Single-phase induction motor water pump current-limiting VVVF control method

Abstract

The invention discloses a single-phase induction motor water pump current-limiting VVVF control method. The method comprises the following steps: step 1, sampling phase current; 2, taking the sampled phase current as an alpha axis, generating virtual beta-axis current by using a second-order generalized integrator, then adding the quadratic sum of the alpha-axis current and the quadratic sum of the beta-axis current, then dividing the quadratic sum of the alpha-axis current and the quadratic sum of the beta-axis current into a root, and calculating the amplitude of the phase current; 3, the maximum amplitude of the phase current is judged, and when the amplitude exceeds a set threshold value, the calculated phase current amplitude and a given value are subtracted and put into a single-side PI controller; and 4, adding the output of the single-side PI controller of the current limiting ring and the PI output of the voltage ring to obtain a voltage signal u, then obtaining a voltage signal and a frequency signal through frequency conversion control, and then calculating an SVPWM (Space Vector Pulse Width Modulation) driving single-phase motor through the obtained voltage signal and frequency signal. The method is obvious in control effect, easy to implement, low in hardware circuit cost and high in system stability.

Description

Technical Field

[0001] This invention belongs to the field of single-phase induction motor water pump control technology, and specifically relates to a current-limiting VVVF control method for a single-phase induction motor water pump. Background Technology

[0002] Single-phase induction motor water pumps have advantages such as compact structure, convenient operation, stable operation, and easy control, and are widely used in agricultural irrigation, domestic water supply, urban drainage, and fire protection systems. Variable Voltage Variable Frequency (VVVF) speed control is a commonly used method for controlling induction motors. It achieves smooth motor start-up and speed control by coordinating the amplitude and frequency of the input AC voltage, typically with a linear or piecewise linear relationship between the two.

[0003] In typical VVVF control of single-phase induction motor water pumps, situations such as unsuitable given voltage and frequency curves, pump startup under heavy load, increased operating resistance due to bearing or rotor failures, or sudden rotor jamming can lead to excessive motor slip, resulting in low torque and high current. Without protection, this can easily cause severe motor overheating due to overcurrent or overload, frequently triggering system overcurrent protection and even damaging the drive board due to overcurrent or overheating. Both overcurrent protection triggering and drive board damage significantly impact usability and are unacceptable for any product.

[0004] To address the issue of excessive phase current caused by various complex situations, commercially available water pumps typically employ soft-start methods. Chinese patent "A Water Pump Soft Starter Circuit" (Applicant: Chengdu Senwo Electric Co., Ltd., Application No.: CN202421231696) designs a hardware soft-start circuit to reduce starting current. Software soft-start reduces starting current by applying a smooth curve to the α-axis voltage. However, soft-start methods cannot completely solve the problem of excessive starting phase current. Furthermore, if the starting interval is very long, causing severe rotor bearing jamming, even a smooth starting curve can still result in excessive current. Additionally, if the starting curve is too slow, it can lead to long starting times, affecting the user experience.

[0005] Chinese patent "Starting Control Method, Device, and Air Conditioner for Single-Phase Asynchronous Motor" (Inventors: Chen Chong; Zeng Chunliang; Song Dechao, Application No.: CN201210062739.6) designs a soft-start method for a single-phase induction motor, using segmented driving. After each segment of the drive signal, the motor speed is detected. If the speed is lower than the set starting speed, it is determined that the start is abnormal. The second segment of the drive signal is then sent based on the difference between the actual speed and the rated speed, and the speed information is detected again. If the set speed is still not reached after several consecutive attempts, it is judged as a stalled start abnormality. This method solves the problem of speed overshoot during startup and the problem of excessive motor starting noise. However, this soft-start method does not limit the current and requires real-time monitoring of the motor speed, which increases the cost of the encoder or requires additional observer algorithms.

[0006] Chinese patent "Electronic Soft-Start Control Method for Single-Phase Asynchronous Motors" (Inventors: Chen Qiuhuang; He Jintao; Liu Yong; Zheng Lei, Application No.: 202510590420.8) designs an energy-saving soft-start method. This method adjusts the conduction time of the starting winding switch according to the motor's starting and load states to reduce unnecessary energy consumption and ensure a smooth and efficient starting process. However, this method does not control the current signal during startup, making it prone to overcurrent.

[0007] Chinese patent "A High-Performance Inverter Power Supply with Soft-Start Function for Single-Phase Asynchronous Motors" (Inventors: Long Meizhi; Wang Yu, Application No.: 201601560917.6) designs a soft-start method for single-phase induction motors. This method mainly includes a current-limiting loop module and a soft-start module. By limiting the voltage amplitude through the error between the effective value of the collected AC output current and the given value, a hardware-based control method for soft-starting single-phase induction motors is realized. The circuit structure of this method is simple and reliable, and it can limit the starting current. However, the hardware circuit design for collecting the AC current amplitude has certain costs and occupies product design space.

[0008] In practical applications, single-phase motors typically have two windings: a starting winding and a running winding. These are used to help the motor start and maintain stable operation, respectively. For small-load single-phase induction motors, these two windings are identical and can be interchanged. However, most high-power single-phase induction motors, to increase starting torque, have a smaller coil, more turns, and higher resistance in the secondary winding compared to the primary winding. This leads to asymmetry in single-phase induction motors when using VVVF vector control; the two-phase currents are not equal, and parameters cannot be calculated based on the turns ratio. Therefore, current loop control for phase current decoupling is quite complex in practical applications. Thus, limiting the starting current using a current-limiting loop by calculating the current magnitude is simpler and more stable. Furthermore, the current-limiting loop does not need to consider the asymmetry of the single-phase induction motor; it only needs to limit the larger phase current (generally referring to the current on the running winding). Currently, in induction motors, methods for calculating the current amplitude in the current-limiting loop include direct hardware current sampling and methods such as software local maximum detection. Summary of the Invention

[0009] To overcome the shortcomings of existing technologies and solve the problem of easy overcurrent during startup in single-phase induction motor water pumps, this invention proposes a current-limiting VVVF control method for single-phase induction motor water pumps that is accurate and stable. By adding a phase current sampling circuit to collect the current of a certain phase, the current-limiting VVVF control of the single-phase water pump can be completed. Furthermore, the algorithm contains an improved second-order general integrator (SOGI) that can efficiently filter the phase current, resulting in significant control effects, ease of implementation, low hardware circuit cost, and strong system stability.

[0010] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows:

[0011] A current-limiting VVVF control method for a single-phase induction motor water pump includes the following steps:

[0012] Step 1: Sample the phase current;

[0013] Step 2: Using the sampled phase current as the α-axis, a virtual β-axis current is generated using a second-order generalized integrator (SOGI). Then, the sum of the squares of the α-axis current and the β-axis current is added together and the square root is taken to calculate the amplitude of the phase current.

[0014] Step 3: Determine the maximum amplitude of the phase current. When the amplitude exceeds the set threshold, subtract the calculated phase current amplitude from the given value and input it into the single-sided PI controller. The single-sided PI controller means that the PI output result is only positive or negative. For current limiting loops, single-sided PI can make the system more reliable and stable.

[0015] Step 4: Add the output of the single-sided PI controller of the current limiting loop to the PI output of the voltage loop to obtain the voltage signal u. Then, obtain the voltage signal and frequency signal through frequency conversion control. Finally, calculate the SVPWM to drive the single-phase motor using the obtained voltage signal and frequency signal.

[0016] Furthermore, in step 1, the phase current is sampled by installing a sampling resistor on one lower arm of the single-phase drive inverter H-bridge. This is a preferred sampling method, but other phase current detection methods can also be used.

[0017] Preferably, in step 1, when designing the hardware circuit, a sampling resistor (using constantan wire) is added between one lower arm (randomly selected) of the single-phase drive inverter H-bridge and ground. Then, the two ends of the sampling resistor are connected to the operational amplifier differentially and then to the ADC sampling port of the chip. When sampling the phase current, the chip should first sample the bias.

[0018] Furthermore, in step 2, the second-order generalized integrator (SOGI) algorithm can generate a 90° phase shift in the input AC sinusoidal signal, resulting in two sinusoidal signals. SOGI can also filter out higher harmonics from the input sinusoidal signal. This invention employs an improved SOGI algorithm in the virtual phase current method, and its transfer function can be written as:

[0019]

[0020] In the formula, D(s) is the transfer function of the α-axis signal, Q(s) is the transfer function of the β-axis signal, and x is the input signal of the second-order generalized integrator. α The α-axis signal is the output of the second-order generalized integrator, x. β The β-axis signal output by the second-order generalized integrator, k b ω represents the gain of the second-order generalized integrator, and ω is the frequency of the input signal.

[0021] The improved second-order generalized integrator used in this step can eliminate the DC component of the input signal, playing a significant role in eliminating the attenuation. After obtaining the virtual β-axis current derived from the phase current and the filtered α-axis current, the amplitude I of the phase current can be calculated. m The calculation formula is:

[0022]

[0023] Furthermore, in step 3, the amplitude I of the phase current obtained in S2 is... m With the given maximum value I mref Subtract to determine I m with I mref The size of I mref <Im Enable the PI controller. Considering system reliability and safety, the maximum output value of the PI controller is set to 0, that is, the PI controller is designed as a single-sided PI with only negative output. Then the error (I) is... mref -I m The input is fed into a single-sided PI controller, and the PI controller output is obtained through PI calculation.

[0024] In step 4

[0025] After performing a PI calculation, the result of the PI calculation is added to the output of the pressure loop to obtain...

[0026] u(t)=u PIPre (t)+u PICur (t) (4);

[0027] Where u(t) is the voltage signal, u PIPre (t) represents the output of the voltage loop, u PICur (t) represents the output of the current limiting loop.

[0028] Then, based on the SVPWM modulation output duty cycle, the chip sends a drive signal to the driver chip. The driver chip controls the switching of the switching transistor, thereby generating two sinusoidal current waveforms 180° out of phase, which are then fed into the single-phase induction motor. This allows the PI controller to adjust the value of u in a timely manner when the current exceeds the rated amplitude, keeping the phase current near the given value while maintaining torque output. This allows the pump, even if the rotor is stuck, to start slowly. It is recommended to add jamming protection during this process. Excessive pump load, rusted or jammed pump rotor, or direct rotor jamming can cause the pump to remain in a starting state for an extended period, generating waveforms and torque but without the pump rotor moving, potentially damaging the pump. The action time of the current-limiting PI controller can be monitored. If the start-up time is too long, the system should stop and restart or issue a fault warning, prompting the user to shut down the motor and manually rotate the rotor.

[0029] The main features of the single-phase water pump current-limiting VVVF control method of the present invention are as follows:

[0030] 1) The current-limiting VVVF control method for single-phase water pumps only requires sampling the phase current of a single bridge arm, resulting in low hardware costs;

[0031] 2) By using an improved second-order generalized integrator to virtually generate a β-axis signal with a 90° phase difference, the DC component of the input signal can be eliminated, the amplitude attenuation can be improved, and the current limiting control of the single-phase water pump can be made more robust.

[0032] 3) Unilateral PI current limiting control is only performed when the phase current exceeds the rated value, resulting in stronger system reliability;

[0033] The beneficial effects of this invention are: it solves the problem of excessive starting current caused by rotor jamming when starting a single-phase water pump, and also ensures that the current can be limited in time when the current is too high during the operation of the water pump; only one sampling resistor is needed to occupy one ADC sampling port to realize the VVVF control method for current limiting of a single-phase water pump, and the hardware cost is low. Attached Figure Description

[0034] Figure 1 This is a control block diagram of the single-phase induction motor water pump current limiting VVVF control method of the present invention;

[0035] Figure 2 This is the sampling hardware circuit diagram of the single-phase water pump VVVF control algorithm of the present invention;

[0036] Figure 3 This is the control block diagram of the improved second-order generalized integrator;

[0037] Figure 4 This is a graph showing the phase current and the current magnitude calculated using a second-order generalized integrator.

[0038] Figure 5 This is the current measured in the experiment of this invention without the control of the current-limiting ring to trigger overcurrent protection;

[0039] Figure 6 This is the starting current controlled by the current limiting loop, which was experimentally measured in this invention. Detailed Implementation

[0040] The present invention will be further described below with reference to the accompanying drawings.

[0041] refer to Figures 1-6 A current-limiting VVVF control method for a single-phase induction motor water pump includes the following steps:

[0042] Step 1: Select a master control chip with ADC sampling, pulse width modulation (PWM) signal output, and a linkage mechanism between PWM events and the ADC sampling signal source. Here, the LCM039 is selected. Select an ADC channel as the phase current sampling channel, and select an advanced timer (e.g., TIM1-CH1 and TIM1-CH1N) to generate a PWM drive signal to control the single-phase motor. Because the phase current signal contains both positive and negative currents, the phase current bias needs to be sampled after power-on, and the sampled bias is used as the zero amplitude point of the phase current. When the chip receives the start signal, it provides a slowly increasing voltage signal and a slowly increasing frequency. At this point, the phase current already has a current signal.

[0043] Step 2: As Figure 1 , Figure 2 , Figure 3 and Figure 4As shown, the chip obtains the phase current signal by subtracting the sampling bias from the sampling signal obtained by the ADC sampling channel, and uses the sampled phase current signal as the input signal of SOGI.

[0044] The second-order generalized integrator (SOGI) algorithm can generate a 90° phase shift on the input AC sinusoidal signal, resulting in two sinusoidal signals. Furthermore, SOGI can filter out higher harmonics from the input sinusoidal signal. This invention employs an improved SOGI algorithm for the virtual phase current method, and its transfer function can be written as:

[0045]

[0046] In the formula, D(s) is the transfer function of the α-axis signal, Q(s) is the transfer function of the β-axis signal, and x is the input signal of the second-order generalized integrator. α The α-axis signal is the output of the second-order generalized integrator, x. β The β-axis signal output by the second-order generalized integrator, k b ω represents the gain of the second-order generalized integrator, and ω is the frequency of the input signal.

[0047] The improved second-order generalized integrator used in this step can eliminate the DC component of the input signal, playing a significant role in eliminating the attenuation. After obtaining the virtual β-axis current derived from the phase current and the filtered α-axis current, the amplitude I of the phase current can be calculated. m The calculation formula is:

[0048]

[0049] In practice, implementing SOGI requires first performing bilinear discretization on the SOGI transfer function;

[0050]

[0051] In the formula, T is the time constant, and the expression for the SOGI output signal obtained after discretization is:

[0052]

[0053]

[0054] In the formula, y α (k), y α (k-1), y α (k-2) represents the α-axis output signal for the k-th, (k-1)-th, and (k-2)-th beats, respectively, and x(k), x(k-1), and x(k-2) represent the input signals for the k-th, (k-1)-th, and (k-2)-th beats, respectively. β (k), y β (k-1), y β(k-2) represents the β-axis output signal for the k-th, (k-1)-th, and (k-2)-th pulses. After obtaining the α and β-axis signals, the amplitude I of the phase current is calculated according to formula (3). m :

[0055] Step 3: Calculate the amplitude I of the phase current. m Then, it is compared with the rated phase current amplitude. If the sampled phase current amplitude is greater than the rated phase current amplitude, the PI controller is enabled.

[0056] The amplitude I of the phase current obtained in S2 m With the given maximum value I mref Subtract to determine I m with I mref The size of I mref m Enable the PI controller. Considering system reliability and safety, the maximum output value of the PI controller is set to 0, that is, the PI controller is designed as a single-sided PI with only negative output. Then the error (I) is... mref -I m The input is fed into a single-sided PI controller, and the PI controller output is obtained through PI calculation.

[0057] Step 4: Add the output of the single-sided PI controller of the current limiting loop to the PI output of the voltage loop to obtain...

[0058] u(t)=u PIPre (t)+u PICur (t) (4);

[0059] Where u(t) is the voltage signal, u PIPre (t) represents the output of the voltage loop, u PICur (t) represents the output of the current limiting loop;

[0060] Then, voltage and frequency signals are obtained through frequency conversion control. SVPWM is then used to drive a single-phase motor, and SVPWM is used to generate a duty cycle to drive a single-phase water pump.

[0061] Applying the method to a single-phase water pump system, the amplitude of the extracted phase current is compared with a given value, and then applied to a voltage signal via a one-sided PI converter to limit the water pump system current. The preferred water pump system current is the starting current.

[0062] In this embodiment, the method proposed in this invention can obtain a stable phase current amplitude and achieve current limiting for the water pump system by sampling only a single phase current. It solves the problem of excessive starting current and easy start-up failure in single-phase induction motor water pump systems more simply and stably using lower hardware costs. ​

[0063] The embodiments described in this specification are merely examples of implementations of the inventive concept and are for illustrative purposes only. The scope of protection of this invention should not be considered limited to the specific forms described in these embodiments; rather, it extends to equivalent technical means conceived by those skilled in the art based on the inventive concept.

Claims

1. A current-limiting VVVF control method for a single-phase induction motor water pump, characterized in that, The method includes the following steps: Step 1: Sample the phase current; Step 2: Using the sampled phase current as the α-axis, use the improved second-order generalized integrator to simulate the β-axis virtual current of the phase current, and then calculate the phase current amplitude. Step 3: Determine the maximum amplitude of the phase current. When the amplitude exceeds the set threshold, subtract the calculated maximum amplitude from the given phase current value and input it into the current limiting loop single-sided PI controller. Step 4: Add the output of the single-sided PI controller of the current limiting loop to the PI output of the voltage loop to obtain the voltage signal u. Then, obtain the voltage signal and frequency signal through frequency conversion control. Finally, calculate the SVPWM to drive the single-phase motor using the obtained voltage signal and frequency signal.

2. The single-phase induction motor water pump current limiting VVVF control method as described in claim 1, characterized in that, In step 1, the method for sampling the phase current is as follows: a sampling resistor is installed on one of the lower arms of the single-phase drive inverter H-bridge.

3. The single-phase induction motor water pump current limiting VVVF control method as described in claim 2, characterized in that, In S1, only the phase current of a single bridge arm is collected; in S2, the phase current with a 90° phase difference is virtually generated by improving the second-order generalized integrator, and the amplitude is calculated by taking the square root of the sum of the squares.

4. The single-phase induction motor water pump current limiting VVVF control method as described in claim 3, characterized in that, In S2, the transfer function of the improved second-order generalized integrator is written in the following form: In the formula, D(s) is the transfer function of the α-axis signal, Q(s) is the transfer function of the β-axis signal, and x is the input signal of the second-order generalized integrator. α The α-axis signal is the output of the second-order generalized integrator, x. β The β-axis signal output by the second-order generalized integrator, k b ω is the gain of the second-order generalized integrator, and ω is the frequency of the input signal. After obtaining the virtual β-axis current derived from the phase current and the filtered α-axis current, the amplitude I of the phase current is calculated. m The calculation formula is:

5. The single-phase induction motor water pump current limiting VVVF control method as described in claim 4, characterized in that, In S3, the maximum amplitude I of the phase current obtained in S2 is... m With the given maximum value I mref Subtract to determine I m with I mref The size of I mref m Enable the PI controller; considering the system's reliability and safety, set the maximum output value of the PI controller to 0, that is, design the PI controller as a single-sided PI with only negative output, and then calculate the error (I0). mref -I m The input is fed into a single-sided PI controller, and the PI controller output is obtained through PI calculation.​ 6. The single-phase induction motor water pump current limiting VVVF control method as described in claim 5, characterized in that, In step S4, a PI calculation is performed, and then the result of the PI calculation is added to the output of the pressure ring to obtain... u(t)=u PIPre (t)+u PICur (t) (4); Where u(t) is the voltage signal, u PIPre (t) represents the output of the voltage loop, u PICur (t) represents the output of the current limiting loop.

7. A current-limiting VVVF control method for a single-phase induction motor water pump as described in any one of claims 1 to 6, characterized in that: When the method is applied to a single-phase water pump system, the amplitude of the extracted phase current is compared with a given value, and then applied to the voltage signal through a single-sided PI converter, thereby limiting the current of the water pump system.

8. The single-phase induction motor water pump current limiting VVVF control method as described in claim 7, characterized in that, Its features are: The current in the water pump system is the starting current.

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