DC motor controller

Abstract

To provide a compact and highly efficient DC motor controller.SOLUTION: In a DC motor controller comprising: a plurality of converters having two inputs and two outputs for converting an AC or a DC into a predetermined DC voltage value; and one changeover switch, in which a drive voltage of a DC motor can be adjusted, an input-side voltage terminal of the plurality of converters is connected in parallel, and an output-side voltage terminal of the plurality of converters is connected in series. Among the plurality of converters, a high-side voltage terminal, which is an output-side voltage terminal that is not connected to the converter on the high-side side, is connectable to one end of the DC motor. A low-side of the output-side voltage terminal of each of the plurality of converters is connected to the changeover switch, and the changeover switch is connectable to the other end of the DC motor.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] Embodiments of the present invention relate to voltage variation techniques required to control the speed of a DC motor. [Background technology]

[0002] Control circuits for motors used in various fields such as power tools and home appliances have been developed. Patent Document 1 discloses a motor control device that performs variable speed drive using pulse width modulation (PWM).

[0003] On the other hand, Patent Document 2 discloses a power generation system that can supply low-cost, highly efficient power to a plurality of devices with different battery voltage specifications. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-141057 [Patent Document 2] Japanese Patent Publication No. 2023-147363 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 requires a switching device because the motor is controlled by changing the PWM frequency. This causes a spike voltage when the voltage is turned on. The high pulse peak current flowing through the motor when the spike voltage occurs does not become a current that is useful for generating torque for the motor, and this causes the problem of deteriorating motor efficiency.

[0006] Furthermore, Patent Document 2 requires an adjustment circuit for aggregating and distributing the variable power generated by multiple power generation modules. This adjustment circuit includes multiple voltage adjustment switches for connecting the power output units of adjacent modules in series, and switches for distributing the power to multiple devices. The need for multiple voltage adjustment switches poses a problem in that switching cannot be done with a single switch (at a single location).

[0007] The present invention was completed through extensive research focusing on these problems, and its purpose is to provide a small, highly efficient DC motor controller. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a DC motor controller capable of adjusting the drive voltage of a DC motor, comprising a plurality of two-input, two-output converters for converting AC or DC to a predetermined DC voltage value, and one change-over switch, wherein the input voltage terminals of the plurality of converters are connected in parallel, and the output voltage terminals of the plurality of converters are connected in series, and a high-side voltage terminal, which is an unconnected output voltage terminal of a high-side converter among the plurality of converters, is connectable to one end of the DC motor, and the low sides of the output voltage terminals of the plurality of converters are each connected to the change-over switch, and the change-over switch is connectable to the other end of the DC motor. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a small-sized and highly efficient DC motor controller. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a block diagram showing a configuration of a DC motor controller 100 according to an embodiment of the present invention. [Figure 2] FIG. 10 is a block diagram showing the configuration of a DC motor controller 100′ according to another embodiment of the present invention. [Figure 3] FIG. 1 is a diagram for explaining pulse voltages of a general PWM controller. [Figure 4] 10 is a graph showing the results of a load test on a DC motor comparing the DC motor controller 100 (set to DC 10V) with only a general PWM controller. [Figure 5] 10 is a graph showing the results of a load test on a DC motor comparing the DC motor controller 100 (set to DC 20V) with only a general PWM controller. [Figure 6] 10 is a graph showing the results of a load test on a DC motor comparing the DC motor controller 100 (set to DC 30V) with only a general PWM controller. [Figure 7] 10 is a graph showing the results of a load test on a DC motor comparing the DC motor controller 100 (set to DC 45V) with only a general PWM controller. [Figure 8] 10 is a graph showing the results of a load test on a DC motor comparing a DC motor controller 100' (equivalent to DC 12V) with only a general PWM controller. [Figure 9] 10 is a graph showing the results of a load test on a DC motor comparing a DC motor controller 100' (equivalent to DC 24V) with only a general PWM controller. [Figure 10] 10 is a graph showing the results of a load test on a DC motor comparing a DC motor controller 100' (equivalent to DC 36V) with only a general PWM controller. [Figure 11] 10 is a graph showing the results of a load test on a DC motor comparing a DC motor controller 100' (equivalent to DC 48V) with only a general PWM controller. [Figure 12] FIG. 10 is a block diagram showing the configuration of a DC motor controller 500 according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] An embodiment of the present invention will be described with reference to the drawings. The DC motor controller according to this embodiment uses a two-input, two-output AC-DC converter as the converter. Of the input / output terminals, the one with the higher voltage is called the high side, and the one with the lower voltage is called the low side.

[0012] (DC motor controller according to embodiment 1) Fig. 1 is a block diagram showing the configuration of a DC motor controller 100 according to an embodiment of the present invention. An AC power supply device 200 outputs 100V AC (alternating current) from a power outlet such as that found in a typical home. The DC motor controller 100 converts the 100V AC from the AC power supply device 200 into DC of a predetermined voltage and outputs it to a DC motor 300. The DC motor 300 drives the motor at a rotation speed corresponding to the DC from the DC motor controller 100. Here, a brushed DC motor is used as the DC motor 300.

[0013] The DC motor controller 100 comprises multiple AC-DC converters 110 and one changeover switch 130. Here, the input voltage value is constant at AC 100 V and the output voltage value is constant at DC 5 V, and ten compact AC-DC converters 110 are used. A rotary switch with multiple contacts is used as the changeover switch 130.

[0014] The input voltage terminals of each AC-DC converter 110 are connected in parallel (i.e., the high-side input terminals are electrically connected and the low-side input terminals are electrically connected). On the other hand, the output voltage terminals of each AC-DC converter 110 are connected in series (i.e., the low-side output terminal of the nth stage is electrically connected to the high-side output terminal of the (n+1)th stage, where n is a natural number). The high-side output terminal of the top-stage (first-stage) AC-DC converter 110-1 is electrically connected to the DC motor 300. The low-side output terminal of the first-stage AC-DC converter 110-1 is connected to the high-side output terminal of the next-stage (second-stage) AC-DC converter 110-2.

[0015] Here, the reason why semiconductor diodes 120 are provided between the output voltage terminals of all the AC-DC converters is as a safety measure to protect against reverse voltage occurring between the output voltage terminals of each AC-DC converter due to the series connection of the output voltage terminals as described above. An isolated converter is usually used for AC-DC converters (or DC-DC converters) that allow for such a series connection of output voltage terminals. It should be noted that semiconductor diode 120 is not an essential component of the present invention.

[0016] Similarly, the low-side output terminal of the second-stage AC-DC converter 110-2 is connected to the high-side output terminal of the third-stage AC-DC converter 110-3. The series connection on the output terminal side between the AC-DC converters continues all the way to the bottom-most (tenth) AC-DC converter 110-10, but is shown by dotted lines due to space constraints in the drawing. Similarly, the semiconductor diode 120-10 also continues all the way to the bottom.

[0017] The low-side output terminal of each of AC-DC converters 110-1 to 110-10 can be electrically connected to changeover switch 130. Changeover switch 130 can electrically connect DC motor 300 to any one of the low-side output terminals of AC-DC converters 110-1 to 110-10.

[0018] For example, when the changeover switch 130 selects the low-side output terminal of the first-stage AC-DC converter 110-1, DC 5V is input to the DC motor 300. When switching to the low-side output terminal of the second-stage AC-DC converter 110-2, the input voltage to the DC motor 300 switches to DC 10V. When switching to the low-side output terminal of the third-stage AC-DC converter 110-3, the input voltage to the DC motor 300 switches to DC 15V. Similarly, when switching to the low-side output terminal of the tenth-stage AC-DC converter 110-10, the input voltage to the DC motor 300 switches to DC 50V.

[0019] In this way, DC motor controller 100 can switch the input voltage to DC motor 300 in 5V increments within a range of 5V to 50V. Furthermore, because the output voltage value of each of AC-DC converters 110-1 to 110-10 is kept constant at 5V, voltage can be adjusted in stages using only one selector switch 130, making it easy to change the rotation speed of DC motor 300 in stages. Taking advantage of these advantages, DC motor controller 100 can be applied to small electrical appliances such as electric toothbrushes in which the rotation speed of the motor is changed using a strength switch or the like.

[0020] According to this embodiment, by using multiple small AC-DC converters with the same constant output voltage, the DC motor controller can also be made smaller. Therefore, unlike a linear DC stabilized power supply, it does not require a large installation space. Furthermore, unlike PAM (Pulse Amplitude Modulation) inverters, which are often used to control the motor rotation speed of high-value-added home appliances such as room air conditioners, refrigerators, and washing machines, the circuit configuration is not as complex, making it suitable for mass production. While this embodiment illustrates an application example to a 100V AC commercial power supply, using a DC-DC converter as the converter can also be applied to DC power sources such as solar power generation systems and storage batteries.

[0021] (DC motor controller according to the second embodiment) Figure 2 is a block diagram showing the configuration of a DC motor controller 100' according to another embodiment of the present invention. The same components as those in the DC motor controller 100 of Figure 1 are given the same reference numerals, and their description will be omitted. The difference from Figure 1 is that a PWM controller 400 is connected in series between the high-side output terminal of the first-stage AC-DC converter 110-1 and the DC motor 300. The PWM controller 400 is a general PWM type controller. The PWM type is also called a pulse width modulation type.

[0022] The pulse voltage (PWM amplitude voltage) of the PWM controller 400 is preferably set to a value equal to or greater than the output voltage (5V in this embodiment) of the AC-DC converter 110, but as small as possible (e.g., equal to or greater than 5V). More preferably, the pulse voltage (pulse width) is set to the same value as the DC output voltage (5V). A voltage below 4.9V results in an insufficient voltage, while a voltage above 5.1V results in an excessive voltage. While excessive voltage does not interfere with operation, it leads to energy waste and should be limited. In the load test described below, a PWM modulation controller with a pulse width of 9V is used as the PWM controller 400. Specifically, by varying the on-time width of a pulse train with a pulse width of 9V (i.e., varying the duty cycle), and adding (superimposing) it on the output voltage of the DC motor controller 100′, PWM modulation is performed to achieve a predetermined DC voltage value.

[0023] By using such a PWM controller 400 in combination, the DC motor controller 100' in Fig. 2, unlike the DC motor controller 100 in Fig. 1, is able to continuously adjust the input voltage to the DC motor 300. For example, when the input voltage to the DC motor 300 is to be linearly increased or decreased in the range from 5V to 10V, the selector switch 130 in Fig. 2 selects the low-side output terminal of the first-stage AC-DC converter 110-1. In this case, the output voltage is DC 5V, and further, PWM modulation with a pulse width of 9V is used to add (also called superimpose) in the range from DC 0V equivalent (duty ratio is 0.0) to DC 5V equivalent (duty ratio is 0.56).

[0024] Figure 3 is a diagram explaining the pulse voltage of a typical PWM controller. The PWM method adjusts the pulse voltage (input voltage) to the equivalent desired DC output voltage by high-speed switching, while keeping the pulse period the same. For this reason, the higher the pulse voltage, the larger the spike voltage that occurs when the voltage is turned on. The high pulse peak current that flows through the DC motor when a spike voltage occurs does not become a current that is useful as torque for the DC motor, and reduces motor efficiency. The pulse voltage is also called the PWM amplitude voltage.

[0025] As described above, it is known that the PWM method generally generates a spike voltage at the rising edge of the pulse voltage (at the beginning of each cycle). In order to suppress this spike voltage, it is preferable to set the PWM amplitude voltage of the PWM controller 400 in Fig. 2 to the minimum voltage (DC 9V in this embodiment) that can drive the PWM controller 400 and to be equal to or higher than the DC voltage of 5V of the AC-DC converter 110.

[0026] Furthermore, in order to absorb the attenuation of spike voltages due to the PWM method and stabilize the square wave of the PWM amplitude voltage, it is preferable to set the duty ratio of the PWM controller 400 to 0.5 or more.

[0027] (Load Test 1: DC Motor Controller 100 According to Example 1) We will now explain load tests on DC motors in the following two cases: driving a DC motor 300 using the DC motor controller 100 of FIG. 1 (Example 1), and driving a DC motor of the same specifications using only a general PWM controller (Prior Art). Four DC voltages were set. FIG. 4 shows the case of 10 V DC, FIG. 5 shows the case of 20 V DC, FIG. 6 shows the case of 30 V DC, and FIG. 7 shows the case of 45 V DC. In (a) of FIGS. 4 to 7, the horizontal axis represents motor torque and the vertical axis represents motor efficiency. In (b) and (c) of FIGS. 4 to 7, the horizontal axis represents time and the vertical axis represents voltage.

[0028] The specifications of the DC motors used in Example 1 and the conventional example are the same: a rated voltage of 48 V, a rated output of 117 W, a rated torque of 0.932 N m, and a rated rotational speed of 1200 rpm. The PWM controller is a PWM modulation controller with a pulse width of 48 V that can output a rated voltage of 48 V to the DC motor at a duty ratio of 1. The maximum continuous capacity of AC-DC converters 110-1 to 110-10 is 200 W each, and the maximum capacity of DC motor controller 100 is estimated to be 2 kW. Meanwhile, the conventional PWM controller used for comparison has an instantaneous maximum of approximately 2.9 kW. The reason for setting the maximum capacity of DC motor controller 100 at 2 kW is that the maximum power that can be used on one circuit (branch breaker that carries electricity to each room or outlet) in an average household is 2 kW.

[0029] FIG. 4 is a graph showing the results of a DC motor load test comparing the DC motor controller 100 (set to DC 10V) with a general PWM controller alone. Two methods for setting the input voltage to the DC motor to DC 10V are described. FIG. 4(b) shows the case of Example 1, in which the selector switch 130 in FIG. 1 selects the low-side output terminal of the second-stage AC-DC converter 110-2. It can be seen that the output voltage in this case is constant at DC 10V. On the other hand, FIG. 4(c) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed to achieve an output equivalent to DC 10V. It can be seen that the on-duty period of the pulse train with a pulse width of 48V is narrower (i.e., the duty ratio is smaller) than in FIGS. 5 to 7, which will be described later.

[0030] 4(a) plots measured values ​​at DC 10 V with filled circles and shows them as a solid line, and also plots measured values ​​with conventional PWM modulation with a pulse width of 48 V with open squares and shows them as a dotted line. Comparing the case of a low load (or light load) with a torque of about 200 mN m, it can be seen that the DC motor controller 100 (Example 1) is about 2% more efficient than the case of only a PWM controller (conventional example).

[0031] FIG. 5 is a graph showing the results of a DC motor load test comparing the DC motor controller 100 (set to DC 20V) with a general PWM controller alone. Two methods for setting the input voltage to the DC motor to DC 20V are described. FIG. 5(b) shows the case of Example 1, in which the selector switch 130 in FIG. 1 selects the low-side output terminal of the fourth-stage AC-DC converter (not shown). It can be seen that the output voltage in this case is constant at DC 20V. On the other hand, FIG. 5(c) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed to achieve the equivalent of DC 20V. It can be seen that the duty ratio is larger than in FIG. 4(c).

[0032] 5(a) plots measured values ​​at DC 20V with filled circles and shows them as a solid line, and also plots measured values ​​with conventional PWM modulation with a pulse width of 48V with open squares and shows them as a dotted line. Comparing the case of a low load with a torque of 400 mN m or less, it can be seen that DC motor controller 100 (Example 1) is approximately 1% more efficient than the case of only a PWM controller (conventional example).

[0033] FIG. 6 is a graph showing the results of a DC motor load test comparing the DC motor controller 100 (set to DC 30V) with a general PWM controller alone. There are two methods for setting the input voltage to the DC motor to DC 30V. FIG. 6(b) shows the case of Example 1, in which the selector switch 130 in FIG. 1 selects the low-side output terminal of the sixth-stage AC-DC converter (not shown). It can be seen that the output voltage in this case is constant at DC 30V. On the other hand, FIG. 6(c) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed to achieve the equivalent of DC 30V. It can be seen that the duty ratio is larger than in FIG. 5(c).

[0034] 6(a) plots measured values ​​at DC 30V with filled circles and shows them as a solid line, and also plots measured values ​​with conventional PWM modulation with a pulse width of 48V with open squares and shows them as a dotted line. Comparing the case of a low load with a torque of 600 mN m or less, it can be seen that DC motor controller 100 (Example 1) is approximately 1% more efficient than the case of only a PWM controller (conventional example).

[0035] FIG. 7 is a graph showing the results of a DC motor load test comparing the DC motor controller 100 (set to DC 45V) with a general PWM controller alone. Two methods for setting the input voltage to the DC motor to DC 45V are described. FIG. 7(b) shows the case of Example 1, in which the selector switch 130 in FIG. 1 selects the low-side output terminal of the ninth-stage AC-DC converter (not shown). It can be seen that the output voltage in this case is constant at DC 45V. On the other hand, FIG. 7(c) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed to achieve the equivalent of DC 45V. It can be seen that the duty ratio is larger than in FIG. 6(c).

[0036] 7(a) plots measured values ​​at DC 45V with filled circles and shows them as a solid line, and also plots measured values ​​with conventional PWM modulation with a pulse width of 48V with open squares and shows them as a dotted line. Comparing the plots, it can be seen that DC motor controller 100 (Example 1) is more efficient than the PWM controller alone (conventional example) at loads of 200mN m or less, and that the efficiency is roughly the same even at loads higher than 200mN m.

[0037] 4 to 7, the DC motor controller 100 (first embodiment) can increase the efficiency of the DC motor 300 when the DC motor is operated at a voltage lower than the rated voltage of the DC motor.

[0038] (Load Test 2: DC Motor Controller 100' According to Example 2) We will now describe load tests on a DC motor when driving a DC motor 300 using the DC motor controller 100' of Figure 2 (Example 2) and when driving a DC motor of the same specifications using only a general PWM controller (Prior Art). Four DC voltages were set. Figure 8 shows the equivalent DC voltage of 12 V, Figure 9 shows the equivalent DC voltage of 24 V, Figure 10 shows the equivalent DC voltage of 36 V, and Figure 11 shows the equivalent DC voltage of 48 V. The term "equivalent" here refers to the addition of a predetermined DC voltage equivalent to that of a PWM controller using PWM modulation with a pulse width of 9 V, since the configuration of the DC motor controller 100' of Figure 2 adds a PWM controller 400 (PWM modulation method with a pulse width of 9 V) to the DC motor controller 100 of Figure 1.

[0039] In (a) of Figures 8 to 11, the horizontal axis represents torque and the vertical axis represents efficiency. In (b), (c), and (d) of Figures 8 to 11, the horizontal axis represents time and the vertical axis represents voltage. The DC motor, general PWM controller, and AC-DC converter used were the same as those used in Load Test 1.

[0040] FIG. 8 is a graph showing the results of a DC motor load test comparing the DC motor controller 100′ (equivalent to DC 12V) with a general PWM controller alone. Three methods for setting the input voltage to the DC motor equivalent to DC 12V are described. FIG. 8(b) shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the first-stage AC-DC converter 110-1. In this case, the output voltage is DC 5V, and a DC 7V equivalent (duty ratio of 0.78) is added using PWM modulation with a pulse width of 9V. The 9V pulse voltage is derived from the minimum voltage of DC 9V that can drive the PWM controller 400 in FIG. 2. FIG. 8(c) also shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the second-stage AC-DC converter 110-2. In this case, the output voltage is DC 10V, and a DC 2V equivalent (duty ratio of 0.22) is added using PWM modulation with a pulse width of 9V. On the other hand, FIG. 8(d) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed so as to be equivalent to DC 12V.

[0041] In FIG. 8(a), measured values ​​for PWM modulation with DC 5V and a pulse width of 9V (Example 2, and a duty ratio of 0.78) are plotted with filled circles and a solid line, measured values ​​for PWM modulation with DC 10V and a pulse width of 9V (Example 2, and a duty ratio of 0.22) are plotted with open triangles and a dashed-dotted line, and measured values ​​for conventional PWM modulation with a pulse width of 48V are plotted with open squares and a dotted line. When comparing the results for a low load (or light load) of 400 mN m or less, it can be seen that the DC motor controller 100′ (Example 2) is up to 2% more efficient than the PWM controller alone (the conventional example). It can also be seen that even in Example 2, duty ratios of 0.5 or greater generally result in higher efficiency than duty ratios of less than 0.5.

[0042] FIG. 9 is a graph showing the results of a DC motor load test comparing the DC motor controller 100′ (equivalent to DC 24V) with a general PWM controller alone. Three methods for setting the input voltage value to a DC motor equivalent to DC 24V are described. FIG. 9(b) shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the third-stage AC-DC converter 110-3. In this case, the output voltage is DC 15V, and a DC 9V equivalent (duty ratio of 1.0) is added using PWM modulation with a pulse width of 9V. FIG. 9(c) also shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the fourth-stage AC-DC converter (not shown). In this case, the output voltage is DC 20V, and a DC 4V equivalent (duty ratio of 0.44) is added using PWM modulation with a pulse width of 9V. On the other hand, FIG. 9(d) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed so as to be equivalent to DC 24V.

[0043] 9(a) plots measured values ​​with PWM modulation of DC 15V + pulse width 9V (Example 2, and duty ratio 1.0) as filled circles and shown as a solid line, and also plots measured values ​​with PWM modulation of DC 20V + pulse width 9V (Example 2, and duty ratio 0.44) as open triangles and shown as a dash-dot line, and further plots measured values ​​with conventional PWM modulation of pulse width 48V as open squares and shown as a dotted line. Comparing the case of a low load (or light load) of 300 mN m or less, it can be seen that the efficiency of DC motor controller 100' (Example 2) is about 1% higher than that of a PWM controller alone (conventional example).

[0044] FIG. 10 is a graph showing the results of a DC motor load test comparing the DC motor controller 100′ (equivalent to DC 36V) with a general PWM controller alone. Three methods for setting the input voltage to the DC motor equivalent to DC 36V are described. FIG. 10(b) shows the second embodiment, in which the selector switch 130 in FIG. 1 selects the low-side output terminal of the sixth-stage AC-DC converter (not shown). In this case, the output voltage is DC 30V, and a DC 6V equivalent (duty ratio of 0.67) is added using PWM modulation with a pulse width of 9V. FIG. 10(c) also shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the seventh-stage AC-DC converter (not shown). In this case, the output voltage is DC 35V, and a DC 1V equivalent (duty ratio of 0.11) is added using PWM modulation with a pulse width of 9V. On the other hand, FIG. 9(d) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed so as to be equivalent to DC 36V.

[0045] 10(a) plots measured values ​​with PWM modulation of DC 30V + pulse width 9V (Example 2, and duty ratio 0.67) as filled circles and displays them as a solid line, while measured values ​​with PWM modulation of DC 35V + pulse width 9V (Example 2, and duty ratio 0.11) as open triangles and displays them as a dashed-dotted line, and further plots measured values ​​with conventional PWM modulation of pulse width 48V as open squares and displays them as a dotted line. Overall, it can be seen that DC motor controller 100' (Example 2) is more efficient than the case where only a PWM controller is used (conventional example).

[0046] FIG. 11 is a graph showing the results of a DC motor load test comparing the DC motor controller 100′ (equivalent to DC 48V) with a general PWM controller alone. Three methods for setting the input voltage to the DC motor equivalent to DC 48V are described. FIG. 11(b) shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the eighth-stage AC-DC converter (not shown). In this case, the output voltage is DC 40V, and a DC 8V equivalent (duty ratio of 0.89) is added using PWM modulation with a pulse width of 9V. FIG. 11(c) also shows the second embodiment, in which the selector switch 130 in FIG. 2 selects the low-side output terminal of the ninth-stage AC-DC converter (not shown). In this case, the output voltage is DC 45V, and a DC 3V equivalent (duty ratio of 0.33) is added using PWM modulation with a pulse width of 9V. On the other hand, FIG. 11(d) shows the case of a conventional example, in which PWM modulation with a pulse width of 48V is performed so as to be equivalent to DC 48V.

[0047] 11(a) plots measured values ​​with DC 40V + pulse width 9V PWM modulation (Example 2, and duty ratio 0.89) as filled circles and displays them as a solid line, while also plotting measured values ​​with DC 45V + pulse width 9V PWM modulation (Example 2, and duty ratio 0.33) as open triangles and displays them as a dashed-dotted line, and further plotting measured values ​​with conventional PWM modulation with a pulse width of 48V as open squares and displays them as a dotted line. Overall, it can be seen that the DC motor controller 100' (Example 2) is more efficient than the case where only a PWM controller is used (conventional example).

[0048] (Action and effect) The DC motor controllers 100 and 100' (FIGS. 1 and 2) of this embodiment can provide a small, highly efficient DC motor controller. Furthermore, because the output voltages of the multiple AC-DC converters (or DC-DC converters) in FIG. 1 are constant and the same value, the rotation speed of the DC motor 300 can be easily changed using only one changeover switch 130.

[0049] 2 makes it possible to linearly increase and decrease the input voltage to the DC motor 300 within a predetermined range, improving motor efficiency by several percent, particularly under low loads, compared to a conventional DC motor controller using only a PWM controller. Furthermore, by setting the amplitude of the pulse voltage of the PWM controller 400 to a value (e.g., 5 V) that is equal to or greater than the output voltage of the multiple AC-DC converters 110 (or DC-DC converters), it becomes possible to suppress the spike voltage of the PWM controller 400. Furthermore, by setting the duty ratio of the PWM controller 400 to 0.5 or greater, it becomes possible to absorb the attenuation of spike voltages due to the PWM method and stabilize the square wave of the PWM amplitude voltage, particularly during low-speed operation when the motor drive voltage is low, thereby enabling highly efficient motor operation.

[0050] (DC motor controller according to the third embodiment) Figure 12 is a block diagram showing the configuration of a DC motor controller 500 according to another embodiment of the present invention. The same components as those in DC motor controller 100 in Figure 1 are given the same reference numerals, and their description will be omitted. The difference from Figure 1 is that three AC-DC converters 510 are used, and the maximum continuous capacity of AC-DC converters 510-1 to 510-3 is 60 W each, while the maximum capacity of DC motor controller 500 is estimated to be 180 W.

[0051] According to this embodiment, by using three small (60 W) AC-DC converters 510 with the same constant output voltage, the DC motor controller 500 can also be made smaller. A product to which this embodiment can be applied is a handheld grinder. By incorporating the DC motor controller 500, DC motor 300, and selector switch 130 into the handheld grinder, it is possible to configure a handheld grinder with three output levels (strong, medium, and weak buttons).

[0052] Unlike the PWM method, this embodiment is less likely to generate spike voltages and can be applied to products that require a constant output, such as grinders.

[0053] (Variation) Although the embodiments (including modifications) of the present invention have been described above, two or more of these embodiments may be combined and implemented. Alternatively, one of these embodiments may be partially implemented. Furthermore, two or more of these embodiments may be partially combined and implemented. For example, since the DC motor controller 100 receives 100V AC current from the AC power supply 200, multiple AC-DC converters 110 are used. However, this is not limited to this. If the input is DC current, multiple DC-DC converters may be used. Furthermore, the selector switch 130 may be a mechanical switch such as a push button switch or a slide switch, or a semiconductor switch. Furthermore, the DC motor 300 may be a brushless DC motor. In addition, if the output voltage of the AC-DC converter 110 is 5V, the PWM controller 400 may be a PWM controller with a minimum drive voltage of DC 5V that outputs a pulse voltage of 5V when the minimum value DC 5V is input.

[0054] Furthermore, the present invention is not limited to the above-described embodiments. Various modifications within the scope of the claims and within the scope of those skilled in the art are also included in the present invention. For example, end products incorporating the compact, highly efficient DC motor controller of this embodiment may include power tools such as grinders that operate within the rated voltage of the DC motor, or products that require long-term use, such as drones. Furthermore, as a replacement for conventional DC motor controllers that use only PWM controllers, the controller may also be applied in fields such as LED dimming. Furthermore, the controller does not require the complex circuit configuration and circuit control of the PAM system, making it suitable for mass production, and may be used in high-value-added home appliances that use the PAM system. [Explanation of symbols]

[0055] 100, 100', 500 DC motor controller 110, 510 AC-DC converter 120 Semiconductor Diode 130 Switch 200 AC power supply 300 DC motor 400 PWM controller

Claims

1. a plurality of converters each having two inputs and two outputs for converting AC or DC into a predetermined DC voltage value; One changeover switch and A DC motor controller capable of adjusting a drive voltage of a DC motor, comprising: input side voltage terminals of the plurality of converters are connected in parallel; output voltage terminals of the plurality of converters are connected in series; a high-side voltage terminal, which is an unconnected output voltage terminal of a high-side converter among the plurality of converters, can be connected to one end of the DC motor; low sides of output voltage terminals of the plurality of converters are connected to the changeover switches, The changeover switch is connectable to the other end of the DC motor.

2. 2. The DC motor controller according to claim 1, wherein the output voltages of the plurality of converters are constant and the same value.

3. The DC motor controller according to claim 2 , further comprising a PWM controller, wherein the high-side voltage terminal is connectable to one end of the DC motor via the PWM controller.

4. 4. The DC motor controller according to claim 3, wherein the amplitude of the pulse voltage of said PWM controller is set to a value equal to or greater than the output voltage values ​​of said plurality of converters and as small as possible.

5. 5. The DC motor controller according to claim 4, wherein the set value is the same as the output voltage value.

6. 4. The DC motor controller of claim 3, wherein the PWM controller has a duty ratio of 0.5 or greater.

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