i(110) +T i(101) +T i(111) =T ia (i=1,2), T i(110) +T i(010) +T i(011) +T i(1110 =T ib (i=1,2), T i(011) +T i(101) +T i(001) +T i(111) =T ic (i=1,2), and substituting into equation (7), we get:

[0123] u iref =(T ia u i1 +T ib u i3 +T ic u i5 ) / T s (8)

[0124] From the above analysis, we can see that T ia / T s T ib / T s T ic / T s(i = 1, 2) represent the duty cycles of the PWM waves of each phase of the two motors under the centralized modulation strategy. Therefore, it can be seen from equation (8) that the synthesis of the reference voltage vector of each motor is only related to the duty cycle of the PWM waves of each phase. However, in the current reconstruction blind zone, the five-arm inverter uses a pulse shift strategy to shift the drive signal left and right, which will not change T. ia T ib T ic The values ​​of (i = 1, 2) are such that pulse shift will not affect the magnitude and phase of the voltage vectors output by the two motors.

[0125] The overall control structure diagram of the system is as follows: Figure 7 As shown in Table 2. To verify the feasibility and effectiveness of the phase current reconstruction algorithm for the five-bridge inverter with dual permanent magnet motors proposed in this invention, experiments were conducted on two permanent magnet synchronous motors with identical parameters. The parameters of the permanent magnet motors are shown in Table 2.

[0126] Table 2 Permanent Magnet Motor Parameters

[0127]

[0128]

[0129] The switching frequency used in the experiment was 5kHz. The experimental system adopted the TMS320F28379D dual-core DSP processor manufactured by TI. This processor's CPU core can accept a maximum clock frequency of 200MHz, exhibiting superior computing performance. The experimental program was written and debugged in C language using CCS10.0 (Code Composer Studio). The experimental program mainly consists of two parts: the main program and the interrupt routine. The execution flow of the main program is as follows: Figure 8 As shown in (a), first, the peripherals and registers required for control are initialized. Then, interrupts are disabled and external interrupts are initialized. Next, the sub-modules used are initialized. Finally, A / D conversion is started, and the main interrupt is enabled. The execution flow of the main interrupt routine and the EPWM sub-interrupt routine is as follows: Figure 8 (b) and Figure 8 As shown in (c). In this experiment, six 12A current sensors were used to measure the actual phase current information of two permanent magnet motors, which was then compared with the reconstructed phase current. The experimental results were all obtained under closed-loop control using the reconstructed current.

[0130] first, Figure 9 The experimental results of two permanent magnet motors running at 50 r / min under a 2 Nm load are presented. From top to bottom, the actual three-phase current, reconstructed three-phase current, actual current and reconstructed current of phase a, and reconstructed error of phase a current are presented for the two permanent magnet motors. Figure 9 (b) are respectively Figure 9(a) is a magnified view of a portion of the image. As shown in the figure, the reconstructed current and actual current of each phase of the two permanent magnet motors remain consistent. Therefore, the pulse shift strategy can achieve current reconstruction in the low-modulation region. The maximum current reconstruction error of PMSM1 is 0.38A, with an average error of 0.19A. The maximum current reconstruction error of PMSM2 is 0.36A, with an average error of 0.18A. The reconstructed current is used for the closed-loop control of the permanent magnet motors, allowing them to operate stably. The experimental results verify the feasibility and effectiveness of the proposed pulse shift strategy when both permanent magnet motors are operating in the low-modulation region.

[0131] Then, when PMSM1 operates at a constant speed of 400 r / min under a 5 Nm load and PMSM2 operates at a constant speed of 300 r / min under a 6 Nm load, the actual three-phase current, reconstructed three-phase current, actual current and reconstructed current of phase a, and the reconstructed error of phase a current of the two permanent magnet motors are as follows: Figure 10 As shown. Figure 10 (b) is Figure 10 (a) is a magnified view of a portion of the image. As can be seen from the figure, the pulse shifting strategy effectively solves the problem of the effective vector sampling method failing to reconstruct the phase currents of the two permanent magnet motors within the sector boundary region. The maximum current reconstruction error of PMSM1 is 0.41A, with an average error of 0.2A, while the maximum current reconstruction error of PMSM2 is 0.42A, with an average error of 0.21A. The current reconstruction errors are relatively small. Using the reconstructed current to control the permanent magnet motors does not affect the steady-state performance of the two permanent magnet motors.

[0132] Furthermore, the experimental results when PMSM1 was running at a constant speed of 700 r / min under a load of 5 Nm and PMSM2 was running at a constant speed of 50 r / min under a load of 2 Nm are as follows: Figure 11 As shown in the figure, from top to bottom, the actual three-phase current, reconstructed three-phase current, actual current and reconstructed current of phase a, and the reconstructed error of phase a current are displayed for the two permanent magnet motors. Figure 11 (b) is Figure 11 (a) is a magnified view of a portion of the image. As shown in the figure, the pulse shifting strategy can achieve current reconfiguration when one permanent magnet motor is running at high speed and the other at low speed, and both permanent magnet motors exhibit good steady-state performance. The maximum reconfiguration error of PMSM1 is 0.42A, with an average error of 0.21A, while the maximum reconfiguration error of PMSM2 is 0.36A, with an average error of 0.18A.

[0133] The above two sets of experimental results verify the feasibility and effectiveness of the proposed pulse shifting strategy when the two permanent magnet motors are operating in the sector boundary region and the new blind zone region.

[0134] To verify the dynamic performance of the proposed pulse shifting strategy, acceleration and deceleration experiments of the permanent magnet motor were first conducted. The specific operating conditions were as follows: the reference speed of PMSM1 was a triangular wave from 100 r / min to 500 r / min, and a 5 Nm load was applied; PMSM2 operated at a constant speed of 300 r / min under a 6 Nm load. Figure 12 The actual three-phase current, reconstructed three-phase current, actual current and reconstructed current of phase a, and the reconstructed error of phase a current are given for two permanent magnet motors. Figure 12 (b) is Figure 12 A magnified view of a portion of (a). (From) Figure 12 (a) shows that the pulse shift strategy can reconstruct the phase currents of the two permanent magnet motors during acceleration and deceleration. The maximum reconstruction error and average error of PMSM1 are 0.45A and 0.23A, respectively, while the maximum reconstruction error of PMSM2 is 0.43A and the average error is 0.22A. From Figure 12 (b) It can be seen that during the speed change of PMSM1, the reconfiguration current of each phase of the two permanent magnet motors can still be consistent with the actual current, and the permanent magnet motors are operating stably.

[0135] Then, load increase and decrease experiments were conducted on the permanent magnet motors. Specifically, PMSM1 was started with a 2 Nm load at 300 r / min, the load increased to 5 Nm after 3 seconds, and then to 2 Nm after 7 seconds; PMSM2 was started with a 6 Nm load at a constant speed of 300 r / min. The experimental results are as follows: Figure 13 As shown, from top to bottom, the actual three-phase current, reconstructed three-phase current, actual current and reconstructed current of phase a, and reconstructed error of phase a current are displayed for the two permanent magnet motors. Figure 13 (b) is Figure 13 A magnified view of a portion of (a). (From) Figure 13 (a) shows that the pulse shifting strategy can achieve current reconfiguration of the two permanent magnet motors during load increase and decrease. The maximum reconfiguration error of PMSM1 is 0.43A, and the average error is 0.21A. The maximum reconfiguration error of PMSM2 is 0.44A, and the average error is 0.22A. From Figure 13 (b) It can be seen that when the load of PMSM1 changes abruptly, the reconfiguration current of each phase of the two permanent magnet motors can still follow the actual current, and the two permanent magnet motors operate stably. From the above two sets of experimental results, it can be seen that using the proposed pulse shift strategy for phase current reconfiguration can achieve independent control of the two permanent magnet motors, and the permanent magnet motors have good dynamic control performance.

[0136] In summary, the method of this invention can reduce system size and avoid the impact of parameter differences between different current sensors. Furthermore, it can serve as a backup solution to increase system reliability when the current sensor detecting phase current fails. This invention first employs a centralized modulation strategy for a five-arm inverter to improve the speed range of the two permanent magnet motors. Secondly, based on the centralized strategy, an effective vector sampling method is proposed for phase current reconstruction of the two permanent magnet motors. However, due to some non-ideal factors, a phase current reconstruction blind zone exists. Within the phase current reconstruction blind zone, the inability to accurately sample the DC bus current within the sampling interval leads to current reconstruction failure. Then, a pulse shift strategy is proposed. This strategy achieves current reconstruction by shifting the inverter's drive signal left and right within the blind zone to ensure accurate sampling of the DC bus current in each sampling interval.

[0137] This invention proposes a pulse-shifting processing method based on a centralized modulation strategy, successfully achieving phase current reconstruction of two motors within the current reconstruction dead zone. The reconstructed phase current remains consistent with the actual measured phase current. The current reconstruction error is related to the operating region of the voltage vectors of the two motors and the applied load. When the voltage vectors of the two motors are in the low modulation region and the load is light, the reconstruction error accounts for a relatively large percentage of the actual current, but the reconstructed current can be used for closed-loop control of the two motors, and the two motors exhibit good control performance. Experimental results verify the effectiveness and feasibility of the proposed pulse-shifting strategy.

[0138] Although the present invention has been described above in conjunction with the figures, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many modifications under the guidance of the present invention without departing from the spirit of the present invention, and these modifications are all within the protection scope of the present invention.

Claims

1. A method for reconstructing the phase current of a dual permanent magnet motor in a five-bridge inverter, characterized in that: For the dual permanent magnet motors in the five-bridge inverter, the effective vector sampling method is used to reconstruct the phase current based on the correspondence between the DC bus current and the phase current of the two permanent magnet motors in different switching states. Furthermore, under the phase current reconstruction blind zone introduced by non-ideal factors, the dual permanent magnet motor pulse shift method is used to correct the phase current reconstruction. The effective vector sampling method involves placing a current sensor on the DC bus of each of the five arms in the five-arm inverter dual permanent magnet motor. The five PWM signals of the five-arm inverter in each control cycle include four different switching states. During the duration of each switching state, the DC bus current is sampled by the current sensor to obtain four DC bus currents. Then, based on the relationship between each DC bus current and the phase currents of the two permanent magnet motors, two phase currents of each permanent magnet motor are obtained. Finally, based on the fact that the sum of the three-phase currents of the permanent magnet motor stator windings is zero (using a star connection), the remaining third phase current of each permanent magnet motor is obtained, thus achieving current reconfiguration of the two permanent magnet motors. The five-arm inverter driving the dual permanent magnet motor system adopts a centralized modulation strategy, and each control cycle includes four different switching states.

2. The method for reconstructing phase current of a dual permanent magnet motor in a five-bridge inverter according to claim 1, characterized in that: The aforementioned dual permanent magnet motor pulse shifting method involves shifting the drive signals of each arm of the five-arm inverter left and right within the phase current reconstruction blind zone. This ensures that the sampling interval of the DC bus current corresponding to the four switching states in each control cycle meets the sampling requirements, thereby accurately sampling the DC bus current and realizing the phase current reconstruction of the two permanent magnet motors.

3. The method for reconstructing phase current of a dual permanent magnet motor in a five-bridge inverter according to claim 1, characterized in that: The method first determines the phase current reconstruction dead zone: When a phase current reconfiguration dead zone occurs, the driving signals of each bridge arm are first shifted and corrected using the dual permanent magnet motor pulse shifting method, and then the effective vector sampling method is used for phase current reconfiguration. When there is no phase current reconfiguration blind zone, the effective vector sampling method is directly used for phase current reconfiguration.

4. The method for reconstructing phase current of a dual permanent magnet motor in a five-bridge inverter according to claim 3, characterized in that: The method for determining whether a phase current reconfiguration dead zone has occurred is based on the following formula: In the formula, T min T represents the minimum time required to complete DC bus current sampling. set T represents the time it takes for the current to reach steady state due to the parasitic parameters of the switching transistor and the inductance of the permanent magnet motor. on T is the turn-on time of the power switch transistor. AD T represents the delay time between the filter circuit and the AD sampling; d Dead time; When the above formula is satisfied, the DC bus current sampling interval meets the sampling requirements and no current reconstruction blind zone occurs; If the above formula is not met, the DC bus current sampling interval will not meet the sampling requirements, resulting in a current reconstruction blind zone.

5. The method for reconstructing phase current of a dual permanent magnet motor in a five-bridge inverter according to claim 4, characterized in that: The specific method of pulse shifting using dual permanent magnet motors is as follows: First, the sampling interval is obtained by processing the relationship between the sampling interval of the DC bus current and the duty cycle of each phase of the five-arm inverter according to the following formula: In the formula, ΔT1, ΔT2, ΔT3 and ΔT4 are the action times of the first, second, third and fourth switching states, respectively, which are the sampling interval times of the DC bus current in the first, second, third and fourth switching states, respectively. λ n This is the duty cycle of the nth bridge arm, where n represents the arm's index (n = 1, 2, 3, 4, 5), and λ1 to λ5 are the duty cycles of the five bridge arms arranged from largest to smallest. s Indicates the discrete control period; Then, the drive signals for the five bridge arms are pulse-shifted in sequence as follows: If ΔT1 <T min The drive signal of the bridge arm corresponding to the maximum duty cycle λ1 is shifted forward by T. min -ΔT1; If ΔT2 <T min The drive signals of the bridge arms corresponding to the largest duty cycle λ1 and the second largest duty cycle λ2 are shifted forward by T. min -ΔT2; If ΔT1 <T min and ΔT2 <T min The drive signal of the bridge arm corresponding to the maximum duty cycle λ1 is shifted forward by 2T. min -ΔT1- ΔT2, shifts the drive signal of the bridge arm corresponding to the second largest duty cycle λ2 forward by T. min -ΔT2; If ΔT3 <T min The drive signals for the bridge arms corresponding to the second smallest duty cycle λ4 and the smallest duty cycle λ5 are shifted backward by T. min -ΔT3; If ΔT4 <T min The drive signal of the bridge arm corresponding to the minimum duty cycle λ5 is shifted backward by T. min -ΔT4; If ΔT3 <T min and ΔT4 <T min The drive signal of the bridge arm corresponding to the second smallest duty cycle λ4 is shifted backward by T. min -ΔT3, and shift the drive signal of the bridge arm corresponding to the minimum duty cycle λ5 backward by 2T. min -ΔT3-ΔT4.

6. A method for reconstructing phase current of a dual permanent magnet motor in a five-bridge inverter according to claim 1 or 3, characterized in that: The effective vector sampling method is specifically as follows: The relationship between the five bridge arm phase currents and the DC bus currents obtained from four samplings under four different switching states is expressed by the following formula. The input processing yields the phase currents of the five bridge arms: Where, λ n It is the duty cycle of the nth bridge arm, where n represents the number of the bridge arm, n=1, 2, 3, 4, 5, and λ1~λ5 are the duty cycles of the five bridge arms arranged from largest to smallest. It is a duty cycle of λ n The phase current corresponding to the bridge arm; i sam1 i sam2 i sam3 i sam4 These are the DC bus currents sampled during the action time of the four switching states; Among them, i sam1 It is the DC bus current sampled during the first switching state's operating time, i sam2 It is the DC bus current sampled during the second switching state's operating time, i sam3 It is the DC bus current sampled during the third switch state's operating time, i sam4 It is the DC bus current sampled during the fourth switch state's operating time.

7. The method for reconstructing phase current of a dual permanent magnet motor in a five-bridge inverter according to claim 1, characterized in that: The five-arm inverter dual permanent magnet motor includes two permanent magnet motors and an inverter consisting of five arms. The midpoints of three arms are connected to the three-phase lines of one of the permanent magnet motors, and the midpoints of three arms are connected to the three-phase lines of the other permanent magnet motor. There is one and only one shared arm among the three arms connected to the two permanent magnet motors as a common arm.

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