A direct current variable pitch motor control system

Abstract

The application relates to a direct-current variable-pitch motor control system, which is characterized by including a closed-loop control method of four speed feedback units in two speed feedback signal modes, four speed feedback modes covering all speed feedback modes of a variable-pitch system and capable of being flexibly and simply switched; in addition, the application also includes an open-loop control method for emergency treatment in the case that a motor speed feedback unit of the direct-current variable-pitch motor is faulty or signal loss occurs, the direct-current variable-pitch motor can track the speed signal before the emergency and a current control signal, so that the variable-pitch motor is ensured to stably operate and the wind driven generator is ensured to be safe; the application also proposes a steady-state control method of open-loop and closed-loop units and a switching process, which prevents motor current from suddenly jumping and prevents motor speed from suddenly changing. The design of the application is suitable for variable speed feedback modes of the direct-current motor used for variable-pitch control, and ensures that the wind driven generator set is reliable and safe.

Description

Technical Field

[0001] This invention belongs to the field of DC motor control, and particularly relates to a DC motor control system for pitch systems. Background Technology

[0002] DC pitch control systems have long been a core component of wind turbines due to their reliability and safety, and occupy a significant market share in China's onshore wind power pitch systems.

[0003] The core actuators of a DC pitch system consist of a DC pitch motor and a pitch driver. Due to its reliable and simple feathering characteristics, the DC pitch motor is widely used in pitch systems. Therefore, the DC pitch motor drive unit not only needs to match the performance of the pitch motor and extend its operating range, but also needs to improve reliability and safety, making it one of the core key components of the pitch control system. The control strategy of the pitch driver mainly adopts the traditional method of speed control outer loop and current control inner loop. However, due to the special operating conditions of pitch systems and the different pitch design schemes of various manufacturers, coupled with the technical needs for upgrades and modifications after a certain number of years of service, different requirements are placed on the speed feedback method of the pitch motor. Furthermore, to ensure system safety, new requirements are also placed on the open-loop operation of the pitch motor. From the currently available literature, there are limited patents and materials involving DC pitch driver control methods and strategies, and even fewer specifically addressing open-loop control of DC pitch drivers. Based on the operating conditions of DC pitch motors, this patent proposes a control system that integrates multiple speed feedback methods. It can achieve smooth switching between open-loop and closed-loop control of DC pitch motors, ensuring that the motor speed does not jump suddenly and the motor current does not change abruptly when the speed feedback method is disconnected, thereby improving system safety. Summary of the Invention

[0004] Based on the conventional control schemes of current DC pitch drives, this invention provides a closed-loop control method based on digital and analog speed feedback to expand the application scope of DC pitch motors in the upgrading and transformation of DC pitch systems. To improve the control stability of the pitch motor, achieve smooth connection between open and closed loop switching speeds, and achieve smooth transition of open and closed loop switching currents, this invention provides an open-loop control method based on speed tracking and current loop tracking.

[0005] To achieve the above objectives, a technical solution for a DC pitch motor control system is as follows:

[0006] The DC pitch motor control system mainly consists of two parts: a closed-loop control unit and an open-loop control unit, as well as a steady-state control algorithm to ensure that the motor speed does not jump abruptly and the current does not change abruptly during the open-loop and closed-loop operation and switching processes.

[0007] The closed-loop control unit mainly includes the speed loop control unit, the current loop control unit, and the speed setting and rotational speed selection of the matching speed loop control unit, as well as the current feedback of the matching current loop control unit.

[0008] The closed-loop control unit operates as follows: the difference between the speed setpoint and the speed feedback value is calculated and output by the PID algorithm of the speed loop control unit. This output value is then compared with the current feedback value and output by the PID algorithm of the current loop control unit, becoming the chopper output unit control signal, which in turn controls the motor speed and current.

[0009] The speed setpoint is the desired operating speed of the DC pitch motor. This setpoint can be an analog signal, a digital signal, or a signal given via communication with a host computer, or it can be a position control output setting. The speed setpoint is normalized within the control method, with the negative maximum speed setting to the positive maximum speed setting normalized to -100% to 100% within the control method.

[0010] The speed feedback unit is used to obtain the actual operating speed of the pitch motor. DC pitch motors typically use a tachogenerator as the speed feedback unit. However, due to increased service life, the accuracy and performance of the tachogenerator decrease due to mechanical wear, and replacement is difficult. Therefore, this invention adds an incremental encoder, an absolute encoder, and a resolver encoder, differentiating it from the industry's single-channel speed feedback method and expanding the application range of the driver and motor. The tachogenerator and resolver encoder are analog feedback methods, while the incremental encoder and absolute encoder are digital feedback methods. The speed feedback method is selected via software switch, allowing for flexible and varied feedback components, improving the breadth and duration of application of the DC pitch motor during its service life. For analog feedback, algorithms such as multiple sampling and mean filtering are used to reduce interference from inaccurate and unstable signals. For digital signal feedback, algorithms such as interrupt priority and inertial filtering are used to reduce interference from wiring and operating environment issues. The speed feedback value is per-unit normalized within the control method, with the negative maximum feedback speed to the positive maximum feedback speed being per-unit normalized to -100% to 100%.

[0011] The current feedback unit is used to obtain the actual current magnitude during the operation of the pitch motor. Since the DC motor only has single-phase current, the current sampling adopts a weighted filtering algorithm; that is, the previous sampled value (which can be the value after mean filtering or inertial filtering) and the current sampled value each account for a certain proportion and are then summed to obtain the actual current sampled value. The current sampled value is normalized within the control method, and the negative maximum sampled current to the positive maximum sampled current is normalized to -100% to 100% within the control method.

[0012] The speed loop control unit is used to eliminate the error between the speed setpoint and the speed feedback value and uses a proportional-derivative-integral algorithm to output the value as the input value of the current loop control unit. The output of the speed loop control unit and the processing result of the current feedback unit are sampled in the same dimension.

[0013] The current loop control unit eliminates the error between the current loop setpoint and the pitch motor current sampling value and uses a proportional-derivative-integral algorithm to output the value as the input value of the chopper control unit.

[0014] The chopper control unit is used to control the DC pitch motor. The chopper output unit uses pulse width modulation control (PWM control) for the control of the DC pitch motor. Its output has a duty cycle of 0~100% to adjust the motor speed.

[0015] The open-loop control unit mainly includes a speed tracking unit, a current loop control tracking unit, a DC driver open-loop controller, a current limiting unit, and a motor feedback disconnection detection unit that matches the open-loop control unit.

[0016] The open-loop control unit operates as follows: The pitch motor feedback disconnection detection unit determines whether the speed feedback is disconnected based on the sampled changes in the speed feedback signal. Upon detecting a disconnection, the open-loop control unit records the pitch motor speed during the last closed-loop control as its input. This speed is then converted into a duty cycle signal A within the open-loop control unit using a conversion, per-unit, and normalization method. Simultaneously, to ensure motor stability during the switch between closed-loop and open-loop control, the open-loop control unit records the current loop control unit's output signal during the last closed-loop control, using it as another input signal B. The open-loop control unit's output signal C has the same dimensions as the current loop control unit's output, ensuring stability during the open-loop / closed-loop transition. C is a piecewise function of the aforementioned duty cycle signal A and the other input signal B. To ensure open-loop controller stability, a transition time T1 is set, and a weighted average algorithm is used. The functional relationship is as follows:

[0017] C=f(A); t <T1

[0018] C = K1 * f(A) + K2 * f(B); t = T1;

[0019] C = f(B); t > T1;

[0020] Where K1 and K2 are constants;

[0021] The output signal C is used as the motor control signal for the chopper unit in the event of a feedback disconnection.

[0022] The motor feedback disconnection detection unit samples and measures the speed feedback signal of the DC pitch motor. Based on the set speed and operating conditions, when the feedback signal is an analog quantity, it determines whether there is speed loss and feedback disconnection based on the magnitude of the continuously sampled analog quantity within a certain time range; when the feedback signal is a digital quantity, it determines whether there is speed loss and feedback disconnection based on the number of square waves captured within a certain time range.

[0023] The speed tracking unit records the speed feedback value for each program execution cycle in a stack within the control method. When the speed feedback is continuous, the stack pops the previous recorded value and pushes in the latest speed feedback value. When the speed feedback is interrupted, the latest speed feedback value is used as the speed tracking value.

[0024] The current loop tracking unit records the output value of the current loop control unit in each program execution cycle using a stack within the control method. When the speed feedback is continuous, the stack pops the previously recorded value and pushes in the latest current loop control unit output value. When the speed feedback is disconnected, the latest current loop control unit output value is used as the current loop tracking value.

[0025] The current limiting unit collects the DC pitch motor current in real time. When it detects that the current changes too much after multiple consecutive samplings, the open-loop control unit will compensate the output signal C according to the rate of current change to ensure that the current does not change abruptly during the open-loop control process.

[0026] The system also includes a motor stability control algorithm, which mainly includes cycle control of each loop during closed-loop operation, cycle control of each loop during open-loop operation, and generation of output signals from the chopper control unit.

[0027] The steady-state algorithm working principle of open-loop and closed-loop operation and switching process: After selecting a reasonable operating cycle for each loop in closed-loop and open-loop operation, the control signal of the chopper output unit adopts the form of a piecewise function of the output of the current loop control unit and the output of the open-loop controller, so as to smoothly transition from closed-loop control to open-loop control state.

[0028] The closed-loop operation cycle control uses the speed loop control unit as the outer loop and the current loop control unit as the inner loop. Faster execution of the current loop control unit and relatively slower execution of the speed loop control unit contribute to greater loop stability. Simultaneously, the chopper output unit operates at a higher speed than the current loop control unit.

[0029] During open-loop operation, the operating cycle control of each loop is such that the execution speed of the open-loop control unit is the same as that of the current loop control unit.

[0030] The chopper control unit output signal E is generated by setting a transition time T2. During the transition time T2, the output signal E of the current loop control unit and the output signal C of the open loop controller are output using a weighted average and piecewise function processing method, so as to smoothly transition from closed loop control to open loop control.

[0031] Its functional relationship is as follows:

[0032] E=f(D); t <T2;

[0033] E= K3* f(D)+ K4* f(C); t=T2;

[0034] E = f(C); t > T2;

[0035] K3 and K4 are constants.

[0036] The beneficial effects of this invention are:

[0037] A DC pitch motor control system integrates four speed measurement methods, including analog speed feedback units such as tachogenerator feedback and resolver encoder feedback, and digital feedback units such as absolute encoder feedback and incremental encoder feedback. These methods can be easily selected via software switches according to operating conditions, greatly expanding the application range and lifespan of older wind turbine DC pitch motors. This invention not only solves the problems of smooth switching between open and closed loops and open-loop operation of DC motors, but also addresses the issue of stable and reliable operation of DC pitch motors during these processes, making it suitable for wind power generation applications with high reliability requirements. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the principle of the present invention.

[0039] Figure 2 This is a schematic diagram of the closed-loop control method using resolver feedback in this invention.

[0040] Figure 3 This invention relates to the principle of open-loop control in the event of loss or disconnection of feedback from the speed measurement unit.

[0041] Figure 4 This is a schematic diagram of the steady-state control method for pitch motors during closed-loop control, open-loop control, and switching between them. Detailed Implementation

[0042] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0043] Figure 1A principle block diagram of the present invention is provided. This control system samples and measures the speed feedback signal of the DC pitch motor. Based on the set speed and operating conditions, when the feedback signal is an analog quantity, it determines whether speed is lost based on the magnitude of the continuously sampled analog quantity within a certain time range, and the feedback is disconnected. When the feedback signal is a digital quantity, it determines whether speed is lost based on the number of square waves captured within a certain time range, and the feedback is disconnected. If the feedback is normal, the system enters a closed-loop control process; if the feedback is lost or disconnected, it enters an open-loop control process. During the closed-loop control process, a software switch selects a mode that matches the actual feedback channel of the pitch motor. The difference between the speed feedback quantity and the speed setpoint is used as the input of the speed loop control unit; the difference between the output of the speed loop control unit and the pitch motor current is used as the input of the current loop control unit; the output of the current loop control unit serves as the input signal of the chopper control unit, controlling the speed and current of the pitch motor. During open-loop control, the open-loop control unit records the pitch motor speed during the last closed-loop control as its input, and converts this speed into a duty cycle signal A within the open-loop control unit using conversion, per-unit scaling, and normalization methods. Simultaneously, to ensure motor stability during the switch between closed-loop and open-loop control, the open-loop control unit records the current loop control unit's output signal during the last closed-loop control, and uses this signal as another input signal B. The output signal C of the open-loop control unit is a piecewise function of the aforementioned duty cycle signal A and the other input signal B. To ensure the stability of the open-loop controller, a transition time T1 is set, and a weighted average algorithm is used, with the following functional relationship:

[0044] C=f(A); t <T1;

[0045] C = K1 * f(A) + K2 * f(B); t = T1;

[0046] C = f(B); t > T1;

[0047] Where K1 and K2 are constants;

[0048] This output signal is used as the motor control signal for the chopper unit in the event of a feedback disconnection.

[0049] Figure 2 and Figure 3 The control principle diagrams for DC motors in both closed-loop and open-loop states are given. Figure 2The set speed of the pitch motor is defined by a programmable logic controller (PLC) via communication (CANOPEN), and speed feedback uses resolver feedback. This closed-loop control method is also commonly used for pitch motors. The difference between the communication-set speed and the resolver feedback speed serves as the input to the speed loop control unit, which is responsible for eliminating this error. The difference between the speed loop control unit output and the current feedback serves as the input to the current loop control unit, which is also responsible for eliminating this error. The output signal of the current loop control unit serves as the input signal to the chopper output unit to control the motor current and speed. Figure 3 The open-loop control principle diagram is given for situations where speed feedback is disconnected or lost. The speed tracking unit records the DC pitch motor speed before the disconnection (at this time, the speed feedback unit is not yet disconnected, and the speed is measurable), and the current loop tracking unit records the output signal of the current loop control unit before the disconnection. Both tracking units serve as inputs to the open-loop controller, and the output of the open-loop control unit is a piecewise function of the signals from the two tracking units. Under open-loop control, the output of the chopper unit is a piecewise function of the output of the open-loop control unit and the output of the current loop control unit before the disconnection.

[0050] Figure 4 This is a principle block diagram of one embodiment of the present invention. To ensure system control stability, the speed setting, speed feedback judgment and signal acquisition of the closed-loop control unit, the speed tracking of the speed loop control unit, and the speed tracking of the open-loop control unit are all executed in execution cycle one. The current loop control unit of the closed-loop control unit, the open-loop controller of the open-loop control unit, the current limiting compensation unit, the chopper output unit, and the current feedback unit used in both open-loop and closed-loop control are executed in execution cycle two. The ratio of execution cycle one to execution cycle two is 10:1. The input signal D of the chopper output unit is defined as the output signal of the current loop control unit, the input signal C is the compensation signal of the open-loop controller after current limiting, and the output signal E controls the operation of the DC pitch motor. To achieve stability in the switching between closed-loop and open-loop control and to prevent sudden current changes or abnormal speed jumps in the motor, the control method for signal E is as follows:

[0051] In closed-loop control, signal E is a function of signal D, i.e., E = f(D).

[0052] In open-loop control, a state transition time T2 is defined. Before timer t enters the transition time T2, signal E remains a function of signal D. After timer t exceeds the transition time T2, signal E becomes a function of signal C, i.e., E = f(C). During the transition time T2, signal E is a function of both signal C and signal D, i.e., E = K3 * f(D) + K4 * f(C); where K3 and K4 are constants.

[0053] This invention takes a DC motor as an example, but is not limited to this type of motor. This invention can also be applied to other types of motors, such as separately excited motors and compound excited motors.

Claims

1. A DC pitch motor control system, characterized in that: Includes closed-loop control units and open-loop control units; The closed-loop control unit includes: a speed loop control unit, whose input values ​​are the speed setpoint and the pitch motor speed feedback value; the output value is the difference between the two values ​​output by the PID algorithm of the speed loop control unit; a current loop control unit, whose input values ​​are the output value of the speed loop control unit and the pitch motor current feedback value; the output value is the difference between the two values ​​output by the PID algorithm of the current loop control unit; and a chopper output unit, which uses a pulse width modulation control method to convert the received current loop control unit output value into a duty cycle of 0~100% for adjusting the motor speed. The open-loop control unit includes: a motor feedback disconnection detection unit, which samples and measures the DC pitch motor speed feedback signal to determine if speed is lost and detects disconnection, thereby enabling the motor to switch from closed-loop to open-loop mode; a speed tracking unit, which records the pitch motor speed during the last closed-loop control as input signal A of the open-loop control unit; a current loop control tracking unit, which records the output signal of the current loop control unit during the last closed-loop control as another input signal B of the open-loop control unit; and a DC driver open-loop controller, which takes input signals A and B, and outputs signal C as a piecewise function of signals A and B. To ensure the stability of the open-loop controller, a transition time T1 is set, and a weighted average algorithm is adopted, with the following functional relationship: C=f(A); t <T1 C = K1 * f(A) + K2 * f(B); t = T1; C = f(B); t > T1; Where K1 and K2 are constants; The current limiting unit collects the DC pitch motor current in real time and compensates the signal C according to the rate of current change.

2. The DC pitch motor control system according to claim 1, characterized in that: It includes a current feedback unit for acquiring the current of the DC pitch motor, and the current sampling uses a weighted filtering algorithm to input the acquired current value into the current loop control unit.

3. The DC pitch motor control system according to claim 1, characterized in that: It includes a speed feedback unit for detecting the operating speed of a DC pitch motor, which integrates two methods: analog speed measurement feedback and digital speed measurement feedback. The analog speed measurement feedback includes tachogenerator and resolver feedback, while the digital speed measurement feedback includes incremental encoder feedback and absolute encoder feedback.

4. A DC pitch motor control system according to any one of claims 1-3, characterized in that: The system also includes a motor stability control algorithm, which has the following characteristics: a) The speed loop control unit is used as the outer loop, and the current loop control unit is used as the inner loop; the execution cycles of the outer loop and the inner loop are different, and the fast execution of the current loop control unit and the relatively slow execution of the speed loop control unit make the loop more stable; The execution speed of the chopper output unit is higher than or equal to the execution speed of the current loop control unit, depending on the actual operating conditions. c. The execution speed of the open-loop control unit is the same as that of the current loop control unit. The chopper output unit control signal E is a piecewise function of the current loop control unit output D and the open-loop controller output C after current limiting. To ensure a smooth transition from closed-loop control to open-loop control, a transition time T2 is set. During the transition time, a weighted method is used to gradually transition to open-loop control. The weight values ​​can be adjusted according to the actual situation. Its functional relationship is as follows: E=f(D); t <T2; E= K3* f(D)+ K4* f(C); t=T2; E = f(C); t > T2; K3 and K4 are constants.

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