阅读说明：本技术 一种基于fpga的同步电机励磁方法 (synchronous motor excitation method based on FPGA ) 是由 蒋珺 段巍 王成胜 李凡 兰志明 杨琼涛 杨培 于 2019-09-25 设计创作，主要内容包括：本发明公开了一种基于FPGA的同步电机励磁方法,属于励磁控制领域。首先利用给定基准电流与传感器测定的实际电机励磁绕组电流计算偏差值,并输入自适应PID调节器,经最优反馈增益模块计算最优控制参数值,跟踪辨识器实时变化,实现最优控制输出。然后结合与主电路进线同步电压信号,作为移相触发单元的输入控制信号,求取六脉波晶闸管的触发角α,经放大输入六脉波晶闸管整流电路中；输出实际的电机励磁绕组电压施加给电动机,得到实际励磁绕组电流,被传感器测定反馈计算偏差值,形成闭环。本发明基于励磁控制板,运用优化改进的控制流程,可有效降低生产成本,同时也能快速地根据现场实际工况,调整励磁电压,安全稳定地完成对电动机的励磁控制。(the invention discloses a synchronous motor excitation method based on an FPGA (field programmable gate array), and belongs to the field of excitation control. Firstly, a deviation value is calculated by utilizing a given reference current and an actual motor exciting winding current measured by a sensor, the deviation value is input into an adaptive PID regulator, an optimal control parameter value is calculated by an optimal feedback gain module, and the real-time change of an identifier is tracked to realize optimal control output. Then combining a synchronous voltage signal with the incoming line of the main circuit as an input control signal of the phase-shifting trigger unit, solving a trigger angle alpha of the six-pulse thyristor, and amplifying and inputting the trigger angle alpha into a rectifying circuit of the six-pulse thyristor; and outputting the actual voltage of the motor excitation winding to apply to the motor to obtain the actual current of the excitation winding, and measuring a feedback calculation deviation value by a sensor to form a closed loop. The invention is based on the excitation control board, and uses the optimized and improved control flow, so that the production cost can be effectively reduced, and meanwhile, the excitation voltage can be quickly adjusted according to the actual working condition on site, and the excitation control of the motor can be safely and stably completed.)

1. A synchronous motor excitation method based on FPGA is characterized by comprising the following steps:

Step one, according to the working condition of a test site, combining the delivery parameters of a motor and utilizing a given reference current i_stActual motor field winding current i measured with sensor_tCalculating a deviation value epsilon;

The deviation value calculation formula is as follows: e ═ i_st-i_t；

Inputting the deviation value epsilon into a self-adaptive PID regulator, calculating an optimal control parameter value through an optimal feedback gain module, and tracking the real-time change of an identifier to realize optimal control output u;

The self-adaptive PID regulator is characterized in that an identifier and an optimal feedback gain module are added on the basis of a traditional PID regulator body;

according to the optimal feedback control theory, the optimal control rule is designed as follows: k (K) · X (K);

X (k) is a state variable; k (K) is an optimal feedback gain matrix;

K(k)＝-R^-1B^TA^-T[P(k)-Q]＝[k₁(k),k₂(k),k₃(k)]；

R＝[1]；X(k+1)＝A·X(k)+B·ε(k)；B＝[0 1 b₀]^T，a_i、b_jthe i is 1,2, 3; j is 0,1, 2;

P (k) is the solution of the discrete Riccati equation, where P (k) is Q + A^TP(k)[I+BR^-1B^TP(k)]^-1A；

I is an identity matrix, Q ═ diag [ 110100]；k₁(k),k₂(k),k₃(k) Respectively representing the proportionality coefficient K in the transfer function of a conventional PID regulator_PIntegral coefficient K_IAnd a differential coefficient K_DI.e. K_P＝k₁(k)，K_I＝k₂(k)，K_D＝k₃(k) The control parameters of the self-adaptive PID regulator are ensured to change along with the system in real time, thereby realizing optimal control;

Step three, optimally controlling output u to combine with voltage signal u synchronous with main circuit inlet wire voltage_sAs an input control signal of the phase shift trigger unit, the trigger angle alpha of the six-pulse thyristor is obtained;

The method specifically comprises the following steps:

Inputting a signal: given reference current i_stSynchronous voltage signal u_sCombining an auxiliary signal, firstly, realizing signal isolation and amplitude conversion through a sampling chip, then, inputting a signal which is in accordance with a voltage range after conversion into an FPGA control chip, calculating a trigger angle alpha value of a six-pulse thyristor, and outputting a trigger angle by combining a software phase-locked loop unit in the control chip; the formula is as follows:

α＝0.69-1.57×[U/(2.34×U₀)-0.77]

U is the effective value of the excitation voltage output by the expected rectification circuit, and is 2.34U₀cos α, wherein U₀The effective value of three-phase incoming line of the six-pulse thyristor rectification circuit is obtained;

fourthly, amplifying the power of the trigger angle alpha output by the FPGA control chip through a power tube and a pulse transformer, and inputting the actual trigger pulse into a six-pulse-wave thyristor rectification circuit;

step five, main circuit three-phase incoming line voltage u_iVoltage u obtained via an excitation transformer₀as input of six-pulse wave thyristor rectifier circuit, actual motor exciting winding voltage E is output_dApplied to the motor to obtain the actual field winding current i of the motor_tAnd the feedback measured by the sensor calculates the deviation value epsilon to form a closed loop.

2. The synchronous motor excitation method based on the FPGA as recited in claim 1, wherein the given reference current in the first step comprehensively considers test site conditions and motor delivery parameters;

The field working condition is as follows: load type, driver type, motor operating frequency and motor operating speed;

The factory parameters of the motor include: rated voltage, rated current, pole pair number and connection mode of the motor.

3. The method for exciting an FPGA-based synchronous motor according to claim 1, wherein the control parameters capable of dynamically tracking the system change in the second step include: a proportionality coefficient, an integral coefficient, and a differential coefficient.

4. The synchronous motor excitation method based on the FPGA as recited in claim 1, characterized in that: and step three, the phase-locked loop module applied in the phase-shifting trigger unit can judge whether the main circuit power supply voltage signal is balanced in real time, and intelligently selects the simplest and most convenient and effective method under different conditions, so that the response speed of the system is accelerated, and the safety and reliability of the excitation trigger angle are ensured.

Technical Field

The invention belongs to the field of excitation control, and particularly relates to a synchronous motor excitation method based on an FPGA (field programmable gate array).

Background

The power supply for supplying excitation current to the synchronous machine and its accessories are generally called excitation system, which generally consists of two main parts, an excitation power unit and an excitation regulator, wherein the excitation power unit supplies excitation current to the rotor of the synchronous machine, and the excitation regulator controls the output of the excitation power unit according to an input signal and a given regulation criterion.

The automatic excitation regulator of the excitation system has a considerable influence on improving the stability of the parallel unit of the power system, and the excitation system has the following main functions: correspondingly adjusting the exciting current according to the change of the motor load so as to maintain the terminal voltage of the motor as a given value; controlling reactive power distribution among motors which run in parallel; the static stability and the transient stability of the parallel operation of the motors are improved; when the interior of the motor fails, the demagnetization is carried out to reduce the failure loss degree; maximum and minimum excitation limits are imposed on the machine depending on operational requirements.

The excitation function of the traditional motor is basically selected from international leading foreign equipment, such as Siemens 6RA70, the cost is high, the excitation control can be automatically adjusted under various working conditions, but certain functions are redundant for common application sites, so that the method for effectively and reliably exciting the synchronous motor at low cost has certain practical significance.

Disclosure of Invention

The invention aims to provide a synchronous motor excitation method based on an FPGA (field programmable gate array), which is used for realizing the excitation function of a synchronous motor.

a synchronous motor excitation method based on FPGA specifically comprises the following steps:

Step one, according to the working condition of a test site, combining the delivery parameters of a motor and utilizing a given reference current i_stActual motor field winding current i measured with sensor_tA deviation value epsilon is calculated.

The field conditions generally refer to: load type, driver type, motor running frequency, motor running speed and the like;

the factory parameters of the motor include: rated voltage, rated current, pole pair number, connection mode and the like of the motor.

the deviation value calculation formula is as follows: e ═ i_st-i_t；

And step two, inputting the deviation value epsilon into the self-adaptive PID regulator, calculating an optimal control parameter value through the optimal feedback gain module, and tracking the real-time change of the identifier to realize the optimal control output u.

The control parameters include: a proportionality coefficient, an integral coefficient, and a differential coefficient;

The self-adaptive PID regulator is characterized in that an identifier and an optimal feedback gain module are added on the basis of a traditional PID regulator body;

According to the optimal feedback control theory, the optimal control rule is designed as follows: k (K) · X (K);

X (k) is a state variable; k (K) is an optimal feedback gain matrix;

K(k)＝-R^-1B^TA^-T[P(k)-Q]＝[k₁(k),k₂(k),k₃(k)]；

R＝[1]；X(k+1)＝A·X(k)+B·ε(k)；B＝[0 1 b₀]^T，a_i、b_jThe i is 1,2, 3; j is 0,1, 2.

P (k) is the solution of the discrete Riccati equation, where P (k) is Q + A^TP(k)[I+BR^-1B^TP(k)]^-1A；

i is an identity matrix, Q ═ diag [ 110100]；k₁(k),k₂(k),k₃(k) respectively representing the proportionality coefficient K in the transfer function of a conventional PID regulator_PIntegral coefficient K_IAnd a differential coefficient K_Di.e. K_P＝k₁(k)，K_I＝k₂(k)，K_D＝k₃(k) And the control parameters of the self-adaptive PID regulator are ensured to change along with the system in real time, so that the optimal control is realized.

Step three, optimally controlling output u to combine with voltage signal u synchronous with main circuit inlet wire voltage_sThe trigger angle alpha of the six-pulse thyristor is obtained as an input control signal of the phase-shift trigger unit.

The method specifically comprises the following steps:

Inputting a signal: given reference current i_stSynchronous voltage signal u_sCombining an auxiliary signal, firstly, realizing signal isolation and amplitude conversion through a sampling chip, then, inputting a signal which is in accordance with a voltage range after conversion into an FPGA control chip, calculating a trigger angle alpha value of a six-pulse thyristor, and outputting a trigger angle by combining a software phase-locked loop unit in the control chip; the formula is as follows:

α＝0.69-1.57×[U/(2.34×U₀)-0.77]

U is the effective value of the optimal control U of the expected rectifier circuit output, and is 2.34U₀cos α, wherein U₀Is an effective value of three-phase incoming line of a six-pulse wave thyristor rectification circuit.

Fourthly, amplifying the power of the trigger angle alpha output by the FPGA control chip through a power tube and a pulse transformer, and inputting the actual trigger pulse into a six-pulse-wave thyristor rectification circuit;

the six-pulse wave thyristor is sequentially conducted according to a control time sequence, the trigger pulse after power amplification adopts a double narrow pulse form, the leading edges of the two narrow pulses are in phase difference of 60 degrees, and the pulse width is 20-30 degrees.

Step five, main circuit three-phase incoming line voltage u_iVoltage u obtained via an excitation transformer₀As input of six-pulse wave thyristor rectifier circuit, actual motor exciting winding voltage E is output_dApplied to the motor to obtain the actual field winding current i of the motor_tand the feedback measured by the sensor calculates the deviation value epsilon to form a closed loop.

Compared with the prior art, the invention has the advantages that:

An FPGA-based synchronous motor excitation method can effectively reduce production cost, quickly adjust excitation voltage according to on-site actual working conditions, and safely and stably complete the excitation function of a motor.

Drawings

FIG. 1 is a schematic diagram of an FPGA-based synchronous motor excitation method according to the present invention;

FIG. 2 is a flow chart of an FPGA-based synchronous motor excitation method according to the present invention;

FIG. 3 is a circuit structure diagram of an excitation device based on an FPGA control chip according to the present invention;

Fig. 4 is a block diagram of the synchronous motor excitation device based on the FPGA.

Detailed Description

the invention is further described with reference to the following figures and specific examples.

A synchronous motor excitation method based on FPGA is disclosed, as shown in figure 1, the actual excitation winding current i of the motor_tin combination with a given reference current i_stCalculating a deviation value epsilon, inputting the deviation value epsilon into an adaptive PID regulator in combination with an auxiliary signal, realizing optimal control output u through an optimal feedback gain module, and combining a synchronous voltage signal u of a main circuit inlet wire_sObtaining a trigger angle alpha of the six-pulse thyristor, and inputting actual trigger pulses into a rectification circuit of the six-pulse thyristor after power amplification; outputting actual motor field winding voltage E_dapplied to the motor to obtain the actual field winding current i of the motor_tAnd the feedback measured by the sensor calculates the deviation value epsilon to form a closed loop.

As shown in fig. 2, the method specifically comprises the following steps:

Step one, according to the working condition of a test site, combining the delivery parameters of a motor and utilizing a given reference current i_stActual motor field winding current i measured with sensor_tA deviation value epsilon is calculated.

The field conditions generally refer to: load type, driver type, motor running frequency, motor running speed and the like;

the factory parameters of the motor include: rated voltage, rated current, pole pair number, connection mode and the like of the motor.

the deviation value calculation formula is as follows: e ═ i_st-i_t；

And step two, taking the deviation value epsilon as the input quantity of the self-adaptive PID regulator, combining an auxiliary signal, identifying the parameters of the motor in real time, substituting the identification parameters into a discrete Riccati equation, and solving the optimal feedback gain to be used as the proportional, integral and differential coefficients of the traditional PID regulator, so as to optimize and improve the traditional PID regulator and realize the optimal control output u.

the auxiliary signal includes: minimum excitation limit, maximum excitation limit, scaling when the excitation current given input is 0, etc.

The self-adaptive PID regulator is added with self-correcting control on the basis of the traditional PID regulator body, and comprises an identifier and an optimal feedback gain module;

The identifier identifies the excitation system when the parameters or the running state of the motor change.

the optimal feedback gain module is used for calculating optimal feedback gain.

When the excitation control is researched, the synchronous motor can be approximately described by a first-order hysteresis link, and the transfer function is as follows:Wherein K_GShowing the motor amplification factor, T_dRepresents its time constant; s is the symbol of the S domain.

the transfer functions of the phase-shift trigger, the power amplification and the six-pulse wave thyristor rectifier are subjected to Taylor series expansion, and high order is omitted, so that the simplified transfer function is as follows:

K_ZFor a voltage amplification factor, T_Zis the time constant of the amplification unit;

the signal detection unit is described as a first-order inertia element, and the transfer function of the signal detection unit is as follows:

K_RFor input-output of a proportional coefficient, T_Ris the time constant of the measurement loop.

Thus, for an adaptive PID controller, the control object can be equivalent to a third order model, which is converted into a 3 rd order discrete mathematical model common to the Z domain, expressed as:

Wherein u is the excitation voltage expected to be output by the thyristor rectifier circuit, and the deviation value epsilon is used as the input quantity of the identifier, a_i、b_jThe i is 1,2, 3; j is 0,1, 2.

when the parameters or operating conditions of the motor change, a_i、b_jThe excitation system is required to be identified, the identifier in the excitation method is based on a recursive least square identification method, the relevant intrinsic parameters of the system are input by auxiliary signals, and an identification model can be written as follows:

In the formula b₀Can be given directly by the auxiliary signal value without taking part in the identification, theta [ -a [ ]₃ -a₂ -a₁ b₂ b₁]^T，Wherein u (k) and epsilon (k) are corresponding discrete time sequence values in the digital control system, and substituted to solve a_i、b_j。

In order to simplify the calculation, the input quantity, the output quantity and the current output quantity of the previous period are selected as state variables, and X is equal to [ Z ]^-1ε(Z),Z^-1u(Z),u(Z)]^TThe equation of state is X (k +1) ═ A.X (k) + B.epsilon (k), whereB＝[0 1 b₀]^T。

according to the optimal feedback control theory, the optimal control rule is designed as follows: k (K) · X (K);

k (K) is the optimal feedback gain matrix, K (K) ═ R^-1B^TA^-T[P(k)-Q]＝[k₁(k),k₂(k),k₃(k)]Wherein P (k) is the solution of the discrete Riccati equation, and P (k) is Q + A^TP(k)[I+BR^-1B^TP(k)]^-1A, I is unit matrix, Q ═ diag [ 110100 [ ]]，R＝[1]。

The transfer function of a conventional PID regulator is

K_P、K_I、K_DGenerally, the constant is a fixed constant calculated according to engineering experience, and K is calculated in the method_P＝k₁(k)，K_I＝k₂(k)，K_D＝k₃(k) The parameters of the self-adaptive PID regulator can be changed in real time along with the system, so that the optimal control is realized.

Step three, optimally controlling output u to combine with voltage signal u synchronous with main circuit inlet wire voltage_sThe trigger angle alpha of the six-pulse thyristor is obtained as an input control signal of the phase-shift trigger unit.

For a six-pulse thyristor rectifier circuit, due to the existence of an induced voltage, an excitation winding of a synchronous motor is equivalent to a resistive load, and therefore theoretically, the effective value of the excitation voltage of a rectified output is expected to be: u is 2.34U₀cosα；

In the formula of U₀the three-phase incoming line is an effective value of a thyristor rectification circuit.

In order to save the storage space of the control chip, the inverse cosine function value is obtained by adopting a Taylor expansion fitting method, and the following steps are obtained: alpha is 0.69-1.57X [ U/(2.34 XU)₀)-0.77]。

In the excitation system, all three-phase alternating current is taken from three-phase incoming line voltage u of the main circuit_iOutput voltage u of exciting transformer₀The phase position is consistent with the main circuit voltage, the amplitude value is variable,u₀＝N₁·u_i(ii) a In the formula N₁Is a transformation ratio coefficient;

As shown in FIG. 3, since the sampling chip of the FPGA excitation control board has a voltage range limitation, the sending of the pulse trigger signal needs to be performed by the input u of the excitation rectifying circuit₀For time reference and in order to avoid superposition interference, a proper step-down transformer is selected to obtain a synchronous voltage signal u consistent with the phase of the three-phase incoming line voltage of the main circuit_s，u_s＝N₂·u_iTherefore u is_sAnd u₀Synchronization is also maintained.

The actual significance of the firing angle alpha is relative to the input u of the excitation rectifier circuit₀Phase offset of the nominal zero point, synchronization signal u_sexcept for the variation of amplitude, the rest information is equal to u₀Therefore, the pulse triggering time can be accurately positioned by tracking the phase of the pulse through a software phase-locked loop method.

When the trigger angle alpha is different, the phase-shifting delay of the emission of the pulse signal relative to the zero point of the synchronous signal is different, and the synchronous voltage signal u_sthe phase tracking of the FPGA is mainly completed through a software phase-locked loop unit designed in the FPGA excitation control board. The phase-locked loop unit can intelligently identify the synchronous voltage signal u_sDegree of balance, i.e. main circuit three-phase incoming line voltage u_iIs also the input voltage u of the excitation rectifier circuit₀The degree of equilibrium of (c). At u_sunder the condition of three-phase complete symmetry, a simpler and faster single synchronous coordinate system software phase-locked loop method is selected; when unbalanced conditions such as voltage drop, phase angle mutation or single-phase short-time grounding occur, the method is switched to a double-synchronous coordinate system decoupling software phase-locked loop method with higher adjusting performance, so that the input voltage phase of the excitation rectifying circuit is accurately tracked in real time, and the accuracy and the reliability of generating the trigger pulse are ensured.

Fourthly, the FPGA control chip calculates the output trigger angle alpha, performs power amplification through a power tube and a pulse transformer, and inputs actual trigger pulse into a six-pulse thyristor rectification circuit;

Because the FPGA excitation control board sends out trigger pulses with smaller power, the six-pulse wave thyristor can be really triggered after power amplification is carried out through the power tube and the pulse transformer, and the six-pulse wave thyristor in the excitation rectifying circuit is sequentially conducted according to a control time sequence. The trigger pulse output by the power amplification link adopts a double narrow pulse form, namely when a narrow pulse is transmitted to a thyristor, a narrow pulse is sent to the previous thyristor, the phase difference of the leading edges of the two narrow pulses is 60 degrees, and the pulse width is 20-30 degrees.

Step five, main circuit three-phase incoming line voltage u_ivoltage u obtained via an excitation transformer₀As input of six-pulse wave thyristor rectifier circuit, actual motor exciting winding voltage E is output_dapplied to the motor to obtain the actual field winding current i of the motor_tAnd the feedback measured by the sensor calculates the deviation value epsilon to form a closed loop.

The synchronous motor excitation method based on the FPGA is established on a synchronous motor excitation device, and comprises an excitation control board, a power amplification circuit and a six-pulse thyristor rectification circuit as shown in figure 4.

the excitation control board samples, analyzes and adjusts data of a main circuit where the synchronous motor is located, outputs a pulse trigger angle, and controls the turn-on time of the six-pulse thyristor, so that the excitation voltage is controlled, and the purpose of excitation is achieved. The excitation control panel mainly comprises a sampling chip and an FPGA control chip, the FPGA control chip is used as a main control chip, and the sampling chip is responsible for converting an analog quantity into a digital quantity for an input synchronous voltage signal, a given current signal and an auxiliary signal so as to meet the signal input condition of the FPGA chip; specifically completing excitation control in an FPGA control chip, comparing a given current with a feedback excitation winding current to make a difference, and generating a corresponding trigger angle alpha through self-adaptive PID (proportion integration differentiation) regulation and phase-shifting triggering.

the ADS8365 is selected by the sampling chip, and the EPF10K30A is selected by the FPGA control chip.

The phase-shifting trigger aims to track synchronous voltage signals, calculate trigger angles and send out trigger pulses at corresponding time. The intelligent software phase-locked loop is a key module, can replace the traditional hardware synchronous circuit, and has the main functions of judging whether the main circuit power supply voltage signal is balanced in real time and intelligently selecting the simplest and most convenient and effective method under different conditions, so that the system response speed is accelerated, and the safety and reliability of the excitation trigger angle are ensured.

The power amplifying circuit is used for amplifying pulse signals, so that trigger pulses have enough gradient, amplitude and pulse width, and reliable conduction of the thyristor is ensured; meanwhile, the excitation control board and the thyristor rectification circuit are isolated, and the control effect is prevented from being influenced by mutual electromagnetic interference.

The six-pulse wave thyristor rectification circuit is used for outputting excitation voltage, providing voltage for a rotor excitation winding of the motor and generating excitation current.