Input voltage phase detection circuit for soft starter of central air conditioner

Abstract

Embodiments of the present disclosure disclose an input voltage phase detection circuit for a central air conditioner soft starter. A specific embodiment of the input voltage phase detection circuit comprises an input capacitor, a diode, a unidirectional optocoupler, a current-limiting resistor and a controller, the unidirectional optocoupler comprising a light-emitting diode and a photosensitive triode; one end of the input capacitor is electrically connected to the cathode of the diode and the anode of the light-emitting diode, and the other end is electrically connected to an input power grid; the anode of the diode and the cathode of the light-emitting diode are electrically connected, and both are electrically connected to the input power grid; one end of the current-limiting resistor is electrically connected to a pin of the controller and the collector of the photosensitive triode, and the other end is electrically connected to a power supply end of the controller; the emitter of the photosensitive triode is grounded. The embodiment smoothes the harmonic fluctuation caused by the grid voltage distortion through the cooperation of the input capacitor, the diode and the unidirectional optocoupler. Thus, the detection accuracy of the grid voltage zero-crossing signal and the voltage phase signal is improved.

Description

Technical Field

[0001] The embodiments disclosed herein relate to the field of air conditioning control technology, and more specifically to an input voltage phase detection circuit for a central air conditioning soft starter. Background Technology

[0002] Currently, central air conditioning compressors often experience high starting currents during startup, which can easily impact or even damage the power grid and other loads. To mitigate this, soft starters are commonly used to drive the compressor. The working principle is as follows: the soft starter first detects the phase of the input voltage (grid voltage), using the zero-crossing point of the grid voltage as a reference point to adjust the conduction angle of the thyristor (SCR). This gradually increases the stator voltage of the compressor motor and smoothly raises the current, ultimately achieving a soft start and reducing the impact of the starting current. Accurate detection of the zero-crossing point of the grid voltage is a crucial prerequisite for stable control of the thyristor conduction angle. Currently, phase detection circuits are commonly used to detect the zero-crossing point of the grid voltage.

[0003] However, when using commonly used phase detection circuits, the following technical problems often arise: As the proportion of nonlinear loads in the power grid increases, grid voltage distortion (the actual waveform of the grid voltage deviates from the standard sine wave) becomes more and more serious. The commonly used phase detection circuits are prone to signal distortion or loss, which makes it impossible for the controller to properly identify the zero-crossing reference point. Consequently, it cannot accurately trigger the thyristor to conduct, making it impossible for the soft starter to achieve effective soft starting. The compressor starting current will still remain at a large value, causing impact or even damage to the power grid and other loads.

[0004] The information disclosed in this background section is only intended to enhance the understanding of the background of the present disclosure concept, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0005] The summary portion of this disclosure is intended to provide a brief overview of the concepts, which will be described in detail in the detailed description portion. This summary portion is not intended to identify key or essential features of the claimed technical solutions, nor is it intended to limit the scope of the claimed technical solutions.

[0006] Some embodiments of this disclosure provide an input voltage phase detection circuit for a central air conditioning soft starter to solve one or more of the technical problems mentioned in the background section above.

[0007] Some embodiments of this disclosure provide an input voltage phase detection circuit for a central air conditioning soft starter. The input voltage phase detection circuit includes an input-side capacitor, a diode, a unidirectional optocoupler, a current-limiting resistor, and a controller. The unidirectional optocoupler includes a light-emitting diode (LED) and a phototransistor. One end of the input-side capacitor is electrically connected to both the cathode and anode of the LED. The other end of the input-side capacitor is electrically connected to the input power grid. The anode and cathode of the LED are electrically connected, and both are also electrically connected to the input power grid. One end of the current-limiting resistor is electrically connected to both a pin of the controller and the collector of the phototransistor. The other end of the current-limiting resistor is electrically connected to the power supply terminal of the controller. The emitter of the phototransistor is grounded.

[0008] Optionally, the diode described above can be a switching diode or a rectifier diode.

[0009] Optionally, the input-side capacitor is a safety capacitor or a polyester film capacitor.

[0010] Optionally, the aforementioned input voltage phase detection circuit is integrated into the soft starter of the central air conditioner, and the output terminal of the aforementioned controller is connected to the gate drive circuit of the thyristor inside the aforementioned soft starter.

[0011] Optionally, the controller is configured to perform the following steps: capturing voltage zero-crossing pulse signals at a preset frequency; recording the timestamps corresponding to each voltage zero-crossing pulse signal captured consecutively within a preset time period to obtain a timestamp set; in response to the number of timestamps in the timestamp set being greater than a preset value, generating a time interval between every two adjacent timestamps in the timestamp set based on the timestamp set to obtain a time interval set; sorting the time intervals in the time interval set to obtain a sorted time interval set; performing extremum removal processing on the sorted time interval set to obtain an extremum-removed time interval set; generating an average time interval value based on the extremum-removed time interval set; and generating the frequency value of the input power grid based on the average time interval value.

[0012] Optionally, the controller is also configured to perform the following steps: generating a capture time window based on the frequency value.

[0013] Optionally, the controller is further configured to perform the following steps: in response to capturing a voltage zero-crossing pulse signal within the capture time window, determining the timestamp corresponding to the captured voltage zero-crossing pulse signal as the wave transmission reference point.

[0014] Optionally, the controller is further configured to perform the following steps: in response to the failure to capture a voltage zero-crossing pulse signal within the capture time window, determine a wave transmission reference point based on the frequency value and the timestamp corresponding to the previously captured voltage zero-crossing pulse signal.

[0015] Some embodiments of this disclosure provide an input voltage phase detection circuit for a central air conditioning soft starter, which can improve the detection accuracy of the grid voltage zero-crossing signal, thereby improving the triggering accuracy of the soft starter for the thyristor (SCR), achieving smooth soft starting of the compressor, and ultimately reducing the risk of damage to the grid and other loads on the grid. Specifically, the reason why most voltage phase detection circuits have poor detection accuracy for the grid voltage zero-crossing signal is that: as the proportion of nonlinear loads in the grid increases, grid voltage distortion becomes more severe, and existing commonly used phase detection circuits lack targeted anti-interference design, making them susceptible to harmonic interference generated by voltage distortion, detecting false zero-crossing signals, and causing abnormal thyristor triggering. Based on this, some embodiments of this disclosure provide an input voltage phase detection circuit for a central air conditioning soft starter. The input voltage phase detection circuit includes an input-side capacitor, a diode, a unidirectional optocoupler, a current-limiting resistor, and a controller. The unidirectional optocoupler includes a light-emitting diode (LED) and a phototransistor. One end of the input-side capacitor is electrically connected to both the cathode and anode of the LED. The other end of the input-side capacitor is electrically connected to the input power grid. The anode and cathode of the LED are electrically connected, and both are also electrically connected to the input power grid. One end of the current-limiting resistor is electrically connected to both a pin of the controller and the collector of the phototransistor. The other end of the current-limiting resistor is electrically connected to the power supply terminal of the controller. The emitter of the phototransistor is grounded. By employing a combination of an input-side capacitor, a diode, and a unidirectional optocoupler, a "current threshold" mechanism for zero-crossing detection is constructed. The input-side capacitor smooths harmonic fluctuations caused by grid voltage distortion through charging and discharging, while the diode blocks reverse current interference through its unidirectional conduction characteristic, allowing only effective forward or reverse charging / discharging current to flow through the unidirectional optocoupler. Furthermore, a pulse signal is generated only when this charging / discharging current reaches the conduction threshold of the unidirectional optocoupler. This mechanism can filter out minute fluctuations caused by harmonics (i.e., false zero-crossing signals). Therefore, the detection accuracy of grid voltage zero-crossing signals can be improved. Attached Figure Description

[0016] The above and other features, advantages, and aspects of the embodiments of this disclosure will become more apparent from the accompanying drawings and the following detailed description. Throughout the drawings, the same or similar reference numerals denote the same or similar elements. It should be understood that the drawings are schematic, and elements are not necessarily drawn to scale.

[0017] Figure 1This is a circuit diagram of an input voltage phase detection circuit for a central air conditioning soft starter according to some embodiments of this disclosure; Figure 2 This is a schematic diagram of the zero-crossing signal detected by the input voltage phase detection circuit for a central air conditioning soft starter according to some embodiments of this disclosure. Detailed Implementation

[0018] Embodiments of this disclosure will now be described in more detail with reference to the accompanying drawings. While some embodiments of this disclosure are shown in the drawings, it should be understood that this disclosure can be implemented in various forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the accompanying drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0019] It should also be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings. Unless otherwise specified, the embodiments and features described in this disclosure can be combined with each other.

[0020] It should be noted that the concepts of "first" and "second" mentioned in this disclosure are used only to distinguish different devices, modules or units, and are not used to limit the order of functions performed by these devices, modules or units or their interdependencies.

[0021] It should be noted that the terms "a" and "a plurality of" used in this disclosure are illustrative rather than restrictive, and those skilled in the art should understand that, unless otherwise expressly indicated in the context, they should be understood as "one or more".

[0022] This disclosure will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] Figure 1 This is a circuit diagram of an input voltage phase detection circuit for a central air conditioning soft starter according to some embodiments of the present disclosure. Figure 1 It includes input-side capacitor 1, diode 2, unidirectional optocoupler 3, and current-limiting resistor 4.

[0024] In some embodiments, the input voltage phase detection circuit may include an input-side capacitor 1, a diode 2, a unidirectional optocoupler 3, a current-limiting resistor 4, and a controller. The input-side capacitor 1 can be a capacitor directly connected to the input power grid at one end. The input-side capacitor 1 can smooth fluctuations in the input power grid voltage during the charging and discharging process, especially buffering harmonic interference caused by power grid distortion, providing a stable current basis for zero-crossing detection. Its capacitance value can be flexibly selected according to the power grid voltage level and detection accuracy requirements, and is not specifically limited here. The current-limiting resistor 4 can be a resistor used to limit the current flowing through the controller. The current-limiting resistor 4 can keep the current within the rated input range of the controller, reducing the risk of damage to the controller due to excessive current. The resistance value of the current-limiting resistor 4 can be preset according to the pin parameters of the controller, and is not specifically limited here. The controller can be a microcontroller (MCU), and is not specifically limited here. The controller can be used to determine whether the detected voltage zero-crossing signal is valid. The aforementioned unidirectional optocoupler 3 may include a light-emitting diode (LED) and a phototransistor. The LED serves as the signal transmitting element on the primary side of the optocoupler, generating an optical signal when energized. The phototransistor serves as the signal receiving element on the secondary side of the optocoupler, conducting upon sensing the optical signal from the primary side, thus converting the optical signal into an electrical signal and simultaneously achieving electrical isolation between the power grid side and the controller side. One end of the input-side capacitor 1 can be electrically connected to both the cathode of the diode 2 and the anode of the LED. The other end of the input-side capacitor 1 can be electrically connected to the input power grid, directly receiving the power grid voltage signal and converting changes in the power grid voltage into changes in its own charging and discharging state, providing a prerequisite for subsequent signal conversion. The anode of the diode 2 can be electrically connected to the cathode of the LED, and both can be electrically connected to the input power grid (i.e., the end not directly connected to the input-side capacitor). The diode 2 utilizes its unidirectional conduction characteristic, allowing current to flow only in a specific direction, blocking reverse current interference to the primary side of the unidirectional optocoupler 3, and improving the matching degree between the triggering logic of the optical signal and the phase change of the power grid voltage. One end of the aforementioned current-limiting resistor 4 can be electrically connected to both a pin of the controller and the collector of the phototransistor. The other end of the current-limiting resistor 4 can be electrically connected to the power supply terminal of the controller. The power supply terminal refers to the port used to supply power to the controller. The emitter of the phototransistor can be grounded to form a complete signal loop, allowing the electrical signal generated when the phototransistor is turned on to be transmitted to the controller. Furthermore, central air conditioning systems typically require three-phase power for operation; therefore, three sets of the aforementioned input voltage phase detection circuits can be installed to simultaneously detect the zero-crossing pulse signal of each phase of the three-phase power supply.It should be noted that the three sets of input voltage phase detection circuits for detecting three-phase electricity can share the same controller. The ports in each of the three sets of input voltage phase detection circuits that need to be electrically connected to the controller pins can be electrically connected to three independent input pins of the same controller.

[0025] Optionally, diode 2 can be either a switching diode or a rectifier diode. Switching diodes are characterized by fast response speed, quickly switching on or off according to the phase change of the mains voltage, thus meeting the real-time requirements of zero-crossing detection. Rectifier diodes offer advantages such as stable unidirectional conductivity and a wide voltage rating range, maintaining stable operation under different mains voltage levels and distortion scenarios. The two types of diodes can be flexibly selected based on the specific application scenario and performance requirements of the circuit; no specific limitations are imposed here.

[0026] Optionally, the input-side capacitor 1 can be a safety capacitor or a polyester film capacitor. Safety capacitors are characterized by high voltage resistance, excellent insulation performance, and high safety, and can adapt to fluctuations in mains voltage and instantaneous high-voltage surges. Polyester film capacitors have the advantages of rapid charging and discharging response, good capacitance stability, and low loss, which can improve the accuracy of transmitting phase change information of the mains voltage.

[0027] Optionally, the aforementioned input voltage phase detection circuit can be integrated into the soft starter of the central air conditioner. This integrated design saves internal installation space in the soft starter, simplifies the overall wiring structure, and reduces the impact of line interference on the detection signal. The output of the controller can be connected to the gate drive circuit of the thyristor inside the soft starter. The controller can convert the captured and processed zero-crossing signal into a corresponding electrical signal, which is then transmitted to the thyristor via the gate drive circuit. This provides a phase reference for adjusting the thyristor's conduction angle, ensuring that the thyristor's conduction state matches the phase of the mains voltage, thereby assisting the soft starter in achieving a smooth compressor start.

[0028] Optionally, the controller described above can be configured to perform the following steps: The first step is to capture the voltage zero-crossing pulse signal according to a preset frequency. This voltage zero-crossing pulse signal can refer to the low-level pulse signal generated by the input voltage phase detection circuit of the central air conditioning soft starter, corresponding to the zero-crossing point of the mains voltage. (See reference here.) Figure 2 , Figure 2 This is a schematic diagram of the zero-crossing signal detected by the input voltage phase detection circuit for a central air conditioning soft starter according to some embodiments of this disclosure. It should be noted that... Figure 2The coordinate system shown illustrates the relationship between voltage and time, with the horizontal axis representing time and the vertical axis representing voltage. When the voltage curve crosses the horizontal axis, a zero-crossing pulse signal is generated. This zero-crossing pulse signal can be used to reflect the moment when the grid voltage crosses 0V within a sine wave cycle. The preset frequency refers to the fixed sampling frequency at which the controller captures the pulse signal. For example, the preset frequency can be higher than twice the grid frequency to reduce the risk of missing true pulses; such as a preset frequency of 150Hz. In practice, the controller can capture the zero-crossing pulse signal according to the preset frequency.

[0029] The second step involves recording the timestamps corresponding to each voltage zero-crossing pulse signal captured consecutively within a preset time period, thus obtaining a timestamp set. The timestamps can refer to the real-time count value (unit: μs) of the controller's internal timer. The preset time can refer to the pre-set acquisition duration to obtain a sufficient number of valid pulse signals. For example, the preset time can be 100ms, without specific limitation. The timestamp set can be an array storing the timestamps corresponding to all captured pulse signals. The array in the timestamp set can be stored sequentially according to the capture order. In practice, after capturing a voltage zero-crossing pulse signal, the controller can read the timer value and determine this value as the timestamp of the captured voltage zero-crossing pulse signal. The timestamps corresponding to each voltage zero-crossing pulse signal captured within the preset time period are compiled into an array, and this array is defined as the timestamp set.

[0030] The third step involves generating a time interval set based on the timestamp set, in response to the number of timestamps in the timestamp set exceeding a preset value. The preset value can refer to a minimum number of timestamps, such as three, set to improve the accuracy of subsequent steps. A larger number of timestamps in the timestamp set improves the accuracy of subsequent calculations of the input power grid frequency. The time interval set can be an array storing the differences between all adjacent timestamps. The number of elements in the time interval set can be equal to the number of elements in the timestamp set minus one. In practice, the controller can iterate through the timestamp set using a loop, calculating the differences between adjacent elements and storing them in the time interval set. The calculation logic for the time interval can be subtracting the previous timestamp from the next timestamp.

[0031] The fourth step is to sort the time intervals in the time interval set to obtain a sorted time interval set. The sorting can be in ascending or descending order. Sorting facilitates the rapid identification and removal of outliers in subsequent steps. The sorted time interval set refers to a set of time intervals whose elements are arranged in ascending or descending order. In practice, the controller can use the bubble sort algorithm to sort the time intervals in the time interval set to obtain the sorted time interval set. For example, if the time interval set is [9800μs, 10200μs, 9900μs, 10100μs, 10000μs, 9700μs, 10300μs, 9950μs, 10050μs], the sorted time interval set after ascending order is [9700μs, 9800μs, 9900μs, 9950μs, 10000μs, 10050μs, 10100μs, 10200μs, 10300μs].

[0032] The fifth step is to perform extremum removal processing on the sorted time interval set to obtain the extremum-removed time interval set. The extrema mentioned above can refer to the maximum and minimum values ​​in the sorted time interval set. This type of data is usually caused by power grid distortion (such as harmonic interference) or pulse signal interference. This type of data is considered anomalous, and retaining it will affect the accuracy of subsequent frequency calculations. The extremum removal method can be the first and last value removal method, that is, removing the first and last values ​​in the sorted time interval set. The specific number of elements removed at each end can be preset by the operator. For example, if the sorted time interval set is [9700μs, 9800μs, 9900μs, 9950μs, 10000μs, 10050μs, 10100μs, 10200μs, 10300μs], then the time interval set after extremum removal processing can be [9800μs, 9900μs, 9950μs, 10000μs, 10050μs, 10100μs, 10200μs].

[0033] Step 6: Generate the average time interval based on the time interval set after removing extrema. This average time interval can refer to the average of all time intervals in the time interval set after removing extrema. In practice, the controller can divide the sum of all time intervals in the time interval set after removing extrema by the number of time intervals in the set to obtain a quotient, which is then determined as the average time interval. For example, if the set of time intervals after removing extrema is [9800μs, 9900μs, 9950μs, 10000μs, 10050μs, 10100μs, 10200μs], then the number of time intervals contained in this set is 7. The sum of all time intervals in this set is 9800+9900+9950+10000+10050+10100+10200=70000μs. Therefore, the average time interval is 70000μs / 7=10000μs. This average time interval reflects the average time interval of the collected voltage zero-crossing pulse signals and serves as a reference for subsequent calculations of the power grid frequency.

[0034] Step 7: Generate the frequency value of the input power grid based on the average time interval. The voltage of the input power grid is a sine wave, and the time interval between adjacent zero-crossing points is half a cycle. Therefore, the grid period is twice the average time interval. Since the period and frequency are inversely related, the grid frequency value is 1 / (2 × average time interval). In practice, the controller can convert the unit of the average time interval to seconds, and then substitute the converted average time interval into the following formula to obtain the frequency value of the input power grid: Frequency value = 1 / (2 × average time interval) The frequency value mentioned above can refer to the frequency value of the input power grid, and the average time interval can refer to the average time interval after converting the unit to seconds. For example, if the average time interval is 10000μs, or 0.01s, then the period of the input power grid is 2×0.01s=0.02s, and the frequency value of the input power grid is 1 / 0.02s=50Hz.

[0035] Alternatively, the controller described above can also be configured to perform the following steps: The first step is to generate a capture time window based on the frequency value. The frequency value can refer to the frequency of the input power grid. The capture time window can be a fixed time range set to filter voltage zero-crossing pulse signals. This capture time window can be used to filter false voltage zero-crossing pulse signals caused by power grid distortion, and can assist the controller in capturing valid signals that conform to the power grid's periodic patterns. In practice, the controller can generate a capture time window based on the frequency value through the following steps: Step one: Based on the frequency value of the input power grid, generate the input power grid half-cycle. In practice, the controller described above can substitute the frequency value of the input power grid into the following formula to obtain the input power grid half-cycle: Power grid half-cycle = 1 / (2 × frequency value) The aforementioned grid half-cycle can refer to half-cycle of the input grid, and the aforementioned frequency value can refer to the frequency value of the input grid. For example, when the aforementioned frequency value is 50Hz, the aforementioned grid half-cycle is 0.01 seconds.

[0036] Step two: Multiply the input grid half-cycle by a preset percentage to obtain the window radius. This preset percentage can be set by the operator, for example, 10%, and is not specifically limited here. The window radius can refer to half the total duration of the capture time window, representing the time length. For example, if the input grid half-cycle is 10 milliseconds and the preset percentage is 10%, then the window radius is 1 millisecond, indicating that the total duration of the capture time window to be generated is 2 milliseconds.

[0037] Step 3: Add the timestamp corresponding to the previously captured voltage zero-crossing pulse signal to half the input grid cycle to obtain the theoretical zero-crossing time. The theoretical zero-crossing time can refer to the time when the voltage crosses zero when the input voltage is a standard sine wave. For example, if the timestamp corresponding to the previously captured voltage zero-crossing pulse signal is 9800μs, and the half-cycle of the input grid is 10 milliseconds (10000μs), then the theoretical zero-crossing time is 9800μs + 10000μs = 19800μs.

[0038] Step four: Using the theoretical zero-crossing time as the center, extend the window radius by one unit before and after it to obtain the capture time window. For example, if the theoretical zero-crossing time is 19800μs and the window radius is 1 millisecond (1000μs), then the time interval [18800, 20800] is the capture time window.

[0039] Alternatively, the controller described above can also be configured to perform the following steps: First step, in response to capturing a voltage zero-crossing pulse signal within the capture time window, determine the timestamp corresponding to the captured voltage zero-crossing pulse signal as the wave generation reference point. Herein, the above-mentioned wave generation reference point may refer to the specific moment when the input grid voltage crosses zero, which can be represented by the timestamp corresponding to the voltage zero-crossing pulse signal. The above-mentioned wave generation reference point can characterize the starting time of sending a driving pulse to the thyristor. In practice, the above-mentioned controller can store the timestamp corresponding to the voltage zero-crossing pulse signal captured within the capture time window into a dedicated variable of the wave generation reference point. By screening through the capture time window, the synchronization between the wave generation reference point and the true zero-crossing point of the power grid can be improved, and the interference of false pulses can be reduced.

[0040] Optionally, the above-mentioned controller can also be configured to perform the following steps: First step, in response to not capturing a voltage zero-crossing pulse signal within the capture time window, determine the wave generation reference point based on the frequency value and the timestamp corresponding to the last captured voltage zero-crossing pulse signal. In the scenario where a voltage zero-crossing pulse signal is not captured, it is usually due to severe distortion of the power grid (such as strong harmonic superposition, voltage dip), resulting in the detection circuit not generating an effective pulse, or the pulse signal exceeding the capture time window. The above-mentioned frequency value can be the frequency value of the above-mentioned input power grid. In practice, the above-mentioned controller obtains the theoretical zero-crossing time through the frequency value and the timestamp corresponding to the last captured voltage zero-crossing pulse signal in the manner described in the first step to the third step above, and determines the obtained theoretical zero-crossing time as the wave generation reference point.

[0041] In the process of adopting the technical solution to solve the technical problems in the above-mentioned background technology, for the application scenarios to be applied: large central air-conditioning water systems with multiple compressors in parallel, such as large factories, commercial complexes, and transportation hubs. There are often the following technical problems: large central air-conditioning water systems with multiple compressors in parallel have relatively high requirements for the consistency of multi-machine synchronous startup. In the current commonly used detection circuits, the synchronization is prone to failure in the usage scenario of multiple compressors in parallel, which may burn out the compressor motor. For the following required characteristics of this application scenario: adapting to the demand for multi-machine parallel three-phase synchronous start-stop control, adapting to the stable operation demand of component parameter long-term drift, and adapting to the power grid load fluctuation demand of compressor loading and unloading, we decided to adopt the following solution: Optionally, the above-mentioned input voltage phase detection circuit can also include two sets of sub-branch circuits. The two sets of sub-branch circuits can be three-phase detection branches supporting the main detection branch, and are used to cooperate with the main detection branch to complete the voltage phase detection of the three-phase power grid. The above-mentioned main detection branch can refer to Figure 1The circuit corresponding to the aforementioned input voltage phase detection circuit is the circuit after removing the aforementioned controller. Each of the two sets of secondary branch circuits can have the same structure as the aforementioned main detection branch. The aforementioned main detection branch and the two sets of secondary branch circuits can be independently connected to different pins of the aforementioned controller. The different pins of the aforementioned controller can be independent external interrupt capture pins on the controller. The two sets of secondary branch circuits can maintain the same signal transmission characteristics as the aforementioned main detection branch to ensure unified processing of the three detection signals. The input terminals of the aforementioned input-side capacitor and the two sets of secondary branch circuits can be connected to the three phase lines of the input power grid. The three phase lines of the input power grid can be the R-phase, S-phase, and T-phase of a three-phase power grid. The input terminal of the aforementioned input-side capacitor can be connected to one of the phase lines, and the input terminals of the two sets of secondary branch circuits can be connected to the other two phase lines to achieve voltage phase detection for each phase line of the three-phase power grid. Both sets of secondary branch circuits can be grounded together with the emitter of the aforementioned phototransistor. The aforementioned common grounding design allows the two sets of secondary branch circuits and the main detection branch to share the same potential reference, ensuring consistency in the potential references of the three detection signals. The input-side capacitor can be a metallized film capacitor. Metallized film capacitors possess low dielectric loss and good frequency characteristics, enabling stable voltage signal transmission in AC circuits, making them suitable for grid voltage phase detection applications. A temperature sensor can be installed in the mounting area of ​​the input-side capacitor and the unidirectional optocoupler, and the data output terminal of the temperature sensor can be connected to the controller. The temperature sensor can be a surface-mount digital temperature sensor used to collect ambient temperature data from the mounting area of ​​the input-side capacitor and the unidirectional optocoupler. The data output terminal of the temperature sensor can be connected to the corresponding pin of the controller via a serial communication line, allowing the controller to receive the temperature data transmitted by the temperature sensor. A DC resistor and a power inductor can be connected in series before the input terminals of the input-side capacitor and the two sets of secondary branch circuits. The DC resistor can be a metal film resistor, and the power inductor can be a wire-wound power inductor; their series connection forms an input filter circuit for processing the input grid voltage signal. Signal shaping circuits composed of Schmitt trigger mode comparators can be provided between the collector of the aforementioned phototransistor and the pin of the aforementioned controller, and between the two sets of secondary branch circuits and the pin of the aforementioned controller. These signal shaping circuits can primarily consist of Schmitt trigger mode comparators, which can have a positive input terminal, an inverting input terminal, and an output terminal. The positive or inverting input terminal can be connected to a reference voltage. The output terminal of the aforementioned phototransistor can be connected to the other input terminal of the comparator, and the output terminal of the comparator can be connected to the pin of the aforementioned controller. The reference voltage can serve as the voltage threshold for the comparator.The comparator in the Schmitt trigger mode described above can be a single-threshold comparator with hysteresis characteristics. The signal shaping circuit described above can smooth the waveform of the irregular voltage signal output by the phototransistor, converting the fluctuating and ambiguous voltage signal into a square wave signal with clear edges and regularity, making it easier for the controller to identify and capture the voltage zero-crossing pulse signal.

[0042] The above-mentioned optional embodiments, as an inventive point of this disclosure, solve the technical problem that "currently commonly used detection circuits are prone to synchronization failure in multi-compressor parallel operation scenarios." The specific factors causing the synchronization failure of currently commonly used detection circuits in multi-compressor parallel operation scenarios are as follows: In scenarios such as large commercial complexes, the central air conditioning water system dynamically changes in real time according to the scale of customer flow and outdoor temperature and humidity to match dynamic cooling demand and take energy saving into account. This causes the compressors to frequently perform load increase and decrease operations, which in turn causes grid voltage fluctuations and harmonic interference, resulting in different degrees of distortion and timing disorder of the three-phase detection signals. If the above factors are solved, the synchronization of the detection circuit can be improved in multi-compressor parallel operation scenarios. To achieve this effect, this disclosure also provides a three-phase synchronous detection scheme for multi-compressor parallel operation scenarios. On the one hand, it adopts a three-way completely isomorphic design of the main detection branch and two sets of auxiliary branch circuits, coupled with independent capture pins and a common ground reference, unifying the transmission path and potential reference of the three-phase signals from a hardware structure perspective, weakening the synchronization deviation caused by structural and parameter dispersion. On the other hand, a filter circuit composed of an input stage DC resistor and a power inductor suppresses grid fluctuation interference, while a Schmitt trigger mode comparator normalizes the signal waveform. Combined with environmental data collected by a temperature sensor, this provides support for parameter stability and reduces the impact of component drift and signal distortion on synchronization. Therefore, in scenarios with multiple compressors operating in parallel, the synchronization of the detection circuit is improved.

[0043] In addressing the common problem of synchronization failure in currently used detection circuits, the application scenario—a large central air conditioning water system with multiple compressors in parallel—often presents the following additional technical challenges: currently used detection circuits suffer from poor phase detection accuracy due to component temperature drift that cannot be compensated for during long-term operation. To meet the specific requirements of this application scenario—real-time dynamic compensation for component temperature drift, stable detection accuracy under high and low temperature environments, and automatic correction for long-term parameter drift—we have decided to adopt the following solution: Alternatively, the controller described above can also be configured to perform the following steps: The first step is to collect ambient temperature data of the installation area using a temperature sensor to obtain the ambient temperature value. The installation area can refer to the area on the circuit board where the input capacitor and the unidirectional optocoupler are mounted. The ambient temperature value can be temperature data stored numerically in the controller, for example, 30°C. In practice, the controller can read the temperature signal transmitted by the temperature sensor at a preset sampling frequency, convert the analog temperature signal into a digital signal, and obtain the ambient temperature value. The preset sampling frequency can be once every 100 milliseconds, and is not specifically limited here.

[0044] The second step involves dynamically compensating for the capacitance drift of the input-side capacitor, the forward voltage drop drift of the LED, and the current transfer ratio drift of the phototransistor based on the difference between the ambient temperature and the preset reference temperature. The preset reference temperature can be a temperature value (e.g., 25°C) pre-stored by the operator in the controller. The difference can be the temperature deviation obtained by subtracting the preset reference temperature from the ambient temperature. The capacitance drift of the input-side capacitor refers to the capacitance deviation of the metallized film capacitor due to temperature changes. The forward voltage drop drift of the LED refers to the deviation of the LED's forward voltage in the unidirectional optocoupler due to temperature changes. The current transfer ratio drift of the phototransistor refers to the deviation of the phototransistor's current amplification capability due to temperature changes. The dynamic compensation refers to the controller adjusting the circuit detection parameters accordingly based on the temperature deviation. In practice, the controller can use the calculated temperature difference to call pre-stored temperature compensation coefficients to correct the capacitance drift, forward voltage drop drift, and current transfer ratio drift, thereby adjusting the circuit's detection parameters. The temperature compensation coefficients can be fixed offset values ​​for the input capacitor, LED, and phototransistor per 1°C change in temperature; these are standard correction parameters pre-stored in the controller. The controller can multiply the temperature compensation coefficients by the temperature difference to quickly calculate the drift amount, then perform a reverse correction to complete the compensation. For example, if the preset reference temperature is 25°C and the controller collects an ambient temperature of 55°C, the calculated temperature difference is 30°C. The temperature compensation coefficients are recorded as follows: the temperature compensation coefficient for the metallized film capacitor is 0.02μF per 1°C; the temperature compensation coefficient for the forward voltage drop of the LED is 2mV per 1°C; and the temperature compensation coefficient for the current transfer ratio of the phototransistor is 0.1% per 1°C. For a temperature difference of 30°C, the capacitance drift of the input capacitor can be corrected in reverse, the forward voltage drop drift can be compensated accordingly, and the current transfer ratio drift can be calibrated and adjusted. A compensation resistor can be connected in series with the input terminals of the input capacitor and the two sets of secondary circuits. This compensation resistor, together with the temperature sensor and the controller, forms a temperature compensation circuit, allowing the controller to adjust the operating parameters of the compensation resistor to offset the temperature-induced parameter shifts in the input capacitor, the LED, and the phototransistor, thus maintaining stable operating parameters of the phase detection circuit. The compensation resistor can be a precision low-temperature drift resistor. A temperature-coefficient matching Zener diode can be connected in parallel across the unidirectional optocoupler and the LEDs in the two sets of secondary circuits.The aforementioned temperature-coefficient matched Zener diode can be a Zener diode adapted to the temperature variation characteristics of the aforementioned LED. Connected in parallel across the LED, it allows for corresponding adjustments to the LED's operating parameters based on temperature changes. A constant current resistor can be connected in series between the collector of the phototransistor, the two sets of secondary branch circuits, and the signal shaping circuit. This constant current resistor can be a high-precision metal film resistor; its series connection in the circuit stabilizes the current output by the phototransistor, improving the stability of the electrical signal transmitted to the signal shaping circuit.

[0045] The above-mentioned optional embodiments, as an inventive point of this disclosure, solve the technical problem that "currently commonly used detection circuits suffer from poor phase detection accuracy due to component temperature drift and inability to compensate for it during long-term operation." The specific factors causing poor phase detection accuracy due to component temperature drift and inability to compensate for it during long-term operation are as follows: Under long-term continuous operation, the circuit's operating environment is prone to temperature fluctuations, and core components such as the input-side capacitor will experience significant temperature drift with temperature changes. Furthermore, parameter aging drift will occur after long-term operation. Solving these factors can improve the poor phase detection accuracy under long-term operation. To achieve this effect, this disclosure also provides a solution adapted to long-term operation. On one hand, a temperature sensor collects the ambient temperature in real time, and performs real-time dynamic compensation for the capacitance drift of the input-side capacitor, the forward voltage drop drift of the light-emitting diode, and the current transfer ratio drift of the phototransistor. This, combined with a compensation resistor, forms a temperature compensation circuit to complete the real-time correction of component temperature drift. On the other hand, by connecting a temperature-coefficient-matched Zener diode in parallel across the LED and a constant-current resistor in series between the phototransistor and the signal shaping circuit, the operating parameters of the components are stabilized at the hardware level. This adapts to fluctuating temperature environments, suppresses parameter aging drift during long-term operation, and reduces signal distortion. This improves the technical problem of poor phase detection accuracy.

[0046] In addressing the technical challenges mentioned above, the application scenarios, such as hospitals and data centers, often present additional technical issues. These scenarios have zero downtime tolerance. For example, in a data center, an air conditioning outage can lead to server crashes and data loss. Currently used detection circuits suffer from insufficient power switching and detection redundancy in these critical load scenarios, resulting in abnormal phase detection. Considering the following requirements for this application scenario: continuous phase tracking adaptable to seamless dual-power switching, stable undervoltage and overvoltage detection across a wide voltage range, and synchronous detection with dual-redundant hot standby for critical loads, we have decided to adopt the following solution: Optionally, the above input voltage phase detection circuit may also be provided with a backup detection circuit. The backup detection circuit may be a redundant detection branch配套 with the main detection circuit, and is used to undertake the relevant work of voltage phase detection when the main detection circuit fails. The backup detection circuit may have the same structure as the input voltage phase detection circuit and may share the above controller. The backup detection circuit may have the same signal processing characteristics as the input voltage phase detection circuit. Sharing the above controller can make the processing and calculation process of the detection signal unified. The output ends of the backup detection circuit and the above phototransistor may be independently electrically connected to the dual-channel synchronous capture pins of the above controller, and an independent signal shaping circuit may be provided at the front end of each capture pin. The dual-channel synchronous capture pins may be two independent and synchronously triggerable external interrupt pins on the above controller, respectively used to receive the electrical signals transmitted by the main detection circuit and the backup detection circuit. The above independent Schmitt trigger type signal shaping circuit can respectively shape the input signals of the corresponding pins, and the processing processes of the two signals do not interfere with each other. The signal shaping circuit may be the signal shaping circuit composed of a comparator in the Schmitt trigger mode, which can convert the fluctuating and fuzzy analog signal output by the phototransistor into a regular square wave signal with clear edges, facilitating the above controller to accurately capture the voltage zero-crossing signal. An isolation circuit may be provided between the backup detection circuit and the input voltage phase detection circuit. The isolation circuit may be an optoelectronic isolation circuit, which is used to separate the electrical circuits of the backup detection circuit and the input voltage phase detection circuit and reduce the signal crosstalk between the two circuits. The input voltage phase detection circuit may be correspondingly connected to the main power supply, and the backup detection circuit may be correspondingly connected to the standby power supply. The main power supply may be the normal working power supply of the central air-conditioning soft starter, and the standby power supply may be the supporting power supply under emergency conditions. The two power supplies respectively provide power support for the corresponding detection circuits. Isolation diodes may be connected in series at the front ends of the input side capacitors of the input voltage phase detection circuit and the backup detection circuit. The isolation diodes may be unidirectional conduction rectifier diodes. Connected in series at the front end of the input side capacitor, they can limit the unidirectional conduction of the input electrical signal and prevent reverse current from flowing into the circuit. The input side capacitors of the input voltage phase detection circuit and the backup detection circuit may both be safety capacitors, and bidirectional transient voltage suppressor diodes may be connected in parallel at both ends. The safety capacitor has good voltage resistance characteristics and can adapt to a wide range of input voltage conditions. When the power grid has under-voltage and over-voltage fluctuations, it can stably transmit voltage signals and reduce the possibility of components being broken down. The bidirectional transient voltage suppressor diodes may be connected in parallel at both ends of the input side capacitor and are used to process the instantaneous voltage spike signals in the input circuit.

[0047] The above-mentioned optional embodiments, as an inventive point of this disclosure, solve the technical problem that "currently commonly used detection circuits are prone to phase detection anomalies." The specific factors causing these anomalies are as follows: commonly used detection circuits employ only a single-channel detection structure without redundant backup design; phase detection is prone to interruptions during dual-power supply switching; and they lack wide-voltage protection devices. During the switching of primary and backup power supplies, instantaneous voltage fluctuations can occur, leading to short-term undervoltage or overvoltage, which can easily cause signal distortion and component damage. Solving these factors can improve the stability of the phase detection function. To achieve this, this disclosure also provides a dual-power supply redundant wide-voltage phase detection scheme for critical load scenarios. On one hand, it adopts a dual-channel isomorphic design for the primary and backup detection circuits, corresponding to the primary and backup power supplies respectively. Combined with the controller's dual-channel synchronous capture pins and independent shaping circuit, it achieves continuous phase tracking during dual-power supply switching, meeting the synchronous detection requirements of dual-channel redundant hot standby for critical loads. On the other hand, a wide-voltage protection and unidirectional conduction circuit is constructed using safety capacitors, bidirectional transient suppression diodes, and isolation diodes. Combined with opto-isolation circuits to block signal crosstalk, this system adapts to undervoltage, overvoltage fluctuations, and voltage spikes in the power grid, stabilizing signal transmission. This improves the stability of the phase detection function.

[0048] Some embodiments of this disclosure provide an input voltage phase detection circuit for a central air conditioning soft starter, which can improve the detection accuracy of the grid voltage zero-crossing signal, thereby improving the triggering accuracy of the soft starter for the thyristor (SCR), achieving smooth soft starting of the compressor, and ultimately reducing the risk of damage to the grid and other loads on the grid. Specifically, the reason why most voltage phase detection circuits have poor detection accuracy for the grid voltage zero-crossing signal is that: as the proportion of nonlinear loads in the grid increases, grid voltage distortion becomes more severe, and existing commonly used phase detection circuits lack targeted anti-interference design, making them susceptible to harmonic interference generated by voltage distortion, detecting false zero-crossing signals, and causing abnormal thyristor triggering. Based on this, some embodiments of this disclosure provide an input voltage phase detection circuit for a central air conditioning soft starter. The input voltage phase detection circuit includes an input-side capacitor, a diode, a unidirectional optocoupler, a current-limiting resistor, and a controller. The unidirectional optocoupler includes a light-emitting diode (LED) and a phototransistor. One end of the input-side capacitor is electrically connected to both the cathode and anode of the LED. The other end of the input-side capacitor is electrically connected to the input power grid. The anode and cathode of the LED are electrically connected, and both are also electrically connected to the input power grid. One end of the current-limiting resistor is electrically connected to both a pin of the controller and the collector of the phototransistor. The other end of the current-limiting resistor is electrically connected to the power supply terminal of the controller. The emitter of the phototransistor is grounded. By employing a combination of an input-side capacitor, a diode, and a unidirectional optocoupler, a "current threshold" mechanism for zero-crossing detection is constructed. The input-side capacitor smooths harmonic fluctuations caused by grid voltage distortion through charging and discharging, while the diode blocks reverse current interference through its unidirectional conduction characteristic, allowing only effective forward or reverse charging / discharging current to flow through the unidirectional optocoupler. Furthermore, a pulse signal is generated only when this charging / discharging current reaches the conduction threshold of the unidirectional optocoupler. This mechanism can filter out minute fluctuations caused by harmonics (i.e., false zero-crossing signals). Therefore, the detection accuracy of grid voltage zero-crossing signals can be improved.

[0049] The above description is merely a selection of preferred embodiments of this disclosure and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in the embodiments of this disclosure is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the above-described inventive concept. For example, technical solutions formed by substituting the above-described features with (but not limited to) technical features with similar functions disclosed in the embodiments of this disclosure.

Claims

1. An input voltage phase detection circuit for a central air conditioning soft starter, characterized in that, The input voltage phase detection circuit includes an input-side capacitor, a diode, a unidirectional optocoupler, a current-limiting resistor, and a controller. The unidirectional optical coupler includes a light-emitting diode and a phototransistor; One end of the input-side capacitor is electrically connected to both the cathode of the diode and the anode of the light-emitting diode. The other end of the input-side capacitor is electrically connected to the input power grid. The anode of the diode is electrically connected to the cathode of the light-emitting diode, and both are electrically connected to the input power grid. One end of the current-limiting resistor is electrically connected to both the pin of the controller and the collector of the phototransistor. The other end of the current-limiting resistor is electrically connected to the power supply terminal of the controller; The emitter of the phototransistor is grounded.

2. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 1, characterized in that, The diode is either a switching diode or a rectifier diode.

3. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 1, characterized in that, The input-side capacitor is a safety capacitor or a polyester film capacitor.

4. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 1, characterized in that, The input voltage phase detection circuit is integrated into the soft starter of the central air conditioner, and the output terminal of the controller is connected to the gate drive circuit of the thyristor inside the soft starter.

5. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 1, characterized in that, The controller is configured to perform the following steps: Capture the voltage zero-crossing pulse signal according to the preset frequency; Record the timestamps corresponding to each voltage zero-crossing pulse signal captured continuously within a preset time period to obtain a timestamp set; In response to the fact that the number of timestamps in the timestamp set is greater than a preset value, a time interval between every two adjacent timestamps in the timestamp set is generated based on the timestamp set to obtain a time interval set; Sort the time intervals in the time interval set to obtain a sorted time interval set; The sorted time interval set is subjected to extremum removal processing to obtain the extremum-removed time interval set; Based on the set of time intervals after removing extrema, generate the average time interval; The frequency value of the input power grid is generated based on the average value of the time interval.

6. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 5, characterized in that, The controller is also configured to perform the following steps: A capture time window is generated based on the frequency value.

7. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 6, characterized in that, The controller is also configured to perform the following steps: In response to the capture of a voltage zero-crossing pulse signal within the capture time window, the timestamp corresponding to the captured voltage zero-crossing pulse signal is determined as the wave transmission reference point.

8. The input voltage phase detection circuit for a central air conditioning soft starter according to claim 6, characterized in that, The controller is also configured to perform the following steps: In response to the failure to capture a voltage zero-crossing pulse signal within the capture time window, a wave transmission reference point is determined based on the frequency value and the timestamp corresponding to the previously captured voltage zero-crossing pulse signal.

Images