A direct voltage prediction control method of a permanent magnet synchronous motor driving system

Abstract

The application discloses a direct voltage prediction control method of a permanent magnet synchronous motor driving system, which is used for a motor side converter and a grid side converter in parallel connection, the control method selects a voltage vector by evaluating a newly defined cost function, the selected voltage vector can generate a DC bus voltage closer to its set point at k+2 moment, and can reduce active power of subsequent voltage error, thereby realizing adjustment on the DC link voltage and power flow; and for a steady state error of the driving system, a Kalman filter is added, disturbance caused by parameter mismatch is estimated through the Kalman filter, and is used for correcting a power expression, so as to compensate the steady state power error.

Description

Technical Field

[0001] This invention relates to power electronics technology, and more specifically to a direct voltage prediction control method for a permanent magnet synchronous motor drive system. Background Technology

[0002] Back-to-back (BTB) converters are commonly used in medium- and high-power motor drive systems. In existing technologies, PI-MPC is one of the common solutions for controlling the PMSG system fed by the BTB converter. It uses an additional PI controller to generate an active power reference for the internal power controller to track. However, this control method requires an external PI controller to form a PI control loop to generate a power setpoint (i.e., power reference) for the internal MPC controller. However, there is a common integral saturation problem in the PI control loop, and the dynamic response of the system is slow.

[0003] In view of this, this application has conducted in-depth research on this basis, resulting in this case. Summary of the Invention

[0004] The purpose of this invention is to provide a direct voltage prediction control method for a permanent magnet synchronous motor drive system, which eliminates the need for an external PI control loop, avoids performance degradation caused by integral saturation problems common in PI control loops, and improves dynamic response.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A direct voltage prediction control method for a permanent magnet synchronous motor drive system, the permanent magnet synchronous motor drive system including a motor-side converter and a grid-side converter connected in parallel, the control method comprising the following steps:

[0007] S1. The cost function is established as follows:

[0008] In the formula, For the cost function on the motor side, , and These are the active component, the bus voltage component, and the reactive component of the cost function, respectively. Indicates the reactive power reference on the grid side;

[0009] It is the DC link voltage setpoint; It is the DC bus voltage at time k+2, based on time The expression is predicted, that is, through... Shifting forward one step in the discrete model at time 1 get; Adjustment coefficient, Represent the set of positive real numbers; It is a weighting factor used to adjust reactive power; Constraints representing active power. Constraints representing reactive power;

[0010] The active power generated by the permanent magnet synchronous motor. = , For torque reference, Angular velocity of a permanent magnet synchronous motor The position is calculated in the position estimator using feedback encoder signals from the motor shaft of the permanent magnet synchronous motor. The active power value at time k+2 is represented by shifting the instantaneous power formula forward by one step. The expression obtained predicts the result; This represents the estimated grid-side reactive power at time k+2;

[0011] S2. Select the voltage vector from the cost function, as follows:

[0012] Adjusting a term in the cost function to approach zero to track a reference variable, assuming... =0 and =0, if voltage vector middle Then in > The voltage vector will be Selected in;

[0013] If the voltage vector middle Then in the voltage vector Select to generate less than of The voltage vector;

[0014] exist Reaching steady state hour, , choose to The voltage vector.

[0015] The method for compensating steady-state error based on disturbances in the corrected power expression is as follows:

[0016] S1-1. The mathematical model of the Kalman filter is established as follows:

[0017] (1),

[0018] (2),

[0019] In the formula, This indicates active power disturbance. This indicates reactive power disturbance. This represents the active power disturbance at time k-1. This represents the reactive power disturbance at time k-1. The active power at time k. The reactive power at time k is shown. This represents the active power at time k-1. This represents the reactive power at time k-1. and These are the state vectors at time k and time k-1, respectively. It is the sampling period; It is a state matrix. , , , , , , These are manually defined matrix symbols; among them, , , = , , , ; , Both are commonly used mathematical matrices; Represents the resistance in the grid-side converter. The nominal value, Indicating the inductance in the grid-side converter The nominal value, It is the sampling frequency. It is the grid-side electrical angular velocity; Covariance matrix Process noise: ,in It is a mathematical symbol representing a random variable. Following the principle that the mean is 0 and the covariance matrix is The normal distribution;

[0020] S1-2: Based on the mathematical model in step 1-1, the prior estimate of the state vector is as follows:

[0021] (3),

[0022] In the formula, State vector Prior estimates, Indicates interval [ The state vector calculated within the [inner] domain The posterior estimate;

[0023] S1-3: Define the accuracy covariance of the prior estimate as follows: (4), where E represents the expected value and T represents the matrix transpose, both of which are mathematical symbols;

[0024] The precision covariance is calculated in the following way. In the formula, ; Indicates the interval [ The accuracy covariance of the posterior estimate of the state vector obtained in [ ];

[0025] S1-4: Kalman Gain Posterior estimation of the state vector The calculation formulas are as follows:

[0026] ,

[0027] ,

[0028] The corrected power prediction expression is as follows ,in Updated for use in the next sampling period; It is the identity matrix, which is a square matrix where all elements on the diagonal from the top left to the top right are 1, and all other elements are 0.

[0029] In step S2, Reaching steady state At that time, Add to middle.

[0030] In step S1, the instantaneous power is: In the formula, It is the sampling frequency. It is the grid-side electrical angular velocity. Indicates inductance. and These are respectively represented as grid-side voltage, grid-side current, inductor reactance, and inductor resistance, where, This represents the α component of the grid-side voltage at time k+1. This represents the β component of the grid-side voltage at time k+1. This represents the α component of the grid-side voltage at time k+1. This represents the β component of the grid-side voltage at time k+1.

[0031] With the above structure, the present invention has the following beneficial effects: by evaluating the newly defined cost function, the present invention enables the selected voltage vector to not only generate a DC bus voltage closer to its set point at the instant of k+2, but also to generate active power that reduces subsequent voltage errors, thereby achieving regulation of DC link voltage and power flow within a cost function.

[0032] Furthermore, this invention uses a Kalman filter to estimate the disturbances caused by parameter mismatch and uses it to correct the power expression, thereby eliminating steady-state deviations even under variable parameters and improving system robustness. Attached Figure Description

[0033] Figure 1 It is a back-to-back permanent magnet synchronous motor drive system.

[0034] Figure 2 This is a control principle diagram of a traditional PI-MPC.

[0035] Figure 3 This is a schematic diagram of the control principle of the dynamic predictive control method of the present invention.

[0036] Figure 4 This is a schematic diagram of experimental waveforms related to DC bus voltage and reactive power regulation in the dynamic predictive control method of this invention. Detailed Implementation

[0037] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0038] This invention provides a direct voltage prediction control method for a permanent magnet synchronous motor drive system, such as... Figure 1 As shown, the permanent magnet synchronous motor adopts a conventional back-to-back permanent magnet synchronous motor. Correspondingly, the permanent magnet synchronous motor drive system adopts a conventional back-to-back permanent magnet synchronous motor drive system. The drive system includes a permanent magnet synchronous motor (PMSG), a motor-side converter (MSC), and a grid-side converter (GSC). The motor-side converter and the grid-side converter are connected to the grid in a conventional manner, and the permanent magnet synchronous motor (PMSG) is connected to the motor-side converter (MSC) in a conventional manner.

[0039] like Figure 1-4 As shown, the direct voltage prediction control method provided in this embodiment is based on the above-mentioned drive system, and the control method includes the following steps:

[0040] S1. The cost function is established as follows:

[0041] In the formula, Let be the cost function on the motor side, and be the optimal voltage vector; It is the active component of the cost function. It is the bus voltage component of the cost function. It is the reactive component of the cost function; where, the above-mentioned , and The expression is as follows: , = , .

[0042] The above This is the DC link voltage setpoint, a value that is manually set. This represents the reference reactive power on the grid side, which is a manually set value. Adjustment coefficient, Represent the set of positive real numbers; It is a weighting factor used to adjust reactive power; Constraints representing active power. This represents a constraint on reactive power.

[0043] It is the DC bus voltage at time k+2, based on time The expression is predicted, that is, through... Shifting forward one step in the discrete model at time 1 It is found that the discrete model uses existing conventional first-order Euler discretization, which is a conventional technique, and the above-mentioned It is the input quantity measured by a voltage sensor.

[0044] This represents the active power generated by the permanent magnet synchronous motor, where... = , For torque reference, torque reference It is set manually by external parties; Angular velocity of a permanent magnet synchronous motor The position is calculated in the position estimator using feedback encoder signals from the motor shaft of the permanent magnet synchronous motor; where the angular velocity is... The calculation is a conventional calculation, so it will not be described in detail.

[0045] The active power value at time k+2 is represented by shifting the instantaneous power formula forward by one step. The expression obtained predicts the result; This represents the estimated grid-side reactive power at time k+2.

[0046] The instantaneous power formula mentioned above is:

[0047] ,

[0048] In the formula, It is the sampling frequency. It is the grid-side electrical angular velocity. Indicates inductance. and These are respectively represented as grid-side voltage, grid-side current, inductor reactance, and inductor resistance, where, This represents the α component of the grid-side voltage at time k+1. This represents the β component of the grid-side voltage at time k+1. This represents the α component of the grid-side voltage at time k+1. This represents the β component of the grid-side voltage at time k+1.

[0049] S2. Select the voltage vector from the cost function, as follows:

[0050] The terms in the cost function are adjusted to approach zero to track the reference variable; therefore, it can be assumed that... =0 and =0, if voltage vector middle Then in > The voltage vector will be Selected in;

[0051] If the voltage vector middle Then in the voltage vector Select to generate less than of The voltage vector;

[0052] exist Reaching steady state hour, , choose to The voltage vector.

[0053] As a preferred approach, the power expression is corrected to compensate for the steady-state error based on the disturbance in the corrected power expression. The specific method is as follows:

[0054] S1-1. The mathematical model of the Kalman filter is established as follows:

[0055] (1),

[0056] (2),

[0057] In the formula, This indicates active power disturbance. This indicates reactive power disturbance. This represents the active power disturbance at time k-1. This represents the reactive power disturbance at time k-1. The active power at time k. The reactive power at time k is shown. This represents the active power at time k-1. This represents the reactive power at time k-1. and These are the state vectors at time k and time k-1, respectively. It is the sampling period.

[0058] The above It is a state matrix. , , , , , , These are manually defined matrix symbols without any specific meaning; they are used here. , , = , , , ,in, , Both are commonly used mathematical matrices; here Indicates the resistance in the grid-side converter The nominal value, Indicating the inductance in the grid-side converter The nominal value, It is the sampling frequency. It is the electric angular velocity on the grid side.

[0059] It should be noted that in the above expression (1), The meaning is , The meaning is Similarly, expressions (1) and (2) express meaning in this way.

[0060] To elaborate further, Indicating the inductance in the grid-side converter The nominal value; Covariance matrix Process noise: ,in, It is a mathematical symbol representing a random variable. Following the principle that the mean is 0 and the covariance matrix is It follows a normal distribution.

[0061] S1-2. Based on the mathematical model in step S3-1, the prior estimate of the state vector is as follows:

[0062] (3),

[0063] In the formula, State vector Prior estimates, Indicates interval [ The state vector calculated within the [inner] domain The posterior estimate;

[0064] S1-3. Define the accuracy covariance of the prior estimate as follows: (4) In the formula, E represents the expected value and T represents the matrix transpose, both of which are mathematical symbols.

[0065] The precision covariance is calculated in the following way. In the formula, It is a matrix The transpose operation; Indicates the interval [ The accuracy covariance of the posterior estimate of the state vector obtained in ].

[0066] S1-4, Kalman gain Posterior estimation of the state vector The calculation formulas are as follows:

[0067] ,

[0068] ,

[0069] The corrected power prediction expression is as follows ,in Updated for use in the next sampling period; It is the identity matrix, which is a square matrix where all elements on the diagonal from the top left to the top right are 1, and all other elements are 0.

[0070] It should be noted that, as Figure 2-3 As shown, the setting and / or acquisition of other parameters in this invention, except for the aforementioned improvements, are all existing technologies, i.e., they can be obtained using existing PI-MPC control methods for permanent magnet synchronous motor drive systems, such as in step S4 above. and To obtain, It is the motor rotor angle, obtained by a position sensor; It is the motor rotor speed, obtained from a speed sensor; This is the DC bus voltage value at time k, obtained by sampling from a voltage sensor. Furthermore, This represents the estimated motor-side switching state at time k. This represents the estimated motor-side switching state at time k. In this embodiment, the voltage vector corresponding to the cost function is obtained according to step S2 to output the optimal solution for the motor-side switching state and the grid-side switching state.

[0071] Furthermore, in step S2, taking the PMSG power generation method as an example, the adjustment process is explained as follows, where the negative PMSG active power is... The negative active power of the PMSG grid side is .

[0072] In the cost function described above, This helps in selecting the voltage vector, and the selected voltage vector will... The DC bus voltage is generated instantaneously, which is closer to its set point, so the following situation exists.

[0073] 1. If the voltage vector middle Then in The voltage vector where the active power generated at any given moment is greater than the PMSG generation power will be Selected in, that is, in > The voltage vector will be The fact that the PMSG was selected means that not all the power generated by the PMSG is transmitted to the grid, but is used to charge the DC link capacitor and increase the DC link voltage.

[0074] 2. If the voltage vector middle Then in the voltage vector The middle tendency to choose will produce less than of The voltage vector is such that, in this case, not only is all the power generated by the PMSG sent to the grid, but the DC link capacitor will also be discharged to contribute its power to the grid, thereby reducing the DC link voltage.

[0075] 3. In Reaching steady state At this time, all the power generated by the PMSG is fed into the grid, and ideally the DC link capacitors will not charge or discharge. , choose to The voltage vector.

[0076] in, At that time, because the motor-side converter will actually generate PMSG power Power is also consumed when transmitting power to the grid (conduction losses, switching losses, etc.), which means that the actual power that the motor-side converter can transmit to the grid side is less than... If you choose to use it under these circumstances = The voltage vector not only means that all the power from the PMSG is fed to the grid, but also that the DC link capacitors are discharged to contribute their power to the grid. This causes the regulated DC bus voltage to be lower than its set value. Therefore, in order to eliminate steady-state voltage error, Add to For example, if the required reference power is 1000W, then the actual reference power input to the system is 1000W+. .

[0077] The above description is only a preferred embodiment of this invention. Any equivalent changes and modifications made within the scope of the claims of this invention shall fall within the scope of the claims of this invention.

Claims

1. A direct voltage prediction control method for a permanent magnet synchronous motor drive system, the permanent magnet synchronous motor drive system comprising a motor-side converter and a grid-side converter connected in parallel, characterized in that, The control method includes the following steps: S1. The cost function is established as follows: In the formula , and These are the active component, the bus voltage component, and the reactive component of the cost function, respectively. Indicates the reactive power reference on the grid side; It is the DC link voltage setpoint; It is the DC bus voltage at time k+2, based on time The expression is predicted, that is, through... Shifting forward one step in the discrete model at time 1 get; Adjustment coefficient, Represent the set of positive real numbers; It is a weighting factor used to adjust reactive power; Constraints representing active power. Constraints representing reactive power; The active power generated by the permanent magnet synchronous motor. = , For torque reference, Angular velocity of a permanent magnet synchronous motor The position is calculated in the position estimator using feedback encoder signals from the motor shaft of the permanent magnet synchronous motor. The active power value at time k+2 is represented by shifting the instantaneous power formula forward by one step. The expression obtained predicts the result; This represents the estimated grid-side reactive power at time k+2; S2. Select the voltage vector from the cost function, as follows: Adjusting a term in the cost function to approach zero to track a reference variable, assuming... =0 and =0, if voltage vector middle Then in > The voltage vector will be Selected in; If the voltage vector middle Then in the voltage vector Select to generate less than of The voltage vector; exist Reaching steady state hour, , choose to Voltage vector; In step S1, the instantaneous power is: In the formula, It is the sampling frequency. It is the grid-side electrical angular velocity. Indicates inductance. and These are respectively represented as grid-side voltage, grid-side current, inductor reactance, and inductor resistance, where, This represents the α component of the grid-side voltage at time k+1. This represents the β component of the grid-side voltage at time k+1. This represents the α component of the grid-side voltage at time k+1. This represents the β component of the grid-side voltage at time k+1.

2. The direct voltage prediction control method for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: The method for compensating steady-state error based on disturbances in the corrected power expression is as follows: S1-1. The mathematical model of the Kalman filter is established as follows: （1）， （2）， In the formula, This indicates active power disturbance. This indicates reactive power disturbance. This represents the active power disturbance at time k-1. This represents the reactive power disturbance at time k-1. The active power at time k. The reactive power at time k is shown. This represents the active power at time k-1. This represents the reactive power at time k-1. and These are the state vectors at time k and time k-1, respectively. It is the sampling period; It is a state matrix. , , , , , , These are manually defined matrix symbols; among them, , , = , , , ; , Both are commonly used mathematical matrices; Represents the resistance in the grid-side converter. The nominal value, Indicating the inductance in the grid-side converter The nominal value, It is the sampling frequency. It is the grid-side electrical angular velocity; Covariance matrix Process noise: ,in It is a mathematical symbol representing a random variable. Following the principle that the mean is 0 and the covariance matrix is The normal distribution; S1-2: Based on the mathematical model in step 1-1, the prior estimate of the state vector is as follows: （3）， In the formula, State vector Prior estimates, Indicates interval [ The state vector calculated within the [inner] domain The posterior estimate; S1-3: Define the accuracy covariance of the prior estimate as follows: (4), where E represents the expected value and T represents the matrix transpose, both of which are mathematical symbols; The precision covariance is calculated in the following way. In the formula, ; Indicates the interval [ The accuracy covariance of the posterior estimate of the state vector obtained in [ ]; S1-4: Kalman Gain Posterior estimation of the state vector The calculation formulas are as follows: ， ， The corrected power prediction expression is as follows ,in Updated for use in the next sampling period; It is an identity matrix, which is a square matrix where all elements on the diagonal from the top left to the top right are 1, and all other elements are 0.

3. The direct voltage prediction control method for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: In step S2, Reaching steady state At that time, Add to middle.

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