Dynamic prediction control method of permanent magnet synchronous motor driving system

Abstract

The invention discloses a dynamic predictive control method for a permanent magnet synchronous motor driving system, which is used for a motor side converter and a grid side converter which are connected in a grid-connected manner, and comprises the following steps of: acquiring an actual direct current bus voltage reference # imgabs0 #, generating a grid side active power reference # imgabs1 # of the grid side converter through a dynamic reference module, and performing dynamic predictive control on the grid side active power reference # imgabs1 # of the grid side converter. The optimal voltage vector # imgabs2 is then obtained by evaluating a predefined cost function. The dynamic parameter module is adopted in the grid-side converter to generate the active power reference, an additional PI controller is not needed, and the cost function comprises power constraint, so that the actual direct current bus voltage reference is kept in a safe range, overlarge charging or discharging current is avoided, and the reliability of the system is improved. And performance reduction caused by a common integral saturation problem in a PI control loop is also avoided.

Description

Technical Field

[0001] The invention relates to power electronics technology, and more specifically to a dynamic prediction control method for a permanent magnet synchronous motor drive system. Background Art

[0002] In the prior art, PI-MPC is one of the commonly used solutions for controlling a back-to-back (BTB) converter-fed PMSG system. 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 additional independent PI controller to form a PI control loop to provide a power set point for the internal MPC controller. However, there is a common integral saturation problem in the PI control loop, which easily leads to a degradation in the performance of the back-to-back converter.

[0003] In view of this, the applicant conducted in-depth research on this basis, which led to this case. Summary of the invention

[0004] The object of the present invention is to provide a dynamic predictive control method for a permanent magnet synchronous motor drive system, which is capable of limiting the maximum power level without the need for an additional PI control loop and avoiding performance degradation due to the integral saturation problem common in the PI control loop.

[0005] To achieve the above object, the solution of the present invention is: A dynamic predictive 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 to the grid, the control method comprising the following steps: S1. Get the actual DC bus voltage reference at each moment , the actual DC bus voltage reference The expression is: (1), In the formula, represents the DC bus voltage reference, Reach The number of steps, Indicates the actual value of the DC bus voltage at time k, obtained by sampling the voltage sensor; S2, to achieve the actual DC bus voltage reference at the next moment , a dynamic reference module is used to generate the grid-side active power reference of the grid-side converter , the grid-side active power reference The expression is: (2) , In the formula, represents the d-axis component of the grid-side voltage in the grid-side converter, represents the resistance value in the grid-side converter, Indicates the power consumed by the grid-side resistor in the grid-side converter; is the torque reference; is the actual speed, obtained by sampling the speed sensor; is the bus capacitance parameter, Ts is the sampling period; Represents motor and DC link capacitors Total power; Solve to obtain the grid-side active power reference The expression is: (3); S3. Select the optimal voltage vector by evaluating a predefined cost function , the cost function is: , In the formula, is the active power at time k+2, is the reactive power weight coefficient, is the reactive power reference, is the reactive power at time k+2, is the bus voltage weight coefficient, is the bus voltage at time k+2; and denote the constraints of active power and reactive power respectively; The calculation formula is: , where is the sampling period, is the bus capacitance value, is the motor side switch signal at time k+1, is the grid-side switch signal at time k+1; is the motor side current at time k+1, is the grid-side current at time k+1; S4, obtained through step S3 and , represents the motor side cost function and Represents the improved grid-side cost function, and then outputs the estimated motor-side switch state at time k+1 to the machine-side converter and the estimated grid-side switch state at time k+1 to the grid-side converter.

[0006] In step S2, the grid-side active power reference Add , the grid-side active power reference The expression is: .

[0007] In step S1, the actual DC bus voltage reference at each moment is calculated using the dynamic reference module prediction range. , the expression is, , In the formula, represents the reference prediction range used in steady state, represents the adjustment coefficient, represents the set of positive integers, represents the DC bus voltage at time k.

[0008] After adopting the above structure, the present invention has the following beneficial effects: 1. The present invention ensures that the actual DC bus voltage reference is accurate by evaluating a predefined cost function, since the maximum power constraint is also included in the cost function. Staying within a safe range and avoiding excessive charging or discharging currents effectively prevents significant overshoot of the DC link voltage and performance degradation caused by integral saturation problems common in PI control loops; at the same time, because the active power and DC link voltage are used to generate an appropriate reference, no additional voltage control loop is required.

[0009] 2. The present invention applies a dynamic reference module prediction range to calculate the actual DC bus voltage reference at each moment, thereby reducing the dynamic response time by reducing the prediction range and ensuring the control performance of the steady-state DC bus voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a back-to-back permanent magnet synchronous motor drive system; Figure 2 This is the control schematic diagram of the traditional PI-MPC; Figure 3 This is a control principle diagram of the dynamic predictive control method of the present invention. DETAILED DESCRIPTION

[0011] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0012] The present invention provides a dynamic prediction control method for a permanent magnet synchronous motor drive system. Figure 1-3As shown, the permanent magnet synchronous motor drive system adopts a conventional back-to-back permanent magnet synchronous motor drive system, which 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 is connected to the motor-side converter (MSC) in a conventional manner.

[0013] The dynamic prediction control method provided in this embodiment is based on the above-mentioned drive system, and the control method includes the following steps: S1. Get the actual DC bus voltage reference at each moment , the actual DC bus voltage reference The expression of is, (1), In the formula, Indicates the DC bus voltage reference; Indicates that the DC bus reference voltage has been reached The number of steps is calculated by the following formula: is the DC bus voltage value at time k, which can be obtained by sampling the voltage sensor; It is the DC bus voltage reference and is set manually.

[0014] S2, using the dynamic reference module to generate the grid-side active power of the grid-side converter , the dynamic reference module is: (2) , In the formula, represents the d-axis component of the grid-side voltage in the grid-side converter, represents the resistance value in the grid-side converter, represents the power consumed by the grid-side resistor in the grid-side converter, represents the motor speed at time k, It is the PMSM torque reference, which is set manually; is the DC bus capacitance value, is the sampling frequency.

[0015] in, , is the motor (PMSG) power, is the DC link capacitor In other words, Represents the motor (PMSG) and DC link capacitor total power.

[0016] Preferably, in order to eliminate the steady-state error, add , to compensate for the errors caused by switching power loss and conduction power loss, so that the dynamic reference module, that is, the grid-side active power The expression is: .

[0017] Solving the above formula, we get the dynamic reference module as: .

[0018] S3. Select the optimal voltage vector by evaluating a predefined cost function , the expression of the cost function is: , In the formula, represents the estimated grid-side active power at time k+2, represents the estimated grid-side reactive power at time k+2, Indicates the grid-side reactive power reference, is the DC bus voltage at time k+2, is the reactive power weight coefficient, is the DC bus voltage weight coefficient, It is the reactive power reference, which is set manually; is the bus voltage at time k+2; and They represent the constraints of active power and reactive power respectively; wherein, the power reference at each moment mentioned above is obtained from the filtered DC bus voltage reference.

[0019] Furthermore, the above The calculation formula is: , where is the sampling period, is the bus capacitance value, is the motor side switch signal at time k+1, is the grid-side switch signal at time k+1; is the motor side current at time k+1, is the grid-side current at time k+1.

[0020] Further, through the above step S3, we can get and , represents the motor side cost function and It represents the improved grid-side cost function, and then the estimated motor-side switch state at time k+1 is output to the machine-side converter and the estimated grid-side switch state at time k+1 is output to the grid-side converter in the same way as the conventional PI-MPC control method.

[0021] It should be noted that if Figure 2-3 As shown, the setting and / or acquisition of other parameters of the present invention except for the aforementioned improvement of the present invention are all prior art, that is, they can be obtained by using the existing PI-MPC control method used in the permanent magnet synchronous motor drive system, for example, in the above step S4 and For example, is the motor rotor angle, obtained by the position sensor; is the motor rotor speed, obtained by the speed sensor; is the DC bus voltage value at time k, obtained by sampling the voltage sensor; is the motor side switching signal at time k, that is, the calculated optimal switching signal at time k+1.

[0022] As a preferred method, in step S1, the actual DC bus voltage reference at each moment is calculated by using the dynamic reference prediction range. , the expression is, , In the formula, represents the reference prediction range used in steady state, represents the adjustment coefficient, represents the set of positive integers, represents the DC bus voltage at time k.

[0023] Thus, the DC bus voltage tracking performance depends largely on the number of steps mentioned above. , and the number of steps As a trade-off between dynamic response time and steady-state DC bus voltage ripple, in order to improve the dynamic performance of the present invention, the present invention adopts the above-mentioned dynamic prediction step to calculate the actual DC bus voltage reference at each moment, so as to reduce the dynamic response time by reducing the prediction step, so as to ensure the control performance of the steady-state DC bus voltage.

[0024] The present invention provides a dynamic predictive control method for a permanent magnet synchronous motor drive system. The present invention only needs to evaluate a predefined cost function. Since the maximum power constraint is also included in the cost function, the reference voltage value is ensured. It keeps the voltage within a safe range and avoids excessive charging or discharging current, effectively preventing significant overshoot of the DC circuit voltage, and also ensures that the DC link capacitor will not be damaged by voltage overshoot, thus increasing its service life.

[0025] Furthermore, the dynamic predictive control method of the present invention generates an appropriate reference through active power and DC link voltage, that is, the DC bus voltage is adjusted by following the specified trajectory of the voltage reference and the power reference, without the need for an additional voltage control loop (i.e., PI control loop), avoiding the performance degradation caused by the common integral saturation problem in the conventional voltage control loop (i.e., PI control loop), and ensuring the control performance of the drive system, i.e., unity grid-side power factor, low current harmonics and stable current bus voltage.

[0026] The above description is only a preferred embodiment of the present embodiment, and all equivalent changes and modifications made within the scope of the claims of the present invention should fall within the scope of the claims of the present invention.

Claims

1. A dynamic predictive 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 to the grid, characterized in that: The control method comprises the following steps: S1. Get the actual DC bus voltage reference at each moment , the actual DC bus voltage reference The expression is: （1）， In the formula, represents the DC bus voltage reference, Reach The number of steps, Indicates the actual value of the DC bus voltage at time k, obtained by sampling the voltage sensor; S2, to achieve the actual DC bus voltage reference at the next moment , a dynamic reference module is used to generate the grid-side active power reference of the grid-side converter , the grid-side active power reference The expression is: （2） ， In the formula, represents the d-axis component of the grid-side voltage in the grid-side converter, represents the resistance value in the grid-side converter, Indicates the power consumed by the grid-side resistor in the grid-side converter; is the torque reference; is the actual speed, obtained by sampling the speed sensor; is the bus capacitance parameter, Ts is the sampling period; Represents motor and DC link capacitors Total power; Solve to obtain the grid-side active power reference The expression is: （3）； S3. Select the optimal voltage vector by evaluating a predefined cost function , the cost function is: ， In the formula, is the active power at time k+2, is the reactive power weight coefficient, is the reactive power reference, is the reactive power at time k+2, is the bus voltage weight coefficient, is the bus voltage at time k+2; and denote the constraints of active power and reactive power respectively; The calculation formula is: , where is the sampling period, is the bus capacitance value, is the motor side switch signal at time k+1, is the grid-side switch signal at time k+1; is the motor side current at time k+1, is the grid-side current at time k+1; S4, obtained through step S3 and , represents the motor side cost function and It represents the improved grid-side cost function, and then outputs the estimated motor-side switch state at time k+1 to the machine-side converter and the estimated grid-side switch state at time k+1 to the grid-side converter respectively.

2. The dynamic predictive control method for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: In step S2, the grid-side active power reference Add , the grid-side active power reference The expression is: 。 3. The dynamic predictive control method for a permanent magnet synchronous motor drive system according to claim 1, characterized in that: In step S1, the actual DC bus voltage reference at each moment is calculated using the dynamic reference module prediction range. , the expression is, ， In the formula, represents the reference prediction range used in steady state, represents the adjustment coefficient, represents the set of positive integers, represents the DC bus voltage at time k.

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