High-voltage brushless electric tool power module

Abstract

The utility model relates to the technical field of high-voltage brushless electric tool power supplies, in particular to a high-voltage brushless electric tool power module. The system comprises a rectifier bridge, a filtering unit and an inverter. The positive electrode output end of the rectifier bridge is connected with the inverter through the filtering unit, the filtering module is used for rectifying and filtering voltage output by the rectifier bridge and then sending the voltage to the inverter, and the inverter is used for inverting the rectified and filtered direct-current voltage into alternating-current voltage with the frequency related to the rotating speed of a motor of the high-voltage brushless tool. And the motor of the high-voltage brushless tool is driven to rotate. The inverter is characterized in that the filtering unit comprises a valley-fill passive PFC (Power Factor Correction) and a high-frequency filtering capacitor C3, and the valley-fill passive PFC and the high-frequency filtering capacitor C3 are connected in parallel between the rectifier bridge and the inverter. By adopting the module, the burr fluctuation of the rectified bus voltage can be reduced, and an inverter power tube is ensured not to be broken down.

Description

Technical Field

[0001] The utility model relates to the technical field of high-voltage brushless electric tool power supply, in particular to a high-voltage brushless electric tool power module. Background Art

[0002] There are two main ways to drive high-voltage permanent magnet brushless electric tool motors. One is to use the square wave current generated by the three-phase six-step method to drive the permanent magnet brushless motor with square wave back electromotive force. Figure 1 As shown. The control algorithm of this solution is simple and reliable, and the voltage utilization rate is high. Another method is to use the sine wave current generated by SPWM or SVPWM to drive the permanent magnet brushless motor with a sine wave back electromotive force, such as Figure 2 This solution has the advantages of stable torque, low vibration and noise, and high efficiency, which can improve the working quality of power tools and greatly reduce the fatigue of tool users.

[0003] like Figure 3 As shown, the power supply systems used in the above two solutions usually use a rectifier bridge to rectify and filter the AC power into DC power and then use it as a power supply to the permanent magnet brushless motor. The rectifier bridge converts the full-wave periodic AC power into two half-wave DC power. The filter capacitor at the back end of the rectifier bridge is one of the design difficulties of the system. If the filter capacitor at the back end of the rectifier bridge has a large capacitance, this capacitor will filter the two half-wave DC power into DC power with nearly equal amplitude. At this time, the motor can run at full load at any time, with high motor output and high efficiency. However, this large capacitor solution makes the current output by the rectifier bridge a large burr current injected into the capacitor, such as Figure 4 As shown. This solution results in a very low power factor of the entire power system, which has an adverse impact on the power grid and is not conducive to the tool meeting the safety requirements of electromagnetic compatibility. If the filter capacitor at the rear end of the rectifier bridge has a small capacitance, the voltage input to the motor is close to two half-waves, and the amplitude oscillation is large, such as Figure 5 As shown. When the half-wave voltage is high, the motor runs at full load; but when the half-wave voltage is low, the motor has almost no output. Therefore, this small filter capacitor design will result in low motor output and low efficiency. However, the small filter capacitor solution has the advantage of high power factor.

[0004] The applicant applied for a high-voltage brushless tool power system on April 29, 2024. The scheme mentioned that the valley-filling passive PFC was used instead of the filter capacitor to rectify and filter the output voltage of the rectifier bridge. However, if Figure 6As shown in the figure, when the valley-filling passive PFC technology is applied to the high-voltage permanent magnet brushless motor drive, the power tube of the three-phase inverter bridge is frequently switched on and off, so the motor line current has a current reverse charging effect on this PFC circuit. When the current is reversed, the two capacitors in this passive PFC circuit are charged in series, and the bus voltage is increased to the sum of the two capacitor voltages. When there is no current reverse charging, the bus voltage returns to the voltage value after the AC power is rectified and filtered. Due to the parasitic inductance in the circuit between the full-wave rectifier bridge and the valley-filling passive PFC module, the bus current will produce synchronous fluctuations as the rectifier bridge power devices switch. When the bus current decreases, this inductance will induce voltage glitches, such as Figure 7 The amplitude of this voltage glitch may be much higher than the amplitude of the rectified half-wave voltage, increasing the risk of voltage breakdown of the inverter circuit power device. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide a high-voltage brushless electric tool power module, which can reduce the burr fluctuation of the bus voltage after rectification and ensure that the inverter power tube will not be broken down.

[0006] In order to solve the above problems, the following technical solutions are provided:

[0007] The high-voltage brushless electric tool power module of the utility model includes a rectifier bridge, a filter unit and an inverter. The positive output end of the rectifier bridge is connected to the inverter through the filter unit. The filter module is used to rectify and filter the voltage output by the rectifier bridge and send it to the inverter. The inverter is used to invert the rectified and filtered DC voltage into an AC voltage with a frequency related to the motor speed of the high-voltage brushless tool, driving the motor of the high-voltage brushless tool to rotate, so as to convert electrical energy into mechanical energy. It is characterized in that the filter unit is a valley-filling passive PFC and a high-frequency filter capacitor C3, and the valley-filling passive PFC and the high-frequency filter capacitor C3 are connected in parallel between the rectifier bridge and the inverter.

[0008] Wherein, the capacitance of the high frequency filter capacitor C3 is 0.5uF-40uF,

[0009] The high-frequency filter capacitor C3 is a single capacitor or a combination of multiple capacitors connected in parallel.

[0010] The high-frequency filter capacitor C3 is a single capacitor or a combination of multiple capacitors connected in parallel.

[0011] The valley-fill passive PFC comprises a diode D1, a diode D2, a diode D3, a capacitor C1 and a capacitor C2, the cathode of the diode D2 and the anode of the capacitor C1 are both connected to the anode output terminal of the rectifier bridge, the anode of the diode D2 is respectively connected to the cathode of the diode D3 and the anode of the capacitor C2, the cathode of the capacitor C1 is respectively connected to the anode of the diode D3 and the cathode of the diode D1, the cathode of the capacitor C2 and the anode of the diode D3 are grounded; one end of the high-frequency filter capacitor C3 is connected to the anode output terminal of the rectifier bridge, and the other end of the high-frequency filter capacitor C3 is grounded; the anode output terminal of the rectifier bridge is connected to the inverter.

[0012] The above solution has the following advantages:

[0013] Since the filter unit of the high-voltage brushless electric tool power module of the utility model is a valley-filling passive PFC and a high-frequency filter capacitor C3, the valley-filling passive PFC and the high-frequency filter capacitor C3 are connected in parallel between the rectifier bridge and the inverter. The high-frequency filter capacitor C3 is used to filter the voltage burr, which significantly reduces the amplitude of the voltage burr, thereby greatly reducing the risk of the power tube of the inverter being broken down. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a waveform diagram of a permanent magnet brushless motor with square wave back electromotive force driven by a square wave current generated by a three-phase six-step method;

[0015] Figure 2 It is a waveform diagram of a permanent magnet brushless motor with a sinusoidal back electromotive force driven by a sinusoidal current generated by SPWM or SVPWM;

[0016] Figure 3 It is a circuit diagram of a high-voltage brushless electric tool power module using a capacitor as a filter unit in the background art;

[0017] Figure 4 yes Figure 3 Current and voltage waveforms of the circuit using a large capacitor solution;

[0018] Figure 5 yes Figure 3 Current and voltage waveforms of the circuit using a small capacitor solution;

[0019] Figure 6 It is a circuit diagram of a high-voltage brushless electric tool power module using a valley-filling passive PFC as a filter unit in the background art;

[0020] Figure 7 Is adopted Figure 6 Circuit waveform diagram;

[0021] Figure 8It is a circuit diagram of a high-voltage brushless electric tool power module of the utility model;

[0022] Fig. 9 This is a circuit diagram of the utility model of a high-voltage brushless electric tool power module after adding a filter inductor.

[0023] Fig.10 Is adopted Figure 8 China Circuit and Figure 6 Waveform comparison diagram of the circuit in the figure;

[0024] Fig.11 Is adopted Fig. 9 China Circuit and Figure 6 Waveform comparison chart of the circuit in . DETAILED DESCRIPTION

[0025] The utility model is further described in detail below in conjunction with the accompanying drawings.

[0026] like Figure 8 As shown, the high-voltage brushless electric tool power module of the utility model includes a rectifier bridge 2, a filter unit and an inverter 4. The rectifier bridge 2 is four diodes connected end to end. The specific structure of the rectifier bridge 2 belongs to the prior art and will not be repeated here. The positive input terminal and the negative input terminal of the rectifier bridge 2 are connected to the municipal power 1, that is, 220V AC power, and the negative output terminal of the rectifier bridge 2 is grounded. The rectifier bridge 2 performs full-wave rectification on the AC sinusoidal municipal power and converts it into two half-wave pulsating DC power. The positive output terminal of the rectifier bridge 2 is connected to the inverter 4 through the filter unit, and the filter module rectifies and filters the voltage output by the rectifier bridge 2 and sends it to the inverter 4. The inverter 4 is used to invert the rectified and filtered DC voltage into an AC voltage with a frequency related to the rotation speed of the motor 5 of the high-voltage brushless tool, and drive the motor 5 of the high-voltage brushless tool to rotate so as to convert electrical energy into mechanical energy.

[0027] The filtering unit is a valley-filling passive PFC3 and a high-frequency filter capacitor C3. The valley-filling passive PFC3 and the high-frequency filter capacitor C3 are connected in parallel between the rectifier bridge 2 and the inverter 4. The valley-filling passive PFC3 contains a diode D1, a diode D2, a diode D3, a capacitor C1 and a capacitor C2. The cathode of the diode D2 and the anode of the capacitor C1 are both connected to the positive output terminal of the rectifier bridge 2. The anode of the diode D2 is respectively connected to the cathode of the diode D3 and the anode of the capacitor C2. The cathode of the capacitor C1 is respectively connected to the anode of the diode D3 and the cathode of the diode D1. The cathode of the capacitor C2 and the anode of the diode D3 are grounded. One end of the high-frequency filter capacitor C3 is connected to the anode output terminal of the rectifier bridge 2, and the other end of the high-frequency filter capacitor C3 is grounded. The anode output terminal of the rectifier bridge 2 is connected to the inverter 4.

[0028] The working principle of the valley-filling passive PFC3 is that when the voltage amplitude of the two half-wave pulsating DC output by the rectifier bridge 2 rises to a certain level, the single-phase conducting diodes D1 and D2 are closed, and D3 is opened. At this time, capacitors C1 and C2 are connected in series, and the rectifier circuit charges the two capacitors, and the voltage borne by a single capacitor is half of the rectified voltage. Until C1 and C2 are fully charged, the diode D3 is closed to play an isolation role. When the voltage drops from the peak value of the pulsating DC voltage to the valley value, the output voltage will drop accordingly. When the output voltage is lower than the voltage of a single capacitor, capacitors C1 and C2 begin to discharge through their respective diodes D1 and D2, respectively, to fill the output voltage. At this time, diode D3 plays an isolation role. Capacitors C1 and C2 are charged in series, and the charging capacity is small; but C1 and C2 are discharged in parallel, and the discharge capacity is large. This charging and discharging method of the filter capacitor makes the voltage output after the rectifier bridge 2 more stable, and changes the original pulse peak current waveform into a current waveform close to a sine wave, thereby achieving the purpose of correcting the power factor. The high-frequency filter capacitor C3 filters the burrs of the bus voltage after rectification.

[0029] The high-frequency filter capacitor C3 can be a single capacitor or a combination of multiple capacitors. If the capacitance of this filter capacitor is too small, the filtering effect on the bus voltage burr is not good; if the capacitance of this filter capacitor is too large, the power factor of the system is reduced. Therefore, after comprehensive consideration, the capacitance of this filter capacitor is selected between 0.5 microfarads and 40 microfarads.

[0030] There is parasitic inductance in the circuit between the full-wave rectifier bridge 2 and the valley-filling passive PFC3 module. As the power devices of the rectifier bridge 2 switch, the bus current will fluctuate synchronously. When the bus current decreases, this inductance will induce voltage glitches, the amplitude of which may be much higher than the amplitude of the rectified half-wave voltage, increasing the risk of voltage breakdown of the power devices of the inverter circuit. The added filter capacitor can significantly reduce the amplitude of this voltage glitches and improve the operational safety performance of the circuit.

[0031] The specific permanent magnet synchronous motor selected is a 4-pole 6-slot structure, with a stator outer diameter of 48mm and a stator stack length of 40mm. Its back electromotive force coefficient is 7V / krpm, phase resistance is 1.14Ω, d-axis inductance is 2.39mH, q-axis inductance is 3.89mH, rated voltage AC 220V power supply, rated speed is 27krpm, rated power is 1.3kW, and overload power is 2.6kW. The capacitance value of the valley-fill PFC is 120 microfarads, and the capacitance value of the filter capacitor is 10 microfarads. The bus voltage comparison between the scheme with and without filter capacitor is as follows: Fig.10 As shown, it can be seen that the filter capacitor can significantly reduce the bus voltage burrs.

[0032] like Fig. 9As shown, in order to reduce bus current spikes, some possible embodiments may add a filter inductor after the full-wave rectifier bridge 2. After adding the filter inductor, the bus voltage comparison between the scheme without filter capacitor and the scheme with filter capacitor is as follows: Fig.11 Therefore, the added filter capacitor can significantly reduce the amplitude of the voltage glitch and improve the circuit's operational safety performance.

[0033] The high-voltage brushless electric tool power module of the utility model uses a valley-filling passive PFC circuit with a high-frequency filter capacitor, which reduces the bus voltage burrs after rectification, not only making the motor current more stable, but also reducing the risk of voltage breakdown of the inverter 4 power device.

Claims

1. A high-voltage brushless electric tool power module, comprising a rectifier bridge, a filter unit and an inverter; the positive output end of the rectifier bridge is connected to the inverter through the filter unit, the filter module is used to rectify and filter the voltage output by the rectifier bridge and send it to the inverter, the inverter is used to invert the rectified and filtered DC voltage into an AC voltage with a frequency related to the motor speed of the high-voltage brushless tool, driving the motor of the high-voltage brushless tool to rotate, so as to convert electrical energy into mechanical energy; characterized in that, The filtering unit is a valley-filling passive PFC and a high-frequency filtering capacitor C3, and the valley-filling passive PFC and the high-frequency filtering capacitor C3 are connected in parallel between the rectifier bridge and the inverter.

2. The high-voltage brushless electric tool power module according to claim 1, characterized in that: The capacitance of the high frequency filter capacitor C3 is 0.5uF-40uF.

3. The high-voltage brushless electric tool power module according to claim 1, characterized in that: The high-frequency filter capacitor C3 is a single capacitor or a combination of multiple capacitors connected in parallel.

4. The high-voltage brushless electric tool power module according to claim 1, characterized in that: The valley-fill passive PFC comprises a diode D1, a diode D2, a diode D3, a capacitor C1 and a capacitor C2, the cathode of the diode D2 and the anode of the capacitor C1 are both connected to the anode output terminal of the rectifier bridge, the anode of the diode D2 is respectively connected to the cathode of the diode D3 and the anode of the capacitor C2, the cathode of the capacitor C1 is respectively connected to the anode of the diode D3 and the cathode of the diode D1, the cathode of the capacitor C2 and the anode of the diode D3 are grounded; one end of the high-frequency filter capacitor C3 is connected to the anode output terminal of the rectifier bridge, and the other end of the high-frequency filter capacitor C3 is grounded; the anode output terminal of the rectifier bridge is connected to the inverter.

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